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About a year ago a large group of astronomers began to assemble what some of them were calling ''the world's best telescope.'' Their ambitious instrument is still far from complete, but they recently took it for a test run. Within minutes, to their joy and astonishment, they had discovered three or four brown dwarfs, objects that occupy the niche between planet and star.
''It gave me shivers when I heard about it,'' said Dr. Alex Szalay, a Johns Hopkins astronomer who is one of the telescope's chief architects.
It wasn't the brown dwarfs themselves that excited Dr. Szalay; hundreds of them have been discovered in the past decade. But he and many other astronomers believe that the means used to discover these objects heralds the beginning of a new era of astronomy, and even a new era of science.
The telescope that Dr. Szalay and his colleagues have constructed is not built of glass and metal. It is a virtual observatory, consisting of terabytes of data collected by dozens of telescopes on Earth and in space, and the software necessary to mine these data for scientific gems.
Like much of the rest of science, astronomy has been the beneficiary -- and victim -- of Moore's Law, which states that the capacity of computers and other silicon-based devices like charge-coupled devices, or C.C.D.'s, doubles every 18 months. (The C.C.D has largely replaced photographic film in astronomical cameras.)Continue reading the main story
Projects like the National Virtual Observatory, which was created in response to the tsunami of data that is threatening to drown astronomers, is creating a new branch of science, Dr. Szalay believes.
Science, he points out, was ''originally empirical, like Leonardo making wonderful drawings of nature.'' He continued: ''Next came the theorists who tried to write down the equations that explained the observed behaviors, like Kepler or Einstein. Then, when we got to complex enough systems like the clustering of a million galaxies, there came computer simulations, the computational branch of science. Now we are getting into the data exploration part of science, which is kind of a little bit of them all.''
Because its primary tools are computers rather than giant, multimillion telescopes, this new form of astronomy has the potential to democratize science.
''If at the same time most of the telescopes in the world are actually putting all of their data online with proper explanations,'' Dr. Szalay said, ''then it doesn't matter where somebody is sitting, they can access all the data -- either somebody in Baltimore, or somebody from Africa who got a Ph.D. in the U.S. and returned there and doesn't have access to a telescope but suddenly has a bunch of students. They can actually get to first-class data.''
In the past 25 years the number of C.C.D. pixels in all the world's telescopes has increased by a factor of 3,000, with each pixel acting as a miniature astronomical instrument. The result, Dr. Szalay says, is that the total amount of astronomical data collected every year is doubling even while the amount spent on astronomy remains constant.
''We are getting overwhelmed,'' Dr. Szalay says. ''With this explosion it's not just that individual telescopes are getting more and more data, but also the threshold gets lower, so that more and more groups are putting big cameras on their instruments. Even amateur astronomers today can generate gigabytes of data per night by attaching a digital camera to their telescope.''
The problem is how to mine this vast store of data for the riches it almost certainly contains. Astronomers have been busy over the past couple of decades compiling complete surveys of the sky, encyclopedic catalogs of millions of astronomical objects viewed at many different wavelengths. These surveys exist in about 10 different spectral bands, from X-rays to the infrared, with each survey giving a different view of the universe.
The surveys contain about 100 terabytes (one terabyte is 1,000 gigabytes) of data, roughly five times as much as the Library of Congress holds. Unlike the Library of Congress, however, this information does not reside in a single place.
''There is no Library of Congress for astronomy,'' Dr. Szalay says, and as long as the data continue to accumulate at an exponential pace, there will never be one. Instead, ''there will always be 8 or 10 large projects that contain 90 percent of the world's data at any one time.''
The goal of the National Virtual Observatory is to make sure that ''the current generation of professional and amateur astronomers are not overwhelmed by the chores of getting the actual data,'' Dr. Szalay says. ''So we have to make it simple and easy for them to use the data in a friendly way.''
In the first stage of the project this has meant creating tools that can search through different databases without requiring the searchers to be experts in their individual details. As a kind of shakedown cruise, the researchers at the National Virtual Observatory decided to focus on the data contained in two large sky surveys known as the Sloan Digital Sky Survey, which looks at the sky in the visible band of the spectrum and the Two Micron All Sky Survey, or 2MASS, which looks at the sky in the infrared.
''The reason we did those two is that they're very deep, they dig out objects that are very faint, much fainter than other surveys have been able to generate,'' said Dr. Bruce Berriman, a California Institute of Technology astronomer involved in the demonstration. ''Because it goes to very faint objects you're able to dig out sources that are unusual or important in ways other projects can't do.''
In particular, by combining the surveys they hoped to spot brown dwarfs. Brown dwarfs are essentially failed stars, lumps of matter bigger than a planet but not large enough to kindle the thermonuclear fire of a star. As a result, they are relatively cool, emit very little light and are therefore difficult to spot.
The temperature of a star, like that of a glowing piece of metal, determines the color of light that it emits: the cooler the star the redder the light. The light from the brown dwarfs that the astronomers were searching for straddles the border between the infrared and the visible. This means that a brown dwarf should appear in the very shortest wavelength band of the infrared 2MASS survey and also in the longest wavelength band of the visible Sloan survey.
An astronomer looking at just the data from, say, the Sloan survey and seeing an object in a single band would probably dismiss it.
''Chances are pretty good that that single band detection is a piece of junk, some sort of artifact in the detectors in the telescope, a glint off a bright star, any number of things,'' said Dr. Davy Kirkpatrick, a member of the Caltech team. But if that same object also appears in the 2MASS data then the chances shoot up that it is something worth looking at more closely.
The astronomers developed a program that could access these different databases and search them for matches. Within a few minutes the computer spit out a half a dozen or so candidates for possible brown dwarfs. Most of these had been previously noticed in the data, which others had sifted through manually.
Finding these brown dwarfs was supposed to be the goal of the demonstration, a debugging run to prove that the software worked. But the computer also found several candidates for new brown dwarfs.
''Astronomers' first reaction when you find a new result is that there's something wrong,'' Dr. Berriman said. But after looking at the data more closely ''it slowly dawned on us that this was something real, that this was a brown dwarf we found.''
''Then our eyes started to widen up a little bit at the prospect of what might be coming in the future,'' he continued.
Dr. Szalay says, ''This shows how many new things will come out in this process once hundreds of astronomers are using it all over the place.''
What makes this result even more impressive is that the overlap of the two surveys covered something less than one two-hundredth of the sky, and yet they almost instantly found objects that astronomers, poring over data for weeks, had previously missed.
Another aspect of the National Virtual Observatory is the creation of an astronomical search engine, a kind of Google for astronomy that will allow amateurs and professionals to find astronomical resources.
''Were you to go to Google right now and type in the word galaxy, you wouldn't just get a whole bunch of astronomy sites,'' Dr. Berriman says. ''You'd also find out about the L.A. Galaxy soccer team. There's even a town in Texas called Galaxy, with its own Web page. That's no good to astronomers because there's so much clutter in the sites.''
To help solve this problem the National Virtual Observatory is creating an online registry of astronomical resources that should be available to the public early next year.
The registry, and indeed the entire virtual observatory project, is intended as a tool for anyone interested in astronomy.
''One of the major components of the registry is collecting information about the suitability of the resource for educational purposes, for amateurs, for students,'' said Dr. Robert Hanisch of the Space Telescope Science Institute in Baltimore. ''We have a subgroup of our project concentrating on what kind of information does that clientele need to know.''
The success of the National Virtual Observatory and similar projects means that exploring the heavens will no longer be limited to those few hearty individuals willing to sit freezing on mountaintops, waiting for the clouds to clear. Adding myriad seeking eyes and pondering brains to those already contemplating our place in the universe will be the greatest achievement of this new technology.Continue reading the main story | 0.802284 | 3.644075 |
As I decompress from the Tennessee Valley Interstellar Workshop (and review my notes for next week’s report), I have the pleasure of bringing you Andrew LePage’s incisive essay into a key exoplanet question. Are some of the planets now considered potentially habitable actually unlikely to support life? Recent work gives us some hard numbers on just how large and massive a planet can be before it is more likely to be closer to Neptune than the Earth in composition. The transition from rocky to non-rocky planets is particularly important now, when our instruments are just becoming able to detect planets small enough to qualify as habitable. LePage, who writes the excellent Drew ex Machina, remains optimistic about habitable planets in the galaxy, but so far the case for many of those identified as such may be weaker than we had thought. A prolific writer, Drew is also a Senior Project Scientist at Visidyne, Inc., where he specializes in the processing and analysis of remote sensing data.
by Andrew LePage
For much of the modern era, astronomy has benefitted greatly from the efforts of amateur scientists. But while amateur astronomers equipped with telescopes have certainly filled many important niches left by the far less numerous professionals in the field, others interested in astronomy equipped with nothing more than a computer and an Internet connection are capable of making important contributions as well. One project taking advantage of this resource is Planet Hunters.
