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The volcano is located in Mars's western hemisphere at approximately 18.65 N and 226.2 E, just to the northwestern edge of the Tharsis Bulge. The western portion of the volcano lies in the Amazonis quadrangle and the central and eastern portions in the Tharsis quadrangle.
The top of Olympus Mons is the highest point on Mars. By one measure, it has a height of nearly 22 km (13.6 mi or 72,000 ft).. Olympus Mons stands about two and a half times as tall as Mount Everest's height above sea level, and is currently the largest volcano discovered in the Solar System.
At 600 km (370 mi) in diameter the footprint of Olympus Mons covers an area of land comparable to the size of France.
It is the youngest of the large volcanoes on Mars and some of the evidence from the ancient lava flows suggest a range in age from 115 million years old to 2000 million years old. This is relatively recent in comparison to most of Mars' other geology.
Much of the terrain is obscured by fine dust covering the underlying bedrock but Olympus Mons probably has the same composition to most of the dark areas on Mars which were formed by volcanic eruptions. The surface of Mars, including Olympus Mons is basalt of a type (tholeiites) similar to that of Earth's oceanic crust. This is the general conclusion drawn from Martian meteorites, analyses of soils and rocks at robotic landing sites, and information gathered with orbiting spacecraft.
Lava flows consisting of this composition would have low viscosity producing a watery flow that creates a typical shield volcanoes. Olympus Mons has a very gradual slope of, on average, only 5°. It would be a long but very gentle climb up Olympus Mons.
High-altitude clouds frequently drift over the Olympus Mons summit, and airborne Martian dust is still present. The typical atmospheric pressure at the top of Olympus Mons is about 12% of the average Martian surface pressure.
As with tall mountains on the Earth, there has been much snowfall on Olympus Mons. Scientists see much evidence for glaciers.
Olmypus Mons has been known to astronomers since the late 19th century as the albedo feature Nix Olympica (Latin for "Olympic Snow"). Its mountainous nature was suspected well before space probes confirmed its identity as a mountain.
Unfortunately Olympus Mons is an unlikely landing location for automated space probes in the near future. The high elevations preclude parachute-assisted landings because the atmosphere above is not sufficient to slow the spacecraft down before landing. Moreover, Olympus Mons stands in one of the dustiest regions of Mars. This would likely make rock samples hard to come by and the dust layer would also likely cause severe maneuvering problems for rovers.
- Plescia | first1 = J. B. | year = 2004 | title = Morphometric Properties of Martian Volcanoes | url = | journal = J. Geophys. Res. | volume = 109 | issue = | page = E03003
- McSween Jr., H. Y., Taylor, G. J., and Wyatt, M. B. 2009. Elemental Composition of the Martian Crust. Science, v. 324(5928), p.736-739, doi: 10.1126/science.1165871.
- "Mars Crust : Made of Basalt" http://www.psrd.hawaii.edu/May09/Mars.Basaltic.Crust.html
- Wikipedia Olympus Mons https://en.wikipedia.org/w/index.php?title=Olympus_Mons
- Hartmann, W.K. A Traveler’s Guide to Mars: The Mysterious Landscapes of the Red Planet. Workman: New York, 2003, p. 300.
- Public Access to Standard Temperature-Pressure Profiles
- Basilevsky, A. (2006). "Geological recent tectonic, volcanic and fluvial activity on the eastern flank of the Olympus Mons volcano, Mars". Geophysical Research Letters 33 (13): 13201, L13201. doi:10.1029/2006GL026396.
- Patrick Moore. 1977. Guide to Mars. London (UK). Cutterworth Press, p. 96 | 0.811185 | 3.835874 |
Part of the evidence we have for dark matter is through its gravitational effect on the motion of stars. The first evidence for dark matter came from the motion of stars in our galaxy, which indicated there must be a large quantity of unseen mass in our galaxy. So why is it that when we look for the gravitational effect of dark matter on nearby stars, we don’t see anything? It turns out that tells us something very interesting about the nature dark matter.1
In 2012, a survey was done of about 400 red giant stars within a range of 13,000 light years from the Sun. The motions of these stars were studied to look for the influence of dark matter on their motion, and the results were published in the Astrophysical Journal. What the team found was that the motions of the stars could be accounted for by the stars, dust and gas in the region. There wasn’t any evidence of dark matter within the region. So does this mean there isn’t any dark matter in the region around our Sun? Not quite.
The basic model of dark matter in the Milky Way is that it exists in a halo around our galaxy, with most of our galaxy’s mass being dark matter rather than regular matter (stars, gas, dust). Just how the dark matter is distributed within the halo depends upon the specific type of dark matter.
Observations of the universe on a large scale indicate that dark matter must be cold, meaning that the motion of dark matter particles must be relatively slow. We also know through sky surveys that dark matter is not something like primordial black holes. This means the leading candidate for dark matter are WIMPs, or Weakly Interacting Massive Particles.
The simplest models for WIMPs suppose that they not only don’t interact strongly with light, they also don’t strongly interact with each other. If that’s the case, then the gravitational interactions between WIMPs would cause the galactic halo to have an ever greater density as you get toward the center of the galaxy. If this were the case, then the variation of dark matter density should affect local stellar motion. So it seems observational evidence doesn’t support these simple WIMP models.
An alternative is that while dark matter particles don’t interact strongly with light and regular matter, they do interact with other. This would mean that the dark matter halo could thermally equalize through their interactions, and as a result the central region of the halo would be fairly uniform in density. If that is the case, then it wouldn’t have a large effect on local stellar motions. So it would seem that this study supports the idea that dark matter is self-interacting, or at least has some mechanism to thermally equalize.
To be fair, the fact that we see no evidence of dark matter within the 13,000 light year back yard of our Sun could indicate that there is no dark matter in this region. It doesn’t seem likely given what we know of dark matter so far, but we can’t rule it out as a possibility. Either way, what we’re learning is that dark matter is even more complex and subtle than we had thought.
Bidin, C. Moni, G. Carraro, and R. A. Méndez. “Kinematical and Chemical Vertical Structure of the Galactic Thick Disk. I. Thick Disk Kinematics.” The Astrophysical Journal 747.2 (2012): 101. ↩︎ | 0.815489 | 4.101198 |
Did you know that if planet Earth were invaded by angry hungry aliens from a distant Death Star ship, the best offering to avoid possible violence or slavery believe it or not would be to hand over our silicon-based sand and rocks? Which way do all of our planets in our Solar System rotate? Have you ever wondered why comets such as Halley’s Comet, Pons-Gambart, and Ikeya-Zhang Comets take 75, 188, and 366 earth-years respectively to come around?
Questions like these and their answers fascinated me camping outside as a boy looking up into the night sky with astonishment. How far away is that star, I would ask myself, which lead to another question and another. Limitless.
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A 100-foot telescope and multi-million dollar observatory are not necessary to begin an intermediate knowledge of the celestial. Your outstretched arm, hand and fingers can suffice in determining an object’s angular size. Clamp your hand in a fist. Across your knuckles is about 10 degrees. Don’t believe me? Taking that fist and starting at the horizon count how many “fisted-hands” it takes to count upwards to straight up, or zenith (the top of the sky). It will be about nine hands, or 90 degrees. Three fingers together are about 5 degrees across and one finger, like the pinky finger, will be about 1 degree. A full moon then, when using this form of measurement will be about a half-degree (0.5°).
Finding the position of an object in the sky is a bit more difficult. If you don’t carry around a Cross Staff, or Astrolab, or even what amateur golfers use today: a GPS app; if you can find due north then you can still navigate the sky with your hand. The azimuth, or angular measurement parallel to the horizon in a spherical coordinate system, determines the cardinal points: north, south, east, and west. North is of course 0 degrees, east will be 90 degrees, south is 180 degrees, and due west will be 270 degrees. The angle above the horizon will be, you guessed it, altitude. Keeping our basic sky-gazing simple, when measuring from the horizon to the zenith, only 0-90 degrees is needed. Now you have the quickest most convenient tools to examine the never-ending sky.
A simple pair of binoculars can reveal more of the heavens beyond your naked eye. If you surveyed the full moon, you could easily find many craters or the four brightest moons of Jupiter. With the same binoculars you might be able to find Saturn’s brightest and biggest moon: Titan. If you want to see even more of the night sky, you will have to have binoculars stronger than 7x (times); in other words massively big and expensive type binoculars that will require a tripod or something steady and stationary to mount your 8x plus binoculars. Beyond high-powered binoculars gets us into complex telescopes and well beyond the scope of this post.
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Under the Stars
Some star-maps, a flashlight, items to keep you comfortable or warm, and some patience will be all you need to find stars, constellations, and other sorted celestial performers. The further away from light-pollution you can get (i.e. large towns or cities) the better. Finding cardinal points is easiest with a compass or map; they both work fine. If you can remember where on the horizon the Sunset took place, then you have a general idea which direction is west. Keep in mind though the seasonal factors: during winter the Sun recedes a little south of due west and during summer it sets a little north of due west. In spring and fall, the Sun sets quite close to due west.
If you can view your sky maps with a red-lighted flashlight, then your pupils won’t close up in its light. A normal white flashlight will cause your views from map-to-sky and back again to be greatly hindered by your widening and retracting pupils causing delays in their adjustments and testing your patience. Having red-lenses to cover the bulb or flashlights using a “red-LED” bulb can be purchased at most camping-sporting stores. Also, when you’ve been out a few times and can easily locate previous stars and/or constellations, moving on to unexplored areas becomes quicker and easier as your mapping-spotting skills improve.
One more star-gazing tip: A clear sky is usually pretty cold relative to your latitude. The further away you are from the equator, the colder the clear sky will be and the quicker your sitting-still body will get. Dress warmer than normal, a toboggan or hat might be good, and even bring along a Thermos of hot soup or tea, or as I often do, a warm stout toddy! If you want to “impress” a certain co-stargazer, bring along reclining folding-chairs and a quilt. He or she will be in for a superb relaxing long evening of fun.
The following four seasonal sky maps are near 35 degrees north latitude in North America; in other words, a straight line from Lompoc, CA to Fayetteville, NC. Sky maps from your particular location can be found on the internet or from a local nearby planetarium store. The six bi-monthly descriptions below are incorporated into the flow or movement of the sky maps.
Sirius: The Five-month King of Stars
From late December through mid-April, in the southeasterly sky, the brightest star of all stars in our sky is Sirius. It is the brightest because it is the closest star to Earth: about 8-light years away and closing. Yes, you read correctly, Sirius is getting closer to our Solar System and will be noticeably brighter in about 50,000 to 60,000 years. After that it will begin moving away, but for the next 200,000 years or so it will always be the King of All Stars. During winter and spring Sirius is a great reference point if you are just starting out as a new astronomer.
Serving King Sirius and moving to the west and slightly up is his Viceroy Rigel, then further up are Viceroys Betelgeuse (better known as Beatlejuice), Procyon to the east, and finally back toward the west and near straight up is Aldebaran. Straight up, or near zenith, and more north is his lone Viceroy Capella. These five stars represent magnitudes about 2.5 times less than Sirius but are so bright they can all be spotted in a large city with light-pollution. King Sirius’ “court” is the primary reason the winter skies are the favorite season for stargazers; they jump out to you!
Galaxies Galore and A New Prince
Heading into spring (March – early May) you’ll notice that Sirius and his viceroys have moved toward the western horizon. Back to the southern horizon is a darker starless sky by comparison. Yet due east near the horizon comes the newest viceroy or Prince: Arcturus which has been led by the largest cluster of galaxies – almost halfway up to the zenith – called the Virgo Clusters. They include more than 1,300 galaxies. Off toward the north and halfway to zenith you can find the Big Dipper.
Another Viceroy and King Sirius Departs
While Sirius drops down behind the western horizon and Procyon and Capella soon follow, the newest member to the court arrives: Viceroy Vega. Almost to the northeastern horizon, Vega’s brightness equals that of his predecessors and brings with him the Northern Cross with Deneb (touching the horizon) as its crown. It is now May through early July. Move to the southeastern horizon close to Earth’s surface, and the claws of Scorpius have appeared with Antares as its heart. Near the zenith sits Arcturus, 2nd in command for about two-plus months, while Sirius vacations in his summer palace doing “unseen” kingly jollies for the next four.
The Milky Way’s Majesty
July and August are the best times to see the center of our galaxy particularly with binoculars. Like a following royal parade, Vega brings along in the eastern sky not only Altair, a star slightly brighter than the previous Deneb, but also the globular-cluster M13 near zenith, and the star-clusters M11, M39, and the best clusters M6 and M7. And as if that wasn’t enough, the nebulas M8, M20, and M17 between Scorpius and Sagittarius to the south (about 10° up from horizon), round off the fat center of our majestic Milky Way.
The gaudiness of summer and the Milky Way drift into the southwest horizon causing many astronomers to say the night sky is the tamest from September through late October. It is perhaps no coincidence then that fall and October are celebrated as Halloween, or hallow the dead and dying. The Viceroy Arcturus has all but vanished behind the western horizon, leaving only Prince Vega near the zenith. The return of Capella and the first of King Sirius’ court are probably not yet visible to the northeast. A seemingly dark “blanket” ensues.
Not to worry, as all great exciting events take place to the south – sexual overtones intended – magnitude 1.16 star Fomalhaut rises out of Earth’s vagina to remind us that with persistence comes birth… and for better or worse, MANY MORE THINGS to come! Can I get an Amen!? Because Fomalhaut is the lone bright star in this part of the sky, many space agencies and orbital spacecraft engineers use the star as a point of reference for their machines. Their computerized satellites or crafts are programmed to find Fomalhaut and then align themselves. There is less of a chance for other mistaken bright stars nearby; a computer optic no-brainer if you will.
Because the heavens are darkest during this time of year, many scientist and expert stargazers use their high-powered telescopes to search out darker phenomena. This goes to show that a certain darkness is needed to truly see the stars.
The Mira and Algol Light Show
As King Sirius’ court of brightest stars rise again in the east, with a set of binoculars (certainly a telescope) a dance or battle can be seen more clearly between two stars; technically between the star Mira “The Wonderful” and the double-star system Algol “The Winking Demon.”
Mira is in the middle of Cetus the Whale, a quiet faint constellation of stars about 45 degrees up from the southeast horizon between Aquarius (to the southwest) and Orion (to the lower east) and the returning Aldebaran, Rigel, and Betelgeuse. Mira fades from a semi-bright magnitude 2 to a very dim magnitude 10 in less than eleven months. Mira means “the Wonderful” in Arabic and signifies her dramatic leaving and return. This happens due to her near-death lifespan and being unstable, pulsating prior to burn-out. When Mira is big and cool, most of its light is only visible in the infrared spectrum. When she is small and hot, she radiates most of her light at the far end of the visible spectrum; red in a telescope. Mira has quite possibly already turned into a planetary nebula then white dwarf, but we won’t witness this for another 35,000 Earth-years because she is about 350-light years away.
Algol in Arabic means “the Demon” and they called the double-star system this because astonishingly one star eclipses the other every 2.87 days! This makes its brightness dip from a 2.2 magnitude to a 3.5 magnitude creating the winking demons. This change can be seen by the naked eye. Algol can be located up about 60 degrees from the easterly approaching the zenith during mid-November to mid-January.
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As you may have noticed, it is impossible to include all the major fascinating parts of stargazing and our cosmos in a 1,000 word blog-post – the commonly recommended length. This post is around twice that long. Therefore, I am including further website resources to explore should you want to know more, even become a well-informed astronomer.
P.S. To answer the two initial questions in the beginning all our planets rotate counter-clockwise around the Sun. And about those once-in-a-lifetime comets and why they take so long to return and why they keep coming back… it is because of our Sun’s gravitational control. It extends out to the Kuiper Belt which is well beyond the outer planet Neptune, or about 2.8 billion miles from our Sun. Perspective: and our Sun is one of the smallest Suns in the galaxy and cosmos!
This work by Professor Taboo is licensed under a Creative Commons Attribution-NoDerivs 3.0 Unported License.
Permissions beyond the scope of this license may be available at https://professortaboo.wordpress.com. | 0.941892 | 3.181132 |
This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of April 2009. The month sees the return of the borderline major meteor shower, the Lyrids. The highlight of the month is the lunar occultation of Venus right before dawn on April 22.
Note: If anyone has pictures or observations of these objects/events and want to share them, send me a comment. I’ll post them here.
Mercury – This month brings us the best opportunity of the year to observe Mercury in the evening sky (for Northern Hemisphere observers). Mercury will be at its highest on April 26, though even then it will be low in the western sky 30-60 minutes after sunset.
The Moon will also located just above Mercury on the evening of April 26. The image below shows what the scene will look like from North America. Note that the Pleiades open star cluster will be located between Mercury and the Moon. It will be a great sight via your eye or binoculars. In a telescope, Mercury will appear as a fat crescent with ~36% of its disk illuminated.
Saturn – Saturn is the only planet visible in the evening sky. By the end of twilight, Saturn is high in the southeast under the eastern part of the constellation of Leo.
This year Saturn is dimmer than usual. At magnitude +0.6 to +0.7, there are at least 11 stars that are brighter than it. The reason is that the rings of Saturn contribute a lot to the brightness of Saturn. But this year, is a ring plane crossing year meaning that the rings are nearly edge-on. As a result, the rings are reflecting much less light in the Earth’s direction this year. Saturn’s appearance through a telescope will match the below image taken by Bob Lunsford on March 28. Note the small dark spot near the top edge of Saturn’s disk, this is a shadow cast by Saturn’s largest moon, Titan.
The Moon will pass a relatively distant 5.5 degrees to the south of Saturn on the evening of April 6.
Venus – After spending the past few months dominating the evening sky, Venus will now spend the rest of the year as a morning object. If you live south of the Equator, Venus will appear to rocket higher and higher every morning. In fact it should be an easy sight by the 2nd week of April if you have a clear eastern horizon. Venus will reach its highest in late May.
For those of us north of the Equator, Venus will take a little longer to gain altitude. Though it is already visible for observers with a clear eastern horizon, Venus will slowly climb higher every night. For northern observers, Venus won’t reach its highest till August. Regardless of where you are observing, Venus will be at its brightest on April 29 though it is always a very bright object.
For binocular and telescope users, Venus will start the month as a large thin crescent, 59″ across and only ~2% illuminated. By mid-month, it will have shrunk to ~50″ across but it will also become a fatter crescent with ~12% of the disk illuminated. By the end of the month, it is 39″ across and 25% illuminated
Venus is also involved in the coolest event of the month. On the morning of April 22, the Moon will occult (or pass in front) of Venus for observers in most of North America. The below map from the International Occultation Timing Association (IOTA) shows where the occultation will be visible. Times for the beginning and end of the occultation can be found at IOTA’s site. I’ll write more about this as the date draws closer.
The following diagram gives a good representation of what the occultation will look like right before the Moon passes in front of Venus on the morning of April 22. Note that Mars will be located nearby as well. For those with binoculars or a telescope, Venus will appear as a thin crescent similar to, but much smaller than, the Moon.
Jupiter – Jupiter rises a few hours before sunrise. Other than Venus, it is the brightest “star” in the morning sky at magnitude -2.2. Due to Jupiter’s location in the southern constellation of Capricornus , it never gets very high this year.
Mars – Mars can be seen very low in the eastern sky all month long. At magnitude +1.2, it is only as bright as some of the brighter stars. Venus will pass a distant 5.5 degrees to the north of Mars on April 24. As a result, Mars will be located just below the spectacular Moon-Venus occultation.
The month of March experiences no major showers and only a few minor ones. It continues the annual lull in meteor activity from mid-January to mid-April.
Sporadic meteors are not part of any known meteor shower. They represent the background flux of meteors. Except for the few days per year when a major shower is active, most meteors that are observed are Sporadics. This is especially true for meteors observed during the evening. During April, 8 or so Sporadic meteors can be observed per hour from a dark moonless sky.
Major Meteor Showers
April brings the first major meteor shower since the Quadrantids in early January. The Lyrids are produced by Comet Thatcher, a comet on a ~400 years orbit that has only been observed in 1861. The Lyrids, on the other hand, can be seen every year.
The radiant is located between the constellations of Lyra and Hercules. Though the radiant rises during the evening, the best time to see Lyrids is after 11 pm when the radiant is high in the sky.
The shower is active from April 16 to 25 with a peak on the morning of April 22. The shower only shows good levels of activity on the night of the peak. Even then, this is the most minor of the major showers with a peak rate of ~15-25 meteors per hour.
Though there are no predictions on enhanced activity, the Lyrids have been known to put on grand displays. The 1st great display goes back almost 25oo years while the last happened in 1982. So you never know, this year could be the next good display.
Minor Meteor Showers
Minor showers produce so few meteors that they are hard to notice above the background of regular meteors.
Pi Puppids (PPI)
The Pi Puppids are usually a very low activity shower. In 1977 and 1982, the shower put on a good display with up to 60 meteors per hour being observed. This shower radiates from the far southern constellation of Puppis and can not be seen from most of North America and Europe.
We now know that the Pi Puppids are created by Comet 26P/Grigg-Skjellerup. P/G-S is a small Jupiter family comet that orbits the Sun once every 5.3 years.
There are no predictions for enhanced material this year. The shower is active from April 15-28 with a peak on April 23. At its best we should expect 1-2 meteors per hour with even that number being optimistic for northern observers.
Eta Aquarids (ETA)
The Eta Aquarids are a major shower, especially for southern hemisphere observers, when they peak on May 5. During the month of April, the shower can be considered a minor shower.
The ETA were produced by Comet Halley which also gives us the Orionids in October. Models suggest that the ETA were released by Comet Halley no later than 837 AD. The Orionids are easy to see because the particles are hitting the Earth from the anti-solar direction. This means the meteor shower can be seen in the middle of the night. The ETA are produced by meteoroids moving outbound from the Sun, as a result the radiant is located relatively close to the Sun. This means that the ETA radiant is only visible for an hour or so before twilight.
The shower spans from April 19 to May 28 with a peak around May 5 with a maximum ZHR of ~60. The last week of April will see some low activity (ZHR < 10) from the ETAs.
Additional information on these showers and other minor showers not included here can be found at the following sites: Robert Lunsford’s Meteor Activity Outlook, Wayne Hally’s and Mark Davis’s NAMN Notes, and the International Meteor Organization’s 2008 Meteor Shower Calendar.
Naked Eye Comets (V < 6.0)
Binocular Comets (V < 8.0)
Small Telescope Comets (V < 10.0)
Comet C/2009 E1 (Itagaki)
This recently discovered comet was found by amateur astronomer Koichi Itagaki of Yamagata, Japan. Comet C/2009 E1 (Itagaki) is a long-period comet which will come within 0.60 AU of the Sun at perihelion on April 7. It is also periodic in that it returns once every ~250 years according to the latest orbit.
This is the 1st comet to bear Koichi Itagaki’s name but it is not his 1st discovery. Back in 1968, he was a co-discoverer of Comet Tago-Honda-Yamamoto. Due to the rule that only the 1st 3 discoverers can have their name attached to a comet, his name was left off. Only a few months ago, he also re-discovered long-lost comet Giacobini.
The comet is located in the evening sky north of the constellation of Aries. As the month progresses the comet will move north of the Sun as it travels through Triangulum, northern Pisces and Andromeda. Only observers with a clear view of the northwestern horizon in the evening and northeastern horizon in the morning will be able to see the comet. By May the comet will only be visible in the morning sky and will be much easier to see.
At magnitude ~8.0 to 8.5, the comet is bright enough to be seen in a reasonably sized backyard telescope. Having said that, I was just barely able to see it from my backyard in Tucson with my 12″ telescope due to the city lights and the bright twilight.
A finder chart for Comet Itagaki can be found at Comet Chasing.
A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany).
Comet C/2009 F6 (Yi-SWAN)
A new comet has been discovered that should be the brightest comet in the sky this month. Comet C/2009 F6 (Yi-SWAN) is a long-period comet which will pass within 1.27 AU of the Sun on May 8. The comet is currently around magnitude 8.5 making it bright enough to be seen in small telescopes. Right now the nearly Full Moon will make observing the comet difficult but in a few days the Moon will not be a problem for evening observers. The comet is located north of the Sun. For southern hemisphere observers, you are out of luck. For northern observers, the comet can be observed in both the evening and morning sky.
Currently the comet is located in Cassiopeia. It is moving to the east and will enter Perseus by mid-month. The comet should continue to brighten as it approaches perihelion and may be as bright as magnitude 8.0.
On the morning of April 21, I was able to observe Yi-SWAN with 30×125 binoculars. My observing location isn’t too dark with a limiting magnitude of ~+5.5. Even then, the summer Milky Way was faintly visible. The comet was barely visible as it was large and diffuse. Interestingly, the comet was not visible during multiple attempts to observe it during the evening hours. The darker morning sky most definitely helped.
The comet was found by Dae-am Yi of Yeongwol-kun, Gangwon-do, South Korea on March 26. He noticed the obvious blue-green glow of a comet on 2 images he took with a Canon 5D digital camera and a 90-mm f/2.8 lens. The other discoverer was Robert Matson of Irvine, CA. Mr. Matson found the comet on a series of images taken with the SWAN instrument on the SOHO (Solar Heliospheric Observatory) spacecraft starting on March 29. The SWAN insturment images the entire sky for solar Lyman-alpha particles that are backscattered off of neutral hydrogen atoms. In this way, SWAN can monitor the activity of the far-side of the Sun. This instrument is also excellent at detecting the glow of hydrogan in the extended coma of comets.
Comet C/2007 N3 (Lulin)
Comet Lulin was discovered by the Lulin Sky Survey in Taiwan on 2007 July 11. At the time the comet was located beyond the orbit of Jupiter. The comet will be closest to the Sun on 2009 January 10 at 1.21 AU from the Sun. It will be closest to Earth in late-February when it will be only 0.41 AU from us.
The comet is fading after its closest approach to Earth in late February. It is a evening object and spends all of April moving westward through western Gemini. The comet starts the month around magnitude 8.5 and should fade to magnitude 10.0 or fainter by the end of the month.
A finder chart for Comet Lulin can be found at Comet Chasing.
Comet C/2006 W3 (Christensen)
This comet was discovered over 2 years ago on 2006 November 18 by Eric Christensen of the Catalina Sky Survey north of Tucson. At the time the comet was located at 8.7 AU from the Sun which is nearly the distance of Saturn. The comet continues to move closer to the Sun and Earth and is currently 3.8 AU from the Sun and 3.4 AU from the Earth.
The comet is currently around magnitude 9.5 and will slowly brighten during the month. It is moving near the border of Lacerta and Pegasus. The comet is best seen in the early morning. I was able to observe the comet visually with my backyard 12″ reflecting telescope back in November. Being small and condensed, the comet was fairly easy to see.
The comet will continue to brighten as it approaches perihelion at a still rather distant 3.12 AU from the Sun on 2009 July 6. At that time, the comet will be 8th magnitude and visible in many smaller backyard telescopes and even binoculars from dark sites. Christensen should remain bright enough to see in modest sized backyard telescopes for all of 2009.
On the morning of April 21, I was able to observe this comet with both 30×125 binoculars and a 12″ dobsonian. The comet was much easier to see in the 12″. Observation was made under a moderately light polluted sky with a limiting mag of ~+5.5.
A finder chart for Comet Christensen can be found at Comet Chasing.
Binocular and Small Telescope Asteroids (V < 10.0)
Ceres is the biggest asteroid in the Main Belt with a diameter of 585 miles or 975 km. It is so big that it is now considered a Dwarf Planet. Classified as a carbonaceous (carbon-rich) Cg-type asteroid, there are suggestions that it may be rich in volatile material such as water. Some even propose that an ocean exists below its surface. Ceres is one of two targets for NASA’s Dawn spacecraft which is scheduled to visit it in 2015. Last month Ceres was at opposition (at its closest to the Earth and at its brightest). This month Ceres will fade from from magnitude 7.4 to 8.0 as it ends is retrograde motion just north of Leo. If you are observing Saturn with a telescope or pair of binoculars, try your hand at finding Ceres with one of the finder charts linked below.
Pallas is also a carbonaceous asteroid though with a slightly bluish B-type spectrum. Due to its high inclination (tilt of its orbit with respect to Earth’s orbit) of 34 degrees it is a difficult target for future spacecraft missions. Pallas is large with dimensions of 350x334x301 miles or 582x556x501 km. This month it continues moving north, leaving the constellation of Orion and entering Monoceros. It fades from magnitude 8.7 to 8.9 over the course of the month.
Flora is a large asteroid roughly 136x136x113 km in dimension. It is innermost large asteroid in the Main Belt. As a result, it can get bright enough for backyard observers with modest sized telescopes and binoculars. Flora is a stoney S-type asteroid and also the largest member of the Flora family. This family was created when a large impact occured on Flora. The other family members are pieces of Flora that were thrown off by the impact.
Flora starts the month at magnitude 10.0. It reaches its maximum brightness on April 22 at magnitude 9.8. By the end of the month, it has slightly faded to 9.9. Flora and Irene provide us with a 2-for since both objects are located within 5 degrees of each other.
Since there I have not been able to find a nice star chart showing the position of Flora, here is one I made with the C2A program. It also shows the position of Irene.
Irene was discovered by John Russel Hind in 1851, being only the 14th asteroid known at the time (if you are wondering ~400,000 asteroids have been discovered to date, we’ve come a long way). It is an S-type asteroid with a stoney or silicate composition. Its takes 6.3 years to orbit the Sun.
This month Irene will brighten from magnitude 9.2 to a maximum of 8.9 on April 24 as it retrogrades through western Virgo. Remember Flora is located within 5 degrees of Irene.
Discovered in 1851, Eunomia is one of the largest stoney S-type asteroids. Its dimensions are roughly 357×255×212 km. Similar to Flora, Eunomia is also the parent body of its own family.
Eunomia spends all of April in the constellation of Corvus, just to the south of Virgo. With opposition on April 2, the asteroid is as bright as it’s going to get this year at magnitude 9.8. As the month progresses it will fade to 10.0. This year Eunomia is at aphelion, its furthest from the Sun making this one of its faintest oppositions. When at perihelion, it can get as bright as magnitude ~8.
Since there I have not been able to find a nice star chart showing the position of Eunomia, here is one I made with the C2A program.
Discovered in 1854, Amphitrite was the 29th asteroid to be discovered. Similar to Euterpe, Amphitrite is also a stoney S-type asteroid. With an average diameter of 127 miles (212 km) it is bigger than Euterpe though its further distance from the Earth and Sun keeps it from getting as bright.
Amphitrite fades from magnitude 9.5 to 10.1 this month. It spends the entire month in eastern Virgo not far from Saturn. If you are observing Saturn, take a short star-hopping trip to Amphitrite
Since there I have not been able to find a nice star chart showing the position of Amphitrie, here is one I made with the C2A program. | 0.855769 | 3.429623 |
An iron-poor type known as aubrite is a better fit (see the box on page 31).
But a piece of Mercury should be much darker than an aubrite. It might also smell faintly of sulfur, appear heavily shocked, exhibit signifi cant exposure to cosmic rays, and even be slightly magnetic.
All previous candidates for pieces of Mercury (called angrites and aubrites; S&T: April 2012, page 31) are close but imperfect matches to the surface composition found by NASA's Messenger spacecraft.
"NWA 7325 is tantalizing, and certainly more consistent with the Messenger results than either angrites or aubrites," he explains, "but we need a [spacecraftreturned sample] for 'ground truth'."
We have not yet identified any other parent asteroids with as much certainty, but we know from their composition that the Aubrites
and the Ureilite meteorites are rocks from the mantles of two different asteroids that had violently explosive eruptions, which ejected what should have become their crustal rocks into space at escape velocity. | 0.868163 | 3.221114 |
Gibbous ♏ Scorpio
Moon phase on 18 April 2030 Thursday is Full Moon, 15 days old Moon is in Scorpio.Share this page: twitter facebook linkedin
Moon rises at sunset and sets at sunrise. It is visible all night and it is high in the sky around midnight.
Moon is passing first ∠4° of ♏ Scorpio tropical zodiac sector.
Lunar disc appears visually 2.8% wider than solar disc. Moon and Sun apparent angular diameters are ∠1965" and ∠1910".
The Full Moon this days is the Pink of April 2030.
There is high Full Moon ocean tide on this date. Combined Sun and Moon gravitational tidal force working on Earth is strong, because of the Sun-Earth-Moon syzygy alignment.
The Moon is 15 days old. Earth's natural satellite is moving through the middle part of current synodic month. This is lunation 374 of Meeus index or 1327 from Brown series.
Length of current 374 lunation is 29 days, 16 hours and 10 minutes. This is the year's longest synodic month of 2030. It is 1 minute longer than next lunation 375 length.
Length of current synodic month is 3 hours and 26 minutes longer than the mean length of synodic month, but it is still 3 hours and 37 minutes shorter, compared to 21st century longest.
This New Moon true anomaly is ∠139°. At beginning of next synodic month true anomaly will be ∠165.9°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
11 days after point of apogee on 6 April 2030 at 18:47 in ♉ Taurus. The lunar orbit is getting closer, while the Moon is moving inward the Earth. It will keep this direction for the next day, until it get to the point of next perigee on 19 April 2030 at 03:44 in ♏ Scorpio.
Moon is 364 800 km (226 676 mi) away from Earth on this date. Moon moves closer next day until perigee, when Earth-Moon distance will reach 358 706 km (222 890 mi).
10 days after its descending node on 8 April 2030 at 08:29 in ♊ Gemini, the Moon is following the southern part of its orbit for the next 2 days, until it will cross the ecliptic from South to North in ascending node on 21 April 2030 at 09:46 in ♐ Sagittarius.
24 days after beginning of current draconic month in ♐ Sagittarius, the Moon is moving from the second to the final part of it.
10 days after previous North standstill on 8 April 2030 at 08:53 in ♊ Gemini, when Moon has reached northern declination of ∠22.881°. Next 2 days the lunar orbit moves southward to face South declination of ∠-22.812° in the next southern standstill on 21 April 2030 at 11:15 in ♐ Sagittarius.
The Moon is in Full Moon geocentric opposition with the Sun on this date and this alignment forms Sun-Earth-Moon syzygy. | 0.860247 | 3.110381 |
JACKSON HOLE, Wyoming -- There is mounting evidence of the role of water in Mars' evolution. That fact appears to have been favorable to the development of life -- and the leftover calling card of past biology may be preserved in that world's geologic record.
Scientists from around the world have gathered here to present what is known, as well as agree on need-to-know essentials, at The Second Conference on Early Mars: Geologic, Hydrologic, and Climate Evolution and the Implications for Life.
Even more compelling is the thought that life may well have taken a beating and kept on ticking over time. And if so, where on the planet is it today? Scientists are admittedly awash in new data.
Mars is being scrutinized daily by the largest contingent of sensor-laden orbiters and rovers ever sent there. But teasing out the planet's secrets is a daunting, long-term task. A crossbreeding of research talents to investigate Mars has proven essential.
"Mars is a hellishly complicated and enormously large planet," noted Steve Squyres of Cornell University and leader of the science teams for the Mars Exploration Rovers (MER) -- Spirit and Opportunity -- that remain alive, well, and hard at work.
Mars has a total land surface area the same as the total land area of the Earth, Squyres said. No surface mission is going to address the global truths about Mars.
"Our mission is fundamentally addressing issues of ancient water and habitability at two specific sites. And extrapolating those broadly and globally is dangerous business," Squyres told SPACE.com .
The influx of new data received from the MER rovers has been striking.
Yet the richness, the diversity, and the complexity of the two landing sites -- Gusev Crater and Meridiani Planum -- outstrips what you could do if there were 10 MER machines at each site, each operating for a decade, Squyres advised.
"The thing about a rover mission is that, as long as you can keep moving, there's always something new over the horizon," Squyres related. "A rover's work is never done."
The twin land rovers, the European Mars Express, as well as NASA's Mars Global Surveyor and Mars Odyssey orbiters - all these spacecraft are making contributions to grasp the nature of the martian surface.
"But like it is in any particular discipline, as you learn more you ask more questions," said Steve Clifford, lead organizer of the conference from the Lunar and Planetary Institute in Houston, Texas. "You begin to realize the things you thought you had a good handle on...well, maybe you don't."
For instance, the history of water on Mars, its state and distribution and the role of water in the evolution of the planet today - there's a revolution underway in our understanding of this issue and others, Clifford said. Furthermore, is water lurking subsurface at Mars and how might that boost the prospect for life today?
Clifford said the first Early Mars meeting was held in 1997, spurred by the revelations over the so-called "Mars rock" - the ALH84001 meteorite -- and claims that it possibly carried evidence for martian microbial life.
Now jump ahead some seven years later. "There are a lot of pieces to the puzzle," Clifford explained, regarding the environment that might have existed very early in martian geologic history.
"It's very likely if there was a biosphere on Mars, there's a signature of that biosphere preserved in the ice that might be present in the northern plains of the planet," Clifford said. Major questions in his mind: Where the water went? And where a biosphere that could have evolved on Mars might go in order to survive to the present day?
"The key is an interdisciplinary approach. If you just have one particular discipline, you don't develop the synergies. You don't develop eureka moments," Clifford said.
Water: pervasive and long-lived?
Mars researchers are in "a real struggle" trying to put everything into context, said Laurie Leshin, a planetary scientist at Arizona State University in Tempe, Arizona. "Think about trying to understand the Earth by landing on a bicycle in Alabama and Australia. We have to keep in mind that Mars is a complex, enormous planet."
Leshin said there is no concrete evidence that there ever was life on Mars. But that possibility has been bolstered by the realization that there's an incredible diversity and distribution of life on Earth, she said.
"I'm more optimistic this year than I was last year," Leshin said about the life on Mars issue and environments on the planet conducive to life. "But it's tricky still."
"I'm still not at that early Mars was warm and wet conclusion," Leshin added.
Nevertheless, the two ancient terrains visited by Spirit and Opportunity and two hits on some kind of water, "that's good," Leshin said. "Whether it was pervasive and long-lived and all over the place and oceanic, who knows...we just don't know."
Boot marks on Mars
Thanks to the onslaught of data streaming in from on-duty Mars spacecraft, the outlook that the red planet was once a habitat for life is far higher today than in the past.
That's the notion of Dave Des Marais, a Mars Exploration Rover long-term planning leader from NASA's Ames Research Center, located near San Francisco, California. The question used to be: "Is there any place we can go on Mars' surface and find evidence of liquid water?" Today, the inquiry is: "Given the places on the surface where there was liquid water, what's the best place to go to increase our chances of seeing, potentially, evidence of life?"
"So I think we've notched the whole thing up," Des Marais told SPACE.com . "We know liquid water was there and was there a long time. Amongst all these places where water has expressed itself, which is the best one that allows us to take that next step...toward discovering evidence of life?"
Des Marais said robotic explorers are setting the stage for follow-up human expeditions to the red planet.
Prior to humans putting their boot marks on Mars, a milestone still ahead is robotic return to Earth of martian samples. "The first return sample has to be more than a handful of loose dust. I'm definitely more upbeat about getting really great stuff in the first sample return today than a year ago," Des Marais stated.
"The human mission to Mars is going to be such a huge investment. When it goes, I just want it to be a smashing success. What we do in the robotic phase of Mars exploration will really set us up for a smashing success when humans go there," Des Marais concluded. | 0.867935 | 3.293091 |
June 13, 2012
Electric planets exist in an electric Solar System.
“The main aurora oval on Jupiter we think should dim when the solar wind blows harder, but what we see is that actually gets brighter, which is totally counter intuitive and we still don’t know why.”
— Jonathan Nichols, University of Leicester
Jupiter is 142,984 kilometers in diameter at its equator. That distinction is important because Jupiter rotates so fast that a day lasts only 9.925 hours. That rapid rotational velocity means that its equatorial diameter is 9275 kilometers more than the distance between its poles.
The gas giant’s magnetosphere extends outward in a toroidal field for approximately 650 million kilometers, reaching beyond Saturn’s orbit. Energetic ions are trapped by Jupiter’s magnetic field, similar to the Van Allen radiation belts that surround Earth. However, the radiation emitted by Jupiter’s field is thousands of times greater, and would be instantly fatal to an unarmored cosmonaut. This means that any manned missions to Jupiter space would require a spacecraft with heavy shielding.
The Galileo spacecraft discovered electric currents flowing around the planet, just as Electric Universe theorists predicted. As the moon Io revolves around Jupiter, electrical power greater than 2 trillion watts is dissipated between them. This electric current travels along Jupiter’s magnetic field lines, creating lightning in the planet’s upper atmosphere, as well as intense aurorae at the poles.
Jupiter’s rings are formed out of a thin sheet of material encircling the planet, and were unknown until about thirty years ago. The ring structure is quite diffuse, making observations difficult unless they are in correct alignment with the Sun. The outer radius begins at 129,000 kilometers, almost the same distance as the moon Adrastea. The four small moons, Metis, Adrastea, Amalthea and Thebe, are said to influence the structure of Jupiter’s rings in the same way that the “shepherd moons” of Saturn govern the shape of its huge ring formation.
More than twelve years ago, Wal Thornhill addressed the “volcanic” plumes on Jupiter’s moon Io and demonstrated that they are plasma discharges from the moon to the gas giant. Some planetary scientists later began to acknowledge the electrical connection between them when Io’s “footprint” was seen in the polar aurora on Jupiter. In fact, all four of Jupiter’s largest moons were discovered to leave their marks in the aurora in the shape of “tails” flowing within the plasma column. Later, when NASA launched New Horizons on a mission to study Pluto and Charon, the “plumes” of Tvashtar, a gigantic volcano on Io, were found to be filamentary in structure with indications that they are actually cathode jet discharges from the electric “hot spots” linking the moon with Jupiter.
Astronomers suggested that “tides” on Io from the “kneading” effect of Jupiter’s gravity cause the charged particles to be released in the “volcanic” plumes. The particles then flow as an electric current to Jupiter. Since electricity does not flow in one direction the one-way connection cannot be correct, so how is the electricity moving between Io and Jupiter?
Conventional theories assume that the Universe is electrically neutral, so when observational evidence confirms electrically active plasma for instance, localized phenomena no matter how improbable are invoked. Tidal forces and volcanoes are presented as the cause for the activity seen on Io and the evidence for electric circuits is ignored. In the case of Jupiter’s rings, the same thing is happening. The ring charge is said to be caused by sunlight and shadow rather than by an electric circuit between Jupiter and the Sun.
An electrical interaction between Jupiter and its moons means that they are charged bodies and are not electrically neutral. Jupiter exists in a dynamic electrical relationship to the Sun and it is now known that charged particles from the Sun and not “reconnecting magnetic field lines” power the planetary aurorae. Just like the aurorae, the ring system on Jupiter is probably behaving in similar fashion to what is seen on Saturn, so a similar explanation is most likely correct.
The gas giant planets all have rings in some form or another. The plasma torus that surrounds each of them and the electric currents flowing along the polar axes and then out the equatorial plane are the likely cause for their persistence. No one knows for sure how planetary ring systems are formed and maintained, but rather than seeking the answer in strictly mechanical action electricity and current flow through dusty plasma will provide more reasonable explanations. | 0.900476 | 4.001054 |
August 02, 2012
Did tectonic and volcanic forces create the wide, parallel trenches on the Moon?
The Moon has seen cataclysmic devastation at some time in its past. There are giant craters, wide and deep valleys, and multi-kilometer long rilles crisscrossing its surface.
Conventional theories postulate that the Moon has undergone intense selenological activity early in its history. The rilles and offset slip faults, known as “graben,” are said to result from slow crustal movements similar to those that cause terrestrial earthquakes. This theory implies that the Moon was born long ages ago, perhaps several billion years or more ago, and has not changed much since.
Most scientific theories are parochial in nature. They take their cues from what is observed on Earth, and use those data to model formations observed on other celestial bodies. However, since there is no evidence that the Moon was once subjected to tectonic activity, Electric Universe theory proposes that the idea should be reversed: structures in space ought to model what is found on Earth.
A recent press release states that lunar graben formed when the Moon’s crust pulled apart. The “stretching” created two parallel faults, allowing the surface between them to collapse into a valley. Thomas Watters, lead author of an upcoming paper in the journal Nature Geoscience wrote: “The graben tell us forces acting to shrink the moon were overcome in places by forces acting to pull it apart. This means the contractional forces shrinking the moon cannot be large, or the small graben might never form.”
Similar formations are observed wherever telescopes and satellites look. A reasonable hypothesis would demonstrate how airless, frozen bodies can compare to hot, wet planets like Earth. Since consensus scientific reports give electricity little credence, although it is many orders of magnitude more powerful than gravity, thermal shock or crustal spreading is nothing when compared to the effects of a multi-trillion joule electrical discharge.
Selenologists possess few tools that can help them understand planetary scarring, since there are no courses in electricity needed in their field. Plasma physicists realize that charged objects immersed in electric fields develop Langmuir sheaths, named after plasma pioneer Irving Langmuir. Langmuir sheaths isolate charged objects from each other inside double layers. If the charged objects are planets or moons, they might be surrounded by double layer plasmaspheres.
Laboratory experiments demonstrate that when charge sheaths collide they cause electrical breakdown. A large enough charge flow will initiate an electric arc. If smaller charge sheaths in the laboratory behave in a certain fashion, then larger planetary sheaths could trigger gigantic lightning bolts. Such interplanetary discharges could rip rock strata apart, carve surfaces with a plasma “torch” effect, and create intense heat through electromagnetic induction.
The Moon does not possess a plasmasphere. However, that does not mean that it was not enveloped in a charge sheath at some time in the past. Also, during part of its orbital path Earth’s plasmasphere encompasses the Moon, so electric discharge effects involving our planet could easily have included it.
Rather than stretching or collapse, the rilles and graben on the Moon could have been incised by electric discharges at some time in the recent past. | 0.87263 | 3.795656 |
DARMSTADT, Germany—A robotic probe has become the first craft to land on a comet, a historic moment for space exploration and one that offers the promise of fresh insights into what comets are made of and how they behave.
Rocket scientists at the European Space Agency’s mission control here erupted in cheers as they received the first signal that the Rosetta mission’s probe, called Philae, had touched down on the forbidding landscape of a small comet known as 67P/Churyumov-Gerasimenko.
It is still not clear where exactly the probe has landed or if it was damaged. Philae, which is about the size of a small fridge, was aimed for a relatively flat elliptical landing area about 550 yards in diameter, away from deep crevices, large boulders and sharp peaks.
If it landed intact, Philae is expected to quickly snap a few photographs and beam them back to Earth—in the first images ever taken from the surface of a comet. (It takes nearly half an hour for a signal from the comet to reach earth.)
The comet has extremely low gravity. To prevent the probe from bouncing back into space, it carries a pair of harpoons designed to fire immediately and fix the probe to the ground. A thruster on the top was simultaneously expected to push the probe downward to help in the anchoring, but scientists discovered overnight that the thruster couldn’t be activated and that the harpoons would have to do the job alone.
Made of ancient ice, dust and other materials, comets are objects of scientific curiosity because they have survived virtually intact from the earliest days of the solar system, more than 4.6 billion years ago.
Because comets carry water and organic molecules, scientists also hope that the Rosetta mission will provide insights into whether comets could have brought water to Earth and possibly kick-started life here.
After a decadelong trek through the solar system, the spacecraft Rosetta made a rendezvous with the comet in August.
- Webcast: Live From ESA Mission Control
- Video: A Decade of the Rosetta Mission in 90 Seconds
- Seven Questions With Rosetta Project Scientist Matt Taylor
- Video: William Shatner Wishes Rosetta Good Luck
- Scientists Gear Up for Bid to Land Probe on Comet (Nov. 11, 2014)
- The Numbers: How Probes Get ‘Gravity Assists’ (Aug. 29, 2014)
- Rosetta Mission Reaches Comet (Aug. 11, 2014)
Corrections & Amplifications
Confirmation of the Rosetta probe’s successful touchdown on the comet is expected in a one-hour window around 1602 GMT (11:02 a.m. ET). An earlier version of this article and a headline incorrectly said confirmation is expected around 1702 GMT (12:02 ET). (Nov. 12, 2014) | 0.810474 | 3.565306 |
In order for this radiative force to cause the deuterons to fuse, it must be larger than the repulsive Coulomb force
at the seperation where the attractive strong force can take over and fuse the two deuterons, a distance of [d.sub.s] = 1.6 x [10.sup.-15] m.
(When two charges are very close, this coulomb force
can be very strong.)
The solar sail is a recent invention in the domain of propellantless propulsion of the spacecraft , based on electrostatic Coulomb force
. The force results from the momentum exchange between the flow of ions or electrons and the positively charged or negatively charged conductive body, respectively.
Stability of NPs depends on the intermolecular forces among them, such as van der Waals force and Coulomb force
. Intermolecular forces of NPs are influenced by the size of NPs and their distance, so which can affect the aggregation behavior of NPs in water.
Around 1930, a theory called field theory, was developed that the electromagnetic force arises due to the exchange of photons between the electric charges (Coulomb force
But as more and more protons get packed into a nucleus, the strong force begins to be overwhelmed by the Coulomb force
, which causes particles of the same charge to repel each other.
The first analytical analysis of forced vibrations with friction sliding was performed by den Hartog (1931), who approximated the non-linear friction Coulomb force
as an equivalent viscous damping.
The chaos-regularity border is qualitatively defined by comparing and equating the strengths of the Coulomb force
with the magnetic force acting on the moving point charge e with mass [m.sub.e].
Simulation time has been dramatically reduced by an embedded "MD Engine(R)," a dedicated computation board for high-speed computation of nonbonded interactions such as coulomb force
and intermolecular force that account for more than 99% in many cases of molecular dynamics simulation.
As it passes through a plasma, the high energy beam will redistribute the electrons so that the net Coulomb force
is decreased but the magnetic force is not affected.
As a counter example to the gravitational force, consider the free space Coulomb force
([e.sup.2]/[r.sup.2]) between two charges e separated by the distance r.
Components of the Coulomb force
per unit volume are determined as the product of space charge density and the field strength: | 0.867784 | 3.895405 |
I don't like to give comfort to tinfoilers
But it would be an elegant solution to the Fermi Paradox. Any sufficiently advanced species starts mucking about with particle accelerators and soon builds one that gobbles them up.
Here on the Reg Large Hadron Collider (LHC) desk, where we follow the rollercoaster triumphs and disasters which occur at the world's mightiest particle-thrasher, there are occasional quiet spells. Right now, for instance, the titanic machine is shut down for a couple of days' technical tweaks. On such days we cast about us …
If the black hole escapes, the chance of it striking the moon or sun are just ridiculously tiny: draw a sphere around the earth, that just includes the moon. Let's use spherical coordinates. The moon typically occupies 1/2 degree of the sky, so in our spherical coordinates that's 1/720th along the phi-axis and 1/360th along the theta-axis, or roughly 4 chances in a million of striking the moon. The sun has about the same half-degree appearance in the sky, so similar chances of being hit.
Most of space is empty.... hence the name.
Tiny Blackholes are constantly being formed and then explode. If they didn't, they would have collected in the center of the Sun long before now and gobbled it up.There are much more powerful collisions at the Center of the Sun than we could ever make here on Earth in a Lab. My biggest fear from Tiny Blackholes is that they may explode with the force of a hand grenade. It is possible they they could be formed in the LHC and spin out at nearly the speed of light and detonate within milliseconds somewhere within a mile or so of the LHC itself.
I understand sweet cock all about subatomic physics or indeed any of this cosmic stuff, but even I can see a flaw in his argument...
Surely a black hole has no more gravitational attraction that the matter it was originally made from? If you collapsed the entire planet into a singularity wouldn't that singularity still have the same gravitational pull as the planet, pre collapse? So if you collapse some tiny particles into even tinier black holes then those tine black holes would have no more ability to eat the planet than the original particles. And since these particles are already present and the planet hasn't been eaten does that not disprove the good Doctor's theory?
Actually, your post displays some of the traits that make a good scientist:
You admit that there are things you do not know;
You do not profess absolute certainty in what you do know;
You start with simple, common-sense questions based on things like the conservation of mass/energy;
You address them with things that are known empirically.
If enough people thought like that, we might not have a Tinfoil Tuesday.
I think its about the seperation - a singularity has infinite density and zero size / radius so as the gravitational attraction is inversely proportional to the separation distance, other particles can get so close that the gravity is much higher. It only needs to eat enough other particles to outweigh the energy of the hawking radiation and it will keep growing forever. Then again, I may not have much more idea than you. No doubt some more boffinly commentards will sort us out shortly ....
The singularity is effectively a point, but that's not the important criterion. The event horizon is; that is the point at which the escape velocity reaches the speed of light. A massive black hole has a large event horizon while a tiny one has a very small one, but every event horizon has a definite and finite size.
As the radius of the event horizon drops, the gradient of the gravitational field gets steeper. That in fact is what drives Hawking radiation and the enormous energy output of a microscopic black hole. It's also why a supermassive black hole will last for trillions of years while a microscopic one vanishes in a tiny puff of logic and a flash of gamma radiation.
Now if they report on your report on their report and someone then reports on that report of your report on their report of your report of their report reporting on this report Rinse&repeat
Ummm will we create a black hole and all disappear into Paris before the LHC?
Sometimes, some articles, provoke such thought and emotion that to actual express anything becomes impossible as everything tries to run out of your mouth like a room full of school kids completely failing to leave through the door at the same time. Would be nice to have a Wittgenstein icon or failing that a Tex Avery dropped-jaw icon for such moments...
I always find these tinfoilers so funny.
Lets look at his argument - although these collisions are happening all the time with cosmic rays hitting earth particles, his excuse that this doesnt create black holes is that - they do in fact but the momentum of the cosmic ray diverts them away at extremely high velocity. Funny how we dont see these black holes at all (flying away from as often as they are), or the ones that come from other planets in our solar system, or other solar systems for that matter. the ones from other solar systems would surely come flying through here every now and then and probably would have collected more mass and become somewhat bigger by now, you would think wouldnt you? But no we dont see any of these... hmmm...
But no the LHC is dangerous because your hitting 2 particles head on, and so there will be no momentum for the resulting black hole to be propelled away from us and so it will stay and kill us all! Umm so what happens to all the cosmic rays that hit head on in space directly above our heads. Ok its probably not that common but surely were talking at least 1 every 10 years or so somewhere in the vicinty of Earth? Have you seen any black holes sitting around earth recently? They dont have any momentum anymore so they should just be sitting around too, eating everything in sight, like a fat kid at a childrens party... but nope i dont see any around, do you?
I somehow dont think i will be worrying too much just yet, even with the good docs theories...
The fact that white dwarfs and neutron stars actually exist is proof enough that "black hole eatout" is not going to happen anytime soon as these objects have not yet captured anything in spite of having a density compared to which our Gaiaball is akin to a light smoke.
Still, compressing the Moon into a Black Hole? That would be awesome! But I am sure you better be on the far Earth hemisphere during the last second of infall unless you like being a crispy critter.
Surely the best reason not to destroy the planet....
"And CERN is the good uncle of the planet. And they would destroy this World. They would lose all credit with a majority of young people on the planet."
CERN..please don't destroy the planet - you will lose all credit (credibility?) with the young...only a majority mind you - not all of them.
Black holes were predicted in the 18th century using Newtonian gravitation and (as it happens) the (Schwarzschild) radius of the event horizon is the same as that deduced under general relativity. It's hard to avoid the conclusion that a sufficiently large and dense object will have an escape velocity greater than the speed of light.
For further reading, I can recommend "An Introduction to Modern Cosmology" by Andrew Liddle, which tackles many of the aspects of cosmological theory without the need for Tensor Analysis.
If by "predicted in the 18th century" you are referring to the Michell-Laplace dark body, no they weren't. This is a misunderstanding of the definition of escape velocity. This and other errors in black hole theory are explained in accessible form here: http://www.ptep-online.com/index_files/2006/PP-05-10.PDF
Schwarzchild's paper is here: http://www.sjcrothers.plasmaresources.com/schwarzschild.pdf
Hilbert's (commonly but incorrectly referred to as Schwarzchild's) is here: http://www.sjcrothers.plasmaresources.com/hilbert.pdf
The black hole theory and its history are a neat example of how failure to examine the underlying assumptions of a theory leads to false conclusions. Once the erroneous basis is commonly known, academic reputations based on the false conclusions will be wiped out.
To the person who wanted to know what was at the centre of the Milky Way, it is thought to be a plasma focus in an electrical discharge. This theory is taken seriously by people such as the IEEE and their journal IEEE Transactions on Plasma Science.
Tensor Analysis *is* necessary to understand Hilbert's error and why no fewer than four derivations of the solution to Einstein's field equation are mutually consistent and contradict Hilbert.
I'm no physicist but my understanding is that a black hole is a an uber-dense body held together by the force of gravity.
Following this reasoning, if you DID manage to make a teeny black hole then surely it would be so small that it's gravitational force would also be teeny (it would only consist of a handful of atoms). With such a low gravitational force to hold it together, my further thought is that it certainly wouldn't have enough gravitational pull to drag anything else into it, and indeed would simply dissipate again almost instantly.
Got to be careful of Pooh Pooh you know...
"...never ignore a pooh-pooh. I knew a Major, who got pooh-poohed, made the mistake of ignoring the pooh-pooh. He pooh-poohed it! Fatal error! 'Cos it turned out all along that the soldier who pooh-poohed him had been pooh-poohing a lot of other officers who pooh-poohed their pooh-poohs. In the end, we had to disband the regiment. Morale totally destroyed... by pooh-pooh! ..."
It (and every other star in the sky) represents a far more convincing demonstration of CERN's basic argument (that nature is doing this all the time without destroying anything). The sun is a far bigger target and has a dense core of particles moving at very high speeds. The chances that no "mini-black-hole" has ever been stopped dead in its tracks somewhere in the sun's core at some point in the last 5 billion years are surely pretty small.
And yet the observational evidence for stars being short-lived objects is pretty thin.
CERN's safety report (it's on their website) says "it is expected that all black holes are ultimately unstable" and their "expected lifetime would be very short."
So, if everything is as 'expected', then CERN finds out some more about the universe than they know now; but, if not , then we all get to die in a way no-one has ever died before.
I wonder if there's anything they haven't thought of...
Eating the Earth in a few years? I think not.
A black hole located at the centre of the Earth would swallow the entire meaningful planet in less than an few hours if it didn't evaporate... So long as it has an event horizon matter would fall into it under the force of the planets own gravity... that collapse would happen now if it wasnt for the pressure of the inner atoms repelling the ones higher up against the force of gravity...
If there was an event horizon there would be no atoms able to affect an opposing pressure, the whole planet would fall towards the centre and pass through the event horizon unopposed... Even if the mass of a black hole did not increase as more matter fell into it, the whole earth would soon be going bye bye as the effect of its own gravity being centred at the core would accelerated the contents of the planet towards the black hole.
By the way El Reg, if you wanna advance the cause of science, start linking to Richard Muller's PFFP.
Mark, if you want to advance the cause of science how about starting with some simple maths:
1. Given the collision energy at the LHC what is the diameter of the event horizon if a black hole is created?
2. How does that compare to the diameter of electron orbit around the proton/neutron core of an atom.
3. Therefore, as the blackhole oscilates from one side of the earth, through the centre, to the other side just how much matter is impacted by the event horizon?
Clue: it's very, very, like you-know *very* small...
All perfectly valid points - but I was actually considering the matter from a theoretical standpoint of a black hole at rest. There are a few things you may wish to consider though:
1) 15 TeV is the energy of individual proton collisions - not the entire beam. There is the possibility that the whole beam would be deposited through the singularity in less than 100 microseconds.
2) You presume that nothing but the singularity is stationary - this is not the case. Consider the enormous heat underground - Once you get to the mantle you're talking between 500 and 1000 Celsius. That is a *lot* of kinetic energy moving a lot of very dense matter about - significantly increasing interceptions with the event horizon.
3) Even beyond the event horizon there are forces which would accelerate additional matter towards the singularity.
So yes, while your points are well taken, and while I do not think that the LHC is going to implode us, the sun, or anywhere else for that matter... I do think there is a lot more theoretical discussion to be had on the matter.
Even if I believed "black holes" existed i wouldn't be worried about the LHC.
And if it does end Humanity, oh well, its not like we haven't had the ability to start some colonies elsewhere in the solar system for a long time now.
Bootnote; the equations for "black holes" require some special case tinkering to allow them to work. Most physicists will tell you that when an equation yields infinite values (gravity, density) as part of its solution you need to check your equation and starting assumptions.
Super massive objects with super luminal escape velocity's I can accept, infinite gravity/density at the core of it? No.
the coming collapse of the Earth into a marble-sized black hole will mean that we won't have to pay off all those budget deficits that are being racked up!
Paris--because, like a black hole, she's dense, attracts things (pageviews, celeb boyfriends, paparazzi) and her arrival has been heralded as the harbinger of the end of our civilization...
I instinctively distrust any mechanism named after the person citing it as a reason for/against something happening. "Hawking" radiation just happens to be the excuse Professor Hawking gives for the evaporation of black holes, does it? How convenient!
Not only that. I believe that the cosmic ray black hole menace is a reality, and that I was hit by one such infalling microhole only this morning. It passed right through me, of course, but in doing so took out the neuron responsible for knowing where my car keys were and made me late for work.
But of course such empirical proof is nothing to the so-called scientists of today, who require people have labs and staff and grants and gangs of sycophants and the ability to do hard sums before they'll listen to reason.
because I believe the LHC doesn't exist! WHERE'S THE PROOF? Has anyone actually seen a proton collision? Sure we have pretty computer-generated pictures, but I also have computer-generated pictures of giant pliers over Bromwich, which PROVES that the LHC is FALSE.
Therefore, no threat from micro-black holes, except for the accounting black hole - where's the money going?
"How We Lost The Moon, A True Story by Frank W. Allen" was in the Peter Crowther (PS Publishing) edited anthology Moonshots and was collected in Dozois' 17th. Here Paul J. McAuley describes how an experiment on the Moon goes badly wrong, as a black hole is created which begins, inexorably, to feed on the Moon itself.
(Of which I will say no more because you really do not want to know.)
Oh hell, fire that sucker up. Micro black holes?
Last week they were experimenting with stranglets*.
Strangelets for God's sake.
Go out and Google quark stars and strangelets.
Who cares about some pansy ass black hole?
*We are all going to die.
Hawking formula for temperature of black hole T = (hbar c^3) / (8 pi k G M) can easily be transformed to T = (hbar g) / (2 pi k c).
Compare it with Unruh formula for the temperature of accelerated rod T = (hbar a) / (2 pi k c).
If you use the Bell paradox for rods of different length you will come to conclusion that T=T(r).
Using mc^2=hbar c / R_c one can receive the temperature at the depth R_c:
T = mgR_c / (2 pi k).
Or at the any depth R, if g=const:
T = mgR / (2 pi k).
Or in differential form:
dT/dR = mg /(2 pi k).
Changing the depth R by the distance from the center of gravitating object, r:
dT/dr = -mg /(2 pi k).
This is a formula of gravitational gradient of temperature! It was received in the analogues form by Loschmidt and after by Tsiolkovsky and by … and by me in the form:
dT/dr = -(2/5)mg / k.
This temperature gradient does not lead to thermal exchange. This temperature gradient is quite good proved by the experimental observations.
So, there is no any process of BH evaporation. Hawking formula describes the luminosity of usual stars.
The most dangerous objects are not black holes, but magnetic holes or condensates of strange matter.
The amount of dark matter in the Galaxy is 6 times bigger than the usual barionic matter. Contact of microscopic droplet of dark matter with ordinary matter will transform the Solar system into a cosmic corpse.
I give 50% probability that CERN will explode the Earth in a couple of weeks. The 30-th of March it will collide protons with the energy 2*3.5 TeV.
The "fast moving and so they cannot be captured" argument against possible BHs produced by cosmic rays fails when you consider Neutron stars. The have densities at or above atomic nuclei and would easily trap any BH produced when a cosmic rays hits them. Since we have never seen one disappear, and have known some to exist for thousands of years, this puts a rather large holes in that theory as well.
As I tell my students when they ask - the only time that you should worry is when you see large numbers of us particle physicists boarding rockets for the moon. Until then you can be pretty certain that we are not going to do anything dangerous to the Earth. This worked fine until one student asked whether that was why CERN had a space plane - thank you Dan Brown! (and no we do not have a space plane - otherwise I would not spend my time crossing the atlantic to do shifts in economy class!)
"As I tell my students when they ask - the only time that you should worry is when you see large numbers of us particle physicists boarding rockets for the moon."
You really are a particle physicist, aren't you? With no concept of what reality actually involves?
What rockets? What would you do there? Eat cheese?
Biting the hand that feeds IT © 1998–2020 | 0.849809 | 3.15229 |
A galaxy is a massive, gravitationally bound system consisting of stars, an interstellar medium of gas and dust, and dark matter. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (1012) stars, all orbiting a common center of mass. Galaxies can also contain many multiple star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.
Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with curving, dusty arms. Galaxies with irregular or unusual shapes are known as peculiar galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a star burst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.
There are probably more than 100 billion (1011) galaxies in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or mega parsecs). Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called super clusters. These larger structures are generally arranged into sheets and filaments, which surround immense...
Please join StudyMode to read the full document | 0.851456 | 3.78419 |
From what I've read, planets orbiting red dwarf stars would most likely be tidally locked. Under what circumstances might this change? For example, if a planet had been the recipient of some kind of large impact over the course of its existence? We theorize that in the Solar System, Venus's reverse orbit might have been caused by a big impact. If such a thing were to occur on a planet orbiting a red dwarf, could it spin on some kind of "normal" rotational period (e.g., 5-100 hour days).
1) A possibility to make a planet less tidally locked would be libration.
Luna, the Moon, has libration that makes it seem to wobble very slightly as it orbits the Earth.
Tidal locking means that the period that the Moon takes to revolve or orbit 360 degrees around the Earth is exactly the same as the period it takes the moon to rotate 360 degrees. So one side of the Moon always faces the Earth and one side always faces away from the Earth. This is because the average orbital speed and the average rotation speed of the Moon are identical.
But the speeds at any particilar moment are not exactly identical. The orbits of all astronomical objects are elliptical and thus deviate more or less from perfectly circular orbits. Thus objects speed up and slow down as they orbit other objects. So the Moon sometimes travels faster and sometime slower than it's average orbital speed. But the Moon cannot speed up or slow down its rotation, it has to always rotate at its average rotation speed.
So a total of 59 percent of the Lunar surface is visible from Earth, instead of fifty percent.
So if your planet orbited its sun in exactly 3 Earth days or 72 Earth hours, it would orbit at an average rate of 120 degrees per Earth day or 5 degrees per Earth hour. And if tidally locked it would rotate at exactly 120 degrees per Earth day or 5 degrees per Earth hour. And if the planet's orbit is highly eccentric the planet's variable orbital speed would sometimes be faster or slower than it's exact rotation rate, thus making for a lot of libration and for a lot more than 59 percent of the planet's surface to sometimes be in daylight.
In our solar system the planet Mercury has an orbital eccentricity of 0.2563 and is 1.5177 times farther from the Sun at Aphelion distance than at Perihelion distance. If Mercury was tidally locked to the Sun its libration would be 23.65 degrees due to its eccentric orbit.
Of course the same tidal forces that would tend to lock the planet's rotation would also tend to make its orbit more and more circular with time.
2) Maybe, like Mercury, its orbit and rotation might become locked in a 2:3 resonance.
Mercury has an orbital period or year that is 87.9691 Earth days long. It has a rotation period relative to distant stars (or sidereal day) 56.646 Earth days long. That means that it's solar day, it's day relative to the sun, is two Mercurian years, or about 176 Earth days long.
If another solar system had a much smaller scale version of Mercury's orbit and rotation, each might be, for example, one twentieth as long as that of Mercury.
The hypothetical planet could have an orbital period or year that is 4.398 Earth days long, with a rotational period period relative to distant stars (or sidereal day) of 2.8323 Earth days. That means that it's solar day, it's day relative to its sun, would two of its years, or about 8.796 Earth days long.
So divide those figures by three to get a year 1.442 Earth days long, a sidereal day 0.9441 Earth days long, and a solar day 2.932 Earth days, or 70.368 Earth hours, long.
Can a star have such a close habitable zone that a planet would have a year only 1.442 Earth days, or 34.608 Earth hours, long?
Here is a discussion of distances of habitable planets from their stars:
Apparently K3-137b has the shortest known year of any know exoplanet, 4.31 hours, orbiting a red dwarf - except that PSR J1719-1438 orbits a pulsar every 2.2 hours. But they are not listed as potentially habitable planets.
The list of known exoplanets in the conservative habitable zone includes ones with years 12.4, 9.2, 6.1, and 4.05 Earth days long. They orbit TRAPPIST-1, a M8V type star. I don't know if a M9V typed star could be enough dimmer to have a planet orbiting it in the habitable zone with a year as short as 1.442 Earth days.
For a solar day 100 Earth hours long, a habitable planet with Mercury-like resonance would have a year 2.0492 Earth days long, a sidereal day 1.341 Earth days, long and a solar day 4.0984 Earth days, or 98.3616 hours long.
It is possible that your planet could orbit in the habitable zone of a brown dwarf, intermediate between a planet and and star. Thus it might have a year and a solar day shorter than a planet orbiting even the dimmest red dwarf star.
But it seems very likely such a planet would be tidally locked.
I may point out that the apparent movement of the sun in Mercury's sky is sometimes very odd, and that different places on Mercury's equator will have significantly different temperatures during their noonday periods. If this planet planet orbits a red star in the habitable zone the tropics and the temperate zone would be divided by longitude as well as latitude.
Why does Mercury have a 2:3 orbit: spin resonance? Scientists are still coming up with ideas and computer simulations to explain it.
For example, some scientists have proposed that Mercury was once tidally locked to the Sun but a massive asteroid strike changed its rotation period, similar to what paltrysum suggested.
Other computer simulations suggest that a 2:3 resonance is a more natural situation and likely to occur a lot in extrasolar planets.
You should look for other questions and answers about habitable planets in 2:3 resonances.
There is also the suggestion that a habitable planet could actually be a habitable moon of giant planet in the habitable zone of a red star. Thus the habitable moon would be tidally locked to the planet instead of to the star and would have periods of daylight and darkness.
It should be noted that it has been calculated that the orbit of a moon will not be stable unless its month is one ninth or less the length of it's planet's year - the length of the planet's year should be at least 9 times the length of the moon's month. If it is desired that the day on the moon, equal in length to the moon's month, should be about 5 to 100 Earth hours, the length of the planet's year should be at least 45 to 900 Earth hours, or 1.875 to 37.5 Earth days, and it can be several times as long. Thus the length of the planet's year can be made to fit into the the possible length of a year in the habitable zone of a red dwarf star.