The Planet Hunters project was originally started four years ago by the Zooinverse citizen science program to enlist the public’s help in searching through the huge photometric database of NASA’s Kepler mission looking for transits caused by extrasolar planets. While automated systems have been able to uncover thousands of candidate planets, they are limited to finding only what their programmers designed them to find – multiple, well defined transits occurring at regular intervals. The much more adaptable human brain is able to spot patterns in the changes in the brightness of stars that a computer program might miss but could still indicate the presence of an extrasolar planet. Currently in Version 2.0, the Planet Hunters project has uncovered 60 planet candidates to date through the efforts of 300,000 volunteers worldwide.
A paper by a team of astronomers with Joseph Schmitt (Yale University) as the lead author was just published in The Astrophysical Journal which describes the latest find by Planet Hunters. The target of interest for this paper is a billion year old, Sun-like star called Kepler 289 located about 2,300 light years away. Automated searches of the Kepler data had earlier found two planets orbiting this distant star: a large super-Earth with a radius 2.2 times that of the Earth (or RE) in a 34.5-day orbit originally designated Kepler 289b (called PH3 b in the new paper) and a gas giant with a radius of 11.6 RE in 125.8-day orbit, Kepler 289c (now also known as PH3 d). The new planet, PH3 c, has a radius of 2.7 RE and a mean orbital period of 66.1 days. With a mean stellar flux about 11 times that of Earth, this planet is highly unlikely to be habitable but its properties have profound implications for assessing the potential habitability of other extrasolar planets.
The planet had been missed by earlier automated searches because its orbital period varies regularly by 10.5 hours over the course of ten orbits due to its strong interactions with the other two planets, especially PH3 d. Because of this strong dynamical interaction, it was possible for Schmitt et al. to use the Transit Timing Variations or TTVs observed in the Kepler data to compute the masses of these three planets much more precisely than could be done using precision radial velocity measurements. The mass of the outer planet, PH3 d, was found to be 132±17 times that of Earth (or ME) or approximately equivalent to that of Saturn. The mass of the inner planet, PH3 b, was poorly constrained with a value of 7.3±6.8 ME. The newest discovery, PH3 c, was found to have a mass of 4.0±0.9 ME which, when combined with the radius determined using Kepler data, yields a mean density of 1.2±0.3 g/cm3 or only about one-fifth that of the Earth. Models indicate that this density is consistent with PH3 c possessing a deep, hot atmosphere of hydrogen and helium making up about half of its radius or around 2% of its total mass.
PH3 c is yet another example of a growing list of known low-density planets with masses just a few times that of the Earth that are obviously not terrestrial or rocky in composition. Before the Kepler mission, such planets were thought to exist but their exact properties were unknown because none are present in our solar system. As a result, the position in parameter space of the transition from rocky to non-rocky planets and the characteristics of this transition were unknown. So when astronomers were developing size-related nomenclature to categorize the planets they expected to find using Kepler, they somewhat arbitrarily defined “super-Earth” to be any planet with a radius in the 1.25 to 2.0 RE range regardless of its actual composition. Planets in the 2.0 to 4.0 RE range were dubbed “Neptune-size”. This has generated some confusion over the term “super-Earth” and has led to claims about the potential habitability of these planets being made in the total absence of an understanding of the true nature of these planets. Now that Kepler has found planets in this size range, astronomers have started to examine the mass-radius relationship of super-Earths.
The first hints about the characteristics of this transition from rocky to non-rocky planets were discussed in a series of papers published earlier this year. Using planetary radii determined from Kepler data and masses found by precision radial velocity measurements and analysis of TTVs, it was found that the density of super-Earths tended to rise with increasing radius as would be expected of rocky planets. But somewhere around the 1.5 to 2.0 RE range, a transition is passed where larger planets tended to become less dense instead. The interpretation of this result is that planets with radii greater than about 1.5 RE are increasingly likely to have substantial envelopes of various volatiles such as water (including high pressure forms of ice at high temperatures) and thick atmospheres rich in hydrogen and helium that decrease a planet’s bulk density. As a result, these planets can no longer be considered terrestrial or rocky planets like the Earth but would be classified as mini-Neptunes or gas dwarfs depending on the exact ratios of rock, water and gas.
Image: It now appears that many of the fanciful artist depictions of super-Earths are wrong and that most of these planets are more like Neptune than the Earth (NASA Ames/JPL-Caltech).
A detailed statistical study of this transition was submitted for publication this past July by Leslie Rogers (a Hubble Fellow at the California Institute of Technology) who is also one of the coauthors of the PH3 c discovery paper. In her study, Rogers confined her analysis to transiting planets with radii less than 4 RE whose masses had been constrained by precision radial velocity measurements. She excluded planets with masses determined by TTV analysis since this sample may be affected by selection biases that favor low-density planets (for a planet of a given mass, a large low-density planet is more likely to produce a detectable transit event than a smaller high-density planet). Rogers then determined the probability that each of the 47 planets in her Kepler-derived sample were rocky planets by comparing the properties of those planets and the associated measurement uncertainties to models of planets with various compositions. Next, she performed a statistical analysis to assess three different models for the mass-radius distribution for the sample of planets. One model assumed an abrupt, step-wise transition from rocky to non-rocky planets while the other two models assumed different types of gradual transitions where some fraction of the population of planets of a given radius were rocky while the balance were non-rocky.
Rogers’ analysis clearly showed that a transition took place between rocky and non-rocky planets at 1.5 RE with a sudden step-wise transition being mildly favored over more gradual ones. Taking into account the uncertainties in her analysis, Rogers found that the transition from rocky to non-rocky planets takes place at no greater than about 1.6 RE at a 95% confidence level. Assuming a simple linear transition in the proportions of rocky and non-rocky planets, no more than 5% of planets with radii of about 2.6 RE will have densities compatible with a rocky composition to a 95% confidence level. PH3 c, with a radius of 2.7 RE, exceeds the threshold found by Rogers and, based on its density, is clearly not a terrestrial planet.
An obvious potential counterexample to Rogers’ maximum rocky planet size threshold is the case of Kepler 10c, which made the news early this year. Kepler 10c, with a radius of 2.35 RE determined by Kepler measurements and a Neptune-like mass of 17 ME determined by radial velocity measurements, was found to have a density of 7.1±1.0 g/cm3. While this density, which is greater than Earth’s, might lead some to conclude that Kepler 10c is a solid, predominantly rocky planet, Rogers counters that its density is in fact inconsistent with a rocky composition by more than one-sigma. Comparing the measured properties of this planet with various models, she finds that there is only about a 10% probability that Kepler 10c is in fact predominantly rocky in composition. It is much more likely that it possesses a substantial volatile envelope albeit smaller than Neptune’s given its higher density.
While much more work remains to be done to better characterize the planetary mass-radius function and the transition from rocky to non-rocky planets, one of the immediate impacts of this work is on the assessment of the potential habitability of extrasolar planets. About nine planets found to date in the Kepler data have been claimed by some to be potentially habitable. Unfortunately, all but two of these planets, Kepler 62f and 186f, have radii greater than 1.6 RE and it is therefore improbable that they are terrestrial planets, never mind potentially habitable planets.
This still leaves about a dozen planets that have been frequently cited as being potentially habitable that were discovered by precision radial velocity surveys whose radii are not known. However, we do know their MPsini values where MP is the planet’s actual mass and i is the inclination of the orbit to our line of sight. Since this angle cannot be derived from radial velocity measurements alone, only the minimum mass of the planet can be determined or the probability that the actual mass is in some range. Despite this limitation, the MPsini values can serve as a useful proxy for radius.
Rogers optimistically estimates that her 1.6 RE threshold corresponds to a planet with a mass of about 6 ME assuming an Earth-like composition (which is still ~50% larger than the measured mass of PH3 c, which is now known to be a non-rocky planet). About half of the planets that some have claimed to be potentially habitable have minimum masses that exceed this optimistic 6 ME threshold while the rest have better than even odds of their actual masses exceeding this threshold. If the threshold for the transition from rocky to non-rocky planets is closer to the 4 ME mass of PH3 c, the odds of any of these planets being terrestrial planets are worse still. The unfortunate conclusion is that none of the planets discovered so far by precision radial velocity surveys are likely to be terrestrial planets and are therefore poor candidates for being potentially habitable.
Please do not get me wrong: I have always been a firm believer that the galaxy is filled with habitable terrestrial planets (and moons, too!). But in the rush to find such planets, it now seems that too many overly optimistic claims have been made about too many planets before enough information was available to properly gauge their bulk properties. Preliminary results of the planetary mass-radius relationship now hints that the maximum size of a terrestrial planet is probably about 1½ times the radius of the Earth or around 4 to 6 times Earth’s mass. Any potentially habitable planet, in addition to having to be inside the habitable zone of the star it orbits, must also be smaller than this. Unfortunately, while recent work suggests that planets of this size might be common, our technology is only just able to detect them at this time. With luck, over the coming years as more data come in, we will finally have a more realistic list of potentially habitable planet candidates that will bear up better under close scrutiny.
The discovery paper for PH3 c by Schmitt et al., “Planet Hunters VII: Discovery of a New Low-Mass, Low Density Planet (PH3 c) Orbiting Kepler-289 with Mass Measurements of Two Additional Planets (PH3 b and d)”, The Astrophysical Journal, Vol. 795, No. 2, ID 167 (November 10, 2014) can be found here. The paper by Leslie Rogers submitted to The Astrophysical Journal, “Most 1.6 Earth-Radius Planets are not Rocky”, can be found here.
For a fuller discussion of how Rogers’ work impacts the most promising planets thought by many to be potentially habitable, please refer to Habitable Planet Reality Check: Terrestrial Planet Size Limit on my website Drew Ex Machina. | 0.810136 | 3.716978 |
It is the moonís small mass and low gravity that prevents it from keeping hold of even a tenuously thin atmosphere. But oxygen neednít exist only in gaseous form above the ground. It can also be entrained safely in certain kinds of rocks. Gather the rubble and either treat it with chemicals or blast it with heat, and you can free up unlimited quantities of oxygen both for breathing and for rocket fuel.
The lunar mineral that may hold the most oxygen promise is ilmenite, a titanium oxide brought back from the moonís Taurus-Littrow region by the Apollo 17 crew in 1972. To determine how heavy the ilmenite concentrations are at that site and to look for other outcroppings as well, NASA recently decided to conduct telescope surveys of four lunar regions: Taurus-Littrow, Hadley-Apenninelanding site of Apollo 15the unexplored Aristarchus impact crater and nearby Schroterís Valley. Though ground-based telescopes would ordinarily be suitable for this work, in this case they wouldnít do, since the scientists were looking for ultraviolet reflections of ilmenite, a frequency of light absorbed by Earthís atmosphere. The only way to conduct the work was to get above that blinding blanket and look across clear, airless space. When Hubble did that, it quickly spotted paydirt.
The telescope found what appears to be ilmenite deposits not only at the Apollo 17 site, where it was known to be, but also in Schroterís Valley and in especially high concentrations in Aristarchus crater. Aristarchus would make an especially good landing site for future geologists, because the impacts that create craters blasts away surface material, providing a detailed look far below ground. Combine that with the ready lode of oxygen-rich ilmenite, and youíve got a prime spot for a future moon base.
Striking as the Hubble images are, there is one thing they couldnít reveal. The telescopeís giant eye can see lunar objects no smaller than 60 yards across. Somewhere in Taurus-Littrow and Hadley-Apennine are the comparatively tiny, truck-sized descent stages of the Apollo lunar modules, left behind when the crews blasted off. Neither of those metal relics has been seen in the more than 30 years since human beings last walked on the moon. Only if the U.S. actually commits itself to its new lunar plans will they be seen again any time soon. | 0.802571 | 3.638326 |
Tuesday, November 13, 2012
The Sky This Week - Thursday November 15 to Thursday November 22
Morning sky on Sunday November 18 looking east as seen from Adelaide at 5:30 am local daylight saving time in South Australia. Saturn ius rising in the dawn sky and is coming close to Venus. Similar views will be seen elsewhere at the equivalent local time (click to embiggen).
The First Quarter Moon is Wednesday November 21.
Jupiter is still seen above the north-western horizon in the early morning sky. Jupiter is below the Hyades, between the red star Aldebaran and the dimmer blue white star Elnath. Jupiter moves slowly towards Aldebaran during the week.
Jupiter, Aldebaran and the red star Betelgeuse in Orion form a long thin triangle in the sky. With the Pleiades cluster and the constellation of Orion close by, this is a beautiful sight.
Jupiter is now seen in the late evening sky, rising shortly before 9:30 pm local daylight saving time and is moderately high by midnight.
Bright white Venus is now low above the eastern horizon, but is still not too difficult to see. It continues sinking lower over the week. Venus looks like a waxing Moon when seen through even a small telescope.
Venus is in the constellation of Virgo. Venus is now relatively low to the horizon, but still clearly visible in twlight skies. It will become harder to see over the coming weeks. Venus will still be bright, but hard to see from cluttered horizons.
Saturn is now visible above the horizon before dawn, but will be difficult to see until the end of the week. Saturn rises towards Venus during the week.
Evening sky looking west as seen from Adelaide at 9:00 pm local daylight time on Friday November 16. Mars is in Sagittarius with the crescent Moon nearby. Similar views will be seen elsewhere at the equivalent local time. Click to embiggen.
Mercury is now lost in the twilight.
Mars is in the constellation Ophiuchus, but enters Sagittarius by the end of the week. Mars is second brightest object in the western sky (after the red star Antares, which is just a little brighter than Mars). Mars's distinctive red colour makes it relatively easy to spot.
Mars will be in binocular range of several beautiful clusters for most of the month. The crescent Moon visits Mars on the 16th.
Mars sets shortly after 11:00 pm local daylight saving time.
Mars was at opposition on March 4, when it was biggest and brightest as seen from Earth. Sadly, this is a poor opposition and Mars will be fairly small in modest telescopes.
The Leonid meteor shower peaks on the17th, but is best seen on the morning of the 18th. Unfortunately, there will be very few meteors this year, less than one every 10 minutes.
There are lots of interesting things in the sky to view with a telescope. If you don't have a telescope, now is a good time to visit one of your local astronomical societies open nights or the local planetariums.
Printable PDF maps of the Eastern sky at 10 pm AEDST, Western sky at 10 pm AEDST. For further details and more information on what's up in the sky, see Southern Skywatch.
Cloud cover predictions can be found at SkippySky.
Labels: weekly sky | 0.835727 | 3.073298 |
The rings of Neptune consist primarily of five principal rings and were first discovered (as ... Since Voyager 2's fly-by, the brightest rings (Adams and Le Verrier) have been .... However, many publications do not mention the Arago ring at all.
Neptune is the eighth and farthest known planet from the Sun in the Solar System . In the Solar ... On both occasions, Galileo seems to have mistaken Neptune for a fixed star ..... Neptune has a planetary ring system, though one much less substantial than ..... "The Case of the Pilfered Planet – Did the British steal Neptune?".
Yes, Neptune has several faint rings around it. There are three ... There are areas of the rings which are much thicker than other areas of the rings. These thicker ...
Where did it go? Does Neptune have rings? Does Neptune have moons? How many? Why is Neptune named "Neptune?" Does Neptune have a magnetic Field ...
Evidence for incomplete arcs around Neptune first arose in the mid-1980s, when stellar occultation experiments were found to occasionally show an extra.
Mar 12, 2012 ... Neptune was not discovered until 1846 and its rings were only ... We have written many articles about Neptune here at Universe Today.
May 12, 2017 ... Neptune is the farthest planet from the sun and was the first to be ... flown by Neptune – Voyager 2 in 1989 – meaning that astronomers have done ... technology does not make it possible to view how much atmosphere is on ...
Neptune - Neptune's moons and rings: Neptune has at least 14 moons and six ... based on the assumption that they reflect about as much light as Proteus and ... that any rings present do not completely encircle Neptune but instead have the ...
Apr 22, 2009 ... The newest moons don't have official names yet. Neptune's rings are much darker than Saturn's bright rings. Saturn's rings are made of ice, which ... How did life evolve on Earth? The answer to this question can help us ... | 0.879663 | 3.066007 |
Eta Carinae, formerly known as Eta Argus, a stellar system containing at least two stars with a combined luminosity greater than five million times that of the Sun.
What is Eta Carinae?
Eta Carinae is located around 7,500 light-years (2,300 parsecs) distant in the constellation Carina. Previously a 4th-magnitude star, it brightened in 1837 to become brighter than Rigel marking the start of the Great Eruption. It became the second-brightest star in the sky between 11 and 14 March 1843 before fading well below naked eye visibility after 1856. In a smaller eruption, it reached 6th magnitude in 1892 before fading again. It has brightened consistently since about 1940, becoming brighter than magnitude 4.5 by 2014. Eta Carinae is circumpolar south of latitude 30°S, so it is never visible north of about latitude 30°N.
The two main stars of the Eta Carinae system have an eccentric orbit with a period of 5.54 years. The primary is a peculiar star similar to a luminous blue variable (LBV) that is expected to explode as a supernova in the astronomically near future. This is the only star known to produce ultraviolet laser emission. The secondary star is hot and also highly luminous, probably of spectral class O, around 30–80 times as massive as the Sun. The system is heavily obscured by the Homunculus Nebula, material ejected from the primary during the Great Eruption. It is a member of the Trumpler 16 open cluster within the much larger Carina Nebula. Although unrelated to the star or nebula, the weak Eta Carinids meteor shower has a radiant very close to Eta Carinae.3
As a 4th-magnitude star, Eta Carinae is comfortably visible to the naked eye in all but the most light-polluted skies in inner city areas according to the Bortle scale. Its brightness has varied over a wide range, from the second-brightest star in the sky at one point in the 19th century to well below naked eye visibility. Its location at around 60°S in the far Southern Celestial Hemisphere means it cannot be seen by observers in Europe and much of North America.
Image: NASA / JPL-Caltech
Text: Wikipedia contributors. “Eta Carinae.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 2 Aug. 2017. Web. 2 Aug. 2017 | 0.842355 | 3.615001 |
Distant Dust Disk Mixes Fact with Fiction
by Brian Thomas, M.S.
Sometimes, separating observation from speculation presents a challenge. For example, a recent news report of a possible planet in outer space mixed an observation with ideas of distant planet formation. Does this news coverage provide enough detail to help tease apart what is seen from what was unseen?