You should look for other questions and answers about habitable moons of giant planets in the habitable zones of red dwarf stars.
Are you talking about planets in the goldilocks zone?
If not, simply have the planet be further away from the star. The reason it is thought that planets in the goldilocks zone (the band around a sun where liquid water is possible) of a red dwarf would likely be tidally locked is because they'd have to be so close to their parent star, since red dwarfs are small and dim. If you remove this constraint, you can just move the planet away and it would be able to rotate freely.
In this case the planet wouldn't be terrestrial, but it wouldn't be tidally locked.
If so, and you are in fact talking about planets in the habitable zone, then one proposed solution (which I found on the astromony stackexchange), would be to have the planet be part of a double system with the other member either being a very large moon or even a fellow planet (depending on your definitions).
Systems like these exist in the real world. The Pluto–Charon system being one such example.
In this fashion both bodies would be tidally locked to each other (much as the Moon is to Earth), but not tidally locked to their star. | 0.853408 | 3.85612 |
This is an image of Neptune.
Click on image for full size
An Overview of Neptune's Atmosphere
Neptune's atmosphere shows a striped pattern of clouds. This cloud pattern is very similar to that of Jupiter and Saturn. Neptune even has a Great Dark Spot similar to Jupiter's Great Red Spot.
The structure of Neptune's atmosphere, as on Earth, consists of a troposphere, stratosphere, mesosphere, and thermosphere.
The evolution of Neptune's atmosphere is similar to that of the other Giant planets. The composition of Neptune clouds is thought to be methane crystals.
Motions in the cloud patterns give clues about Neptune's meteorology, which is similar to that of Jupiter and Saturn.
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Neptune's atmosphere shows a striped pattern of clouds. This cloud pattern is very similar to that of Jupiter and Saturn. Neptune even has a Great Dark Spot similar to Jupiter's Great Red Spot. The structure...more | 0.846972 | 3.383989 |
Yves Couder's bouncing droplets Was Einstein wrong again?
One quantum mechanics interpretation is de Broglie-Bohm pilot wave theory where a particle is guided by the so-called quantum potential. While the mathematics of it are well known, the question is if we can actually simulate it in the laboratory. Enter the world of Yves Couder's bouncing droplets. The setting is that of an oil bath to which vibration is applied from below. The amplitude is low enough to prevent creating waves. When a droplet is dropped on the surface it will bounce and create a wave. Then the wave and droplet interact creating a wave-particle "duality". See the Morgan Freemen's video below from the Science Chanel: "Through the Wormhole".
The question is if this experiment can be understood as a genuine explanation of quantum mechanics. Yves Couder does not make such a claim but at minute 3:36 Morgan Freeman claims somebody does and I am not sure what the argument really is. Perhaps Bill Nye the science guy could provide some quantum mechanics clarifications. Here is another video that enlightens us a bit more:
But what would bounce in the case of quantum mechanics? Nothing at all, in other words the aether.The aether was disposed as a concept by Einstein in his special theory of relativity, but Bohmian mechanics does allow speeds higher than the speed of light, so could Einstein have been wrong?
Einstein was wrong on several occasions: it is generally accepted that he lost his debate with Bohr, his first prediction of the bending of light rays by the Sun during an eclipse was off by a factor of two, and he attempted to publish a paper in which he predicted that gravitational waves do not exist. So was he correct in his special theory of relativity?And what would power the vibrations in the case of quantum mechanics? Uri Geller seems to suggest that the Big Bang echo that still reverberates today as the cosmic microwave background radiation could provide the vibration similar with what Couder does to the oil bath. But what about the special theory of relativity itself? What is the correct theory? The director of the Einstein Centre for Local-Realistic Physics, Joy Christian, has generalized the theory of inertial structures and provided the correct replacement of the special theory of relativity which can be put to the test by observations of oscillating flavor ratios of ultrahigh energy cosmic neutrinos, or of altering pulse rates of extreme energy binary pulsars. This genuine breakthrough in correcting special theory of relativity was followed by more amazing breakthroughs in understanding quantum mechanics and uncovering the deep geometric structure of a complete description of reality as a parallelized 7-sphere. Moreover, in a related work of the same quality and caliber, it looks like torsion energy is mostly responsible for the mass of fermions as Fred Diether III, the operating director of the center, has shown. Should the Nobel committee withdraw Peter Higgs' prize and awarded it instead to Fred Diether and Joy Christian? You bet. At the very minimum, what mathematicians call Hodge duality should be renamed Christian duality in honor of the correct generalization of it which put to shame the quantum foundation community. Unfortunately this community follow blindly the dogma of "the most pointless" discovery, Bell's theorem. Just like von Neumann theorem was discredited, so too Bell's theorem is a modern scandal as well. 4/1/2016 | 0.837503 | 3.162027 |
Ever wonder how in the world the Hubble Space Telescope (HST) takes those awesomely fascinating photos of galaxies, stars, planets, nubulaes, and supernova remnants more that are a gazillion light years away from us?
Here's The Process: Scientists point the HST to a particular region of space. The HST exposes an image for a long time to collect more light rather than zooming in on them. It collects as many photons as possible on optical sensors which relays the data to computers here on earth which recombines the data into pictures.
The HST takes pictures using the full spectrum of light from infrared to ultraviolet that the human eye cannot see. It even uses X-rays. It uses lenses that either captures or filters different wavelengths. It sees or filters out different colors such as red, blue, and green . This tells us what we are looking at, such as hydrogen atoms, oxygen atoms, and nitrogen ions.
Example:Hydrogen emits red light. If the HST did not do filter out the color red, most pictures would be kind of reddish as hydrogen is by far the most abundant element in the universe. Hence, astronomers can tell by color just what the heck they are looking at. By combining these images scientists can create full-color pictures.
And the images are enhanced too. There is nothing wrong with doing this.
|The Sombrero Galaxy| | 0.873792 | 3.060319 |
CloudSat and CALIPSO were designed to complement each other in the 1990s. They launched together on the same rocket in 2006. Then they spent more than 10 years orbiting Earth in formation with a coterie of other satellites in what's known as the A-Train, or afternoon constellation.
Flying together enables the A Train satellites to gather diverse measurements of the Earth below at nearly the same time as they circle the globe pole-to-pole, crossing the equator around 1:30 p.m. local time every day. The nearly simultaneous observations allow scientists to build a more sophisticated understanding of the Earth system than would be possible if the measurements were separated. Other members of the A Train include NASA's Aqua, Orbiting Carbon Observatory-2 and Aura spacecraft, along with the Japan Aerospace Exploration Agency’s Global Change Observation Mission - Water (GCOM-W1) satellite.
In the A-Train, measurements from CloudSat's radar and CALIPSO's lidar were combined to revolutionize the way scientists see clouds and the tiny particles suspended in the atmosphere collectively known as aerosols. Scientists have long known that there are important interrelationships between clouds and aerosols, but prior to the launch of CALIPSO and CloudSat, did not have the tools to understand how they interact.
The scene above shows two tropical cyclones from September 20, 2017 — Hurricane Maria near the Caribbean Sea and Tropical Storm José off the northeast U.S. coast. Data from the CALIPSO lidar and CloudSat radar appear as vertical slices in the atmosphere. CALIPSO lidar data is visualized as a bluish slice, with red and yellow colors denoting more scattering off of clouds and aerosols. CloudSat radar data is superimposed on the CALIPSO slice in brighter colors. Areas of heavier precipitation, found in each storm’s spiral bands, appear in red and pink. Credits: NASA/Roman Kowch
It was a beautiful partnership forged in labs around the world: At NASA's Langley Research Center in Hampton, Virginia, which provided the aerosol-measuring lidar carried by CALIPSO; at the Centre National d'études Spatiales, or CNES, in Toulouse, France, which provided the CALIPSO spacecraft; at the Canadian Space Agency, or CSA, in Montreal, Canada and the Jet Propulsion Lab in Pasadena, California, which built the radar on CloudSat; and at the labs of Ball Aerospace Corporation in Boulder, Colorado, which build the CloudSat spacecraft.
CloudSat and CALIPSO orbited and took measurements together for almost 12 years in the A-Train. Then, in February 2018, facing a mechanical challenge, CloudSat had to exit the A-Train, moving to a lower orbit — leaving
CALIPSO behind and the future of their partnership uncertain.
Read more about how CloudSat and CALIPSO are working together again! | 0.833123 | 3.402202 |
The stars have at all times been a fascinating subject. A variety of know that scientists and astronomers have put a variety of work into enhancing the expertise with telescopes in order that they may have better outcomes of viewing the celebs, planets, and different objects that they might uncover throughout the galaxy.
Our academic program is designed to serve both the novice stargazer who needs to discover the workings of the Universe and our place inside it, and also majors who will make astronomy a central a part of their future lives. House probes have visited most planets in the Solar System, and orbiters and rovers are homing in on the habitability of Mars.
Astronomers of early civilizations carried out methodical observations of the night sky, and astronomical artifacts have been discovered from much earlier intervals. They observe gentle coming from stars, planetary programs and galaxies which have been just formed for us, on Earth.
If you happen to go in the summer, as most individuals do, you will not be seeing any stars apart from the solar. Astronomers once thought asteroids have been boring, wayward area rocks that merely orbit around the Sun. The study of stars and stellar evolution is fundamental to our understanding of the universe.
U.S. Bureau Of Labor Statistics
Many people are focused on what lies past the Earth and moon. We notice that GJ 357 is a high correct movement star with zero.139′′ per 12 months in RA and −zero.990′′ per 12 months in Dec primarily based on the Gaia Information Release 2 (DR2) information ( Gaia Collaboration 2018 ). It signifies that the star was about zero.8′′ to the west and about 6′′ to the north at the time of the FastCam statement.
Many historic civilizations employed individuals with some data of the night sky and the motions of the Solar and Moon, though in many circumstances the identities of these historic astronomers have long since been lost. An international group of astronomers, together with Jonathan Tan from the College of Virginia, have made observations of a molecular cloud that’s collapsing to kind two huge protostars that can ultimately develop into a binary star system.
TheAstronomy conference collection goals to build a dynamic and inventive neighborhood of scientists and educators to use the potential supplied by fashionable computing and the web within the era of information-pushed astronomy. Theoretical astronomy is oriented toward the development of laptop or analytical fashions to describe astronomical objects and phenomena. Our photo voltaic system is situated within the Milky Method Galaxy, a group of 200 billion stars (together with their planetary techniques).… Read More.. | 0.899936 | 3.410674 |
One of the most puzzling astronomical discoveries of the last decade has just gotten a little bit clearer. Astronomers still don't know what's producing the brief, powerful bursts of radio waves they've been detecting, but for the first time, they've been able to see where one of them is coming from.
Astronomers first detected these so-called Fast Radio Bursts in 2007. Until now, all 16 FRBs that have been reported have all been found by combing through archival data.
But Evan Keane, an astronomer with the Square Kilometer Array Organization, says he and his colleagues wanted to catch one in the act. That way, they could point other telescopes in the direction of the FRB to search for clues about its origin.
"I was in South Africa when it happened," Keane says. He'd been in a long engineering meeting the day before and had been planning to sleep in that Saturday morning. "But of course, my phone started going crazy in the morning" with people calling to say the computer had found an FRB. They called it FRB 150418, for the day it was found.
Keane and his colleagues immediately alerted a network of telescopes they had assembled around the world to help pinpoint and characterize an FRB if and when they found one.
The Australia Telescope Compact Array at the Paul Wild Observatory was able observe the radio "afterglow" from FRB 150418. ATCA is an array of six 22-meter antennas used for radio astronomy, and it was able to localize the source with a thousand times the accuracy of the Parkes telescope.
Then, the Japanese Subaru telescope took up the search. Subaru is a large optical telescope located on Mauna Kea in Hawaii. It was able to see the patch of sky where ATCA showed FRB 150418 had come from.
"There's only one thing there," Keane says, "and it's a galaxy, an eliptical galaxy."
An elliptical galaxy 6 billion light years away.
Unfortunately, Keane says, knowing that doesn't explain what's generating the massive pulse of radio energy.
But knowing how far away that object is lets you do some extremely interesting calculations. That's because the different frequencies that make up the radio burst don't all arrive at the exact same time. The longer frequencies are delayed.
"And the reason for that delay is the stuff that the signal has gone through — the particles and dust in the intervening space," Keane says. And by measuring the delay, you can measure how many particles there are between us and the galaxy.
And knowing how many particles there are between are between here and a galaxy 6 billion light years away gives you an estimate of how much that slice (or cylinder, if you'd prefer) of the universe weighs.
Although what's generating these FRBs is still a mystery, the new discovery gives some hints. Keane says the galaxy where the FRB originated is comprised mostly of older stars. "Our conclusion [is] that FRB 150418 is likely to be from a one-off event in an older stellar population," he and his colleagues write in the journal Nature, in a paper describing the find.
Keane's organization, the Square Kilometer Array Organization, is designing a giant radio telescope that should be able to detect lots more of these FRBs. Maybe enough to figure what's making them.
And before you ask, there's no good evidence that FRBs are being generated by extraterrestrials. | 0.840391 | 3.901919 |
Aerial view of LIGO Hanford Observatory. LIGO Laboratory
The Nobel Prize-winning project that hunts for gravitational waves— ripples in space and time—is about to begin the longest and most sensitive observational run to date. The National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO) received a series of upgrades to its lasers, mirrors and other components and will start its third Advanced LIGO observing run on April 1. Several Rochester Institute of Technology researchers who are members of the LIGO Scientific Collaboration are preparing to pore over the new data to help uncover some of the universe’s biggest mysteries.
LIGO made history with the first direct detection of gravitational waves in 2015. The ripples traveled to Earth from a pair of colliding black holes located 1.3 billion light-years away. Since then, the LIGO-Virgo detector network has uncovered nine additional black hole mergers and one explosive smashup of two neutron stars.
RIT’s Center for Computational Relativity and Gravitation (CCRG) has a large and active group of 18 faculty, students and postdoctoral researchers involved in the LIGO Scientific Collaboration. They are excited about what a new, more sensitive observing run can uncover and expect to see an even greater number of black hole mergers and other extreme events, such as additional neutron-neutron star mergers or a yet-to-be-seen black hole-neutron star merger.
A. Sue Weisler
RIT’s Center for Computational Relativity and Gravitation (CCRG) has a large and active group of 18 faculty, students and postdoctoral researchers involved in the LIGO Scientific Collaboration. From left to right, Professor Carlos Lousto, Assistant Professor Richard O’Shaughnessy, Professor Manuela Campanelli, Associate Professor John Whelan.
“Big data is transforming our world, not because any one individual observation or even instrument provides transformative insight, but because combining data from many of them reveals things we haven’t known before,” said Richard O’Shaughnessy, assistant professor in the School of Mathematical Sciences. O’Shaughnessy’s research focuses on how to discover and interpret gravitational waves produced by merging compact binaries like black holes and neutron stars. “With this third run, we’re at the bridge of having clues about compact binaries that were previously completely inaccessible.”
LIGO, which consists of twin detectors located in Washington and Louisiana, will be joined in the new observing run by Virgo, the European-based gravitational-wave detector, located at the European Gravitational Observatory (EGO) in Italy. The three enhanced sensors working together will allow more precise triangulation of the sources of gravitational waves. This is an important step toward multi-messenger astronomy, the coordinated observation and interpretation of different signals.
In addition to events like black hole and neutron star mergers, LIGO scientists search for weaker, continuous signals like those from spinning neutron stars, where the gravitational wave signal could be identified using a long stretch of data.
“As someone studying continuous waves, the improved sensitivity and the longer observing run means we can probe into our sources in a more interesting way,” said John Whelan, associate professor in the School of Mathematical Sciences and principal investigator of RIT’s group in the LIGO Scientific Collaboration. Whelan develops and implements methods to search for gravitational waves and currently leads an effort targeting Scorpius X-1, one of the most promising sources of continuous gravitational waves. “Scorpius X-1 is the first source of x-rays discovered outside the solar system. It is the brightest continuous source of x-rays besides the sun, and it’s a binary system of a neutron star and another less massive star.”
The observing run is expected to last roughly one year, and researchers at RIT expect to begin publishing new findings based on the observations later this year and will have more once the run is complete.
Professor Manuela Campanelli, director of the CCRG, said: “We are very excited about the science that will come out of the new observation run, especially within the context of multi-messenger astronomy. LIGO is an important tool to help reveal the hidden side of the universe and I am proud of the faculty, students and postdoctoral researchers that are a part of the LIGO Scientific Collaboration.”
More Information about the LIGO-Virgo collaborations:
LIGO is funded by NSF and operated by Caltech and MIT, which conceived of LIGO and led the Initial and Advanced LIGO projects. Financial support for the Advanced LIGO project was led by the NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council-OzGrav) making significant commitments and contributions to the project. Nearly 1,300 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. A list of additional partners is available at https://my.ligo.org/census.php.
The Virgo Collaboration is currently composed of approximately 350 scientists, engineers, and technicians from about 70 institutes from Belgium, France, Germany, Hungary, Italy, the Netherlands, Poland, and Spain. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and Nikhef in the Netherlands. A list of the Virgo Collaboration members can be found at http://public.virgo-gw.eu/the-virgo-collaboration/. More information is available on the Virgo website at http://www.virgo-gw.eu. | 0.80901 | 3.66946 |
The North Pole ain’t what it used to be. Well, the geographic North Pole stays fixed over time (mostly because we define it to stay fixed over time) but the magnetic north pole constantly moves. And over the past decade it’s been moving out of Canada towards Siberia four times faster than it has in the past couple centuries. Armed with data from the ESA’s Swarm satellite, scientists might finally know why: the shifting of our magnetic field north pole is caused by a titanic struggle between two competing massive magnetic plumes.Continue reading “Magnetic north is migrating towards Siberia. Here’s why”
When NASA’s Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (Insight) lander set down on Mars in November of 2018, it began its two-year primary mission of studying Mars’ seismology and interior environment. And now, just over a year and a half later, the results of the lander’s first twelve months on the Martian surface have been released in a series of studies.
One of these studies, which was recently published in the journal Nature Geosciences, shared some rather interesting finds about magnetic fields on Mars. According to the research team behind it, the magnetic field within the crater where InSight’s landed is ten times stronger than expected. These findings could help scientists resolve key mysteries about Mars’ formation and subsequent evolution.Continue reading “Magnetic Fields Around Mars InSight are 10x Stronger than Scientists Expected”
For decades, scientists have held that the Earth-Moon system formed as a result of a collision between Earth and a Mars-sized object roughly 4.5 billion years ago. Known as the Giant Impact Hypothesis, this theory explains why Earth and the Moon are similar in structure and composition. Interestingly enough, scientists have also determined that during its early history, the Moon had a magnetosphere – much like Earth does today.
However, a new study led by researchers at MIT (with support provided by NASA) indicates that at one time, the Moon’s magnetic field may have actually been stronger than Earth’s. They were also able to place tighter constraints on when this field petered out, claiming it would have happened about 1 billion years ago. These findings have helped resolve the mystery of what mechanism powered the Moon’s magnetic field over time.Continue reading “The Moon’s Magnetosphere Used to be Twice as Strong as the Earth’s”
For many reasons, Venus is sometimes referred to as “Earth’s Twin” (or “Sister Planet”, depending on who you ask). Like Earth, it is terrestrial (i.e. rocky) in nature, composed of silicate minerals and metals that are differentiated between an iron-nickel core and silicate mantle and crust. But when it comes to their respective atmospheres and magnetic fields, our two planets could not be more different.
For some time, astronomers have struggled to answer why Earth has a magnetic field (which allows it to retain a thick atmosphere) and Venus do not. According to a new study conducted by an international team of scientists, it may have something to do with a massive impact that occurred in the past. Since Venus appears to have never suffered such an impact, its never developed the dynamo needed to generate a magnetic field.
The study, titled “Formation, stratification, and mixing of the cores of Earth and Venus“, recently appeared in the scientific journal Earth and Science Planetary Letters. The study was led by Seth A. Jacobson of Northwestern University, and included members from the Observatory de la Côte d’Azur, the University of Bayreuth, the Tokyo Institute of Technology, and the Carnegie Institution of Washington.
For the sake of their study, Jacobson and his colleagues began considering how terrestrial planets form in the first place. According to the most widely-accepted models of planet formation, terrestrial planets are not formed in a single stage, but from a series of accretion events characterized by collisions with planetesimals and planetary embryos – most of which have cores of their own.
Recent studies on high-pressure mineral physics and on orbital dynamics have also indicated that planetary cores develop a stratified structure as they accrete. The reason for this has to do with how a higher abundance of light elements are incorporated in with liquid metal during the process, which would then sink to form the core of the planet as temperatures and pressure increased.
Such a stratified core would be incapable of convection, which is believed to be what allows for Earth’s magnetic field. What’s more, such models are incompatible with seismological studies that indicate that Earth’s core consists mostly of iron and nickel, while approximately 10% of its weight is made up of light elements – such as silicon, oxygen, sulfur, and others. It’s outer core is similarly homogeneous, and composed of much the same elements.
As Dr. Jacobson explained to Universe Today via email:
“The terrestrial planets grew from a sequence of accretionary (impact) events, so the core also grew in a multi-stage fashion. Multi-stage core formation creates a layered stably stratified density structure in the core because light elements are increasingly incorporated in later core additions. Light elements like O, Si, and S increasingly partition into core forming liquids during core formation when pressures and temperatures are higher, so later core forming events incorporate more of these elements into the core because the Earth is bigger and pressures and temperatures are therefore higher.
“This establishes a stable stratification which prevents a long-lasting geodynamo and a planetary magnetic field. This is our hypothesis for Venus. In the case of Earth, we think the Moon-forming impact was violent enough to mechanically mix the core of the Earth and allow a long-lasting geodynamo to generate today’s planetary magnetic field.”
To add to this state of confusion, paleomagnetic studies have been conducted that indicate that Earth’s magnetic field has existed for at least 4.2 billion years (roughly 340 million years after it formed). As such, the question naturally arises as to what could account for the current state of convection and how it came about. For the sake of their study, Jacobson and his team considering the possibility that a massive impact could account for this. As Jacobson indicated:
“Energetic impacts mechanically mix the core and so can destroy stable stratification. Stable stratification prevents convection which inhibits a geodynamo. Removing the stratification allows the dynamo to operate.”
Basically, the energy of this impact would have shaken up the core, creating a single homogeneous region within which a long-lasting geodynamo could operate. Given the age of Earth’s magnetic field, this is consistent with the Theia impact theory, where a Mars-sized object is believed to have collided with Earth 4.51 billion years ago and led to the formation of the Earth-Moon system.
This impact could have caused Earth’s core to go from being stratified to homogeneous, and over the course of the next 300 million years, pressure and temperature conditions could have caused it to differentiate between a solid inner core and liquid outer core. Thanks to rotation in the outer core, the result was a dynamo effect that protected our atmosphere as it formed.
The seeds of this theory were presented last year at the 47th Lunar and Planetary Science Conference in The Woodlands, Texas. During a presentation titled “Dynamical Mixing of Planetary Cores by Giant Impacts“, Dr. Miki Nakajima of Caltech – one of the co-authors on this latest study – and David J. Stevenson of the Carnegie Institution of Washington. At the time, they indicated that the stratification of Earth’s core may have been reset by the same impact that formed the Moon.
It was Nakajima and Stevenson’s study that showed how the most violent impacts could stir the core of planets late in their accretion. Building on this, Jacobson and the other co-authors applied models of how Earth and Venus accreted from a disk of solids and gas about a proto-Sun. They also applied calculations of how Earth and Venus grew, based on the chemistry of the mantle and core of each planet through each accretion event.
The significance of this study, in terms of how it relates to the evolution of Earth and the emergence of life, cannot be understated. If Earth’s magnetosphere is the result of a late energetic impact, then such impacts could very well be the difference between our planet being habitable or being either too cold and arid (like Mars) or too hot and hellish (like Venus). As Jacobson concluded:
“Planetary magnetic fields shield planets and life on the planet from harmful cosmic radiation. If a late, violent and giant impact is necessary for a planetary magnetic field then such an impact may be necessary for life.”
Looking beyond our Solar System, this paper also has implications in the study of extra-solar planets. Here too, the difference between a planet being habitable or not may come down to high-energy impacts being a part of the system’s early history. In the future, when studying extra-solar planets and looking for signs of habitability, scientists may very well be forced to ask one simple question: “Was it hit hard enough?”
Further Reading: Earth Science and Planetary Letters
When it comes to the study of planets, moons, and stars, magnetic fields are kind of a big deal. Believed to be the result of convection in a planet, these fields can be the difference between a planet giving rise to life or becoming a lifeless ball of rock. For some time, scientists have known that has a Earth’s magnetic field, which is powered by a dynamo effect created by convection in its liquid, outer core.
Scientists have also long held that the Moon once had a magnetic field, which was also powered by convection in its core. Previously, it was believed that this field disappeared roughly 1 billion years after the Moon formed (ca. 3 to 3.5 billion years ago). But according to a new study from the Massachusetts Institute of Technology (MIT), it now appears that the Moon’s magnetic field continued to exist for another billion years.
The study, titled “A two-billion-year history for the lunar dynamo“, recently appeared in the journal Science Advances. Led by Dr. Sonia Tikoo, an Assistant Professor at Rutger’s University and a former researcher at MIT, the team analyzed ancient lunar rocks collected by NASA’s Apollo 15 mission. What they found was that the rock showed signs of a being in magnetic field when it was formed between 1 and 2.5 billion years ago.
The age of this rock sample means that it is significantly younger than others returned by the Apollo missions. Using a technique they developed, the team examined the sample’s glassy composition with a magnometer to determine its magnetic properties. They then exposed the sample to a lab-generated magnetic field and other conditions that were similar to those that existed on the Moon when the rock would have formed.
This was done by placing the rocks into a specially-designed oxygen-deprived oven, which was built with the help of Clement Suavet and Timothy Grove – two researchers from MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) and co-authors on the study. The team then exposed the rocks to a tenuous, oxygen-free environment and heated them to extreme temperatures.
As Benjamin Weiss – a professor of planetary sciences at EAPS – explained:
“You see how magnetized it gets from getting heated in that known magnetic field, then you compare that field to the natural magnetic field you measured beforehand, and from that you can figure out what the ancient field strength was… In this way, we finally have gotten an accurate measurement of the lunar field.”
From this, they determined the lunar rock became magnetized in a field with a strength of about 5 microtesla. That’s many times weaker than Earth’s magnetic field when measured from the surface (25 – 65 microteslas), and two orders of magnitude weaker than what it was 3 to 4 billion years ago. These findings were quite significant, since they may help to resolve an enduring mystery about the Moon.
Previously, scientists suspected that the Moon’s magnetic field died out 1.5 billion years after the Moon formed (ca. 3 billion years ago). However, they were unsure if this process happened rapidly, or if the Moon’s magnetic field endured, but in a weakened state. The results of this study indicate that the magnetic field did in fact linger for an additional billion years, dissipating about 2.5 billion years ago.
As Weiss indicated, this study raises new questions about the Moon’s geological history:
“The concept of a planetary magnetic field produced by moving liquid metal is an idea that is really only a few decades old. What powers this motion on Earth and other bodies, particularly on the moon, is not well-understood. We can figure this out by knowing the lifetime of the lunar dynamo.”
In other words, this new timeline of the Moon casts some doubt on the theory that a lunar dynamo alone is what powered its magnetic field in the past. Basically, it is now seen as a distinct possibility that the Moon’s magnetic field was powered by two mechanisms. Whereas one allowed for a dynamo in the core that powered its magnetic field for a good billion years after the Moon’s formation, a second one kept it going afterwards.
In the past, scientists have proposed that the Moon’s dynamo was powered by Earth’s gravitational pull, which would have caused tidal flexing in the Moon’s interior (much in the same way that Jupiter and Saturn’s powerful gravity drives geological activity in their moons interiors). In addition, the Moon once orbited much closer to Earth, which may have been enough to power its once-stronger magnetic field.
However, the Moon gradually moved away from Earth, eventually reaching its current orbit about 3 billion years ago. This coincides with the timeline of the Moon’s magnetic field, which began to dissipate at about the same time. This could mean that by about 3 billion years ago, without the gravitational pull of the Earth, the core slowly cooled. One billion years later, the core had solidified to the point that it arrested the Moon;s magnetic field. As Weiss explained:
“As the moon cools, its core acts like a lava lamp – low-density stuff rises because it’s hot or because its composition is different from that of the surrounding fluid. That’s how we think the Earth’s dynamo works, and that’s what we suggest the late lunar dynamo was doing as well… Today the moon’s field is essentially zero. And we now know it turned off somewhere between the formation of this rock and today.”
These findings were made possible thanks in part by the availability of younger lunar rocks. In the future, the researchers are planning on analyzing even younger samples to precisely determine where the Moon’s dynamo died out completely. This will not only serve to validate the findings of this study, but could also lead to a more comprehensive timeline of the Moon’s geological history.
The results of these and other studies that seek to understand how the Moon formed and changed over time will also go a long way towards improving our understanding of how Earth, the Solar System, and extra-solar systems came to be.
Back in of August of 2016, the existence of an Earth-like planet right next door to our Solar System was confirmed. To make matters even more exciting, it was confirmed that this planet orbits within its star’s habitable zone too. Since that time, astronomers and exoplanet-hunters have been busy trying to determine all they can about this rocky planet, known as Proxima b. Foremost on everyone’s mind has been just how likely it is to be habitable.
However, numerous studies have emerged since that time that indicate that Proxima b, given the fact that it orbits an M-type (red dwarf), would have a hard time supporting life. This was certainly the conclusion reached in a new study led by researchers from NASA’s Goddard Space Flight Center. As they showed, a planet like Proxima b would not be able to retain an Earth-like atmosphere for very long.
Red dwarf stars are the most common in the Universe, accounting for an estimated 70% of stars in our galaxy alone. As such, astronomers are naturally interested in knowing just how likely they are at supporting habitable planets. And given the distance between our Solar System and Proxima Centauri – 4.246 light years – Proxima b is considered ideal for studying the habitability of red dwarf star systems.
On top of all that, the fact that Proxima b is believed to be similar in size and composition to Earth makes it an especially appealing target for research. The study was led by Dr. Katherine Garcia-Sage of NASA’s Goddard Space Flight Center and the Catholic University of America in Washington, DC. As she told Universe Today via email:
“So far, not many Earth-sized exoplanets have been found orbiting in the temperate zone of their star. That doesn’t mean they don’t exist – larger planets are found more often, because they are easier to detect – but Proxima b is of interest because it’s not only Earth-sized and at the right distance from its star, but it’s also orbiting the closest star to our Solar System.”
For the sake of determining the likelihood of Proxima b being habitable, the research team sought to address the chief concerns facing rocky planets that orbit red dwarf stars. These include the planet’s distance from their stars, the variability of red dwarfs, and the presence (or absence) of magnetic fields. Distance is of particular importance, since habitable zones (aka. temperate zones) around red dwarfs are much closer and tighter.
“Red dwarfs are cooler than our own Sun, so the temperate zone is closer to the star than Earth is to the Sun,” said Dr. Garcia-Sage. “But these stars may be very magnetically active, and being so close to a magnetically active star means that these planets are in a very different space environment than what the Earth experiences. At those distances from the star, the ultraviolet and x-ray radiation may be quite large. The stellar wind may be stronger. There could be stellar flares and energetic particles from the star that ionize and heat the upper atmosphere.”
In addition, red dwarf stars are known for being unstable and variable in nature when compared to our Sun. As such, planets orbiting in close proximity would have to contend with flare ups and intense solar wind, which could gradually strip away their atmospheres. This raises another important aspect of exoplanet habitability research, which is the presence of magnetic fields.
To put it simply, Earth’s atmosphere is protected by a magnetic field that is driven by a dynamo effect in its outer core. This “magnetosphere” has prevented solar wind from stripping our atmosphere away, thus giving life a chance to emerge and evolve. In contrast, Mars lost its magnetosphere roughly 4.2 billion years ago, which led to its atmosphere being depleted and its surface becoming the cold, desiccated place it is today.
To test Proxima b’s potential habitability and capacity to retain liquid surface water, the team therefore assumed the presence of an Earth-like atmosphere and a magnetic field around the planet. They then accounted for the enhanced radiation coming from Proxima b. This was provided by the Harvard Smithsonian Center for Astrophysics (CfA), where researchers determined the ultraviolet and x-ray spectrum of Proxima Centauri for this project.
From all of this, they constructed models that began to calculate the rate of atmospheric loss, using Earth’s atmosphere as a template. As Dr. Garcia-Sage explained:
“At Earth, the upper atmosphere is ionized and heated by ultraviolet and x-ray radiation from the Sun. Some of these ions and electrons escape from the upper atmosphere at the north and south poles. We have a model that calculates how fast the upper atmosphere is lost through these processes (it’s not very fast at Earth)… We then used that radiation as the input for our model and calculated a range of possible escape rates for Proxima Centauri b, based on varying levels of magnetic activity.”
What they found was not very encouraging. In essence, Proxima b would not be able to retain an Earth-like atmosphere when subjected to Proxima Centauri’s intense radiation, even with the presence of a magnetic field. This means that unless Proxima b has had a very different kind of atmospheric history than Earth, it is most likely a lifeless ball of rock.
However, as Dr. Garcia-Sage put it, there are other factors to consider which their study simply can’t account for:
“We found that atmospheric losses are much stronger than they are at Earth, and the for high levels of magnetic activity that we expect at Proxima b, the escape rate was fast enough that an entire Earth-like atmosphere could be lost to space. That doesn’t take into account other things like volcanic activity or impacts with comets that might be able to replenish the atmosphere, but it does mean that when we’re trying to understand what processes shaped the atmosphere of Proxima b, we have to take into account the magnetic activity of the star. And understanding the atmosphere is an important part of understanding whether liquid water could exist on the surface of the planet and whether life could have evolved.”
So it’s not all bad news, but it doesn’t inspire a lot of confidence either. Unless Proxima b is a volcanically-active planet and subject to a lot of cometary impacts, it is not likely be temperate, water-bearing world. Most likely, its climate will be analogous to Mars – cold, dry, and with water existing mostly in the form of ice. And as for indigenous life emerging there, that’s not too likely either.
These and other recent studies have painted a rather bleak picture about the habitability of red dwarf star systems. Given that these are the most common types of stars in the known Universe, the statistical likelihood of finding a habitable planet beyond our Solar System appears to be dropping. Not exactly good news at all for those hoping that life will be found out there within their lifetimes!
But it is important to remember that what we can say definitely at this point about extra-solar planets is limited. In the coming years and decades, next-generation missions – like the James Webb Space Telescope (JWST) and the Transiting Exoplanet Survey Satellite (TESS) – are sure to paint a more detailed picture. In the meantime, there’s still plenty of stars in the Universe, even if most of them are extremely far away!
Further Reading: The Astrophysical Journal Letters
If you’ve read enough of our articles, you know I’ve got an uneasy alliance with the Sun. Sure, it provides the energy we need for all life on Earth. But, it’s a great big ongoing thermonuclear reaction, and it’s right there! As soon as we get fusion, Sun, in like, 30 years or so, I tell you, we’ll be the ones laughing.
But to be honest, we still have so many questions about the Sun. For starters, we don’t fully understand the solar wind blasting out of the Sun. This constant wind of charged particles is constantly blowing out into space, but sometimes it’s stronger, and sometimes it’s weaker.
What are the factors that contribute to the solar wind? And as you know, these charged particles are not healthy for the human body, or for our precious electronics. In fact, the Sun occasionally releases enormous blasts that can damage our satellites and electrical grids.
How can we predict the intensity so that we can be better prepared for dangerous solar storms? Especially the Carrington-class events that might take down huge portions of our modern society.
Perhaps the biggest mystery with the Sun is the temperature of its corona. The surface of the Sun is hot, like 5,500 degrees Celsius. But if you rise up into the atmosphere of the Sun, into its corona, the temperature jumps beyond a million degrees.
The list of mysteries is long. And to start understanding what’s going on, we’ll need to get much much closer to the Sun.
Good news, NASA has a new mission in the works to do just that.
The mission is called the Parker Solar Probe. Actually, last week, it was called the Solar Probe Plus, but then NASA renamed it, and that reminded me to do a video on it.
It’s pretty normal for NASA to rename their spacecraft, usually after a dead astronomer/space scientist, like Kepler, Chandra, etc. This time, though, they renamed it for a legendary solar astronomer Eugene Parker, who developed much of our modern thinking on the Sun’s solar wind. Parker just turned 90 and this is the first time NASA has named it after someone living.
Anyway, back to the spacecraft.
The mission is due to launch in early August 2018 on a Delta IV Heavy, so we’re still more than a year away at this point. When it does, it’ll carry the spacecraft on a very unusual trajectory through the inner Solar System.
The problem is that the Sun is actually a very difficult place to reach. In fact, it’s the hardest place to get to in the entire Solar System.
Remember that the Earth is traveling around the Sun at a velocity of 30 km/s. That’s almost three times the velocity it takes to get into orbit. That’s a lot of velocity.
In order to be able to get anywhere near the Sun, the probe needs to shed velocity. And in order to do this, it’s going to use gravitational slingshots with Venus. We’ve talked about gravitational slingshots in the past, and how you can use them to speed up a spacecraft, but you can actually do the reverse.
The Parker Solar Probe will fall down into Venus’ gravity well, and give orbital velocity to Venus. This will put it on a new trajectory which takes it closer to the Sun. It’ll do a total of 7 flybys in 7 years, each of which will tweak its trajectory and shed some of that orbital momentum.
You know, trying to explain orbital maneuvering is tough. I highly recommend that you try out Kerbal Space Program. I’ve learned more about orbital mechanics by playing that game for a few months than I have in almost 2 decades of space journalism. Go ahead, try to get to the Sun, I challenge you.
Anyway, with each Venus flyby, the Parker Solar Probe will get closer and closer to the Sun, well within the orbit of Mercury. Far closer than any spacecraft has ever gotten to the Sun. At its closest point, it’ll only be 5.9 million kilometers from the Sun. Just for comparison, the Earth orbits at an average distance of about 150 million kilometers. That’s close.
And over the course of its entire mission, the spacecraft is expected to make a total of 24 complete orbits of the Sun, analyzing that plasma ball from every angle.
The orbit is also highly elliptical, which means that it’s going really really fast at its closest point. Almost 725,000 km/h.
In order to withstand the intense temperatures of being this close to the Sun, NASA has engineered the Parker Solar Probe to shed heat. It’s equipped with an 11.5 cm-thick shield made of carbon-composite. For that short time it spends really close to the Sun, the spacecraft will keep the shield up, blocking that heat from reaching the rest of its instruments.
And it’s going to get hot. We’re talking about more than 1,300 degrees Celsius, which is about 475 times as much energy as a spacecraft receives here on Earth. In the outer Solar System, the problem is that there just isn’t enough energy to power solar panels. But where Parker is going, there’s just too much energy.
Now we’ve talked about the engineering difficulties of getting a spacecraft this close to the Sun, let’s talk about the science.
The biggest question astronomers are looking to solve is, how does the corona get so hot. The surface is 5,500 Celsius. As you get farther away from the Sun, you’d expect the temperature to go down. And it certainly does once you get as far as the orbit of the Earth.
But the Sun’s corona, or its outer atmosphere, extends millions of kilometers into space. You can see it during a solar eclipse as this faint glow around the Sun. Instead of dropping, the temperature rises to more than a million degrees.
What could be causing this? There are a couple of ideas. Plasma waves pushed off the Sun could bunch up and release their heat into the corona. You could also get the crisscrossing of magnetic field lines that create mini-flares within the corona, heating it up.
The second great mystery is the solar wind, the stream of charged protons and electrons coming from the Sun. Instead of a constant blowing wind, it can go faster or slower. And when the speed changes, the contents of the wind change too.
There’s the slow wind, that goes a mere 1.1 million km/h and seems to emanate from the Sun’s equatorial regions. And then the fast wind, which seems to be coming out of coronal holes, cooler parts in the Sun’s corona, and can be going at 2.7 million km/h.
Why does the solar wind speed change? Why does its consistency change?
The Parker Solar Probe is equipped with four major instruments, each of which will gather data from the Sun and its environment.
The FIELDS experiment will measure the electric and magnetic fields and waves around the Sun. We know that much of the Sun’s behavior is driven by the complex interaction between charged plasma in the Sun. In fact, many physicists agree that magnetohydrodynamics is easily one of the most complicated fields you can get into.
Integrated Science Investigation of the Sun, or ISOIS (which I suspect needs a renaming) will measure the charged particles streaming off the Sun, during regular solar activity and during dangerous solar storms. Can we get any warning before these events occur, giving astronauts more time to protect themselves?
Wide-field Imager for Solar PRobe or WISPR is its telescope and camera. It’s going to be taking close up, high resolution images of the Sun and its corona that will blow our collective minds… I hope. I mean, if it’s just a bunch of interesting data and no pretty pictures, it’s going to be hard to make cool videos showcasing the results of the mission. You hear me NASA, we want pictures and videos. And science, sure.
And then the Solar Wind Electrons Alphas and Protons Investigation, or SWEAP, will measure type, velocity, temperature and density of particles around the Sun, to help us understand the environment around it.
One interesting side note, the spacecraft will be carrying a tiny chip on board with photos of Eugene Parker and a copy of his original 1958 paper explaining the Sun’s solar wind.
I know we’re still more than a year away from liftoff, and several years away before the science data starts pouring in. But you’ll be hearing more and more about this mission shortly, and I’m pretty excited about what it’s going to accomplish. So stay tuned, and once the science comes in, I’m sure you’ll hear plenty more about it.
When the Apollo astronauts returned to Earth, they came bearing 380.96 kilograms (839.87 lb) of Moon rocks. From the study of these samples, scientists learned a great deal about the Moon’s composition, as well as its history of formation and evolution. For example, the fact that some of these rocks were magnetized revealed that roughly 3 billion years ago, the Moon had a magnetic field.
Much like Earth, this field would have been the result of a dynamo effect in the Moon’s core. But until recently, scientists have been unable to explain how the Moon could maintain such a dynamo effect for so long. But thanks to a new study by a team of scientists from the Astromaterials Research and Exploration Science (ARES) Division at NASA’s Johnson Space Center, we might finally have a answer.
To recap, the Earth’s magnetic core is an integral part of what keeps our planet habitable. Believed to be the result of a liquid outer core that rotates in the opposite direction as the planet, this field protects the surface from much of the Sun’s radiation. It also ensures that our atmosphere is not slowly stripped away by solar wind, which is what happened with Mars.
For the sake of their study, which was recently published in the journal Earth and Planetary Science Letters, the ARES team sought to determine how a molten, churning core could generate a magnetic field on the Moon. While scientists have understood how the Moon’s core could have powered such a field in the past, they have been unclear as to how it could have been maintained it for such a long time.
Towards this end, the ARES team considered multiple lines of geochemical and geophysical evidence to put constraints on the core’s composition. As Kevin Righter, the lead of the JSC’s high pressure experimental petrology lab and the lead author of the study, explained in a NASA press release:
“Our work ties together physical and chemical constraints and helps us understand how the moon acquired and maintained its magnetic field – a difficult problem to tackle for any inner solar system body. We created several synthetic core compositions based on the latest geochemical data from the moon, and equilibrated them at the pressures and temperatures of the lunar interior.”
Specifically, the ARES scientists conducted simulations of how the core would have evolved over time, based on varying levels of nickel, sulfur and carbon content. This consisted of preparing powders or iron, nickel, sulfur and carbon and mixing them in the proper proportions – based on recent analyses of Apollo rock samples.
Once these mixtures were prepared, they subjected them to heat and pressure conditions consistent with what exists at the Moon’s core. They also varied these temperatures and pressures based on the possibility that the Moon underwent changes in temperature during its early and later history – i.e. hotter during its early history and cooler later on.
What they found was that a lunar core composed of iron/nickel that had a small amount of sulfur and carbon – specifically 0.5% sulfur and 0.375% carbon by weight – fit the bill. Such a core would have a high melting point and would have likely started crystallizing early in the Moon’s history, thus providing the necessary heat to drive the dynamo and power a lunar magnetic field.
This field would have eventually died out after heat flow led the core to cool, thus arresting the dynamo effect. Not only do these results provide an explanation for all the paleomagnetic and seismic data we currently have on the Moon, it is also consistent with everything we know about the Moon’s geochemical and geophysical makeup.
Prior to this, core models tended to place the Moon’s sulfur content much higher. This would mean that it had a much lower melting point, and would have meant crystallization could not have occurred until much more recently in its history. Other theories have been proposed, ranging from sheer forces to impacts providing the necessary heat to power a dynamo.
However, the ARES team’s study provides a much simpler explanation, and one which happens to fit with all that we know about the Moon. Naturally, additional studies will be needed before there is any certainty on the issue. No doubt, this will first require that human beings establish a permanent outpost on the Moon to conduct research.
But it appears that for the time being, one of the deeper mysteries of the Earth-Moon system might be resolved at last.
Water. It’s always about the water when it comes to sizing up a planet’s potential to support life. Mars may possess some liquid water in the form of occasional salty flows down crater walls, but most appears to be locked up in polar ice or hidden deep underground. Set a cup of the stuff out on a sunny Martian day today and depending on conditions, it could quickly freeze or simply bubble away to vapor in the planet’s ultra-thin atmosphere.
Evidence of abundant liquid water in former flooded plains and sinuous river beds can be found nearly everywhere on Mars. NASA’s Curiosity rover has found mineral deposits that only form in liquid water and pebbles rounded by an ancient stream that once burbled across the floor of Gale Crater. And therein lies the paradox. Water appears to have gushed willy-nilly across the Red Planet 3 to 4 billion years ago, so what’s up today?
Blame Mars’ wimpy atmosphere. Thicker, juicier air and the increase in atmospheric pressure that comes with it would keep the water in that cup stable. A thicker atmosphere would also seal in the heat, helping to keep the planet warm enough for liquid water to pool and flow.
Different ideas have been proposed to explain the putative thinning of the air including the loss of the planet’s magnetic field, which serves as a defense against the solar wind.
Convection currents within its molten nickel-iron core likely generated Mars’ original magnetic defenses. But sometime early in the planet’s history the currents stopped either because the core cooled or was disrupted by asteroid impacts. Without a churning core, the magnetic field withered, allowing the solar wind to strip away the atmosphere, molecule by molecule.
Solar wind eats away the Martian atmosphere
Measurements from NASA’s current MAVEN mission indicate that the solar wind strips away gas at a rate of about 100 grams (equivalent to roughly 1/4 pound) every second. “Like the theft of a few coins from a cash register every day, the loss becomes significant over time,” said Bruce Jakosky, MAVEN principal investigator.
Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) suggest a different, less cut-and-dried scenario. Based on their studies, early Mars may have been warmed now and again by a powerful greenhouse effect. In a paper published in Geophysical Research Letters, researchers found that interactions between methane, carbon dioxide and hydrogen in the early Martian atmosphere may have created warm periods when the planet could support liquid water on its surface.
The team first considered the effects of CO2, an obvious choice since it comprises 95% of Mars’ present day atmosphere and famously traps heat. But when you take into account that the Sun shone 30% fainter 4 billion years ago compared to today, CO2 alone couldn’t cut it.
“You can do climate calculations where you add CO2 and build up to hundreds of times the present day atmospheric pressure on Mars, and you still never get to temperatures that are even close to the melting point,” said Robin Wordsworth, assistant professor of environmental science and engineering at SEAS, and first author of the paper.
Carbon dioxide isn’t the only gas capable of preventing heat from escaping into space. Methane or CH4 will do the job, too. Billions of years ago, when the planet was more geologically active, volcanoes could have tapped into deep sources of methane and released bursts of the gas into the Martian atmosphere. Similar to what happens on Saturn’s moon Titan, solar ultraviolet light would snap the molecule in two, liberating hydrogen gas in the process.
When Wordsworth and his team looked at what happens when methane, hydrogen and carbon dioxide collide and then interact with sunlight, they discovered that the combination strongly absorbed heat.
Carl Sagan, American astronomer and astronomy popularizer, first speculated that hydrogen warming could have been important on early Mars back in 1977, but this is the first time scientists have been able to calculate its greenhouse effect accurately. It is also the first time that methane has been shown to be an effective greenhouse gas on early Mars.
When you take methane into consideration, Mars may have had episodes of warmth based on geological activity associated with earthquakes and volcanoes. There have been at least three volcanic epochs during the planet’s history — 3.5 billion years ago (evidenced by lunar mare-like plains), 3 billion years ago (smaller shield volcanoes) and 1 to 2 billion years ago, when giant shield volcanoes such as Olympus Mons were active. So we have three potential methane bursts that could rejigger the atmosphere to allow for a mellower Mars.
The sheer size of Olympus Mons practically shouts massive eruptions over a long period of time. During the in-between times, hydrogen, a lightweight gas, would have continued to escape into space until replenished by the next geological upheaval.
“This research shows that the warming effects of both methane and hydrogen have been underestimated by a significant amount,” said Wordsworth. “We discovered that methane and hydrogen, and their interaction with carbon dioxide, were much better at warming early Mars than had previously been believed.”
” … maybe we’re on Mars because of the magnificent science that can be done there — the gates of the wonder world are opening in our time. Maybe we’re on Mars because we have to be, because there’s a deep nomadic impulse built into us by the evolutionary process, we come after all, from hunter gatherers, and for 99.9% of our tenure on Earth we’ve been wanderers. And, the next place to wander to, is Mars. But whatever the reason you’re on Mars is, I’m glad you’re there. And I wish I was with you.”
Isn’t modern society great? With all this technology surrounding us in all directions. It’s like a cocoon of sweet, fluffy silicon. There are chips in my fitness tracker, my bluetooth headset, mobile phone, car keys and that’s just on my body.
At all times in the Cain household, there dozens of internet devices connected to my wifi router. I’m not sure how we got to the point, but there’s one thing I know for sure, more is better. If I could use two smartphones at the same time, I totally would.
And I’m sure you agree, that without all this technology, life would be a pale shadow of its current glory. Without these devices, we’d have to actually interact with each other. Maybe enjoy the beauty of nature, or something boring like that.
It turns out, that terrible burning orb in the sky, the Sun, is fully willing and capable of bricking our precious technology. It’s done so in the past, and it’s likely to take a swipe at us in the future.
I’m talking about solar storms, of course, tremendous blasts of particles and radiation from the Sun which can interact with the Earth’s magnetosphere and overwhelm anything with a wire.
In fact, we got a sneak preview of this back in 1859, when a massive solar storm engulfed the Earth and ruined our old timey technology. It was known as the Carrington Event.
Follow your imagination back to Thursday, September 1st, 1859. This was squarely in the middle of the Victorian age.
And not the awesome, fictional Steampunk Victorian age where spectacled gentleman and ladies of adventure plied the skies in their steam-powered brass dirigibles.
No, it was the regular crappy Victorian age of cholera and child labor. Technology was making huge leaps and bounds, however, and the first telegraph lines and electrical grids were getting laid down.
Imagine a really primitive version of today’s electrical grid and internet.
On that fateful morning, the British astronomer Richard Carrington turned his solar telescope to the Sun, and was amazed at the huge sunspot complex staring back at him. So impressed that he drew this picture of it.
While he was observing the sunspot, Carrington noticed it flash brightly, right in his telescope, becoming a large kidney-shaped bright white flare.
Carrington realized he was seeing unprecedented activity on the surface of the Sun. Within a minute, the activity died down and faded away.
And then about 5 minutes later. Aurora activity erupted across the entire planet. We’re not talking about those rare Northern Lights enjoyed by the Alaskans, Canadians and Northern Europeans in the audience. We’re talking about everyone, everywhere on Earth. Even in the tropics.
In fact, the brilliant auroras were so bright you could read a book to them.
The beautiful night time auroras was just one effect from the monster solar flare. The other impact was that telegraph lines and electrical grids were overwhelmed by the electricity pushed through their wires. Operators got electrical shocks from their telegraph machines, and the telegraph paper lit on fire.
What happened? The most powerful solar flare ever observed is what happened.
A solar flare occurs because the Sun’s magnetic field lines can get tangled up in the solar atmosphere. In a moment, the magnetic fields reorganize themselves, and a huge wave of particles and radiation is released.
Flares happen in three stages. First, you get the precursor stage, with a blast of soft X-ray radiation. This is followed by the impulsive stage, where protons and electrons are accelerated off the surface of the Sun. And finally, the decay stage, with another burp of X-rays as the flare dies down.
These stages can happen in just a few seconds or drag out over an hour.
Remember those particles hurled off into space? They take several hours or a few days to reach Earth and interact with our planet’s protective magnetosphere, and then we get to see beautiful auroras in the sky.
This geomagnetic storm causes the Earth’s magnetosphere to jiggle around, which drives charges through wires back and forth, burning out circuits, killing satellites, overloading electrical grids.
Back in 1859, this wasn’t a huge deal, when our quaint technology hadn’t progressed beyond the occasional telegraph tower.
Today, our entire civilization depends on wires. There are wires in the hundreds of satellites flying overhead that we depend on for communications and navigation. Our homes and businesses are connected by an enormous electrical grid. Airplanes, cars, smartphones, this camera I’m using.
Everything is electronic, or controlled by electronics.
Think it can’t happen? We got a sneak preview back in March, 1989 when a much smaller geomagnetic storm crashed into the Earth. People as far south as Florida and Cuba could see auroras in the sky, while North America’s entire interconnected electrical grid groaned under the strain.
The Canadian province of Quebec’s electrical grid wasn’t able to handle the load and went entirely offline. For 12 hours, in the freezing Quebec winter, almost the entire province was without power. I’m telling you, that place gets cold, so this was really bad timing.
Satellites went offline, including NASA’s TDRS-1 communication satellite, which suffered 250 separate glitches during the storm.
And on July 23, 2012, a Carrington-class solar superstorm blasted off the Sun, and off into space. Fortunately, it missed the Earth, and we were spared the mayhem.
If a solar storm of that magnitude did strike the Earth, the cleanup might cost $2 trillion, according to a study by the National Academy of Sciences.
It’s been 160 years since the Carrington Event, and according to ice core samples, this was the most powerful solar flare over the last 500 years or so. Solar astronomers estimate solar storms like this happen twice a millennium, which means we’re not likely to experience another one in our lifetimes.
But if we do, it’ll cause worldwide destruction of technology and anyone reliant on it. You might want to have a contingency plan with some topic starters when you can’t access the internet for a few days. Locate nearby interesting nature spots to explore and enjoy while you wait for our technological civilization to be rebuilt.
Have you ever seen an aurora in your lifetime? Give me the details of your experience in the comments. | 0.881723 | 3.590888 |
by Jeff Foust
Gravitational Waves: How Einstein’s Spacetime Ripples Reveal the Secrets of the Universe
by Brian Clegg
Icon Books Ltd., 2018
ebook, 176 pp., illus.
For once, the term “multimessenger astronomy” didn’t refer to gravitational waves. Last week, astronomers used that term, which has become a buzzword in the field in the last few years, to describe a neutrino detection at a facility at the South Pole that, combined with other ground-based and space-based observatories operating in the electromagnetic spectrum, linked that detection to an active galaxy called a “blazar” billions of light-years away. Astronomers conclude that such galaxies may be the source of high-energy cosmic rays.
However, more often the phrase multimessenger astronomy has referred to the combination of electromagnetic observations—from radio through the visible to gamma-rays—with gravitational waves, particularly after the first confirmed direct detection of them announced more than two years ago and subsequent efforts to link those detections with other observations to track down their sources.
Gravitational waves have become a popular topic in the last few years, thanks to the detections of them by the Laser Interferometer Gravitational-Wave Observatory (LIGO) after decades of work. And while much has been written about that discovery and the science of gravitational waves, it can be difficult to get a concise overview.
Gravitational Waves by British science writer Brian Clegg attempts to do just that. In less than 200 pages, he offers an overview of what gravitational waves are, past efforts to detect them, and the LIGO discovery. It’s familiar reading for those who have followed the field in the last few years, but it makes for a good introduction at a level accessible for general readers rather than scientists.
There’s not much new in the book, and Clegg relies on other published accounts of the LIGO discovery and research in the field rather than doing much in the way of his own interviews or reporting. That’s fine so long as you’re a beginner to the subject and are looking for a broad overview, rather that someone already familiar with the topic and looking for new insights or angles.
Clegg, though, offers a little bit of opinion on the topic, particularly in the final chapter. He does a little soul-searching to ask the question of whether LIGO, whose overall cost exceeds $1 billion, is worth the expense. That includes some criticism of the International Space Station, which arguably was saved 25 years ago at the expense of the Superconducting Super Collider. “Instead of spending significantly less than the Large Hadron Collider for an arguably better piece of equipment, ten times the cost of the SSC has now been spent on the Space Station with no significant scientific outcomes whatsoever,” he argues. (The ISS, of course, has never been exclusively or primarily a science project, unlike the SSC and LIGO.)
He concludes it’s worthwhile to spend funds on projects like LIGO even if there is no payoff beyond science. “By detecting gravitational waves and pushing back the boundaries of our understanding, we confirm the strength of the human spirit,” he writes at the book’s conclusion. That is, perhaps, a very different kind of multimessenger astronomy. | 0.81051 | 3.994458 |
One of the main ideas of Comet Hunters is to see what activity in the asteroid belt looks like on a whole when we have the sensitivity of a 8-m class telescope. The Large Synoptic Survey Telescope (LSST) expected to start full science operations in 2022 will be surveying the sky nightly providing a new inventory of the Solar System. Michael Knight,a research scientist at the University of Maryland, has written a nicely blog post talking about cometary activity in the era of LSST. You can read it here.
I know it’s been a long time since we’ve posted on the blog. As most astronomers and planetary scientists, the science team is juggling multiple projects and other support and service duties. It’s a new year, and some of us have have more time to devote back to Comet Hunters. Many thanks to our Talk moderators who have been pointing out are tirelessly pointing out questions and helping out with new members of the Comet Hunters community.
We’ve still been having issues getting new HSC subject images ready for the site, for now I’ve paused that workflow to focus on the Archival search, which is planned to be the project’s first paper. Thanks to your help we’ve moved through of the search, and we’ve uploaded the new batch of images. This set will basically finish off our sample of asteroids we wanted to search for the first paper. That’s why we decided to focus on this right now, rather than the HSC search.
This batch of Archival images includes some of the asteroids observed at launch but has improved positional accuracy and has sources identified in the images that were popping up as blank. It will important to have these classifications so that all the asteroid observations were produced the same way .
Thanks for your help with Comet Hunters. More news soon.
I am Ishan, a summer student at ASIAA, Taiwan. I started working with the Comet Hunters team, about 3 weeks ago, on creating simulated Main-Belt Comet (MBC) images. Using appropriate mathematical functions, we are trying to create asteroid images with variable attributes like the direction of motion, brightness of tail and coma, etc. When ready, these images will be fed into the Comet Hunters website intermixed with the real images. How the project as a whole performs on these images will help us gain better insight into how well Comet Hunters can find different strengths of cometary activity and thus the true number of main-belt comets. For example, we can figure out up to what minimum brightness level of the coma (with respect to the nucleus) of the asteroid do the volunteers generally detect it.
For my present work, I am considering the nucleus to be just one pixel wide. For modelling the coma around it, we are using a 1/r profile centered around the nucleus. A sample coma is shown below. Note that the actual coma will be much fainter than the nucleus.
As we can see, there is ‘cross’ visible at the center. This is due to the fact that we are plotting a circular function in square pixel-grid. Now when we trail this image in a randomly chosen direction, we get a weird output.
As you can see, there is a skewed ‘X’ at the center of the trail. To check whether the trailing function is faulty, I fed it with a simple 2D gaussian coma. The resultant image looks pretty decent!
We are currently trying to figure out the issue with the 1/r profile. Maybe using polar coordinates will resolve this. I will get back to you with the developments!
The science team is working on incorporating data from the Hyper Suprime-Cam (HSC) survey into Comet Hunters. We started with the archival Suprime-Cam data first to get a better understanding of what are the false positives and challenges for identifying Main-Belt Comets (MBCs) in data from 8-10-m class telescopes. We’ll continue with both datasets as there’s more Suprime-Cam asteroids, but when we have the chance we’ll move to reviewing the new HSC observations hopefully a few days after they’re taken.Most previous asteroid detection surveys are using 1-3-m class telescopes, so there are bound to be surprises that we wanted to know about before we developed the decision tree for the HSC snapshots on to the site. So we launched Comet Hunters with the archival Suprime-Cam images first. Now that things are going smoothly, we can turn our attention to the HSC data.
We combined your classifications from the first batch of Suprime-Cam images and had 125 candidates in need of further vetting. Thanks to volunteer Tadeáš Cernohous who on Talk went through our list comparing repeat images of the asteroid at slightly different positions in the same batch of subjects. What we learned that all of the candidates are unfortunately blends with stationary background sources. There are lots of faint background blobs that the asteroid moves on top of overlapping in the images creating very tail-like features. All of these images the science team would have had said has a tail.
A few examples are below (all blends with faint background sources):
There’s a lot more blends than we had anticipated given some of the team’s past experience with 2-m asteroid survey data. It’s still very much worth digging into the rest of the Suprime-Cam archive to look for MBCs. There might be many blends, but there could still be undiscovered MBCs too! Knowing that the background blends rate is much higher because of the increase in the photon collecting bucket is extremely useful. From the candidates, we could see the blends are faint blobby structures that would be likely hard to get a source extractor to pick up in all cases. Because of the quality of the HSC data and the repeat observation cadence we can try and take this into account possibly by checking the image of the asteroid and the repeat image of the same position take later on in the same night (not all Suprime-Cam images will have that and are taken in all types of sky conditions).
Now the Comet Hunters team is thinking about how best to develop a classification interface for the HSC data to include this. In the meantime, there are new Suprime-Cam images in need of review at http://www.comethunters.org if you have a minute or two to spare.
You might have noticed the blue banner currently on the Comet Hunters website. That’s because thanks to your help, we’ve completed the classifications needed to retire all the images that were live on the site. The team has been working to process a new batch of asteroid images. We’ve taken our time to improve on some of the data reduction issues you might have noticed in the launch images (streaked asteroids, more off center asteroids images, and some bad quality images). By having people spot and comment on these features in the images, we’ve been able to refine the data processing pipeline for this next batch of images. We will have those images live ASAP. Stay tuned to this space.
Most of the Comet Hunters science team chatted today, and we’ve decided to put on Talk our top comet candidates based on your classifications. As we’ve found thanks to your classifications and Talk comments, overlaps with background sources are a huge source of false positives for 8-m class telescope images of asteroids when you’re searching for comet-like tails. If you’re interested, we could use your help to review other images to see if the potential tail is a background galaxy or star when you view the same area after the asteroid has moved. More details here.
After classifying the asteroid image in the main interface, you’re presented with an option to discuss the image you’ve seen in Comet Hunters Talk, if you hit the ‘Talk’ button.
Thanks to our Talk moderators, we now have a list of preferred hashtags (see below) we’d like suggest you use on Talk to help flag images in ways above and beyond what we can learn from the classification interface and the questions we ask you there.
We aim to also do a search using these preferred hashtags later on in the year to search for comet candidates and identify false positives.
#tail – see a very clear and definite tail. Currently many people use this for any sign of a tail, but we’d like you to use this for anything you’re very sure of it. If you think there’s any chance it might a faint background star or galaxy then use the #possible tag. (example)
#offcentercandidate – you see a tail but it’s on a source not in the center of the crosshairs
These are suggestions. Talk enables flexible labeling, so if you don’t find any hashtags from the list above that matches what you see, definitely create a new one!
Main-belt comets have a wide variety of appearances, or “morphologies”, depending on the strength of their activity, nucleus size, angle at which they are viewed from the Earth, just to name a few of the factors involved. As you look through objects in Comet Hunters, you may wonder what kind of features you should be looking out for. This can be a hard question to answer given the diversity of possible morphologies of main-belt comets though, so in this case, it is perhaps easier to show, rather than tell.
So, first, here is a gallery of representative images of nine of the main-belt comets known to date.
As you can see, main-belt comets can have long, thin tails like 133P, or broad ones like P/2013 R3 or P/2012 T1, or curved ones like 324P or 313P. Some are strongly active, like 238P and P/2013 R3, while others are only weakly active, like 133P, 176P, and P/2012 T1. Some may even have two dust tails, like 288P in the above images, or may be in the process of breaking apart, like P/2013 R3. As you can see, it is not really possible to describe the “typical” appearance of a main-belt comet.
Complicating matters more, the appearance of an individual main-belt comet can vary over time, as its activity strength changes as it approaches and then passes through perihelion (its closest approach to the Sun in its orbit), and/or due to changes in observing conditions between different observations (i.e., on different nights or even different times in the same night, or at different observatories at different locations in the world under different weather conditions). Below are several series of observations of various main-belt comets taken over periods of several weeks, months, or years using a variety of telescopes (ranging in sizes in terms of primary mirror diameter from 1.5m to 10m) to help illustrate this point:
133P/Elst-Pizarro in 2002 and 2007 (from Hsieh et al. 2010, Monthly Notices of the Royal Astronomical Society, Vol. 403, p. 363-377)
176P/LINEAR in 2005 (from Hsieh et al. 2011, Astronomical Journal, Vol. 142, article 29)
238P/Read in 2005 (a-c) and 2007 (d) (from Hsieh et al. 2009, Astronomical Journal, Vol. 137, p. 157-168)
238P/Read in 2010 (from Hsieh et al. 2011, Astrophysical Journal Letters, Vol. 736, article L18)
324P/La Sagra in 2010-2011 (from Hsieh et al. 2012, Astronomical Journal, Vol. 143, article 104)
288P/(300163) 2006 VW139 in 2011 (from Hsieh et al. 2012, Astrophysical Journal Letters, Vol. 748, article L15)
P/2012 T1 (PANSTARRS) in 2012 (from Hsieh et al. 2012, Astrophysical Journal Letters, Vol. 771, article L1)
313P/Gibbs in 2003 (a-c) and 2014 (d-h) (from Hsieh et al. 2015, Astrophysical Journal Letters, Vol. 800, article L16)
Note: Many of these images are created by adding together several individual images to make a composite image equivalent to leaving the telescope shutter open for up to several hours in some cases. During this time, the main-belt comet appears to move relative to the background stars. From the comet’s perspective though, the stars appear to move, and so the series of dotted streaks you see in many of the above images are background stars or galaxies that have been imaged several times (while “moving” between exposures) and then combined together into a single image, keeping the comet at the center of the image at all times.
This rich variety in main-belt comet morphologies is a big reason why we started the Comet Hunters project, given the difficulty of creating computer algorithms capable of identifying several different types of activity. There are still some things that computers can do better than the human eye (such as measure small differences in the profile “widths” of candidate objects as compared to nearby stars), but we hope that the combination of citizen science and modern computing, we will be able to discover many more new main-belt comets. | 0.829405 | 3.288983 |
Conditions for viewing the Perseids are not favorable this year. The full moon will occur on August 10 and the shower peaks only 3 nights later. Yet I would still make an effort to view meteor activity on the nights of August 12 and 13 despite the less than favorable conditions. The Perseids are a strong shower that produces many bright meteors. Despite the bright moonlight an observer should be able to see at least 20 Perseids per hour between midnight and dawn. These are better rates than 95% of all other nights regardless of lunar conditions. Therefore if your skies are clear these nights, make an effort to see this display of celestial fireworks.
As the sun sets in mid-August, the Perseid radiant lies near the northern horizon for viewers located in mid-northern latitudes. This is certainly not the prime time to view Perseid activity but it may be worth your effort to try and catch some Perseid earthgrazers at this time. This year on the night of August 12/13, the 90% illuminated moon will rise at approximately 21:00 or 9pm local daylight time. With the moon low in the east its brilliance will be diminished by the atmosphere. For an hour or so beginning at the time you can see stars in the dimming skies, you have the opportunity to see Perseid meteors that just skim the upper atmosphere. These are much different than Perseid meteors you see later in the night. With less resistance from air molecules these meteors last much longer and create long trails across the sky, often nearly stretching from horizon to horizon. With the low radiant altitude there will not be many of these meteors to see. Any that you do manage to witness will be memorable. Sky & Telescope magazine has a nice article on these meteors in their August 2014 issue.
As the night progresses the Perseid activity will continue to be low as the moon rises higher in the sky, attaining its full brilliance. Not until after midnight will the Perseid radiant gain sufficient altitude to produce pleasing results. Anytime from midnight to dawn will be the best time to see the most activity. I would suggest facing away from the moon and concentrate your view at approximately one-half the way up in the sky. Most of the faint Perseids will be obscured by the bright moonlight. But the bright meteors you do manage to see will often be colorful and the brightest may leave persistent trains that remain in the sky after the meteor itself has disappeared.
If your skies are cloudy on August 12 or 13, the following nights should also produce decent activity with the moon rising slightly later in the evening. Note that the activity will fall approximately 50% each night after maximum so there will not be much left of this shower by the time the moon is out of the way. The two nights prior to maximum are usually good too but the moon will be closer to full and will lie above the horizon the entire night.
Regardless of what night you view, be sure to share your counts and impressions of the display with us! | 0.862622 | 3.399262 |
During this period the moon wanes from half illuminated to nearly its new phase. During this entire period the moon is only visible during the morning hours, allowing dark skies prior to midnight. This weekend the waning crescent moon will rise during the early morning hours. Since it will be less than half illuminated it will not compromise meteor watching unless you view directly toward the moon. As the week progresses viewing conditions improve as the lunar phase thins plus the moon rises later each night. The estimated total hourly meteor rates for evening observers this week is near 4 as seen from the northern hemisphere and 3 as seen from southern tropical latitudes. For morning observers the estimated total hourly rates should be near 17 for observers located in mid-northern latitudes and 12 for south tropical observers. Rates are slightly reduced during the morning hours due to moonlight. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Note that the hourly rates listed below are estimates as viewed from dark sky sites away from urban light sources. Observers viewing from urban areas will see less activity as only the brightest meteors will be visible from such locations.