Astronomers used the Near-Infrared Camera and Multi-Object Spectrometer on the Hubble telescope to image what they called a "protoplanetary disk" in infrared light.1 The TW Hydrae Disk consists of fine particles in a flat, round plane, with a small red-dwarf star in its center. Scientists find fascination in an apparent gap in the distant disk. They propose a planet-like object could be plowing up the debris as it slowly revolves around its star.
Is a gap in a dust disk enough evidence to assert a "protoplanet?" The very name means that planets are forming there, but the mere act of naming is not the same as evidence.
Even if an exoplanet orbits out there, no scientific rationale suggests that the planet is actually forming, and there are several reasons to think otherwise. In fact, the very NASA news release itself seems to contradict the secular claim of planet formation by a slow and gradual accretion of debris.
First, evolution-based speculations about the timing of planet formation conflict with speculations about when the red dwarf star formed. The red dwarf is supposedly "only 8 million years old, making it an unlikely star to host a planet, according to this theory. There has not been enough time for a planet to grow through the slow accumulation of smaller debris."1 When accounting for its great distance from its star—and that star's tiny size—the possible planet would supposedly have needed two billion years to form!
In contrast to a planet existing for millions of years before its star supposedly evolved, naturalistic planet formation stories tell of stars forming first, so that their gravity could then help planet formation.
In addition, evolutionary models require pebble-sized debris to seed a protoplanet, but the observed gap lies in an area of the disk populated by tiny dust-sized grains.
All things considered, if this distant dust disk does hold an exoplanet, supernatural creation would account for it most sensibly.
From observations in our own solar system, we know that worlds can create gaps in orbiting disks. Saturn's rings, for example, contain several gaps due to the gravitational influence of Saturn's orbiting moons. "It is very feasible that a planet may be the cause of the gap in the disk of TW Hydrae,” said astronomer and Institute for Creation Research Director of Physical Sciences Jason Lisle. “But the notion that such a planet has formed from such material is merely a story."
- Harrington, J. D. and D. Weaver. NASA's Hubble Uncovers Evidence of Farthest Planet Forming from its Star. NASA press release, June 13, 2013.
Image credit: NASA/ESA/Hubble.
* Mr. Thomas is Science Writer at the Institute for Creation Research.
Article posted on June 21, 2013. | 0.859667 | 3.807399 |
Earth may have 'infected' Titan with life
The various meteoric slappings sustained by Earth over the millenia may have seeded other parts of the solar system with life, if calculations by Canadian scientists are to be believed.
Planetary scientist Brett Gladman and colleagues at the University of British Columbia in Vancouver worked out that for material to be thrown up with enough force to exit Earth's atmosphere, it would take an impact from a meteor 10 to 50km across. They reckon such impacts, which include the famous 'dinosaur-killer' that formed the Chicxulub crater, send about 600m potenitally life-bearing rock fragments into solar orbit.
The team looked at whether the fragments' microbial passengers might find a home on one of the solar system's potentially sustaining worlds. Speaking at the Lunar and Planetary Science Conference in League City, Texas, Gladman said in the course of five million years Jupiter's moon Europa would get 100 hits and Saturn's Titan be seeded 30 times.
Despite its lower hit rate, the researchers think Titan more likely to have been fertilised. They calculated that Jupiter's gravity would pile the fragments into frozen Europa too fast. Titan's thick atmosphere whould split the fragments and slow the descent meanwhile.
Gladman was asked if he thought Earthly microbes would be able to endure Titan's freezing temperatures. He said: "That's for you people to decide, I'm just the pizza delivery boy."
The finding tips the panspermia theory on its head, and makes it a more interesting proposition. This once-fashionable idea of how life got started on Earth postulates that it was brought here by rocks from other worlds. While an undeniably diverting speculation, a cosmic common ancestry seems unprovable. Advocates cling to the apparently short time it took from Earth's formation to the emergence of life - around half a billion years. However, with a sample size of precisely one we cannot know the likelihood of life.
More crucially, panspermia contributes nothing to the quest for a complete theory of how life can emerge spontaneously - an important missing piece in the evolutionary jigsaw. The idea simply shifts the problem to another world. ® | 0.892917 | 3.273076 |
Origins of the Earth and Moon
History of Earth. (2008, September 4). In Wikipedia, The Free Encyclopedia. Retrieved 20:06, September 9, 2008, from http://en.wikipedia.org/w/index.php?title=History_of_Earth&oldid=236195965. Edited for content by B.Rick.
The Earth formed as part of the birth of the Solar System: what eventually became the solar system initially existed as a large, rotating cloud of dust, rocks, and gas. It was composed of hydrogen and helium produced in the Big Bang, as well as heavier elements ejected by supernovas.
Then, as one theory suggests, about 4.6 billion years ago a nearby star was destroyed in a supernova and the explosion sent a shock wave through the solar nebula. The solar nebula cloud began to rotate. Gravity and inertia flattened it into a protoplanetary disk. Most of the mass concentrated in the middle and began to heat up.
The infall of material, increase in rotational speed and the crush of gravity created an enormous amount of kinetic heat at the center of the cloud. Its inability to transfer that energy away resulted in the disk's center heating up. Ultimately, nuclear fusion of hydrogen into helium began, and eventually, after contraction, ignited to create the Sun.
Meanwhile, gravity caused matter to condense around the objects outside of the new sun's gravity grasp. Dust particles and the rest of the protoplanetary disk began separating into rings. Successively larger fragments collided with one another and became larger objects, ultimately destined to become protoplanets. These included one collection approximately 150 million kilometers from the center: Earth. The solar wind of the newly formed star cleared out most of the material in the disk that had not already condensed into larger bodies.
The origin of the Moon is still uncertain, although much evidence exists for the giant impact hypothesis. Earth may not have been the only planet forming 150 million kilometers from the Sun. It is hypothesized that another collection occurred 150 million kilometers from both the Sun and the Earth.
This planet, named Theia, is thought to have been smaller than the current Earth, probably about the size and mass of Mars. Its orbit may at first have been stable, but destabilized as Earth increased its mass by the accretion of more and more material. Theia swung back and forth relative to Earth until, finally, an estimated 4.533 billion years ago, it collided at a low, oblique angle.
The low speed and angle were not enough to destroy Earth, but a large portion of its crust was ejected into space. Heavier elements from Theia sank to Earth’s core, while the remaining material and ejecta condensed into a single body within a couple of weeks. Under the influence of its own gravity, this became a more spherical body: the Moon.
The impact is also thought to have changed Earth’s axis to produce the large 23.5° axial tilt that is responsible for Earth’s seasons. It may also have sped up Earth’s rotation and initiated the planet’s plate tectonics. | 0.842042 | 3.489114 |
Find That Planet! Teachers' Page
- Topics: Comets; Using star maps to find things in the sky; Celestial coordinates
- Grade Levels: 6-12
- Student Prerequisites: Able to read maps; Know what latitude and longitude are.
- Time Requirements: Approximately 1 hour preparation time and 2 hours class time
- Students meet a challenge that requires use of the Internet for acquiring information, images,
or other media.
- Students get the idea that computers are powerful tools not only for games, but for finding
out about many subjects on the worldwide web.
- Students will learn to use star maps for finding a planet.
- Students will plot a planet path on star maps with coordinate grids.
- Students be able to find out when a planet is visible.
Materials Required For This Activity:
- Computer(s) connected to Internet
- Star Maps with coordinate grids
- Optional: Constellation Posters--(how
to make them)
- Visit the JPL ephemeris web site and familiarize yourself with how it works.
- Decide if you can have students print out star maps during the activity, of if you should print
them before hand and make photocopies for each student.
- You may find a map with the planet positions already plotted for the current month at the
Sky & Telescope magazine website (http://www.skypub.com/)
under "Monthly Sky Charts."
- Optional: You can recreate the night sky, at least the near-horizon part of it, with posters
of the constellations that will be visible at each of the cardinal directions at the particular time that you would
like students to practice finding the comet. This classroom "Horizon Planetarium" idea is from the GEMS guide Earth,
Moon, and Stars from Lawrence Hall of Science
Be sure that students have a firm understanding of the concept of celestial coordinates and what
an ephemeris is.
When students go to the JPL Ephemeris Generator, they will need to click on 4 buttons to provide
- Select New Body (Planet)
- Select New Location (observation postion on Earth--your town--you may need to find your Earth
coordinates for this or just choose a nearby city that is on the preset listing)
- Set Time Span (Year/Month/Day/Hours/Minutes) and Interval between coordinate listings (days,
hours or minutes)
- Select New Output Quantities -- here you should start simple: check only #2. Apparent RA and
DEC (Right Ascension and Declination) and possibly # 29 Constellation ID. Later, if students really get into it,
the following may be of interest:
4. Apparent AZ and EL (Azimuth and Elevation angles)
5. Rates; AZ and EL (Rate of change in Azimuth and Elevation Angles)
9. Visual magnitude and surface brightness
20. Observer range and range-rate (Distance to object and rate of change of distance to object)
21. One-way light-time (another way to express distance to object)
If students need practice using star maps, try out the Activity (#5) from the GEMS guide Earth, Moon, and Stars in which the classroom is made into
a "planetarium" with constellations posters hanging on the walls.
One tricky part is judging when a planet is visible at night. It is all well and good to pick
a planet and a time that you want to see it, but the heavens do not always acquiesce to our wishes--the planet
may be up only in the daytime in a particular time period. A few trials with the ephemeris generator may be necessary
before successfully plotting a planet on a chart when the planet is really up when the sky is dark.
Mail questions or comments: [email protected]
1997-2001 Regents of the University of California | 0.864172 | 3.099253 |
There just might be a tenth planet in the solar system.
Scientists have found evidence that an unseen planet is lurking around the edges of the solar system, Tech Times reports. Different from Planet Nine, this mass is hiding in the Kuiper Belt, and could actually be Earth’s closer and smaller relative.
There have been missions to scour the universe for distant planets and solar systems that have produced impressive results. Scientists have found planets, galaxies and far-off solar systems that match – and even surpass – this one.
Advanced technologies have allowed astronomers and other scientists to make huge steps forward in space exploration. One of these is the University of Arizona’s Lunar and Planetary Laboratory (LPL) which Renu Malhotra and Kat Volk used to discover a planetary mass hiding in the Kuiper Belt. This mass was found by observing its effects on the space rocks circling the belt.
The Kuiper Belt contains space rocks, icy bodies, minor planets and other dwarf planets on the outskirts of the Earth’s solar system. The Kuiper Belt objects (KBO) orbit the sun in a specific manner. But Volk and Malhotra observed that the most distant KBOs appeared to have their own path.
Specifically, some KOBs are tilted away from the plane by eight degrees, meaning there is something that might be interfering with the orbital plane of the outer solar system. This would be an object large enough to disrupt activity.
Volk believes that this warp can be explained by an unseen mass, likely as large as Mars. In short, a large object such as a planet could be hiding in the Kuiper Belt.
Malhotra and Volk calculated to make sure their observation was not a statistical fluke, and found that the average plane does warp away, leaving only the slimmest 1-2% chance that the warp is a fluke.
The scientists think that the reason this object has never been seen before is because it has been hiding all this time in the galactic plane – an area that solar system surveys avoid because it has so many stars. | 0.842258 | 3.18135 |
Seven terrestrial exoplanets around a nearby star
An international team of astronomers has discovered a compact analogue of our inner solar system about 40 light-years away. Brice-Olivier Demory of the Center of Space and Habitability at the University of Bern, analysed the data collected with NASA’s Spitzer Space Telescope and calculated that the newly detected exoplanets all have masses less or similar to the Earth.
TRAPPIST-1 is the name of the small, ultracool star that is the new hot topic in astronomy and the search for life outside our solar system. Observing the star with telescopes from the ground and space during an extensive campaign, an international team found that there are at least seven terrestrial planets around TRAPPIST-1. Their temperatures are low enough to make possible liquid water on the surfaces, as the researchers report in the journal «Nature». «Looking for life elsewhere, this system is probably our best bet as of today», says Brice-Olivier Demory, professor at the University of Bern’s Center for Space and Habitability and one of the authors of the «Nature» paper.
The configuration of these exoplanets orbiting a dwarf star makes it possible to study their atmospheric properties with current and future telescopes. «The James Webb Space Telescope, Hubble’s successor, will have the possibility to detect the signature of ozone if this molecule is present in the atmosphere of one of these planets,» explains Demory: «This could be an indicator for biological activity on the planet.» But the astrophysicist warns that we must remain extremely careful about inferring biological activity from afar and that everything could be different than expected.
Observing from all over the world and space
A year ago, the astronomers had already detected three Earth-sized planets orbiting the star TRAPPIST-1. The planets pass in front of the star in so called transits and periodically dim the starlight by a small amount. After this discovery the researchers observed the star for months with different telescopes in Chile, Morocco, Hawaii, La Palma and South Africa, and in September 2016, NASA’s Spitzer Space Telescope monitored TRAPPIST-1 for 20 days. Exploiting all the data the astronomers found that the TRAPPIST-1 system is a compact analogue of our inner solar system with at least seven planets.
Bernese computer simulations confirmed
«My task was to make an independent analysis of the Spitzer data as well as a dynamic analysis of the system that allowed to compute the masses of these planets,» explains Demory. He found that some of the detected planets have densities similar to the Earth and most probably a rocky composition. In a paper published in October 2016, two researchers of the University of Bern, Yann Alibert and Willy Benz, had already predicted based on their computer simulations that such planets around dwarf stars should be common.
Earth-like exoplanets orbiting dwarf stars are easier to observe than real Earth-twins around solar-type stars. Since these dwarfs are also much cooler, the temperature zone that allows water to be liquid on the surface of the planet is much closer to the star. And exoplanets that are close to their host star revolve more rapidly and produce more transits in a given timeframe. «About 15 percent of the stars in our neighbourhood are very cool stars like TRAPPIST-1,» says Brice-Olivier Demory: «We have a list of about 600 targets that we will observe in the future.» To monitor the candidate stars in the northern hemisphere the Center for Space and Habitability (CSH) of the University of Bern is leading a consortium that builds a new telescope in Mexico.
Publication details: Michaël Gillon, Amaury Triaud, Brice-Oliver Demory et al.: «Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1», Nature 22 February 2017, http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html
Prof. Brice-Olivier Demory
Center of Space and Habitability (CSH), University of Bern
«Earth-like exoplanets around the dwarf star TRAPPIST-1»
Short talks and panel discussion with Prof. Brice-Olivier Demory, Prof. Yann Alibert, Prof. Kevin Heng, Zoë Lehmann and Science Fiction author Laurence Suhner, who published a short novel about TRAPPIST-1 in Nature.
University of Bern, Thursday, 9 March 2017, 18.30 h
Information and registration: www.unibe.ch/trappist1
Credit: ESO/L. Calçada/spaceengine.org
ESO media release | 0.826797 | 3.7308 |
Images taken by the AMIE camera carried by ESA’s SMART-1 mission have been used to create digital elevation model of the peak, which is almost continuously exposed to sunlight.
“AMIE is not a stereo camera, so producing a 3-D model of the surface has been a challenge,” said Dr Koschny. “We’ve used a technique where we use the brightness of reflected light to determine the slope and, by comparing several images, put together a model that produces a shadow pattern that matches those observed by SMART-1.”
AMIE took a total of 113 images of the peak, located close to the rim of the Shackleton Crater which lies on the lunar south pole. In all but four of the images, the peak was illuminated by sunlight. This is of particular interest in planning future manned missions to the Moon, as it would mean that solar panels could be used almost constantly to generate an electricity supply for a lunar base.
In addition, the shadowed craters nearby are in constant darkness and may hold water ice deposited over millennia by cometary impacts and hydrogen and oxygen particles contained in the solar wind. This potential water supply would also be a vital resource for any lunar base.
The team, led by Dr Björn Grieger of ESA’s European Space Astronomy Centre in Madrid, selected five of the AMIE images showing the peak illuminated from different angles. They mapped all the pixels onto a grid, defining the bright and dark areas. The data from the five images were then compared to produce estimates of the slope angles and the rendered elevation model was iteratively adjusted to produce a shadow match. The original AMIE images were then projected onto the retrieved model. To clearly visualise the topography, the elevation has been exaggerated five times.
SMART-1 orbited the Moon between November 2004 and September 2006, covering a full seasonal cycle.
Anita Heward | alfa
New quantum phenomena in graphene superlattices
19.09.2017 | Graphene Flagship
Solar wind impacts on giant 'space hurricanes' may affect satellite safety
19.09.2017 | Embry-Riddle Aeronautical University
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.
MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...
Pathogenic bacteria are becoming resistant to common antibiotics to an ever increasing degree. One of the most difficult germs is Pseudomonas aeruginosa, a...
Scientists from the MPI for Chemical Energy Conversion report in the first issue of the new journal JOULE.
Cell Press has just released the first issue of Joule, a new journal dedicated to sustainable energy research. In this issue James Birrell, Olaf Rüdiger,...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
19.09.2017 | Event News
19.09.2017 | Physics and Astronomy
19.09.2017 | Power and Electrical Engineering | 0.841903 | 3.699313 |
September 4, 2014
Cosmic Forecast: Dark Clouds Will Give Way To Sunshine
Richard Hook, ESO
Lupus 4, a spider-shaped blob of gas and dust, blots out background stars like a dark cloud on a moonless night in this intriguing new image. Although gloomy for now, dense pockets of material within clouds such as Lupus 4 are where new stars form and where they will later burst into radiant life. The Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile captured this new picture.[ Watch the Video: A Close-Up View Of The Dark Cloud Lupus 4 ]
Lupus 4 is located about 400 light-years away from Earth, straddling the constellations of Lupus (The Wolf) and Norma (The Carpenter's Square). The cloud is one of several affiliated dark clouds found in a loose star cluster called the Scorpius–Centaurus OB association. An OB association is a relatively young, yet widely dispersed grouping of stars . The stars likely had a common origin in a gigantic cloud of material.
Because the association, and its Lupus clouds, form the closest such grouping to the Sun, they are a prime target for studying how stars grow up together before going their separate ways. The Sun, along with most stars in our galaxy, is thought to have started out in a similar environment.