The radiant (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning November 15/16. These positions do not change greatly day to day so the listed coordinates may be used during this entire period. Most star atlases (available at science stores and planetariums) will provide maps with grid lines of the celestial coordinates so that you may find out exactly where these positions are located in the sky. A planisphere or computer planetarium program is also useful in showing the sky at any time of night on any date of the year. Activity from each radiant is best seen when it is positioned highest in the sky, either due north or south along the meridian, depending on your latitude. It must be remembered that meteor activity is rarely seen at the radiant position. Rather they shoot outwards from the radiant so it is best to center your field of view so that the radiant lies at the edge and not the center. Viewing there will allow you to easily trace the path of each meteor back to the radiant (if it is a shower member) or in another direction if it is a sporadic. Meteor activity is not seen from radiants that are located below the horizon. The positions below are listed in a west to east manner in order of right ascension (celestial longitude). The positions listed first are located further west therefore are accessible earlier in the night while those listed further down the list rise later in the night.
These sources of meteoric activity are expected to be active this week:
The Andromedids (AND) are still active from a radiant located at 01:40 (025) +34, which lies in western Triangulum, 6 degrees west of the 2nd magnitude star Mirach (Beta Andromede). This is a famous shower that produced some brilliant displays during the 19th century. Since then the main orbit of the particles from comet 3D/Biela have moved away from the Earth. Still, remnants may be seen from October 26 through November 20 with maximum activity occurring on November 8. These meteors are best seen near 2300 (10pm) local standard time (LST) when the radiant lies highest above the horizon. Rates would most likely be less than 1 per hour no matter your location. With an entry velocity of 16 km/sec., the average Andromedid meteor would be of slow velocity.
The Southern Taurids (STA) are still active from a large radiant centered at 04:04 (061) +16. This position lies in western Taurus, 8 degrees west of the 1st magnitude orange star known as Aldebaran (Alpha Tauri). These meteors may be seen all night long but the radiant is best placed near midnight LST when it lies on the meridian and is located highest in the sky. Rates at this time should be near 1 per hour regardless of your location. With an entry velocity of 29 km/sec., the average Southern Taurid meteor would be of slow velocity.
The Northern Taurids (NTA) are active from a large radiant centered at 04:08 (062) +23. This position lies in western Taurus, 4 degrees southeast from the famous naked eye open cluster known and the Pleiades or Seven Sisters. The radiant is best placed near midnight LST, when it lies highest above the horizon. Meteors from the Northern Taurids strike the atmosphere at 27km/sec., which would produce meteors of slow velocity. Expected rates would be near 3 per hour as seen from the northern hemisphere and 2 per hour as seen from south of the equator.
The November Orionids (NOO) are now active from a radiant located at 05:28 (082) +16. This area of the sky is located on the Orion/Taurus border, twelve degrees east of the first magnitude orange star Aldebaran (Alpha Tauri).. The peak for this radiant is not until November 28th, so current rates would be less than than one shower member per hour, no matter your location. This location is close to the Taurid complex, but far enough east to be distinguishable. The faster velocity of the November Orionids should help distinguish these meteors from the slower, but more numerous Taurids. The radiant is best placed for viewing near 0200 LST when it lies on the meridian and is highest above the horizon. With an entry velocity of 44 km/sec., the November Orionids would be of medium speed.
The Alpha Monocerotids (AMO) are a variable shower known for strong but short outbursts in 1985 and 1995. In most years just a few of meteors from this source are seen near November 22nd. Activity is limited to November 21-23 with a radiant located at 07:52 (118) +01. The area of the sky is located in southeastern Canis Minor just 5 degrees southeast of the brilliant 0 magnitude star known Procyon (Alpha Canis Minoris). The radiant was thought to originate in nearby Monoceros but recent refinements have placed it within Canis Minor. These meteors are best seen near 0400 LST, when the radiant lies highest above the horizon. With an entry velocity of 68 km/sec., most activity from this radiant would be of swift speed.
The last of the Orionids (ORI) will be seen this week from a radiant located at 07:56 (119) +15, which places it on the Gemini/ Cancer border, 12 degrees east of the 4th magnitude star known as Lambda Geminorum. This area of the sky is best placed in the sky near 0400 LST, when it lies highest above the horizon. Rates this week should be less than 1 per hour no matter your location. With an entry velocity of 67 km/sec., most activity from this radiant would be of swift speed.
The Leonids (LEO) are now the most active radiant in the sky, producing a half dozen shower members per hour during the last couple of hours before dawn. Maximum is predicted for Monday morning the 17th, when hourly rates may reach 10 per hour. The Earth also encounters the trail produced in 1567 near 09:17 Universal Time on November 21st. Rates for this secondary encounter are expected to be low with no noticeable increase in activity. It does bear watching though as lunar conditions are excellent. The radiant is currently located at 10:16 (154) +22. This position lies in northwestern Leo, within the “sickle” of Leo, two degrees northwest of the second magnitude double star Algeiba (Gamma Leonis). The Leonid radiant is best placed during the last hour before morning twilight when the radiant lies highest in a dark sky. Leonids may be seen from the southern hemisphere but the viewing conditions are not quite as favorable as those north of the equator. With an entry velocity of 70 km/sec., most activity from this radiant would be of swift speed with numerous persistent trains on the brighter meteors.
The November Iota Draconids (NID) were discovered by Dr. Peter Brown during his 7 year meteoroid stream survey using the Canadian Meteor Orbit Radar. This source is active from November 11 through the 1st of December with maximum activity occurring on November 26th. The radiant is currently located at 12:08 (182) +74. This area of the sky lies in western Draco, 5 degrees northwest of the fourth magnitude star Kappa Draconis. The radiant is best placed during the last hour before morning twilight when the radiant lies highest in a dark sky. Since maximum activity is still more than a week away current rates would be less than one shower member per hour, no matter your location. Due to the high northerly declination of the radiant these meteors are not visible from most of the southern hemisphere. Only southern equatorial regions would have any chance of seeing activity from this source. Meteors from the November Iota Draconids strike the atmosphere at 41km/sec., which would produce meteors of medium velocity.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately 8 sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near 3 per hour. As seen from the tropical southern latitudes (25S), morning rates would be near 5 per hour as seen from rural observing sites and 2 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Moonlight reduces the number of meteors seen during the morning hours during this period.
The list below offers the information from above in tabular form. Rates and positions are exact for Saturday night/Sunday morning except where noted in the shower descriptions.
|SHOWER||DATE OF MAXIMUM ACTIVITY||CELESTIAL POSITION||ENTRY VELOCITY||CULMINATION||HOURLY RATE||CLASS|
|RA (RA in Deg.) DEC||Km/Sec||Local Standard Time||North-South|
|Andromedids (AND)||Nov 08||01:40 (025) +34||16||22:00||<1 – <1||III|
|Southern Taurids (STA)||Oct 10||04:04 (061) +16||29||00:00||1 – 1||II|
|Northern Taurids (NTA)||Nov 11||04:08 (062) +23||27||00:00||3 – 2||II|
|November Orionids (NOO)||Nov 28||05:28 (082) +16||44||02:00||<1 – <1||II|
|Alpha Monocerotids (AMO)||Nov 22||07:52 (118) +01||68||04:00||<1 – <1||III|
|Orionids (ORI)||Oct 22||07:56 (119) +15||67||04:00||<1 – <1||I|
|Leonids (LEO)||Nov 18||10:16 (154) +22||70||06:00||5 – 4||III|
|Nov. Iota Draconids (NID)||Nov 21||12:08 (182) +74||41||08:00||<1 – <1||IV| | 0.811505 | 3.603845 |
|Top: Lightning and neon lights are commonplace generators of plasma. Bottom left: A plasma globe, illustrating some of the more complex plasma phenomena, including filamentation. Bottom right: A plasma trail from the Space Shuttle Atlantis during re-entry into Earth's atmosphere, as seen from the International Space Station.|
Plasma (from Ancient Greek πλάσμα, meaning 'moldable substance') is one of the four fundamental states of matter, and was first described by chemist Irving Langmuir in the 1920s. It consists of a gas of ions – atoms which have some of their orbital electrons removed – and free electrons. Plasma can be artificially generated by heating a neutral gas or subjecting it to a strong electromagnetic field to the point where an ionized gaseous substance becomes increasingly electrically conductive. The resulting charged ions and electrons become influenced by long-range electromagnetic fields, making the plasma dynamics more sensitive to these fields than a neutral gas.
Plasma and ionized gases have properties and display behaviours unlike those of the other states, and the transition between them is mostly a matter of nomenclature and subject to interpretation. Based on the temperature and density of the environment that contains a plasma, partially ionized or fully ionized forms of plasma may be produced. Neon signs and lightning are examples of partially ionized plasmas. The Earth's ionosphere is a plasma and the magnetosphere contains plasma in the Earth's surrounding space environment. The interior of the Sun is an example of fully ionized plasma, along with the solar corona and stars.
Positive charges in ions are achieved by stripping away electrons orbiting the atomic nuclei, where the total number of electrons removed is related to either increasing temperature or the local density of other ionized matter. This also can be accompanied by the dissociation of molecular bonds, though this process is distinctly different from chemical processes of ion interactions in liquids or the behaviour of shared ions in metals. The response of plasma to electromagnetic fields is used in many modern technological devices, such as plasma televisions or plasma etching.
Plasma may be the most abundant form of ordinary matter in the universe, although this hypothesis is currently tentative based on the existence and unknown properties of dark matter. Plasma is mostly associated with stars, extending to the rarefied intracluster medium and possibly the intergalactic regions.
The word plasma comes from Ancient Greek πλάσμα, meaning 'moldable substance' or 'jelly', and describes the behaviour of the ionized atomic nuclei and the electrons within the surrounding region of the plasma. Very simply, each of these nuclei are suspended in a movable sea of electrons. Plasma was first identified in a Crookes tube, and so described by Sir William Crookes in 1879 (he called it "radiant matter"). The nature of this "cathode ray" matter was subsequently identified by British physicist Sir J.J. Thomson in 1897.
The term "plasma" was introduced as a description of ionised gas by Irving Langmuir in 1928. Lewi Tonks and Harold Mott-Smith, both of whom worked with Irving Langmuir in the 1920s, recall that Langmuir first used the word "plasma" in analogy with blood. Mott-Smith recalls, in particular, that the transport of electrons from thermionic filaments reminded Langmuir of "the way blood plasma carries red and white corpuscles and germs."
Langmuir described the plasma he observed as follows:
- "Except near the electrodes, where there are sheaths containing very few electrons, the ionized gas contains ions and electrons in about equal numbers so that the resultant space charge is very small. We shall use the name plasma to describe this region containing balanced charges of ions and electrons."
Properties and parameters
Plasma is a state of matter in which an ionized gaseous substance becomes highly electrically conductive to the point that long-range electric and magnetic fields dominate the behaviour of the matter. The plasma state can be contrasted with the other states: solid, liquid, and gas.
Plasma is an electrically neutral medium of unbound positive and negative particles (i.e. the overall charge of a plasma is roughly zero). Although these particles are unbound, they are not "free" in the sense of not experiencing forces. Moving charged particles generate an electric current within a magnetic field, and any movement of a charged plasma particle affects and is affected by the fields created by the other charges. In turn this governs collective behaviour with many degrees of variation. Three factors define a plasma:
- The plasma approximation: The plasma approximation applies when the plasma parameter, Λ, representing the number of charge carriers within a sphere (called the Debye sphere whose radius is the Debye screening length) surrounding a given charged particle, is sufficiently high as to shield the electrostatic influence of the particle outside of the sphere.
- Bulk interactions: The Debye screening length (defined above) is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, where boundary effects may take place. When this criterion is satisfied, the plasma is quasineutral.
- Plasma frequency: The electron plasma frequency (measuring plasma oscillations of the electrons) is large compared to the electron-neutral collision frequency (measuring frequency of collisions between electrons and neutral particles). When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics.
Plasma temperature is commonly measured in kelvin or electronvolts and is, informally, a measure of the thermal kinetic energy per particle. High temperatures are usually needed to sustain ionisation, which is a defining feature of a plasma. The degree of plasma ionisation is determined by the electron temperature relative to the ionization energy (and more weakly by the density), in a relationship called the Saha equation. At low temperatures, ions and electrons tend to recombine into bound states—atoms—and the plasma will eventually become a gas.
In most cases the electrons are close enough to thermal equilibrium that their temperature is relatively well-defined; this is true even when there is a significant deviation from a Maxwellian energy distribution function, for example, due to UV radiation, energetic particles, or strong electric fields. Because of the large difference in mass, the electrons come to thermodynamic equilibrium amongst themselves much faster than they come into equilibrium with the ions or neutral atoms. For this reason, the ion temperature may be very different from (usually lower than) the electron temperature. This is especially common in weakly ionized technological plasmas, where the ions are often near the ambient temperature.
Fully vs. partially (weakly) ionized gases
For plasma to exist, ionisation is necessary. The term "plasma density" by itself usually refers to the "electron density", that is, the number of free electrons per unit volume. The degree of ionisation of a plasma is the proportion of atoms that have lost or gained electrons, and is controlled by the electron and ion temperatures and electron-ion vs electron-neutral collision frequencies. The degree of ionisation, , is defined as , where is the number density of ions and is the number density of neutral atoms. The electron density is related to this by the average charge state[further explanation needed] of the ions through , where is the number density of electrons.
In a plasma, the electron-ion collision frequency is much greater than the electron-neutral collision frequency . Therefore, with a weak degree of ionization , the electron-ion collision frequency can equal the electron-neutral collision frequency: is the limit separating a plasma from being partially or fully ionized.
- The term fully ionized gas introduced by Lyman Spitzer does not mean the degree of ionization is unity, but only that the plasma is in a Coulomb-collision dominated regime, i.e. when , which can correspond to a degree of ionization as low as 0.01%.
- A partially or weakly ionized gas means the plasma is not dominated by Coulomb collisions, i.e. when .
Most of "technological" (engineered) plasmas are weakly ionized gases.
Thermal vs. nonthermal (cold) plasmas
Based on the relative temperatures of the electrons, ions and neutrals, plasmas are classified as "thermal" or "non-thermal" (also referred to as "cold plasmas").
- Thermal plasmas have electrons and the heavy particles at the same temperature, i.e. they are in thermal equilibrium with each other.
- Nonthermal plasmas on the other hand are non-equilibrium ionized gases, with two temperatures: ions and neutrals stay at a low temperature (sometimes room temperature), whereas electrons are much hotter. (). A kind of common nonthermal plasma is the mercury-vapor gas within a fluorescent lamp, where the "electrons gas" reaches a temperature of 10,000 kelvins while the rest of the gas stays barely above room temperature, so the bulb can even be touched with hands while operating.
Since plasmas are very good electrical conductors, electric potentials play an important role.[clarification needed] The average potential in the space between charged particles, independent of how it can be measured, is called the "plasma potential", or the "space potential". If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a Debye sheath. The good electrical conductivity of plasmas makes their electric fields very small. This results in the important concept of "quasineutrality", which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma (), but on the scale of the Debye length there can be charge imbalance. In the special case that double layers are formed, the charge separation can extend some tens of Debye lengths.
The magnitude of the potentials and electric fields must be determined by means other than simply finding the net charge density. A common example is to assume that the electrons satisfy the Boltzmann relation:
Differentiating this relation provides a means to calculate the electric field from the density:
It is possible to produce a plasma that is not quasineutral. An electron beam, for example, has only negative charges. The density of a non-neutral plasma must generally be very low, or it must be very small, otherwise, it will be dissipated by the repulsive electrostatic force.
In astrophysical plasmas, Debye screening prevents electric fields from directly affecting the plasma over large distances, i.e., greater than the Debye length. However, the existence of charged particles causes the plasma to generate, and be affected by, magnetic fields. This can and does cause extremely complex behaviour, such as the generation of plasma double layers, an object that separates charge over a few tens of Debye lengths. The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics.
Plasma with a magnetic field strong enough to influence the motion of the charged particles is said to be magnetized. A common quantitative criterion is that a particle on average completes at least one gyration around the magnetic field before making a collision, i.e., , where is the "electron gyrofrequency" and is the "electron collision rate". It is often the case that the electrons are magnetized while the ions are not. Magnetized plasmas are anisotropic, meaning that their properties in the direction parallel to the magnetic field are different from those perpendicular to it. While electric fields in plasmas are usually small due to the high conductivity, the electric field associated with a plasma moving in a magnetic field is given by (where is the electric field, is the velocity, and is the magnetic field), and is not affected by Debye shielding.
Comparison of plasma and gas phases
Plasma is often called the fourth state of matter after solid, liquids and gases, despite plasma typically being an ionized gas. It is distinct from these and other lower-energy states of matter. Although it is closely related to the gas phase in that it also has no definite form or volume, it differs in a number of ways, including the following:
|Electrical conductivity||Very low: Air is an excellent insulator until it breaks down into plasma at electric field strengths above 30 kilovolts per centimeter.||Usually very high: For many purposes, the conductivity of a plasma may be treated as infinite.|
|Independently acting species||One: All gas particles behave in a similar way, influenced by gravity and by collisions with one another.||Two or three: Electrons, ions, protons and neutrons can be distinguished by the sign and value of their charge so that they behave independently in many circumstances, with different bulk velocities and temperatures, allowing phenomena such as new types of waves and instabilities.|
|Velocity distribution||Maxwellian: Collisions usually lead to a Maxwellian velocity distribution of all gas particles, with very few relatively fast particles.||Often non-Maxwellian: Collisional interactions are often weak in hot plasmas and external forcing can drive the plasma far from local equilibrium and lead to a significant population of unusually fast particles.|
|Interactions||Binary: Two-particle collisions are the rule, three-body collisions extremely rare.||Collective: Waves, or organized motion of plasma, are very important because the particles can interact at long ranges through the electric and magnetic forces.|
Plasmas in space science and astronomy
Above the Earth's surface, the ionosphere is a plasma, and the magnetosphere contains plasma. Within our Solar System, interplanetary space is filled with the plasma expelled via the solar wind, extending from the Sun's surface out to the heliopause. Furthermore, all the distant stars, and much of interstellar space or intergalactic space is also likely filled with plasma, albeit at very low densities. Astrophysical plasmas are also observed in Accretion disks around stars or compact objects like white dwarfs, neutron stars, or black holes in close binary star systems. Plasma is associated with ejection of material in astrophysical jets, which have been observed with accreting black holes or in active galaxies like M87's jet that possibly extends out to 5,000 light-years.
Plasmas can appear in nature in various forms and locations, which can be usefully broadly summarised in the following Table:
|Artificially produced||Terrestrial plasmas||Space and astrophysical plasmas|
Complex plasma phenomena
Although the underlying equations governing plasmas are relatively simple, plasma behaviour is extraordinarily varied and subtle: the emergence of unexpected behaviour from a simple model is a typical feature of a complex system. Such systems lie in some sense on the boundary between ordered and disordered behaviour and cannot typically be described either by simple, smooth, mathematical functions, or by pure randomness. The spontaneous formation of interesting spatial features on a wide range of length scales is one manifestation of plasma complexity. The features are interesting, for example, because they are very sharp, spatially intermittent (the distance between features is much larger than the features themselves), or have a fractal form. Many of these features were first studied in the laboratory, and have subsequently been recognized throughout the universe. Examples of complexity and complex structures in plasmas include:
Striations or string-like structures, also known as Birkeland currents, are seen in many plasmas, like the plasma ball, the aurora, lightning, electric arcs, solar flares, and supernova remnants. They are sometimes associated with larger current densities, and the interaction with the magnetic field can form a magnetic rope structure. High power microwave breakdown at atmospheric pressure also leads to the formation of filamentary structures. (See also Plasma pinch)
Filamentation also refers to the self-focusing of a high power laser pulse. At high powers, the nonlinear part of the index of refraction becomes important and causes a higher index of refraction in the center of the laser beam, where the laser is brighter than at the edges, causing a feedback that focuses the laser even more. The tighter focused laser has a higher peak brightness (irradiance) that forms a plasma. The plasma has an index of refraction lower than one, and causes a defocusing of the laser beam. The interplay of the focusing index of refraction, and the defocusing plasma makes the formation of a long filament of plasma that can be micrometers to kilometers in length. One interesting aspect of the filamentation generated plasma is the relatively low ion density due to defocusing effects of the ionized electrons. (See also Filament propagation)
The strength and range of the electric force and the good conductivity of plasmas usually ensure that the densities of positive and negative charges in any sizeable region are equal ("quasineutrality"). A plasma with a significant excess of charge density, or, in the extreme case, is composed of a single species, is called a non-neutral plasma. In such a plasma, electric fields play a dominant role. Examples are charged particle beams, an electron cloud in a Penning trap and positron plasmas.
Dusty plasma/grain plasma
A dusty plasma contains tiny charged particles of dust (typically found in space). The dust particles acquire high charges and interact with each other. A plasma that contains larger particles is called grain plasma. Under laboratory conditions, dusty plasmas are also called complex plasmas.
Impermeable plasma is a type of thermal plasma which acts like an impermeable solid with respect to gas or cold plasma and can be physically pushed. Interaction of cold gas and thermal plasma was briefly studied by a group led by Hannes Alfvén in 1960s and 1970s for its possible applications in insulation of fusion plasma from the reactor walls. However, later it was found that the external magnetic fields in this configuration could induce kink instabilities in the plasma and subsequently lead to an unexpectedly high heat loss to the walls. In 2013, a group of materials scientists reported that they have successfully generated stable impermeable plasma with no magnetic confinement using only an ultrahigh-pressure blanket of cold gas. While spectroscopic data on the characteristics of plasma were claimed to be difficult to obtain due to the high pressure, the passive effect of plasma on synthesis of different nanostructures clearly suggested the effective confinement. They also showed that upon maintaining the impermeability for a few tens of seconds, screening of ions at the plasma-gas interface could give rise to a strong secondary mode of heating (known as viscous heating) leading to different kinetics of reactions and formation of complex nanomaterials.
To completely describe the state of a plasma, all of the particle locations and velocities that describe the electromagnetic field in the plasma region would need to be written down. However, it is generally not practical or necessary to keep track of all the particles in a plasma. Therefore, plasma physicists commonly use less detailed descriptions, of which there are two main types:
Fluid models describe plasmas in terms of smoothed quantities, like density and averaged velocity around each position (see Plasma parameters). One simple fluid model, magnetohydrodynamics, treats the plasma as a single fluid governed by a combination of Maxwell's equations and the Navier–Stokes equations. A more general description is the two-fluid plasma picture, where the ions and electrons are described separately. Fluid models are often accurate when collisionality is sufficiently high to keep the plasma velocity distribution close to a Maxwell–Boltzmann distribution. Because fluid models usually describe the plasma in terms of a single flow at a certain temperature at each spatial location, they can neither capture velocity space structures like beams or double layers, nor resolve wave-particle effects.
Kinetic models describe the particle velocity distribution function at each point in the plasma and therefore do not need to assume a Maxwell–Boltzmann distribution. A kinetic description is often necessary for collisionless plasmas. There are two common approaches to kinetic description of a plasma. One is based on representing the smoothed distribution function on a grid in velocity and position. The other, known as the particle-in-cell (PIC) technique, includes kinetic information by following the trajectories of a large number of individual particles. Kinetic models are generally more computationally intensive than fluid models. The Vlasov equation may be used to describe the dynamics of a system of charged particles interacting with an electromagnetic field. In magnetized plasmas, a gyrokinetic approach can substantially reduce the computational expense of a fully kinetic simulation.
Most artificial plasmas are generated by the application of electric and/or magnetic fields through a gas. Plasma generated in a laboratory setting and for industrial use can be generally categorized by:
- The type of power source used to generate the plasma—DC, AC (typically with radio frequency (RF)) and microwave
- The pressure they operate at—vacuum pressure (< 10 mTorr or 1 Pa), moderate pressure (≈1 Torr or 100 Pa), atmospheric pressure (760 Torr or 100 kPa)
- The degree of ionisation within the plasma—fully, partially, or weakly ionized
- The temperature relationships within the plasma—thermal plasma (), non-thermal or "cold" plasma ()
- The electrode configuration used to generate the plasma
- The magnetization of the particles within the plasma—magnetized (both ion and electrons are trapped in Larmor orbits by the magnetic field), partially magnetized (the electrons but not the ions are trapped by the magnetic field), non-magnetized (the magnetic field is too weak to trap the particles in orbits but may generate Lorentz forces)
Generation of artificial plasma
Just like the many uses of plasma, there are several means for its generation, however, one principle is common to all of them: there must be energy input to produce and sustain it. For this case, plasma is generated when an electric current is applied across a dielectric gas or fluid (an electrically non-conducting material) as can be seen in the adjacent image, which shows a discharge tube as a simple example (DC used for simplicity).
The potential difference and subsequent electric field pull the bound electrons (negative) toward the anode (positive electrode) while the cathode (negative electrode) pulls the nucleus. As the voltage increases, the current stresses the material (by electric polarization) beyond its dielectric limit (termed strength) into a stage of electrical breakdown, marked by an electric spark, where the material transforms from being an insulator into a conductor (as it becomes increasingly ionized). The underlying process is the Townsend avalanche, where collisions between electrons and neutral gas atoms create more ions and electrons (as can be seen in the figure on the right). The first impact of an electron on an atom results in one ion and two electrons. Therefore, the number of charged particles increases rapidly (in the millions) only "after about 20 successive sets of collisions", mainly due to a small mean free path (average distance travelled between collisions).
With ample current density and ionisation, this forms a luminous electric arc (a continuous electric discharge similar to lightning) between the electrodes.[Note 1] Electrical resistance along the continuous electric arc creates heat, which dissociates more gas molecules and ionises the resulting atoms (where degree of ionisation is determined by temperature), and as per the sequence: solid-liquid-gas-plasma, the gas is gradually turned into a thermal plasma.[Note 2] A thermal plasma is in thermal equilibrium, which is to say that the temperature is relatively homogeneous throughout the heavy particles (i.e. atoms, molecules and ions) and electrons. This is so because when thermal plasmas are generated, electrical energy is given to electrons, which, due to their great mobility and large numbers, are able to disperse it rapidly and by elastic collision (without energy loss) to the heavy particles.[Note 3]
Examples of industrial/commercial plasma
Because of their sizable temperature and density ranges, plasmas find applications in many fields of research, technology and industry. For example, in: industrial and extractive metallurgy, surface treatments such as plasma spraying (coating), etching in microelectronics, metal cutting and welding; as well as in everyday vehicle exhaust cleanup and fluorescent/luminescent lamps, fuel ignition, while even playing a part in supersonic combustion engines for aerospace engineering.
- Glow discharge plasmas: non-thermal plasmas generated by the application of DC or low frequency RF (<100 kHz) electric field to the gap between two metal electrodes. Probably the most common plasma; this is the type of plasma generated within fluorescent light tubes.
- Capacitively coupled plasma (CCP): similar to glow discharge plasmas, but generated with high frequency RF electric fields, typically 13.56 MHz. These differ from glow discharges in that the sheaths are much less intense. These are widely used in the microfabrication and integrated circuit manufacturing industries for plasma etching and plasma enhanced chemical vapor deposition.
- Cascaded Arc Plasma Source: a device to produce low temperature (≈1eV) high density plasmas (HDP).
- Inductively coupled plasma (ICP): similar to a CCP and with similar applications but the electrode consists of a coil wrapped around the chamber where plasma is formed.
- Wave heated plasma: similar to CCP and ICP in that it is typically RF (or microwave). Examples include helicon discharge and electron cyclotron resonance (ECR).
- Arc discharge: this is a high power thermal discharge of very high temperature (≈10,000 K). It can be generated using various power supplies. It is commonly used in metallurgical processes. For example, it is used to smelt minerals containing Al2O3 to produce aluminium.
- Corona discharge: this is a non-thermal discharge generated by the application of high voltage to sharp electrode tips. It is commonly used in ozone generators and particle precipitators.
- Dielectric barrier discharge (DBD): this is a non-thermal discharge generated by the application of high voltages across small gaps wherein a non-conducting coating prevents the transition of the plasma discharge into an arc. It is often mislabeled 'Corona' discharge in industry and has similar application to corona discharges. It is also widely used in the web treatment of fabrics. The application of the discharge to synthetic fabrics and plastics functionalizes the surface and allows for paints, glues and similar materials to adhere. The dielectric barrier discharge was used in the mid-1990s to show that low temperature atmospheric pressure plasma is effective in inactivating bacterial cells. This work and later experiments using mammalian cells led to the establishment of a new field of research known as plasma medicine. The dielectric barrier discharge configuration was also used in the design of low temperature plasma jets. These plasma jets are produced by fast propagating guided ionisation waves known as plasma bullets.
- Capacitive discharge: this is a nonthermal plasma generated by the application of RF power (e.g., 13.56 MHz) to one powered electrode, with a grounded electrode held at a small separation distance on the order of 1 cm. Such discharges are commonly stabilized using a noble gas such as helium or argon.
- "Piezoelectric direct discharge plasma:" is a nonthermal plasma generated at the high-side of a piezoelectric transformer (PT). This generation variant is particularly suited for high efficient and compact devices where a separate high voltage power supply is not desired.
A world effort was triggered in the 1960s to study magnetohydrodynamic converters in order to bring MHD power conversion to market with commercial power plants of a new kind, converting the kinetic energy of a high velocity plasma into electricity with no moving parts at a high efficiency. Research was also conducted in the field of supersonic and hypersonic aerodynamics to study plasma interaction with magnetic fields to eventually achieve passive and even active flow control around vehicles or projectiles, in order to soften and mitigate shock waves, lower thermal transfer and reduce drag.
Such ionized gases used in "plasma technology" ("technological" or "engineered" plasmas) are usually weakly ionized gases in the sense that only a tiny fraction of the gas molecules are ionized. These kinds of weakly ionized gases are also nonthermal "cold" plasmas. In the presence of magnetics fields, the study of such magnetized nonthermal weakly ionized gases involves resistive magnetohydrodynamics with low magnetic Reynolds number, a challenging field of plasma physics where calculations require dyadic tensors in a 7-dimensional phase space. When used in combination with a high Hall parameter, a critical value triggers the problematic electrothermal instability which limited these technological developments.
Plasmas are the object of study of the academic field of plasma science or plasma physics, including sub-disciplines such as space plasma physics. It currently involves the following fields of active research and features across many journals, whose interest includes:
- Plasma torch
- Ambipolar diffusion
- Hannes Alfvén Prize
- Plasma channel
- Plasma parameters
- Plasma nitriding
- Magnetohydrodynamics (MHD)
- Magnetohydrodynamic converter
- Electrically powered spacecraft propulsion
- Plasma propulsion engine
- Electric field screening
- List of plasma physicists
- List of plasma physics articles
- Important publications in plasma physics
- IEEE Nuclear and Plasma Sciences Society
- Quark-gluon plasma
- Nikola Tesla
- Space physics
- Total electron content
- Plasma display
- The material undergoes various "regimes" or stages (e.g. saturation, breakdown, glow, transition and thermal arc) as the voltage is increased under the voltage-current relationship. The voltage rises to its maximum value in the saturation stage, and thereafter it undergoes fluctuations of the various stages; while the current progressively increases throughout.
- Across literature, there appears to be no strict definition on where the boundary is between a gas and plasma. Nevertheless, it is enough to say that at 2,000°C the gas molecules become atomized, and ionized at 3,000 °C and "in this state, [the] gas has a liquid like viscosity at atmospheric pressure and the free electric charges confer relatively high electrical conductivities that can approach those of metals."
- Note that non-thermal, or non-equilibrium plasmas are not as ionized and have lower energy densities, and thus the temperature is not dispersed evenly among the particles, where some heavy ones remain "cold".
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A desolate site in Siberia will soon become the forefront of international research into the secrets of the Universe, after the world’s biggest gamma ray detection array scientists are creating there comes into operation.
The Tunka Valley, located in about 100km west of Lake Baikal, close to Russia’s border with Mongolia, is already operating a large-scale experiment studying cosmic rays and gamma rays.
Cosmic rays are charged particles accelerated to energies beyond human capabilities by strong magnetic fields in outer space. Supernovae, quasars, galactic nuclei are all likely sources of the particles. Gamma rays are electromagnetic radiation of high frequency and energy.
Both the hadrons of the cosmic rays and gamma photons trigger kilometers-long cascades of secondary ionized particles and radiation when they enter atmosphere. These can be detected as short weak bursts of light caused by the Cherenkov Effect. Characteristics of those air showers provide clues into the nature of the particles that caused them and by extension the astronomic objects they came from.
The site at Tunka, which is run by a collaboration of Russian and German astrophysicists, currently has 175 photomultiplier stations, sensitive light detectors that are hunting for Cherenkov radiation on moonless cloudless night. The array is spread across the area of about 3 sq km. The technique is different from traditional imaging telescopes, but allows greater sensitivity thanks to a large area of detection.
Now the already impressive Tunka observatory will be considerably expanded, Irkutsk State University, the principle operator of the experiment, reports on Tuesday. The Tunka-HiSCORE experiment would include some 1,000 detectors set across at least 10 sq km by the time the facility is complete in three years, according to Nikolay Budnev, head of the university’s Applied Physics branch.
The site “will be a most important contribution to the study of the most intriguing secrets of creation – the creation and the future of the Universe,” Budnev told in an interview to a local newspaper describing the project.
Razmik Mirzoyan from the Max Planck Institute for Physics in Germany’s Munich is heading the ambitious pairing. He headed the MAGIC collaboration, the twin gamma-ray telescope on La Palma, one of the Canary Islands. | 0.852263 | 3.203207 |
eso1441 — Photo Release
The Hot Blue Stars of Messier 47
17 December 2014
This spectacular image of the star cluster Messier 47 was taken using the Wide Field Imager camera, installed on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. This young open cluster is dominated by a sprinkling of brilliant blue stars but also contains a few contrasting red giant stars.
Messier 47 is located approximately 1600 light-years from Earth, in the constellation of Puppis (the poop deck of the mythological ship Argo). It was first noticed some time before 1654 by Italian astronomer Giovanni Battista Hodierna and was later independently discovered by Charles Messier himself, who apparently had no knowledge of Hodierna’s earlier observation.
Although it is bright and easy to see, Messier 47 is one of the least densely populated open clusters. Only around 50 stars are visible in a region about 12 light-years across, compared to other similar objects which can contain thousands of stars.
Messier 47 has not always been so easy to identify. In fact, for years it was considered missing, as Messier had recorded the coordinates incorrectly. The cluster was later rediscovered and given another catalogue designation — NGC 2422. The nature of Messier’s mistake, and the firm conclusion that Messier 47 and NGC 2422 are indeed the same object, was only established in 1959 by Canadian astronomer T. F. Morris.
The bright blue–white colours of these stars are an indication of their temperature, with hotter stars appearing bluer and cooler stars appearing redder. This relationship between colour, brightness and temperature can be visualised by use of the Planck curve. But the more detailed study of the colours of stars using spectroscopy also tells astronomers a lot more — including how fast the stars are spinning and their chemical compositions. There are also a few bright red stars in the picture — these are red giant stars that are further through their short life cycles than the less massive and longer-lived blue stars .
By chance Messier 47 appears close in the sky to another contrasting star cluster — Messier 46. Messier 47 is relatively close, at around 1600 light-years, but Messier 46 is located around 5500 light-years away and contains a lot more stars, with at least 500 stars present. Despite containing more stars, it appears significantly fainter due to its greater distance.
Messier 46 could be considered to be the older sister of Messier 47, with the former being approximately 300 million years old compared to the latter’s 78 million years. Consequently, many of the most massive and brilliant of the stars in Messier 46 have already run through their short lives and are no longer visible, so most stars within this older cluster appear redder and cooler.
This image of Messier 47 was produced as part of the ESO Cosmic Gems programme .
The lifetime of a star depends primarily on its mass. Massive stars, containing many times as much material as the Sun, have short lives measured in millions of years. On the other hand much less massive stars can continue to shine for many billions of years. In a cluster, the stars all have about the same age and same initial chemical composition. So the brilliant massive stars evolve quickest, become red giants sooner, and end their lives first, leaving the less massive and cooler ones to long outlive them.
The ESO Cosmic Gems programme is an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for science observations. All data collected may also be suitable for scientific purposes, and are made available to astronomers through ESO’s science archive.
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
- Photos of the MPG/ESO 2.2-metre telescope
- Other photos taken with the MPG/ESO 2.2-metre telescope
- Photos of La Silla
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655 | 0.808015 | 3.592714 |
Neutron stars are leftovers of massive stars (10-50 times as massive as our Sun) that have collapsed under their own weight. Most are only about 20 km in diameter, but they are so compact that a teaspoon of neutron star stuff would weigh about one hundred million tons. Two other physical properties characterize a neutron star: their fast rotation and strong magnetic field. Magnetars form a class of neutron stars with ultra-strong magnetic fields, approximately a thousand times stronger than that of ordinary neutron stars, making them the strongest known magnets in the cosmos. But astronomers have been unsure exactly why magnetars shine in X-rays. Data from ESA’s XMM-Newton and Integral orbiting observatories are being used to test, for the first time, the X-ray properties of magnetars.
So far, about 15 magnetars have been found. Five of them are known as soft gamma repeaters, or SGRs, because they sporadically release large, short bursts (lasting about 0.1 s) of low energy (soft) gamma rays and hard X-rays. The rest, about 10, are associated with anomalous X-ray pulsars, or AXPs. Although SGRs and AXPs were first thought to be different objects, we now know that they share many properties and that their activity is sustained by their strong magnetic fields.
Magnetars are different from ‘ordinary’ neutron stars because their internal magnetic field is thought to be strong enough to twist the stellar crust. Like in a circuit fed by a gigantic battery, this twist produces currents in the form of electron clouds which flow around the star. These currents interact with the radiation coming from the stellar surface, producing the X-rays.
Until now, scientists could not test their predictions, because it is not possible to produce such ultra-strong magnetic fields in laboratories on Earth.
To understand this phenomenon, a team led by Dr Nanda Rea from the University of Amsterdam used XMM-Newton and Integral data to search for these dense electron clouds around all known magnetars, for the first time.
Rea’s team found evidence that large electron currents do actually exist, and were able to measure the electron density which is a thousand times stronger than in a ‘normal’ pulsar. They have also measured the typical velocity at which the electron currents flow. With it, scientists have now established a link between an observed phenomenon and an actual physical process, an important clue in the puzzle of understanding these celestial objects.
The team is now working hard to develop and test more detailed models on the same line, to fully understand the behavior of matter under the influence of such strong magnetic fields. | 0.822491 | 4.083632 |
Editor’s note: This guest post was written by Andy Tomaswick, an electrical engineer who follows space science and technology.
One of the most technically difficult tasks of any future manned missions to Mars is to get the astronauts safely on the ground. The combination of the high speed needed for a short trip in space and the much lighter Martian atmosphere creates an aerodynamics problem that has been solved only for robotic spacecraft so far. If people will one day walk Mars’ dusty surface, we will need to develop better Entry Descent and Landing (EDL) technologies first.
Those technologies are part of a recent meeting of the Lunar Planetary Institute (LPI), The Concepts and Approaches for Mars Exploration conference, held June 12-14 in Houston, which concentrated on the latest advances in technologies that might solve the EDL problem.
Of the multitude of technologies that were presented at the meeting, most seemed to involve a multi-tiered system comprising several different strategies. The different technologies that will fill those tiers are partly mission-dependent and all still need more testing. Three of the most widely discussed were Hypersonic Inflatable Aerodynamic Decelerators (HIADs), Supersonic Retro Propulsion (SRP), and various forms of aerobraking.
HIADs are essentially large heat shields, commonly found many types of manned reentry capsule used in the last 50 years of spaceflight. They work by using a large surface area to create enough drag through the atmosphere of a planet to slow the traveling craft to a reasonable speed. Since this strategy has worked so well on Earth for years, it is natural to translate the technology to Mars. There is a problem with the translation though.
HIADs rely on air resistance for its ability to decelerate the craft. Since Mars has a much thinner atmosphere than Earth, that resistance is not nearly as effective at slowing reentry. Because of this drop in effectiveness, HIADs are only considered for use with other technologies. Since it is also used as a heat shield, it must be attached to the ship at the beginning of reentry, when the air friction causes massive heating on some surfaces. Once the vehicle has slowed to a speed where heating is no longer an issue, the HIAD is released in order to allow other technologies to take over the rest of the braking process.
One of those other technologies is SRP. In many schemes, after the HIAD is released, SRP becomes primarily responsible for slowing the craft down. SRP is the type of landing technology commonly found in science fiction. The general idea is very simple. The same types of engines that accelerate the spacecraft to escape velocity on Earth can be turned around and used to stop that velocity upon reaching a destination. To slow the ship down, either flip the original rocket boosters around upon reentry or design forward-facing rockets that will only be used during landing. The chemical rocket technology needed for this strategy is already well understood, but rocket engines work differently when they are traveling at supersonic speeds. More testing must be done to design engines that can deal with the stresses of such velocities. SRPs also use fuel, which the craft will be required to carry the entire distance to Mars, making its journey more costly. The SRPs of most strategies are also jettisoned at some point during the descent. The weight shed and the difficulty of a controlled descent while following a pillar of flame to a landing site help lead to that decision.
Once the SRP boosters fall away, in most designs an aerobraking technology would take over. A commonly discussed technology at the conference was the ballute, a combination balloon and parachute. The idea behind this technology is to capture the air that is rushing past the landing craft and use it to fill a ballute that is tethered to the craft. The compression of the air rushing into the ballute would cause the gas to heat up, in effect creating a hot air balloon that would have similar lifting properties to those used on Earth. Assuming enough air is rushed into the ballute, it could provide the final deceleration needed to gently drop the landing craft off on the Martian surface, with minimal stress on the payload. However, the total amount this technology would slow the craft down is dependent on the amount of air it could inject into its structure. With more air come larger ballute, and more stresses on the material the ballute is made out of. With those considerations, it is not being considered as a stand-alone EDL technology.
These strategies barely scratch the surface of proposed EDL methods that could be used by a human mission to Mars. Curiosity, the newest rover soon set to land on Mars, is using several, including a unique form of SRP known as the Sky Crane. The results of its systems will help scientists like those at the LPI conference determine what suite of EDL technologies will be the most effective for any future human missions to Mars.
Lead image caption: Artist’s concept of Hypersonic Inflatable Aerodynamic Decelerator slowing the atmospheric entry of a spacecraft. Credit: NASA
Second image caption: Supersonic jets are fired forward of a spacecraft in order to decelerate the vehicle during entry into the Martian atmosphere prior to parachute deployment. The image is of the Mars Science Lab at Mach 12 with 4 supersonic retropropulsion jets. Credit: NASA | 0.816659 | 3.537457 |
What might well be the best meteor shower of 2018 heads our way Thursday night into the pre-dawn hours of Friday morning (Dec. 13-14): It’s the annual performance of the Geminid meteor shower.
The Geminids get their name from the constellation of Gemini, the twins. During the overnight hours of Thursday to Friday, the night of this shower’s maximum, the meteors will appear to emanate from a spot in the sky near the bright star Castor in Gemini.
But how unfortunate that the Geminids are relegated to December, when nights get very cold across much of the United States. While August’s Perseids get the most attention, because they appear on balmy summer nights when many people are on vacation, knowledgeable skywatchers know that the “cold Geminids” almost always surpass the Perseids. So, if you are willing to brave a long lookout of possible-subfreezing temperatures, you will be amply rewarded.
Bright … and faint
In studies of past Geminid displays, these meteors scored high marks for both quality and quantity. The Perseids or Leonids seem to whiz across your line of sight in a second or less, but the Geminids are noticeably slower. I’ve often said they resemble “celestial field mice” as they scurry across the sky, producing good numbers of bright, graceful, yellowish-white meteors and fireballs. The Geminids also include many dim meteors, with surprisingly fewer shower members of medium brightness. In other words the meteors you’ll see will be either quite bright or rather faint.
The Geminids typically encounter Earth at around 22 miles (35 kilometers) per second. That’s about half the speed of a Leonid meteor. And only about 2 to 4 percent of all Geminids leave a persistent train in their wake. That’s probably due to their composition: At 2 grams per cubic centimeter (1.15 oz per cubic inch) on average, Geminid meteoroids (the term for meteors before they hit the atmosphere) are several times denser than the cometary bits of fine dust that make up most meteor showers.
This may be because of their origin: They seem to have come not from a comet but from 3200 Phaethon, an Earth-crossing asteroid. Then again, the Geminids may be comet debris after all; some astronomers think Phaethon is the dead nucleus of a burned-out comet that somehow got trapped into an unusually tight orbit.
According to Margaret Campbell-Brown and Peter Brown in the 2018 “Observer’s Handbook” of the Royal Astronomical Society of Canada, peak activity for the Geminids this year is projected to occur at or near 7 a.m. EST (1200 GMT) on Dec. 14. That timing strongly favors North America.
Under normal conditions on the night of maximum activity, from midnight to 4 a.m. local time with ideal dark-sky conditions, an average of at least 60 to 120 Geminid meteors should burst across the sky each hour. (Light pollution will greatly cut down on the numbers, however.) The best time for Geminid viewing will come at 2 a.m., when the constellation Gemini will stand almost directly overhead. (Note that the times in this paragraph refer to your local time zone, wherever you’re watching from.)
The Geminids perform superbly in most years. However, as was the case for last month’s Leonids, the moon will pose a small hindrance. It will reach first-quarter phase on Dec. 15, the day after the Geminid peak. On the evening of Thursday, Dec. 13, the moon will shine brightly in the dim constellation of Aquarius, the water carrier. That means that moonlight could wash out some of the fainter Geminids. However, the moon will set by around 10:30 p.m. local time on Thursday, leaving the sky dark and moonless for the balance of the night and making for perfect viewing conditions.
Slow rise … and rapid decline
The Earth moves quickly through this meteor stream.
Two nights before the peak, hourly rates average one-quarter peak strength. On the night before the peak, about half as many Geminids appear as compared to the night of maximum. After maximum, the numbers drop off sharply. The night after the peak, the shower is once again down to about one-quarter peak strength, and two nights after the peak, only a handful of residual stragglers will remain.
Another interesting fact is that the meteors seen right up to the night of the peak are generally faint, but after the peak, the preponderance of visible meteors are especially bright.
I alluded to this earlier, but I will remind you once again: This time of year, meteor watching can be a long, cold business. You may be lying down on a long lawn chair or snuggled up in a sleeping bag waiting to catch sight of a meteor. If they don’t appear right away, and if you’re cold and uncomfortable, I suppose you’re not going to look for meteors for very long!
Don’t expect meteors to appear at equally spaced intervals of, say, 1 per minute. Instead, you’ll probably experience what some have called the “clumping effect.” You may see a sudden burst of activity, followed by a lull of several minutes or more.
Therefore, make sure you make yourself warm and comfortable. Hot cocoa, tea or coffee can take the edge off the chill, while also providing a slight stimulus (but avoid alcoholic beverages). It’s even better if you can watch the shower with friends. That way, you can keep each other awake, as well as cover more sky.
A few more tips: Look up for as wide a view of the sky as possible. Perhaps listen to some music as you watch. Lastly, give your eyes time to dark-adapt before you look — and good luck!
About the Author: Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers’ Almanac and other publications, and he is an on-camera meteorologist for Verizon FiOS1 News in New York’s lower Hudson Valley. Follow us on Twitter @Spacedotcom and on Facebook. Original article on Space.com.
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Io, the innermost of Jupiter’s four largest moons, has always been a source of wonder for astronomers and scientists. In addition to its pockmarked and ashen surface, it is the most volcanically active object in the Solar System, with about 240 active regions. This is due to the immense tidal forces that Jupiter provides, which create oceans of lava beneath the surface and huge volcanoes blasting it hundreds of kilometers into space.
Naturally, these eruptions are not visible directly from Earth unless one is using infrared cameras. But recently, a new series of eruptions were observed by Dr. Imke de Pater, Professor of Astronomy and of Earth and Planetary Science at the University of California in Berkeley. She was using the Keck II telescope on Mauna Kea in Hawaii on August 15, 2013 when it immediately became apparent something big was happening at Io.
In a telephone interview with Universe Today, de Pater claims this eruption is one of the top 10 most powerful eruptions that have been seen on Io, and she just happened to have the best seat in the house to observe it.
When you are right at the telescope and see the data, this is something you can see immediately, especially with a big eruption like that. It is a very energetic eruption that covers over a 30 square kilometer area. For Earth, that is big, and for Io it is very big too. It really is one of the biggest eruptions we have seen.
However, the fact that it occurred in the Rarog Patera region of Io, aptly named for a Czech fire deity, is somewhat unusual. While many regions of Io are volcanically active, de Pater said she’s not been able to find any other previous activity that has been reported in the Rarog Patera area, which the team finds very interesting.
According to Ashley Davies of NASA’s Jet Propulsion Laboratory in Pasedena, California, Rarog Patera was identified as a small, relatively innocuous hot spot by the Galileo spacecraft during its encounter with the Jovian moon during the late 90’s. However, the observations made indicated that the volcanic activity was at a level way, way below what was seen on Aug 15.
Though we cannot see the eruptions directly, observation using the Keck telescope in the past have ascertained there are likely fountains of lava gushing from volcanically active fissures. But unlike volcanic eruptions here on Earth, which are already awesome and frightening to behold, eruptions on Io would be roughly 1000 times as powerful.
And since Io has no atmosphere to speak of, and the planet’s mass is significantly less than that of Earth’s (0.015 that of Earth’s to exact), the lava shoots off into space. Thus, for anyone standing on the moon’s surface, the result would look very much like a space launch at night, with plumes of flames reaching from the ground and extending indefinitely into the sky.
We never know about eruptions – they can last hours, days months or years, so we have no idea how long it will stay active. but we are very excited about it.
No data or imagery has been released on the new eruption yet since the team is still making their observations and will be writing a paper on this topic. One thing is clear at this point, though. Despite its mysterious nature, Io still has a few surprises left for Earth scientists.
And for more information on the mysterious planet of Io, check out this Astronomycast podcast, featuring an interview with Dr. Pamela Gay of Southern Illinois University: | 0.88758 | 3.836879 |
The elusive Planet Nine does exist, and maybe ten times the mass of the Earth and twenty times away from the Sun than Neptune, NASA scientists say. Planet Nine could turn out to be our solar systems missing super-Earth - a planet with a mass higher than the Earths, but substantially lower than the masses of ice giants Uranus and Neptune. The signs so far are indirect, mainly its gravitational footprints, but that adds up to a compelling case, they said.
"There are now five different lines of observational evidence pointing to the existence of Planet Nine," said Konstantin Batygin, a planetary astrophysicist at California Institute of Technology (Caltech) in the US. "If you were to remove this explanation and imagine Planet Nine does not exist, then you generate more problems than you solve. All of a sudden, you have five different puzzles, and you must come up with five different theories to explain them," said Batygin. Six known objects in the distant Kuiper Belt, a region of icy bodies stretching from Neptune outward towards interstellar space, all have elliptical orbits pointing in the same direction, researchers said.
However, these orbits also are tilted the same way, about 30 degrees "downward" compared to the pancake-like plane within which the planets orbit the Sun, they said.
Computer simulations of the solar system with Planet Nine included show there should be more objects tilted with respect to the solar plane. The tilt would be on the order of 90 degrees as if the plane of the solar system and these objects formed an "X" when viewed edge-on.
Caltech graduate student, Elizabeth Bailey, showed that Planet Nine could have tilted the planets of our solar system during the last 4.5 billion years.
In the study published in the Astronomical Journal, researchers wondered why the plane in which the planets orbit is tilted about 6 degrees compared to the Sun's equator. "Over long periods of time, Planet Nine will make the entire solar-system plane precess or wobble, just like a top on a table," Batygin said.
The last telltale sign of Planet Nines presence involves the solar systems contrarians: objects from the Kuiper Belt that orbit in the opposite direction from everything else in the solar system, researchers said. Planet Nines orbital influence would explain why these bodies from the distant Kuiper Belt end up "polluting" the inner Kuiper Belt, they said. "No other model can explain the weirdness of these high- inclination orbits," Batygin said. "It turns out that Planet Nine provides a natural avenue for their generation. These things have been twisted out of the solar system plane with help from Planet Nine and then scattered inward by Neptune," said Batygin.
"The possibility of a new planet is certainly an exciting one for me as a planetary scientist and for all of us," said Jim Green, director of NASA's Planetary Science Division. "This is not, however, the detection or discovery of a new planet," said Green. "What we're seeing is an early prediction based on modelling from limited observations. Its the start of a process that could lead to an exciting result," he said.... | 0.855258 | 3.67136 |
Science, Tech, Math › Science Star Death Leads to Cosmic Enrichment Share Flipboard Email Print Getty Images / Bento Fotography Science Astronomy Stars, Planets, and Galaxies An Introduction to Astronomy Important Astronomers Solar System Space Exploration Chemistry Biology Physics Geology Weather & Climate By Carolyn Collins Petersen Astronomy Expert M.S., Journalism and Mass Communications, University of Colorado - Boulder B.S., Education, University of Colorado Carolyn Collins Petersen is an astronomy expert and the author of seven books on space science. She previously worked on a Hubble Space Telescope instrument team. our editorial process Facebook Facebook Carolyn Collins Petersen Updated July 03, 2019 Star Death in the Southern Hemisphere Sky Stars, like every other object we can see in the universe. have a definite life cycle. They're born in clouds of gas and dust, they "live" their lives, and eventually, they come to an end. This is true for every star we know about, no matter its size or mass. Some very massive stars die in cataclysmic explosions called supernovae. That's not the fate of our star, which will have a more "gentle" ending. Sun-like stars (those that are around the same mass or age as our Sun) come to the ends of their lives and become planetary nebulae. These are objects in the sky that once appeared almost "planetary" looking to astronomers of a century or more ago who had low-power telescopes compared to today's observatories. They have nothing to do with planets and everything to do with the evolution of certain kinds of stars. Astronomers suspect that our own Sun may end its days as a planetary nebula, if conditions permit. If it does, it will lose much of its mass to space and what remains of the Sun will heat the surrounding cloud of gas and dust and make it glow. To anyone looking at it through a telescope from another planet, the dying Sun will resemble a cosmic ghost. Observing the Owl Nebula The European Southern Observatory caught a view of one such ghostly remnant, nicknamed the "Southern Owl" Nebula. The expanding cloud of gas and dust measures about four light-years across and contains materials that once were created inside the star and its atmosphere. Now, those elements (such as hydrogen, helium, carbon, oxygen, nitrogen and others) are being spread to interstellar space, possibly to enrich a new generation of stars. The Southern Owl (which has the official name of ESO 378-1) is a relatively short-lived phenomenon. It will probably last only a few tens of thousands of years before the cloud dissipates completely. All that will be left is a fading white dwarf star. What Makes a Planetary Nebula? For a planetary nebula to form, an aging star must be the right stellar type: it should have a mass less than about eight times that of the Sun. Stars that are more massive will end their lives in dramatic fashion as supernova explosions. They, too, spread their material out, enriching the space between stars (also known as the "interstellar medium"). As the less-massive stars age, they begin to lose their outer layers of gas through the action of stellar winds. The Sun has a stellar wind that we call the "solar wind", which is a gentler version of the tempests emitted by old, dying stars. After the outer layers of the dying star have dissipated, the remaining hot stellar core heats up, and begins to radiate ultraviolet light. That UV radiation energizes (ionizes) the surrounding gas and causes it to glow. The Long, Last Breath of the Sun Once the planetary nebula has faded away, the leftover stellar remnant will burn for another billion years, consuming all its remaining fuel. It will then become a tiny — but hot and very dense — white dwarf that will slowly cool over billions of years. The Sun could produce a planetary nebula several billion years in the future and then spend its twilight years as a white dwarf emitting visible and ulltraviolet light, and even x-ray radiation. Planetary nebulae play a crucial role in the chemical enrichment and evolution of the universe. Elements are created inside these stars and returned to enrich the interstellar medium. They combine to form new stars, build planets, and — if conditions are right — play a role in the formation and evolution of life. We (and the rest of Earth's life) all owe our existence to the ancient stars that lived and then transformed to become white dwarfs, or blew up as supernovae that scattered their elements to space. This is why we can think of ourselves as "star stuff", or even more poetically—as star dust memories of the ghostly death of a star. | 0.932213 | 3.614928 |
JHU Performs First Lab Simulation of Exoplanet Atmospheric Chemistry
Scientists have conducted the first lab experiments on haze formation in simulated exoplanet atmospheres, an important step for understanding upcoming observations of planets outside the solar system with the James Webb Space Telescope.
The simulations are necessary to establish models of the atmospheres of far-distant worlds, models that can be used to look for signs of life outside the solar system. Results of the studies appeared this week in Nature Astronomy.
“One of the reasons why we’re starting to do this work is to understand if having a haze layer on these planets would make them more or less habitable,” said the paper’s lead author, Sarah Hörst, assistant professor of Earth and planetary sciences at the Johns Hopkins University.
With telescopes available today, planetary scientists and astronomers can learn what gases make up the atmospheres of exoplanets. “Each gas has a fingerprint that’s unique to it,” Hörst said. “If you measure a large enough spectral range, you can look at how all the fingerprints are superimposed on top of each other.”
Current telescopes, however, do not work as well with every type of exoplanet. They fall short with exoplanets that have hazy atmospheres. Haze consists of solid particles suspended in gas, altering the way light interacts with the gas. This muting of spectral fingerprints makes measuring the gas composition more challenging.
Hörst believes this research can help the exoplanet science community determine which types of atmospheres are likely to be hazy. With haze clouding up a telescope’s ability to tell scientists which gases make up an exoplanet’s atmosphere – if not the amounts of them – our ability to detect life elsewhere is a murkier prospect.
Planets larger than Earth and smaller than Neptune, called super-Earths and mini-Neptunes, are the predominant types of exoplanets, or planets outside our solar system. As this class of planets is not found in our solar system, our limited knowledge makes them more difficult to study.
With the coming launch of the James Webb Space Telescope, scientists hope to be able to examine the atmospheres of these exoplanets in greater detail. JWST will be capable of looking back even further in time than Hubble with a light collecting area around 6.25 times greater. Orbiting around the sun a million miles from Earth, JWST will help researchers measure the composition of extrasolar planet atmospheres and even search for the building blocks of life.
“Part of what we’re trying to help people figure out is basically where you would want to look,” said Hörst of future uses of the James Webb Space Telescope.
Given that our solar system has no super-Earths or mini-Neptunes for comparison, scientists don’t have “ground truths” for the atmospheres of these exoplanets. Using computer models, Hörst’s team was able to put together a series of atmospheric compositions that model super-Earths or mini-Neptunes. By varying levels of three dominant gases (carbon dioxide, hydrogen, gaseous water), four other gases (helium, carbon monoxide, methane, nitrogen) and three sets of temperatures, they assembled nine different “planets.”
The computer modeling proposed different percentages of gases, which the scientists mixed in a chamber and heated. Over three days, the heated mixture flowed through a plasma discharge, a setup that initiated chemical reactions within the chamber.
“The energy breaks up the gas molecules that we start with. They react with each other and make new things and sometimes they’ll make a solid particle [creating haze] and sometimes they won’t,” Hörst said.
“The fundamental question for this paper was: Which of these gas mixtures – which of these atmospheres – will we expect to be hazy?” said Hörst.
The researchers found that all nine variants made haze in varying amounts. The surprise lay in which combinations made more. The team found the most haze particles in two of the water-dominant atmospheres. “We had this idea for a long time that methane chemistry was the one true path to make a haze, and we know that’s not true now,” said Hörst, referring to compounds abundant in both hydrogen and carbon.
Furthermore, the scientists found differences in the colors of the particles, which could affect how much heat is trapped by the haze. “Having a haze layer can change the temperature structure of an atmosphere,” said Hörst. “It can prevent really energetic photons from reaching a surface.”
Like the ozone layer that now protects life on Earth from harmful radiation, scientists have speculated a primitive haze layer may have shielded life in the very beginning. This could be meaningful in our search for external life.
For Hörst’s group, the next steps involve analyzing the different hazes to see how the color and size of the particles affect how the particles interact with light. They also plan to try other compositions, temperatures, energy sources and examine the composition of the haze produced.
“The production rates were the very, very first step of what’s going to be a long process in trying to figure out which atmospheres are hazy and what the impact of the haze particles is,” Hörst said. | 0.8874 | 3.768286 |
NASA’s Fermi Gamma-ray Space Telescope has identified the farthest gamma-ray blazars, a type of galaxy whose intense emissions are powered by supersized black holes. Light from the most distant object began its journey to us when the universe was 1.4 billion years old, or nearly 10 per cent of its present age.
“Despite their youth, these far-flung blazars host some of the most massive black holes known,” says Roopesh Ojha, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “That they developed so early in cosmic history challenges current ideas of how supermassive black holes form and grow, and we want to find more of these objects to help us better understand the process.”
Blazars constitute roughly half of the gamma-ray sources detected by Fermi’s Large Area Telescope (LAT). Astronomers think their high-energy emissions are powered by matter heated and torn apart as it falls from a storage, or accretion, disc toward a supermassive black hole with a million or more times the Sun’s mass. A small part of this infalling material becomes redirected into a pair of particle jets, which blast outward in opposite directions at nearly the speed of light. Blazars appear bright in all forms of light, including gamma rays, the highest-energy light, when one of the jets happens to point almost directly toward us.
Previously, the most distant blazars detected by Fermi emitted their light when the universe was about 2.1 billion years old. Earlier observations showed that the most distant blazars produce most of their light at energies right in between the range detected by the LAT and current X-ray satellites, which made finding them extremely difficult.
Then, in 2015, the Fermi team released a full reprocessing of all LAT data, called Pass 8, that ushered in so many improvements astronomers said it was like having a brand new instrument. The LAT’s boosted sensitivity at lower energies increased the chances of discovering more far-off blazars.
The research team was led by Vaidehi Paliya and Marco Ajello at Clemson University in South Carolina and included Dario Gasparrini at the Italian Space Agency’s Science Data Center in Rome as well as Ojha. They began by searching for the most distant sources in a catalog of 1.4 million quasars, a galaxy class closely related to blazars. Because only the brightest sources can be detected at great cosmic distances, they then eliminated all but the brightest objects at radio wavelengths from the list. With a final sample of about 1,100 objects, the scientists then examined LAT data for all of them, resulting in the detection of five new gamma-ray blazars.
Expressed in terms of redshift, astronomers’ preferred measure of the deep cosmos, the new blazars range from redshift 3.3 to 4.31, which means the light we now detect from them started on its way when the universe was between 1.9 and 1.4 billion years old, respectively.
“Once we found these sources, we collected all the available multiwavelength data on them and derived properties like the black hole mass, the accretion disc luminosity, and the jet power,” says Paliya.
Two of the blazars boast black holes of a billion solar masses or more. All of the objects possess extremely luminous accretion discs that emit more than two trillion times the energy output of our Sun. This means matter is continuously falling inward, corralled into a disc and heated before making the final plunge to the black hole.
“The main question now is how these huge black holes could have formed in such a young universe,” says Gasparrini. “We don’t know what mechanisms triggered their rapid development.”
In the meantime, the team plans to continue a deep search for additional examples.
“We think Fermi has detected just the tip of the iceberg, the first examples of a galaxy population that previously has not been detected in gamma rays,” says Ajello. | 0.877675 | 4.04012 |
In the Southern Hemisphere, the Magellanic Clouds, or the galaxy’s satellite galaxies (revolves around Milky Way), are visible. The Magellanic Clouds are named for the Portuguese explorer Ferdinand Magellan, the first circumnavigator of the world. Because of interstellar dust (rocky planets and other material), we can only see 6,000 stars, but the Milky Way has 100 billion stars total. The farthest are 4,000 light years away. Earth’s atmosphere smears the sky, so stars appear to twinkle. About 10^6 stars— old as the universe— inhabit In globular clusters (~200 in Milky Way’s halo).
All pictures of the Milky Way are artists’ conceptions because no telescope can travel high enough (billions of light years) to capture the entire galaxy.
Shapley’s Subdivision of the Milky Way
- Nuclear Bulge: (10^6 solar masses) nucleus in the center, old stars (red)
- The Disk: (10^11 solar masses) thin, diffuse layer of material revolving around the bulge; the Sun is half-way on the disk; all young stars
- The Halo: hot gas about 100,000 K
- Galactic Corona: mass exists but unseen; 5-10 times as much mass as the nucleus, disk, and halo together, 95% of galaxy mass unknown matter
- Visible Matter: 96% stars, 4% interstellar gas
- (13.6 billion years ago) A gas cloud of 75% hydrogen and 25% helium with mass ~ 1 trillion solar masses
- Contraction and rotation form spherical shape
- Inner part flattens to form disk of younger stars
- Galactic rotation forms spiral arms
- Supernovae gives off more heavy elements that eventually become the Sun | 0.888915 | 3.574038 |
Postdoc Spotlight: Looking at Planetary System Evolution with Meredith MacGregor
Gas, dust, and small objects. In the beginning, it’s a whole lot of nothing. After these materials collide and combine to eventually make planets, the material that’s left behind forms debris rings around the mature planetary systems. Astronomers call these rings circumstellar disks. We see this in our own backyard, in the dark, cold, and mysterious disk known as the Kuiper Belt surrounding the Sun 4 billion miles out towards the edge of the Solar System.
Circumstellar disks can betray the secrets of a planetary system. Astronomers in planets far away from us could use the structure of the Kuiper Belt to infer the presence of Neptune in our Solar System. Eventually, this knowledge would lead them to learn how the early Solar System evolved into inner rocky planets, outer gas and ice giant planets, and the remnant Asteroid and Kuiper Belts that we see today.
How can astronomers do that? We’ll let NSF Astronomy and Astrophysics Postdoctoral Fellow Meredith MacGregor explain. In our latest Postdoc Spotlight installment, she takes us through her journey from kindergarten science fairs to stars trillions of miles away.
DTM: Can you give us the rundown of what you do at DTM?
Meredith MacGregor: I am working to answer big questions in astronomy that I’m really excited about. One is, how do planetary systems form in the first place? And then related to that I am now very interested in what makes these planetary systems habitable. When you image circumstellar disks, you end up imaging the star as well, so I now have gotten very into looking at stellar activity and what that means for the disks and the planets surrounding their star.
DTM: What does the word “habitable” mean for you?
MM: The part of habitability that I’m most focusing on right now is the role that stellar activity plays. Stars are active, including our Sun, meaning they emit what we call flares, bursts of high-energy radiation. Large solar flares are typically accompanied by releases of charged particles called coronal mass ejections, or CMEs. On Earth we are nicely protected by our magnetic field and atmosphere, keeping these damaging particles from actually penetrating to the planet’s surface. So we don’t really see the effect of the Sun’s activity on a daily basis. But M Dwarfs, the cooler, redder types of star that many exoplanet missions have been focusing on, are much more active than our own Sun. And the planets, in order to be in the “habitable” zone—which basically means at a distance from the star that you could have liquid water—are much closer in, so they are getting hit by generally a lot more of this radiation. If you are getting hit by flares and CMEs at the rate that we think stars are putting them off, you might expect those planets not to be habitable as a result.
DTM: How did you go from studying circumstellar disks to this part of habitability?
MM: This happened in my first year of being a postdoc here at DTM. I did my doctoral work on circumstellar disks and came here intending to continue that work. But there was a paper that came out just as I was starting—It made a claim that the nearest planetary system to us, Proxima Centauri, had a system of multiple debris disks around it. That would be exciting because it would make it somewhat like our own Solar System. Alycia Weinberger and I had a conversation about it during journal club, and we both decided that we were deeply skeptical about the original analysis. Afterwards, Alycia suggested that I download the archival data and see what’s in it.
DTM: So then what happened?
MM: The paper presented an averaged image, but the star had actually been observed 15 different times spread out over several months. I quickly noticed that the data showed nothing, nothing, nothing, and then this beautiful light curve in which the star brightened by a factor of a thousand and then decayed back into nothing. The only thing that produces a light curve like that is a stellar flare. Essentially, in 14 of these observations, there was no excess signal from the star. Then, in the last observation, it was very clear that the star had undergone a huge flaring event.
We had just discovered something completely new. It was very exciting because we’d never detected a flare from an M-dwarf in the millimeter before. It’s a wavelength regime where we just had no idea that M-dwarfs even flared. Even from the Sun, we’ve only detected a handful of flares at millimeter wavelengths. It’s really a whole new area of stellar astrophysics, and it was fun to open it up sort of by chance. Since then, I’ve taken this result and built it into a whole new research program where we are going to go back and do a large project to actually understand the mechanisms that produce stellar flares at these wavelengths.
DTM: This finding was new and exciting astrophysics. What was the reaction from the field?
MM: Other scientists in the field thought this was an exciting result for a number of reasons. One, it’s a neat story of interpreting a dataset one way, doing a sanity check, and discovering something completely different. It’s a nice story of science changing and correcting itself. In the exoplanet community, I think this has reminded everybody that stars are active and exciting, and that we need to keep that in mind when talking about habitability.
DTM: You also had other exciting news looking at another planetary system. What was that about?
MM: My other area of research is looking at circumstellar disks. Recently, I have gotten observations of several systems with ALMA, the Atacama Large Millimeter/submillimeter Array, that are really exciting because they can tell us about the planetary systems that shaped the surrounding disks. Just before I started here at Carnegie, we got an image of the Fomalhaut debris disk with ALMA. Fomalhaut is a truly beautiful ring of dust. It’s remarkable because the actual ring is located really far out at about 110 astronomical units (AU) or 110 times the distance of the Earth to the Sun. But the disk is only about 10 AU wide, so it’s this beautifully narrow and eccentric ring of dust quite far out from the star. Something has to be shaping it out there, but it had never been well imaged with ALMA because of its angular scale on the sky. It’s very nearby, only about 7 parsecs (1 parsec is about 19 trillion miles) away from us, so it’s very extended on the sky. To image it well with ALMA, you actually have to do a mosaic image.
The end result of this work was the first complete millimeter map of the Fomalhaut debris disk. It was gorgeous. In fact, it was the Astronomy Picture of the Day, which was super fun. We also detected CO2 gas in it, and we think that this points to the composition of the bodies in the ring being cometary. We were also able to robustly measure the geometry and eccentricity of the ring and actually detected something called apocentric glow, which had been predicted theoretically but never seen before. Since the ring is eccentric, there is an over density of material at the apocenter side of the disk, farthest from the star, which we see as a brightening at that location in the ALMA image.
DTM: How did you get into this kind of work initially and how did that evolve into what you do now?
MM: I did science fairs all throughout high school and always knew I wanted to do physics. I really liked using math to explain how the world works. My very first science project was when I was in kindergarten. It was how a syphon helps a toilet flush. I still remember the experience of standing in the science fair—I had this whole demo with cups and tubing in between them, and everybody would come around and I would say, “this is how a toilet flushes!”