American astronomer Edward Emerson Barnard is credited with the earliest descriptions of the Lupus dark clouds in the astronomical literature, back in 1927. Lupus 3, neighbor to Lupus 4, is the best studied, thanks to the presence of at least 40 fledgling stars formed over the last three million years, and which are on the cusp of igniting their fusion furnaces. The main energy source in these adolescent stars, known as T Tauri stars, is the heat generated by their gravitational contraction. That is in contrast to the fusion of hydrogen and other elements which powers mature stars such as the Sun.
[ Watch the Video: Zooming In On The Dark Cloud Lupus 4 ]
Observations of the cold darkness of Lupus 4 have turned up only a few T Tauri stars. Yet promisingly for Lupus 4 in terms of future star formation is a dense, starless core of material in the cloud. Given a few million years, that core should develop into T Tauri stars. Comparing Lupus 3 and Lupus 4 in this way suggests that the former is older than the latter, because its contents have had more time to develop into stars.
How many stars might eventually start to shine within Lupus 4? It is hard to say, as mass estimates for Lupus 4 vary. Two studies agree on a figure of around 250 times the mass of the Sun, though another, using a different method, arrives at a figure of around 1600 solar masses. Either way, the cloud contains ample material to give rise to plenty of bright new stars. Rather as earthly clouds make way for sunshine, so, too, shall this cosmic dark cloud eventually dissipate and give way to brilliant starlight.
The "OB" refers to the hot, bright, short-lived stars of spectral types O and B that are still shining brilliantly within the widely dispersed cluster as it travels through the Milky Way galaxy.
Shop Amazon - Rent eTextbooks - Save up to 80% | 0.909571 | 3.86032 |
The perihelion is the point in the orbit of a planet, asteroid or comet where[& when] it is nearest to the sun. It is the opposite of aphelion, which is where [& when] the orbit of the object is farthest from the sun.
The word perihelion stems from the Greek words "peri," meaning near, and "Helios," meaning the Greek god of the sun. (The similar word, perigee, refers to the nearest point in some object's orbit of earth.)
All planets, comets and asteroids in our solar system have approximately elliptical (a kind of non-circular) orbits (any single revolution of a body around the sun is only approximately elliptical, because the phenomenon known as precession of the perihelion prevents the orbit from being a simple closed curve such as an ellipse). Thus, they all have a closest and a farthest point from the sun: a perihelion and an aphelion. Orbital eccentricity measures the flatness of the orbit.
Earth comes closest to the sun every year around January 3. It is farthest from the sun every year around July 4. The difference in distance between Earth's nearest point to the sun in January and farthest point from the sun in July is 3.1 million miles (5 million kilometers). Earth is about 91.4 million miles (147.1 million kilometers) from the sun in early January, in contrast to about 94.5 million miles (152 million kilometers) in early July.
When Earth is closest to the sun, it is winter in the northern hemisphere and summer in the southern hemisphere. Thus it is possible to see that Earth's distance from the sun does not noticeably cause the seasons to change; the relatively minor effects of differences in distance is somewhat masked by the mainly oceanic southern hemisphere vs the half- continental northern hemisphere. Therefore, the Earth's seasons come and go mainly because Earth does not rotate with its axis exactly upright with respect to the plane of our world’s orbit around the sun. Earth's axial tilt is 23.5 degrees. This puts the Sun farther south in December and January, so the north has winter and the south has summer. Thus winter falls on that part of the globe where sunlight strikes least directly. Summer falls on that part of the globe where sunlight strikes most directly. | 0.828139 | 3.689507 |
Sometime in November, if all goes well, astronomers will fulfill a dream that humankind has had ever since we first marveled at one of those impetuous dots of light with a long tail streaking across the night sky. They will catch a comet. The Rosetta spacecraft, launched in 2004 by the European Space Agency, will have closed in on Comet 67P/Churyumov-Gerasimenko after looping more than 3.7 billion miles through our solar system. It will deploy a 220-pound lander that will fire thrusters and alight on the comet’s surface. A sampling device will drill down more than nine inches and collect material from the 2 1/2-mile-wide icy dust ball for on-site chemical analysis. An imaging system will take pictures. The data, to be gathered over the course of at least three months, will be transmitted back to Rosetta and then to receiving stations on Earth, where astronomers hope the information will yield new insights into the origins of the solar system itself. That’s because comet cores, unlike planet cores, have changed very little in the last 4.5 billion years and still hold in their icy depths the chemical fingerprints of the solar system’s birth. The lander, named Philae, will remain on the comet after the mission ends, but, says ESA’s Matt Taylor, no one knows how long the machine will survive. Rosetta, the first spacecraft propelled through deep space on solar power alone, will cease operating in early 2016. As it passes the 418 million-mile mark from the Sun, its solar panels will no longer be able to capture enough energy to run its instruments. | 0.860415 | 3.144608 |
Home > News > Astronomers Image the Surface and Atmosphere of the Red Supergiant Star Antares
Astronomers Image the Surface and Atmosphere of the Red Supergiant Star Antares Posted by Guy Pirro on 8/25/2017 8:11 PM
Using ESO's Very Large Telescope Interferometer (VLTI), astronomers in Chile have constructed the most detailed image ever of a star -- the red supergiant Antares. They have also made the first map of the velocities of material in the atmosphere of a star other than the Sun, revealing unexpected turbulence in Antares' huge extended atmosphere. (Image Credit: ESO, K. Ohnaka - Universidad Catolica del Norte, G. Weigelt - Max Planck Institut fur Radioastronomie, and K.H. Hofmann - Max Planck Institut fur Radioastronomie)
To the unaided eye the famous bright star Antares shines with a strong red tint in the heart of the constellation Scorpius. It is a huge and comparatively cool red supergiant in the late stages of its life, on the way to becoming a supernova.
Antares is considered by astronomers to be a typical red supergiant star. These huge dying stars are formed with between nine and forty times the mass of the Sun. When a star becomes a red supergiant, its atmosphere extends outward so it becomes large and luminous, but low density. Antares now has a mass about 12 times that of the Sun and a diameter about 700 times larger than the Sun's. It is thought that it started life with a mass more like 15 times that of the Sun and has shed three solar masses of material during its life.
A team of astronomers, led by Keiichi Ohnaka, of the Universidad Catolica del Norte in Chile, used ESO's Very Large Telescope Interferometer (VLTI) at the Paranal Observatory in Chile to map Antares' surface and to measure the motions of the surface material. This is the best image of the surface and atmosphere of any star other than the Sun.
The VLTI is a unique facility that can combine the light from up to four telescopes, either the 8.2 meter Unit Telescopes, or the smaller Auxiliary Telescopes, to create a virtual telescope equivalent to a single mirror up to 200 meters across. This allows it to resolve fine details far beyond what can be seen with a single telescope alone.
Using ESO's Very Large Telescope Interferometer astronomers have constructed the most detailed image ever of a star -- the red supergiant star Antares. (Video Credit: ESO)
"How stars like Antares lose mass so quickly in the final phase of their evolution has been a problem for over half a century," said Keiichi Ohnaka. "The VLTI is the only facility that can directly measure the gas motions in the extended atmosphere of Antares -- a crucial step towards clarifying this problem. The next challenge is to identify what's driving the turbulent motions."
Using the new results, the team has created the first two dimensional velocity map of the atmosphere of a star other than the Sun. They did this using the VLTI with three of the Auxiliary Telescopes and an instrument called AMBER to make separate images of the surface of Antares over a small range of infrared wavelengths. The team then used this data to calculate the difference between the speed of the atmospheric gas at different positions on the star and the average speed over the entire star. This resulted in a map of the relative speed of the atmospheric gas across the entire disc of Antares -- the first ever created for a star other than the Sun.
This video starts from a wide field view of the Milky Way, including the prominent constellation Scorpius (The Scopion). It zooms in towards Scorpius' bright red heart -- the red supergiant star Antares. The final view shows an image of the surface of Antares taken with ESO's Very Large Telescope Interferometer. (Video Credit: ESO, K. Ohnaka, N. Risinger - Skysurvey.org. Music: Astral Electronic)
The velocity of material on the surface of Antares that is moving towards or away from Earth can be measured by the Doppler Effect, which shifts spectral lines either towards the red or blue ends of the spectrum, depending on whether the material is receding from or approaching the observer.
The astronomers found turbulent, low density gas much further from the star than predicted and concluded that the movement could not result from convection, that is, from large scale movement of matter which transfers energy from the core to the outer atmosphere of many stars. Convection is the process whereby cold material moves downwards and hot material moves upwards in a circular pattern. The process occurs on Earth in the atmosphere and ocean currents, but it also moves gas around within stars. They reason that a new, currently unknown, process may be needed to explain these movements in the extended atmospheres of red supergiants like Antares.
"In the future, this observing technique can be applied to different types of stars to study their surfaces and atmospheres in unprecedented detail. This has been limited to just the Sun up to now," concludes Ohnaka. "Our work brings stellar astrophysics to a new dimension and opens an entirely new window to observe stars." | 0.867141 | 3.617034 |
For countless generations, human beings have looked out at the night sky and wondered if they were alone in the universe. With the discovery of other planets in our Solar System, the true extent of the Milky Way galaxy, and other galaxies beyond our own, this question has only deepened and become more profound.