As I got older and away from toilet flushing, I focused into physics. I started college and was sure I was going to be a physicist. But, I took a class in astronomy and found it fascinating. I ended up adding astronomy as my second major, and as I went along, I took more and more astronomy courses and fewer physics courses. I spent a summer at the National Radio Astronomy Observatory (NRAO) in Charlottesville, VA and started learning about radio astronomy. I was attracted to the challenge of radio astronomy. Many people are put off by the techniques and complexity of getting an image at radio wavelengths, and I loved getting to master such a difficult but powerful technique.
I started grad school and met with possible advisors who worked in radio astronomy, and I ultimately picked my advisor because of ALMA. The first proposal results came out right as I showed up for graduate school, and one of the people I met with had a proposal accepted in this first AMLA cycle. It just seemed too cool of an opportunity to let it pass.
DTM: It seems you had a special connection with ALMA. What does the telescope array mean for you?
MM: ALMA is really an amazing facility. It has completely changed how we understand basically everything in radio astronomy. In circumstellar disks, this is particularly clear. Before ALMA we had all these images of disks that just looked like blobs. We knew there was material there, but we had no idea what it looked like. With ALMA, all of a sudden we started seeing all of their detailed structure. In the time that I have been a graduate student into a postdoc, circumstellar disks went from being more of a niche field to a fascinating, newsworthy subject. I feel especially connected to ALMA because I had heard about it when I was a summer student at NRAO, and I knew it was coming online. Then, my graduate trajectory basically started as ALMA started. I feel like I have kind of grown up with the field, with me being a researcher in it as it grows and as ALMA continues to improve.
DTM: You also have a peculiar fellowship here at Carnegie. What does it entail?
I am excited to be a National Science Foundation Astronomy and Astrophysics postdoctoral fellow because the NSF cares deeply about broader impacts and giving back to the scientific community. As a fellow, I am able to pursue my own independent research as well as a broader impact project. I wanted to have the chance to continue doing outreach and teaching as a postdoc.
DTM: How come?
MM: I certainly benefited a lot from having mentors and teachers who saw that I was excited about science and then nurtured that. I didn’t appreciate necessarily how special that was until I moved along in my career. You know, astrophysics is still very largely male dominated, and I think that’s a shame. When I went into college I noticed there was only one tenured woman in the faculty at Harvard. I want to be the person who can inspire and mentor younger generations so that we can keep astrophysics going in a direction of becoming more diverse and inclusive. We are getting there, but there’s still a lot of work to be done.
DTM: So how exactly do you do that here?
MM: I chose to come to Carnegie for a number of reasons. One: research wise, it’s an amazing place to answer the questions that I want to answer. In particular, I really wanted to work with Alycia Weinberger. I never had a chance to have such an awesome female mentor before, and getting to work with someone like her was just like a dream.
I also wanted to come here because Carnegie has CASE, the Carnegie Academy for Science Education, which already has in place a robust outreach and teaching component. I have been working very closely with them for the last year to develop a curriculum and teach it in the First Light program.MacGregor teaching astronomy at the Carnegie Academy for Science Education's First Light Program. Credit: Carnegie Institution for Science.
DTM: What has CASE been like?
MM: I have worked with CASE to develop a curriculum on astronomy, specifically exoplanets and astrobiology for D.C. middle schoolers. I am currently teaching this curriculum along with CASE staff at Carnegie headquarters every Saturday afternoon. It’s fun! The students have incredibly high energy and ask a lot of questions that make me think about my own research in a whole new light. So, coming here to DTM has given me the opportunity to do both my science and my broader impacts at a very high level.
DTM Postdoc Spotlights, conversations in which we feature our postdocs in astronomy, geochemistry, cosmochemistry, and geophysics, are edited for clarity and length. | 0.853277 | 3.952061 |
How old is the Earth? How did it come to have water? Meteorites may hold clues to these age-old questions.
4.6 billion years ago
Dr Caroline Smith, meteorite expertExplore
The Wold Cottage meteorite, which fell in 1795 near Wold Cottage farm, Yorkshire, was the first recorded meteorite fall in the UK.
Its discovery helped confirm that meteorites come from space. Previously, many people believed that rocks that fell from the sky had been ejected into the air by nearby volcanoes - but there are no active volcanoes in Yorkshire.
This prompted scientist Joseph Banks to investigate. He commissioned a worldwide comparison of these stones from the sky and found them to be similar to each other but not to rocks on Earth.
This helped ignite scholarly interest in meteorites and their origins, eventually leading to the development of meteoritics as a discipline.
Mervyn Herbert Nevil Story-Maskelyne (1823-1911) was a driving force in the development of optical mineralogy - the study of minerals and rocks under a microscope.
Working at the Museum as Keeper of Mineralogy from 1857, when the post was created, until 1880, he was one of the first people to study meteorites by slicing them into thin sections for the microscope.
During this time, he also greatly expanded the Museum's mineral collection, tripling its size in his first six years and adding at least 43,000 specimens in total.
George Thurland Prior (1862-1936) was one of the first scientists to classify meteorites based on their chemical composition. He worked at the Museum from 1887 until his retirement in 1927 - initially in the laboratories, then as Keeper of Mineralogy from 1909.
While in the laboratory, he helped to describe many new minerals from around the world, but when he became Keeper of Mineralogy, he turned his attention to meteorites.
Prior established a classification of meteorites according to their iron and nickel content, and in 1923 published a catalogue of all of the meteorites then known to science. His laws are still used today as a basis for classifying meteorites.
The Vigarano meteorite fell near the town of Vigarano Pieve in Italy in 1910.
It is a carbonaceous chondrite meteorite, meaning it is composed mostly of rock, rather than metal, and contains round grains called chondrules. Many carbonaceous meteorites also contain high levels of carbon compounds, hence the name 'carbonaceous'. They show visible white patches that are rich in calcium and aluminium.
There are many kinds of carbonaceous chondrites, and the Vigarano meteorite is the type specimen for the CV group of meteorites - the original specimen on which the description of the whole group is based.
Research on these meteorites has revealed that they formed around 4.6 billion years ago, around the same time as the solar system. This makes them particularly valuable for research into the early solar system.
However, CV meteorites also contain microscopic diamonds. Analysis suggests these diamonds are older than both the Earth and the Sun. This means these components came from outside our solar system, and could be the product of ancient stars.
The fall of the Cold Bokkeveld meteorite in 1838 was the first observed fall of a CM2 meteorite - a group of rocky, carbon-containing meteorites.
Since then, there have been a further 14 observed CM2 meteorite falls, although most of these meteorites were smaller than Cold Bokkeveld.
In fact, many of the micrometeorites that fall to Earth are made of CM-like material, meaning that the Earth accumulates many tonnes of it every year.
Scientists have also found water-containing minerals inside these meteorites, suggesting that the ancient bodies they broke away from held liquid water. These meteorites therefore could have brought this water - and potentially the building blocks of life - to our planet.
Two essential building blocks for life are water and organic compounds (molecules made of carbon and hydrogen). These are found wherever there is life on Earth, as well as in meteorites such as Ivuna.
This makes the meteorites vitally important in unravelling the origins of life on Earth - they could even tell us about life on other planets. Some theories suggest the elements for life arrived on Earth in meteorites.
Ivuna is also the type specimen of the very rare CI class of meteorite. CI meteorites are extremely rich in volatile components that are easily lost when they come into contact with the atmosphere. Fortunately, the Ivuna meteorite has been kept in a sealed nitrogen environment ever since it fell in 1938, protecting it from Earth's atmosphere and making it invaluable for research.
Working with the Nakhla meteorite, which fell in Egypt in 1911, Museum scientist Dr Robert (Bob) Hutchison discovered it was younger than most of the other meteorites in the collection. This finding in 1975 led to the idea that some meteorites, including Nakhla, came from Mars.
Dr Hutchinson also identified water in the meteorite, making him and his collaborators the first to identify water in a Martian meteorite, although the discovery was largely overlooked at the time.
This work was done with increasingly sophisticated equipment at the Museum, from simple optical microscopes to a scanning electron microscope and an electron microprobe.
The Tissint meteorite, which fell in 2011, is the Museum's largest Martian meteorite. This piece weighs 1.1 kilogrammes.
Scientists know it came from Mars because it contains tiny bubbles of gas that have the same chemical makeup as the planet's atmosphere.
By looking at the meteorite's exposure to cosmic rays, we can also tell it was ejected from Mars's surface approximately 700,000 years ago.
Martian meteorites are absolutely critical to our study of Mars because they are the only physical samples of the planet we have on Earth. While many missions have landed on the surface of Mars, allowing us to study the planet remotely, these meteorites permit much more detailed and accurate analyses of the planet's composition.
Through careful observation and description geology pioneers revolutionised the way we study the rocks and minerals beneath our feet.
4.5 billion years ago
Prof Richard Herrington, mineralogistExplore
'William Smith was probably the first person to realise that geological strata could be mapped using the fossils they contained. It was an incredibly important thing because geological mapping is now crucial in things like mineral resource exploration and civil engineering.' Dr Paul Taylor, palaeobiologist
William Smith was the first to produce a geological map of an entire nation. While working as a surveyor and visiting various coal mines in Somerset, UK, he noticed that certain fossils were only found in particular layers of rock, or strata. He used this principle to trace strata across the British Isles, eventually publishing his completed map in 1815.
The map was meticulously hand-coloured, using an innovative colour and shading system to represent each of the 23 rock layers.
Although it failed to make the impact Smith had hoped with scientists at the time, the map provided valuable information about the subsurface for canal builders, miners, landowners and agriculturists. The map is now considered an incredible achievement, and Smith's names for strata are still used by geologists today.
'Smith has been justifiably referred to as the father of English geology. This ammonite is still used to mark the base of Jurassic rocks in Britain.' Dr Paul Taylor, palaeobiologist
At 200 million years old, these are among the earliest recorded British ammonites. Despite their great age, the fossils have well-preserved mother-of-pearl on their shells. Mother-of-pearl formed the original outer layer of the living creatures' shells - it usually wears away over time, but can be preserved in fine clays.
The ammonites are part of William Smith's collection, which contains fossils and rocks collected across the British Isles. Smith identified layers of rock by the fossils they contained, using this principle to trace layers across great distances and map the surface geology of England and Wales for the first time. The map was remarkably accurate, and many of Smith's fossil associations still hold true today.
During his first six years as Keeper of Minerals at the British Museum, Mervyn Herbert Nevil Story-Maskelyne tripled the size of the meteorite collection. He was also a driving force in the development of optical mineralogy - the detailed study of minerals and rocks under a microscope.
This microscope was designed by Maskelyne and built in 1863. It was the first to include a rotating stage for viewing minerals under cross-polarised light.
When light is polarised, it can only vibrate in one direction. The way the light interacts with a mineral helps reveal its underlying crystal structure, a property that cannot be determined by the naked eye. Mineralogists today still use cross-polarised light microscopy as a preliminary tool to identify and classify minerals.
'It may look like a potato with sticks in it, but this optical indicatrix model was instrumental in working out the mathematics of optics in mineral microscopy.' Mike Rumsey, mineralogist
This putty ellipsoid was made by Sir Lazarus Fletcher, Keeper of Mineralogy (1880-1909) at the Natural History Museum. It represents the optical indicatrix, a geometric figure used to describe how light is transmitted by a crystal. The two sticks marked in blue can be moved along a groove, depending on the mineral being modelled. The other three sticks are fixed in place.
The model was part of early work on optical phenomena associated with crystals. Studies revealed that the optical properties of crystals were fundamentally linked to their symmetry and physical properties.
One such optical phenomenon is double refraction, where a light ray entering a crystal is split into two rays. The earliest observations of this were in the mineral calcite. When an object is viewed through a well-formed calcite crystal, it appears as two identical images side-by-side. If the crystal is rotated, only one image moves, and at a specific angle the two images merge.
A key development in explaining phenomena such as double refraction was understanding the link between the optical properties of crystals and their symmetry. These studies revealed that the seven mineral crystal systems fell into three optical classes: isotropic, uniaxial and biaxial. Out of these careful observations came the science of crystal optics, inspiring the invention of many scientific and everyday instruments, including polarisers and optical switches.
'Rashleigh's Specimens of British Minerals was a major contribution to mineralogical literature, history and illustration. It remains one of the most significant early visual records of minerals, some of which were previously unknown or undescribed.' Andrea Hart, Library Special Collections Manager
Philip Rashleigh was a keen amateur mineralogist who amassed one of the earliest and finest private collections ever assembled. His comprehensive collection contains extremely rare specimens, including minerals from mines that have since been decommissioned.
Although he knew that accurately representing the sheen and colour of minerals would be a difficult task, Rashleigh saw scientific value in producing illustrations of his specimens. He commissioned Henry Bone and other artists to draw some of his finest specimens in a series of two publications. This was to be the first illustrated book on British minerals, and is still considered one of the finest.
After Rashleigh's death in 1811, the mineral collection changed hands several times and was acquired by the Museum in 1964.
'Up until 1801, a lot of our mineral collection was Sir Hans Sloane's curious stuff. But from this point on, researchers started using and looking at the collection from a scientific perspective. It was the beginning of us becoming a mineralogical research institute, rather than just being custodians of pretty things.' Mike Rumsey, mineralogist
This piece of columbite belonged to Sir Hans Sloane, whose enormous collection was gifted to the British Museum when he died in 1753. His collection, which included this mineral, eventually formed much of the original material in the Natural History Museum.
The mineral sat in the British Museum's collection for years, described only as 'a very heavy black stone... with golden streaks'. Nearly 50 years later, British Museum geochemist Charles Hatchett came across the columbite and analysed its composition. He found that it contained an element previously unknown to science. He named the element columbium (Cb), but it was later renamed to niobium (Nb).
The fossil record provides an imperfect but invaluable window into the past, revealing the evolution of life on our planet.
3642-66 million years ago
Prof Paul Barrett, vertebrate palaeontologistExplore
'These microscopic structures are so intriguing, and their biotic origin is so hotly debated, because at the time they were discovered they were considered to be the very first fossil evidence of oxygen-producing, photosynthetic life.' Dr Peta Hayes, Curator of Palaeobotany
This piece of chert from Pilbara, Western Australia is around 3,462 million years old. It is still unclear whether it contains the world's oldest fossil evidence of life on Earth, in the form of microbes. The alternative theory is that the structures it contains are just mineral growths that resemble simple organisms.
The Apex chert caused a flurry of excitement in 1993 when it was first described by US scientist Bill Schopf, on sabbatical at the Natural History Museum. Schopf entered the type specimen into the Museum's collection, where it still sits today.
The most recent analysis of the Apex chert supports the theory that the tiny structures are mineralogical, not biological. But the debate continues and the specimen is still in demand for further study. The Apex chert 'fossils' ignited conversations about the age of life on Earth, fundamental to understanding the mechanisms and timescales of evolution.
'[Lang's work] is exceptional in its botanical and geological importance. Considering the unpromising nature of the material, the information obtained is amazing.' AC Seward FRS
At 415 million years old, this tiny structure is one of the earliest known land-dwelling plants. It was one of many unusual plant fossils uncovered in and around Herefordshire, England. The ancient plants lacked leaves of any kind and measured no more than 6 centimetres in length.
The fossils, with their odd features and poor preservation, were cast aside by most scientists - except for British palaeobotanist William Henry Lang. In 1937, Lang set out to study the unpromising remains with new microscopy techniques. Using his talent for identifying and classifying fossil plants, he proved that the fossils were a goldmine of data about the earliest life on land.
Even though the plants had been transported and buried in marine or river sediments, Lang was able to show they lived on land. He named the plant Cooksonia, a genus that has since come to represent the original body plan of early land plants.
Lang identified and extracted spores in the fossils that measured just 25 to 38 nanometres - billionths of a metre - in diameter, a feat that would have been technologically difficult at the time. This proved the plants had spore-bearing organs.
Scientists are still collecting and studying Cooksonia fossils, confirming and extending Lang's original theories.
'This is an extraordinary fossil, not just because it is the earliest insect known, but because the structure of its jaws is similar to flying insects today, suggesting an early origin of flight.' Claire Mellish, Curator of Palaeoarthropods
At 410 million years old, Rhyniognatha hirsti is the world's oldest known insect. Insects probably evolved around 80 million years earlier, when plants were colonising the land for the first time.
This fossil is one of the earliest land-dwelling arthropods, a group that includes insects, spiders and millipedes. It provides a unique insight into a time of major change in ecological diversity and animal physiology.
Insects are thought to have evolved from crustaceans. They were the first animals to develop flight, allowing them to adapt and diversify during times of global climate change. Insects are now the most species-rich group of animals on Earth.
The R. hirsti insect is preserved inside a piece of Rhynie chert, a glass-like Scottish rock that contains exceptionally preserved fossils. Found near the village of Rhynie in Aberdeenshire, the Rhynie chert fossils offer a window into past at a time when the first plants and animals were making the leap onto land.
A flurry of scientific activity accompanied the first discovery of Rhynie chert fossils between 1910 and 1913. Since then, further collecting and analysis have revealed a diverse range of fossils, including primitive plants, algae, fungi, lichen and arthropods. As scientists apply the latest imaging techniques, genetic analyses and understanding to Rhynie chert specimens, we are learning more about the diversity of early life on land and how organisms interacted with each other.
'Hylonomus records a key moment in evolutionary history when amniotes - creatures that encapsulate their young in a complex set of membranes, either within the mother or within an egg - first developed the water-tight skins and shelled eggs that allowed them to invade the land so successfully.' Prof Paul Barrett, vertebrate palaeontologist
Hylonomous lyelli lived 312 million years ago, making it the earliest known true reptile. It was a small, lizard-like animal that may have used its sharp teeth to eat insects.
Fossils like this one provide evidence of a time in Earth's history when vertebrates - animals with backbones - were finally able to leave the water and fully colonise dry land. The first reptiles diversified into an extremely successful group that at one time included the dinosaurs and huge marine reptiles.
'The discovery of dinosaurs underlined how different life had been in the geological past and, of course, they still fire our imaginations today.' Dr Paul Taylor, palaeobiologist
Although he was a medical doctor, Dr Gideon Mantell had a keen interest in geology. He uncovered a number of unusual fossils in Sussex during the nineteenth century.
His wife Mary Mantell found these fossil teeth in a pile of rubble while accompanying him on his rounds. Dr Mantell struggled to identify the animal they belonged to, but would eventually interpret them as the remains of an ancient and enormous reptile. He named the species Iguanodon, because its teeth resembled those of the modern iguana.
This was one of the first described examples of a group of enormous Mesozoic reptiles, later known as the dinosaurs. Despite Dr Mantell's monumental discovery, it is actually Museum founder Sir Richard Owen who is credited with coining the name Dinosauria.
'As the earliest known dinosaur, Nyasasaurus parringtoni gives us the first glimpse of what would become the major group of terrestrial animals for the next 150 million years.' Prof Paul Barrett, vertebrate palaeontologist
Nyasasaurus parringtoni lived around 245 million years ago, making it the earliest known dinosaur.
The Museum holds the type specimen of N. parringtoni - a partial skeleton that includes vertebrae and an arm bone. Based on these fossils, N. parringtoni was formally described and named a new species in 2012.
Dinosaurs are distinguished by a number of anatomical quirks, among them the characteristics of their limb bones. This early reptile represents the roots of the dinosaur family tree. Fossils from the period reveal early dinosaurs to be a minor group of unusual, bipedal reptiles, living in a world dominated by other groups.
'Stegosaurus fossil finds are rare. Having the world's most complete example here for research means we can begin to uncover the secrets behind the evolution and behaviour of this intriguing dinosaur species.' Prof Paul Barrett, vertebrate palaeontologist
The world's most complete Stegosaurus skeleton was unveiled at the Museum in 2014. Scientists estimated the body mass of the animal by digitising more than 300 bones of its skeleton and producing a 3D model. This allowed them to calculate how much the Stegosaurus weighed - as much as a small rhino - which would have influenced how much food it ate and how it walked around.
Dinosaur skulls are often squashed during the fossilisation process, but the bones of this Stegosaurus skull are all three-dimensional. This makes it one of the most scientifically valuable dinosaur skulls ever found.
Future studies of the specimen may answer some of our long-held questions about Stegosaurus, including the function of its bony back plates.
'The sheer number of well-preserved specimens allows us to ask lots of interesting questions about their palaeobiology, using the latest scientific techniques.' Dr Pip Brewer, Curator of Fossil Mammals.
Fossils of early mammals are extremely rare, but fissure deposits in south Wales hold a surprising abundance of important fossil fragments. The Museum's Welsh fissure collection contains over 10,000 tiny bones and teeth of two early mammals, Morganucodon and Kuehneotherium, from the beginning of the Jurassic period, 200 million years ago.
Thanks to these deposits, Morganucodon is one of the best-known early mammals in the world. At 200 million years old, it is also one of the oldest and most primitive. Morganucodon was a small, slender animal that ate insects such as beetles.
Museum scientists are now using new technology, including synchrotron CT scanning, to learn more about these specimens and further our understanding of early mammal evolution.
'These specimens kick-started many debates over the nature of past life and ecosystems, and fuelled important discussions about deep time and the origins of major animal groups.' Prof Paul Barrett, vertebrate palaeontologist
Mary Anning was the world's first professional fossil hunter. She discovered many of the most spectacular specimens of Mesozoic reptiles, fish and invertebrates in Lyme Regis in Dorset, England.
The huge reptile fossils she presented were unlike anything academics of the time had ever seen. They were the world's first glimpse into a Mesozoic age (225 to 65 million years ago) of giant reptiles on land and under the sea.
Many of the icthyosaurs and plesiosaurs that now line the Museum's Fossil Marine Reptiles gallery were collected by Anning herself.
'Archaeopteryx is truly one of the most important fossils of all time, helping establish a direct evolutionary link between two major groups and fuelling early evolutionary debates.' Prof Paul Barrett, vertebrate palaeontologist
An icon of evolutionary debate, Archaeopteryx is now generally accepted as the earliest known bird. It was named in 1861, just two years after the publication of Charles Darwin's On the Origin of Species.
The fossils showed traits typical of both birds and reptiles, providing a real-world example of Darwin's predicted transitional forms - species that represent the step between two seemingly distinct groups.
Archaeopteryx kick-started the debate over whether birds evolved from dinosaurs, and had a major impact on our ideas about evolutionary processes.
Some key fossils from the last 60 million years display characteristics of living species, helping scientists to classify the extinct creatures.
800,000-500 years ago
Prof Adrian Lister, palaeobiologistExplore
'This was the very beginning of mammoth fossils being studied in Europe. This and other fossils eventually proved the existence of an extinct Pleistocene megafauna in geologically quite recent times.' Dr Paul Taylor, palaeobiologist
This Siberian woolly mammoth tooth was one of the first mammoth fossils brought to Europe and studied by naturalists. Sir Hans Sloane examined the fossil tooth in 1728 and added it to his ever-expanding collection of worldly objects.
Sloane realised the tooth came from a relative of modern elephants, but interpreted this as meaning Siberia had experienced a tropical climate before the biblical flood killed the inhabitants. Other scholars disagreed with Sloane and developed their own theories.
Specimens like this one kick-started the scientific study of mammoth fossils in Europe, igniting debates about the evolution of extinct megafauna. The number of plates in the tooth indicates that it belonged to a species that is rare in Siberia, so the specimen is of considerable scientific as well as historic significance.
'Owen realised the mastodon skeleton was vastly too big because he compared it with modern elephant skeletons. He was one of first people who really thought about reconstructing skeletons using modern analogue animals.' Prof Adrian Lister, palaeobiologist
Albert Koch unearthed hundreds of huge bones in Missouri, USA, in 1840. He reconstructed a skeleton poorly, padding it with extra bones and displaying the tusks pointing downwards. Koch named the creature Missourium, even though it was very similar to previous finds of creatures called mastodons.
The monstrous skeleton was exhibited around the USA, and in 1841 was shipped across the Atlantic and displayed at Piccadilly in London. Richard Owen, then employed by the Royal College of Surgeons, came to see the reconstructed animal and was immediately suspicious of its size and the placement of its tusks.
Owen persuaded the British Museum to purchase Koch's entire collection of bones, including the mastodon skeleton. He then disassembled the skeleton and remounted it, removing the extra bones and flipping the tusks into their correct positions.
The Mammut americanum skeleton still stands in the Natural History Museum galleries, unchanged since Owen reassembled it.
'Owen's work is a wonderful demonstration of how knowledge and comparative anatomy can be used to interpret fossils of extinct creatures like the moa.' Dr Paul Taylor, palaeobiologist
Museum founder Sir Richard Owen was famous for being able to look at small pieces of bone and correctly reconstruct animals. The bone Owen is holding in this portrait was sent to him from New Zealand in 1839.
Initially he had just one broken piece of bone to look at, but Owen used his anatomical knowledge to infer that it came from an enormous bird that could not fly and had gone extinct. It was a bold theory, as such a bird had never been seen in neither nature nor the fossil record. But Owen was proved correct when palaeontologists later found complete skeletons of the giant flightless bird, which stood up to 3.6 metres tall. Owen named the species Dinornis novaezealandiae.
'The antlers of Megaloceros show the amount of resource - perhaps even a handicap - that animals are willing to give to sexual selection.' Prof Adrian Lister, palaeobiologist
Antlers of the now-extinct Megaloceros played a role in historical arguments about an early evolutionary idea: orthogenesis.
Now considered an outdated theory, orthogenesis is the idea that organisms are compelled to evolve in one direction due to an internal driving force. This is different to natural selection, in which organisms evolve in response to environmental pressures, such as climate change or food availability.
Some scientists pointed to giant deer antlers as evidence for orthogenesis. The antlers had evolved to be so large that it was difficult to see how they could be useful to the animal, and were believed instead the result of evolution pointing in the direction of ever bigger antlers.
Once a popular theory, orthogenesis fell out of fashion as evidence overwhelmingly supported the theory of natural selection. We now know that the giant deer's antlers could be used in fighting. The larger the antlers, the more likely a male would be to 'win' a female and reproduce. This demonstrates the great power of sexual selection in driving evolution.
More recently, Museum scientists extracted DNA from Megaloceros fossils and found that the giant deer are related to modern fallow deer.
'When on board H.M.S. 'Beagle,' as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent.' Charles Darwin, in On the Origin of Species
Charles Darwin found this sloth jaw in 1832, while exploring the geology of Argentina during his voyage aboard HMS Beagle.
The jaw resembled that of the living sloth, but it was much larger. The discovery of a now-extinct animal in an area that its living relative inhabited was a light-bulb moment for Darwin.
After the voyage, he spent many years thinking about the relationship between extinct and living species and the idea of descent with modification, which could have led to the diversification of sloths in South America before the large ones went extinct. These thoughts were to become the basis of his theory of evolution by natural selection, a radical idea that was met with great scepticism from many scholars of the time.
Richard Owen named the sloth Mylodon darwinii in honour of the man who discovered it.
Thanks to the fossil record, we know that humans have evolved over millions of years, through a complex process of change.
500,000-10,000 years ago
Prof Chris Stringer, human origins expertExplore
At around 500,000 years old, this Homo heidelbergensis tibia (shinbone) is one of the oldest human fossils ever discovered in Britain.
It was excavated in 1993 from a quarry site in Boxgrove, West Sussex, by a team led by University College London.
The bone has been chewed at one end by an ancient carnivore, but scientists can still use it to make estimates about the individual's build and gender. From its length, width and density they can estimate that the person was male and, standing about 1.8 metres tall, would have been larger and more robust than an average modern human.
This build suggests Homo heidelbergensis was suited to a cooler environment than those found in Africa, fitting with the idea that the species adapted to new conditions as it spread across the world. The adaptations are also similar to those found in Neanderthals, lending evidence to the idea that Homo heidelbergensis gave rise to Neanderthals and modern humans.
Made around 420,000 years ago and unearthed in Clacton-on-Sea, Essex, this yew spear point is the oldest preserved wooden spear in the world.
Scientists believe that its owner, perhaps a member of the species Homo heidelbergensis, would have used this as a lethal weapon. They would have needed to spear their prey at close range in order to generate enough force to pierce the animal's skin. Modifications to the spear, thought to have been made by flint tools, were used to shape the weapon.
Similar spears, made mainly from spruce, have been found in Schöningen, Germany, among the remains of horses dating from around 300,000 years ago.
This skull was the first early human fossil discovered in Africa.
It belongs to Homo heidelbergensis, which, along with its predecessor Homo erectus, was one of the first human species to live across large areas of the world. Homo heidelbergensis fossils have been discovered in Africa and across Europe.
Homo heidelbergensis became established as a species around 600,000 years ago. As populations separated and encountered new environments, regional differences began to emerge.
These populations may have given rise to later species such as Neanderthals (Homo neanderthalensis) in Europe, and modern humans (Homo sapiens) in Africa.
Homo heidelbergensis fossils show a mix of Homo erectus features and later human characteristics. In some regions, Homo heidelbergensis became more adapted to the cold than previous humans and had an average brain capacity almost as large as humans today. This skull, approximately 300,000 years old, has a capacity of 1,280 cubic centimetres - the current average is 1,350 cubic centimetres.
This is the first known adult skull of a Neanderthal (Homo neanderthalensis) ever discovered.
It was found in a quarry in Gibraltar in 1848 - eight years before a similar skull in Germany's Neander Valley was discovered, and sixteen years before that skull was named as an extinct human species separate from us.
This skull's significance was therefore not understood at the time, but after the Neander Valley discovery in 1856, it was re-examined and recognised as belonging to the same extinct human species.
Since then, scientists have explored Gibraltar further and found evidence that Neanderthals inhabited this area for tens of thousands of years, likely due to the mild and stable climate. This region may have been one of the last places in which Neanderthals survived.
This skull, discovered in Gough's Cave in Somerset, UK, belonged to a male commonly known as Cheddar Man.
At about 10,000 years old, his is the oldest nearly complete modern human (Homo sapiens) skeleton ever found in Britain.
From the presence of wisdom teeth in his jaw, scientists can tell he was an adult male. The rest of his skeleton suggests he was around 166 centimetres tall and relatively slender.
The hole in his forehead, above his right eye, could have been the site of an infection that may have killed him. This infection may have spread from the sinuses or been caused by an injury to the head.
No one lived in Britain 20,000 years ago because the region was largely covered by ice. As the climate warmed about 15,000 years ago, plants, animals and humans began to return.
This skull belongs to a group of hunter-gatherers who migrated into Britain from nearby mainland Europe. At that time, the climate was only beginning to warm up, so there was still a lot of water held in the ice caps. This meant that sea levels were lower and it was possible to walk from mainland Europe to Britain.
The skull is one of a number of human bones, belonging to adults and children, found in Gough's Cave in Somerset, UK. Many of the bones show clear evidence of cannibalism. For example, shoulder bones and ribs were cracked open and gnawed to extract marrow, and skulls were shaped into cups or bowls. Scientists believe these people could have been cannibalised as part of a ritual practice.
This skull cup shows clear cut marks and dents, revealing it was thoroughly cleaned of any soft tissue shortly after death. After the bones of the face and the base of the skull were removed, it was painstakingly shaped into a cup.
Gough's Cave therefore provides a fascinating insight into the culture of the modern humans (Homo sapiens) who lived there around 14,700 years ago.
For centuries, natural historians have observed and recorded the world around them, contributing to our understanding of life on Earth.
Paul Cooper, Special Collections LibrarianExplore
'The more I observe nature, the less prone I am to consider any statement about her to be impossible.' Pliny the Elder
Compiled by Pliny the Elder (AD 23-79) but published 14 centuries later in 1469, Historia Naturalis was the first printed book on natural history. It is thought to contain at least 30,000 pieces of information, touching upon all knowledge of the natural world during Pliny's time. Its breadth of subject matter made it a model for all later encyclopaedias.
It would have been an enormous undertaking - Historia Naturalis consists of 37 books on topics ranging from astronomy to zoology. For example, volume three looks at the animal kingdom, with separate books on aquatic creatures, snakes, insects, birds and land animals.
Pliny studied many of these subjects from the perspective of our interaction with nature. He dedicated entire books to subjects such as agriculture and viticulture - the study and production of grapes.
The Museum's Library holds one of the 100 copies printed in 1469, making it the oldest published book in the Museum's collections. It is also Pliny's last and only surviving work, as he died in AD 79 in the eruption of Mount Vesuvius.
'[W]hat greater delight is there than to behold the Earth apparelled with plants?' John Gerard
Herbals are books that describe the appearance and medicinal properties of plants. They were predominantly used by early doctors as guides for prescribing and preparing ointments and medicines. The earliest known herbals date back to the ancient Greeks, who compiled catalogues of plants with healing properties.
The Herball or Generall Historie of Plantes, written by John Gerard (1545-1612) and published in 1597, expands on this tradition. It notes not just medicinal but culinary uses for plants, as well as their habitats, physical descriptions and seasons. Gerard saw the catalogue as a means of preserving botanical knowledge for all.
After Gerard died, his book was revised and extended by botanist Thomas Johnson, resulting in two later editions, published in 1633 and 1636.
The Herball is notable for featuring a number of plants that we now take for granted, but were new to Europeans in the late-sixteenth century - for example, the potato plant, which can be seen in the frontispiece to the book. This illustration is one of the earliest depictions of a potato.
'By the help of microscopes, there is nothing so small, as to escape our inquiry.' Robert Hooke
Using a microscope of his own construction, English scientist Robert Hooke (1635-1703) discovered a virtually unexplored world. Through Micrographia, he shared his observations of previously unknown tiny organisms and new details of larger life usually beyond the reach of the naked eye.
Published in 1665, the book contains 66 observations on a wide range of topics, from fossils to fungi, accompanied by detailed text and accurate illustrations engraved by Hooke himself. Many of his observations of everyday organisms led to a new understanding of their mechanisms. For example, he examined the leaves of stinging nettles and found sharp, silica needles that can pierce skin. Experimenting on himself, Hooke saw a fluid being forced up through these needles and into the skin, which explained how the plants deliver their painful sting.
Micrographia also included the first use of the word 'cell' in the context of a living thing. By examining thin sections of cork with his microscope, Hooke saw a series of little chambers (or 'cells'). These, we now know, are the non-living cell walls that remain after cells die off.
'Art and nature shall always be wrestling until they eventually conquer one another so that the victory is the same stroke and line: that which is conquered, conquers at the same time.' Maria Sibylla Merian
Maria Sibylla Merian (1647-1717) was a German naturalist and one of the first scientists to depict the life cycles of insects and the plants on which they feed. Her eye for detail, interest in first-hand observation and drive to explore the unknown significantly contributed to the advancement of entomology in the seventeenth and eighteenth centuries.
Merian's highly acclaimed book, Metamorphosis Insectorum Surinamensium, was first published in 1705. The work highlighted the life cycles of insects from Surinam, now the Republic of Suriname.
Many of the depicted insects and plants were new or little known to European scientists. The book would therefore have been many people's introduction to plants such as pineapples, pomegranates, bananas, guavas and cashews, as well as the insects that live on them.
Merian's detailed work was held in high esteem by many within the scientific community and beyond. For example, Carl Linnaeus referred to her exquisite illustrations for several plants and over 100 animal species in his seminal work on the classification of the natural world.
Locupletissimi Rerum Naturalium Thesauri Accurata Descriptio, also known as Seba's Thesaurus, originated as a way for the pharmacist and zoologist Albertus Seba (1665-1736) to showcase his vast natural history collections.
Initially published in 1734, it was internationally renowned throughout the eighteenth century, and almost 300 years later the book and collections still have a significant influence on scientific study. In fact, some of Seba's specimens now reside at the Museum, including anacondas, bats, tigers and fish.
The four volumes contain 449 lifelike depictions of specimens, sometimes in a contextual background similar to those found in Maria Sybilla Merian's work. The first volume focuses on the flora and fauna of Asia and South America, while snakes dominate the second volume. The third concentrates on marine life and features a tremendous variety of scallops, squids, sea urchins and fish, while the final volume covers mostly insects, minerals and fossils.
Carl Linnaeus used many of the original specimens in Seba's collection in his classification system. He later referred to Seba's work in subsequent research more than 250 times. In addition, a good deal of Seba's material also became type specimens - the original specimens on which new species descriptions are based.
'[I]f we would understand how 'tis that Nature gives Life and Motion to these Automata, we must unloose the Case, and [...] observe how she joyns them all together.' Edward Tyson
Edward Tyson (1651-1708) is regarded as the father of comparative anatomy, the scientific discipline that studies the similarities and differences between different species.
For instance, his work on porpoises revealed that while they looked like fish on the outside, their internal organs and skeletons were more similar to four-legged land animals, such as dogs. Tyson began to realise that these animals formed a group - a concept that wasn't formally recognised until Linnaeus defined the concept of mammals in 1758.
Tyson was also one of the first people to draw comparisons between humans and non-human animals. This line of thinking would have been incendiary at the time as it challenged the idea that humans are distinct from the rest of the animal world.
By dissecting a chimpanzee that had been brought to England, Tyson discovered it was more similar to a human than to a monkey, essentially identifying that chimpanzees belonged to a new group of animals: the apes. This work laid the foundation for later theories of evolution.
Botanist Carl Linnaeus revolutionised the naming of living things by making scientific names short, easy to remember and universally recognisable.
Dr Sandy Knapp, botanistExplore
Swedish botanist Carl Linnaeus revolutionised the naming of living things by making scientific names short, easy to remember and universally recognisable. Linnaeus gave plants two Latin names, one for genus and one for species, together known as a binomial name. He originally called the species name 'the trivial name'. Prior to this, scientific names for species were often long and unwieldy. For example, the humble tomato, which was called Solanum caule inermi herbaceo, foliis pinnatis incisis, racemis simplicibus, became Solanum lycopersicum.
Linnaeus revealed his new binomial naming system in the catalogue of plants Species Plantarum, which he published in 1753. The plants described were specimens and illustrations found in the collections of great collectors such as Dutch businessman George Clifford, botanists and travellers Dr Paul Hermann and Sir Hans Sloane, and early naturalist Albertus Seba. Linnaeus gave binomial names to animals five years later in 1758.
Linnaeus encouraged his students to travel the world and bring back new and exciting specimens for him to study - people like Daniel Solander, who sailed with botanist Sir Joseph Banks on Cook's voyage to Australasia on HMS Endeavour.
Linnaeus spent his life grouping living things into defined hierarchies and giving them individual names. From 1753 until his death in 1778, he named thousands of plants and animals in this way. This binomial system was adopted by other scientists and became the standard way of naming organisms that is still used today.
Linnaeus launched his career in 1735 with a system for classifying plants based on their reproductive structures.
After reading a book about the sexual life of flowers, he reached the conclusion that stamens and pistils must be the most important characters for classifying plants. He studied the plants and formed a system which divided them into 24 classes based on their sexual structures. The 24th consisted of plants without flowers, the cryptogams.
The sexual system was first presented in Linnaeus' famous production Systema Naturae in 1735. Georg Dionysius Ehret's illustration shown here depicts the characters Linnaeus used to determine 24 classes of plants. Linnaeus arranged plants according to his own sexual system, classifying them into groups based on the number and form of their male and female parts. It was his goal to group all known plants according to his classification system.
Ehret's illustration is a powerful insight to the greatest and most prolific botanical artist of the 1700s. While his finished watercolours are without doubt magnificent, his sketches reveal the artist behind them. They show the time he took to understand a subject before depicting it on paper, as well as his notes and thoughts, scrutinising not just the adult plant but the seeds and flowers. Ehret (1708–1770) was a lover of plants first, and an artist second.
'... no surer criterion for determining species has occurred to me than the distinguishing features that perpetuate themselves in propagation from seed...one species never springs from the seed of another nor vice versa.' John W Ray (1627-1705)
John Ray, known as the 'father of British botany', contributed several important concepts to the field of plant taxonomy.
Ray worked towards a natural classification of plants that was based on more than one data set. He felt that rather than using a single character, the classification should ideally make use of all available information for as many parts of the plant as possible. Ray set out his new classification of plants in Methodus Plantarum Nova (1682), in which he discusses some basic aspects of their biology. He was also the first to define a species in his book Historia Plantarum in 1686, shown above.
Ray worked to popularise the study of plants, to make it a scientific discipline and to systematise previous knowledge of plants into a workable whole. If not for the innovative use of binomials by Linnaeus, John Ray might have been more widely remembered as the true 'father of plant taxonomy'.
The Clifford Herbarium contains over 3,000 specimens collected by George Clifford (1685-1760), an extraordinarily wealthy Anglo-Dutch director of the Dutch India Company.
The herbarium includes plants that were newly cultivated in Europe at the time of collection, as well as specimens from collectors around the world. Clifford had a great passion for plants, and his garden at Hartekamp was inspired by the famous botanists of his time, such as Hermann Boerhaave (1668-1739).
On a visit to the home of botanist Johannes Burman (1706-1779), Clifford was introduced to an up-and-coming young Swedish botanist, Carl Linnaeus. Clifford was keen to employ Linnaeus at Hartekamp. So in 1735 Linnaeus started his dream job of supervising the hothouses and naming and classifying specimens according to his new system.
During his stay Linnaeus produced an important botanical work, Hortus Cliffortianus (1737), considered a precursor of his Species Plantarum (1753).
Linnaeus described many new species from living and dried specimens in Clifford's possession. Many of the plants in the Clifford Herbarium are the actual specimens that Linnaeus first described and assigned a scientific name to for that plant species - the type specimens.
The Hermann Herbarium is one of the earliest and most important collections of Sri Lankan plants. It contains more than 400 species, which were picked, dried and named by the physician Paul Hermann (1646 -1695).
Hermann spent five years in Sri Lanka (then Ceylon) as chief medical officer to the Dutch East Indies Company, which managed the island under Dutch rule. His collection, in five bound volumes, didn't achieve lasting importance until after Hermann's death in 1695.
The volumes seem to have disappeared from sight until 1744, when they reappeared in the possession of the Danish Apothecary-Royal, August Günther. Günther loaned the volumes to Linnaeus, who set about identifying the plant species and placing them in his new sexual classification system. Linnaeus used them as the basis for his book on Ceylon's plants, Flora Zeylanica, published in 1747. You can see Hermann's handwriting under each plant and, beneath that, a reference number written by Linnaeus.
In 1753 Linnaeus published his Species Plantarum, in which he used binomial names for the first time. Most of the Sri Lankan taxa in Systema Natura were from Flora Zeylanica, so the Hermann Herbarium is very rich in Linnaean type material.
The scientific name Theobroma cacao was given to the cocoa plant by Carl Linnaeus in 1753, in his famous book Species Plantarum. This cocoa plant was brought back to London from Jamaica in 1689 by the collector and doctor Hans Sloane. The name Theobroma cacao is from the Greek 'theobroma', meaning drink of the gods.
Linnaeus used the text and drawings from Sloane's collections as the basis for descriptions of this and other species found in his plant catalogue. Sloane employed a local artist, the Reverend Garret Moore, to illustrate many of the specimens, but others, such as the cocoa leaf, were drawn by the talented artist Everhardus Kickius on Sloane's return to England (far left).
Sloane saw local people boiling cocoa seeds to make a drink. When he tasted it, he found it too bitter for his palate so he added milk and sugar. After Sloane returned to England he sold the recipe. Cadbury reworked the drink and later created the chocolate bar.
Eight of Sloane's 265 volumes of specimens came from Jamaica, each filled with carefully dried and mounted plants. The volumes are still often used by scientists, as they are powerful record of the biodiversity of the West Indies.
In his long life, noted physician, scientist and collector Sir Hans Sloane amassed one of the greatest collections of plants, animals, antiquities, coins and many other objects of his time. Sloane's collections are the founding core of the Natural History Museum's collections and occupy a central position in its history.
A Swedish pupil of Linnaeus, Daniel Solander came to Britain in 1760 and was employed as an assistant at the British Museum. He was then engaged by Sir Joseph Banks to sail with HMS Endeavour.
HMS Endeavour set sail from England in 1768, captained by the English explorer and navigator Captain Cook to record the transit of Venus across the face of the Sun, from the vantage point of Tahiti. But at the last minute botanist Sir Joseph Banks and his team of scientists, artists, servants and two dogs boarded to carry out another, secret, mission: to investigate rumours of a huge land mass known as Terra Australis Incognita. They were away for three years, during which Solander and Banks collected and described an important collection of plants and animals from Australia, New Zealand and the South Pacific islands.
This picture was painted by the young and talented artist Sydney Parkinson, who was appointed by Sir Joseph Banks as a natural history artist for the voyage. Paintings such as this showed Western eyes what lay beyond their shores, before the invention of photography. It was hard work for Parkinson and sadly he never made it home, dying of dysentery and fever on the return journey, aged 26.
'[the] collection of plants was...grown so immensely large that it was necessary that some extraordinary care should be taken of them least they should spoil.' Sir Joseph Banks.
Daniel Solander came to Britain in 1760, on the advice of his professor at the University of Uppsala, Carl Linnaeus. Solander was initially employed as an assistant at the British Museum before being engaged by Banks to sail with the Endeavour in 1768. Solander brought a set of unique skills to the voyage. He had first-hand knowledge of the new method of plant classification devised by Linnaeus, and together with Banks was able to accurately classify the plants they collected, even though the vast majority of species were new to them both.
Banks and Solander discovered many new species, including exotic tree ferns. They also paid close attention to plants that might be grown for economic reasons, including New Zealand Flax, Phormium tenax, used by the indigenous population for clothing and now a common garden plant in Europe.
Banks and Solander also worked closely with the artist Sydney Parkinson, who was on board the ship, instructing him in how they wished the plants to be drawn and which parts were to be depicted, urging him to capture the plants' forms while they were still fresh. To keep up with the two botanists, Parkinson resorted to making brief outline drawings of the plants, with specific areas partly coloured in so that they could be finished later.
Over 3,000 plant specimens were collected on the three-year voyage, including an estimated 1,000 or more new species. Re-examination of the collections has led to the description of even more new species as recently as the 1980s.
Returning home in 1771, the adventurers were hailed as heroes - especially Banks, with his exciting accounts of Maori warriors and exotic animals. After the voyage Solander became Banks's assistant and librarian, even declining a professorship at St Petersburg University to remain in London.
Hippochrenes amplus is a kind of fossil conch shell (a gastropod mollusc). This is the type specimen, described and named by Daniel Solander in 1766. Daniel Solander used Linnaean binomial system to name the fossil. His original name for it was Strombus amplus but the species has since been transferred to the genus Hippochrenes.
Solander (1733-1782) was a pupil of Carl Linnaeus. His description of this species may be the first time Linnaean nomenclature was used to name a fossil, rather than a living plant or animal. Solander return to the British Museum in 1763 and his publication on the Eocene Barton Beds of Hampshire, a layer of clays rich in mollusc fossils, was published in 1766.
Originating from Eocene deposits in Hordel, Hampshire in 1749, the collector of this specimen is unknown. The specimen was given to the Museum as part of the fossil shell collection of Gustavus Brander (1720–1787), a Trustee of the British Museum.
This plant was given the scientific name Banksia serrata by Carl Linnaeus's son, in honour of the great eighteenth-century naturalist Sir Joseph Banks.
Banks was the first European to see the plant growing in its native Australia, while aboard HMS Endeavour (1768–1771). Banks brought it and specimens of other closely related new species back to England, where the new genus Banksia was named after him. The artwork of Banksia (far right) was prepared from a drawing by Sydney Parkinson, a young and talented artist on board Endeavour who helped produce 18 volumes of plant drawings from the voyage.
In total Banks collected more than 3,000 plants on the trip, about 900 of which were new to science. The specimens Banks collected accounted for approximately 110 new genera and 1,300 new species. Some 75 different species bear his name, as do a group of islands near Vanuatu in the Pacific and a peninsula in New Zealand. A suggestion was made to name Australia 'Banksia', but it was not adopted.
Banks is probably best remembered for his botanical legacy. He sponsored numerous voyages, enabling young naturalists and artists to record their discoveries. As King George III's advisor at Kew, he also introduced countless plants to the UK and developed an interest in the economic value of species, for example identifying Assam as a prime spot to cultivate tea to export home.
Banks' famous plant collection is now held at the Museum, along with insects and shells that he acquired throughout his life. These are all still valued research tools, as well as important historical artefacts.
The theory of evolution by natural selection, devised independently by Charles Darwin and Alfred Russel Wallace, underpins modern biology.
Dr Tim Littlewood, evolutionary biologistExplore
'If there is the slightest foundation for these remarks, the zoology of archipelagoes will be well worth examining; for such facts would undermine the stability of species.' Charles Darwin
This bird, collected by Darwin in the Galápagos Islands, is the very first Floreana mockingbird (Nesomimus trifasciatus) described by science.
Although finches are the most famous Galápagos residents to have drawn Darwin's attention, it was these mockingbirds that laid the foundation for his theory of evolution by natural selection, an idea that took him 20 years to publish.
When he first arrived in the Galápagos in 1835, Darwin collected a number of mockingbird specimens. On one island (Chatham Island, now San Cristóbal Island), he noticed a mockingbird similar to those he had seen in Chile. On another island (Charles Island, now Floreana Island), however, he found the mockingbirds to be quite different. He later found a third species on Isabela Island.
These finds were Darwin's first hint that species could indeed evolve over time, thus refuting the so-called 'stability of species' theory. He reasoned that a single species from the mainland could have colonised the archipelago and gradually evolved into different species on different islands.
'Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that [...] one species had been taken and modified for different ends.' Charles Darwin
Some of the most famous birds of all time, Darwin's finches from the Galápagos Islands are the perfect model of evolution in action. The 13 species all look roughly the same - brown or black and sparrow-sized - but their beaks are considerably different, brilliantly adapted to what they eat.
For example, those feeding on hard-to-crack seeds have big, strong beaks, while those targeting tiny insects have smaller, pointed beaks.
Darwin collected the birds during his five-year voyage on HMS Beagle. His journey inspired him to question how the diversity of life came to be, leading many years later to his book On the Origin of Species.
Yet at first he did not see the significance of these birds, thinking they were a mix of wrens, blackbirds, finches and warblers. It was only when John Gould, the famous English ornithologist, identified all the birds as finches that the pieces came together.
Darwin realised that the birds were related not just to one another, but also to the finches on the South American mainland. He suggested that, rather than being created as they were, they likely descended from common ancestors that had flown to the Galápagos Islands and adapted to their new environment.
'Can you see any good reason why the natural selection of ... individual differences should not make a new species?' Charles Darwin
The humble pigeon was crucial to Darwin's theory of evolution by natural selection. He learnt to breed them, corresponded with pigeon fanciers from as far afield as India and Iran, and showed how different characteristics can be selected and exaggerated over generations. For example, he was able to produce pigeons with extra tail feathers by picking the right parents.
From these experiments, Darwin concluded that, in the wild, offspring inherit characteristics that helped their parents survive, and this allows species to change over millions of years. He also worked out that all domesticated pigeons are descended from one common ancestor, the rock dove.
Darwin gave his personal collection of pigeons to the Museum in 1867 and 1868, as part of a bigger collection of domestic birds including ducks, chickens and canaries. The pigeons came with his handwritten notes and labels, and you can even see his writing on some of the bones. The 60 skins and 60 or so skeletons were a vital inspiration for his theory of evolution by natural selection and feature extensively in his book On the Origin of Species.
'[T]he variability of the toes which have been already modified for purposes of swimming [...] enable an allied species to pass through the air like the flying lizard.' Alfred Russel Wallace
Wallace discovered this frog, now known as Wallace's flying frog (Racophorus nigropalmatus), in the Borneo jungle in 1855. Fascinated by the frog's ability to glide through the air, he painted this picture and wrote on the back 'descended from a high tree as if flying'.
Wallace was already interested in the idea of evolution, and for him the discovery of this frog was yet another hole in the idea that species were fixed and unchanging from the moment of their creation. It was clearly a frog - a group of animals not previously known for their flying ability - yet it had turned its webbed toes to another use. The frog was not a perfect swimmer, nor a perfect flier, but it had the ability to do both. Its form suggested that it had adapted, rather than been created.
'Every species has come into existence coincident both in space and time with a pre-existing closely allied species.' Alfred Russel Wallace
This is a reprint of the first paper in which Wallace publicly discusses evolution. The title is 'On the Law which has Regulated the Introduction of New Species', but it is generally called the Sarawak Law paper since Wallace wrote it in 1855 while in the Sarawak region of Borneo.
In the paper, he asked why species similar to each other in appearance are often located near one another, both geographically and in the fossil record: 'the most closely allied species [are] found in geographical proximity. The question forces itself upon every thinking mind - why are these things so?'
To answer this question, Wallace proposed the Sarawak Law: 'Every species has come into existence coincident both in space and time with a pre-existing closely allied species.' In other words, new species evolve from existing ones, rather than simply appearing where they are. This explains why similar species are found near one another in both space and time.
More broadly, Wallace suggested that the distribution of animals and plants is related to gradual geological changes over time. For example, the formation of an island isolating two groups of a species from one other leads them to evolve into separate species. These ideas are part of a concept we now call biogeography.
'In this archipelago there are two distinct faunas […] yet there is nothing on the map or on the face of the islands to mark their limits.' Alfred Russel Wallace
Alongside his work in developing the theory of evolution by natural selection, Wallace (and his vast collection of specimens) contributed to the growth of a new field: evolutionary biogeography.
Evolutionary biogeography studies the distribution of plants and animals around the world, and supplies key evidence that evolution is taking place.
Wallace himself famously encountered this process when crossing from the island of Bali to the island of Lombok, both in modern-day Indonesia. He noted a big difference in the species found on either side of the narrow strait between the islands, and realised that he had crossed an invisible dividing line - now known as the Wallace Line.
We know today that the Wallace Line arises because the species on either side were isolated from each other in the past, and thus have different evolutionary histories.
'On taking it out of my net and opening the glorious wings, my heart began to beat violently … so great was the excitement.' Alfred Russel Wallace
Part of Wallace's inspiration for the theory of evolution came from the huge variation he witnessed among the insects, birds and other animals he collected on his travels. Many of the 126,000 specimens he collected in the Malay Archipelago are now in the Museum.
This magnificent butterfly, known as Wallace's golden birdwing butterfly (Ornithoptera croesus), is one of the most famous insects Wallace discovered. He caught it on the Indonesian island of Bacan in 1859, during his eight-year expedition around the Malay Archipelago.
Wallace's understanding of these creatures also led him to formulate the earliest modern definition of species (now known as the biological species concept) in an important paper he wrote about the swallowtail butterflies of the Malay Archipelago: 'Species are merely those strongly marked races or local forms which, when in contact, do not intermix, and [are] incapable of producing a fertile hybrid offspring.'
'The life of wild animals is a struggle for existence [...] in which the weakest and least perfectly organized must always succumb.' Alfred Russel Wallace
The theory of evolution by natural selection was jointly proposed by Darwin and Wallace in this scientific article, which was first read at a meeting of the Linnean Society of London on 1 July 1858.
At that point, Darwin had been working privately on the theory for 20 years, but in early 1858 he received a letter from Wallace that completely changed his plans. Wallace, feverish with malaria on an island in the Malay Archipelago, had a flash of inspiration: he realised that species evolved through natural selection. He immediately wrote an essay on the subject, sending it to Darwin because he knew Darwin was interested in the subject.
Darwin's friends suggested that, rather than lose priority, and to avoid looking as though he had stolen Wallace's idea, he should announce his work jointly with Wallace. This paper was the result. It is split into three parts: first, an extract from a manuscript by Darwin; second, an abstract of a letter from Darwin to Professor Asa Gray, dated 1857, included to reinforce that Darwin did not steal Wallace's ideas; and, finally, the essay written by Wallace.
The essay's unexpected arrival spurred Darwin into writing his famous book On the Origin of Species, which was published 15 months later in November 1859.
'From the war of nature, from famine and death, [...] the production of the higher animals directly follows.' Charles Darwin
This is one of five pages of notes held by the Museum that were handwritten by Darwin for his book On the Origin of Species. It was produced for the chapter on instinct and is a precious legacy of one of the most influential books ever written. Its annotations and redactions are a record of his thoughts throughout the book's development. By the time the book was published in 1859, Darwin had spent 20 years refining his ideas.
In the book, Darwin revealed his theory of evolution through natural selection. He saw that all living things shared a common ancestry, but that over time, organisms change, with those best suited to their environment more likely to survive. This process, he explained, helped produce the great diversity of the natural world.
When first published, the book had the longer title On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, but it was renamed On the Origin of Species in 1872, with the sixth edition.
It was an instant bestseller, although also a direct challenge to the widely held belief that God created, and still controlled, everything.
The marine trade routes of the eighteenth century and the empire building of the nineteenth opened up new opportunities for exploration of the natural world.
Clare Valentine, Head of Life Science CollectionsExplore
Few animals have confused the scientific world as much as the duck-billed platypus Ornithorhynchus anatinus. When the first platypus specimen arrived from Australia in 1798 scientists were convinced it was a fake. How could an animal covered in fur also have a bird's beak? Many fakes were being produced at the time - particularly in China - by stitching together leftover animal parts. Such fakes included the eastern monkey, with the body of a monkey and the tail of a fish. Not only did the platypus look odd from the outside, but its insides were strange, too. If it was a mammal, as the fur would suggest, where were the uterus and milk glands, the other typical mammalian features? The platypus did not have them.
It took a year of careful study before scientists felt reassured the platypus was not a joke, but a new and remarkable animal to science. The monotremes - the platypus and the echidnas - are thought to be the most primitive of living mammals and are the only ones that lay eggs instead of giving birth to live young. The platypus is also unique as it is the only mammal known to detect electric fields, which it uses to find its prey. It is also one of the few mammals able to produce venom.
The Natural History Museum has the original duck-billed platypus specimen from 1798, now the type specimen. The Museum also holds Ferdinand Bauer's platypus watercolour, based on his sketches from the HMS Investigator voyage to Australia in the early 1800s. The picture was one of the first attempts by a European artist to record Australian flora and fauna. Relatively unknown during their lifetimes, brothers Ferdinand and Franz Bauer are recognised today as pioneers of scientific natural history illustration.
One of the main aims of the British East India Company was to work out how best to exploit India's natural products. The company established several botanical gardens to conduct scientific projects and experiments. Experts were appointed to direct the work of the gardens and the Company sponsored expeditions and surveys throughout its territories.
One such expert was Thomas Hardwicke, who in 1778 entered the military service of the Company at the age of 22. By 1819 he had progressed to the rank of Major General and from 1820 was Commandant of Artillery until his retirement in 1823. During his time in India and the subcontinent he amassed a large and splendid collection of natural history specimens and continued to collect during his retirement in London. Hardwicke's bequest to the British Museum included his books, drawings (which amounted to more than 59 volumes), quadrupeds, skins and zoological specimens in spirits. He also left cabinets of minerals, rocks, fossils and shells. The largest part of his collection was birds from around the world which formed part of his 'Museum room' at his house in Lambeth. His collections are still studied by scientists today.
Before his death in 1835 Hardwicke published two volumes of Illustrations of Indian Zoology, consisting of 202 colour plates from his art collection. Like most of those in the service of the Company who created collections of drawings, he was not the artist. His works were collated from a whole army of artists that he commissioned to draw for him, as well as interested persons who sent him drawings they acquired while on their travels.
Illustrations of African wildlife by explorers like William Cornwallis Harris gripped the imagination of the Victorian public, making national heroes of the explorers.
Harris made a name for himself by publishing The Wild Sports of Southern Africa in 1839, which told of his hunting expeditions from 1836 to 1837. Harris explains in the opening passage of his book, 'From my boyhood upwards I have been taxed by the facetious with shooting madness, and truly a most delightful mania I have ever found it'. His account of the trip is full of hunting exploits, earning him the reputation as the originator of the safari.
Harris was a member of the Engineering Corps of the East India Company and was based in India from 1825. In 1836 he fell ill and was sent to Cape Town to recuperate. Harris was a keen naturalist and an accomplished artist. As well as hunting animals Harris spent time drawing scenes he came across including animals and people of the region. From a young age Harris frequently found his 'thoughts wander to the wilds of Africa' and he often dreamed of encountering the animals of that land, seeing the 'slender and swan-like neck of the stately giraffe' and the 'gigantic elephants'.
Big game hunters provided museums and scientists with animals for study and display. This African elephant, photographed here in 1910, just three years after his arrival, stood proudly in the Museum’s Hintze Hall. The elephant was obtained from the taxidermists Rowland Ward Ltd and was later nicknamed George. The Museum has Asian elephants too, some brought back to London Zoo by Bertie, Prince of Wales (the future King Edward VII) following his tour of India during 1875-76.
Being able to study similar animals from different continents allowed scientists to compare and contrast the features and evolution of both. These comparisons continue today as Museum scientists, in collaboration with colleagues in the UK, Israel and elsewhere, investigate the evolutionary origin of the Asian elephant. They compare fossils from northern India, Pakistan and the Middle East, many of which are in the Museum collections. Fossils from Bethlehem, excavated in the 1930s, are probably more than three million years old and may represent the earliest record of the Asian elephant lineage outside of Africa, which still retained many features of earlier mammoth. More recent remains, between 500,000 and 200,000 years old, still do not show fully-evolved Asian elephant features, suggesting that the modern species arose later.
Museum scientists and collaborators have also properly defined, for the first time since Linnaeus named the species in 1758, a type specimen (lectotype) for the Asian elephant Elephas maximus from a specimen in the collection.
Michael Rogers Oldfield Thomas (1858-1929), the 'founding father of modern systematic mammalogy', was one of the most important mammal collectors of the nineteenth and twentieth centuries. He made a significant contribution to the development of the mammal collections at the Natural History Museum. Thomas described more than 2,000 mammal species and subspecies for the first time.
In 1891 Thomas married Mary Kane, the daughter of Sir Andrew Clark, and heiress to a small fortune. Together he and his wife supported mammal collectors, financing collecting expeditions across the world. He also did fieldwork himself in Western Europe and South America. His wife shared his interest in natural history, and accompanied him on collecting trips.
He was appointed to the Museum Secretary's office in 1876 and transferred to the Zoological Department in 1878. In 1896 William Henry Flower took control of the department and hired Richard Lydekker to rearrange the exhibitions. This allowed Thomas to concentrate on studying the vast mammal collection he had acquired. Although officially retired from the Museum in 1923, he continued his work without interruption.
Baron Walter Rothschild, born into the prominent banking family, showed an early love of natural history and went on to become a prolific collector and respected scientist. Being a wealthy man, he was able to sponsor collectors in many parts of the world and mount his own expeditions to North Africa and elsewhere.
His chief areas of expertise were insects, birds and large animals such as the gorilla, polar bear and giant tortoise. His father built him a museum at the corner of Tring Park, the family home, and, after just a few years struggling with the mysteries of banking, he was allowed to pursue his passion undisturbed. His museum, managed by professional curators, was open to the public from 1891, although Rothschild himself became increasingly shy and reclusive.
Elected a Trustee of the Natural History Museum in 1899 he decided to leave his entire institution, every case, specimen and label, to the Museum. On his death in 1937 the Museum took ownership of buildings and land at Tring along with a large collection of stuffed mammals, birds, reptiles and fish, displayed in galleries that are still open to the public today. Rothschild also left research collections of an estimated 2.5 million butterflies and moths, 2,000 bird skins and a magnificent library of manuscripts and printed books.
Scientists on board HMS Challenger discovered a huge diversity of life in the deep sea, disproving the theory that nothing lived below 550 metres. These jars and slides are from the voyage, the first major expedition to investigate every physical and biological aspect of the oceans.
HMS Challenger left British shores in 1872 for a three-and-a-half-year voyage around the world. Experts on board brought back thousands of jars, bottles, tins and tubes of samples from the ocean floor. Many of the dried and cleaned sediments looked like sand, but were actually made up of billions of microfossils, tiny shells of single-celled organisms.
At the time little was known about the deep ocean. Some scientists even argued life could not exist deeper than 550 metres. So when telegraphic cables, trailed along the ocean floor, were raised for repair and found covered in tiny crustaceans, it sparked a quest to find out more.
Challenger criss-crossed the oceans - from South America to the Cape of Good Hope, from Antarctica to Australia, onto the Fiji Islands and Japan, then around the southern tip of South America and back up to Britain. The team of scientists on board recorded temperatures, currents and depths of more than eight kilometres. Fifty volumes of research were produced and they are a unique legacy still in use today.
The giant squid is a rare and mysterious creature, once thought only to exist in stories of sea monsters called krakens.
This 8.62-metre giant-squid Architeuthis dux was caught off the coast of the Falkland Islands in 2004 and offered to the Museum. So little is known about the giant squid it was too good an opportunity for the Museum to miss. The nearly complete specimen, caught at a depth of 220 metres proved a challenge to preserve and store.
The squid was caught alive and immediately frozen allowing DNA samples to be taken before decay set in. In 2013, these samples helped prove that there is just one species of giant squid, Architeuthis dux.
Most of what we know about the giant squid comes from the remains of dead squid recovered from the stomachs of their predators, sperm whales. The giant squid can probably grow up to 14 metres long with eyes the size of footballs, teeth-filled suckers and a strong beak. Scientists have tried to estimate how long giant squid live and how quickly they grow by examining structures such as the gladius (the pen), the eye lens and the statolith (a sensory organ). But exactly how they grow and develop, how they find a mate, and if they are solitary or shoaling animals are still mysteries.
Once defrosted the squid was placed in a specially constructed case and put on display in the Museum's Darwin Centre.
Intrepid expeditions to Antarctica for scientific and geographical research revealed extraordinary species such as the emperor penguins.
Penguins are so familiar to us now it's hard to imagine people seeing them for the first time. This is one of the first emperor penguins ever collected, from sometime between 1839 and 1843. The specimen was collected in Antarctic waters by a 22-year-old naturalist, Joseph Dalton Hooker. Hooker was part of a team travelling on the British naval ships Erebus and Terror, in search of the South Magnetic Pole. When he returned to the UK, everything he collected was examined and named by other naturalists and experts, and the large bird was officially called Aptenodytes forsteri.
Scientists on the fateful British Terra Nova Antarctic Expedition (1910–1913) collected penguin eggs and their embryos. The team's zoologist Edward Wilson was on his second journey to the South Pole, led by Scott. He came back to collect penguin eggs, desperate to study the embryos to test a theory that birds were evolved from reptiles. Accompanied by his close friends and colleagues Henry Robertson Bowers and Apsley Cherry-Gerrard, he left the main camp in search of the colony. They faced torturous conditions of freezing winds and huge ice ridges, their sledges pulling heavy on their backs. But 19 days later they collected five precious eggs, two of which broke. Back at camp, Wilson and Bowers were selected to join Scott on his final push to the pole. They never returned. It was left to Cherry-Gerrard, heavy with grief after losing his team mates, to deliver the embryos and eggshells to the Museum in person.
The coelacanth is probably the most famous fish of the twentieth century. It was widely believed to have died out with the dinosaurs 65 million years ago and was only known from fossils. It's odd-shaped tail, thick scales and bony head plates were all signs of a very ancient creature. But in 1938 one swam into a fisherman's net off the coast of South Africa.
Since then, a living colony of more than 300 of these metre-long fish has been found in deep water near the Comoros Islands, northwest of Madagascar.Two individuals from another species were found thousands of kilometres away in Indonesia.
This specimen was caught in the 1960s and would have been deep blue in colour when alive. Its large-lobed fins have earned it the name 'old four legs', which in fact has scientific basis - some scientists believe the coelacanth is distantly related to four-legged land vertebrates. Reports that it is the missing link between these land animals and fish are far-fetched, but it's likely the coelacanth is descended from the same ancestor. Both species are now listed as critically endangered on the International Union for Conservation of Nature’s Red List.
Today, hundreds of scientists use the Museum's collections to investigate globally significant questions, from 'What are the origins of life?' to 'How can we secure a sustainable future?'.
Dr Vince Smith, cybertaxonomistExplore
'We have shown that asteroids were responsible for the majority of water and nitrogen delivered to the Moon, between 4.5 and 4.3 billion years ago. It is an exciting finding, because the Earth probably got its water in exactly the same way. We now know much more about the types of objects impacting on both the Moon and the Earth in the time just after they formed.' Prof Sara Russell, Head of Mineral and Planetary Sciences
The Ivuna meteorite fell to Earth in Tanzania in 1938. Beneath its modest grey exterior, water lies trapped inside its minerals, hiding clues about the beginnings of the solar system and the source of water on the Moon and Earth.
The Museum houses a world-class collection of rare meteorites like Ivuna and samples from the Apollo missions. Prof Russell and her fellow researchers looked at chemical data from lunar samples and data from meteorites and comets. They found the chemical compounds of the lunar samples matched the composition of meteorites like Ivuna but not the comets.
Previous studies have shown that water on the Moon has a similar chemical makeup to Earth's water. This suggests that the Moon's water was either inherited from the Earth before the two bodies split or delivered to the Earth-Moon system shortly after they formed. When the planets began forming, they experienced a near-constant barrage of meteorite impacts. This research suggests that meteorites like Ivuna brought water to the Moon as well as the Earth billions of years ago.
'Genetic research shows that most people outside of Africa have about 2% Neanderthal DNA. We think that the modern humans who spread into Asia around 60,000 years ago interbred with the Neanderthals. Since these migrants were the ancestors of all people outside of Africa, they took their small bits of Neanderthal DNA with them as they spread out across the rest of the world.' Prof Chris Stringer, human origins expert
Expert Prof Chris Stringer discusses what this Neanderthal inheritance may have meant for the early modern humans who migrated out of Africa, and what it means for us today.
Interbreeding may have helped early modern humans adapt quickly to new environments, as they acquired genes from Neanderthals who had lived there for many thousands of years.
Some Neanderthal DNA is found in parts of the human genome that are associated with skin and hair, maybe giving our ancestors thicker hair and skin that helped them cope better with the colder climate, or a greater resistance to diseases. Other DNA inherited from Neanderthals seems to help boost immunity, perhaps providing a quick fix against local infections.
But it's not all good news. Neanderthal DNA in modern humans seems to be associated with an increased risk of developing diseases such as thrombosis, lupus and Crohn's. Some of the negative effects in modern humans may have been triggered by our immune systems or changes to our lifestyles over many thousands of years.
'The mammoths are sounding a warning to us today, that big animals like the elephants, far from the being resistant to extinction, are often the most vulnerable' Prof Adrian Lister, palaeobiologist
Climate change or hunting by humans - what caused the extinction of these Ice Age elephants? Mammoth expert Prof Lister talks us through his research findings and the stark warning they sound for the future of mammoths' living relatives, African and Asian elephants. Find out how Prof Lister uses Museum collections for his research into the last major extinction of large mammals.
Woolly mammoths roamed parts of Earth's northern hemisphere for at least half a million years. They were still in their heyday 20,000 years ago but within the next 10,000 years they were reduced to isolated populations off the coasts of Siberia and Alaska. By 4,000 years ago they were gone.
'I get a real thrill from finding things that no one has seen before, but there's also a longer term satisfaction from correcting past mistakes and understanding the real diversity hidden in the collection.' Dr Jon Todd, systematist
These 51 shells were collected in Lake Tanganyika, the deepest and oldest water body in Africa. Scientists studying specimens in 1953 noted that the empty shells had a huge range of shapes and sizes, but they had little knowledge of the soft-parts of the animals inside, how they reproduced or where and how they lived. Based on the empty shells alone, they classified these animals as one extremely variable species.
We now know that the shells actually represent 51 different species belonging to the genus Lavigeria.
This hidden diversity was revealed by a combination of scuba diving and genetic analysis. Museum scientists Ellinor Michel and Jon Todd collected live snails from the lake, recording the different sites and habitats in which they lived. DNA sequencing confirmed their suspicion that those snails with significantly different morphologies and ecologies are indeed separate species.
Because Lake Tanganyika is a closed ecosystem unconnected to the ocean, it is ideal for studying how new species emerge and go extinct in isolation. Understanding species diversity in the lake is also key for developing conservation programmes that target specific groups at risk from human degradation of the environment.
In terms of revealing undiscovered species, reinterpreting historic collections is almost as fruitful as exploring new habitats. Research on heritage collections goes hand-in-hand with exploring new frontiers to reveal the real biodiversity in the world around us.
'Although the bones of these animals had been studied for over 180 years, no clear picture of their origins had been reached.' Prof Ian Barnes, molecular evolutionary biologist
Toxodon platensis was the last survivor of a huge group of South American ungulates, or hooved animals. Toxodon were a puzzling group of mammals that lived from 50 million to just ten thousand years ago. Charles Darwin collected the first known specimen of Toxodon on the Beagle voyage, and it was studied by the Museum's founder, Richard Owen, who described its odd combination of rodent-, hippo- and whale-like features. Darwin called them the ‘strangest animals ever discovered’, and until recently the origins of Toxodon and the other South American ungulates have remained a mystery.
Museum scientists were part of an international team who analysed 48 fossils of Toxodon platensis and Macrauchenia patachonica, another species whose remains Darwin collected 180 years ago when he visited Uruguay and Argentina on the Beagle voyage. The team began by looking for ancient DNA but this had not survived in the fossils. They instead studied collagen, a structural protein found in all animal bones that can survive for millions of years. Chemical structures inside the proteins can be compared between different species, revealing clues about how closely the species are related.
Although Toxodon most closely resembles a large hippo and the Macrauchenia a fat, long-legged camel with a trunk, the scientists determined that the closest living relatives of South America’s ungulates were the perissodactyls - the group that includes horses, rhinos and tapirs. This makes them part of Laurasiatheria, one of the major groups of mammals that have placentas.
Marine biologist Dr Adrian Glover, is examining biodiversity deep in the Southern Ocean in Antarctica to understand how marine ecosystems may deal with future climate change.
Dr Glover shows us some of the high-tech equipment that is revolutionising the study of deep-sea biology, making it easier to collect specimens and even discover species new to science.
High-latitude ecosystems, such as the Antarctic, experience extreme variations in productivity and food supply between seasons and years. By examining how marine ecosystems respond to these changes, scientists can test how they may respond to global change.
Dr Glover and his team use DNA and data on the shape and structure of creatures from samples collected by the British Antarctic Survey BIOPEARL project from the West Antarctic.
'We know that the landscape is going to change a lot in the future as the population grows, but we haven't really known how biodiversity will change in response. With PREDICTS we're building global models that help us to predict how land-use change will affect local biodiversity - and us - in the future.' Prof Andy Purvis, PREDICTS lead scientist and biodiversity researcher
Museum scientists have shown for the first time the extent to which human land use has affected the diversity of wildlife in ecosystems around the world. The research team assessed changes in biodiversity caused by the conversion of land for agriculture and urbanisation from 1500 until the present day.
'What the figures show is that if you were to go out and sample a site, anywhere in the world, on average you'd find 13.6% fewer species than you would have done in 1500. And that appears to be because of major land-use changes by humans,' says lead scientist Prof Purvis.
That figure is a global average, so local biodiversity in some areas is still relatively intact, but others - including Western Europe - have experienced losses in excess of 20% to 30% since the industrial revolution.
This research is part of a major collaborative project called known as PREDICTS: Projecting Responses of Ecological Diversity In Changing Terrestrial Systems. The team brought together a huge database of evidence to complete the largest survey ever on the impact of humanity on local biodiversity. The database contains records from 90 countries and 450 scientific papers, representing more than 40,000 species - comprising 1.5% of species that have been formally described by science. It is a vast assemblage of unprecedented geographic and taxonomic coverage.
The team also forecast the future impact of pressures caused by human activities. Under a business-as-usual scenario, the vast majority of countries will see a decrease in their species richness over the next hundred years. However, if humanity protects forested areas and supports carbon markets, almost all countries could actually gain back biodiversity by the end of the century. This work is vital at a time when a growing human population is putting increased pressure on available land.
'It was a bit of a detective story to work out why schistosomiasis occurs in the northern part of the island and not in the south.' Dr Anouk Gouvras, parasitologist
Dr Bonnie Webster and Dr Anouk Gouvras explain how their taxonomic expertise and the Museum's collections are helping to eliminate one of the most prevalent diseases in Africa: schistosomiasis. Follow their detective work to discover why this parasitic disease only develops in the northern part of Zanzibar and not in the south. The scientists reveal the culprit and treat the affected areas in a targeted way.
Schistosomiasis affects 250 million people worldwide. The illness causes a range of devastating symptoms, from painful urination and stunted growth in childhood, to irreversible damage of vital organs. The disease is caused by parasitic worms, which can live in people and aquatic snails.
The scientists are studying the Museum's collection of parasitic worms - schistosomes - and their snail hosts to understand the biology and systematics of these organisms. Their in-depth knowledge allows them to diagnose the schistosome species causing the disease and the snail species harbouring the parasite in fresh water lakes.
'This work would have been impossible without access to the digital collections of British species, allowing us to examine large amounts of data. Changes in butterfly size and habit will help us to understand the wider effects of global climate change on British organisms and ecosystems.' Steve Brooks, entomologist
Climate change is having a dramatic effect on the lives of British butterflies. They are emerging earlier, changing in size and living in new habitats. For example, in warmer summers the adult silver-spotted skipper butterfly emerges earlier from the chrysalis with a larger wingspan and is able to travel further north.
Museum researchers Steve Brooks and Dr Angela Self are using the Museum's digitised collections of native butterfly species to track changes in butterfly behaviour over the last 140 years, a period that has seen unprecedented temperature changes in Britain.
The complex life cycles of butterflies rely on delicate balances within the ecosystem, including temperature and availability of food. Tracking butterfly habits can reveal important lessons about the state of the environment.
The Museum's collections contain data on British butterflies stretching back beyond the nineteenth century - a valuable tool for researchers hoping to uncover long-term trends in our changing ecosystems.
This data is now online for the first time thanks to the Museum's digitisation project, giving Steve Brooks access to 180,000 butterfly specimens from his desktop.
According to Met Office data, average UK temperatures increased by 0.6°C between 1870 and 1970, and since then have increased even more rapidly, going up by 1.5°C in the last 40 years. This change is in part due to rising levels of carbon dioxide and other gases in the atmosphere, which has created a greenhouse effect.
'Digitisation of data will help to address some of the world's greatest challenges - it also helps governments and companies quickly make informed decisions on how to minimise our impact on the natural world.' Prof Ian Owens, Director of Science
We are embarking on an epic journey to digitise one of the world's most important natural history collections: 80 million specimens spanning over four billion years of history. The Museum plans to digitise 20 million specimens over the next five years.
The data will help to address some of the world's greatest challenges. How can we make crops resilient to environmental change? How do we combat diseases? How is climate change affecting pollinators? How do we sustainably extract minerals for new green technologies?
We are starting with collections that will help our scientists ask big questions about environmental change, food supplies for future generations, ecological responses to short-term climate variations and mass extinctions.
Scientists are perfecting the high-speed imaging of herbarium sheets from flowering plant collections belonging to the Museum and the Royal Botanic Gardens, Kew. They will analyse the pictures and specimen labels of wild relatives of crop plants, such as the tomato, potato and aubergine, to track the evolution of tolerance to environmental extremes and response to short-term climate change.
The Museum is digitising our country's amazing collection of dinosaurs, flying reptiles, prehistoric fish, sharks and mammalian ancestors from the Mesozoic era. The data will help scientists answer crucial questions about mass extinctions and how species were distributed across our nation millions of years ago. | 0.847479 | 3.498845 |
Nights begin with Venus and end at Jupiter
The end of British Summer Time means that we now enjoy six hours of official darkness before midnight, though I appreciate that this may not be welcomed by everyone. The starry sky as darkness falls, however, sees only a small shift since a month ago, with the Summer Triangle, formed by the bright stars Vega, Deneb and Altair, now just west of the meridian and toppling into the middle of the western sky by our star map times.
Those maps show the Square of Pegasus high in the south. The star at its top-left, Alpheratz, actually belongs to Andromeda whose other main stars, Mirach and Almach, are nearly equal in brightness and stand level to its left. A spur of two stars above Mirach leads to the oval glow of the Andromeda Galaxy, M31, which is larger than our Milky Way and, at 2.5 million light years, is the most distant object visible to the unaided eye. It is also approaching us at 225 km per second and due to collide with the Milky Way in some 4 billion years’ time.
Binoculars show M31 easily and you will also need them to glimpse more than a handful of stars inside the boundaries of the Square of Pegasus, even under the darkest of skies. In fact, there are only four such stars brighter than the fifth magnitude and another nine to the sixth magnitude, close to the naked eye limit under good conditions. How many can you count?
Mars is the easiest of three bright planets to spot in tonight’s evening sky. As seen from Edinburgh, it stands 11° high in the south as the twilight fades, shining with its customary reddish hue at a magnitude of 0.4, and appearing about half as bright as the star Altair in Aquila, 32° directly above it.
Now moving east-north-eastwards (to the left), Mars is 5° below-right of the Moon on the 6th and crosses from Sagittarius into Capricornus two days later. Soon after this, it enters the region covered by our southern star map, its motion being shown by the arrow. By the 30th, Mars has dimmed slightly to magnitude 0.6 but is almost 6° higher in the south at nightfall, moving to set in the west-south-west at 21:00. It is a disappointingly small telescopic sight, though, its disk shrinking from only 7.5 to 6.5 arcseconds in diameter as it recedes from 188 million to 215 million km.
We need a clear south-western horizon to spy Venus and Saturn, both low down in our early evening twilight. Venus, by far the brighter at magnitude -4.0, is less than 4° high in the south-west thirty minutes after sunset, while Saturn is 4° above and to its right, very much fainter at magnitude 0.6 and only visible through binoculars. The young earthlit Moon may help to locate them – it stands 3° above-right of Saturn on the 2nd and 8° above-left of Venus on the 3rd.
Mercury is out of sight in the evening twilight and Saturn will soon join it as it tracks towards the Sun’s far side. However, Venus’ altitude thirty minutes after sunset improves to 9° by the 30th when it sets for Edinburgh at 18:30 and is a little brighter at magnitude -4.1. Viewed telescopically, Venus shows a dazzling gibbous disk that swells from 14 to 17 arcseconds as its distance falls from 178 million to 149 million km.
Sunrise/sunset times for Edinburgh change from 07:20/16:31 on the 1st to 08:18/15:44 on the 30th. The Moon reaches first quarter on the 7th, full on the 14th, last quarter on the 21 and new on the 28th.
The full moon on the 14th occurs only three hours after the Moon reaches its perigee, the closest point to the Earth in its monthly orbit. As such, this is classed as a supermoon because the full moon appears slightly (7%) wider than it does on average. By my reckoning, this particular lunar perigee, at a distance of 356,509 km, is the closest since 1948 when it also coincided with a supermoon.
Of the other planets, Neptune and Uranus continue as binocular-brightness objects in Aquarius and Pisces respectively in our southern evening sky, while Jupiter, second only to Venus in brightness, is now obvious in the pre-dawn.
Jupiter rises at Edinburgh’s eastern horizon at 04:28 on the 1st and stands more than 15° high in the south-east as morning twilight floods the sky. It outshines every star as it improves from magnitude -1.7 to -1.8 by the 30th when it rises at 03:07 and is almost twice as high in the south-south-east before dawn.
Currently close to the famous double star Porrima in Virgo, Jupiter is 13° above-right of Virgo’s leader Spica and draws 5° closer during the period. Catch it less than 3° to the right of the waning earthlit Moon on the 25th. Jupiter’s distance falls from 944 million to 898 million km during November while its cloud-banded disk is some 32 arcseconds across.
The annual Leonids meteor shower has produced some stunning storms of super-swift meteors in the past, but probably not this year. Active from the 15th to 20th, it is expected to peak at 04:00 on the 17th but with no more than 20 meteors per hour under a dark sky. In fact, the bright moonlight is likely to swamp all but the brightest of these this year. Leonids diverge from a radiant point that lies within the Sickle of Leo which climbs from low in the east-north-east at midnight to pass high in the south before dawn. | 0.873884 | 3.700404 |
Summer Triangle stars as autumn evenings begin
We may be edging towards autumn, but the Summer Triangle, the asterism formed by the bright stars Vega, Altair and Deneb, looms high in the south as night falls and shifts into the high south-west by our star map times later in the evening. Vega, almost overhead as the night begins, is the brightest of the three and lies in the small box-shaped constellation of Lyra the Lyre.
The next brightest, Altair in Aquila the Eagle, stands lower in the middle of our southern sky and, at 16.7 light years (ly), is one of the nearest bright stars to the Sun – eight light years closer than Vega. Flanking Altair, like the two sides of a balance, are the fainter stars Alshain (below Altair) and Tarazed (above) whose names come from “shahin-i tarazu”, the Arabic phrase for a balance.
Deneb, 25° from Vega, lies very high in the south-east at nightfall and overhead at our map times. It marks the tail of Cygnus the Swan which is flying overhead with wings outstretched and its long neck reaching south-westwards to Albireo, traditionally the swan’s beak. Although it is the dimmest corner-star of the Triangle, Deneb is one of the most luminous stars in our galaxy. Current estimates suggest that it shines some 200,000 time more brightly than our Sun from a distance of perhaps 2,600 ly, but its power and distance are hard to measure and the subject of some controversy.
Also controversial is the nature of Albireo. Even small telescopes show it as a beautiful double star in which a brighter golden star contrasts with a dimmer blue one. The mystery concerns whether the pair make up a real binary, with the two stars locked in orbit together by gravity, or whether this is just the chance alignment of two stars at different distances. Now measurement by the European Space Agency’s Gaia spacecraft appear to confirm the chance alignment theory.
The Milky Way, the band of countless distant stars in the plane of our galaxy, flows through the Summer Triangle and close to Deneb as it arches across our evening sky. Scan it through binoculars to glimpse a scattering of other double stars and star clusters.
One interesting stellar group is the so-called Coathanger which lies 8°, a little more than a normal binocular field-of-view, south of Albireo. It is also easy to locate one third of the way from Altair to Vega. Its line of stars, with a hook of stars beneath, gives it the appearance of an upside-down coat hanger. For decades this was regarded as a true star cluster, whose stars formed together, and its alternative designations as Brocchi’s Cluster and Collinder 399 reflect this. In 1998, though, results from the Hipparcos satellite, Gaia’s predecessor, proved that the Coathanger’s stars are at very different distances so that it, like Albireo, is simply a fortuitous chance alignment.
The Sun sinks 11.5° southwards during September to cross the sky’s equator at 02:54 BST on the 23rd. This marks our autumnal equinox and, by one definition, the beginning of autumn in the northern hemisphere. Sunrise/sunset times for Edinburgh change from 06:17/20:07 BST on the 1st at 07:13/18:51 on the 30th. The Moon is at last quarter on the 3rd, new on the 9th, at first quarter on the 17th and full on the 25th.
Venus is brilliant at magnitude -4.4 and 45° from the Sun on the 1st but it is only 4° above Edinburgh’s west-south-western horizon at sunset and sets 35 minutes later as its evening apparition as seen from Scotland comes to an end.
The other inner planet, Mercury, is prominent but low in the east-north-east before dawn until about the 14th. Glimpse it at magnitude -1.1 when it lies 1° above-left of Regulus in Leo on the 6th and 9° below-left of the impressively earthlit waning Moon on the 8th.
Jupiter is conspicuous but very low in the south-west at nightfall, sinking to set in the west-south-west one hour before our map times. Look for it below-right of the Moon on the 13th.
Saturn and Mars are in the far south of our evening sky. Saturn, the fainter of the two at magnitude 0.4 to 0.5, stands above the Teapot of Sagittarius and is just below and right of the Moon on the 17th when a telescope shows that its rings span 38 arcseconds around its 17 arcseconds disk. It sets in the south-west some 70 minutes after our map times.
Mars stands more than 25° east (left) of Saturn, tracks 7° eastwards and northwards in Capricornus and stands near the Moon on the 19th and 20th. It is easily the brightest object (bar the Moon) in the sky at our map times though it more than halves in brightness from magnitude -2.1 to -1.3. As its distance increases from 67 million to 89 million km, its ochre disk shrinks from 21 to 16 arcseconds. The dust storm that blanketed the planet since June has now died down.
Finally, we have a chance to spot the Comet Giacobini-Zinner as it tracks south-eastwards past the bright star Capella in Auriga, low in the north-east at our map times but high in the east before dawn. The comet takes only 6.6 years to orbit the Sun and should appear in binoculars as a small oval greenish smudge only 0.9° to the right of Capella on the evening of the 2nd when it is 60 million km away. Moving at almost 2° per day, it passes less than 7° north-east of Elnath in Taurus (see chart) on the morning of the 11th, just a day after it reaches perihelion, its closest (152 million km) to the Sun.
Diary for 2018 September
Times are BST
2nd 10h Venus 1.4° S of Spica
3rd 03h Moon 1.2° N of Aldebaran
3rd 04h Last quarter
6th 11h Saturn stationary (motion reverses from W to E)
7th 04h Moon 1.1° S of Praesepe in Cancer
7th 19h Neptune at opposition
8th 23h Moon 0.9° N of Mercury
9th 19h New moon
10th 08h Comet Giacobini-Zinner closest to Sun (152 million km)
14th 03h Moon 4° N of Jupiter
16th 14h Mars closest to Sun (206,661,000 km)
17th 00h First quarter
17th 17h Moon 2.1° N of Saturn
20th 08h Moon 5° N of Mars
21st 03h Mercury in superior conjunction
23rd 02:54 Autumnal equinox
25th 04h Full moon
30th 09h Moon 1.4° N of Aldebaran
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on August 31st 2018, with thanks to the newspaper for permission to republish here.
Saturn at its best as noctilucent clouds gleam
The first day of June marks the start of our meteorological summer, though some would argue that summer begins on 21 June when (at 05:25 BST) the Sun reaches its most northerly point at the summer solstice.
Sunrise/sunset times for Edinburgh vary surprisingly little from 04:35/21:47 BST on the 1st, to 04:26/22:03 at the solstice and 04:31/22:02 on the 30th. The Moon is at first quarter on the 1st, full on the 9th, at last quarter on the 17th and new on the 24th.
The Sun is already so far north that our nights remain bathed in twilight and it will be mid-July before Edinburgh sees its next (officially) dark and moonless sky. This is a pity, for the twilight swamps the fainter stars and, from northern Scotland, only the brightest stars and planets are in view.
If we travel south, though, the nights grow longer and darker, and the spectacular Milky Way star fields in Sagittarius and Scorpius climb higher in the south. From London at the solstice, for example, official darkness, with the Sun more than 12° below the horizon, lasts for three hours, while both Barcelona and Rome rejoice in more than six hours.
It is in this same area of sky, low in the south in the middle of the night, that we find the glorious ringed planet Saturn. This stands just below the full moon on the 9th and is at opposition, directly opposite the Sun, on the 15th when it is 1,353 million km away and shines at magnitude 0.0, comparable with the stars Arcturus in Bootes and Vega in Lyra. The latter shines high in the east-north-east at our map times and, together with Altair in Aquila and Deneb in Cygnus, forms the Summer Triangle which is a familiar feature of our nights until late-autumn.
Viewed telescopically, Saturn’s globe appears 18 arcseconds wide at opposition while its rings have their north face tipped 27° towards us and span 41 arcseconds. Sadly, Saturn’s low altitude, no more than 12° for Edinburgh, means that we miss the sharpest views although it should still be possible to spy the inky arc of the Cassini division which separates the outermost of the obvious rings, the A ring, from its neighbouring and brighter B ring.
Other gaps in the rings may be hard to spot from our latitudes – we can only envy the view for observers in the southern hemisphere who have Saturn near the zenith in the middle of their winter’s night. For us, Saturn is less than a Moon’s breadth further south over our next two summers, while the ring-tilt begins to decrease again.
On the other hand, we can sympathize with those southern observers for most of them never see noctilucent clouds, a phenomenon for which we in Scotland are ideally placed. Formed by ice condensing on dust motes, their intricate cirrus-like patterns float at about 82 km, high enough to shine with an electric-blue or pearly hue as they reflect the sunlight after any run-of-the-mill clouds are in darkness. Because of the geometry involving the Sun’s position below our horizon, they are often best seen low in the north-north-west an hour to two after sunset, shifting towards the north-north-east before dawn – along roughly the path taken by the bright star Capella in Auriga during the night.
Jupiter dims slightly from magnitude -2.2 to -2.0 but (after the Moon) remains the most conspicuous object in the sky for most of the night. Indeed, the Moon lies close to the planet on the 3rd – 4th and again on the 30th. As the sky darkens at present, it stands some 30° high and just to the west of the meridian, though by the month’s end it is only half as high and well over in the SW. Our star maps plot it in the west-south-west as it sinks closer to the western horizon where it sets two hours later.
The giant planet is slow-moving in Virgo, about 11° above-right of the star Spica and 3° below-left of the double star Porrima. As its distance grows from 724 million to 789 million km, its disk shrinks from 41 to 37 arcseconds in diameter but remains a favourite target for observers.
The early science results from NASA’s Juno mission to Jupiter were released on 25 May. They reveal the atmosphere to be even more turbulent than was thought, with the polar regions peppered by 1,000 km-wide cyclones that are apparently jostling together chaotically. This is in stark contrast to the meteorology at lower latitudes, where organized parallel bands of cloud dominate in our telescopic views. In addition, the planet’s magnetic field is stronger and more lumpy than was expected. Juno last skimmed 3,500 km above the Jovian clouds on 19 May and is continuing to make close passes every 53 days.
Both Mars and Mercury are hidden in the Sun’s glare this month, the latter reaching superior conjunction on the Sun’s far side on the 21st.
Venus, brilliant at magnitude -4.3 to -4.1, is low above our eastern horizon before dawn. It stands at its furthest west of the Sun in the sky, 46°, on 3 June but it rises only 78 minutes before the Sun and stands 10° high at sunrise as seen from Edinburgh. By the 30th, it climbs to 16° high at sunrise, having risen more than two hours earlier. Between these days, it shrinks in diameter from 24 to 18 arcseconds and changes in phase from 49% to 62% illuminated. It lies left of the waning crescent Moon on the 20th and above the Moon on the following morning.
This is a slightly-revised version of Alan’s article published in The Scotsman on May 31st 2017, with thanks to the newspaper for permission to republish here.
Venus highest and brightest as evening star
If you doubt that February offers our best evening sky of the year, then consider the evidence. The unrivalled constellation of Orion stands astride the meridian at 21:00 GMT tonight, and two hours earlier by February’s end. Around him are arrayed some of the brightest stars in the night sky, including Sirius, the brightest, and Capella, the sixth brightest which shines yellowish in Auriga near the zenith. This month also sees Venus, always the brightest planet, reach its greatest brilliancy and stand at its highest as an evening star.
By our map times, a little later in the evening, Orion has progressed into the south-south-west and Sirius, nipping at his heel as the Dog Star in Canis Major, stands lower down on the meridian. All stars twinkle as their light, from effectively a single point in space, is refracted by turbulence in the Earth’s atmosphere, but Sirius’ multi-hued scintillation is most noticeable simply because it is so bright. On the whole, planets do not twinkle since their light comes from a small disk and not a point.
I mentioned two months ago how Sirius, Betelgeuse at Orion’s shoulder and Procyon, the Lesser Dog Star to the east of Betelgeuse, form a near-perfect equilateral triangle we dub the Winter Triangle. Another larger but less regular asterism, the Winter Hexagon, can be constructed around Betelgeuse. Its sides connect Capella, Aldebaran in Taurus, Rigel at Orion’s knee, Sirius, Procyon and Castor and Pollux in Gemini, the latter pair considered jointly as one vertex of the hexagon.
Aldebaran, found by extending the line of Orion’s Belt up and to the right, just avoids being hidden (occulted) by the Moon on the 5th. At about 22:20 GMT, the northern edge of the Moon slides just 5 arcminutes, or one sixth of the Moon’s diameter, below and left of the star. Earlier that evening, the Moon occults several stars of V-shaped Hyades cluster which, together with Aldebaran, form the Bull’s face.
Sunrise/sunset times for Edinburgh change from 08:07/16:46 on the 1st to 07:06/17:45 on the 28th. The Moon is at first quarter on the 4th and lies to the west of Regulus in Leo when full just after midnight on the night of the 10th/11th. It is then blanketed by the southern part of the Earth’s outer shadow in a penumbral lunar eclipse. The event lasts from 22:34 until 02:53 with an obvious dimming of the upper part of the Moon’s disk apparent near mid-eclipse at 00:33. This time, the Moon misses the central dark umbra of the shadow where all direct sunlight is blocked by the Earth, but only by 160 km or 5% of its diameter.
Following last quarter on the 18th, the Moon is new on the 26th when the narrow track of an annular solar eclipse crosses the south Atlantic from Chile and Argentina to southern Africa. Observers along the track see the Moon’s ink-black disk surrounded by a dazzling ring of sunlight while neighbouring regions, but not Europe, enjoy a partial eclipse of the Sun.
Venus, below and to the right of the crescent Moon as the month begins, stands at it’s highest in the south-west at sunset on the 11th and 12th and blazes at magnitude -4.6, reaching its greatest brilliancy on the 17th. It stands further above-and to the right of the slim impressively-earthlit Moon again on the 28th.
Viewed through a telescope, Venus’ dazzling crescent swells in diameter from 31 to 47 arcseconds and the illuminated portion of the disk shrinks from 40% to 17%. Indeed, steadily-held binoculars should be enough to glimpse its shape. This month its distance falls from 81 million to 53 million km as it begins to swing around its orbit to pass around the Sun’s near side late in March.
Mars stands above and to the left of Venus but is fainter and dimming further from magnitude 1.1 to 1.3 during February. It appears closest to Venus, 5.4°, on the 2nd but the gap between them grows to 12° by the 28th as they track eastwards and northwards through Pisces. Both set before our map times at present but our charts pick them up at midmonth as they pass below-left of Algenib, the star at the bottom-left corner of the Square of Pegasus.
Mars shrinks below 5 arcseconds in diameter this month so few surface details are visible telescopically. This is certainly not the case with Jupiter, whose intricately-detailed cloud-banded disk swells from 39 to 42 arcseconds. We do need to wait, though, for two hours beyond our map times for Jupiter to rise in the east and until the pre-dawn hours for it to stand at its highest in the south. Second only to Venus, it shines at magnitude -2.1 to -2.3 and lies almost 4° due north of Virgo’s leading star Spica where it appears stationary on the 6th when its motion switches from easterly to westerly. Look for the two below-left of the Moon on the 15th and to the right of the Moon on the 16th.
Saturn is a morning object, low down in the south-east after its rises for Edinburgh at 05:25 on the 1st and by 03:48 on the 28th. At magnitude 0.6 to 0.5, it stands on the Ophiuchus-Sagittarius border where it is below-right of the waning Moon on the 21st. It is a pity that telescopic views are hindered by its low altitude because Saturn’s disk, 16 arcseconds wide, is set within wide-open rings which measure 16 by 36 arcseconds and have their northern face tipped 27° towards the Earth. Mercury remains too deep in our south-eastern morning twilight to be seen this month.
This is a slightly-revised version of Alan’s article published in The Scotsman on January 31st 2017, with thanks to the newspaper for permission to republish here.
Venus and Jupiter converge for twilight rendezvous
The perpetual twilight during Scotland’s all-too-brief June nights means that the month is rarely a vintage one for stargazing. Indeed, from the north of the country, all but the brighter stars and planets are swamped by the “gloaming” or, for those in the Northern Isles, the “simmer dim”.
This year, though, we have two powerful excuses for staying up late. Not only is the beautiful world Saturn at its stunning best, but the two brightest planets, Venus and Jupiter, are converging in our western evening sky on their way to a spectacular close conjunction low down in the twilight at the month’s end. Just expect a flurry of UFO reports.
The Sun is at its furthest north over the Tropic of Cancer at 17:38 BST on the 21st, the moment of our summer solstice when days are at their longest over Earth’s northern hemisphere. For Edinburgh, sunrise/sunset times vary from 04:35/21:46 BST on the 1st, to 04:26/22:03 on the 21st and 04:30/22:02 on the 30th. The Moon is full on the 2nd, at last quarter on the 9th, new on the 16th and at first quarter on the 24th.
Venus is brilliant in our western evening sky and sets in the west-north-west just prior to our star map times. It reaches its greatest angular distance of 45° east of the Sun on the 6th and grows even brighter from magnitude -4.3 to -4.4 – bright enough to be glimpsed in broad daylight. However, its motion against the stars is taking it southwards in the sky so that its altitude at Edinburgh’s sunset plunges from 27° on the 1st to 16° by the 30th.
As Venus approaches from 113 million to 77 million km, a telescope shows its disk swelling from 22 to 32 arcseconds across while the sunlit portion falls from 53% to 32%. The planet is said to reach dichotomy when it is 50% illuminated on the 6th, but it seems that optical effects involving its deep cloudy atmosphere mean that observers see the phase occurring several days earlier than predicted when Venus is an evening star.
Venus lies below and left of the Castor and Pollux in Gemini as the month begins, but it tracks east-south-eastwards across Cancer and into Leo to pass 0.9° north of the Praesepe star cluster (use binoculars) on the 13th.
As it does so, it closes on the night’s second brightest planet, Jupiter, which creeps much more slowly from Cancer into Leo. Jupiter stands 21° to the left of Venus on the 1st but is barely 0.4°, less than a Moon’s breadth, above-left of Venus by the evening of the 30th. The giant planet dims slightly from magnitude -1.9 to -1.8 during the period and shrinks from 34 to 32 arcseconds as it recedes from 851 million to 909 million km.
Don’t forget that Jupiter’s four main moons can be followed through a telescope or decent binoculars as they orbit from side to side of the planet. Our own Moon is a 19% sunlit crescent on the 20th when it stands 5° below Jupiter which, in turn, is 6° left of Venus. On the next evening the Moon lies 5° below-left of the star Regulus in Leo which is about to set in the west-north-west at our map times as the Plough stands high above.
Mars and Mercury are not observable this month. Mars reaches conjunction on the Sun’s far side on the 14th while Mercury reaches 22° west of the Sun on the 24th but is swamped by our morning twilight.
The constellations of Hercules and Ophiuchus, both sparsely populated with stars, loom in the south at the map times while the Summer Triangle formed by Vega, Altair and Deneb is high in the east to south-east. Were we under darker skies a few degrees further south, in southern Europe for example, then we might spy the Milky Way flowing through the Triangle as it arches across the eastern sky from Sagittarius and Scorpius in the south. The latter are rich in stars and star clusters, but they hug Scotland’s southern horizon where only the bright yellowish Saturn and the distinctly red supergiant star Antares, half as bright and more than 11° below-left of the planet, stand out.
Saturn stood at opposition on May 23 but is still observable throughout the night as it moves from the south-east at nightfall to the south-west before dawn, peaking only 16° above Edinburgh’s southern horizon thirty minutes before our map times. As the planet edges 2° westwards in eastern Libra, it tracks away from the fine double star Graffias in Scorpius, below and to its left. Look for it close to the Moon on the evenings of the 1st and 28th.
This month Saturn fades a little from magnitude 0.1 to 0.3 but remains a striking telescopic sight. Its iconic ring system is tilted 24° towards us and spans 42 arcseconds around the rotation-flattened 18 arcseconds globe.
On the opposite side of our sky to Saturn is the star Capella in Auriga which transits low across the north from the north-west at dusk to the north-north-east before dawn. It is in this region of our sky that we sometimes see noctilucent clouds. Appearing like wisps, ripples and sheets of silvery-blue cirrus, these form as ice condenses around particles near altitudes of 82 km where they glow in the sunlight after our more familiar weather or troposphere clouds are in darkness. Best seen from latitudes between 50° and 60° N, ideal for Scotland, they appear for just a few weeks around the solstice, from about mid-May to early-August. | 0.910902 | 3.731553 |
The Science of Shooting Stars
by Jim Al-Khalili
As every parent and teacher knows, when it comes to science the topics guaranteed to grab a child’s attention (or an adult’s) are space and dinosaurs. So, after many years of being treated to a bountiful procession of earnest popular science books whose titles always seem to include a subset of the words “creation,” “fabric,” “reality,” “universe,” “elegance” and “beauty,” one called “Dark Matter and the Dinosaurs” was bound to grab my attention. Yet despite the title, this is no children’s book, or even a clever, if blatant, marketing ploy. This is solid, if somewhat speculative, science. As unlikely as it may sound, Lisa Randall’s book hints at a potential connection between the sudden extinction of the dinosaurs 66 million years ago and that mysterious cosmic substance known as dark matter that continues to confound and thrill physicists in equal measure.
Ms. Randall, a Harvard professor, is one of the world’s leading theoretical physicists, and her book — there is no other way of putting this — is a cracking read, combining storytelling of the highest order with a trove of information on subjects as diverse as astrophysics, evolutionary biology, geology and particle physics. What’s remarkable is that it all fits together.
The book begins a little ploddingly. Certainly Ms. Randall is not in a hurry to justify her title or advertise her main thesis. What hooked me, though, was her fascinating disentangling of space terminology: meteoroids (lumps of rock in space that occasionally hit Earth), meteors (the visible streaks of light, or “shooting stars,” that meteoroids create as they burn up in the atmosphere) and meteorites (the surviving fragments of rock that land on Earth if the meteoroid doesn’t completely burn up). OK, got that? Good. Let’s not confuse them anymore. Similarly, larger objects in space that are nevertheless smaller than planets are either giant rocks in the inner solar system (asteroids) or mini worlds of ice and dust in the outer solar system (comets).
Having become captivated, I revised my impression of the book’s pace from “plodding” to a far more generous “unhurried,” for Ms. Randall leads us on an epic journey that begins with asking what wiped out the dinosaurs. We have all heard, of course, that it may have been the stupendously powerful impact of some extraterrestrial body (think asteroid or comet). But what many will not have appreciated is that this event is really no longer in any doubt. Ms. Randall, showing a thorough level of research into a wide range of disciplines, takes the reader by the hand and patiently unpacks the evidence. One of the characters she discusses is the geologist Walter Alvarez, who first proposed the impact hypothesis. His book “T. Rex and the Crater of Doom” did lead me to wonder whether his title had given her the courage to choose her own.
Once we have been persuaded that the extinction of the dinosaurs, and probably other major extinction events in Earth’s history, could have been caused by a comet impact, Ms. Randall moves on to a more interesting question: Are mass extinctions periodic and, if so, why? They certainly seem to be, though she acknowledges that the mass extinctions discernible in the fossil record could have been triggered by any number of causes: volcanic eruptions, tectonic plate movements, climate change brought about by solar cycles or changes in the Earth’s magnetic field, or — the thesis of this book — extraterrestrial impacts.
The whole subject of extinctions is messy and complicated, since it involves biology and geology, and rather than insist on one cause, Ms. Randall cleverly turns to a different question: whether extraterrestrial impacts themselves are cyclic. There is, she points out, persuasive evidence from studying impact craters that large bodies have smashed into the Earth on a regular basis every 20 million to 30 million years or so. This periodicity might, she suggests, come from the way the solar system wobbles up and down as it orbits round the center of our galaxy. The puzzle is why this wobble would lead to an increase in the chances that the Earth will be bombarded by comets.
As you can begin to tell, the sequence of cause and effect starts to get convoluted. But the bottom line, and the topic that Ms. Randall and her colleagues at Harvard are working on, is that it is all down to dark matter, the elusive, invisible “stuff” that is needed if we are to understand how galaxies are able to remain intact and indeed how they formed in the first place. For without the additional gravitational glue provided by dark matter, we would be unable to explain the structure of our universe. Like the impact that wiped out the dinosaurs, the existence of dark matter is not really in doubt any longer — the evidence, from the way stars move within galaxies or the way light is bent round regions of dark matter, is too strong.
But while physicists debate what dark matter might be made of, and how we might go about finding out, Ms. Randall and her team suggest something new: that dark matter may, for reasons I will leave you to find out from the book, form a thin, dense disk in the plane of the galaxy and that the solar system may pass through this disk every — yes, you’ve guessed it — 20 million to 30 million years. The dark matter applies a gentle tug on a junkyard of debris floating around the outer reaches of the solar system, known as the Oort cloud (where, crucially, comets come from), knocking the icy missiles from their orbits and sending a few hurtling earthward.
The whole chain of events may sound tenuous, to say the least, but remember that Walter Alvarez’s suggestion that a comet impact wiped out the dinosaurs 66 million years ago was just as speculative — wacky, even — as recently as the 1980s. Nevertheless, the last third of the book is spent speculating on the nature of dark matter and how likely it is that Ms. Randall’s hypothesis could be correct. The jury is still out and will be for some time, but I do hope she turns out to be right — the book title is too good. | 0.905072 | 3.704513 |
The ground rumbles beneath your feet. You hear a popping noise and a hissing sound. Suddenly, countless gallons of scalding hot water, along with pressurized steam, are propelled hundreds of feet into the air. What is the cause of this strange phenomenon?
Facts about Geysers
- There are two main types of geyser: steam-driven and cold-water.
- Steam geysers are caused when water deep beneath the Earth’s surface gets heated by hot magma and causes pressure to build up.
- On large time scales, geysers are only temporary. There are a number of reasons why a geyser will form or go dormant.
- Geysers exist on other planets and moons, too. On other planets, they spew chemical vapors, ice and dust.
- The most famous geyser is Old Faithful, located in Yellowstone National Park, Wyoming, United States.
- The world’s tallest geyser is Steamboat Geyser, Yellowstone.
What Are Geysers?
The word “geyser” means “to gush,” referring to the movement of steam and water when a geyser erupts. Geysers are underground reservoirs of water that intermittently eject water and steam. Fractures, cavities, and porous areas in the rock above act as “pipes” through which rain and water flow into the reservoirs. When enough pressure builds up in the reservoirs, they erupt.
Geysers don’t last forever. Earthquakes, human activity, the movement of tectonic plates, and other factors can cause a geyser to stop functioning. Even throwing garbage into a geyser may change its conditions enough for it to go dormant.
Why do most geysers spew out hot water?
Surface water from rain and rivers trickles down through the earth, reaching a depth of nearly 7,000 feet (2,000 meters). There, it comes into contact with rocks heated by molten magma deep below the earth’s surface. The water boils, creating pressure. The water and steam are pushed to the surface and erupt from a surface vent. This is called a hydrothermal explosion (hydro means “water,” and thermal means “heat”).
What are the types of geysers?
Geysers can be divided into two main types, steam-driven and cold-water.
Steam-driven geysers can be further be divided into two types – fountain and cone. Fountain geysers erupt from beneath pools of water, usually in short bursts of a few seconds each. Cone geysers, however, consist of mounds of minerals. Cone geysers may erupt continuously for several minutes. Some may erupt for more than an hour at a time.
The other main type is called a cold-water geyser. Instead of heat driving the water from the ground, carbon dioxide (CO2) collects in underground lakes called aquifers. The weight of the water contains the carbon dioxide bubbles until the rock layer above weakens and forms a fissure, or crack, or when humans drill through the rock. The bubbles then expand and propel the water upwards with great force. Only a few of this type of cold-water geyser exist, and they are located in the United States, Germany, Slovakia, and Brazil.
Are there geysers on other planets?
Geysers have been found on Mars and several moons of Jupiter, Saturn and Neptune. Huge eruptions of water vapor were detected on Saturn’s moon Enceladus by the Cassini satellite. The eruption plumes can contain water vapor, chemical vapors, ice and dust.
Scientists refer to these geysers as cryogeysers or cryovolcanoes (cryo meaning “icy cold), because of the low boiling point of the contents in the ejected material. Chemicals such as ammonia are mixed with water on the planetary body, lowering the freezing point of the mixture.
What are some famous Geysers?
Over one thousand geysers are active around the world. Being a relatively rare phenomenon, tourists often visit geysers to see the water spray high into the air. The following are a few of the most well known geysers.
- Old Faithful. Perhaps the most famous geyser in the world, Old Faithful is a cone geyser located in Yellowstone National Park in the United States. This geyser is called old faithful because it is very predictable, with eruptions occurring every forty-four to one hundred and twenty-five minutes. Yellowstone National Park is home to more geysers than anywhere else in the world, with as many as five hundred active geysers observed each year.
- Steamboat Geyser. Located in Yellowstone National Park not far from Old Faithful, the Steamboat Geyser is the tallest currently active geyser in the world. The Steamboat Geyser regularly expels water more than three hundred feet (90 meters) in the air. This geyser is dormant at times, with the length of time between eruptions ranging from a few days to more than fifty years.
- The Great Geysir. Located in Iceland, this geyser was discovered during the 14th century. The word “geyser” is derived from its name. While this geyser is often dormant, it is induced to erupt on special occasions by the addition of certain chemicals.
- Strokkur Geyser. Also located in Iceland, the Strokkur Geyser is known for erupting every five to eight minutes.
- El Tatio. El Tatio is a field of eighty geysers located near active volcanoes of the Andes Mountains in Chile. El Tatio means “oven” in the local Quechua language, describing the geothermal heat. This area is known for its low geysers. Most of the geysers divulge water only to a height of thirty inches (750 millimeters), with the tallest reaching a height of twenty feet (6 meters). | 0.847277 | 3.238683 |
Look up into the night sky and count the moons. You can see only one moon, “the” Moon. But does the Earth have any other moons? Around the Solar System, multiple moons are the rule. Jupiter has 67 natural satellites, even Mars has two asteroid-like moons.
Could Earth have more than one?
Officially, the answer is no. The Earth has a single moon.
It’s possible Earth had more than one moon in the past, millions or even billions of years ago. Strange terrain on the far side of the Moon could be explained by a second moon crashing into it, depositing a layer of material tens of kilometers deep.
Moons could come and go over the billions of years of the Earth’s history.
For example, Mars has two Moons, but not for long. Phobos, the larger moon, is spiraling inward and expected to crash into the planet within the next 10 million years. And so, in the future, Mars will only have a single Moon, Deimos.
It’s also possible that the Earth might capture a Moon in the future. Neptune’s largest moon, Triton, orbits in the opposite direction from the rest of the moons around the planet. This suggests that Triton was actually a captured Kuiper Belt Object which strayed too close to the planet.
In fact, we did capture a 5-metre asteroid called 2006 RH120. It orbited the Earth four times during 2006/2007 before getting ejected again.
So we can assume events like this have happened in the past.
Additionally, we might have more moons, but they haven’t been discovered yet because they’re just too small. Researchers have calculated that there could be meter-sized asteroids in orbit around the Earth, remaining in orbit for hundreds of years before gravitational interactions push them out again.
And there are other objects that interact with Earth’s orbit in strange ways. Scientists don’t consider them moons, but they do stick around in our neighbourhood:
Asteroid 3753 Cruithne is in an orbital resonance with the Earth. It has a highly eccentric orbit, but takes exactly one year to orbit the Sun. From our perspective, it follows a slow, horse-shoe shaped path across the sky. Since the discovery of Cruithne in 1986, several other resonant near-Earth objects have been discovered.
There’s 2010 TK7, the Earth’s only known Trojan asteroid. It leads the Earth in the exact same orbit around the Sun, in a gravitationally stable point in space.
So, the answer… Earth only has a single Moon. Today. We might have had more moons in the past, and we might capture more in the future, but for right now… enjoy the one we’ve got.
Want to learn more? Here are some articles on Universe Today we’ve written about this topic:
What are some objects known as Earth’s other moons?
Did Earth have more than one moon in the past?
Does Earth have many tiny moons?
You might also enjoy this episode of Astronomy Cast: Where did the Moon come from? | 0.879292 | 3.64771 |
Fr.: relaxation dynamique
The evolution over time of a gravitationally → bound system consisting of N components because of encounters between the components, as studied in → stellar dynamics. Due to this process, in a → star cluster, → low-mass stars may acquire larger random velocities, and consequently occupy a larger volume than → high-mass stars. As a result, massive stars sink to the cluster centre on a time-scale that is inversely proportional to their mass. See also → mass segregation.
Fr.: relaxation magnétique
The process by which a magnetic system relaxes to its minimum energy state over time.
Fr.: relaxation sans rayonnement
A process in which a molecule relaxes without emitting a → photon.
Fr.: relaxer, se relaxer
To lessen the force, strength or intensity of something.
m M.E., from O.Fr. relaxer from L. relaxare "relax, loosen, open," from → re- "back" + laxare "loosen," from laxus "loose."
Vâhelidan, from vâ-, → re-, + helidan, heštan "to place, put" from Mid.Pers. hištan, hilidan "to let, set, leave, abandon;" Parthian Mid.Pers. hyrz; O.Pers. hard- "to send forth," ava.hard- "to abandon;" Av. harəz- "to discharge, send out; to filter," hərəzaiti "releases, shoots;" cf. Skt. srj- "to let go or fly, throw, cast, emit, put forth;" Pali sajati "to let loose, send forth."
1) The evolution of the properties of a physical system which has
been disturbed and which regains its equilibrium condition
once the disturbing action has ceased. Relaxation is the response of the
system to the perturbation. The time required by the system to regain
its condition of minimum energy is called the
→ relaxation time.
Verbal noun of → relax.
Fr.: temps de relaxation
The characteristic length of time that is required for a system undergoing → relaxation to move to its equilibrium state. If the system follows an exponential law G = G0 exp(-t / τ), the relaxation time is the time required for G to obtain the fraction 1/e of its initial value G0.
Fr.: système relaxé
P.p. from relax, → relaxation.
Fr.: relaxation résonnante
A process whereby stellar orbit relaxation can be dramatically enhanced in orbits in a nearly Keplerian star cluster close to a → massive black hole (MBH). This process can modify the angular momentum distribution and affect the interaction rates of the stars with the MBH more efficiently than non-resonant relaxation. In the standard relaxation picture, each encounter is random and uncorrelated, so stars undergo a random walk. Relaxation is driven by the diffusion of energy which then leads to angular momentum transfer. However, in a stellar cluster around a MBH, each star will be on a Keplerian orbit, which is a fixed ellipse in space. The orbits of two nearby stars will thus exert correlated torques on one another, which can lead to a direct resonant evolution of the angular momentum. Since resonant relaxation increases the rate of angular momentum scattering, stars reach highly eccentric orbits more rapidly where they can become → extreme mass ratio inspiral (EMRI)s (Rauch, K.P., Tremaine, S., 1996, arXiv:astro-ph/9603018; Gair J.R. et al. 2013, Living Rev. Relativity, 16, (2013), 7 http://www.livingreviews.org/lrr-2013-7, doi:10.12942/lrr-2013-7).
Fr.: relaxation violente
A process in which a dynamical system made up of many objects (star cluster, galaxy cluster) rapidly relaxes from a chaotic initial state to a quasi-equilibrium. | 0.819748 | 3.35975 |
Until his death this month at the age of 91, James Van Allencontinued to do work that had fascinated him since childhood and made him aleading figure of America's Space Age.
Van Allen spent a lifetime exploring the universe, and ismost famous for discovering the radiationbelts circling Earth which now bear his name.
In what would be his last paper, he explored a subject thathits somewhat closer to home: The likelihood of an asteroid colliding with Earth.
The research, published in this month's American Journalof Physics, details how the likelihood of such an event is enhanced by thegravitational pull between the two bodies.
The research shouldn't raise concern about possiblecollisions though, said Dave Tholen, an astronomer at the University of Hawaii. "It can happen, but I wouldn't worry about it. Weare actively discovering near-Earth asteroids and computing their orbits tomonitor the situation."
Tholen saidastronomers are intensely focused these days on an asteroid called Apophis,which is set to pass less than 24,000 miles from Earth on April 13, 2029. Van Allen's paper, which detailshow scientists estimating the probability of a collision should take Earth'sgravitational pull into account, could help researchers calculate whether theasteroid will become a threat.
Colleagues say this and other examples of Van Allen's workare remarkable not only for what he found, but also because of the simpleexperimental designs he employed.
"He really showed that by focusing on the fundamentalquestion and designing simple instruments, you could reveal things about natureyou wouldn't have imagined," said Ed Stone, a physics professor at theCalifornia Institute of Technology.
When the American team launched its first satellite,Explorer 1, into space, Van Allen had the prescience to attach a self-designedradiation detector to it. While the team didn't manage to beat the Russians intospace, his instrument sent back data giving the first evidence of thedonut-shaped ringscircling the Earth.
Working to the end
Frank McDonald, Senior Research Scientist at the University of Maryland, was a post-doctoral student at the University of Iowa during Van Allen's early days there. He worked with him onso-called "rockoons," rockets attached to balloons, which measuredspace radiation even before Explorer 1 went up.
McDonald says the recent paper on asteroids, which hedescribes as more educational than revolutionary, is evidence of Van Allen'scommitment to teaching.
"He was an outstanding mentor, and one of his missions inlife was training students," McDonald said. In addition to teaching science,Van Allen also taught students to be savvy fundraisers for it. "You learnedthat when you wanted to get something from a group, to go in with a statement alreadywritten about what you wanted--whenever I was in D.C., he always urged me tovisit the Office of Naval Research."
That Van Allen would still be publishing into his ninetiescomes as no surprise to McDonald. "You're talking to somebody who just turned81 and comes in every day, so it doesn't surprise me at all. I couldn't imaginehim not doing it and not having him there ten years ahead of me," he said. "And this is a heck of a lot more fun than retiring to Florida. We're still seeing things we neverexpected to see."
- U.S. Space Pioneer James Van Allen Dies at 91
- The Top 10 Space Imaginations at Work
- Daily Space Trivia | 0.837607 | 3.635185 |
When I was at elementary school, my teacher told me that matter exists in three possible states: solid, liquid and gas. She neglected to mention plasma, a special kind of electrified gas that’s a state unto itself. We rarely encounter natural plasma, unless we’re lucky enough to see the Northern lights, or if we look at the Sun through a special filter, or if we poke our head out the window during a lightning storm, as I liked to do when I was a kid. Yet plasma, for all its scarcity in our daily lives, makes up more than 99 per cent of the observable matter in the Universe (that is, if we discount dark matter).
Plasma physics is a rich and diverse field of enquiry, with its own special twist. In some areas of science, intellectual vitality comes from the beauty of grand theories and the search for deep underlying laws – as shown by Albert Einstein’s account of gravity in general relativity, or string theorists’ attempt to replace the Standard Model of subatomic particles with tiny oscillating strands of energy. The study of plasmas also enjoys some remarkably elegant mathematical constructions, but unlike its scientific cousins, it’s mostly been driven by its applications to the real world.
First, though, how do you make a plasma? Imagine heating up a container full of ice, and watching it pass from solid, to liquid, to gas. As the temperature climbs, the water molecules get more energetic and excitable, and move around more and more freely. If you keep going, at something like 12,000 degrees Celsius the atoms themselves will begin to break apart. Electrons will be stripped from their nuclei, leaving behind charged particles known as ions that swirl about in the resulting soup of electrons. This is the plasma state.
The connection between blood and ‘physical’ plasma is more than mere coincidence. In 1927, the American chemist Irving Langmuir observed that the way plasmas carried electrons, ions, molecules and other impurities was similar to how blood plasma ferries around red and white bloodcells and germs. Langmuir was a pioneer in the study of plasmas; with his colleague Lewi Tonks, he also discovered that plasmas are characterised by rapid oscillations of their electrons due to the collective behaviour of the particles.
Another interesting property of plasmas is their capacity to support so-called hydromagnetic waves – bulges that move through the plasma along magnetic field lines, similar to how vibrations travel along a guitar string. When Hannes Alfvén, the Swedish scientist and eventual Nobel prizewinner, first proposed the existence of these waves in 1942, the physics community was skeptical. But after Alfvén delivered a lecture at the University of Chicago, the renowned physicist and faculty member Enrico Fermi came up to him to discuss the theory, conceding that: ‘Of course such waves could exist!’ From that moment on, the scientific consensus was that Alfvén was absolutely correct.
One of the biggest motivators of contemporary plasma science is the promise of controlled thermonuclear fusion, where atoms merge together and release intense but manageable bursts of energy. This would provide an almost limitless source of safe, ‘green’ power, but it’s not an easy task. Before fusion can occur here on Earth, the plasma must be heated to more than 100 million degrees Celsius – about 10 times hotter than the centre of the Sun! But that’s not even the most complicated bit; we managed to reach those temperatures and beyond in the 1990s. What’s worse is that hot plasma is very unstable and doesn’t like to stay at a fixed volume, which means that it’s hard to contain and make useful.
Attempts to achieve controlled thermonuclear fusion date back to the early 1950s. At the time, research was done secretly by the United States as well as the Soviet Union and Great Britain. In the US, Princeton University was the fulcrum for this research. There, the physicist Lyman Spitzer started Project Matterhorn, where a secret coterie of scientists tried to spark and contain fusion in a figure-8-shaped device called a ‘stellarator’. They didn’t have computers, and had to rely only on pen and pencil calculations. While they didn’t solve the puzzle, they ended up developing ‘the energy principle’, which remains a powerful method for testing the ideal stability of a plasma.
Meanwhile, scientists in the Soviet Union were developing a different device: the ‘tokamak’. This machine, designed by the physicists Andrei Sakharov and Igor Tamm, employed a strong magnetic field to corral hot plasma into the shape of a donut. The tokamak was better at keeping the plasma hot and stable, and to this day most of the fusion research programmes rely on a tokamak design. To that end, a consortium of China, the European Union, India, Japan, Korea, Russia and the US has joined together to construct the world’s largest tokamak reactor, expected to open in 2025. However, in recent years there’s also been a renewed enthusiasm for stellarators, and the world’s largest opened in Germany in 2015. Investing in both routes to fusion probably gives us our best chance of ultimately attaining success.
Plasma is also entangled with the physics of the space around Earth, where the stuff gets carried through the void on the winds generated in the upper atmosphere of the Sun. We’re lucky that the Earth’s magnetic field shields us from the charged plasma particles and damaging radiation of such solar wind, but our satellites, spacecraft and astronauts are all exposed. Their capacity to survive in this hostile environment relies on understanding and accommodating ourselves to the quirks of plasma.
In a new field known as ‘space weather’, plasma physics plays a role similar to that of fluid dynamics in terrestrial, atmospheric conditions. I’ve devoted much of my research to something called magnetic reconnection, where the magnetic field lines in the plasma can tear and reconnect, which leads to a rapid release of energy. This process is believed to power the Sun’s eruptive events, such as solar flares, although detailed comprehension remains elusive. In the future, we might be able to predict solar storms the way that we can forecast bad weather in cities.
Looking backward, not forward, in space and time, my hope is that plasma physics will offer insights into how stars, galaxies and galaxy clusters first formed. According to the standard cosmological model, plasma was pervasive in the early Universe; then everything began to cool, and charged electrons and protons bound together to make electrically neutral hydrogen atoms. This state lasted until the first stars and black holes formed and began emitting radiation, at which point the Universe ‘reionised’ and returned to a mostly plasma state.
Finally, plasmas help to explain some of the most spectacular phenomena we’ve observed in the remotest regions of the cosmos. Take far-away black holes, massive objects so dense that even light can’t escape them. They’re practically invisible to direct observation. However, black holes are typically encircled by a rotating disk of plasma matter, which orbits within the black hole’s gravitational pull, and emits high-energy photons that can be observed in the X-ray spectrum, revealing something about this extreme environment.
It’s been an exciting journey for me since the days I thought that solids, liquids and gases were the only kinds of matter that mattered. Plasmas still seem rather exotic, but as we learn to exploit their potential, and widen our view of the cosmos, one day they might seem as normal to us as ice and water. And if we ever achieve controlled nuclear fusion, plasmas might be something we can no longer live without.
This Idea was made possible through the support of a grant from the Templeton Religion Trust to Aeon. The opinions expressed in this publication are those of the author and do not necessarily reflect the views of the Templeton Religion Trust.
Funders to Aeon Magazine are not involved in editorial decision-making, including commissioning or content-approval.
This article was originally published at Aeon and has been republished under Creative Commons. | 0.861674 | 3.947713 |
Last night, following a tip from SkyandTelescope.com, I pointed my binoculars to Gamma Leonis and found Vesta, the second largest asteroid in our solar system. Vesta is currently so bright, that under dark enough skies it can be seen with the naked eye. In the city, though, binoculars or a telescope are required. If you’re keen, you can join me watching it move from night to night by following the diagrams below, which were generated in Stellarium. Note that these directions are written from the point of view of my home in Pretoria.
- Start by finding Mars. Go outside at about 10pm, and face North. If you don’t have a clear view of the Northern part of the sky, move till you find somewhere that does! Mars appears about halfway up the sky (although this is a well-studied optical illusion – it’s actually more like a third of the way up!) as a bright, distinctly reddish-orange star. It is very hard to miss. If you’re uncertain, look at it through your binoculars. It should immediately look different to the other stars – bright, steady, colourful, and visible as a tiny disc (normal stars will still look like points). Once you have Mars, scan towards the right until you find the constellation Leo (The Lion). Leo has a distinctive sickle shape, representing the lion’s head. Most of the surrounding constellations are quite faint, so Leo should not be hard to find.
- Once you’ve identified Leo, home in on the upside down sickle-shape (In the northern hemisphere, it’s the right way up), life up your binoculars and find Gamma Leonis (identified by its traditional name, Algieba, on the chart below). Through the binoculars, this star will be revealed to be two stars near to each other. You will also be able to see Vesta, although since asteroids aren’t very large, it will look like any other star through your binoculars (or even the largest of amateur telescopes). To identify Vesta, proceed to Step 3
Algieba and it’s companion normally appear as two stars. However, Vesta shows up as a third, so that they form a triangle, as seen below. By observing from night to night, you will see Vesta moving. This, in fact, was how asteroids were first discovered – as stars which seemed to move amongst their neighbours so rapidly that the change could be seen from day to day! Below, I show the views from last night and tonight (17 and 18 February, both at 10:00 pm). These charts represent approximately the view as seen through my 10×50 binoculars. | 0.892752 | 3.792422 |
Dr. Dagomar Degroot, Georgetown University
The world is warming, and it is warming fast. According to satellites and weather stations, Earth's average annual temperature will smash the instrumental record this year, likely by around 0.1° C. Last year, global temperatures broke the record by around the same amount. That may not seem impressive, but consider this: temperatures have climbed by about 0.1° C per decade since the 1980s. In just two years, therefore, our planet catapulted two decades into a hotter future.
Global climate change on this scale, with this speed, is unprecedented in the history of human civilization. Yet that history has still coincided with other, smaller but still impressive changes in Earth's climate. Humans may have played a minor role in some of these changes. The key culprits, however, were often violent explosions on Earth that coincided with periods of unusual solar activity. The most dramatic climate changes usually involved global cooling, not warming. The consequences for communities and societies around the world could be profound, in ways that offer lessons for our fate in a changing climate.
One of the coldest periods in the history of human civilization started in the early sixth century CE. Growth rings imprinted in the bark of trees suddenly narrow around 536 CE, and again around 541 CE. This narrowing reveals that trees practically stopped growing as Northern Hemisphere temperatures plunged by as many as 3°C, relative to long-term averages.
Other scientific "proxy" sources that responded to past climate changes reveal the same trend. A large team of interdisciplinary scholars, led by Ulf Büntgen, recently concluded that 536 CE was the first year of a "Late Antique Little Ice Age" - not to be confused with the better-known Little Ice Age of the early modern period - that chilled the Northern Hemisphere and perhaps the globe until 660 CE.
What could have caused this cooling? Cosmogenic isotopes tell us that solar activity had been falling for more than a century, as the sun gradually entered a "grand solar minimum." But that does not explain why Earth's climate changed so profoundly, and so abruptly, in the early sixth century CE.
Scientists now believe that ice cores containing traces of volcanic ash provide compelling evidence for a remarkable series of major eruptions, in 536, 540, and 547 CE. Big volcanic eruptions in the tropics can cool the Earth by releasing sunlight-scattering sulphur into the atmosphere. Trade winds swirling up from the equator bring this sulphur into both hemispheres, which ultimately creates a global volcanic dust veil. When eruptions happen in quick succession, Arctic sea ice can expand dramatically. Since bright sea ice reflects more sunlight than water, the Earth cools in response, which of course leads to more sea ice, more cooling, and so on.
Catastrophic volcanic eruptions, coinciding as they did with a prolonged decline in solar activity, may well have released enough aerosols into the atmosphere to usher in a much cooler climate. Yet sixth-century layers in Greenlandic ice cores may also suggest a very different, and even more exotic, culprit for climatic cooling.
Somehow, microscopic marine organisms of a kind normally found near tropical coasts ended up in ice layers that correspond to 536 and 538 CE. Layers dating from 533 CE also hold nickle and tin, substances that rarely appear in Greenlandic ice. Both metals are common in comets, however.
A team of scientists led by Dallas Abott recently concluded that dust from the tail of Halley's Comet may have started cooling the Earth as early as 533 CE. By reconstructing the past orbits of the comet, scientists discovered that it made a particularly close pass around the Sun in 530 CE. At around that time, Chinese astronomers recorded a remarkably bright comet in the night sky.
Earth regularly passes through debris left in the wake of Halley's Comet, and that debris might have been especially dense in the 530s and 540s. Meteor showers, therefore, may well have left cooling dust in the atmosphere, and metals in the ices of Greenland.
Tidal forces created by the gravity of a massive object - such as the Sun - can easily fragment cometary nuclei, most of which are collections of rubble left over from the primordial solar system. Dust released by such a breakup can dramatically brighten a comet. Perhaps that is what Chinese scientists witnessed in 530 CE, as Halley's Comet swung around the Sun.
According to Abbott and her coauthors, a piece of the comet may then have collided with Earth, launching sea creatures high into the atmosphere. Melted metal and gravity anomalies in the Gulf of Carpentaria off Australia suggest that an impact happened there sometime in the first millennium CE. At around the same time, aboriginal Australians etched symbols into caves that may well have represented comets.
It may well be that an extraordinary confluence of extraterrestrial impacts and volcanic eruptions, coinciding with a gradual fall in solar activity, chilled the Earth in the 530s and 540s CE. These dramatic environmental changes naturally astonished contemporary writers. In 536 CE, Procopius of Caesarea, a major scholar of the Eastern Roman Empire, wrote that the “sun gave forth its light without brightness, like the moon.” According to John of Ephesos, “there was a sign in the sun the like of which had never been seen and reported before in the world . . . The sun became dark and its darkness lasted for one and a half years."
A Syrian chronicler recorded that "The earth and all that is upon it quaked; and the sun began to be darkened by day and the moon by night." Chinese astronomers lost sight of Canopus, one of the brightest stars in the night sky. If there was a dust veil, it may well have been thick enough to obscure the heavens, whatever its origins.
Cassiodorus, a Roman statesman in the service of the Ostrogoths, wrote perhaps the most striking descriptions of the changes in Earth's atmosphere. "Something coming at us from the stars," he explained, had led to a "blue colored sun," a dim full moon, and a "summer without heat." Amid "perpetual frosts" and "unnatural drought," plants refused to grow and "the rays of the stars have been darkened." The cause, to Cassiodorus, must be high in the atmosphere, for "things in mid-space dominate our sight," and the "heat of the heavenly bodies" could not penetrate what seemed like mist.
Of course, we must guard against the assumption that observers such as Cassiodorus or Procopius simply recorded what they saw in the natural world. Descriptions of environmental calamities in ancient, medieval, and even early modern texts can be allegorical, representing social, not environmental developments. Still, many authors wrote eerily similar accounts of the real environmental upheavals in the 530s CE. To the modern eye, that of Cassiodorus in particular may seem to add evidence for a cometary cause of contemporary cooling.
As temperatures plummeted and plants withered, communities around the world suffered. Scientists have examined pollen deposits that reveal sharp drops in the extent of cultivated land across Europe. Shorter growing seasons probably led to food shortages and famines that emptied once-thriving villages. Archaeological evidence suggests, for example, that Swedes abandoned most of their population centers in the sixth century, which were then swallowed by forests. Swedish survivors apparently created new towns in far smaller numbers, in upland areas removed from their former dwelling places.
Famines may have had particularly severe consequences across the densely populated Mediterranean. In 533 CE, just as cometary dust may have started entering Earth's atmosphere, the emperor of the Eastern Roman Empire, Justinian I, embarked on a costly campaign to restore the Western Empire. His subsequent wars in the Mediterranean, combined with a war against the Sassanid Empire that erupted in 540 CE, drew precious resources from the imperial countryside. As growing seasons declined, the demands of war compounded food shortages for millions of imperial citizens. Starvation spread through the empire, but worse was to come.
Malnutrition reduces fat-storing cells that produce the hormone leptin, which plays a key role in controlling the strength of the human immune system. In the sixth century, food shortages therefore weakened immune systems on a grand scale, leaving millions of people more vulnerable to disease. Those who survived famines also migrated to new towns or cities, increasing the likelihood that those infected with diseases would spread them.
Unfortunately for the inhabitants of what was left of the Roman Empire, Yersinia pestis, the pathogen behind the bubonic plague, was about to make its first appearance in Europe. From 541 to 542 CE, the “Plague of Justinian” swept through both the Western and Eastern halves of the Roman Empire, killing as many as fifty million people. In a warmer, more stable climate, the death toll may well have been far lower.
Not surprisingly, Justinian's campaign to retake the Western Empire stalled after the early 530s CE, although the reunified Roman Empire did reach its maximum extent in the 550s CE. Imperial resources were stretched thin, however, and European kingdoms reversed most of the new conquests soon after Justinian's death.
Climatic cooling probably had cultural consequences, too. There are signs, for example, that religious activity surged across Scandinavia as temperatures plunged. In times of crisis, devout Scandinavians offered gold to their gods in a way we might find counterinuitive: by burying it. Dating these underground hoardes is tricky, but it seems that Scandinavians buried most of them in the sixth century CE. These burials contributed to a gold shortage in Scandinavia that would endure for centuries.
The great oral traditions of Norse mythological poetry also date from the sixth century. Most people have heard of Ragnarök: the "twilight of the gods" that ends with the Earth incinerated and reborn. Fewer have come across the concept of Fimbulvetr, the "mighty winter" that heralds the final battle of the gods.
The Prose Edda, a thirteenth-century transcription of Norse mythology, describes Fimbulvetr in vivid detail. “Then snow will drift from all directions," the Edda predicts. "There will then be great frosts and keen winds. The sun will do no good. There will be three of these winters together and no summer between.” According to the Poetic Edda, a collection of poems also committed to writing in the thirteenth century, “The sun turns black . . . The bright stars vanish from the sky.”
These precise descriptions of an apocalyptic winter have no parallel in other religious texts or mythical traditions. Instead, they echo the sixth-century reports of Cassiodorus, Procopius, and other astonished observers of real environmental transformations. Scandinavians fleeing their homes amid catastrophic cooling may well have felt like they were living through a preview of the apocalypse.
The trauma caused by sixth-century environmental changes may therefore be imprinted on Norse mythology. Ideas of a new world in the wake of Ragnarök may also reflect the consequences of real events, such as the new settlements and cultures that emerged amid climatic cooling.
Can these ancient calamities offer any lessons for our warmer future? Perhaps. They suggest, for example, that complex, densely populated societies, far from being insulated from the effects of climate change, may actually be most at risk. When populations brush up against the carrying capacity of agricultural land, sudden environmental shifts can be catastrophic. In these situations, societies already embroiled in resource-draining wars could be particularly vulnerable. The consequences of sixth-century cooling hint, also, that responses to even short-lived climatic upheavals can profoundly alter cultures in ways that endure for centuries, or even millennia.
Ancient societies, of course, have little similarity to our own. Yet their struggles in periods of dramatic climate change may still shed some light on our prospects in a warming world. To understand the future, we would be well served to look back at the distant past.
Abbott, Dallas H., Dee Breger, Pierre E. Biscaye, John A. Barron, Robert A. Juhl, and Patrick McCafferty. "What caused terrestrial dust loading and climate downturns between AD 533 and 540?." Geological Society of America Special Papers 505 (2014): 421-438.
Arjava, Antti. "The mystery cloud of 536 CE in the Mediterranean sources." Dumbarton Oaks Papers 59 (2005): 73-94.
Axboe, Martin. "The year 536 and the Scandinavian gold hoards." Medieval Archaeology 43 (1999).
Gräslund, Bo, and Neil Price. "Twilight of the gods? The ‘dust veil event’ of AD 536 in critical perspective." Antiquity 86:332 (2012): 428-443.
Hamacher, Duane W. "Comet and meteorite traditions of Aboriginal Australians." Encyclopaedia of the History of Science, Technology, and Medicine in Non-Western Cultures (2014): 1-4.
Widgren, Mats. "Climate and causation in the Swedish Iron Age: learning from the present to understand the past." Geografisk Tidsskrift-Danish Journal of Geography 112:2 (2012): 126-134. | 0.843306 | 3.772514 |
Study of atmospheric 'froth' may help GPS communications
When you don't know how to get to an unfamiliar place, you probably rely on a smart phone or other device with a Global Positioning System (GPS) module for guidance. You may not realize that, especially at high latitudes on our planet, signals traveling between GPS satellites and your device can get distorted in Earth's upper atmosphere.