And whereas astronomers and scientists have long suspected that other star systems in our galaxy and the universe had orbiting planets of their own, it has only been within the last few decades that any have been observed. Over time, the methods for detecting these “extrasolar planets” have improved, and the list of those whose existence has been confirmed has grown accordingly (to over 3000!)
An extrasolar planet, also called an exoplanet, is a planet that orbits a star (i.e. is part of a solar system) other than our own. Our Solar System is only one among billions and many of them most likely have their own system of planets. As early as the sixteenth century, there have been astronomers who hypothesized of the existence of extrasolar planets.
The first recorded mention was made by Italian philosopher Giordano Bruno, an early supporter of the Copernican theory. In addition to supporting the idea that the Earth and other planets orbit the Sun (heliocentrism), he put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets.
In the eighteenth century, Isaac Newton made a similar suggestion in the “General Scholium” section which concludes his Principia. Making a comparison to the Sun’s planets, he wrote “And if the fixed stars are the centers of similar systems, they will all be constructed according to a similar design and subject to the dominion of One.”
Since Newton’s time, various claims have been made, but which were rejected by the scientific community as false positives. In the 1980’s, some astronomers claimed that they had identified a some extrasolar planets in nearby star systems, but were unable to confirm their existence until years later.
One of the reasons why extrasolar planets are so difficult to detect is because they are even fainter than the stars they orbit. Additionally, these stars give off light that “washes” the planets out – i.e. obscures them from direct observation. As a result, the first discovery was not made until 1992 when astronomers Aleksander Wolszczan and Dale Frail – using the Arecibo Observatory in Puerto Rico – observed several terrestrial-mass planets orbiting the pulsar PSR B1257+12.
It was not until 1995 that the first confirmation of an exoplanet orbiting a main-sequence star was made. In this case, the planet observed was 51 Pegasi b, a giant planet found in a four-day orbit around the Sun-like star 51 Pegasi (approx 51 light years from our Sun).
Initially, most of the planets detected were gas giants similar to, or larger than, Jupiter – which led to the term “Super-Jupiter” being coined. Far from suggesting that gas giants were more common than rocky (i.e. “Earth-like“) planets, these findings were simply due to the fact that Jupiter-sized planets are simply easier to detect because of their size.
The Kepler Mission:
Named after the Renaissance astronomer Johannes Kepler, the Kepler space observatory was launched by NASA on March 7th, 2009 for the purpose of discovering Earth-like planets orbiting other stars. As part of NASA’s Discovery Program, a series of relatively low-cost project focused on scientific research, Kepler’s mission is to survey a portion of our region of the Milky Way to find evidence of extrasolar planets and estimate how many stars in our galaxy have planetary systems.
Relying on the Transit Method of detection (see below), Kepler’s sole instrument is a photometer that continually monitors the brightness of over 145,000 main sequence stars in a fixed field of view. This data is transmitted back to Earth where it is analyzed by scientists to look for any signs of periodic dimming caused by extrasolar planets transiting (passing) in front of their host star.
The initial planned lifetime of the Kepler mission was 3.5 years, but greater-than-expected results led to the mission being extended. In 2012, the mission was expected to last until 2016, but this changed due to the failure of one the spacecraft’s reaction wheels – which are used for pointing the spacecraft. On May 11, 2013, a second of four reaction wheels failed, disabling the collection of science data and threatening the continuation of the mission.
On August 15, 2013, NASA announced that they had given up trying to fix the two failed reaction wheels and modified the mission accordingly. Rather than scrap Kepler, NASA proposed changing the mission to utilizing Kepler to detect habitable planets around smaller, dimmer red dwarf stars. This proposal, which became known as K2 “Second Light”, was approved on May 16th, 2014.
Since that time, the K2 mission has focused more on brighter stars (such as G- and K-class stars). As of October 13th, 2016, astronomers have confirmed the presence of 3,397 exoplanets and 573 multi-planet systems, the vast majority of which were found using data from Kepler. All told, the space probe has observed over 150,000 stars in the course of its primary and K2 missions.
In November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like and red dwarf stars within the Milky Way. It is estimated that 11 billion of these planets may be orbiting Sun-like stars.
The discovery of exoplanets has also intensified interest in the search for extraterrestrial life, particularly for those that orbit in the host star’s habitable zone. Also known as the “goldilocks zone“, this is the region of the solar system where conditions are warm enough (but not too warm) so that it is possible for liquid water (and therefore life) to exist on the planet’s surface.
The first planet confirmed by Kepler to have an average orbital distance that placed it within its star’s habitable zone was Kepler-22b. This planet is located about 600 light years from Earth in the constellation of Cygnus, and was first observed on May 12th, 2009, and then confirmed on Dec 5th, 2011. Based on all the data obtained, scientists believe that this world is roughly 2.4 times the radius of Earth, and is likely covered in oceans or has a liquid or gaseous outer shell.
Prior to the deployment of Kepler, the vast majority of confirmed exoplanets fell into the category of Jupiter-sized or larger. However, as of Sept. 18th, 2015, Kepler has identified 4,696 potential candidates, many of them falling into the categories of Earth-size or “Super-Earth” size. Many of these are located in the habitable zone of their parent stars, and some even around Sun-like stars.
And according to a recent study from NASA Ames Research Center, analysis of the Kepler mission data indicated that about 24% of M-class stars may harbor potentially habitable, Earth-size planets (i.e. those that are smaller than 1.6 times the radius of Earth’s). Based upon the number of M-class stars in the galaxy, that alone represents about 10 billion potentially habitable, Earth-like worlds.
Meanwhile, analyses of the K2 phase suggests that about one-quarter of the larger stars surveyed may also have Earth-size planet orbiting within their habitable zones. Taken together, the stars observed by Kepler make up about 70% of those found within the Milky Way. So one can estimate that there are literally tens of billions of potentially habitable planets in our galaxy alone.
While some exoplanets have been observed directly with telescopes (a process known as “Direct Imaging”), the vast majority have been detected through indirect methods such as the transit method and the radial-velocity method. In the case of the Transit Method, a planet is observed when crossing the path (i.e. transiting) in front of its parent star’s disk.
When this occurs, the observed brightness of the star drops by a small amount, which can be measured and used to determine the size of the planet. The transit method reveals the radius of a planet, and it has the benefit that it sometimes allows a planet’s atmosphere to be investigated through spectroscopy.
However, it also suffers from a substantial rate of false positives, and generally requires that part of the planet’s orbit intersect a line-of-sight between the host star and Earth. As a result, confirmation from another method is usually considered necessary. Nevertheless, it remains the most widely-used means of detection and is responsible for more exoplanet discoveries than all other methods combined. The Kepler telescope uses this method (see above).
The Radial Velocity (or Doppler Method) involves measuring the star’s radial velocity – i.e. the speed with which it moves towards or away from Earth. The is one means of detecting planets because, as planet’s orbit a star, they exert a gravitational influence that causes the star itself to move in its own small orbit around the system’s center of mass.
This method has the advantage of being applicable to stars with a wide range of characteristics. However, one of its disadvantages is that it cannot determine a planet’s true mass, but can only set a lower limit on that mass. It remains the second-most effective technique employed by exoplanet hunters.
Other methods include Transit Timing Variation (TTV) and Gravitational Microlensing. The former relies on measuring the variations in the times of transit for one planet to determine the existence of others. This method is effective in determining the existence of multiple transiting planets in one system, but requires that the existence of at least one already be confirmed.
In another form of the method, timing the eclipses in an eclipsing binary star can reveal an outer planet that orbits both stars. As of August 2013, a few planets have been found with this method while numerous more were confirmed.
In the case of Gravitational Microlensing, this refers to the effect a star’s gravitational field can have, acting like a lens to magnify the light of a distance background star. Planets orbiting this star can cause detectable anomalies in the magnification over time, thus indicating their presence. This technique is effective in detecting stars that have wider orbits (1-10 AUs) from Sun-like stars.
Other methods exist, and – alone or in combination – have allowed for the detection and confirmation of thousands of planets. As of May 2015, a total of 1921 planets in 1214 planetary systems have been confirmed, as well as 482 multiple planetary systems.
With the winding down of Kepler’s mission, and so many discoveries made within a short period of time, NASA and other federal space agencies plan to continue in the hunt for extrasolar planets. Proposed NASA missions that will pick up where Kepler has left off include the Transiting Exoplanet Survey Satellite (TESS) – which is scheduled for launch sometime in 2017 – and the James Webb Space Telescope, which is to be deployed in October of 2018.
In addition, the European Space Agency (ESA) hopes to continue to map out a significant portion of the Milky Way Galaxy (including exoplanets) using its Gaia spacecraft – which commenced operations in 2013. The Herschel Space Observatory, and ESA mission with participation from NASA, has been in operation since 2009 and is also expected to make many interesting discoveries in the coming years.
There’s a an entire Universe of worlds out there to discover, and we’ve barely scratched the surface!