Researchers at NASA's Jet Propulsion Laboratory, Pasadena, California, in collaboration with the University of New Brunswick in Canada, are studying irregularities in the ionosphere, a part of the atmosphere centered about 217 miles (350 kilometers) above the ground that defines the boundary between Earth and space. The ionosphere is a shell of charged particles (electrons and ions), called plasma, that is produced by solar radiation and energetic particle impact.
The new study, published in the journal Geophysical Research Letters, compares turbulence in the auroral region to that at higher latitudes, and gains insights that could have implications for the mitigation of disturbances in the ionosphere. Auroras are spectacular multicolored lights in the sky that mainly occur when energetic particles driven from the magnetosphere, the protective magnetic bubble that surrounds Earth, crash into the ionosphere below it. The auroral zones are narrow oval-shaped bands over high latitudes outside the polar caps, which are regions around Earth's magnetic poles. This study focused on the atmosphere above the Northern Hemisphere.
"We want to explore the near-Earth plasma and find out how big plasma irregularities need to be to interfere with navigation signals broadcast by GPS," said Esayas Shume. Shume is a researcher at JPL and the California Institute of Technology in Pasadena, and lead author of the study.
If you think of the ionosphere as a fluid, the irregularities comprise regions of lower density (bubbles) in the neighborhood of high-density ionization areas, creating the effect of clumps of more and less intense ionization. This "froth" can interfere with radio signals including those from GPS and aircraft, particularly at high latitudes.
The size of the irregularities in the plasma gives researchers clues about their cause, which help predict when and where they will occur. More turbulence means a bigger disturbance to radio signals.
"One of the key findings is that there are different kinds of irregularities in the auroral zone compared to the polar cap," said Anthony Mannucci, supervisor of the ionospheric and atmospheric remote sensing group at JPL. "We found that the effects on radio signals will be different in these two locations."
The researchers found that abnormalities above the Arctic polar cap are of a smaller scale - about 0.62 to 5 miles (1 to 8 kilometers) - than in the auroral region, where they are 0.62 to 25 miles (1 to 40 kilometers) in diameter.
Why the difference? As Shume explains, the polar cap is connected to solar wind particles and electric fields in interplanetary space. On the other hand, the region of auroras is connected to the energetic particles in Earth's magnetosphere, in which magnetic field lines close around Earth. These are crucial details that explain the different dynamics of the two regions.
To look at irregularities in the ionosphere, researchers used data from the Canadian Space Agency satellite Cascade Smallsat and Ionospheric Polar Explorer (CASSIOPE), which launched in September 2013. The satellite covers the entire region of high latitudes, making it a useful tool for exploring the ionosphere.
The data come from one of the instruments on CASSIOPE that looks at GPS signals as they skim the ionosphere. The instrument was conceived by researchers at the University of New Brunswick.
"It's the first time this kind of imaging has been done from space," said Attila Komjathy, JPL principal investigator and co-author of the study. "No one has observed these dimensional scales of the ionosphere before."
The research has numerous applications. For instance, aircraft flying over the North Pole rely on solid communications with the ground; if they lose these signals, they may be required to change their flight paths, Mannucci said. Radio telescopes may also experience distortion from the ionosphere; understanding the effects could lead to more accurate measurements for astronomy.
"It causes a lot of economic impact when these irregularities flare up and get bigger," he said.
NASA's Deep Space Network, which tracks and communicates with spacecraft, is affected by the ionosphere. Komjathy and colleagues also work on mitigating and correcting for these distortions for the DSN. They can use GPS to measure the delay in signals caused by the ionosphere and then relay that information to spacecraft navigators who are using the DSN's tracking data.
"By understanding the magnitude of the interference, spacecraft navigators can subtract the distortion from the ionosphere to get more accurate spacecraft locations," Mannucci said. | 0.841682 | 3.772611 |
A pair of UMBC physicists used data from the Hubble telescope to enhance understanding about black hole science. In doing so, they provided the first evidence of what happens when plasma jets collide.
In a study recently published in the journal Nature, Eileen Meyer and Markos Georganopoulos reported on how the beguiling beams of radiation interact as they stream away from a black hole at 98 percent of the speed of light.
Over the last 25 years, the Hubble photographed a “supermassive black hole,” which sits at the center of the eliptical galaxy 3C 264, located 260 million light years away from Earth.
Meyer and Georganopoulos found evidence of one of the jets, which assumed a “string of pearls” structure as it streamed away from the black hole. When the photos were assembled into the astronomical equivalent of a time-lapse movie, they found a second, faster jet colliding at the rear.
This produced a “shock collision,” which made the particles a lot brighter, and faster. Astronomers initially said it looked like the jet was moving seven times faster than the speed of light, but that turned out to be an opitcal illusion.
Scientists have hypothesized that the jets of plasma got their energy as a result of faster jets running into slower ones, but evidence has remained elusive. The Baltimore team was the first to confirm that it happened.
“Something like this has never been seen before in an extragalactic jet,” said Meyer, who is finishing up a postdoc at Baltimore’s Space Telescope Science Institute — which serves as the science operations center for Hubble — before moving to UMBC.
The collision will continue over the next few decades. Along with rubbernecking at the crash, astronomers will be looking at how the particles dissipate out into space.
“This will allow us a very rare opportunity to see how the kinetic energy of the collision is dissipated into radiation,” she said.-30-
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By Mark Brown, Wired UK
Astronomer David Nesvorny from the Southwest Research Institute in Texas believes that the solar system might have once contained a fifth gigantic planet, which was ejected deep into the galaxy in a moment of cosmic turmoil.Kuiper belt — the icy-cold ring of asteroids beyond Neptune — and by studying the historical fingerprints left on the craters of the Moon, Nesvorny was able to piece together clues about our solar system’s adolescence.
He found that a dynamic instability, which occurred about 600 million years into the solar system’s life, greatly affected the orbit of our giant planets and scattered smaller bodies. Some moved into the Kuiper belt and others traveled inwards, marking their course as impacts on the Moon and planets.
But that scenario has a flaw. Slow changes in Jupiter’s orbit would have had a large effect on the orbits of the terrestrial planets. All hell would have broken lose, and the Earth could have collided with Mars or Venus. Something had to change.
“Colleagues suggested a clever way around this problem,” says Nesvorny in a press release. Instead of a slow movement, Jupiter’s orbit could have quickly changed, which would have altered the outer solar system but been less harmful to the inner planets.
Unfortunately, this too caused problems. Computer simulations, ran thousands of times, showed that Jupiter’s quick jump had the intended effect, but Uranus or Neptune was always knocked out of the solar system. “Something was clearly wrong,” Nesvorny explains.
So perhaps, instead, the early solar system could have had five giant planets instead of four. By plopping an additional giant planet with a mass similar to that of Uranus or Neptune the simulation worked as planned. Jupiter jumped into place, the inner planets remained unharmed and the outer planets stayed behind.
“The possibility that the solar system had more than four giant planets initially, and ejected some, appears to be conceivable in view of the recent discovery of a large number of free-floating planets in interstellar space, indicating the planet ejection process could be a common occurrence,” says Nesvorny in the release.
Image: Southwest Research Institute [full-resolution version] | 0.850708 | 3.715161 |
- Title: Astrometric Detection of Giant Planets Around Nearby M Dwarfs: The Gaia Potential
- Authors: A. Sozzetti, P. Giacobbe, M. G. Lattanzi, G. Micela, R. Morbidelli, and G. Tinetti
- First Author’s Institution: INAF – Osservatorio Astrofisico di Torino, Pino Torinese, Italy
The Gaia Mission
It’s not too hard to measure the position of a star on the sky: just look up. But the projection of a star’s position on the sky only provides a position in two dimensions (astronomers typically use right ascension and declination, the astronomical analogues to longitude and latitude, respectively). What remains is the distance to the star. To measure such distances, astronomers observe the position of a star at multiple epochs. As the Earth moves around the Sun, the relative positions of stars on the sky change due to a change in viewing angle, a phenomenon known as parallax.
Measuring parallaxes (distances) to the stars is important throughout astrophysics. To determine stellar masses, stellar positions in a color-absolute magnitude diagram (such as the H-R diagram) are analyzed; absolute magnitudes can only be ascertained by measuring the observed brightness (or flux) and distance. Without information about the distances to stars, we would be unable to estimate masses of stars. Other physical properties of stars (metallicity, radius, surface gravity) are also distance-dependent. To understand stars in our galaxy well, we must understand the distances to them very well. The study of measuring positions of stars in the sky (including such distances) is called astrometry.
In the early 1990s, the European Space Agency launched the Hipparcos satellite (named after the father of astrometry). This telescope measured parallaxes for about 100,000 stars. These parallaxes allowed us to measure distances for all stars within 100 parsec (and bright stars within 1000 pc!) to within 10%.
Hipparcos has been incredibly important for astronomers. The original data release has been cited more than 1600 times! As impressive as this mission has been, it’s now 20 years old: we can do better. In this case, “better” is manifested as the Gaia mission. Slated to launch on November 20, Gaia will observe more than 1 billion stars, observing the position of each one 70 times over 5 years. For the nearest stars, this will allow distances to be measured to 0.001%, and will measure distances accurate to ~10% for stars as far away as the galactic center, 10,000 parsec away!
Gaia, by producing observations of a billion stars across our side of the galaxy, will usher in a revolution in astrometry and galactic science. The authors of today’s paper, however, focus on another potential application: planet hunting. As we’ve noted previously, astrometry is most sensitive for detecting giant planets a few AU from their host stars, where both radial velocity and imaging surveys are incomplete. These authors note that recent studies suggest around 6.5±3.0% of M dwarf stars (stars smaller than 0.6 solar masses) host Jupiter-mass planets, and set out to determine if Gaia could detect such companions.
As a planet and star orbit their center of mass, both objects trace ellipses on the sky. Careful observations of a star over many epochs allow this ellipse to be separated from the parallactic motion Gaia was designed to detect. Since it will probe each star in its sample 50 times, Gaia should collect enough data for these two movements to be easily separated. To test this, the authors injected artificial Jupiter-mass planets around each of the 3150 M dwarf stars within 33 parsec. They assigned random orbital elements for each planet’s orbital parameters and let the planet orbit the star, then “observed” its position on the sky 50 times, estimating the expected performance of the Gaia pipeline. Finally, the authors compared the parameters of the planets detected by the Gaia software to the known parameters of the planets they injected.
By testing their injected planets with the Gaia pipeline, the authors find they recover the majority of these fake companions. They detect excess variability in the parallactic signal due to orbital motion around 85% of the sample!. As expected (right), they are most successful at finding Jupiters around the most nearby stars (where the parallactic signal is large and easily separable) and the smallest stars (where the Jupiters are comparatively massive, so the elliptic signal is large and easily separable). For more than 80% of these stars, they find they can measure the planet’s mass to within 10%.
Not all M dwarfs host giant planets, but Sozzetti et al. estimate that, from the 3150 most nearby M dwarfs, Gaia will detect about 100 new giant planets. Moreover, from the sample of M dwarfs within 100 pc, the authors suggest Gaia will find 2500 new planets. Unlike Kepler, which generally only provides estimates of planet radii and orbital periods, many of the Gaia planets will have their full orbits determined. These will be the first planets detected by astrometry (although a few planets detected via other methods have been confirmed by astrometry. The Gaia mission will also allow for unprecedented analyses of planet formation, evolution, dynamics, and populations around the most common types of stars in our galaxy. | 0.911695 | 4.095782 |
I know that if you exceed orbital velocity, you will never fall-back to the planet. My question is not about orbits. It's about brute-force propulsion to achieve altitude. I'm using an intentionally slow velocity to help illustrate my point.
Imagine I have a rocket with very efficient fuel storage. My rocket can store enough energy to accelerate to 100kph shortly after leaving the ground, and continue to maintain that speed (100kph) for a very long period of time.
My rocket just goes straight up. It doesn't try to enter an orbit. As it leaves the atmosphere, it can throttle-back because there's no air resistance. As it continues to gain altitude in inter-planetary space, it can throttle-back even more because Earth's gravitational influence diminishes with distance. It just maintains enough throttle to continue moving away from Earth at 100kph.
At some point, Earth's gravitational influence would be moot, as other bodies (Jupiter, Sun), would gain relative influence. Eventually, far outside the solar system, even the Sun's influence would be insignificant.
My rocket never achieved escape velocity, but it sure did escape.
Assuming that my fuel supply could last long enough, and I wasn't concerned about travel time, could this method allow my rocket to "leave" without achieving escape velocity? | 0.871788 | 3.002818 |
- Open Access
High energy neutrinos to see inside the Earth
Earth, Planets and Space volume 62, pages205–209(2010)
The new chances offered by elementary particles as probes of the internal structure of our planet are briefly reviewed, by paying particular attention to the case of high energy neutrinos. In particular, the new results concerning the shadow of mountains on vτ flux at Pierre Auger Observatory is briefly discussed, and moreover the possibility to use the tail of atmospheric neutrinos to probe the core/mantle transition region is just sketched.
The exploration of the internal structure of the Earth by using elementary particles is what can be now denoted as Geoparticle Physics. The idea is quite old and started with the determination of the thickness of snow layers on a mountain by means of atmospheric muons (George, 1955). The first application of this method was realized to search for unknown burial cavities in the Chephren’s pyramid (Alvarez et al., 1970), but only in recent times it has entered in a phase of first production of quantitative estimates and data, with a general renewed vitality which makes these times very attractive.
This new discipline can be split in two main research fields essentially defined by the nature of the probe: cosmic radiation at high energy (muons or neutrinos) or low energy neutrinos produced by radioactive decays inside the Earth (geo-neutrinos). Hereafter we will focus our attention on the high energy radiation and in particular on the possibility to use neutrinos to probe the very inner part of our planet.
High Energy (HE) neutrino detection is one of the most promising research lines in astroparticle physics. Neutrinos are in fact one of the main components of the cosmic radiation in the high energy regime, and although their fluxes are uncertain and depend on the specific production process, their detection would provide valuable information concerning the sources and the acceleration mechanism in extreme astrophysical environments. For this reason the experimental community is undertaking a relevant effort to construct giant Neutrino Telescopes (NT’s). From this point of view, after the first generation of telescopes has proved the viability of the Cerenkov detection technique under deep water (Balkanov et al., 1999) and ice (Ahrens et al., 2002) by detecting atmospheric neutrinos, one is probably on the verge of the first detections at the IceCube (Ahrens et al., 2004) telescope, being completed at the South Pole, and possibly at the smaller ANTARES (Spurio, 2006) telescope under construction in the Mediterranean. Additionally, ANTARES as well as NESTOR (Aggouras et al., 2006) and NEMO (Migneco et al., 2008) are involved in R&D projects aimed at the construction of a km3 NT in the deep water of the Mediterranean sea, coordinated in the European network KM3NeT (Katz, 2006). In this very exciting scientific framework it has been proposed the idea to use neutrinos, which are elusive particles, to probe the very internal part of the Earth.
In order to use HE neutrinos for geological purposes one has two possible choices: either using an almost known neutrino flux, like in the case of atmospheric neutrinos, or to use the unknown, but expected isotropic and more energetic, extragalactic flux (see Fig. 1). In these two cases the neutrino energies involved are very different and thus consequently the lengths probed (see Fig. 2). The less energetic atmospheric neutrinos, since they have a larger interaction length and can cross distances in rock of the order or larger than the Earth radius, can be used to study the mantle/core structure of our planet. On the other side, UHE neutrinos, like the extragalactic component, may only cross much shorter distances and thus can be used to probe superficial structures (Earth-skimming particles).
2. Neutrino Sensitivity to Matter Distribution
In order to understand how the number of charged lepton events at a km3 NT depends on the density of matter crossed by HE neutrinos, let us remind that the events rate can be written, neglecting for simplicity the energy dependence, as
where dΦ/dΩ (expressed in s−1 m−2 sr−1 GeV−1) represents the solid angle distribution of neutrino flux, Aeff ≈ ρσN A Veff = Veff/λ stands for the effective area, and Ωd is the integration solid angle. Since the effective detector volume is Veff = Apl, where Ap is the detector area projected against the neutrino direction and l is the portion of the neutrino path to which the detector is sensitive, the events rate can be rewritten as
An interesting example of how sensitive is the neutrino interaction probability to matter distribution is provided by Ultra High Energy vτ’s which can be indirectly detected via their production of the charged tau’s. Such leptons, once produced by charged current weak interaction, can emerge from surface if they have crossed few tens of km’s in rock only (Earth-skimming events), see Fig. 2. The detection of UHE Earth-skimming neutrinos can be performed both from giant array detectors like Pierre Auger Observatory (PAO) or from km3 NT. Concerning PAO performances, they have been studied in a series of papers (Miele et al., 2006; Góra et al., 2007). As shown in Fig. 3, by starting from a Digital Elevation Model (DME) of the area nearby PAO one can compute, track by track hitting the experimental set up, the amount of rock really crossed. In Ref (Góra et al., 2007) the distribution of arrival directions of quasi horizontal and up-going Earth-skimming events have been computed, respectively. As one can see from Figs. 4 and 5 the effect of the matter distribution is very tiny, but not vanishing, and would require many years to be detected at PAO Surface Detector. A situation even worse is expected at the PAO Fluorescence Detector where a duty cycle of almost 10% is at work. Nevertheless, an enhancement in the event rate, due to matter effect, is present, and it can be interpreted as a naive neutrino radiography of superficial geological structures. The prediction for the event rate are function of the unknown UHE neutrino flux which, in Góra et al. (2007), has been assumed as the conservative Waxman-Bahcall limit. Of course a more optimistic flux could increase very much the number of events. In this concern the matter effect can also be used as a way to increase the detection performances of the apparatus for UHE neutrinos which are a relevant component of the extragalactic radiation and carry information about the acceleration mechanisms in extreme astrophysical environments. This topic was extensively studied in Cuoco et al. (2007) and Borriello et al. (2008) where the effect of matter distributed nearby an under-sea NT is evaluated for the three proposed Mediterranean sites. More recently the possibility to use the tail of atmospheric neutrinos to make a scan of the internal part of the Earth, namely the core/mantle transition zone, has been envisaged in Ref. (González-García et al., 2008). According to the authors a ten years running time of IceCube would allow to disentangle between a really homogeneous radial density profile and the already well-known Preliminary Reference Earth Model (PREM) (Dziewonski and Anderson, 1981). In particular in Fig. 6 the ratio between the expected event rates for the PREM and the homogeneous model, for different energy thresholds, are reported. As it is clear from the plots, increasing the energy threshold, namely by using more energetic neutrinos, the ratio becomes more and more sensitive to the proper radial density profile. Unfortunately, by using more energetic particles one loses statistics since their flux decreases with a power law, thus it is crucial to find a good compromise between sensitivity to the relevant physical quantity (PREM) and proper statistics required in order to make a statement with a good level of confidence.
Geoparticle physics is a fast growing new discipline which aims to export the large amount of know-how produced in a mature sector like elementary particle physics to geophysics. This idea has already good example of application especially in the use of muons. However, neutrinos either produced by the decay of radioactive nuclei (low energy v—typically denoted as geo-neutrinos) or more energetic ones, like the atmospheric-v can give new and fascinating insights of the very deep interior of our planet. Unfortunately, due to the very elusive nature of these particles, in order to collect proper statistics one needs enormous detectors of at least km3 scale, which however are planned and even under-construction in some cases. Hence, in the near future by using these giant apparatus we will be able to see in practice the potentiality of this new technique.
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Cite this article
Borriello, E., De Lellis, G., Mangano, G. et al. High energy neutrinos to see inside the Earth. Earth Planet Sp 62, 205–209 (2010). https://doi.org/10.5047/eps.2009.06.002
- High energy cosmic rays
- Earth radial density profile | 0.837102 | 3.875973 |
NASA has established a new body to oversee its ongoing efforts to detect and track near-Earth objects (NEOs). The Planetary Defence Coordination Office (PDCO) will control all NASA-funded projects to identify and analyse any asteroids or comets that pass near Earth's orbit around the Sun.
And that's a lot of sky traffic to supervise. Since NASA-funded surveys started to watch for asteroids and comets in 1988, more than 13,500 NEOs have been discovered, and that tally is increasing at a rate of approximately 1,500 per year. Most of these we don't hear about, but some definitely come a little close for comfort.
"Asteroid detection, tracking and defence of our planet is something that NASA, its interagency partners, and the global community take very seriously," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate in Washington. "While there are no known impact threats at this time, the 2013 Chelyabinsk super-fireball and the recent 'Halloween Asteroid' close approach remind us of why we need to remain vigilant and keep our eyes to the sky."
Astronomers have already located more than 90 percent of NEOs larger than 1 kilometre long (3,000 feet) via telescopic surveys of the sky, with the focus now shifting to smaller objects of around 140 metres (450 feet) in length, or about the size of a football field. These NEOs, though significantly smaller than the larger objects, could still pose a considerable risk in the event of an impact, and NASA has given itself the task of detecting 90 percent of this smaller class by the end of the decade.
NASA's new defence office comes at a time when awareness of the potential threats posed by NEOs is perhaps higher than ever. Last year, a consortium of more than 100 scientists and artists joined forces to raise awareness for Asteroid Day, a global movement designed to educate the public on the risks of NEO impacts and ramp up pressure on governments to increase efforts (much like the PDCO).
But this kind of popular awareness has a downside too, with viral hoaxes announcing threats when there aren't any, obliging NASA to step in and clarify the situation.
Fortunately, the PDCO will help set the record straight in the future – in addition to monitoring potentially hazardous objects, the office will work to keep the public informed of the latest NEO science data, issuing notices on things like close passes and warning when NASA has detected potential impacts.
In the event of the latter, the PDCO will work with other US government bodies including the Federal Emergency Management Agency (FEMA) and international counterparts to help coordinate responses to any actual impact threats.
"The formal establishment of the Planetary Defence Coordination Office makes it evident that the agency is committed to perform a leadership role in national and international efforts for detection of these natural impact hazards, and to be engaged in planning if there is a need for planetary defence," said Lindley Johnson, NASA's newly named Planetary Defence Officer (and sorry, but that job title is way cooler than yours).
The long-term goal in planetary defence is to develop Armageddon-style technological measures to deflect or redirect NEOs bound for a collision with Earth. One such method could be NASA's Asteroid Redirect Mission, a robot-based concept that aims to create a kind of gravity tractor, using the mass of a boulder collected from an asteroid to divert it from its original orbit path.
If such emergency measures don't pan out in the event of an impact threat, NASA would work with FEMA and its counterparts to inform them on precise impact timing, location, and effects to help with response operations.
"FEMA is dedicated to protecting against all hazards," said FEMA administrator Craig Fugate, "and the launch of the coordination office will ensure early detection and warning capability, and will further enhance FEMA's collaborative relationship with NASA."
We feel safer already. | 0.856376 | 3.341456 |
Many curious members of the human race would one day personally visit Mars the fourth farthest planet from the Sun. Despite the lethal levels of radiation, the almost complete lack of oxygen and extremely low temperatures, Mars was and remains one of the main contenders for the title of most studied man-made object in the Solar system. While earthly minds are trying to come up with the most effective and cheapest way to get to this, though harsh, but extremely interesting world, the Rover “Curiosity” started its work in 2012 and decided to pour some oil on the fire of human curiosity, providing us with a new panorama of the Martian landscape.
Received new photos of Mars
Little Martian world completely covered with rust, is, in fact, the only full-fledged planet of the Solar system, the surface of which constantly travel through the earth’s robots. However, despite all our advances in the field of creating automated workstations, capable of operating without human intervention, we are still powerless in the face of weather conditions that exist today on Mars. Their impact leads to the existence on the red planet those parts of the landscape and watching them was the main purpose of the Rover “Curiosity”, designed by NASA.
In order to make the most detailed images of the surface of the fourth planet in the history of astronomy, the Rover took a powerful on-Board camera successfully fulfilled the dream of every astrophotograph, showing the Martian landscape with a resolution of 1.8 billion pixels. One of sent Rover photo shows the area of Glen Torridon mountains are sharp and the Central part of Gale crater, where Curiosity landed in August 2012, according to the portal newatlas.com. During its work, the Rover drove 19 kilometers, while examining the surrounding area and making lots of pictures, including 360-degree panoramas and a number of selfies.
Because of the relatively large distance that separates the observer from Mars, the image data can reach the us much more slowly than could be desired. So, in order to obtain a single high quality panorama of the planet, scientists were required to unite in one more than 1000 images, which were made by the Rover for four days from noon until two o’clock in the afternoon Martian time. Such a strict condition to be fulfilled in order to ensure that the lighting on all images was the same for convenience of the further installation before sending it to the Ground. It is known that all the pictures were taken with a special lens built into the Rover, while an additional lens device was used to create the panorama at a lower resolution almost 650 million pixels, capturing the deck of the Rover and robotic arm, visible below. | 0.801463 | 3.091209 |
LAWRENCE — Can’t find your house keys? Frustrated by that sock that seemed to disappear during laundry?
Don’t feel so bad. It turns out scientists have a hard time detecting some 95 percent of the matter and energy that make up the universe, according to NASA.
Indeed, the nature of “dark matter” and “dark energy” might be the most outstanding riddle in science. The presence of dark matter and dark energy has been established in cosmology through gravitational effects on scales from the size of a galaxy to that of the universe. But, neither the Standard Model of physics nor Einstein’s General Relativity can account for dark matter and dark energy. According to experts, “beyond the standard model” physics are needed to resolve properties of dark matter and dark energy at the microscopic level.
Now, a research team from the University of Kansas has earned a three-year, $750,000 grant from the U.S. Department of Energy EPSCoR State/National Lab Partnership program as well as $150,000 in matching funds from the state of Kansas to hunt new ways to detect and understand dark matter and dark energy.
Particle theorists K.C. Kong and Ian Lewis, and astrophysicists and cosmologists Mikhail Medvedev and Sergei Shandarin will partner with scientists at DOE’s Fermi National Accelerator Laboratory and Argonne National Laboratory to carry out the investigation.
“Most of the universe is a question mark,” said Lewis, assistant professor of physics & astronomy at KU. “Two of the biggest puzzles in fundamental physics are dark matter and dark energy — a whole bunch of matter in the universe we don’t understand. These are ‘known unknowns,’ or big questions out there we know we don’t understand, and those are what we are going after.”
The KU team will work with scientists running supercolliders like the Large Hadron Collider and neutrino detectors at Fermilab, and also generate computer models to guide experiments looking for indications of dark matter and dark energy.
“The group is proposing a comprehensive program that includes very sensitive detectors and accelerators, and state-of-the-art numerical simulations in conjunction with a deep understanding of the complex and exotic dark matter possible interactions and dark energy effects,” said Hume Feldman, professor and chair of physics & astronomy at KU. “Since there are many possible scenarios involved, it is absolutely necessary to explore a wide variety of cosmic energy scales and intensity frontiers, each sensitive to different possible configurations and scenarios of the dark sector.”
At Fermilab, KU particle physicists Lewis and Kong will propose new ways to search for dark matter using instruments designed to measure neutrinos, subatomic particles with almost no mass.
“Experimentalists will hopefully perform these searches,” Lewis said.
The KU physicist said equipment designed to look for neutrinos is well-suited to look for dark matter as well.
“Neutrinos are very weak interacting particles, and their experiments are built to see these rare events anyway, and you could look for dark matter events with those same experiments,” he said. “We’ll use the same detectors, but try to find a new way to use them. One idea of using the neutrino detectors is that some dark matter could accumulate in the sun and it could annihilate itself into different forms of dark matter that comes streaming out of the sun — and hopefully, you could see that with a neutrino detector.”
In the meantime, Medvedev and Shandarin will partner with Argonne National Laboratory on computer simulations of the cosmos, called “N-body simulations,” to model astrophysical forces under a variety of dark-matter scenarios.
The project, which builds on expertise and strengths in KU’s Department of Physics & Astronomy, could push forward scientific understanding of the fundamental makeup of the cosmos.
“I’m describing it as theoretical physics phenomenology,” Lewis said. “My colleague K.C. Kong and I were interested in seeing how beyond-standard-model physics could show up in experimental data, and what could that tell us about fundamental problems like dark matter. We’re trying to bridge pie-in-the-sky theory with actual experiments, we're kind of experts on that. Medvedev and Shandarin are experts in things like the cosmic web and space physics and what you can do with dark energy.”
Along with the investigation carried out with the KU faculty researchers, the new grant will provide funds for graduate and undergraduate KU students and postdoctoral researchers to study dark matter and dark energy.
“We’re budgeted for graduate students and postdocs in the DOE-EPSCoR grant,” Lewis said. “There are also matching funds from the state of Kansas, including additional funding for graduate and undergraduate students. We also support their travel to Fermilab and Argonne National Laboratory to work with our lab partners.”
Photo: This image shows the distribution of dark matter, galaxies and hot gas in the core of the merging galaxy cluster Abell 520. Credit: NASA | 0.835322 | 3.630094 |
Can there be livable habitats on Titan? A paper just presented at the Division for Planetary Sciences meeting in Cambridge makes the case that several key ingredients of life may be present on the huge moon. Titan possesses liquid reservoirs, organic molecules and the needed energy sources. The question: is the environment simply too cold? With temperatures down to -178 degrees Celsius (-289 degrees Fahrenheit), the chemical reactions to produce life would move ponderously, but perhaps not too slowly to function.
The first images from beneath Titan’s cloud cover made the speculation all the more intense. Methane shows up in clouds as well as in liquid form at the surface at these temperatures, and may provide the analog for Earth’s water in a life-sustaining hydrological cycle. Moreover, there are hints of ice volcanoes that imply the existence of large amounts of water (mixing with ammonia) not far below the surface.
So where does it all lead? From a Southwest Research Institute (San Antonio, TX) news release:
“One promising location for habitability may be hot springs in contact with hydrocarbon reservoirs,” says lead author David H. Grinspoon, a staff scientist in the SwRI Space Science and Engineering Division. “There is no shortage of energy sources [food] because energy-rich hydrocarbons are constantly being manufactured in the upper atmosphere, by the action of sunlight on methane, and falling to the surface.”
The team focuses on acetylene, which could be used by organisms in reaction with hydrogen to release the energy that could power a metabolism. That this is speculative is obvious, but if you’re looking for bizarre forms of life, consider Grinspoon’s other comment:
“The energy released could even be used by organisms to heat their surroundings, helping them to create their own liquid cryoenvironments,” says Grinspoon. “In environments that are energy-rich but liquid-poor, like the near-surface of Titan, natural selection may favor organisms that use their metabolic heat to melt their own watering holes.”
Centauri Dreams‘ take: It has always been natural to look for life in more or less terrestrial terms, but the recent study of extreme environments is showing us even on Earth how wide the parameters for life may be. It’s fascinating to realize that we now must include the satellites of outer planets, like Jupiter’s Europa, Ganymede and Callisto, along with Titan and even poor, battered Enceladus in the list of possibilities. Hard to imagine, but who knows what we may someday find on places as exotic as Triton.
Image: This processed image from Cassini’s Aug. 22, 2005, flyby of Titan reveals mid-latitudes on the moon’s Saturn-facing side. Is it conceivable that a living ecosystem may exist at the moon’s frigid temperatures? Credit: NASA/JPL/Space Science Institute.
And if we do start finding such life forms, it’s going to give a huge impetus to the belief that life is all but ubiquitous in the universe. Whether or not any significant percentage of it is intelligent is another question (Centauri Dreams leaves for philosophers the attempt to define ‘intelligence’). But a galaxy crowded with living worlds is a vision that awaits only the first confirmed sightings of terrestrial planets to go front and center. We should have such sightings within a decade, if not less. Keep your eye on the Kepler mission.
The paper “Possible Niches for Extant Life on Titan in Light of Cassini-Huygens Results” was presented today at the Division for Planetary Sciences meeting in Cambridge. | 0.878903 | 3.883514 |
I’m a bit late with this post, as this supernova has been in the news a bit over the past week. In this new paper in Nature Astronomy, my colleagues and I presented a supernova that released so much energy that it seemingly had to have come from one of the most massive stars in the Universe. The supernova is SN2016aps, and we found it in the PanSTARRS survey 4 years ago, so I’m delighted to finally put these results out into the world. The study took a long time because it took so long for the supernova to fade enough that we could see its host galaxy!
The supernova spectrum showed narrow-ish hydrogen emission lines, telling us that the fast-expanding ejecta were colliding with slow-moving circumstellar gas, which must have been shed by the star in the final years before explosion. This intense collision allowed SN2016aps to convert its kinetic energy to radiation and become extremely luminous, but the total energy in radiation actually exceeded the kinetic energy of nearly all other supernovae! Thus the explosion itself, as well as the light released, must have been unusually powerful.
By modelling the slow fading over two years, we found that the circumstellar shell must have included several tens of solar masses of material, and the supernova itself likely had several tens more, for a total mass of 50-100 solar masses in this star! For comparison, most supernovae come from stars with less than 20 solar masses. To make such a massive and hydrogen rich star, the progenitor system may have initially comprised two stars in a binary, which merged when the more massive star reached a red supergiant phase.
Stars this massive are predicted to encounter a very rare process called the pair instability, which can cause violent pulsations ejecting the stellar envelope or even fully disrupt the star. This has been predicted since the 1960s, but it is unclear whether we have seen a real-world example before. Given the need for a both a huge mass and the ejection of the envelope soon before explosion, SN2016aps might be the best contender yet for a (pulsational) pair instability supernova. | 0.852193 | 3.735703 |
Advancing Basic Science for Humanity
Crowdsourcing the Universe: How Citizen Scientists are Driving Discovery
Legions of volunteer, amateur astronomers are turning their eyes to the sky thanks to online image portals and doing extraordinary science.
ASTRONOMERS ARE INCREASINGLY enlisting volunteer "citizen scientists" to help them examine a seemingly endless stream of images and measurements of the universe. These volunteers' combined efforts are having a powerful impact on the study of the cosmos.
Just last November, a citizen science project called Space Warps announced the discovery of 29 new gravitational lenses, regions in the universe where massive objects bend the paths of photons (from galaxies and other light sources) as they travel toward Earth. As cosmic phenomena go, the lenses are highly prized by scientists because they offer tantalizing glimpses of objects too distant, and dim, to be seen through existing telescopes, as well as key information on the lensing objects themselves.
The Space Warps' haul of lenses is all the more impressive because of how it was obtained. During an eight-month period, about 37,000 volunteers combed through more than 430,000 digital images in a huge, online photo library of deep space. Automated computer programs have identified most of the 500 gravitational lenses on astronomer’s books. However, computers failed to flag the 29 lenses the Space Warps volunteers spotted, speaking to unique skills we humans possess.
The Kavli Foundation spoke with three researchers, all co-authors of two papers published in the Monthly Notices of the Royal Astronomical Society describing the Space Warps findings. In our roundtable, the researchers discussed the findings and the critical role citizen science is playing in furthering astronomical discovery.
The participants were:
- Anupreeta More - is a project researcher at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) at the University of Tokyo. More is a co-principal investigator for Space Warps, a citizen project dedicated to identifying gravitational lenses.
- Aprajita Verma - is a senior researcher in the department of physics at the University of Oxford. Verma is also a co-principal investigator for Space Warps.
- Chris Lintott - is a professor of astrophysics and the citizen science lead at the University of Oxford. Lintott is a co-founder of Galaxy Zoo, a citizen science project in which volunteers classify types of galaxies, and the principal investigator for the Zooniverse citizen science web portal.
The following is an edited transcript of the roundtable discussion. The participants have been provided the opportunity to amend or edit their remarks.
The Kavli Foundation: Anupreeta and Aprajita, where did you get the idea — along with your co-principal investigator Phil Marshall of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University — to put volunteers to work on identifying gravitational lenses starting back in 2013?
ANUPREETA MORE: A few years ago, Chris Lintott gave a talk on citizen science at the Kavli Institute for Cosmological Physics in Chicago, where I was working at the time. It got me thinking about a lens search by citizen scientists.
APRAJITA VERMA: For Phil Marshall and I, Space Warps grew out of Galaxy Zoo. Soon after Galaxy Zoo launched, I started to look at some of the galaxies that were being posted on the Galaxy Zoo user forum that had potential lensed features surrounding them. This was a great by product of the core Galaxy Zoo project. However, we realized that to find these incredibly rare sources, which are often confused with other objects, we really needed a tailored interface to efficiently find lenses. This grew into Space Warps.
TKF: Chris, Galaxy Zoo itself was inspired by Stardust@home, the first astronomy-based citizen science project in which people played an active role. Until then, citizen scientists were often computer owners who offered up free processing power on their devices to aid in machine-driven data analysis. Were you concerned when you started Galaxy Zoo in 2007 that it would be hard to attract volunteers?
CHRIS LINTOTT: Since Stardust@home involved people looking at images of a comet's dust grains brought back by NASA's Stardust space probe, we thought "Well, if people are willing to look at dust grains, then surely they'd be happy to look at our galaxies!" But that turned out to be almost beside the point. As we've done many of these citizen science projects over the years, we've discovered it's not the quality of the images that matter. After all, our galaxies aren't typically beautiful. They are not the Hubble Space Telescope shots that you’d expect to find on the front page of the New York Times. Our galaxies are often fuzzy, little, enigmatic blobs. The Space Warps images are pretty, but again they're not the kind of thing you would sell as a poster in the gift shop at the Kennedy Space Center.
It's actually the ideas that get people excited. I think Space Warps and Galaxy Zoo have been successful because they have done a great job of explaining to people why we need their help. We're saying to them: "Look, if you do this simple task, it allows us to do science." This idea is best shown by Planet Hunters, a citizen science project that searches for exoplanets in data from NASA's Kepler spacecraft. Users are looking at graphs for fun. But because the idea is the discovery of exoplanets, people will put up with looking at data.
VERMA: Gravitational lenses allow us to look at objects, such as very distant galaxies, that are fainter and in much more detail than with the telescopes we have now. It's enabling the kind of science we'll be routinely doing with extremely large telescopes in the future.
MORE: That's right. Something unique about gravitational lensing is that it acts like a natural telescope and allows us to study some really faint, distant galaxies which we wouldn't get to study otherwise. We're seeing these distant galaxies in the early stages of their life cycle, which helps us understand how galaxies evolve over time.
Also, in a gravitational lens system, it's possible for us to study the properties of the foreground galaxies or galaxy groups that are gravitationally lensing the background sources. For example, we can measure the mass of these foreground galaxies and also study how mass is distributed in them.
Anupreeta More's research specialty is gravitational lensing and its applications in measuring the mass distributions of matter and dark matter in galaxies, galaxy clusters and the universe as a whole. (Credit: Anupreeta More)
TKF: Space Warps and other citizen science projects flourish because computer programs sometimes struggle at identifying features in data. Why do computers have trouble spotting the characteristic arc or blobby shapes of gravitational lenses that humans can?
MORE: The problem is that these arc-like images of distant galaxies can have very different shapes and profiles. The process of lensing magnifies these galaxies' images and can distort them. Also, these distant galaxies emit light at different wavelengths and can appear to have different colors. Furthermore, there are structures in these galaxies that can change the shape of the arcs.
VERMA: Also, lots of spiral galaxies have bluish spiral arms that can look like lenses. We call these objects "lens impostors" and we find many more of these false positives compared to rare, true gravitational lenses.
MORE: All these differences make it difficult to automate the process for finding lenses. But human beings are very good at pattern recognition. The dynamic range that our eyes and our brains offer is much greater than a computer algorithm.
LINTOTT: Another thing to bear in mind in astronomy, particularly in Space Warps, is that we're often looking for rare objects. A computer's performance depends very strongly on how many examples you have to "train" it with. When you're dealing with rare things, that's often very difficult to do. We can't assemble large collections of hundreds of thousands of examples of gravitational lenses because we don't have them yet.
Also, people — unlike computers — check beyond what we are telling them to look for when they review images. One of the great Space Warps examples is the discovery of a "red ring" gravitational lens. All the example lenses on the Space Warps site are blue in color. But because we have human classifiers, they had no trouble noticing this red thing that looks a little like these blue things they've been taught to keep an eye out for. Humans have an ability to make intuitive leaps like that, and that's very important.
VERMA: I echo the point that it's very difficult to program diversity and adaptability into any computer algorithm, whereas we kind of get it for free from the citizen scientists! [Laughter]
Aprajita Verma researches galaxy formation and evolution, and is particularly interested in understanding the nature of galaxies at high redshift. She is also involved with two major next generation astronomy telescopes, the European Extremely Large Telescope (E-ELT) and the Large Synoptic Survey Telescope (LSST). (Credit: Aprajita Verma)
TKF: Aprajita and Anupreeta, what’s the importance of the red ring object Chris just mentioned that the Space Warps community discovered in 2014 and has nicknamed 9io9?
VERMA: This object was a really exciting find, and it's a classic example of something we hadn't seen before that citizen scientists quickly found. We think that inside the background galaxy there's both an active black hole, which is producing radio wave emissions, as well as regions of star-formation. They're both stretched by the lensing into these spectacular arcs. It's just a really nice example of what lensing can do. We're still putting in further observations to try and really understand what this object is like.
MORE: In this particular case with 9io9, there is the usual, main lensing galaxy, but then there is also another, small, satellite galaxy, whose mass and gravity are also contributing to the lensing. The satellite galaxy produces visible effects on the lensed images and we can use this to study its mass distribution. There are no other methods besides gravitational lensing which can provide as accurate a mass estimate for galaxies at such great distances.
TKF: Besides 9io9, citizen astrophysicists have turned up other bizarre, previously unknown phenomena. One example is Hanny’s Voorwerp, a galaxy-size gas cloud discovered in 2007 in Galaxy Zoo. More recently, in 2015, Planet Hunters spotted huge decreases in the starlight coming from a star called KIC 8462. The cause could be an eclipsing swarm of comets; another, albeit unlikely, possibility that has set off rampant speculation on the Internet is that an alien megastructure is blocking light from the star. Why does citizen science seemingly work so well at making completely unexpected discoveries?
LINTOTT: I often talk about the human ability to be distracted as a good thing. If we're doing a routine task and something unusual comes along, we stop to pay attention to it. That's rather hard to develop with automated computer systems. They can look for anomalies, but in astronomy, most anomalies are boring, such as satellites crossing in front of the telescope, or the telescope's camera malfunctions.
However, humans are really good at spotting interesting anomalies like Hanny's Voorwerp, which looks like either an amorphous green blob or an evil Kermit the Frog, depending on how you squint at it. [Laughter] The point is, it's something you want to pay attention to.
The other great thing about citizen science is that the volunteers who find these unusual things start to investigate and become advocates for them. Citizen scientists will jump up and down and tell us professional scientists we should pay attention to something. The great Zooniverse discoveries have always been from that combination of somebody who's distracted and then asks questions about what he or she has found.
TKF: Aprajita and Chris, you are both working on the Large Synoptic Survey Telescope (LSST). It will conduct the largest-ever scan of the sky starting in 2022 and should turn up tons of new gravitational lenses. Do you envision a Space Warps-style citizen science project for LSST?
VERMA: Citizens will play a huge role in the LSST, which is a game-changer for lensing. We know of about 500 lenses currently. LSST will find on the order of tens to hundreds of thousands of lenses. We will potentially require the skill that citizen scientists have in looking for exotic and challenging objects.
Also, LSST’s dataset will have a time dimension. We're really going to make a movie of the universe, and this will turn up a number of surprises. I can see citizen scientists being instrumental in a lot of the discoveries LSST will make.
LINTOTT: One thing that's challenging about LSST is the sheer size of the dataset. If you were a citizen scientist, say, who had subscribed to receive text message alerts for when objects change in the sky as LSST makes its movie of the universe, then you would end up with a couple of billion text messages a night. Obviously that would not work. So that means we need to filter the data. We'll dynamically decide whether to assign a task to a machine or to a citizen scientist, or indeed to a professional scientist.
Chris Lintott develops a range of citizen science projects, with a particular focus on galaxy formation. (Credit: Chris Lintott)
TKF: Chris, that comment reminds me of something you said to TIME magazine in 2008: "In many parts of science, we're not constrained by what data we can get, we're constrained by what we can do with the data we have. Citizen science is a very powerful way of solving that problem.” In this era of big data, how important do you all see citizen science being moving forward, given that computers will surely get better at visual recognition tasks?
LINTOTT: In astronomy, if you're looking at things that are routine, like a spiral galaxy or a common type of supernova, I think the machines will take over. They will do so having been trained on the large datasets that citizen scientists will provide. But I think there will be citizen involvement for a long while and it will become more interesting as we use machines to do more of the routine work and filter the data. The tasks for citizen scientists will involve more varied things — more of the unusual, Hanny's Voorwerp-type of discoveries. Plus, a lot of unusual discoveries will need to be followed up, and I'd like to see citizen scientists get further into the process of analysis. Without them, I think we're going to end up with a pile of interesting objects which professional scientists just don't have time to deal with.
VERMA: We have already seen a huge commitment from citizen scientists, particularly those who've spent a long time on Galaxy Zoo and Space Warps. For example, on Space Warps, we have a group of people who are interested in doing gravitational lens modeling, which has long been the domain of the professional astronomer. So we know that there's an appetite there to do further analysis with the objects they’ve found. I think in the future, the citizen science community will work hand-in-hand with professional astronomers.
LINTOTT: Galaxy Zoo has a new lease on life, actually. We just added in new galaxies from a telescope in Chile. These galaxies are relatively close and their images are beautiful. It's our first proper look at the southern sky, so we have an all-new part of the universe to explore. It gives users a chance to be the first to see galaxies — if they get over to Galaxy Zoo quickly!
VERMA: For Space Warps, we are expecting new data and new projects to be online next year.
MORE: Here in Japan, we are leading an imaging survey called the Hyper Suprime-Cam (HSC) survey and it's going to be much larger and deeper than what we have been looking at so far. We expect to find more than an order of magnitude increase in the number of lenses. Currently, we are preparing images of the candidates from the HSC survey and hope to start a new lens search with Space Warps soon.
Arguably the most famous citizen astrophysicist discovery, Hanny's Voorwerp—Dutch for Hanny's Object—is seen here by the Hubble Space Telescope in 2011. The Voorwerp is a gas cloud the size of galaxy and appears green due to glowing oxygen. A Dutch schoolteacher, Hanny van Arkel, spotted the object while volunteering for Galaxy Zoo. Credit: NASA, ESA, W. Keel (University of Alabama), and the Galaxy Zoo Team)
TKF: Is it the thrill of discovery that entices most citizen scientist volunteers? Some of the images in Galaxy Zoo have never been seen before because they were taken by a robotic telescope and stored away. Volunteers therefore have the chance to see something no one else ever has.
MORE: That discovery aspect is personal. I think it's always exciting for anyone.
LINTOTT: When we set up Galaxy Zoo, we thought it would be a huge motivation to see something that's yours and be the first human to lay eyes on a galaxy. Exploring space in that way is something that until Galaxy Zoo only happened on "Star Trek." [Laughter]
In the years since, we've also come to realize that citizen science is a collective endeavor. The people who've been through 10,000 images without finding anything have contributed to the discovery of something like the red ring galaxy just as much as the person who happens to stumble across it. You need to get rid of the empty data as well. I've been surprised by how much our volunteers believe that. It's a far cry from the traditional, public view of scientific discovery in which the lone genius makes the discovery and gets all the credit.
VERMA: We set out with Space Warps for citizen scientists to be part of our collaboration and they've really enabled us to produce important findings. They've inspired us with their dedication and productivity. We've learned from our analysis that basically anyone who joins Space Warps has an impact on the results. We are also especially grateful for a very dedicated, diligent group that has made most of the lens classifications. We look forward to welcoming everyone back in our future projects!
—Adam Hadhazy, Winter 2016 | 0.880219 | 3.098776 |
Mars may be our nearest neighboring planet, but with the conventional rockets we have right now, it will still take us about five months to get there. And that simply isn’t satisfactory. There has got to be a way to make that trip shorter.
There are currently a few ongoing projects working towards this end. There’s the controversial propellant-less EM Drive which no one can explain for certain how it works, but has somehow passed its initial test.
And then there’s Charles Bombardier’s space train concept — the Solar Express that is envisioned to travel at approximately 1,864 miles per second, or 1% the speed of light, and cut travel time to Mars from a few months to just 2 days.
There’s also Positron Dynamics co-founder and CEO Ryan Weed’s antimatter-powered rocket that will make use of matter’s annihilation property — hit matter with its anti-matter counterpart to annihilate each other and generate pure energy that will be used to power the rocket and blast it into space with an accelerated speed that can enable travel to Mars in just a few weeks.
And now comes the latest bet: photonic propulsion — a concept that was explained by NASA scientist and University of California Physics Professor Philip Lubin in a recent video (posted below) released for NASA 360. It basically makes use of a beam of light for propulsion, hence the name photonic propulsion, for photons or visible light particles.
Lubin heads a team of scientists who has recently been given a $100,000 NASA Innovative Advanced Concepts (NIAC) grant to start planning and testing this photonic propulsion project that’s being called Directed Energy Propulsion for Interstellar Exploration or DEEP-IN.
To make the plan work, a laser array first needs to be placed in the Earth’s orbit. This orbiting laser array will then be used to push a solar sail. Much like a normal sail that catches wind to propel water vessels, a solar sail works the same way. Instead of wind, however, it catches light, and uses this to propel a space-bound probe — one that’s ideally ultralight (wafer-thin is how it’s being described), fuel-less, frictionless, and capable of travelling for a longer period of time at a speed that has so far been unattainable — 621 miles per second, or about 30% the speed of light.
While the concept sounds pretty much like another science fiction movie plot, Lubin says it’s not that far-fetched because we already have the technology. It just needs to be enhanced further. If successful, an umanned probe using photonic propulsion is expected to reach Mars in only 3 days, while a manned craft will take about a month — four months faster than any normal spacecraft can do at this time.
It’s a grand new idea, and it comes with a myriad of potential problems, of course. Primarily, there’s the challenge on how the probe would be able to decelerate when it reaches Mars. There’s also the certainty of encountering space debris and how to protect the craft from those. Then there’s ‘time dilation’, the concept that says that as one gets farther out in the universe, the slower time seems to pass. Plus there’s also the matter of how we can beam the information back to Earth.
All those problems aside, the idea that we have in our midst viable tech that can revolutionize space travel is quite an exciting one. Especially because it’s production is not expected to be at an exorbitant cost. By successfully making these solar sails, Mars will just be one among the many possible destinations. So, let’s all patiently wait and root for Lubin’s team to work their way towards the new age of space travel. | 0.84775 | 3.487532 |
Target: Rings and Moons
"Our interest in space has always mainly been focused on the possibility of extraterrestrial life. However, space, being endlessly mysterious, still poses many unanswered questions for scientists. Because of this, scientists have used the Cassini-Huygens satellite to already make many successful discoveries about Saturn, making the planet itself well-understood. However, its moons and rings remain relatively mysterious and the study of these secretive celestial bodies could help us learn more about both our own planet and the possibility of life in outer space. Therefore, the Cassini project should focus the satellite on observing Tethys, Enceladus, and Saturn's rings.
Water and atmosphere are necessities in supporting life. Water's quality of being a universal solvent and changing states in a narrow temperature range make it important in providing the energy that sustain organisms. The existence of an atmosphere is also crucial, because it protects the celestial body from excessive comet impact and radiation. Thus, it is logical to focus on analyzing celestial bodies that have such characteristic.
Enceladus' unique characteristics, which are surprisingly similar to those of Earth, suggest that the moon is an ideal candidate for further research. The most prominent feature is the internal salty ocean. The ocean lies beneath cyrovolcanoes, which are similar to Earth's geysers.The jets of water vapor emitted by the volcanoes are known to contribute to Enceladus' atmosphere. These factors contribute to scientists' claim of Enceladus as one of the best candidates for extraterrestrial life.
In addition to water and atmosphere, Saturn's rings possess additional qualities that resemble those of Earth. The rings contain water in addition to oxygen, which is one of the most vital elements for supporting human life. Moreover, the rings are known to possess not only and atmosphere, but also to have weather. The weather of Saturn is consisted of interaction between the planet and its rings. The rain from the rings seemingly quench the planet, which is very similar to the interaction on Earth. However, the atmosphere of Saturn peculiarly, rains not only water, but also diamonds. While these features may not directly prove the existence of life in the rings, further research on Saturn's rings can provide a better understanding of peculiar phenomenon such as diamond rain as well as of our own planet.
The further analysis of Tethys, Enceladus, and Saturn's rings would be highly fruitful to the general causes of the Cassini Project. Scientists would be able to better understand some of the many mysteries of this region of the solar system and also increase our chances of finding some evidence of extraterrestrial life, whether it has existed now or sometime in the past. By using the Cassini-Huygens satellite to focus on this area, scientists would increase their overall understanding of the solar system more compared to any other target." | 0.875509 | 3.549046 |
The same year that Galileo died in Florence, a premature baby was born to the Newton family in Lincolnshire. Isaac, as he was named, was a sickly child and picked on in school. The school bully, who also happened to be the smartest boy in school, once kicked Newton in the stomach. Newton fought back and beat the bully. He then proceeded to complete his victory by beating the boy in school. At age 18 he entered Trinity College and earned a B.A. degree in mathematics without much distinction.
During Newton’s studies in college, the Black Plague ravaged England and all students were sent home. Newton returned to Lincolnshire where the family lived in seclusion for about 18 months. During that time Newton conceived almost all of the ideas for which he is famous. These include the binomial theorem that is taught in high school algebra, the fundamentals of differential and integral calculus, which he called fluxions and inverse fluxions, a theory on color, that is, the spectrum that creates rainbows and an extension of his theory of gravity as being the force that keeps the moon in orbit around the earth.
Over the next twenty years Newton worked on his Mathematical Principles of Natural Philosophy, natural philosophy being the term then given to the laws of nature. Newton developed a mechanistic interpretation of all physical phenomena, a point of view that dominated physics until the early years of the Twentieth Century when the general theory of relativity and quantum mechanics were developed. However, Newton’s laws and theories, which have come to be called Newtonian or Classical Physics, still govern the ordinary world around us. They explain why cars stay on the roads, why roller coasters can go upside down, and why there are rainbows after a rain storm. The development of his theory of gravity led to a new field of study, celestial mechanics, which in turn advanced astronomy and the study of the cosmos.
It was Newton who first conceived of a satellite orbiting the earth. He did this by observing that a stone thrown from a high point makes an arc as it drops back to earth. He then imagined throwing the stone harder and harder, so that the arc was longer and longer until eventually the stone passed the curvature of the earth before it struck ground, thereby entering into orbit around the earth.
As a person, Newton wasn’t particularly pleasant and was often involved in controversy with his colleagues. He was the arch-type of the absent-minded professor, often forgetting to eat, comb his hair or even complete getting dressed in the morning. He had a cat, for whom he cut an opening in his door so the cat could come and go at her leisure. When the cat had kittens, Newton cut holes for each kitten. He was, however, aware of the achievements of those who came before him. He famously remarked “If I have seen further than others it is because I stood on the shoulders of giants.”
Newton is arguably one of the best-known scientists of all time. The names Newton and Einstein are linked in physics and just as almost everyone knows E=mc2 as the formula that converts mass to energy and vice versa, almost everyone is familiar with Newton’s laws of motion, particularly the Third Law, to every action there is an equal and opposite reaction.
It is safe to say that Newton is the giant on whose shoulders all physicists who followed stood. | 0.833537 | 3.374037 |
Hubble observes tiny galaxy with big heart
Nestled within this field of bright foreground stars lies ESO 495-21, a tiny galaxy with a big heart. ESO 495-21 may be just 3000 light-years across, but that is not stopping the galaxy from furiously forming huge numbers of stars. It may also host a supermassive black hole; this is unusual for a galaxy of its size, and may provide intriguing hints as to how galaxies form and evolve.
Located about 30 million light-years away in the constellation of Pyxis (The Compass), ESO 495-21 is a dwarf starburst galaxy—this means that it is small in size, but ablaze with rapid bursts of star formation. Starburst galaxies form stars at exceptionally high rates, creating stellar newborns of up to 1000 times faster than the Milky Way.
Hubble has studied the bursts of activity within ESO 495-21 several times. Notably, the space telescope has explored the galaxy's multiple super star clusters, very dense regions only a few million years old and packed with massive stars. These spectacular areas can have a huge impact on their host galaxies. Studying them allows astronomers to investigate the earliest stages of their evolution, in a bid to understand how massive stars form and change throughout the Universe.
As well as hosting the cosmic fireworks that are super star clusters, ESO 495-21 also may harbour a supermassive black hole at its core. Astronomers know that almost every large galaxy hosts such an object at its centre, and, in general, the bigger the galaxy, the more massive the black hole. Our home galaxy, the Milky Way, houses a supermassive black hole, Sagittarius A*, which is over four million times as massive as the Sun. ESO 495-21, also known as Henize 2-10) is a dwarf galaxy, only three percent the size of the Milky Way, and yet there are indications that the black hole at its core is over a million times as massive as the Sun—an extremely unusual scenario.
This black hole may offer clues as to how black holes and galaxies evolved in the early Universe. The origin of the central supermassive black holes in galaxies is still a matter of debate—do the galaxies form first and then crush material at their centres into black holes, or do pre-existing black holes gather galaxies around them? Do they evolve together—or could the answer be something else entirely?
With its small size, indistinct shape, and rapid starburst activity, astronomers think ESO 495-21 may be an analogue for some of the first galaxies to have formed in the cosmos. Finding a black hole at the galaxy's heart is therefore a strong indication that black holes may have formed first, with galaxies later developing and evolving around them.
The data comprising this image were gathered by two of the instruments aboard the NASA/ESA Hubble Space Telescope: the Advanced Camera for Surveys and already decommissioned Wide Field Planetary Camera 2/. | 0.830237 | 4.036479 |
When stars reach the end of their life cycle, many will blow off their outer layers in an explosive process known as a supernova. While astronomers have learned much about this phenomena, thanks to sophisticated instruments that are able to study them in multiple wavelengths, there is still a great deal that we don’t know about supernovae and their remnants.
For example, there are still unresolved questions about the mechanisms that power the resulting shock waves from a supernova. However, an international team of researchers recently used data obtained by the Chandra X-Ray Observatory of a nearby supernova (SN1987A) and new simulations to measure the temperature of the atoms in the resulting shock wave.
In a wave of media releases, the latest studies performed by NASA’s Fermi Gamma-ray Space Telescope are lighting up the world of particle astrophysics with the news of how supernovae could be the progenitor of cosmic rays. These subatomic particles are mainly protons, cruising along through space at nearly the speed of light. The rest are electrons and atomic nuclei. When they meet up with a magnetic field, their paths change like a bumper car in an amusement park – but there’s nothing amusing about not knowing their origins. Now, four years of hard work done by scientists at the Kavli Institute for Particle Astrophysics and Cosmology at the Department of Energy’s (DOE) SLAC National Accelerator Laboratory has paid off. There is evidence of how cosmic rays are born.
“The energies of these protons are far beyond what the most powerful particle colliders on Earth can produce,” said Stefan Funk, astrophysicist with the Kavli Institute and Stanford University, who led the analysis. “In the last century we’ve learned a lot about cosmic rays as they arrive here. We’ve even had strong suspicions about the source of their acceleration, but we haven’t had unambiguous evidence to back them up until recently.”
Until now, scientists weren’t clear on some particulars – such as what atomic particles could be responsible for the emissions from interstellar gas. To aid their research, they took a very close look at a pair of gamma ray emitting supernova remnants – known as IC 443 and W44. Why the discrepancy? In this case gamma rays share similar energies with cosmic ray protons and electrons. To set them apart, researchers have uncovered the neutral pion, the product of cosmic ray protons impacting normal protons. When this happens, the pion rapidly decays into a set of gamma rays, leaving a signature decline – one which provides proof in the form of protons. Created in a process known as Fermi Acceleration, the protons remain captive in the rapidly moving shock front of the supernova and aren’t affected by magnetic fields. Thanks to this property, the astronomers were able to trace them back directly to their source.
“The discovery is the smoking gun that these two supernova remnants are producing accelerated protons,” said lead researcher Stefan Funk, an astrophysicist with the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University in California. “Now we can work to better understand how they manage this feat and determine if the process is common to all remnants where we see gamma-ray emission.”
Are they little speedsters? You betcha. Every time the particle passes across the shock front, it gains about 1% more speed – eventually enough to break free as cosmic ray. “Astronauts have documented that they actually see flashes of light associated with cosmic rays,” Funk noted. “It’s one of the reasons I admire their bravery – the environment out there is really quite tough.” The next step in this research, Funk added, is to understand the exact details of the acceleration mechanism and also the maximum energies to which supernova remnants can accelerate protons.
However, the studies don’t end there. More new evidence of supernovae remnants acting like particle accelerators emerged during careful observational analysis by the Serbian astronomer Sladjana Nikolic (Max Planck Institute for Astronomy). They took a look at the composition of the light. Nikolic explains: “This is the first time we were able to take a detailed look at the microphysics in and around the shock region. We found evidence for a precursor region directly in front of the shock, which is thought to be a prerequisite of cosmic ray production. Also, the precursor region is being heated in just the way one would expect if there were protons carrying away energy from the region directly behind the shock.”
Nikolic and her colleagues employed the spectrograph VIMOS at the European Southern Observatory’s Very Large Telescope in Chile to observe and document a short section of the shock front of the supernova SN 1006. This new technique is known as integral field spectroscopy – a first-time process which allows astronomers to thoroughly examine the composition of the light from the supernova remnant. Kevin Heng of the University of Bern, one of the supervisors of Nikolic’s doctoral work, says: “We are particularly proud of the fact that we managed to use integral field spectroscopy in a rather unorthodox way, since it is usually used for the study of high-redshift galaxies. In doing so, we achieved a level of precision that far exceeds all previous studies.”
It really is an intriguing time to be taking closer looks at supernovae remnants – especially in respect to cosmic rays. As Nikolic explains: “This was a pilot project. The emissions we observed from the supernova remnant are very, very faint compared to the usual target objects for this type of instrument. Now that we know what’s possible, it’s really exciting to think about follow-up projects.” Glenn van de Ven of the Max Planck Institute for Astronomy, Nikolic’s other co-supervisor and an expert in integral field spectroscopy, adds: “This kind of novel observational approach could well be the key to solving the puzzle of how cosmic rays are produced in supernova remnants.”
Kavli Institute Director Roger Blandford, who participated in the Fermi analysis, said, “It’s fitting that such a clear demonstration showing supernova remnants accelerate cosmic rays came as we celebrated the 100th anniversary of their discovery. It brings home how quickly our capabilities for discovery are advancing.” | 0.885544 | 4.081093 |
Roy Kilgard, support astronomer and research assistant professor of astronomy, together with Trevor Dorn-Wallstein ’15 and Tyler Desjardin MA ’11, recently presented stunning new images of a spiral galaxy produced by combining data from more than 232 hours of observing time with NASA’s Chandra X-ray Observatory. Similar to the Milky Way, the galaxy is officially known as Messier 51 (M51) or NGC 5194, but nicknamed “the Whirlpool Galaxy.” Located about 30 million light years from Earth, its face-on orientation to Earth offers a perspective astronomers can never get of our own galaxy.
The image showing a vibrant purple swirl was presented June 3 at the 224th meeting of the American Astronomical Society in Boston, Mass. K.D. Kuntz of Johns Hopkins University was also a co-author.
The image also appeared as NASA’s Astronomy Picture of the Day on June 10.
Kilgard told Universe Today, “This is the deepest, high-resolution exposure of the full disk of any spiral galaxy that’s ever been taken in the X-ray.”
Chandra allowed the astronomers to uncover things that can only be detected in X-rays. According to the website for the Chandra observatory: “Most of the X-ray sources are X-ray binaries (XRBs). These systems consist of pairs of objects where a compact star, either a neutron star or, more rarely, a black hole, is capturing material from an orbiting companion star. The infalling material is accelerated by the intense gravitational field of the compact star and heated to millions of degrees, producing a luminous X-ray source. The Chandra observations reveal that at least ten of the XRBs in M51 are bright enough to contain black holes. In eight of these systems the black holes are likely capturing material from companion stars that are much more massive than the Sun.”
Observations have revealed that the Whirlpool Galaxy is in the process of merging with a smaller companion galaxy, visible in the upper left of the composite image. Researchers believe this is triggering waves of rapid star formation.
Also at the American Astronomical Society meeting, Nicole Arulanantham, a second-year graduate student in the Astronomy MA program, was awarded a Chambliss Medal, and astronomy major Ben Tweed ’13 presented a paper. Read more about it here. | 0.824482 | 3.46354 |
For more than eight hours last fall, the Chandra X-Ray Observatory stared at a nondescript galaxy 240 million light-years away. In that time, one of the detectors intercepted exactly four X-ray photons. It sounds like a meager harvest, but those four packets of energy helped astronomers realize that the galaxy contained a type of exploding star that had never been observed before.
Chandra, which is named for Nobel Prize-winning astrophysicist Subrahmanyan Chandrasekhar, who first calculated the ultimate fate of stars like our sun, is the largest and most sensitive X-ray telescope ever built. The spacecraft can produce full-color images of X-ray-emitting objects while measuring the intensity at each X-ray wavelength.
Stars, galaxies, and other astronomical objects all produce light, with a mix of wavelengths that depends on the object’s composition and temperature. Cool interstellar gas clouds, for example, emit primarily longer, infrared wavelengths. Medium-hot stars like our sun peak at visible wavelengths, while the hottest stars shine brightest in the ultraviolet. X-rays come from the hottest objects of all, such as clouds of gas between galaxies or the bands of gas spiraling into black holes.
Earth’s atmosphere absorbs X-rays, so X-ray astronomers must place their telescopes in space. The Chandra telescope was launched by the space shuttle Columbia in 1999 and is today operated by the Chandra X-Ray Center at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Chandra completes one orbit around Earth roughly every two and a half days. Its highly elliptical path takes it up to 83,000 miles away. Most of the time, this path keeps Chandra clear of the Van Allen belts, rings of radioactive particles encircling Earth, so the telescope has to shelter its instruments from the radiation for only a small portion of each orbit.
An optical telescope uses a large, curved-glass primary mirror to gather light, but X-rays would penetrate such a mirror’s reflective coating; an X-ray telescope’s mirrors must be facing almost perpendicular to the path of incoming light so that the photons graze the surface like stones skipping across a pond.
Chandra has four pairs of mirrors. X-rays hit the top mirrors in each pair, then skip down to the secondary mirrors. “You need two bounces to have X-rays come to a focus,” says Martin Weisskopf, Chandra project scientist at NASA’s Marshall Space Flight Center in Huntsville, Alabama, which manages the program. Each mirror is most efficient at reflecting a particular range of X-ray wavelengths.
After bouncing off the mirrors, the X-rays travel down a 26-foot tube toward the telescope’s scientific instruments, located at the other end.
Devices called gratings can be moved into the light path between the mirrors and the instruments. The gratings contain thousands of narrow openings that segregate the X-rays by wavelength. The intensity of radiation at each wavelength reveals the abundance of different elements, along with the object’s density, temperature, and motion toward or away from the telescope.
Beyond the gratings are the scientific instruments. The primary one, called the ACIS, for Advanced CCD Imaging Spectrometer, uses a charge-coupled device detector, similar to those found in digital cameras, to record the position of each X-ray that strikes it, along with the X-ray’s energy level. In many cases, this information can be used to determine which chemical elements are present. | 0.88413 | 4.066553 |
The largest spiral galaxy is believed to be the Malin-1 galaxy which has a spiral 10 times larger than the Milky Way galaxy.
Most astronomers suggest that galaxies formed shortly after a cosmic "big bang" that began the universe some 10 billion to 20 billion years ago. In the milliseconds following this explosion, clouds of gases began to coalesce, collapse, and compress under gravity to form the building blocks of galaxies.
Scientists are divided on just how galaxies first formed. Some believe that smaller clusters of about one million stars, known as globular clusters, formed first and later gathered into galaxies. Others believe that galaxies formed first and that only later did the stars within them begin to gather into smaller clusters.
Elliptical galaxies are elliptical in shape and contain many older stars with little dust or other objects. Not many new stars are known to form elliptical galaxies.
Some of the largest galaxies in the universe are known to be elliptical galaxies with estimates that some are two million light years long and contain a trillion stars.
Irregular galaxies are neither spiral nor elliptical in shape. These galaxies will have more random shapes often because of the gravitational pull from other nearby galaxies.
Lenticular galaxies are galaxies that have aspects of both elliptical and spiral galaxies. They have faint spiral arms and an elliptical halo of stars.
Galaxies can occur completely on their own or they can be found in groups, clusters or superclusters. Sometimes galaxies can merge together which can lead to rapid star formations.
It is thought that our own Milky Way galaxy may merge with the nearby Andromeda galaxy which is only 2 million light years away (not that far away in space terms).
Elliptical galaxies are shaped as their name suggests. They are generally round but stretch longer along one axis than along the other. They may be nearly circular or so elongated that they take on a cigarlike appearance.
Elliptical galaxies contain many older stars, up to one trillion, but little dust and other interstellar matter. Their stars orbit the galactic center, like those in the disks of spiral galaxies, but they do so in more random directions. Few new stars are known to form in elliptical galaxies.
The universe's largest known galaxies are giant elliptical galaxies, which may be as much as two million light-years long. Elliptical galaxies may also be small, in which case they are dubbed dwarf elliptical galaxies.
Galaxies that are not spiral or elliptical are called irregular galaxies. Irregular galaxies appear misshapen and lack a distinct form, often because they are within the gravitational influence of other galaxies close by.
Our solar system is found in the Milky Way. The Milky Way completes a revolution every 250 million years.
The Milky Way is believed to have a mass of 1000 billion times that of the Sun.
The visible disk of the Milky Way is thought to be 100,000 light years in diameter.
We believe that the Milky Way galaxy is 12 billion years old.
Most galaxies that we have studied are understood to be billions of years old. One of the youngest that we have discovered is the 1 Zwicky 18 galaxy that we think is only 500 million years old.
The most common type of galaxies that we have found to date are dwarf elliptical galaxies.
The Hubble Space Telescope has been instrumental in us being able to study distant galaxies and understand about the different types of galaxies. | 0.875245 | 3.96442 |
Astronomers spot signs of supermassive black hole mergersStaff Writer | October 24, 2018
New research, published in the journal Monthly Notices of the Royal Astronomical Society, has found evidence for a large number of double supermassive black holes, likely precursors of gigantic black hole merging events.
Space Jets from binary black holes change direction continuously
Astronomers from the University of Hertfordshire, together with an international team of scientists, have looked at radio maps of powerful jet sources and found signs that would usually be present when looking at black holes that are closely orbiting each other.
Before black holes merge they form a binary black hole, where the two black holes orbit around each other.
Gravitational wave telescopes have been able to evidence the merging of smaller black holes since 2015, by measuring the strong bursts of gravitational waves that are emitted when binary black holes merge, but current technology cannot be used to demonstrate the presence of supermassive binary black holes.
Supermassive black holes emit powerful jets. When supermassive binary black holes orbit it causes the jet emanating from the nucleus of a galaxy to periodically change its direction.
Astronomers from the University of Hertfordshire studied the direction that these jets are emitted in, and variances in these directions; they compared the direction of the jets with the one of the radio lobes (that store all the particles that ever went through the jet channels) to demonstrate that this method can be used to indicate the presence of supermassive binary black holes.
Dr. Martin Krause, lead author and senior lecturer in Astronomy at the University of Hertfordshire, said: "We have studied the jets in different conditions for a long time with computer simulations. In this first systematic comparison to high-resolution radio maps of the most powerful radio sources, we were astonished to find signatures that were compatible with jet precession in three quarters of the sources."
The fact that the most powerful jets are associated with binary black holes could have important consequences for the formation of stars in galaxies; stars form from cold gas, jets heat this gas and thus suppress the formation of stars. A jet that always heads in the same direction only heats a limited amount of gas in its vicinity.
However, jets from binary black holes change direction continuously. Therefore, they can heat much more gas, suppressing the formation of stars much more efficiently, and thus contributing towards keeping the number of stars in galaxies within the observed limits. ■ | 0.897575 | 3.878834 |
Thorne Zytkow Objects, or the Star Within a Star
Developing the Theory
Kip Thorne (of late known for his role in developing Interstellar) and Anna Zytkow were both working at the California Institute of Technology in 1977 on binary star theories. Most stars exist in such a system, but not all of them behave the same way. Particularly, they were interested in the behavior of a massive star in such a system, for the bigger a star is the quicker it burns through its fuel and thus the shorter its life is. That ending is typically a supernova if the star is massive enough. And if you have the right combo, you can have a neutron star (one of several possible outcomes of a supernova) with a red supergiant as its binary companion (Cendes 52, University of Colorado).
And we know many such pairs exist, based off X-ray flares from the neutron star as it reacts to infalling material from the red supergiant. But what would happen if the system was unstable? That is what Thorne and Zytkow investigated. If the pair was unstable enough, they could be flung apart (because of a gravitational slingshot) or they could begin to spiral towards their barycenter, or common point of orbit until they merged. The product would look like a red supergiant but would contain a neutron star at its center. This is what is known as a Thorne Zytkow object (TZO), and according to their work up to 1% of red supergiants could be TZOs (Cendes 52, University of Colorado).
The Weird Physics that Ensue
Okay, now how would such an object even work? Is it as simply as two stars coexisting in one space? Sadly, it is not as simple as that but the possible mechanism that actually occurs is way cooler. In fact, because of the bizarre internal happenings, strange forms of matter that are heavy (on the bottom side of the periodic table) could be created there. The secret here is what the neutron star does to the red supergiant. Normal stars are powered through nuclear fusion, building up smaller elements into larger and larger ones. But the neutron star is a hot object, and through this exchange of heat it actually causes convection to occur. It is a thermonuclear reactor! And through convection, those heavy elements can be brought to the surface and therefore can be seen. Since normal red supergiants wouldn’t make these, we now have a way to spot one by looking for their signatures in the EM spectrum! (Cendes 52, Levesque).
Of course, it would be lovely if things were that simple. Unfortunately, red supergiants have a dirty spectrum because of all the elements that are present in it and distinguishing individual elements can prove to be a challenge. This makes positively identifying one extremely difficult, but Zytkow kept looking as the years wore on, with the knowledge that if you take the expected percentage of existence into account with the elements they produce, it would produce the necessary heavy elements seen in the universe. In fact, because of these heavy elements, the interruption in the irp-process (aka the interrupted rapid proton process) and the high level of convection from the hot material rising, the following spectrum lines should be more pronounced: Rb I, Sr I and Sr II, Y II, Zr I, and Mo I (Cendes 54-5, Levesque).
But something that the theory is unsure of is what the destiny of a TZO is. It could possibly collapse into a black hole or be torn apart by the convection the neutron star produces. If the latter happens, then a neutron star would remain, but what would it appear? Maybe like 1F161348-5055, a supernova remnant from 200 years ago that is now an X-ray object. It is suspected to be a neutron star but completes a rotation in 6.67 hours, way too slow for a neutron star of its age. But if it had been a TZO which was torn apart, then the outer less dense layer of the neutron star could have been ripped off too, lowering the angular momentum and thus slowing it down (Cendes 55).
It may have taken 40 years since the initial theory was founded, but recently the first Thorne Zytkow object was found (possibly). Work done by Emily Levesque (from the University in Boulder, Colorado) and Phillip Massey (from Lowell Observatory) found an unusual red supergiant in the Magellanic Clouds. HV 2112 first stood out because it was unusually bright for a star of that type. In fact, its hydrogen line was exceptionally strong, in fact within the limits predicted by Thorne and Zytkow. Further analysis of the spectrum also showed high levels of lithium, molybdenum, and rubidium, also something predicted by the theory. HV 2112 has the highest levels of these elements ever seen in a star, but certainly it is not definitive proof that it is a TZO (Cendes 50, 54-5; Levesque, University of Colorado).
Cendes, Yvette. “The Weirdest Star in the Universe.” Astronomy Sept. 2015: 50, 52-5. Print.
Levesque, Emily and Philip Massey, Anna N. Zytkow, Nidia Morrell. “Discovery of a Thorne-Zytkov Object Candidate in the Small Magellanic Cloud.” arXiv 1406.0001v1.
University of Colorado, Boulder. “Astronomers Discover First Thorne-Zytkow Object, a Bizarre Type of Hybrid Star.” Astronomy.com. Kalmbach Publishing Co., 09 Jun. 2014. Web. 28 Jun. 2016.
Questions & Answers
© 2017 Leonard Kelley | 0.885234 | 3.992628 |
REMOVING THE NEED FOR GEOLOGICAL
One of the nice features of Ben's Antipodal
Impact Theory is its ability to remove some of the over-elaborate explanations
that have become necessary to explain physical features when using the Standard
These over-elaborate explanations can remind one of the
mechanisms that were used by medieval astronomers who were wedded to a
geocentric model of the universe. If the earth were at the center of the
universe, as was the common assumption before Copernicus, Galileo and others
got into the act, then astronomers had difficulty explaining the retrograde
movements of Mars, Jupiter and Saturn (they could not see any planets out
farther than that until telescopes were involved).
Because these three
planets are located farther from the sun than the earth is, there are times
when their orbits look as if they are going backwards in the sky, rather than
moving in their usual paths. Ancient astronomers explained this phenomenon by
using the device of epicycles.
The epicycle model posits that each of
those planets orbits in a circle within a circle. Therefore, sometimes the
planet actually moves backwards because it is moving backwards faster in the
inner circle than it is moving forwards in the larger orbit.
Brahe and others were able to make more precise measurements of these planets'
movements. it became more difficult to explain the actual results using just
one epicycle ... it became epicycles on epicycles.
Of course, all
of these over-elaborate constructions were rendered unnecessary once the
heliocentric model was used. There was no need for epicycles anymore.
ELIMINATING GEOLOGICAL EPICYCLES
When Ben's Antipodal Impact Theory is used as the basis for
understanding the geological history of the earth, four significant geological
"epicycle" mechanisms of the current Standard Theory can be discarded.
1. Rare Mantle Plumes
2. Mysterious Low
Angle Farallon Plate Activity Forming the Rocky Mountains
Heavy Old Ocean Crust Involved With the Marianas Trench and the Challenger
4. The Many Conflicting Reasons Given for the Major
1. RARE MANTLE PLUMES
Theory posits that hotspots are created by "rare mantle plumes." The reason
given for these rare mantle plumes is the idea that they are a result of
interior convection currents forcing the release of heat from the interior of
While this explanation is possible, just as epicycles are
possible, this explanation is completely unnecessary once hotspots are viewed
from the perspective of Ben's Antipodal Impact Theory. According to this new
theory, hotspots are the logical antipodal result of a large impact from a
celestial object. No rare mantle plumes are needed. We don't need to spend time
worrying about when the next rare mantle plume will occur. Rare mantle plumes
If we stop the impacts, we stop any future hotspots. No
geological epicycles required.
2. THE MYSTERIOUSLY SHALLOW FARALLON
The NOVA television show on PBS has broadcast a one hour
documentary that attempts to explain the unusual fact that the Rocky Mountains
are located far to the interior of the North American Continent. This
documentary posits a mysteriously shallow angled subduction of the Farallon
Most mountain ranges come about as the result of uplift from a
subducting plate. These mountain ranges occur within a few hundred miles of the
subduction zone. The Rocky Mountains Mountains are located almost 1000 miles
from the supposed subduction zone between the Farallon Plate (an offshoot of
the Pacific Plate) and the North American Plate.
The only way for the
Standard Theory to explain this mysterious occurrence is to hypothesize the
scenario where the Farallon Plate is subducted at such a shallow angle that it
does not subduct into the mantle until almost 1000 miles later. This scenario
occurs nowhere else on earth.
However, given the mechanisms of the
Standard Theory, this is the best geological epicycle that can be trotted out.
Ben's Antipodal Impact Theory hypothesizes that the Eastern American
Continent collided with the broken tail of the Siberian Continent 80 MYA to 70
MYA. The Eastern American Continent, with its western edge composed of mafic
oceanic crust, was subducted under the Siberian Tail and caused the uplift of
the high plains and the Rocky Mountains behind them. It was subduction from the
east side, not the west side. No strange geological epicycles are required (see
3. THE MARIANAS TRENCH AND THE CHALLENGER DEEP
The lowest point on the ocean floor is the Marianas Trench, located to
the east of the Mariana Islands in the eastern Pacific Ocean. Not only is this
the deepest trench, but at the southern end of the Marianas Trench Arc is the
Challenger Deep, which extends several thousand feet below even the already
deepest trench on earth. Why is the Marianas Trench so Deep?
Why is the
Challenger Deep even several thousand feet lower still? Again, the NOVA
television show on PBS has broadcast a one hour documentary which explores
these questions. And, again, the answer is based upon the only plausible
explanation that can be extracted from the Standard Theory. And, again, the
show has to create a geological epicycle in order to accomplish this.
The NOVA documentary explains the depth of the Marianas Trench in
general and the Challenger Deep in particular as being the result of the
accumulated heaviness of the seafloor slab as it moves farther and farther from
the mid-ocean ridge in the Pacific and eventually, after millions and millions
of years, reaches its subduction point. The NOVA documentary posits that the
slab's heavy weight at the end point causes it to sink lower and open up a deep
gap at the point of subduction.
However, the documentary does not
explain why subducting slabs to the north and south (especially the south at
the Challenger Deep site) of the Marianas Trench are not as deep or deeper.
They also don't address the strange almost half-circle arc of the Marianas
Trench and why there is another seamount arc on a straighter line just behind
it to the west.
Ben's Antipodal Impact Theory addresses the issue of
the Marianas Trench in Chapter 2.4. According to this new theory, the Marianas
Trench is the trace remains of the crater impact of the object that caused the
uplift of the South American Continent at its antipode 132 MYA. The Marianas
Trench was caused by the deep annular ring of the trailing edge of the crater,
which took over the subduction function from the previous, shallower trench
that was located behind it. Once this subduction was taken over by the crater's
deep annular ring, the subduction system continued to replicate this structure
as the plate continued to be subducted ... much as a winding tidal river
continually retraces its looping path through a salt marsh as the tide goes in
It is especially important to note that the Challenger Deep is
located at the southern end of the Marianas Trench, which would have been the
eastern side of the leading edge of the impact, which we would expect to be the
deepest part of the annular ring at the edge of the crater.
important than this, the Marianas Trench goes from deep to deeper as it
approaches its southern end ... and then it stops! Why is this?
NOVA documentary doesn't address this question. Ben's Antipodal Impact Theory
explains it by realizing that once the southernmost part of an annular ring
from an impact has been reached, the annular ring would bend back to the north,
and, in this case, would have been already subducted, leaving no residual
Once again, rather than needing the construct of a geological
epicycle involving an increasingly heavy slab that occurs nowhere else on earth
(and without this concept extending to the neighboring slabs), Ben's Antipodal
Impact Theory explains the structure with ordinary impact physics. It even
explains the straighter line of seamounts to the west, behind the Marianas. No
geological epicycles required.
4. SOLVING THE MAJOR MASS EXTINCTIONS
The Standard Theory relies on several different possible mechanisms to explain
the earth's major mass extinctions.
1. Impacts of Cosmic Objects
4. Lowering Sea Levels
Based upon the Standard Theory, we are all
just one unhappy random accident away from total annihilation. It is as though
we are constantly spinning a wheel of fortune, wondering which random
geological accident will destroy us next.
But, as we have seen from
examining Ben's Antipodal Impact Theory, these supposedly independent causes of
the major mass extinctions are all the result of just one thing: Impacts and
the impact effects at the antipode of the impact. In other words, if we stop
the impacts, we stop the extinctions.
There are no nefarious geological
extinction monsters waiting to come out of the closet. There are only impacts.
And we can control impacts.
The fiction that we are at the mercy of any
one of a number of possible extinction monsters is a myth of the Standard
Theory. It is a real pleasure to put this geological epicycle out of its
A new theory
should do more than just explain the same facts in a slightly different way. It
should be able to clean up lots of messy stuff that the old theory could never
really deal with very well.
While there are many facets of Ben's
Antipodal Impact Theory which create a simpler, more logical explanation for
the physical evidence that exists today, I believe that these four examples are
the best illustrations of this new theory removing the need for the geological
epicycles of the current Standard Theory. | 0.823324 | 3.51335 |
Is there any reason to send deep space probes (Pioneer and Voyager) along the plane of our solar system (maybe with a slight inclination) instead of perpendicular to the plane of our solar system?
If so what is the reason ?
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The main reason is it's a lot easier. It requires an enormous delta v to change the inclination of the spacecraft such that it would be perpendicular to the plane of the solar system. Furthermore, there isn't that much of interest beyond the ecliptic plane.
The only reason to send a spacecraft perpendicular is to somehow study the poles of the Sun, or to orbit an object significantly outside of the ecliptic plane. This has been done once, with the Ulysses spacecraft. It achieved the required delta v by a carefully planned flyby of Jupiter. This flyby allowed it to have an inclination of 80 degrees around the sun. There aren't many objects worth visiting outside of the Ecliptic plane, so there just hasn't been many missions to make the change.
Because of the slightly fuzzy understanding of planes demonstrated in this question and HyperAnthony's similar question, I want to clear up the matter of planes.
First, keep in mind that planes are two-dimensional. They have zero thickness.
The invariable (or invariant) plane is the plane that passes through the center of mass of the solar system perpendicular to the solar system's angular momentum vector.
The ecliptic plane is the plane on which the Earth's orbit is located.
Generally, most objects are going to be inclined (at an angle away from) these planes. In the case of planets, it is significantly so. Here is a handy chart from Wikipedia that shows the inclinations of each of the planets:
Since all of our destinations in the solar system (and even in the galaxy) are inclined from the ecliptic plane, travel to those destinations involves plane transfer (changing the inclination of the space craft relative to the ecliptic).
The greater the change in inclination, the greater delta v required.
To change inclination to perpendicular to the invariable plane would require "an enormous delta v", as PearsonArtPhoto said in his answer. Just how much would this be? Well, for a simple plane change (where the orbit size stays the same), $\Delta V = 2V_i * sin (\theta / 2)$. $V_i$ is the initial velocity, and $\theta$ is the angle change. That's nearly 1.4 times the initial velocity increase in velocity to transfer from the ecliptic plane to a plane perpendicular to the invariable plane. And that's assuming you don't have to change the size of your orbit (which you will).
In addition to previous points above, I offer the following. Firstly, the dV required to reach the outer planets, or leave the SS, can be partly picked up by repeated gravity assists from the planets (see Rosetta's flight plan with which it can catch a comet). To do this you have to stay in the planes of the fly-by planets. Second, the dV to get a 'polar' or perpendicular orbit can be reduced if either the launch trajectory is north/south or if your path has a fly-by by a pole of another planet. The Voyagers did this after their last planet encounter. (V2 is at about 55deg declination). It can take very little dV to bend an outbound trajectory to meet a planet on a polar orbit approach. By the way, launching into a terrestrial polar orbit uses more energy than an equatorial one because you can't take advantage of the angular velocity the rocket has sitting on the pad.
It costs a lot of energy to change the orbital inclination significantly. That said, NASA has done so with at least two probes, by use of gravity slingshots. Plans for use of a Venus encounter to put a probe into solar polar orbit were public discussion in the 80's, but I have no idea if they are still on the drawing board; the early 90's Ulysses probe was slingshot off of Jupiter.
Most of our probes are being sent to other planets in the system - deviation from the ecliptic plane is thus not in our interest; Voyager 1 being sent off was more to do with getting the desired encounters at Saturn. The joint NASA/ESA Ulysses probe used a jupiter assist to enter a fairly large 80° inclined orbit, specifically to get views of the solar poles. In theory, an encounter with Mars or Venus could do the same, and this was proposed for Pioneer H, but NASA instead put that craft on display in the Smithsonian.
Any orbit intending to avoid the "clutter" of the ecliptic plane still crosses it twice an orbit, and still has risks; further the higher the inclination, the greater the crossing velocity and more severe the potential impact energy. Thus, while it reduces the overall chances of collisions slightly, it increases the risk from each encounter greatly. Further still, there are a lot of small bodies in highly inclined orbits already, and the coronal mass ejection risk isn't reduced either, so the only reasons to do so are for research that requires a highly inclined orbit anyway.
Space telescopes like Gaia and the James Webb will not study planets, but they are still placed in the ecliptic plane of the planets (and Earth's moon) in order to take advantage of their gravity. Another potential "resource" in the ecliptic is shadow from the Sun, and for a radio telescope on the far side of the Moon, a radio shadow from Earth.
Reasons not to stay in the ecliptic would be to study the Sun's poles, like the Ulussey probe did. Oort cloud and Kuiper belt objects can be very inclined and could require missions way outside of the ecliptic. Even such missions would take advantage of gravity assist by planets before they leave the ecliptic.
A space telescope which would not be placed in the ecliptic would be a radio telescope placed so far out that it can use the Sun as a gravitational lens. That's at least 550 AU away, about 14 times the distance to Neptune. And maybe twice that because of the Sun's disturbing corona. It would get great magnification only in the direction of the Sun, so it would be sent on a course away from the object one would like to study. Maybe a specific star or the supermassive black hole at the center of the Milky Way. On an interstellar scale, the plane of the planets in the Solar system becomes irrelevant. | 0.886178 | 3.730219 |
High-precision photometry by telescope defocusing – VII. The ultrashort period planet WASP-103
We present 17 transit light curves of the ultrashort period planetary system WASP-103, a strong candidate for the detection of tidally-induced orbital decay. We use these to establish a high-precision reference epoch for transit timing studies. The time of the reference transit mid-point is now measured to an accuracy of 4.8 s, versus 67.4 s in the discovery paper, aiding future searches for orbital decay. With the help of published spectroscopic measurements and theoretical stellar models, we determine the physical properties of the system to high precision and present a detailed error budget for these calculations. The planet has a Roche lobe filling factor of 0.58, leading to a significant asphericity; we correct its measured mass and mean density for this phenomenon. A high-resolution Lucky Imaging observation shows no evidence for faint stars close enough to contaminate the point spread function of WASP-103. Our data were obtained in the Bessell RI and the SDSS griz passbands and yield a larger planet radius at bluer optical wavelengths, to a confidence level of 7.3σ. Interpreting this as an effect of Rayleigh scattering in the planetary atmosphere leads to a measurement of the planetary mass which is too small by a factor of 5, implying that Rayleigh scattering is not the main cause of the variation of radius with wavelength. | 0.873374 | 3.651947 |
"If one day humans send a robotic lander to the surface of Europa, we need to know what to look for and what tools it should carry," said Robert Pappalardo, the study's lead author, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "There is still a lot of preparation that is needed before we could land on Europa, but studies like these will help us focus on the technologies required to get us there, and on the data needed to help us scout out possible landing locations. Europa is the most likely place in our solar system beyond Earth to have life today, and a landed mission would be the best way to search for signs of life."
The paper was authored by scientists from a number of other NASA centers and universities, including the Johns Hopkins University Applied Physics Laboratory, Laurel, Md.; University of Colorado, Boulder; University of Texas, Austin; and the NASA Goddard Space Flight Center, Greenbelt, Md. The team found the most important questions clustered around composition: what makes up the reddish "freckles" and reddish cracks that stain the icy surface? What kind of chemistry is occurring there? Are there organic molecules, which are among the building blocks of life?
Additional priorities involved improving our images of Europa - getting a look around at features on a human scale to provide context for the compositional measurements. Also among the top priorities were questions related to geological activity and the presence of liquid water: how active is the surface? How much rumbling is there from the periodic gravitational squeezes from its planetary host, the giant planet Jupiter? What do these detections tell us about the characteristics of liquid water below the icy surface?
"Landing on the surface of Europa would be a key step in the astrobiological investigation of that world," said Chris McKay, a senior editor of the journal Astrobiology, who is based at NASA Ames Research Center, Moffett Field, Calif. "This paper outlines the science that could be done on such a lander. The hope would be that surface materials, possibly near the linear crack features, include biomarkers carried up from the ocean."
This work was conducted with Europa study funds from NASA's Science Mission Directorate, Washington, D.C. JPL is a division of the California Institute of Technology, Pasadena.
News Media ContactJia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif. | 0.852995 | 3.171154 |
Canopus facts for kids
Canopus is quite unusual, because its distance from Earth was not known until the 1990s. Before the launching of the Hipparcos satellite telescope, distance estimates for the star varied widely, from 96 light years to 1200 light years. Hipparcos established Canopus as lying 310 light years (96 parsecs) from our solar system.
The difficulty in measuring Canopus' distance stemmed from its being a "less luminous supergiant". Such stars are rare and poorly understood. They are stars that can be either in the process of evolving to or away from red giant status. This in turn made it difficult to know how intrinsically bright Canopus is, and therefore how far away it might be. Direct measurement was the only way to solve the problem. Canopus is too far away for Earth-based parallax observations to be made, so the star's distance was not known with certainty until the early 1990s.
Canopus is 13,600 times more luminous than the Sun and the most intrinsically bright star within about 700 light years. In fact, from 1 astronomical unit, Canopus would have an apparent magnitude of -37. Canopus appears less bright than Sirius in our sky only because Sirius is much closer to the Earth (8.6 light years).
The surface temperature of Canopus is 7350 ± 30 K. Its diameter has been measured at 0.6 astronomical units (the measured angular diameter being 0.006 arcseconds), 65 times that of the Sun. If it were placed at the centre of the solar system, it would extend three-quarters of the way to Mercury. An Earth-like planet would have to lie three times the distance of Pluto for its star to appear the same size in the sky as our own sun. Canopus is a strong source of X-rays, which are probably produced by its corona, magnetically heated to around 15 million K.
Canopus is part of the Scorpius-Centaurus Association, a group of stars which share similar origins.
Images for kids
Canopus seen from Tokyo, Japan. The latitude is 35°38′N.
Canopus Facts for Kids. Kiddle Encyclopedia. | 0.818602 | 3.398541 |
|Terra, Tellus, Gaia, Gaea, the World|
|Adjectives||Earthly, terrestrial, terran, tellurian|
|Epoch J2000[n 1]|
|Aphelion||152100000 km[n 2]|
(94500000 mi; 1.017 AU)
|Perihelion||147095000 km[n 2]|
(91401000 mi; 0.98327 AU)
(92955902 mi; 1.00000102 AU)
Average orbital speed
(107200 km/h; 66600 mph)
|−11.26064° to J2000 ecliptic|
|6371.0 km (3958.8 mi)|
|6378.1 km (3963.2 mi)|
|6356.8 km (3949.9 mi)|
|Volume||1.08321×1012 km3 (2.59876×1011 cu mi)|
|Mass||5.97237×1024 kg (1.31668×1025 lb) |
|5.514 g/cm3 (0.1992 lb/cu in)|
|9.80665 m/s2 (1 g; 32.1740 ft/s2)|
|11.186 km/s |
(40270 km/h; 25020 mph)
Sidereal rotation period
(23h 56m 4.100s)
Equatorial rotation velocity
|0.4651 km/s |
(1674.4 km/h; 1040.4 mph)
|101.325 kPa (at MSL)|
|Composition by volume|
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating estimation and other evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, which is Earth's only natural satellite. Earth orbits around the Sun in 365.256 solar days, a period known as an Earth sidereal year. During this time, Earth rotates about its axis 366.256 times, that is, a sidereal year has 366.256 sidereal days.[n 6]
Earth's axis of rotation is tilted with respect to its orbital plane, producing seasons on Earth. The gravitational interaction between Earth and the Moon causes tides, stabilizes Earth's orientation on its axis, and gradually slows its rotation. Earth is the densest planet in the Solar System and the largest and most massive of the four rocky planets.
Earth's outer layer (lithosphere) is divided into several rigid tectonic plates that migrate across the surface over many millions of years. About 29% of Earth's surface is land consisting of continents and islands. The remaining 71% is covered with water, mostly by oceans but also lakes, rivers and other fresh water, which all together constitute the hydrosphere. The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates Earth's magnetic field, and a convecting mantle that drives plate tectonics.
Within the first billion years of Earth's history, life appeared in the oceans and began to affect Earth's atmosphere and surface, leading to the proliferation of anaerobic and, later, aerobic organisms. Some geological evidence indicates that life may have arisen as early as 4.1 billion years ago. Since then, the combination of Earth's distance from the Sun, physical properties and geological history have allowed life to evolve and thrive. In the history of life on Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinctions. Over 99% of all species that ever lived on Earth are extinct. Estimates of the number of species on Earth today vary widely; most species have not been described. Over 7.7 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
The modern English word Earth developed, via Middle English,[n 7] from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their ancestral root has been reconstructed as *erþō. In its earliest attestation, the word eorðe was already being used to translate the many senses of Latin terra and Greek γῆ gē: the ground,[n 8] its soil,[n 9] dry land,[n 10] the human world,[n 11] the surface of the world (including the sea),[n 12] and the globe itself.[n 13] As with Roman Terra/Tellūs and Greek Gaia, Earth may have been a personified goddess in Germanic paganism: late Norse mythology included Jörð ('Earth'), a giantess often given as the mother of Thor.
Originally, earth was written in lowercase, and from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, and the earth became (and often remained) the Earth, particularly when referenced along with other heavenly bodies. More recently, the name is sometimes simply given as Earth, by analogy with the names of the other planets. House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name (e.g. "Earth's atmosphere") but writes it in lowercase when preceded by the (e.g. "the atmosphere of the earth"). It almost always appears in lowercase in colloquial expressions such as "what on earth are you doing?"
Occasionally, the name Terra // is used in scientific writing and especially in science fiction to distinguish our inhabited planet from others, while in poetry Tellus // has been used to denote personification of the Earth. The Greek poetic name Gaea (Gæa) // is rare, though the alternative spelling Gaia has become common due to the Gaia hypothesis, in which case its pronunciation is // rather than the more Classical //.
There are a number of adjectives for the planet Earth. From Earth itself comes earthly. From Latin Terra come Terran //, Terrestrial //, and (via French) Terrene //, and from Latin Tellus come Tellurian // and, more rarely, Telluric and Tellural. From Greek Gaia and Gaea comes Gaian and Gaean.
An inhabitant of the Earth is an Earthling, a Terran, a Terrestrial, a Tellurian or, rarely, an Earthian.
The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago (BYA). By 4.54±0.04 BYA the primordial Earth had formed. The bodies in the Solar System formed and evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, and dust (including primordial nuclides). According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years (Mys) to form.
A subject of research is the formation of the Moon, some 4.53 BYA. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth. In this view, the mass of Theia was approximately 10 percent of Earth; it hit Earth with a glancing blow and some of its mass merged with Earth. Between approximately 4.1 and 3.8 BYA, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth.
Earth's atmosphere and oceans were formed by volcanic activity and outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids, protoplanets, and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 BYA, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind.
A crust formed when the molten outer layer of Earth cooled to form a solid. The two models that explain land mass propose either a steady growth to the present-day forms or, more likely, a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics, a process ultimately driven by the continuous loss of heat from Earth's interior. Over the period of hundreds of millions of years, the supercontinents have assembled and broken apart. Roughly 750 million years ago (MYA), one of the earliest known supercontinents, Rodinia, began to break apart. The continents later recombined to form Pannotia 600–540 MYA, then finally Pangaea, which also broke apart 180 MYA.
The present pattern of ice ages began about 40 MYA, and then intensified during the Pleistocene about 3 MYA. High-latitude regions have since undergone repeated cycles of glaciation and thaw, repeating about every 40,000–100,000 years. The last continental glaciation ended 10,000 years ago.
Chemical reactions led to the first self-replicating molecules about four billion years ago. A half billion years later, the last common ancestor of all current life arose. The evolution of photosynthesis allowed the Sun's energy to be harvested directly by life forms. The resultant molecular oxygen (O
2) accumulated in the atmosphere and due to interaction with ultraviolet solar radiation, formed a protective ozone layer (O
3) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes. True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized Earth's surface. Among the earliest fossil evidence for life is microbial mat fossils found in 3.48 billion-year-old sandstone in Western Australia, biogenic graphite found in 3.7 billion-year-old metasedimentary rocks in Western Greenland, and remains of biotic material found in 4.1 billion-year-old rocks in Western Australia. The earliest direct evidence of life on Earth is contained in 3.45 billion-year-old Australian rocks showing fossils of microorganisms.
During the Neoproterozoic, 750 to 580 MYA, much of Earth might have been covered in ice. This hypothesis has been termed "Snowball Earth", and it is of particular interest because it preceded the Cambrian explosion, when multicellular life forms significantly increased in complexity. Following the Cambrian explosion, 535 MYA, there have been five mass extinctions. The most recent such event was 66 MYA, when an asteroid impact triggered the extinction of the non-avian dinosaurs and other large reptiles, but spared some small animals such as mammals, which at the time resembled shrews. Mammalian life has diversified over the past 66 Mys, and several million years ago an African ape-like animal such as Orrorin tugenensis gained the ability to stand upright. This facilitated tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain, which led to the evolution of humans. The development of agriculture, and then civilization, led to humans having an influence on Earth and the nature and quantity of other life forms that continues to this day.
Earth's expected long-term future is tied to that of the Sun. Over the next 1.1 billion years, solar luminosity will increase by 10%, and over the next 3.5 billion years by 40%. Earth's increasing surface temperature will accelerate the inorganic carbon cycle, reducing CO
2 concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in approximately 100–900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, making animal life impossible. About a billion years from now, all surface water will have disappeared and the mean global temperature will reach 70 °C (158 °F). Earth is expected to be habitable until the end of photosynthesis about 500 million years from now, but if nitrogen is removed from the atmosphere, life may continue until a runaway greenhouse effect occurs 2.3 billion years from now. Anthropogenic emissions are "probably insufficient" to cause a runaway greenhouse at current solar luminosity. Even if the Sun were eternal and stable, 27% of the water in the modern oceans will descend to the mantle in one billion years, due to reduced steam venting from mid-ocean ridges.
The Sun will evolve to become a red giant in about 5 billion years. Models predict that the Sun will expand to roughly 1 AU (150 million km; 93 million mi), about 250 times its present radius. Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, Earth will move to an orbit 1.7 AU (250 million km; 160 million mi) from the Sun when the star reaches its maximum radius. Most, if not all, remaining life will be destroyed by the Sun's increased luminosity (peaking at about 5,000 times its present level). A 2008 simulation indicates that Earth's orbit will eventually decay due to tidal effects and drag, causing it to enter the Sun's atmosphere and be vaporized.
The shape of Earth is nearly spherical. There is a small flattening at the poles and bulging around the equator due to Earth's rotation. To second order, Earth is approximately an oblate spheroid, whose equatorial diameter is 43 kilometres (27 mi) larger than the pole-to-pole diameter, although the variation is less than 1% of the average radius of the Earth.
The point on the surface farthest from Earth's center of mass is the summit of the equatorial Chimborazo volcano in Ecuador (6,384.4 km or 3,967.1 mi). The average diameter of the reference spheroid is 12,742 kilometres (7,918 mi). Local topography deviates from this idealized spheroid, although on a global scale these deviations are small compared to Earth's radius: the maximum deviation of only 0.17% is at the Mariana Trench (10,911 metres or 35,797 feet below local sea level), whereas Mount Everest (8,848 metres or 29,029 feet above local sea level) represents a deviation of 0.14%.[n 14]
In geodesy, the exact shape that Earth's oceans would adopt in the absence of land and perturbations such as tides and winds is called the geoid. More precisely, the geoid is the surface of gravitational equipotential at mean sea level.
Earth's mass is approximately 5.97×1024 kg (5,970 Yg). It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulphur (2.9%), nickel (1.8%), calcium (1.5%), and aluminum (1.4%), with the remaining 1.2% consisting of trace amounts of other elements. Due to mass segregation, the core region is estimated to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulphur (4.5%), and less than 1% trace elements.
The most common rock constituents of the crust are nearly all oxides: chlorine, sulphur, and fluorine are the important exceptions to this and their total amount in any rock is usually much less than 1%. Over 99% of the crust is composed of 11 oxides, principally silica, alumina, iron oxides, lime, magnesia, potash and soda.
Earth's interior, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties. The outer layer is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity. The thickness of the crust varies from about 6 kilometres (3.7 mi) under the oceans to 30–50 km (19–31 mi) for the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, and it is of the lithosphere that the tectonic plates are composed. Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at 410 and 660 km (250 and 410 mi) below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core. Earth's inner core might rotate at a slightly higher angular velocity than the remainder of the planet, advancing by 0.1–0.5° per year. The radius of the inner core is about one fifth of that of Earth.
Earth cutaway from core to exosphere. Not to scale.
Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). The major heat-producing isotopes within Earth are potassium-40, uranium-238, and thorium-232. At the center, the temperature may be up to 6,000 °C (10,830 °F), and the pressure could reach 360 GPa (52 million psi). Because much of the heat is provided by radioactive decay, scientists postulate that early in Earth's history, before isotopes with short half-lives were depleted, Earth's heat production was much higher. At approximately 3 Gyr, twice the present-day heat would have been produced, increasing the rates of mantle convection and plate tectonics, and allowing the production of uncommon igneous rocks such as komatiites that are rarely formed today.
|Mean mantle concentration
The mean heat loss from Earth is 87 mW m−2, for a global heat loss of 4.42×1013 W. A portion of the core's thermal energy is transported toward the crust by mantle plumes, a form of convection consisting of upwellings of higher-temperature rock. These plumes can produce hotspots and flood basalts. More of the heat in Earth is lost through plate tectonics, by mantle upwelling associated with mid-ocean ridges. The final major mode of heat loss is through conduction through the lithosphere, the majority of which occurs under the oceans because the crust there is much thinner than that of the continents.
Earth's mechanically rigid outer layer, the lithosphere, is divided into tectonic plates. These plates are rigid segments that move relative to each other at one of three boundaries types: At convergent boundaries, two plates come together; at divergent boundaries, two plates are pulled apart; and at transform boundaries, two plates slide past one another laterally. Along these plate boundaries, earthquakes, volcanic activity, mountain-building, and oceanic trench formation can occur. The tectonic plates ride on top of the asthenosphere, the solid but less-viscous part of the upper mantle that can flow and move along with the plates.
As the tectonic plates migrate, oceanic crust is subducted under the leading edges of the plates at convergent boundaries. At the same time, the upwelling of mantle material at divergent boundaries creates mid-ocean ridges. The combination of these processes recycles the oceanic crust back into the mantle. Due to this recycling, most of the ocean floor is less than 100 Ma old. The oldest oceanic crust is located in the Western Pacific and is estimated to be 200 Ma old. By comparison, the oldest dated continental crust is 4,030 Ma.
The seven major plates are the Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, and South American. Other notable plates include the Arabian Plate, the Caribbean Plate, the Nazca Plate off the west coast of South America and the Scotia Plate in the southern Atlantic Ocean. The Australian Plate fused with the Indian Plate between 50 and 55 Mya. The fastest-moving plates are the oceanic plates, with the Cocos Plate advancing at a rate of 75 mm/a (3.0 in/year) and the Pacific Plate moving 52–69 mm/a (2.0–2.7 in/year). At the other extreme, the slowest-moving plate is the Eurasian Plate, progressing at a typical rate of 21 mm/a (0.83 in/year).
The total surface area of Earth is about 510 million km2 (197 million sq mi). Of this, 70.8%, or 361.13 million km2 (139.43 million sq mi), is below sea level and covered by ocean water. Below the ocean's surface are much of the continental shelf, mountains, volcanoes, oceanic trenches, submarine canyons, oceanic plateaus, abyssal plains, and a globe-spanning mid-ocean ridge system. The remaining 29.2%, or 148.94 million km2 (57.51 million sq mi), not covered by water has terrain that varies greatly from place to place and consists of mountains, deserts, plains, plateaus, and other landforms. Tectonics and erosion, volcanic eruptions, flooding, weathering, glaciation, the growth of coral reefs, and meteorite impacts are among the processes that constantly reshape Earth's surface over geological time.
The continental crust consists of lower density material such as the igneous rocks granite and andesite. Less common is basalt, a denser volcanic rock that is the primary constituent of the ocean floors. Sedimentary rock is formed from the accumulation of sediment that becomes buried and compacted together. Nearly 75% of the continental surfaces are covered by sedimentary rocks, although they form about 5% of the crust. The third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types through high pressures, high temperatures, or both. The most abundant silicate minerals on Earth's surface include quartz, feldspars, amphibole, mica, pyroxene and olivine. Common carbonate minerals include calcite (found in limestone) and dolomite.
The elevation of the land surface varies from the low point of −418 m (−1,371 ft) at the Dead Sea, to a maximum altitude of 8,848 m (29,029 ft) at the top of Mount Everest. The mean height of land above sea level is about 797 m (2,615 ft).
The pedosphere is the outermost layer of Earth's continental surface and is composed of soil and subject to soil formation processes. The total arable land is 10.9% of the land surface, with 1.3% being permanent cropland. Close to 40% of Earth's land surface is used for agriculture, or an estimated 16.7 million km2 (6.4 million sq mi) of cropland and 33.5 million km2 (12.9 million sq mi) of pastureland.
The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from other planets in the Solar System. Earth's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m (6,600 ft). The deepest underwater location is Challenger Deep of the Mariana Trench in the Pacific Ocean with a depth of 10,911.4 m (35,799 ft).[n 18]
The mass of the oceans is approximately 1.35×1018 metric tons or about 1/4400 of Earth's total mass. The oceans cover an area of 361.8 million km2 (139.7 million sq mi) with a mean depth of 3,682 m (12,080 ft), resulting in an estimated volume of 1.332 billion km3 (320 million cu mi). If all of Earth's crustal surface were at the same elevation as a smooth sphere, the depth of the resulting world ocean would be 2.7 to 2.8 km (1.68 to 1.74 mi).
The average salinity of Earth's oceans is about 35 grams of salt per kilogram of sea water (3.5% salt). Most of this salt was released from volcanic activity or extracted from cool igneous rocks. The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms. Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir. Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the El Niño–Southern Oscillation.
The atmospheric pressure at Earth's sea level averages 101.325 kPa (14.696 psi), with a scale height of about 8.5 km (5.3 mi). A dry atmosphere is composed of 78.084% nitrogen, 20.946% oxygen, 0.934% argon, and trace amounts of carbon dioxide and other gaseous molecules. Water vapor content varies between 0.01% and 4% but averages about 1%. The height of the troposphere varies with latitude, ranging between 8 km (5 mi) at the poles to 17 km (11 mi) at the equator, with some variation resulting from weather and seasonal factors.
Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 Gya, forming the primarily nitrogen–oxygen atmosphere of today. This change enabled the proliferation of aerobic organisms and, indirectly, the formation of the ozone layer due to the subsequent conversion of atmospheric O
2 into O
3. The ozone layer blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature. This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Water vapor, carbon dioxide, methane, nitrous oxide, and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C (0 °F), in contrast to the current +15 °C (59 °F), and life on Earth probably would not exist in its current form. In May 2017, glints of light, seen as twinkling from an orbiting satellite a million miles away, were found to be reflected light from ice crystals in the atmosphere.
Earth's atmosphere has no definite boundary, slowly becoming thinner and fading into outer space. Three-quarters of the atmosphere's mass is contained within the first 11 km (6.8 mi) of the surface. This lowest layer is called the troposphere. Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower-density air then rises and is replaced by cooler, higher-density air. The result is atmospheric circulation that drives the weather and climate through redistribution of thermal energy.
The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°. Ocean currents are also important factors in determining climate, particularly the thermohaline circulation that distributes thermal energy from the equatorial oceans to the polar regions.
Water vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and falls to the surface as precipitation. Most of the water is then transported to lower elevations by river systems and usually returned to the oceans or deposited into lakes. This water cycle is a vital mechanism for supporting life on land and is a primary factor in the erosion of surface features over geological periods. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topographic features, and temperature differences determine the average precipitation that falls in each region.
The amount of solar energy reaching Earth's surface decreases with increasing latitude. At higher latitudes, the sunlight reaches the surface at lower angles, and it must pass through thicker columns of the atmosphere. As a result, the mean annual air temperature at sea level decreases by about 0.4 °C (0.7 °F) per degree of latitude from the equator. Earth's surface can be subdivided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, temperate and polar climates.
This latitudinal rule has several anomalies:
The commonly used Köppen climate classification system has five broad groups (humid tropics, arid, humid middle latitudes, continental and cold polar), which are further divided into more specific subtypes. The Köppen system rates regions of terrain based on observed temperature and precipitation.
The highest air temperature ever measured on Earth was 56.7 °C (134.1 °F) in Furnace Creek, California, in Death Valley, in 1913. The lowest air temperature ever directly measured on Earth was −89.2 °C (−128.6 °F) at Vostok Station in 1983, but satellites have used remote sensing to measure temperatures as low as −94.7 °C (−138.5 °F) in East Antarctica. These temperature records are only measurements made with modern instruments from the 20th century onwards and likely do not reflect the full range of temperature on Earth.
Above the troposphere, the atmosphere is usually divided into the stratosphere, mesosphere, and thermosphere. Each layer has a different lapse rate, defining the rate of change in temperature with height. Beyond these, the exosphere thins out into the magnetosphere, where the geomagnetic fields interact with the solar wind. Within the stratosphere is the ozone layer, a component that partially shields the surface from ultraviolet light and thus is important for life on Earth. The Kármán line, defined as 100 km above Earth's surface, is a working definition for the boundary between the atmosphere and outer space.
Thermal energy causes some of the molecules at the outer edge of the atmosphere to increase their velocity to the point where they can escape from Earth's gravity. This causes a slow but steady loss of the atmosphere into space. Because unfixed hydrogen has a low molecular mass, it can achieve escape velocity more readily, and it leaks into outer space at a greater rate than other gases. The leakage of hydrogen into space contributes to the shifting of Earth's atmosphere and surface from an initially reducing state to its current oxidizing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is thought to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere. Hence the ability of hydrogen to escape from the atmosphere may have influenced the nature of life that developed on Earth. In the current, oxygen-rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.
The gravity of Earth is the acceleration that is imparted to objects due to the distribution of mass within Earth. Near Earth's surface, gravitational acceleration is approximately 9.8 m/s2 (32 ft/s2). Local differences in topography, geology, and deeper tectonic structure cause local and broad, regional differences in Earth's gravitational field, known as gravity anomalies.
The main part of Earth's magnetic field is generated in the core, the site of a dynamo process that converts the kinetic energy of thermally and compositionally driven convection into electrical and magnetic field energy. The field extends outwards from the core, through the mantle, and up to Earth's surface, where it is, approximately, a dipole. The poles of the dipole are located close to Earth's geographic poles. At the equator of the magnetic field, the magnetic-field strength at the surface is 3.05×10−5 T, with a magnetic dipole moment of 7.79×1022 Am2 at epoch 2000, decreasing nearly 6% per century. The convection movements in the core are chaotic; the magnetic poles drift and periodically change alignment. This causes secular variation of the main field and field reversals at irregular intervals averaging a few times every million years. The most recent reversal occurred approximately 700,000 years ago.
The extent of Earth's magnetic field in space defines the magnetosphere. Ions and electrons of the solar wind are deflected by the magnetosphere; solar wind pressure compresses the dayside of the magnetosphere, to about 10 Earth radii, and extends the nightside magnetosphere into a long tail. Because the velocity of the solar wind is greater than the speed at which waves propagate through the solar wind, a supersonic bow shock precedes the dayside magnetosphere within the solar wind. Charged particles are contained within the magnetosphere; the plasmasphere is defined by low-energy particles that essentially follow magnetic field lines as Earth rotates; the ring current is defined by medium-energy particles that drift relative to the geomagnetic field, but with paths that are still dominated by the magnetic field, and the Van Allen radiation belt are formed by high-energy particles whose motion is essentially random, but otherwise contained by the magnetosphere.
During magnetic storms and substorms, charged particles can be deflected from the outer magnetosphere and especially the magnetotail, directed along field lines into Earth's ionosphere, where atmospheric atoms can be excited and ionized, causing the aurora.
Earth's rotation period relative to the Sun—its mean solar day—is 86,400 seconds of mean solar time (86,400.0025 SI seconds). Because Earth's solar day is now slightly longer than it was during the 19th century due to tidal deceleration, each day varies between 0 and 2 SI ms longer.
Earth's rotation period relative to the fixed stars, called its stellar day by the International Earth Rotation and Reference Systems Service (IERS), is 86,164.0989 seconds of mean solar time (UT1), or 23h 56m 4.0989s.[n 19] Earth's rotation period relative to the precessing or moving mean March equinox, misnamed its sidereal day, is 86,164.0905 seconds of mean solar time (UT1) (23h 56m 4.0905s). Thus the sidereal day is shorter than the stellar day by about 8.4 ms. The length of the mean solar day in SI seconds is available from the IERS for the periods 1623–2005 and 1962–2005.
Apart from meteors within the atmosphere and low-orbiting satellites, the main apparent motion of celestial bodies in Earth's sky is to the west at a rate of 15°/h = 15'/min. For bodies near the celestial equator, this is equivalent to an apparent diameter of the Sun or the Moon every two minutes; from Earth's surface, the apparent sizes of the Sun and the Moon are approximately the same.
Earth orbits the Sun at an average distance of about 150 million km (93 million mi) every 365.2564 mean solar days, or one sidereal year. This gives an apparent movement of the Sun eastward with respect to the stars at a rate of about 1°/day, which is one apparent Sun or Moon diameter every 12 hours. Due to this motion, on average it takes 24 hours—a solar day—for Earth to complete a full rotation about its axis so that the Sun returns to the meridian. The orbital speed of Earth averages about 29.78 km/s (107,200 km/h; 66,600 mph), which is fast enough to travel a distance equal to Earth's diameter, about 12,742 km (7,918 mi), in seven minutes, and the distance to the Moon, 384,000 km (239,000 mi), in about 3.5 hours.
The Moon and Earth orbit a common barycenter every 27.32 days relative to the background stars. When combined with the Earth–Moon system's common orbit around the Sun, the period of the synodic month, from new moon to new moon, is 29.53 days. Viewed from the celestial north pole, the motion of Earth, the Moon, and their axial rotations are all counterclockwise. Viewed from a vantage point above the north poles of both the Sun and Earth, Earth orbits in a counterclockwise direction about the Sun. The orbital and axial planes are not precisely aligned: Earth's axis is tilted some 23.44 degrees from the perpendicular to the Earth–Sun plane (the ecliptic), and the Earth–Moon plane is tilted up to ±5.1 degrees against the Earth–Sun plane. Without this tilt, there would be an eclipse every two weeks, alternating between lunar eclipses and solar eclipses.
The Hill sphere, or the sphere of gravitational influence, of Earth is about 1.5 million km (930,000 mi) in radius.[n 20] This is the maximum distance at which Earth's gravitational influence is stronger than the more distant Sun and planets. Objects must orbit Earth within this radius, or they can become unbound by the gravitational perturbation of the Sun.
The axial tilt of Earth is approximately 23.439281° with the axis of its orbit plane, always pointing towards the Celestial Poles. Due to Earth's axial tilt, the amount of sunlight reaching any given point on the surface varies over the course of the year. This causes the seasonal change in climate, with summer in the Northern Hemisphere occurring when the Tropic of Cancer is facing the Sun, and winter taking place when the Tropic of Capricorn in the Southern Hemisphere faces the Sun. During the summer, the day lasts longer, and the Sun climbs higher in the sky. In winter, the climate becomes cooler and the days shorter. In northern temperate latitudes, the Sun rises north of true east during the summer solstice, and sets north of true west, reversing in the winter. The Sun rises south of true east in the summer for the southern temperate zone and sets south of true west.
Above the Arctic Circle, an extreme case is reached where there is no daylight at all for part of the year, up to six months at the North Pole itself, a polar night. In the Southern Hemisphere, the situation is exactly reversed, with the South Pole oriented opposite the direction of the North Pole. Six months later, this pole will experience a midnight sun, a day of 24 hours, again reversing with the South Pole.
By astronomical convention, the four seasons can be determined by the solstices—the points in the orbit of maximum axial tilt toward or away from the Sun—and the equinoxes, when Earth's rotational axis is aligned with its orbital axis. In the Northern Hemisphere, winter solstice currently occurs around 21 December; summer solstice is near 21 June, spring equinox is around 20 March and autumnal equinox is about 22 or 23 September. In the Southern Hemisphere, the situation is reversed, with the summer and winter solstices exchanged and the spring and autumnal equinox dates swapped.
The angle of Earth's axial tilt is relatively stable over long periods of time. Its axial tilt does undergo nutation; a slight, irregular motion with a main period of 18.6 years. The orientation (rather than the angle) of Earth's axis also changes over time, precessing around in a complete circle over each 25,800 year cycle; this precession is the reason for the difference between a sidereal year and a tropical year. Both of these motions are caused by the varying attraction of the Sun and the Moon on Earth's equatorial bulge. The poles also migrate a few meters across Earth's surface. This polar motion has multiple, cyclical components, which collectively are termed quasiperiodic motion. In addition to an annual component to this motion, there is a 14-month cycle called the Chandler wobble. Earth's rotational velocity also varies in a phenomenon known as length-of-day variation.
In modern times, Earth's perihelion occurs around 3 January, and its aphelion around 4 July. These dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. The changing Earth–Sun distance causes an increase of about 6.9%[n 21] in solar energy reaching Earth at perihelion relative to aphelion. Because the Southern Hemisphere is tilted toward the Sun at about the same time that Earth reaches the closest approach to the Sun, the Southern Hemisphere receives slightly more energy from the Sun than does the northern over the course of a year. This effect is much less significant than the total energy change due to the axial tilt, and most of the excess energy is absorbed by the higher proportion of water in the Southern Hemisphere.
A planet that can sustain life is termed habitable, even if life did not originate there. Earth provides liquid water—an environment where complex organic molecules can assemble and interact, and sufficient energy to sustain metabolism. The distance of Earth from the Sun, as well as its orbital eccentricity, rate of rotation, axial tilt, geological history, sustaining atmosphere, and magnetic field all contribute to the current climatic conditions at the surface.
A planet's life forms inhabit ecosystems, whose total is sometimes said to form a "biosphere". Earth's biosphere is thought to have begun evolving about 3.5 Gya. The biosphere is divided into a number of biomes, inhabited by broadly similar plants and animals. On land, biomes are separated primarily by differences in latitude, height above sea level and humidity. Terrestrial biomes lying within the Arctic or Antarctic Circles, at high altitudes or in extremely arid areas are relatively barren of plant and animal life; species diversity reaches a peak in humid lowlands at equatorial latitudes.
|Unused, productive land||356–445|
Large deposits of fossil fuels are obtained from Earth's crust, consisting of coal, petroleum, and natural gas. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed within the crust through a process of ore genesis, resulting from actions of magmatism, erosion, and plate tectonics. These bodies form concentrated sources for many metals and other useful elements.
Earth's biosphere produces many useful biological products for humans, including food, wood, pharmaceuticals, oxygen, and the recycling of many organic wastes. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land. In 1980, 50.53 million km2 (19.51 million sq mi) of Earth's land surface consisted of forest and woodlands, 67.88 million km2 (26.21 million sq mi) was grasslands and pasture, and 15.01 million km2 (5.80 million sq mi) was cultivated as croplands. The estimated amount of irrigated land in 1993 was 2,481,250 km2 (958,020 sq mi). Humans also live on the land by using building materials to construct shelters.
Large areas of Earth's surface are subject to extreme weather such as tropical cyclones, hurricanes, or typhoons that dominate life in those areas. From 1980 to 2000, these events caused an average of 11,800 human deaths per year. Many places are subject to earthquakes, landslides, tsunamis, volcanic eruptions, tornadoes, sinkholes, blizzards, floods, droughts, wildfires, and other calamities and disasters.
Many localized areas are subject to human-made pollution of the air and water, acid rain and toxic substances, loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, species extinction, soil degradation, soil depletion and erosion.
There is a scientific consensus linking human activities to global warming due to industrial carbon dioxide emissions. This is predicted to produce changes such as the melting of glaciers and ice sheets, more extreme temperature ranges, significant changes in weather and a global rise in average sea levels.
Cartography, the study and practice of map-making, and geography, the study of the lands, features, inhabitants and phenomena on Earth, have historically been the disciplines devoted to depicting Earth. Surveying, the determination of locations and distances, and to a lesser extent navigation, the determination of position and direction, have developed alongside cartography and geography, providing and suitably quantifying the requisite information.
Earth's human population reached approximately seven billion on 31 October 2011. Projections indicate that the world's human population will reach 9.2 billion in 2050. Most of the growth is expected to take place in developing nations. Human population density varies widely around the world, but a majority live in Asia. By 2020, 60% of the world's population is expected to be living in urban, rather than rural, areas.
It is estimated that one-eighth of Earth's surface is suitable for humans to live on – three-quarters of Earth's surface is covered by oceans, leaving one-quarter as land. Half of that land area is desert (14%), high mountains (27%), or other unsuitable terrains. The northernmost permanent settlement in the world is Alert, on Ellesmere Island in Nunavut, Canada. (82°28′N) The southernmost is the Amundsen–Scott South Pole Station, in Antarctica, almost exactly at the South Pole. (90°S)
Independent sovereign nations claim the planet's entire land surface, except for some parts of Antarctica, a few land parcels along the Danube river's western bank, and the unclaimed area of Bir Tawil between Egypt and Sudan. As of 2015[update], there are 193 sovereign states that are member states of the United Nations, plus two observer states and 72 dependent territories and states with limited recognition. Earth has never had a sovereign government with authority over the entire globe, although some nation-states have striven for world domination and failed.
The United Nations is a worldwide intergovernmental organization that was created with the goal of intervening in the disputes between nations, thereby avoiding armed conflict. The U.N. serves primarily as a forum for international diplomacy and international law. When the consensus of the membership permits, it provides a mechanism for armed intervention.
The first human to orbit Earth was Yuri Gagarin on 12 April 1961. In total, about 487 people have visited outer space and reached orbit as of 30 July 2010[update], and, of these, twelve have walked on the Moon. Normally, the only humans in space are those on the International Space Station. The station's crew, made up of six people, is usually replaced every six months. The farthest that humans have traveled from Earth is 400,171 km (248,655 mi), achieved during the Apollo 13 mission in 1970.
|Semi-major axis||384,400 km|
|Orbital period||27d 7h 43.7m|
The Moon is a relatively large, terrestrial, planet-like natural satellite, with a diameter about one-quarter of Earth's. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger relative to the dwarf planet Pluto. The natural satellites of other planets are also referred to as "moons", after Earth's.
The gravitational attraction between Earth and the Moon causes tides on Earth. The same effect on the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit Earth. As a result, it always presents the same face to the planet. As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases; the dark part of the face is separated from the light part by the solar terminator.
Due to their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm/a (1.5 in/year). Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23 µs/yr—add up to significant changes. During the Devonian period, for example, (approximately 410 Mya) there were 400 days in a year, with each day lasting 21.8 hours.
The Moon may have dramatically affected the development of life by moderating the planet's climate. Paleontological evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon. Some theorists think that without this stabilization against the torques applied by the Sun and planets to Earth's equatorial bulge, the rotational axis might be chaotically unstable, exhibiting chaotic changes over millions of years, as appears to be the case for Mars.
Viewed from Earth, the Moon is just far enough away to have almost the same apparent-sized disk as the Sun. The angular size (or solid angle) of these two bodies match because, although the Sun's diameter is about 400 times as large as the Moon's, it is also 400 times more distant. This allows total and annular solar eclipses to occur on Earth.
The most widely accepted theory of the Moon's origin, the giant-impact hypothesis, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. This hypothesis explains (among other things) the Moon's relative lack of iron and volatile elements and the fact that its composition is nearly identical to that of Earth's crust.
Earth has at least five co-orbital asteroids, including 3753 Cruithne and 2002 AA29. A trojan asteroid companion, 2010 TK7, is librating around the leading Lagrange triangular point, L4, in Earth's orbit around the Sun.
As of April 2018[update], there are 1,886 operational, human-made satellites orbiting Earth. There are also inoperative satellites, including Vanguard 1, the oldest satellite currently in orbit, and over 16,000 pieces of tracked space debris.[n 3] Earth's largest artificial satellite is the International Space Station.
Human cultures have developed many views of the planet. Earth is sometimes personified as a deity. In many cultures it is a mother goddess that is also the primary fertility deity, and by the mid-20th century, the Gaia Principle compared Earth's environments and life as a single self-regulating organism leading to broad stabilization of the conditions of habitability. Creation myths in many religions involve the creation of Earth by a supernatural deity or deities.
Scientific investigation has resulted in several culturally transformative shifts in people's view of the planet. Initial belief in a flat Earth was gradually displaced in the Greek colonies of southern Italy during the late 6th century BC by the idea of spherical Earth, which was attributed to both the philosophers Pythagoras and Parmenides. By the end of the 5th century BC, the sphericity of Earth was universally accepted among Greek intellectuals. Earth was generally believed to be the center of the universe until the 16th century, when scientists first conclusively demonstrated that it was a moving object, comparable to the other planets in the Solar System. Due to the efforts of influential Christian scholars and clerics such as James Ussher, who sought to determine the age of Earth through analysis of genealogies in Scripture, Westerners before the 19th century generally believed Earth to be a few thousand years old at most. It was only during the 19th century that geologists realized Earth's age was at least many millions of years.
Lord Kelvin used thermodynamics to estimate the age of Earth to be between 20 million and 400 million years in 1864, sparking a vigorous debate on the subject; it was only when radioactivity and radioactive dating were discovered in the late 19th and early 20th centuries that a reliable mechanism for determining Earth's age was established, proving the planet to be billions of years old. The perception of Earth shifted again in the 20th century when humans first viewed it from orbit, and especially with photographs of Earth returned by the Apollo program. | 0.883492 | 3.382537 |
From: Jet Propulsion Laboratory
Posted: Monday, October 13, 2008
When comet Holmes unexpectedly erupted in 2007, professional and amateur astronomers around the world turned their telescopes toward the spectacular event. Their quest was to find out why the comet had suddenly exploded.
Observations taken of the comet after the explosion by NASA's Spitzer Space Telescope deepen the mystery, showing oddly behaving streamers in the shell of dust surrounding the nucleus of the comet. The data also offer a rare look at the material liberated from within the nucleus, and confirm previous findings from NASA's Stardust and Deep Impact missions.
"The data we got from Spitzer do not look like anything we typically see when looking at comets," said Bill Reach of NASA's Spitzer Science Center at the California Institute of Technology, Pasadena, Calif. Reach is lead investigator of the Spitzer observations. "The comet Holmes explosion gave us a rare glimpse at the inside of a comet nucleus." The findings were presented at the 40th meeting of the Division of Planetary Sciences in Ithaca, N.Y.
Every six years, comet 17P/Holmes speeds away from Jupiter and heads inward toward the sun, traveling the same route typically without incident. However, twice in the last 116 years, in November 1892 and October 2007, comet Holmes exploded as it approached the asteroid belt, and brightened a million-fold overnight.
In an attempt to understand these odd occurrences, astronomers pointed NASA's Spitzer Space Telescope at the comet in November 2007 and March 2008. By using Spitzer's infrared spectrograph instrument, Reach was able to gain valuable insights into the composition of Holmes' solid interior. Like a prism spreading visible-light into a rainbow, the spectrograph breaks up infrared light from the comet into its component parts, revealing the fingerprints of various chemicals.
In November of 2007, Reach noticed a lot of fine silicate dust, or crystallized grains smaller than sand, like crushed gems. He noted that this particular observation revealed materials similar to those seen around other comets where grains have been treated violently, including NASA's Deep Impact mission, which smashed a projectile into comet Tempel 1; NASA's Stardust mission, which swept particles from comet Wild 2 into a collector at 13,000 miles per hour (21,000 kilometers per hour), and the outburst of comet Hale-Bopp in 1995.
"Comet dust is very sensitive, meaning that the grains are very easily destroyed, said Reach. "We think the fine silicates are produced in these violent events by the destruction of larger particles originating inside the comet nucleus."
When Spitzer observed the same portion of the comet again in March 2008, the fine-grained silicate dust was gone and only larger particles were present. "The March observation tells us that there is a very small window for studying composition of comet dust after a violent event like comet Holmes' outburst," said Reach.
Comet Holmes not only has unusual dusty components, it also does not look like a typical comet. According to Jeremie Vaubaillon, a colleague of Reach's at Caltech, pictures snapped from the ground shortly after the outburst revealed streamers in the shell of dust surrounding the comet. Scientists suspect they were produced after the explosion by fragments escaping the comet's nucleus.
In November 2007, the streamers pointed away from the sun, which seemed natural because scientists believed that radiation from the sun was pushing these fragments straight back. However, when Spitzer imaged the same streamers in March 2008, they were surprised to find them still pointing in the same direction as five months before, even though the comet had moved and sunlight was arriving from a different location. "We have never seen anything like this in a comet before. The extended shape still needs to be fully understood," said Vaubaillon.
He notes that the shell surrounding the comet also acts peculiarly. The shape of the shell did not change as expected from November 2007 to March 2008. Vaubaillon said this is because the dust grains seen in March 2008 are relatively large, approximately one millimeter in size, and thus harder to move.
"If the shell was comprised of smaller dust grains, it would have changed as the orientation of the sun changes with time," said Vaubaillon. "This Spitzer image is very unique. No other telescope has seen comet Holmes in this much detail, five months after the explosion."
"Like people, all comets are a little different. We've been studying comets for hundreds of years a 116 years in the case of comet Holmes a but still do not really understand them," said Reach. "However, with the Spitzer observations and data from other telescopes, we are getting closer."
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. For more information about Spitzer, visit http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer .
// end // | 0.800736 | 3.978398 |
- Scientists claim to have identified an extremely rare type of meteor called a minimoon.
- The researchers studied the trajectory of the ultra-bright meteor, which slid across the sky in 2016.
- In 2014, a meteor that entered Earth’s atmosphere was suspected to have come from a minimoon.
You know the moon. You like the moon. It's a pretty good moon! But have you heard of the "minimoons"—also called temporarily captured orbiters—that occasionally orbit Earth? They're small, natural satellites that have been swept up in our planet's orbit and only stay for a short time before being flung out into space or sucked into Earth's atmosphere by gravity.
Scientists suspect there’s probably a 1-yard-wide minimoon circling Earth at any given moment, according to Astronomy.com. Most are tiny, and only one has been officially observed: 2006 RH120, which circled the planet for 11 months before escaping back into space. Spotting them is an exceptionally rare treat.
But spotting meteors that form from them is even rarer—and now a team of scientists from Curtin University in Australia claims to have done just that.
Using data gathered by Australia’s Desert Fireball Network, the researchers identified a meteor that originated from one of these minimoons, according to new research published in The Astronomical Journal. Only one minimoon fireball has ever been spotted, captured on camera in 2014 by a team of researchers in Europe.
The new meteor, dubbed DN160822_03, exploded across the night sky above Australia on August 22, 2016. The scientists classified the unusually bright meteor as a minimoon by calculating its trajectory. They hope that by studying these rare Earth orbiters, they can better understand how these wayward objects find their way over to our planet.
And there may be other benefits in studying the tiny satellites. For example, they could be used for scientific sample return missions, or even for the mining of precious metals and other materials.
“Minimoons are really awesome because they are the most accessible object to get to from Earth in the solar system,” planetary scientist and study author Patrick Shober told Astronomy.com. | 0.866909 | 3.421192 |
Early Tuesday morning (Dec. 27) we all have an opportunity to get our first look at the ringed wonder of the solar system, Saturn, in the early morning sky.
Saturn has been hidden from our view since mid-November, when it was an evening object, and moved progressively lower in the southwest sky until it ultimately disappeared into the glare of the sun. The planet arrived at solar conjunction on Dec. 10 and transitioned into the morning sky. And on Tuesday morning, Saturn will move far enough away from the sun to again be glimpsed visually - weather permitting - low in the southeast sky about 45 minutes before sunrise. [Video: The Planets in December's Sky]
Of course, it does not hurt to have a benchmark to positively make a sighting and that's where the moon comes in; appearing as just a hairline sliver of light, only 3 percent illuminated by the sun. On Tuesday morning, 45 minutes before sunrise, look for the moon low in southeast sky. And if you look straight down below it, close to the horizon, you’ll see a moderately bright "star" shining with a yellow-white hue. That will not be a star, but the planet Saturn.
The distance between the moon and Saturn will measure about 5 degrees. As I have said many times before, your clenched fist held out at arm's length measures roughly 10 degrees. So on Tuesday, Saturn will be about "half a fist" below the razor-thin lunar crescent.
Two things will markedly increase your chances of making a sighting. First, make sure that you do not have any obstructions such buildings or trees toward the southeast part of the sky that could block your view of either the moon or Saturn. Secondly, it would help if you scanned that part of the sky with good binoculars, which will certainly help in your picking out the moon and Saturn against the brightening sky. Once you hit upon the moon, finding Saturn should be easy; just drop an imaginary plum line straight below the moon and you will hit upon Saturn.
The year 2017 will belong to Saturn, for this is the year its magnificent ring system will be at their maximum tilt toward Earth. That will actually come in October, when the tilt will be equal to 27 degrees, though right now the rings are practically at their maximum … currently tilted 26.8-degrees toward us. If you have a telescope, you'll have to wait a while for Saturn to get high enough above the horizon and above any horizon haze for you to get a good view of it. If you try to look at it through a telescope on Tuesday morning, you likely would be disappointed because objects near the horizon tend to have their images quiver or "boil" because of atmospheric instability. You’ll have to wait several more weeks for Saturn to climb high enough in the sky and far enough from the dawn glow to make it worthwhile to look at through a small telescope.
But at least be advised that Saturn has begun the process of emerging back into view and that 2017 promises many great nights observing the sixth planet from the sun. The Lord of the Rings is back!
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for Fios1 News, serving the Hudson Valley of New York. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com. | 0.84727 | 3.428065 |
What something is, is different from what something is not. It is fundamental logical truth that when something is something, it can not also, then, be what it is not.
What physicists seem to have found, however, is that the very basic stuff of reality. . . is both what it is and what it is not. It is both continuous and discontinuous. . . smooth and flowing like a wave, and discrete and moving like a particle.
Physicists today call this wave-particle stuff quantum fields. Quantum fields are invisible ghosts of potentiality. Undisturbed, they are undulating waves of continuous possibility. Disturbed – ‘measured’ – ‘observed’, they are moving particles and events.
Erwin Schroedinger discovered an equation that describes the state of a given quantum field and how it behaves.
“There is no ‘energy’ in the Schroedinger equation, a central point that means that whatever is ‘waving’ in the Schroedinger wave equation is neither energy or matter. It is terribly important that no one knows ‘what’ is waving in the Schroedinger wave equation.” Stuart A. Kauffman.
Slam a quantum field with an intense point of energy. This is what Particle Accelerators do. With long tunnels of electromagnetic and superconducting powers, they drive particles to ever higher speeds, and focus them, with extreme precision, to collide into each other – “like aiming a rifle at a mosquito sitting on the moon“. Leon Lederman From how the bits of debris scatter, and where they scatter, physicists learn about quantum fields.
There are different kinds of quantum fields, it seems, quantum fields of gravity, of electromagnetism, and of nuclear forces. They must be unified in some way. This was something that Albert Einstein was trying to discover in the last thirty years of his life.
Peter Higgs, in Scotland, 37 years ago, figured that a certain other kind of field must also exist, a field that interacts with radiation and energy, and creates mass, and the material world that we can know. When particle accelerators became powerful enough, in 2012, the Higgs field was found.
“Over the 20th century, we came to picture all forms of matter as accumulations of transient disturbances in ubiquitous fields. Some of those fields, when cold, create space filling mists – the Higg’s field is one. Like morning dew, they are spontaneous emanations, thrown off as the fields settle into equilibrium.” Frank Wilczek.
Quantum fields seem layered, creating a giant jello cake Universe, in which some layers are like whipped cream and allow radiation unhindered to travel at the speed of light, the fastest anything can go, and some layers are like caramel, with resistance to movement causing mass and the gravity that creates the planets and galaxies.
The layers jiggle as events occur. . . not totally randomly, but with predictable probability . . and with mysterious unity. Where there is a bounce one way, there is somewhere else a bounce the other way.
There must be other layers. . . A field of consciousness. . .maybe?
“I’d expect complex biochemistry to be consistently biased in the direction that leads closer to consciousness, as gravitation biases motion towards massive objects. I have no evidence for this idea. It’s just the way biology seems to work.” David Gerlenter
And God said . . .
Isaac Newton got the concepts right, perhaps better than anyone else in history. Mass is quantity of matter. Momentum is quantity of motion. Force is change in motion. Change of motion is acceleration. Mass is resistance to force. Force equals mass times acceleration.
This equation “is the basis of our mechanical, civil, hydraulic, acoustic, and other types of engineering; it used to understand surface tension, the flow of fluids in pipes, capillary action, the drift of continents, the propagation of sound in air and in steel, the stability of structures like the Sears Tower or one of the most wonderful of all bridges, the Bronx-Whiteston Bridge Leon Lederman
Alone on his aunt’s farm, to escape the plague after graduating from college, he developed the laws of motion for both the planets in space and falling bodies on earth. To explain his laws, he developed a whole new system of mathematics, the calculus, which gives dynamic change to geometry. He is still the greatest scientist of all time.
He seemed to know that his mind was different.
“Common people did not know how to abstract their thoughts from their senses. Speaking always of relative quantities or measures, they are thus unable to discern the true, real world that lay beyond their perceptual cloaks.”
He was certain that his ideas were correct.
He was not much interested in convincing others. He avoided argument – the ‘legal sphere’. Why waste one’s precious time? He kept his discoveries to himself for almost 20 years, until Edmond Halley, of Halley’s comet, pressured him to publish.
Born into the puritan tradition, an orphan raised by priests, he was a devout believer in God, and an exacting student of the Bible.
He was a ‘natural philosopher’ and that included theology. Getting the concepts right meant getting God right too. Be clear about God so as to be clear about Nature. God is both immanent – in all things, and transcendent – above all things. Absolute Space is the universal presence of God. Absolute Time is the omniscient consciousness of God. The Laws of Nature are Transcendent, like their creator. Gravity, like God, is a omnipresent, a universal power, active everywhere.
“The principles I consider, not as occult qualities supposed to result from the specific Forms of things, but as general laws of Nature, by which the things themselves are formed; their truth appearing to us by Phenomena, though their causes be not yet discovered.”
As We are in God’s image, our reason is God’s gift to us to discover the laws of nature. And as God is unitary, so is truth. Truth must be consistent and agree with observation. Science, for Isaac Newton, was a religious calling, Our human reason can be trusted.
His great treatise, Philosophiae Principia Naturalis Mathematica – the greatest book of science ever written – for him, was written in the tradition of Moses of the Bible.
And yet he remained humble, mindful of what he didn’t know.
“Thus far I have explained the phenomena of the heavens and our sea by the force of gravity, but I have not yet assigned a cause to gravity. . . I have not as yet been able to deduce from phenomena the reasons for these properties of gravity, and I do not ‘feign’ hypothesis.”
Isaac Newton gave the same intensity that he gave to natural philosophy, to the study of Christian history. Any polytheism is blasphemy, and always leads to corruption. . . in all things, in theology. . . and in natural philosophy.
His studies convinced him that the notion of the Trinity was wrong – a giant conspiracy starting at the Council of Nicosia, with the falsely added 1 John 5:7, and 1 Timothy 3:16 verses to the King James Bible. In his time, in England, denial of the Trinity was a capital crime. He kept these views to himself.
Sir Isaac Newton didn’t like music, poetry, or literature. He never married, and had no known personal companion. He was buried in Westminster Abbey . . . ‘like a king’.
A fish won’t stare at you, but an octopus will. They watch you, with their human-like camera eyes, as much as you watch them. They are the smartest animal that has stayed in the sea, the only invertebrate – animals with no backbone – with a large brain. Though as primitive as shell fish, they have as many neurons as a dog.
Octopus are hunters and predators, but with no physical defense. Unlike their ancestors, they did not retain their shells. They can ink the water to escape, and do instantaneous camouflage, and a few are poisonous, but mostly they are mobile, and smart. . . brains over braun. Two thirds of their brain cells are in their eight arms. They can squeeze thru an opening as small as one of their eyes.
They are minds that swim.
Their squishy bodies, with no hard parts, are pure tasty, and quick, digestible meat. They are hunted by all the predators of the sea. Their life span is short, they die shortly after breeding just once. Life is risky, they go for broke.
They are ingenious at escape, and always try. They have been known to open a jar . . . from the inside . . . to get free. They seem able to recognize particular individual humans. When they escape, they are uncanny at picking the moment you aren’t watching them.
“When you work with fish, they have no idea they are in a tank, somewhere unnatural. With octopuses it is totally different. They know they are inside this special place, and you are outside it. All their behaviors are affected by their awareness of captivity.” Peter Godfrey-Smith
They have been found to have perceptual constancy – they understand an object is the same object, from different points of view. They have comparative memory analysis – they can bring past experiences to bear on present situations and decisions . They have curiosity. They will interact with something, even when they know they can’t eat it. They do step by step action, like other animals with consciousness, they can navigate mazes.
They are not considered to be social, but divers have known then to ‘high five’ each other . . . !
They have three hearts and blue-green blood.
We humans are not just conscious, but also are self-conscious, we have awareness of ourselves along with our awareness of the world, an eerie sense of two-ness that haunts us, and we sense that the octopus has that too.
“Meeting an octopus, is, in many ways, the closest we are likely to get to meeting an intelligent alien.” Peter Godfrey-Smith
They may BE alien. Scientists have very recently decided that since their genetics and intelligence are so much a leap from their origins that some of their DNA, literally, may have come from outer space, carried in the spray of meteors from outer space.
“the genome of the Octopus shows a staggering level of complexity, with 33,000 protein-coding genes more than is present in Homo Sapiens. . . the possibility that cryopreserved octopus eggs arrived in icy bolides [in meteors] several hundred million years ago should not be discounted, as that would be a parsimonious cosmic explanation for the Octopus’ sudden emergence on Earth circa 270 million years ago.” Steele, et. al. Progress in Biophysics and Molecular Biology, March 2018.
“All humans of normal intelligence can learn any language, provided they start at a young age. After the age of five or six, a child can almost never become perfectly fluent in a language, and the ability to learn it can completely disappear soon after that. After puberty, it is almost impossible to perfect the pronunciation of a second language.” Gene, Peoples, and Languages, Luigi Luca Cavalli-Sforza.
Do we speak because we think, or do we think because we speak? How does our thinking depend on our language? Did we become smart because we can talk, or can we talk because we are smart?
To Noam Chomsky, we speak because we think, and we think . . . linguistically . . .not because it helps us speak, but because it helps us think. Life is about characters and events, situated in the past, present, and future, and so is our thinking. We function in social groups, with goals of survival, children, cooperation, and deception. We live stories, and so we think stories. Our minds are literary. We are playwrights, and we are one of our characters. Language is always and everywhere structured for stories.
For Chomsky, speech came later, an output of thinking, like a printer is to a computer. Unlike for thinking, there are physical constraints on speech delivery, so speech is less than thinking. By speaking our minds with others, we expand our knowledge. Speaking empowered thinking. Thinking and speaking feedback to enlarge our intelligence and our scope of collective action. The rest is history. We vanquished the bigger and stronger Neanderthal, and everything else. We have taken over the planet.
Noam Chomsky started linguistics in the 1950’s, when the human mind was considered a blank slate, to be filled up with culture and learning. He noted, however, how easily and fast children acquire language without specific instruction. They acquire the skills of language fare faster than it can be taught. He wrote a ground-breaking work, Syntactic Structures, in 1957, in which he posited an innate language ability with a ‘language acquisition device’ in the human mind – a universal, innate and hard-wired brain system that unfolds a language ability – in a child, as it is activated, not learned, by exposure to speech in the early years of childhood.
This was at last a theory of nature and nurture in human development, not one or the other. Chomsky’s theory up-ended the blank slate foundational theory of social science, and launched the field of modern brain science. He is, today, the sixth most cited person in scientific literature . . . of all time . . . just behind William Shakespeare.
People vary in their ability to convert thought into speech. Chomsky, himself, is master thinker/speaker. No one can speak more clearly, more comprehensively, or more spontaneously, or enunciate streams of information as they support reasoned conclusions and opinions about very complex ideas, than Noam Chomsky. He can drive people crazy.
Politics is a different matter.
This great linguist theorist of biological human language is a . . . radical socialist anarchist. Famous for repudiating behaviorism, the blank slate theory of social science, he strangely applies behaviorist rationality to human political nature. Seemingly blind to the biology of tribalism and political behavior of non-linguistic human nature, he forever condemns illogical politics as immoral. . . .
“How is it possible that mathematics, a product of human thought that is independent of experience, fits so excellently the objects of physical reality?” Albert Einstein.
In 1939, at Cambridge University, Ludwig Wittgenstein was lecturing on the Philosophy of Mathematics. By this time, with messianic certainty, he was adamant that mathematics was just a lot of linguistic convention, a bunch of tautologies based on definitions and word play. He thought that seeking mathematical proofs, along with the quest to develop a mathematics without inconsistencies, was pointless. He essentially taught against mathematics.
At the same time, Alan Turing, soon to be one of the great mathematicians of all time, was also at Cambridge, teaching a course in mathematical logic. He was also a student in Wittgenstein’s class. He had proven certain mathematical truths that would eventually be very important for code breaking during the coming war, and for the future of computer programming. He could not agree that mathematical inconsistency didn’t matter.
“The real harm of a system that contains a contradiction, will not come in unless there is an application, in which case a bridge may fall down or something of the sort.”
Turing and Wittgenstein debated each and every class. The other students were bystanders. Wittgenstein would cancel class if Turing wasn’t going to show up. Turing gradually realized that Wittgenstein considered debate. . itself. . . as meaningless. He eventually stopped going.
The Vienna circle philosopher, Moritz Schlick, told his friend Albert Einstein of his allegiance to Wittgenstein’s thinking, finding all philosophy ‘superfluous’ and all metaphysical thinking meaningless. Schlick was the dean of the Vienna school of ‘logical positivists’, philosophers who tried to believe that only observations, verified by experiment, could be considered real or true. Theory and philosophy can never lead to knowledge.
Einstein, like Turing, could not agree. He found the philosophers such as Kant and Mach very helpful. He defended the role of both experiment and theory in scientific advancement. It was not one or the other. All living creatures used thinking in some way! Concepts, as well as observations, theory as well as data, are necessary.
“Physics is an attempt to construct, conceptually, a model of the Real World, as well as its law-governed structure. You will be surprised by Einstein the metaphysician, but in this sense every 4 and 2 legged animal is, de facto, a metaphysician.”
Turing’s legacy is computers, Einstein’s is space travel.
Computers that have logically inconsistent programming will crash.
Space ships, with inaccurate calculations of fuel and trajectory, traveling millions of miles to encircle and land on asteroids, will crash.
The SpaceX robot-guided Falcon 9 rockets ride into sun-synchronous orbit, deliver satellites to geo-synchronous orbit, at the speed of a bullet, and then return, decelerating from 120,000 feet per second to zero feet per second, in a matter of minutes, rotating elegantly from head-first to feet-first, and landing, intact, on a platform 60 square yards in size, floating at sea.
Mathematics, a product independent of human experience, is the pilot.
“What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.” St. Augustine of Hippo.
Everywhere in archeology, in the pyramids of Giza, the stones of Stonehenge, the observatory of Chichen Itza, or the temples of Angkor Was, humans have worshiped the heavens. But. . . not the sun or the moon or the stars themselves. No, humans have been worshiping their . . . predictability. Humans express reverence for this mysterious truth of nature . . . the past informs the future. And for their gift of memory, humans give gratitude to the . . . gods.
Rocks smash or get smashed. Life can get out of the way.
“Brains are predictive devices, and exploit the fact that recurrence is a fundamental property of the world around us. Experience and memory allow the recall of similar situations and the deployment of previously effective actions.” Nature, Vol 497, May 30, 2013.
Memory recall can be unconscious, but with consciousness, memories can more powerfully be re-lived. This may be what consciousness is for. Consciousness sorts the past, present and future, and with it comes a sense of a continuous, uniform, forward-flowing time. Isaac Newton declared that this time was an absolute. For Einstein, time only existed as a part of SpaceTime, not as an independent entity, and only a local one.
“Only ghosts can hear the sounds of an eternally, uniformly occurring tick-tock. Ask an intelligent man who is not a scholar what time is and you will see that he takes time to be this ghostly tick-tock There is no audible tick-tock everywhere in the world that could be considered as time.” Albert Einstein
For Nicholas Humphrey, the sensation of time is a tool of the mind for organizing memory and experience.
“Suppose indeed that human beings travel through life as in a “time ship” that like a spaceship has a prow and a stern and room inside for us to move around“. A History of the Mind, 2008.
And for artists too:
“Thus, what happens in the thick moment of conscious sensation, Monet seems to be suggesting, is not that we blend past, present, and future but rather that we take a single moment and hold on to it just as it is – so that each moment is experienced as it happens for longer than it happens. Seeing Red, 2006.
One physicist, Richard A. Muller, suggests that time very much does exist, and moves forward in the ongoing expansion of SpaceTime that has been happening since the Big Bang.
“Just as space is being generated by the Hubble expansion, so time is being created. The coninuous and ongoing creation of new time sets both thearrow of time and its pace. Every moment, the universe gets a little bigger, and there is a little more time, and it is this leading edge of time that we refer to as Now.” Now, The Physics of Time, 2017.
NOW may be what rides the crest of this wave of new SpaceTime continually being created by our ever expanding Universe, and we, with our conscious awareness, as unique riders on this surf.
“After all, he seems to have a lot to say about what can’t be said.” Bertrand Russell.
Ludwig Wittgenstein came from a very wealthy family of Vienna, in the time before WW I, a family of musicians, professors, and suicides. He went to the same grammar school as Adolf Hitler. His sister was painted by Gustav Klimt, and helped Sigmund Freud escape the Nazis. He fought in WWI, reading Tolstoy’s Gospel in Brief, while voluntarily manning the point, the most dangerous position, on the front. Beethoven was his hero. He was precocious in math, and obsessed by logic.
He would scrutinize his own thinking to find the hidden assumptions that underlie all thinking and the subtle ways that logic fails to be logical. He would puzzle over the use of words in speech – what is subconscious to most of us – and search for hidden patterns. He wanted to know how we know, what we know, what can be known.
“Sometimes my ideas come so quickly that I feel as if my pen is being guided.”
He was perplexed by the riddles of self reference in logic, the great stumbling block in Bertrand Russell’s attempt, in Principia Mathematica, to derive all knowledge from first principles of logic. Is the set of all sets that don’t include themselves, also a set?
He became anti-philosophical, convinced that philosophical questions were merely linguistic puzzles, and that language, with all of its mixing up of perceptions and conceptions, hopelessly impaired thought. Truth can only be known by experience, not with thinking, and only shown, with art perhaps, but not with words. Thought and speech are mere ‘social games’ for living a social human life. . . something, sadly, he himself was not much able to do.
“Whereof one can not speak, thereof one must remain silent”.
With his spooky certitude, and mesmerizing stare, he was considered brilliant. For a time, he was thought to have eclipsed all of conventional philosophy. He was lionized.
John Maynard Keynes: “I have met God, he arrived on the 4:30 train.”
He lived an eccentric, solitary life, much of his time in a remote cabin in Norway. At one point he gave away all of his enormous wealth, and lived thereafter in near poverty. He feared going mad, that he might commit suicide. Three brothers did.
He suffered a constant solipsism, an oppressive self consciousness, haunted by a loss of self connection. Is my thinking about myself also my self?
He was a disorder of self reference, like the paradoxes of logic that so obsessed him.
Insanity and genius are not the same thing.
“He has penetrated deep into mystical ways of thought and feeling, but I think (though he wouldn’t agree) that what he likes best in mysticism is its power to make him stop thinking.” Bertrand Russell.
“Peace in thinking is the wished-for aim of those who philosophize.”
He was trying to think himself out of thinking too much. He didn’t succeed.
“I don’t really know what the interior of anybody else is like – I often feel very fragmented, and as if I have a symphony of different voices, and voice overs, and factoids, going on all the time, and digressions on digressions…” David Foster Wallace
David Foster Wallace was always Meta-thinking – thinking about thinking. He could be insightful, and engaging, and interesting, but get lost in recursions and riddles of semantics, and in puzzles of grammar.
He lived inside his head.
He would talk about the “special sort of buzz” logical thinking could give him.
“a gorgeously simple solution to a problem you suddenly see, after half a notebook with gnarly attempted solutions, you about hear a . . .click“.
Boredom was terrifying. He suffered severe writer’s block. There was this constant, oppressive feeling of something not feeling right, that he wasn’t really, somehow. . . him. He felt a menacing sense of disconnection with himself.
Being a person was like being a ghost.
Substance use gave him great relief, it helped him feel whole. He became addicted with a natural ease.
At a Kenyon College commencement, speaking to an audience of avid readers and writers, he tried to warn them about the dangers of the mental life: be careful! mentation isn’t all it is cracked up to be! you can be a fish swimming in water, and not know what water is. Stay grounded in simple truths, he said, somehow they are really true.
” The word despair is overused and banalized now but it’s a serious word, and I’m using it seriously. It’s close to what people call dread or angst, but it’s not these things, quite it’s more like wanting to die in order to escape the unbearable sadness of knowing I’m small and selfish and going, without a doubt, to die. It’s wanting to jump overboard.”
Julian Jaynes famously noted that the mind of Achilles, in the Iliad – a mind solely and completely in the present – is very different from the mind of Odysseus, in the Odyssey – a mind scheming to manipulate appearance and orchestrate the future. Sometime in antiquity, between the Iliad and the Odyssey, Jaynes thought, the human mind had changed. Perhaps it was the advent of writing, and the emergence of the reading mind. Reading ignites the imagination.
With people like David Foster Wallace, reading can take the imagination too far.
With endless digressions, and foot notes to foot notes, the writing of David Foster Wallace is more a psychiatric exposition than it is literature. He conveys for us his lost, unmoored, and painful experience of being. That is his sad contribution.
“He waited two more days for an opportunity. In the early evening on Friday, September 12, Wallace suggested that his wife go out to prepare for an opening…After she left, he went into the garage and turned on the lights. He wrote her a two page note. Then he crossed through the house to the patio, where he climbed onto a chair and hanged himself.”
Our solar system is not a perfect clock. There have been 16 ice ages in the past million years.
“Small variations in the tilt of the Earth on its axis and variations in the planet’s elliptical path around the sun are all that is necessary to plunge the planet in and out of the freezer. ” Tim Flannery.
Some 120,000 years ago, modern humans migrated out of Africa, and we kept going, first into the middle east, then on to southeast Asia, with a detour down into Australia, then up the eastern Pacific to the Bering Strait, and finally into North America. By 15,000 year ago, we reached the tip of South America.
We evolved in Africa, from a hairy, tree climbing, social primate ancestor. Somehow, over time, we lost most of our hair, gained a lining of body fat, developed upright walking, a descended larynx that enabled speech, special sweat glands for thermal regulation, and a diving reflex for swimming. We became like sea mammals, more suited for water than the forest or savannah. Dolphins are our close cousins in intelligence and communication, the whale is the only other mammal to have menopause. Where and when this happened is a mystery. The Afar Triangle of northeast Africa, on the way out of Africa, may have been a vast, flooded wetlands. We may have had to swim our way out of Africa.
We followed the coastlines, along the beaches and up rivers, as sea gatherers and fishermen. Food was plentiful, rich in value, and easy to harvest. The travel and protection were easier. We love the beach to this day.
Our journey was during a perilous geologic time. A warming earth was melting ice, rising sea levels, lifting and shifting tectonic plates, causing earthquakes and volcanoes. Released by the loss of the weight of the great ice sheets as they melted, continental plates heaved up, and the moon pulled stronger on the increasing tidal waters. The Pacific tectonic plate, being the largest and the thinnest – only 2.5 miles thick – moved and cracked the most, aggravating the ‘ring of fire’ of volcanoes, earthquakes, and tsunami’s that pound all the coasts of the Pacific Ocean.
As modern humans arrived along the South East Asian coast, some 70,000 years ago, the shallow, continental Pacific Sundra shelf waters were flooding, and a great volcano – perhaps the greatest ever volcano – Toba – in Indonesia on the island of Sumatra, erupted. The massive blast of volcanic dust blackened the sky, creating a volcanic winter and mass extinction. Human life all the way back to northern Africa was nearly extinguished.
The surviving humans were pushed inland and north, and eventually into the New World. Floods, tidal waves, receding waters, and exploding volcanoes filled their prehistoric consciousness. This has carried on to our day, in the creation stories of the world, told by their descendants.
The myths are not myths, they are history.
In the beginning the world was in water, and there was darkness. And then light came to the sky, and then the sun appeared and separated the earth from the sky. | 0.891115 | 3.058525 |
Planck is an ESA mission and Europe's first mission to study the relic radiation from the Big Bang. Launched in tandem with ESA's Herschel space telescope on the 14th May 2009; it has now mapped the structure of the Cosmic Microwave Background radiation, receiving it's final deactivation command on the 23rd October 2013, however the results will continue to be analysed over the next few years. Ever since the detection of small fluctuations in the temperature of this radiation, astronomers have used the fluctuations to understand both the origin of the Universe and the formation of galaxies.
Plank is equipped with a powerful telescope and two instruments operating at radio to sub-millimetre wavelengths. The detail and sensitivity of the measurements Planck will provide will help determine fundamental parameters relating to the origin and evolution of the universe.
In order to achieve its scientific objectives, Planck's detectors have to operate at very low and stable temperatures. The spacecraft is therefore equipped with the means of cooling the detectors to levels close to absolute zero. RAL Space has provided thermal analysis for the design of the system, as well as the cooling stage that reduces the temperature from 20K to 4K, using a Joule-Thomson system.
Last updated: 03 March 2016 | 0.853906 | 3.593728 |
Billions of Stars and Galaxies to Be Discovered in the Largest Cosmic Map Ever
The Pan-STARRS telescope in Hawaii spent four years scanning the skies to produce two petabytes of publicly-available data. Now it's up to us to study it.
Need precision observations of a nearby star? Want to measure the light-years to a distant galaxy? Or do you just want to stare into the deep unknown and discover something no one has ever seen before? No problem! The Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) has got you covered after releasing the biggest digital sky survey ever carried out to the world.
"The Pan-STARRS1 Surveys allow anyone to access millions of images and use the database and catalogs containing precision measurements of billions of stars and galaxies," said Ken Chambers, Director of the Pan-STARRS Observatories, in a statement. "Pan-STARRS has made discoveries from Near Earth Objects and Kuiper Belt Objects in the Solar System to lonely planets between the stars; it has mapped the dust in three dimensions in our galaxy and found new streams of stars; and it has found new kinds of exploding stars and distant quasars in the early universe."
The Pan-STARRS project is managed by the University of Hawaii's Institute for Astronomy (IfA) and the vast database is now available by the Space Telescope Science Institute (STScI) in Baltimore, Md. To say this survey is "big" is actually a disservice to just how gargantuan a data management task it is. According the IfA, the entire survey takes up two petabytes of data, which, as the university playfully puts it, "is equivalent to one billion selfies, or one hundred times the total content of Wikipedia."
This heady task was completed by just one telescope atop Haleakalā, on Maui, which scanned the visible and near-infrared sky from 2010 to 2014.
"Pan-STARRS is a relatively small telescope when compared with the big ones we have on Mauna Kea ... but it has the biggest astronomical camera in the world; one and a half billion pixels in the camera compared with the 10 million in your typical digital camera at home," said astronomer Eugene Magnier, of the University of Hawaii. If they had printed the survey in one giant photograph, Magnier added, the photo would be one and a half miles long.
The sheer detail captured in the survey, and the fact that the entire database has been made available online, means that it will be used for many years to come by professional and amateur astronomers to make discoveries about the cosmos.
"It's a census of the universe and the sorts of things people will learn by digging into the details of that census will be enormous," said Kenneth Chambers, also an astronomer at the University of Hawaii.
The researchers estimate there to be three billion astronomical sources in the vast cosmic map, so with this release will likely come a slew of new science.
The survey is supported by NASA and the National Science Foundation, with collaborations across 10 research institutions in four countries, and public access to all of the precious data has been made possible through the Space Telescope Science Institute, which has many years of experience with storing and managing huge quantities of astronomical data for the Hubble Space Telescope and other projects.
So what are you waiting for? An entire universe awaits. | 0.872368 | 3.589696 |
2003: JINA NEW PHYSICS CENTER BRINGS GALAXY TO THE LABORATORY
In a sort of a merger between the laboratory and the stars, Michigan State has joined with two other Midwestern universities to establish a nuclear astrophysics center.
The National Science Foundation (NSF) has awarded $10 million to the University of Notre Dame, Michigan State University and the University of Chicago to establish a Physics Frontier Center for Nuclear Astrophysics.
The Joint Institute for Nuclear Astrophysics -- known as JINA -- is a collaborative effort of the three universities. The five-year NSF grant is intended to foster an interdisciplinary approach to nuclear astrophysics that will coordinate efforts between the astrophysics and nuclear physics communities, as well as those between experimenters, theorists, and astronomical observers.
The scientific goal of JINA is to study the broad range of nuclear processes in our universe that control stellar evolution, trigger supernova events, and lead to thermonuclear explosions observed as novae, x-ray- and gamma-ray bursts.
The creation of JINA comes at a time when new generations of particle accelerators are being built or proposed that will recreate stellar nuclear processes in the laboratory. This includes recently completed Coupled Cyclotron Facility at MSU's National Superconducting Cyclotron Laboratory, the nation's premier rare isotope user facility, and the future Rare Isotope Accelerator, the nuclear science community's highest priority for new construction.
Professor Michael Wiescher, a Notre Dame nuclear astrophysicist, will serve as JINA's first director. Research at JINA also will involve investigators from the University of California at Santa Cruz, the University of California at Santa Barbara, the University of Arizona, and Argonne National Laboratory.
JINA MSU co-principal investigators Tim Beers (left) and Hendrik Schatz (right)
"We now have observatories in orbit that obtain detailed measurements of X-ray emission from such compact objects, but we lack the knowledge of the underlying exotic nuclear physics to effectively use these observations as unique laboratories for the behavior of matter under extreme conditions," said Hendrik Schatz, an MSU nuclear astrophysicist and head of one of the main research components of JINA.
The experimental simulation of nuclear processes at stellar conditions will be performed at accelerator facilities at the University of Notre Dame, Michigan State University, and Argonne National Laboratory. It requires the development of new experimental techniques to obtain the missing information on processes that in nature take only place at the extreme conditions of stellar explosions.
One of the mysteries JINA seeks to address is the origin of the chemical elements, in particular, heavy elements, such as gold and uranium.
"We still don't understand why there is so much gold in the universe. We know these heavy elements are the decay products of very exotic atomic nuclei, but how and where in the universe exactly these have been created still remains an open question" Schatz said. "The experimental and theoretical studies in nuclear physics associated with JINA will provide the basis for an understanding of the detailed nuclear processes involved in the origin of the elements."
Complementing the theoretical and experimental efforts at JINA, co-investigator MSU Professor Timothy Beers is leading a survey of element production in the early Galaxy, as revealed in the spectra of ancient stars. His recent detection of radioactive elements, such as uranium and thorium, in the oldest stars in the Galaxy also provides a valuable means to obtain independent estimates of the age of the Universe.
"High-resolution spectroscopic observations of the oldest stars in our galaxy, made with the Hubble Space Telescope and 8m-class telescopes such as the European VLT, have revealed the presence of the very first heavy elements made in the universe," Beers said. "We are using these data to infer the 'recipe of creation'." Data from the new SOAR telescope, in which MSU is a partner, will also play an important role.
The Physics Frontiers Centers program at NSF was created to support research in making transformational advances in the most promising new scientific areas. This is a way to enable major scientific advances at the intellectual frontiers of physics by providing new resources, not usually available to individual investigators or small university research groups, to advance our understanding of the universe. As part of this grant, JINA will engage in many outreach activities aimed at making these scientific advances accessible to the public, educators and students of all levels. For more information, see: http://www.JINAweb.org.
(Sue Nichols, W. Bauer, MSU) | 0.876933 | 3.408919 |
16 Jul Speeding up science on near-Earth asteroids
By Tina Hilding, Voiland College of Engineering and Architecture
RICHLAND, Wash. – Modeling the shape and movement of near-Earth asteroids is now up to 25 times faster thanks to new Washington State University research.
The WSU scientists improved the software used to track thousands of near-Earth asteroids and comets, which are defined as being within 121 million miles or about 1.3 times the distance to the sun.
Their work provides a valuable new tool for studying asteroids and determining which of them might be on a collision course with Earth.
Matt Engels, a PhD student who has been working with Professor Scott Hudson in the School of Engineering and Applied Sciences at WSU Tri-Cities, is lead author of a paper on the research in the July issue of Astronomy and Computing.
Researchers would like to have better information on asteroids, including which of them might crash into earth. The rocks also can provide valuable scientific information, answering fundamental questions about the creation of our solar system and providing a glimpse into our planetary past. Knowing more about individual asteroid composition also could open up new opportunities for possible asteroid mining.
NASA maintains a catalog that includes information on more than 20,000 near-earth asteroids and comets. In the mid-1990s scientists knew of less than 200 of such outer space rocks, but with better telescopes and more efforts at surveying, the numbers of known asteroids has grown dramatically.
But, there are only a trickle of papers that describe individual asteroids. Once a new asteroid is discovered, modeling it takes several months, if not longer, said Engels. The research is painstaking.
In the mid-1990s, Hudson, who has an asteroid named after him, wrote the primary modeling software tool that researchers use to describe asteroids and their behavior. Using ground-based radar and optics data, the software helps researchers learn important information, such as an asteroid’s possible mineral make-up, current and future orbit, shape, and how it spins in space. In fact, Hudson co-authored a paper published in Science that determined that at least one asteroid, 1950 DA, has a very tiny chance of hitting earth during a precise 20-minute period in March of 2880.
“The software was written for a super computer, so it’s really, really slow,” said Engels, who jumped at improving it for his PhD project. “It can take a long time to do the modeling to draw any conclusions from it, and it takes awhile to crunch the data to write a paper in the first place.”
“It’s taking advantage of the horsepower that is used in computer graphics rendering,” Engels said. “It’s very cost effective and you don’t need a super computer. You can use a consumer level graphics card available for under $500.”
The new version of code works much faster. The researchers revised it to make operations work concurrently instead of performing one at a time. Because the work is very similar to the everyday graphics that modern computers use to crunch out nice displays, the researchers transferred the operations to the computer’s graphics processing units, or GPUs. GPUs are designed to perform complex mathematical and geometric calculations for graphics rendering and have a tremendous amount of power to do parallel calculations.
The improvements to the algorithms could also someday be used for a variety of other purposes, said Engels, who works as a research engineer at Pacific Northwest National Laboratory, such as for modeling systems in the electric power grid or gas and oil industry.
Engels is verifying the code with real asteroid data. He hopes to have it available to the astronomy community later this year. | 0.830495 | 3.300402 |
Just when scientists thought they had a tidy theory for how the giant asteroid Vesta formed, a new paper from NASA’s Dawn mission suggests the history is more complicated.
If Vesta’s formation had followed the script for the formation of rocky planets like our own, heat from the interior would have created distinct, separated layers of rock (generally, a core, mantle and crust). In that story, the mineral olivine should concentrate in the mantle.
However, as described in a paper in this week’s issue of the journal Nature, that’s not what Dawn’s visible and infrared mapping spectrometer (VIR) instrument found. The observations of the huge craters in Vesta’s southern hemisphere that exposed the lower crust and should have excavated the mantle did not find evidence of olivine there. Scientists instead found clear signatures of olivine in the surface material in the northern hemisphere.
“The lack of pure olivine in the deeply excavated basins in Vesta’s southern hemisphere and its unexpected discovery in the northern hemisphere indicate a more complex evolutionary history than inferred from models of Vesta before Dawn arrived,” said Maria Cristina De Sanctis, Dawn co-investigator and VIR leader at the National Institute for Astrophysics in Rome, Italy.
Perhaps Vesta only underwent partial melting, which would create pockets of olivine rather than a global layer. Perhaps the exposed mantle in Vesta’s southern hemisphere was later covered by a layer of other material, which prevented Dawn from seeing the olivine below it.
“These latest findings from Dawn stimulate us to test some different ideas about Vesta’s origin,” said Carol Raymond, Dawn’s deputy principal investigator at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “They also show us what additional information we can learn by going into orbit around places like Vesta to complement the bits that come to us as meteorites or observations from long distances.”
Dawn is currently cruising toward its second destination, the dwarf planet Ceres, which is the biggest member of the main asteroid belt between Mars and Jupiter. It will arrive at Ceres in early 2015.
Source: NASA press release | 0.837747 | 3.818965 |
Survey Says… Earth-Sized Planets Common
NASA Survey Suggests Earth-Sized Planets are Common
An artist’s rendition of Jupiter (left) and Earth (right) transiting the sun, as viewed from outside the solar system. Credit: NASA/Ames Research Center
Nearly one in four stars similar to the Sun may host planets as small as Earth, according to a new study funded by NASA and the University of California.
The study is the most extensive and sensitive planetary census of its kind. Astronomers used the W.M. Keck Observatory in Hawaii for five years to search 166 Sun-like stars near our solar system for planets of various sizes, ranging from three to 1,000 times the mass of Earth. All of the planets in the study orbit close to their stars. The results show more small planets than large ones, indicating small planets are more prevalent in our Milky Way galaxy.
“We studied planets of many masses — like counting boulders, rocks and pebbles in a canyon — and found more rocks than boulders, and more pebbles than rocks. Our ground-based technology can’t see the grains of sand, the Earth-size planets, but we can estimate their numbers,” said Andrew Howard of the University of California, Berkeley, lead author of the new study. “Earth-size planets in our galaxy are like grains of sand sprinkled on a beach — they are everywhere.”
The study appears in the Oct. 29 issue of the journal Science.
A new survey, funded by NASA and the University of California, reveals that small planets are more common than large ones. Credit: NASA/JPL-Caltech/UC Berkeley
The research provides a tantalizing clue that potentially habitable planets could also be common. These hypothesized Earth-size worlds would orbit farther away from their stars, where conditions could be favorable for life. NASA’s Kepler spacecraft is also surveying Sun-like stars for planets and is expected to find the first true Earth-like planets in the next few years.
Howard and his planet-hunting team, which includes principal investigator Geoff Marcy, also of the University of California, Berkeley, looked for planets within 80-light-years of Earth, using the radial velocity, or “wobble,” technique.
They measured the numbers of planets falling into five groups, ranging from 1,000 times the mass of Earth, or about three times the mass of Jupiter, down to three times the mass of Earth. The search was confined to planets orbiting close to their stars — within 0.25 astronomical unit, or a quarter of the distance between our Sun and Earth.
A distinct trend jumped out of the data: smaller planets outnumber larger ones. Only 1.6 percent of stars were found to host giant planets orbiting close in. That includes the three highest-mass planet groups in the study, or planets comparable to Saturn and Jupiter. About 6.5 percent of stars were found to have intermediate-mass planets, with 10 to 30 times the mass of Earth — planets the size of Neptune and Uranus. And 11.8 percent had the so-called “super-Earths,” weighing in at only three to 10 times the mass of Earth.
“During planet formation, small bodies similar to asteroids and comets stick together, eventually growing to Earth-size and beyond. Not all of the planets grow large enough to become giant planets like Saturn and Jupiter,” Howard said. “It’s natural for lots of these building blocks, the small planets, to be left over in this process.”
Scientists hope that NASA’s Kepler spacecraft will soon discover a true Earth-like planet. Image Credit: NASA
The astronomers extrapolated from these survey data to estimate that 23 percent of Sun-like stars in our galaxy host even smaller planets, the Earth-sized ones, orbiting in the hot zone close to a star. “This is the statistical fruit of years of planet-hunting work,” said Marcy. “The data tell us that our galaxy, with its roughly 200 billion stars, has at least 46 billion Earth-size planets, and that’s not counting Earth-size planets that orbit farther away from their stars in the habitable zone.”
The findings challenge a key prediction of some theories of planet formation. Models predict a planet “desert” in the hot-zone region close to stars, or a drop in the numbers of planets with masses less than 30 times that of Earth. This desert was thought to arise because most planets form in the cool, outer region of solar systems, and only the giant planets were thought to migrate in significant numbers into the hot inner region. The new study finds a surplus of close-in, small planets where theories had predicted a scarcity.
“We are at the cusp of understanding the frequency of Earth-sized planets among celestial bodies in the solar neighborhood,” said Mario R. Perez, Keck program scientist at NASA Headquarters in Washington. “This work is part of a key NASA science program and will stimulate new theories to explain the significance and impact of these findings.” | 0.917429 | 3.453675 |
Astrophotography is fairly popular among photographers and amateur astronomers. Images of the night sky can be obtained with the most basic film and digital cameras. For simple star trails, no equipment may be necessary other than common tripods. There is a wide range of commercial equipment geared toward basic and advanced astrophotography. Amateur astronomers and amateur telescope makers also use homemade equipment and modified devices. To achieve the best images, it does however require one to purchase the fastest, wide lens you can afford. This allows for maximum light to enter the lens, f1.4 – f2.8 lenses are the lenses of choice here; they are however expensive.
Depending on the results one is looking for, it is best to capture stunning Milky Way images under low or no light pollution. This often requires one to travel uninhabited regions, like the Karoo or Cederberg in South-Africa, with charming images of windmills and rock formations combined with the Milky Way.
The Milky Way is a barred spiral galaxy some 100 000–120 000 light-years in diameter, which contains 100–400 billion stars! It may contain at least as many planets as well. The Solar System is located within the disc, about 27 000 light-years away from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm. The stars in the inner ≈ (mathematical symbol for is approximately equal to) 10 000 light-years form a bulge and one or more bars that radiate from the bulge. The very center is marked by an intense radio source, named Sagittarius A*, which is likely to be a supermassive black hole. When observing the night sky, the term “Milky Way” is limited to the hazy band of white light some 30° wide, arcing across the sky. To capture the full arc, one needs to capture a panoramic view of several images, and stitch them together.
The Milky Way has a relatively low surface brightness. Its visibility can be greatly reduced by background light such as light pollution or stray light from the Moon. It is readily visible when the limiting magnitude is +5.1 or better and shows a great deal of detail at +6.1. This makes the Milky Way difficult to see from any brightly lit urban or suburban location, but very prominent when viewed from a rural area when the Moon is below the horizon, or on a New Moon.
As viewed from Earth, the visible region of the Milky Way’s Galactic plane occupies an area of the sky that includes 30 constellations. The center of the Milky Way lies in the direction of the constellation Sagittarius; it is here that the Milky Way is brightest. From Sagittarius, the hazy band of white light appears to pass westward to the Galactic anticenter in Auriga. The band then continues westward the rest of the way around the sky, back to Sagittarius. The band divides the night sky into two roughly equal hemispheres.
It is this marvel of Creation, that we as astrophotographers try to capture in as many artistic ways as possible. Our biggest threat to this form of photography is urban expansion with increased light pollution.
Click on the images below to view an enlarged single image.
All my images are available for purchase as prints. Digital images can be used under license agreement. Should you wish to purchase or license my images, please click here for more information, so I can assist you with your needs. | 0.871658 | 3.54628 |
In honor of American Archive Month, NASA has selected eight images from a group of unique celestial objects taken by the Chandra X-Ray Observatory. It's the first time these images have ever been seen by the public — and they're as freaky as they are gorgeous.
The Chandra Data Archive (CDA) allows scientists and the general public to access data collected by the Chandra X-Ray Observatory. This particular batch of images selected by NASA for American Archive Month "represent the observations of thousands of objects that are permanently available to the world thanks to Chandra’s archive," writes the agency in its official release. And here they are:
This object was produced by the explosion of a massive star in the Milky Way galaxy. A Chandra observation of this supernova remnant reveals the presence of extremely high-energy particles produced as the shock wave from this explosion expands into interstellar space. In this image, the X-rays from Chandra (purple) have been combined with optical data from the Digitized Sky Survey (red, green, and blue).
Jets generated by supermassive black holes at the centers of galaxies can transport huge amounts of energy across great distances. 3C353 is a wide, double-lobed source where the galaxy is the tiny point in the center and giant plumes of radiation can be seen in X-rays from Chandra (purple) and radio data from the Very Large Array (orange).
A region of glowing gas in the Sagittarius arm of the Milky Way galaxy, NGC 3576 is located about 9,000 light years from Earth. Such nebulas present a tableau of the drama of the evolution of massive stars, from the formation in vast dark clouds, their relatively brief (a few million years) lives, and the eventual destruction in supernova explosions. The diffuse X-ray data detected by Chandra (blue) are likely due to the winds from young, massive stars that are blowing throughout the nebula. Optical data from ESO are shown in orange and yellow.
This image provides a view into the central region of a galaxy that is similar in overall appearance to our own Milky Way, but contains a much more active supermassive black hole within the white area near the top. This galaxy, known as NGC 4945, is only about 13 million light years from Earth and is seen edge-on. X-rays from Chandra (blue), which have been overlaid on an optical image from the European Space Observatory, reveal the presence of the supermassive black hole at the center of this galaxy.
When radiation and winds from massive young stars impact clouds of cool gas, they can trigger new generations of stars to form. This is what may be happening in this object known as the Elephant Trunk Nebula (or its official name of IC 1396A). X-rays from Chandra (purple) have been combined with optical (red, green, and blue) and infrared (orange and cyan) to give a more complete picture of this source.
This object, also known as G41.1-0.3), is a Galactic supernova remnant with an unusual shape. Researchers think its box-like appearance is produced as the heated remains of the exploded star — detected by Chandra in X-rays (purple) — runs into cooler gas surrounding it. This composite of the area around 3C 397 also contains infrared emission from Spitzer (yellow) and optical data from the Digitized Sky Survey (red, green, and blue).
The details of how massive stars explode remains one of the biggest questions in astrophysics. Located in the neighboring galaxy of the Small Magellanic Cloud, this supernova, SNR B0049-73.6, provides astronomers with another excellent example of such an explosion to study. Chandra observations of the dynamics and composition of the debris from the explosion support the view that the explosion was produced by the collapse of the central core of a star. In this image, X-rays from Chandra (purple) are combined with infrared data from the 2MASS survey (red, green, and blue).
This object is a medium-sized, face-on spiral galaxy about 22 million light years away from Earth. In the past century, eight supernovas have been observed to explode in the arms of this galaxy. Chandra observations (purple) have, in fact, revealed three of the oldest supernovas ever detected in X-rays, giving more credence to its nickname of the “Fireworks Galaxy.” This composite image also includes optical data from the Gemini Observatory in red, yellow, and cyan. | 0.86707 | 3.801316 |
A veteran Mars probe received a two-year missionextension though Sept. 2010 to keep watch over the red planet.
NASA's Mars Odyssey represents the longest-serving of sixspacecraft currently orbiting Mars, after first reaching the planet in 2001. Itsnew extended mission requires changing orbit to gain a bettervantage point for doing infrared mapping of Martian minerals.
The first year of the two-year extended mission carries aprice tag of $11 million through Sept. 2009, said Guy Webster, NASA spokesperson at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
An orbital adjustment should allow Odyssey to look downat sites in mid-afternoon rather than late afternoon. The spacecraft's thermalcamera could then better detect infrared radiation from warmer rocks to betteridentify them.
"This will allow us to do much more sensitivedetection and mappingof minerals," said Jeffrey Plaut, a Mars Odyssey scientist at JPL.
However, the shift to mid-afternoon is also expected tohalt usage of an instrument in Odyssey's Gamma Ray Spectrometer. The gamma raydetector requires the later-hour orbit to avoid overheating a criticalcomponent.
Odyssey began its course change by firing up itsthrusters for almost six minutes on Sept. 30, the last day of its secondtwo-year extension.
"This was our biggest maneuver since 2002, and itwent well," said Gaylon McSmith, Odyssey mission manager at JPL.?"The spacecraft is in good health. The propellant supply is adequate foroperating through at least 2015."
The spacecraft's orbit is synchronized with the sun, sothat local solar time on Mars has been about 5 p.m. wherever Odyssey flew overfrom the north pole to south pole. On the flipside, local time has been roughly5 a.m. as the spacecraft flew from south to north.
The time should gradually change to somewhere between2:30 p.m. and 3 p.m. over the next year or so, as Odyssey's overhead pass getsearlier by about 20 seconds per day.
Odyssey's overall mission so far has helped detect largequantities of water-icenear the surface in the higher latitudes of Mars, which led to NASA's PhoenixMars Lander mission. The spacecraft helped keepan eye on Phoenix as the lander descended to the surface, and continues torelay information from Phoenix back to Earth.
- Video: Digging on Mars
- Frozen Death Looms for Phoenix Mars Lander
- Special Report: Odyssey Mission to Mars | 0.81927 | 3.037559 |
The comet or asteroid hit near Jupiter's South Pole. The color part of this picture shows the area of the impact magnified. There is a white, oval storm. Do you see the black patch below the white oval? That is where the comet or asteroid hit!
Click on image for full size
Images courtesy of NASA, ESA, and H. Hammel (Space Science Institute, Boulder, Colo.), and the Jupiter Impact Team.
Impact on Jupiter - July 2009
Anthony Wesley is an astronomer in Australia. One night in July 2009, Wesley noticed a dark spot on Jupiter that hadn't been there before. He had discovered the remains of a huge impact on Jupiter! A comet or asteroid had collided with the giant planet. The impact left a dark "scar" in Jupiter's atmosphere where the comet or asteroid had exploded.
Nobody saw the object it hit Jupiter. We don't know whether it was a comet or an asteroid. The comet or asteroid was probably a few hundred meters (less than a mile) across. It exploded in Jupiter's upper atmosphere. The explosion made a dark smear in Jupiter's atmosphere. The dark spot is near Jupiter's South Pole. The dark spot is about as big as the Pacific Ocean.
After Wesley reported the impact, lots of other astronomers pointed their telescopes at Jupiter. The Hubble Space Telescope snapped a nice picture. The Keck telescope in Hawaii also took a picture... in infrared "light". Those pictures will help scientists learn about large impacts. Jupiter was hit by another comet not too long ago. In 1994 several pieces of Comet Shoemaker-Levy 9 crashed into Jupiter.
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UCLA astronomers are preparing to observe a star approaching a black hole to test Albert Einstein’s theory of gravity.
In a study published in February, UCLA astronomers in the Galactic Center Group, a research team focused on studying the center of the Milky Way, showed the star S2 is likely a single star, rather than a binary star. This knowledge allows the researchers to use S2 to test Einstein’s theory of gravity as it approaches a black hole later in March.
At the center of the Milky Way galaxy is a large black hole, said Andrea Ghez, professor of physics and astronomy and director of the Galactic Center Group. Black holes have massive gravitational forces, allowing researchers to study gravity under extreme conditions, she said.
“Gravity is one of the four fundamental forces, but it’s the least understood,” Ghez said.
While Einstein’s theory of gravity is mostly accepted, it has not yet been tested in extreme situations, like near black holes, Ghez said. Studying stars near the black hole allows physicists to see if Einstein’s theory of gravity still holds in extreme conditions.
“(The theory of) gravity is fraying,” Ghez said. “Einstein’s had a good run of it … but it can’t explain everything we see.”
Einstein’s general theory of relativity predicts that large objects cause a dip or well in space-time, according to NASA. In Einstein’s model, light coming out of the well will lose energy, or redshift.
The star, S2, is approaching the black hole near the center of the Milky Way galaxy. At the closest point in its orbit, S2’s distance from the black hole will be about ten times the distance from the sun to Saturn, Ghez said.
Devin Chu, an astronomy graduate student and lead author on the study, said as S2 approaches the black hole, the light emitted from the star may seem different. Studying S2 near the black hole is an opportunity to validate Einstein’s theory of gravity, he added.
“The light is trying to escape a gravitational well,” Chu said. “It will appear redshifted.”
To use S2 to study the black hole’s effects on gravity, the researchers first needed to figure out if S2 is a single star or a binary star. If S2 had a companion star, studying the effect of gravity near the black hole on S2’s orbit would be more complicated because both the black hole and the companion star would affect the gravity near S2, Ghez said.
Tuan Do, deputy director of the Galactic Center Group, looked for small deviations from S2’s orbit that could be caused by a companion star.
“If a star has a companion star, its orbit will wobble, they’ll pull on each other,” Do said.
The researchers looked at data collected from 2000 to 2016 on the orbit of S2 and looked for any wobble effects. Making these measurements required high accuracy because S2 moves around the black hole about 200 times faster than the expected wobble effects of companion stars, Do said.
The researchers concluded it is unlikely S2 has a companion star, and, if it did, it would only be about one-tenth of the mass of S2, which is too small to affect any measurements on the black hole’s effect on gravity.
Ghez said this is the first time these scientists have the instruments and technology to measure the black hole’s effects on the star. S2 will approach the black hole March 16, and the scientists will collect data at the W. M. Keck Observatory in Hawaii until S2 is obscured from view in September. It will be another 16 years until S2 approaches the black hole again.
“Every night will be a new measurement,” Ghez said. “We’ve been preparing for this for years.” | 0.923614 | 3.835131 |
ESA Science & Technology - Gaia
The formation of the Sun, the Solar System and the subsequent emergence of life on Earth may be a consequence of a collision between our galaxy, the Milky Way, and a smaller galaxy called Sagittarius, discovered in the 1990s to be orbiting our galactic home.
Astronomers have pondered for years why our galaxy, the Milky Way, is warped. Data from ESA's star-mapping satellite Gaia suggest the distortion might be caused by an ongoing collision with another, smaller, galaxy, which sends ripples through the galactic disc like a rock thrown into water.
A 500-day global observation campaign spearheaded more than three years ago by ESA’s galaxy-mapping powerhouse Gaia has provided unprecedented insights into the binary system of stars that caused an unusual brightening of an even more distant star.
Rather than leaving home young, as expected, stellar 'siblings' prefer to stick together in long-lasting, string-like groups, finds a new study of data from ESA's Gaia spacecraft.
On 31 March 2017, Jupiter's moon Europa passed in front of a background star – a rare event that was captured for the first time by ground-based telescopes thanks to data provided by ESA's Gaia spacecraft. | 0.855713 | 3.290968 |
Remote observations have suggested that Ultima Thule has a lumpy shape, or could even be two bodies in orbit around each other. Image Credits: NASA/JHUAPL/SwRI/Steve Gribben
At 05:33 GMT on New Year’s Day 2019, NASA’s New Horizons made a flyby of the Kuiper Belt Object known as Ultima Thule.
Ahead of the encounter we spoke to Ramy El-Maarry from Birkbeck, University of London, who worked with ESA’s Rosetta team before joining New Horizons as a science team collaborator.
What is New Horizons doing at the moment?
New Horizons is now in its extended mission, looking at small bodies in the Kuiper Belt region.
The Kuiper Belt is the third zone of the Solar System.
If you think of the first zone as being the inner planets, the second zone is the giant planets.
The third zone, the Kuiper Belt zone, has lots of bodies that are potentially sources for comets.
My goal with Ultima Thule is to find out what comets look like before they enter the inner Solar System and become modified by activity.
This is our opportunity to look at a really primordial body that has been in deep freeze for 4.6 billion years and give us a glimpse of what the conditions were like in the early Solar System.
Why was Ultima Thule chosen as the probe’s second destination?
When New Horizons set off for Pluto we didn’t know Ultima Thule existed.
Then around 2014, there was approval for an extended mission and the scientists of the mission began to think what the next target would be.
Astronomers on the team started looking for potential bodies using the Hubble telescope and in 2014 discovered Ultima Thule, which at the time was just called 2014 MU69.
We looked for a name that’s easier to remember and Ultima Thule [the traditional name for places beyond the known world] was finally chosen.
It also had an orbit that had a very low inclination to the solar ecliptic.
This suggests that it wasn’t perturbed that much, so it was in that place in the Kuiper Belt since it formed – it didn’t form much closer to the Sun and then move outwards or vice versa.
It’s orbitally stable and has been in this zone since it formed.
It fits the bill about what we intended to do in terms of science, but the body was essentially chosen because it fit the trajectory.
What do we already know about Ultima Thule?
There wasn’t a lot known at the time it was discovered, however there was a chance for better characterisation when Ultima Thule passed in front of a star.
We were able to use this occultation to get a better understanding of Ultima Thule.
From this we understood that it was a body approximately 30km in diameter that’s quite irregular in shape.
It could either be what we call a binary system where we have two bodies that are orbiting each other in very close proximity, or it could even be a contact binary – a body that has merged, like Comet 67P.
We also know that it is likely reddish in colour.
That could be due to some organic material at the surface that has been altered by interaction with cosmic rays and solar winds.
What do we hope to learn about Ultima Thule?
We hope to learn about the surface geology.
We have some high-resolution cameras to get a better grasp of what the surface looks like.
We’ve also got an imaging spectrometer that will allow us to get information about what the surface is made of.
So together that will give us a lot of information on these bodies.
What will this tell us about the Solar System?
Essentially, we want to know about the conditions when the Solar System formed.
That would give us information about the other planetary systems we know about from exoplanets and so forth.
Looking at Ultima Thule, looking at Kuiper Belt objects, that gives us a better idea about comets in our Solar System.
It will also tell us lots the origin of water in our Solar System, and the origin of life.
What are you looking forward to on the flyby day?
I’m really looking forward to the first images. I think for me that’s the most exciting part.
New Horizons is one of the few missions where you still have an exploration flavour to it.
The flavour of the unknown.
This is a region that has never been explored by any other spacecraft – no one has ever explored a body in the Kuiper Belt at such close distance.
One of the real significances of this flyby is that New Horizons is going to be 3 times closer to Ultima Thule than it was to Pluto.
When will we start to see those images?
It’s a fly by so we’ll hopefully get a few images as we approach.
These will be followed by higher resolutions images as we get to closest approach, and we’ll get other images as we move further away.
The very large distances involved: it takes a long time to download these things, so we get some lower resolution images first, and the rest later at a higher resolution. | 0.861791 | 3.768419 |
During the next couple of weeks skywatchers will be turning their attention to a newly discovered comet that has just swept past the Sun and will soon cruise past Earth on its way back out toward the depths of the outer solar system.
Astronomers, who attempt to forecast the future characteristics and behavior of these cosmic vagabonds, have found this new object to be a better-than-average performer.
The comet is now visible with a simple pair of binoculars, and it's also dimly visible to the naked eye if you know precisely where to look.
The first word about this new comet (catalogued as C/2006 A1) came from the Smithsonian Astrophysical Observatory, Cambridge, Massachusetts, which serves as the clearinghouse in the United States for astronomical discoveries. The SAO also serves in that capacity as an agency of the International Astronomical Union.
On Jan. 2, Grzegorz Pojmanski at the Warsaw University Astronomical Observatory discovered a faint comet on a photograph that was taken on New Year's Day from the Las Campanas Observatory in La Serena, Chile, as part of the All Sky Automated Survey (ASAS). A confirmation photograph was taken on Jan. 4. Later a prediscovery image of the comet dating back to Dec. 29, 2005 was also found.
Interestingly, about seven hours after Pojmanski detected the comet, another astronomer, Dr. Kazimieras Cernis at the Institute of Theoretical Physics and Astronomy at Vilnius, Lithuania, spotted it on ultraviolet images taken a few days earlier from the SOHO satellite. Despite this, however, the comet bears only Pojmanski's name.
A preliminary orbit for the new comet was quickly calculated. At the time of its discovery, the comet was about 113 million miles (181 million kilometers) from the Sun. But orbital elements indicated that on Feb. 22 it would be passing closest to the Sun (called "perihelion") at a distance of 51.6 million miles-not quite half the Earth's average distance from the Sun.
At the time of its discovery, the comet shone at a feeble magnitude of roughly 11 to 12, which is about 100 times dimmer than the faintest stars that can be perceived with the unaided eye. In addition, Comet Pojmanski was buried in the deep southern part of the sky, among the stars of the constellation of Indus (the Indian), and accessible only to observers in the Southern Hemisphere.
But since its discovery, the comet has steadily been progressing on a northward path.
Finally, the comet is becoming poised for visibility for Northern Hemisphere skywatchers, and it is expected to put on its best showing during the last days of February and the first week of March in the dawn morning sky.
What to expect
Preliminary predictions indicated that the comet would dutifully brighten as it approached the Sun. At perihelion, the most optimistic forecasts had Comet Pojmanski attaining a magnitude of +6.5 (generally considered the threshold of naked-eye visibility).
The comet had other plans, however, and has been increasing in brightness at a much faster pace.
On Feb. 7, Andrew Pearce, observing from Nedlands in Western Australia, caught the comet already shining at magnitude +6.4. "This comet appears to be brightening rapidly," noted Mr. Pearce, adding that a faint tail was also becoming visible. Twelve days later, the comet had brightened nearly a full magnitude, according to Mr. Pearce, reaching +5.4. On February 20, Luis Mansilla at the Canopus Observatory in Rosario, Argentina was able to see the comet in 7x50 binoculars despite interference from the Moon and haze near the horizon. He estimated its brightness at +5.3.
Currently, Comet Pojmanski is shining at around magnitude 5, which is roughly about the same brightness as the faintest star in the bowl of the Little Dipper. Sharp-eyed observers in a dark, clear sky can actually glimpse it without any optical aid.
The comet is located in the zodiacal constellation of Capricornus, the Sea Goat. Beginning Feb. 27, skywatchers in the Northern Hemisphere can try locating it, very low above the horizon, somewhat south of due east about 90 minutes before sunrise. You can use Venus as a guide on this morning: the comet will be situated roughly 7 degrees to the left and slightly below the brilliant planet (the width of your fist held at arm's length and projected against the sky is roughly equal to 10 degrees).
As viewed from midnorthern latitudes, Comet Pojmanski will be positioned a little higher above the horizon each morning at the start of morning twilight. While it's only 5 degrees high on Feb. 27, this quickly improves to 10 degrees by March 2; 16 degrees by March 5 and 22 degrees (more than "two fists" up from the horizon) by March 9.
What you can see
In the early morning sky it can be readily picked up in binoculars looking like a small, circular patch of light with a bluish-white hue and an almost star-like center.
The comet will passing closest to Earth on March 5, when it be 71.7 million miles (115.4 million kilometers) away.
In small telescopes the comet's gaseous head or "coma" should appear roughly 1/6 of the Moon's apparent diameter as seen from Earth (an actual linear diameter of 209,000 miles or 335,000 kilometers). It will also likely display a short, faint narrow tail composed chiefly of ionized gases.
Well-known comet expert, John E. Bortle of Stormville, New York compares the view of Comet Pojmanski to that of an "apple on a stick; typical of dust-poor comets."
After March 5, the comet will be receding from both the Sun and Earth and rapidly fade as it heads back out into space, beyond the limits of the outer solar system.
Basic Sky Guides
- Full Moon Fever
- Astrophotography 101
- Sky Calendar & Moon Phases
- 10 Steps to Rewarding Stargazing
- Understanding the Ecliptic and the Zodiac
- False Dawn: All about the Zodiacal Light
- Reading Weather in the Sun, Moon and Stars
- How and Why the Night Sky Changes with the Seasons
- Night Sky Main Page: More Skywatching News & Features
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.
1 AU, or astronomical unit, is the distance from the Sun to Earth, or about 93 million miles.
Magnitude is the standard by which astronomers measure the apparent brightness of objects that appear in the sky. The lower the number, the brighter the object. The brightest stars in the sky are categorized as zero or first magnitude. Negative magnitudes are reserved for the most brilliant objects: the brightest star is Sirius (-1.4); the full Moon is -12.7; the Sun is -26.7. The faintest stars visible under dark skies are around +6.
Degrees measure apparent sizes of objects or distances in the sky, as seen from our vantage point. The Moon is one-half degree in width. The width of your fist held at arm's length is about 10 degrees. The distance from the horizon to the overhead point (called the zenith) is equal to 90 degrees.
Declination is the angular distance measured in degrees, of a celestial body north or south of the celestial equator. If, for an example, a certain star is said to have a declination of +20 degrees, it is located 20 degrees north of the celestial equator. Declination is to a celestial globe as latitude is to a terrestrial globe.
Arc seconds are sometimes used to define the measurement of a sky object's angular diameter. One degree is equal to 60 arc minutes. One arc minute is equal to 60 arc seconds. The Moon appears (on average), one half-degree across, or 30 arc minutes, or 1800 arc seconds. If the disk of Mars is 20 arc seconds across, we can also say that it is 1/90 the apparent width of the Moon (since 1800 divided by 20 equals 90). | 0.852557 | 3.801104 |
The discovery of Makemake's little moon increases the parallels between Pluto and Makemake. This is because both of the small icy worlds are already known to be well-coated in a frozen shell of methane. Furthermore, additional observations of the little moon will readily reveal the density of Makemake--an important result that will indicate if the bulk compositions of Pluto and Makemake are similar. "This new discovery opens a new chapter in comparative planetology in the outer Solar System," Dr. Marc Buie commented in the April 26, 2016 Hubble Press Release. Dr. Buie, the team leader, is also of the Southwest Research Institute.
Many people listen to the weather report on the radio before they head out the door in the morning so they can be prepared for the day to come.
Water in its life-sustaining liquid phase exists beyond our own planet, both in our Solar System--and elsewhere. With oceans of water sloshing around on 71% of our own planet's surface, Earth still remains the only planet known to have stable bodies of liquid water. Liquid water is essential for all known life forms on Earth. The existence of water on the surface of Earth is the outcome of its atmospheric pressure and a stable orbit in our Sun;s circumstellar habitable zone. The habitable zone is that Goldilocks region, surrounding a star, where the temperature is not too hot, not too cold, but just right for life sustaining water to exist in its liquid phase. However, the origin of Earth's water still remains unknown. | 0.844634 | 3.070868 |
The Supernovae - CESAR
Supernovae Detection in Nearby Galaxies
The telescope is going to systematically monitor several hundreds of spiral galaxies that lie less than 300 million light years from our Milky Way, in hopes of capturing the rise in light from a supernova outburst. Supernovae of type-Ia are very important astrophysical objects because of their use as absolute distance indicators.
Supernovae Type Ia
Type Ia supernovae are thought to be interacting binary star systems in which a white dwarf star is obtaining mass via an accretion disk from the star companion. As the white dwarf accretes more and more matter and goes over the Chandrasaekar limit (1.4 solar masses), a thermonuclear explosion results. Since this critical limit of 1.4 solar masses consistently sets the amount of material in the blast, these types of supernovae are more useful as standard candles than other types. Early detection of supernovae explosions is important to get vital spectroscopic information for type classification while the system is still bright and spectroscopy still possible.
Is also important the observation of the outburst maximum light, which gives information about its distance. Assuming the luminosity can be established for the type Ia supernovae, its absolute magnitude is then known. Observation of its apparent magnitude yields the distance to it and the galaxy in which it resides by the so-called distance modulus, m - M = 5 log d - 5, where m and M are the apparent and absolute magnitudes, and d is the distance in parsecs to the supernova and host galaxy.
Supernovae are bright enough to be observed at cosmologically important distances, thereby increasing their significance in the search for those parameters governing the expansion rate of the universe (i.e. Hubble constant).
Supernovae Monitoring Program
Earliest possible observations are desired as the supernova fades from maximum light during the weeks after the outburst. Early detection of supernovae candidates requires systematical vigilance. The appearance of a supernova in any one galaxy is an extremely rare occurrence, but by monitoring many galaxies, the likelihood of discovery increases.
The first phase involved imaging of a few hundred galaxies in order to use these star fields as templates. The images of the galaxy and surrounding star field must be transformed into transparent overlays to be used on site at the telescope. Later, an image of a candidate galaxy is taken and upon CCD readout, the overlay is placed on top of the computer screen to check for any "new" stars in or near the galaxy that are not in the template. In this way, rapid identification can take place without the need for exhaustive photometry and data analysis, or relying on memorization of many star fields. Every successful confirmation is usually followed up quite rapidly with spectroscopic identification from professionals at major observatories.
There are more than enough galaxies accessible by the telescope to ensure some degree of success.
Distribution of Supernovae in nearby galaxies since 1885. Number of objects is plotted versus visual magnitude. | 0.886815 | 4.119878 |
The vast majority of galaxies exist in clusters. These clusters are joined on larger scales by filaments and sheets of galaxies, between which, gigantic galactic voids are nearly entirely free of galaxies. These voids are often hundreds of million of light years across. Only rarely does a lonely galaxy break the emptiness. Our own Milky Way rests in one of these large sheets which borders the Local Void which is nearly 200 million light years across. In that emptiness, there have been tentative identifications of up to sixteen galaxies, but only one has been confirmed to actually be at a distance that places it within the void.
This dwarf galaxy is ESO 461-36 and has been the target of recent study. As expected of galaxies within the void, ESO 461-36 is exceptionally isolated with no galaxies discovered within 10 million light years.
What is surprising for such a lonely galaxy is that when astronomers compared the stellar disc of the galaxy with a mapping of hydrogen gas, the gas disc was tilted by as much as 55°. The team proposes that this may be due to a bar within the galaxy acting as a funnel along which gas could accrete onto the main disc. Another option is that this galaxy was recently involved in a small scale merger. The tidal pull of even a small satellite could potentially draw the gas into a different orbit.
This disc of gas is also unusually extended, being several times as large as the visual portion of the galaxy. While intergalactic space is an excellent vacuum, compared to the space within voids it is a relatively dense environment. This extreme under-density may contribute to the puffing up of the gaseous disc, but with the rarity of void galaxies, there is precious little to which astronomers can compare.
Compared with other dwarf galaxies, ESO 461-36 is also exceptionally dim. To measure brightness, astronomers generally use a measure known as the mass to light ratio in which the mass of the galaxy, in solar masses, is divided by the total luminosity, again using the Sun as a baseline. Typical galaxies have mass to light ratios between 2 and 10. Common dwarf galaxies can have ratios into the 30’s. But ESO 461-36 has a ratio of 89, making it among the dimmest galaxies known.
Eventually, astronomers seek to discover more void galaxies. Not only do such galaxies serve as interesting test beds for the understanding of galactic evolution in secular environments, but they also serve as tests for cosmological models. In particular the ΛCDM model predicts that there should be far more galaxies scattered in the voids than are observed. Future observations could help to resolve such discrepancies. | 0.813057 | 4.030017 |
Astronomers have spotted three supermassive black holes (SMBHs) at the center of three colliding galaxies a billion light years away from Earth. That alone is unusual, but the three black holes are also glowing in x-ray emissions.
This is evidence that all three are also active galactic nuclei (AGN,) gobbling up material and flaring brightly.
This discovery may shed some light on the “final parsec problem,” a long-standing issue in astrophysics and black hole mergers.
Astronomers found the three SMBHs in data from multiple telescopes, including the Sloan Digital Sky Survey (SDSS,) the Chandra X-ray Observatory, and the Wide-field Infrared Survey Explorer (WISE.)
The three black holes are wrapped up in an almost unimaginably epic event; a merger of three galaxies. These triplet mergers may play a critical role in how the most massive black holes grow over time.
The astronomers who found it were not expecting to find three black holes in the center of a triple-galaxy merger.
“We were only looking for pairs of black holes at the time, and yet, through our selection technique, we stumbled upon this amazing system,” said Ryan Pfeifle of George Mason University in Fairfax, Virginia, the first author of a new paper in The Astrophysical Journal describing these results.
“This is the strongest evidence yet found for such a triple system of actively feeding supermassive black holes.”
Triple black hole systems are difficult to spot because there’s so much going on in their neighbourhood. They’re shrouded in gas and dust that makes it challenging to see into. In this study, it took several telescopes operating in different parts of the electromagnetic spectrum to uncover the three holes. It also took the work of some citizen scientists.
They’re not only difficult to spot, but rare.
“Dual and triple black holes are exceedingly rare,” said co-author Shobita Satyapal, also of George Mason, “but such systems are actually a natural consequence of galaxy mergers, which we think is how galaxies grow and evolve.”
The SDSS was the first to spot this triple-merger in visible light, but it was only through Galaxy Zoo, a citizen science project, that it was identified as a system of colliding galaxies.
Then WISE saw that the system was glowing in the infrared, indicating that it was in a phase of galaxy merger when more than one of the black holes was expected to be feeding.
The Sloan and WISE data were just tantalizing clues though, and astronomers turned to the Chandra Observatory and the Large Binocular Telescope (LBT) for more confirmation. Chandra observations showed that there were bright x-ray sources in the center of each galaxy. That’s exactly where scientists expect to find SMBHs.
More evidence showing that SMBHs were there arrived from Chandra and NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) satellite. They found evidence of large amounts of gas and dust near one of the black holes.
That’s expected when black holes are merging. Other optical light data from the SDSS and the LBT provided spectral evidence that’s characteristic of the three SMBHs feeding.
“Optical spectra contain a wealth of information about a galaxy,” said co-author Christina Manzano-King of University of California, Riverside. “They are commonly used to identify actively accreting supermassive black holes and can reflect the impact they have on the galaxies they inhabit.”
With this work, the team of astronomers have developed a way to find more of these triple black hole systems.
“Through the use of these major observatories, we have identified a new way of identifying triple supermassive black holes. Each telescope gives us a different clue about what’s going on in these systems,” said Pfeifle. “We hope to extend our work to find more triples using the same technique.”
They may have also shed some light on the final parsec problem.
The Final Parsec Problem
The final parsec problem is central to our understanding of binary black hole mergers. It’s a theoretical problem that says when two black holes approach each other, their excessive orbital energy stops them from merging. They can get to within a few light years, then the merging process stalls.
When two black holes initially approach each other, their hyperbolic trajectories carry them right past each other. Over time, as the two holes interact with stars in their vicinity, they slingshot the stars gravitationally, transferring some of their orbital energy to a star each time they do it. The emission of gravitational waves also decreases the black holes’ energy.
Eventually the two black holes shed enough orbital energy to slow down and approach each other more closely, and come to within just a few parsecs of each other.
The problem is, as they close the distance, more and more matter is ejected from their vicinity via sling-shotting. That means there’s no more matter for the black holes to interact with and shed more orbital energy. At that point, the merging process stalls. Or it should.
Yet astrophysicists know that black holes merge because they’ve witnessed the powerful gravitational waves. In fact, LIGO (Laser Interferometry Gravitational-Wave Observatory) is discovering a black hole merger about once a week. How they merge with each other at the end is called the final parsec problem.
The team behind this study thinks that they might have an answer. They think that a third black hole, like they’ve observed in this system, could provide the boost needed to get two holes to merge.
As a pair of black holes in a trinary system approach each other, the third hole could influence them to close the final parsec and merge.
According to computer simulations, about 16% of pairs of supermassive black holes in colliding galaxies will have interacted with a third supermassive black hole before they merge.
Those mergers would produce gravitational waves, but the problem is that those waves would be too low-frequency for LIGO or the VIRGO observatory to detect.
To detect those, scientists may have to rely on future observatories like LISA, ESA/NASA’s Laser Interferometer Space Antenna. LISA will observe lower frequency gravitational waves than LIGO or VIRGO and is better-equipped to find super-massive black holes merging.
The paper presenting these results is titled “A Triple AGN in a Mid-Infrared Selected Late Stage Galaxy Merger.” | 0.883823 | 4.044966 |
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