Universe Today has many interesting articles on exoplanets. Here’s What Does “Earthlike” Even Mean & Should It Apply To Proxima Centauri b?, Focusing On ‘Second-Earth’ Candidates In The Kepler Catalog, New Technique to Find Earth-like Exoplanets, Potentially Habitable Exoplanet Confirmed Around Nearest Star!, Planetary Habitability Index Proposes A Less “Earth-Centric” View In Search Of Life, Habitable Earth-Like Exoplanets Might Be Closer Than We Think.
For more information, check out Kepler’s home page at NASA. The Planetary Society’s page on Exoplanets is also interesting, as is NASA Exoplanet Archive – which is maintained with the help of Caltech.
Astronomy Cast has an episode on the subject – Episode 2: In Search of Other Worlds.
- Wikipedia – Exoplanet
- The Extrasolar Planets Encyclopaedia
- The Planetary Society – Extrasolar Planets
- NASA Exoplanet Archive | 0.927753 | 3.796321 |
See that tiny speck just to left of the bluish orb? That’s a planet. It’s one of the best direct images of an exoplanet we’ve ever seen, and it’s made all the more remarkable given that it’s a whopping 1,200 light-years away.
Although you can’t see it, there are actually two planets in this remote star system, dubbed CVSO 30. Four years ago, astronomers used the transit method (where an orbiting planet causes a dip in the host star’s brightness) to detect the first planet, which is parked quite close to its host star. This inner planet requires just 11 hours to make a complete orbit and is located a mere 0.008 au (744,000 miles) from its T-Tauri star (a young, bright star that hasn’t quite entered into its main sequence).
Image: ESO/Schmidt et al.
Astronomers have now detected a second planet (the one shown in the photo), and they did so using direct imaging. To do it, they combined data from the ESO’s Very Large Telescope (VLT) in Chile, the W. M. Keck Observatory in Hawaii, and the Calar Alto Observatory facilities in Spain.
Zoomed image of the exoplanet (Image: ESO/Schmidt et al.)
Unlike its companion, this second planet, dubbed CVSO 30c, is exceptionally far from its star. In fact, it’s so far that astronomers aren’t entirely sure if it even belongs to this planetary system. It’s at a distance of 660 au, requiring a mind-boggling 27,000 years to complete a single orbit. For comparison, Neptune is located 30 au from our Sun. The astronomers speculate that the two planets may have interacted at some point in the past, shooting one away while the other settled in its tight orbit.
Given its brightness, there’s a good chance it’s a Jupiter-like planet. Rocky planets tend to be darker and not very reflective.
If scientists are able to confirm that CVSO 30c orbits this star, it’ll be the first star system to host two planets that were detected by two different techniques, the transit method and direct imaging. [ESO] | 0.868155 | 3.686959 |
Almost every star in our Galaxy is likely to harbor a terrestrial planet, but accurate measurements of an exoplanet’s mass and radius demands accurate knowledge of the properties of its host star. The imminent TESS and CHEOPS missions are slated to discover thousands of new exoplanets. Along with WFIRST, which will directly image nearby planets, these surveys make urgent the need to better characterize stars in the nearby solar neighborhood (< 30 pc). We have compiled the CATalog of Stellar Unified Properties (CATSUP) for 951 stars, including such data as: Gaia astrometry; multiplicity within stellar systems; stellar elemental abundance measurements; standardized spectral types; Ca II H and K stellar activity indices; GALEX NUV and FUV photometry; and X-ray fluxes and luminosities from ROSAT, XMM, and Chandra. We use this data-rich catalog to find correlations, especially between stellar emission indices, colors, and galactic velocity. Additionally, we demonstrate that thick-disk stars in the sample are generally older, have lower activity, and have higher velocities normal to the galactic plane. We anticipate CATSUP will be useful in discerning other trends among stars within the nearby solar neighborhood, for comparing thin-disk vs. thick-disk stars, for comparing stars with and without planets, and for finding correlations between chemical and kinematic properties.
N. Hinkel, E. Mamajek, M. Turnbull, et. al.
Fri, 15 Sep 17
Comments: 21 pages, 14 figures, 6 tables, full CATSUP database included in source data (datafile6.txt) per breakdown in Table 6 and will also be uploaded on Vizier, accepted for publication in ApJ | 0.841966 | 3.661309 |
July 19, 2014
Curiosity Rover Images Show Martian Soils That Are Similar To Earth’s
April Flowers for redOrbit.com - Your Universe Online
A new study from University of Oregon (OU) geologist Gregory Retallack suggests that soil samples taken by NASA's Mars Curiosity rover contain evidence that Mars was once much warmer and wetter. His findings, published online in Geology, are based on images and data of 3.7 billion year old soil collected in the Gale crater.Previous rovers have revealed the Martian landscape is littered with loose rocks created by impacts or layered by catastrophic floods. These formations are in contrast to the smooth contours of soils that soften the landscapes of Earth. Retallack says that recent Curiosity images, however, reveal Earth-like soil profiles. The profiles have cracked surfaces lined with sulfate, ellipsoidal hollows and concentrations of sulfate comparable with soils in Antarctic Dry Valleys and Chile's Atacama Desert.
Retallack is the co-director of paleontology research at the UO Museum of Natural and Cultural History, as well as being an international expert on the recognition of paleosoils — ancient fossilized soils contained in rocks. For this study, he analyzed mineral and chemical data published by researchers with close ties to the Curiosity mission.
"The pictures were the first clue, but then all the data really nailed it," Retallack said in a recent statement. "The key to this discovery has been the superb chemical and mineral analytical capability of the Curiosity Rover, which is an order of magnitude improvement over earlier generations of rovers. The new data show clear chemical weathering trends, and clay accumulation at the expense of the mineral olivine, as expected in soils on Earth. Phosphorus depletion within the profiles is especially tantalizing, because it attributed to microbial activity on Earth."
Retallack cautions that his results do not prove the Red Planet once held life. Rather, he sees his results as adding to the growing pile of evidence that Mars was not always the arid and inhospitable planet that it has been for the last 300 billion years.
Currently, Curiosity is exploring regions of Gale Crater that are topographically higher and geologically younger. The soils in these layers appear to be less conducive to life. Retallack would like to see more missions to Mars that explore older, and more clay-like, terrains.
Curiosity's images include surface cracks, which suggest typical soil clods. Vesicular hollows (rounded holes) and sulfate concentrations found on Mars are both features of desert soils on Earth, according to Retallack.
"None of these features is seen in younger surface soils of Mars," Retallack said. "The exploration of Mars, like that of other planetary bodies, commonly turns up unexpected discoveries, but it is equally unexpected to discover such familiar ground."
Retallack believes the newly discovered soils provide evidence of a more benign and habitable Mars. Dating the soils to 3.7 billion years ago puts them in the transitional period between "an early benign water cycle on Mars to the acidic and arid Mars of today." Most scientists believe that life on Earth began to emerge and diversify approximately 3.5 million years ago. Some, however, have hypothesized that potential evidence could push that timeline farther back. They believe this evidence was destroyed by tectonic activity, which does not occur on Mars. | 0.804685 | 3.418131 |
October 6, 2010
WMAP Project Completes Satellite Operations
After nine years of scanning the sky, the Wilkinson Microwave Anisotropy Probe (WMAP) space mission has concluded its observations of the cosmic microwave background, the oldest light in the universe. The spacecraft has not only given scientists their best look at this remnant glow, but also established the scientific model that describes the history and structure of the universe.
"WMAP has opened a window into the earliest universe that we could scarcely imagine a generation ago," said Gary Hinshaw, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., who manages the mission. "The team is still busy analyzing the complete nine-year set of data, which the scientific community eagerly awaits."WMAP was designed to provide a more detailed look at subtle temperature differences in the cosmic microwave background that were first detected in 1992 by NASA's Cosmic Background Explorer (COBE). The WMAP team has answered many longstanding questions about the universe's age and composition. WMAP acquired its final science data on Aug. 20. On Sept. 8, the satellite fired its thrusters, left its working orbit, and entered into a permanent parking orbit around the sun.
"We launched this mission in 2001, accomplished far more than our initial science objectives, and now the time has come for a responsible conclusion to the satellite's operations," said Charles Bennett, WMAP's principal investigator at Johns Hopkins University in Baltimore.
WMAP detects a signal that is the remnant afterglow of the hot young universe, a pattern frozen in place when the cosmos was only 380,000 years old. As the universe expanded over the next 13 billion years, this light lost energy and stretched into increasingly longer wavelengths. Today, it is detectable as microwaves.
WMAP is in the Guinness Book of World Records for "most accurate measure of the age of the universe." The mission established that the cosmos is 13.75 billion years old, with a degree of error of one percent.
WMAP also showed that normal atoms make up only 4.6 percent of today's cosmos, and it verified that most of the universe consists of two entities scientists don't yet understand.
Dark matter, which makes up 23 percent of the universe, is a material that has yet to be detected in the laboratory. Dark energy is a gravitationally repulsive entity which may be a feature of the vacuum itself. WMAP confirmed its existence and determined that it fills 72 percent of the cosmos.
Another important WMAP breakthrough involves a hypothesized cosmic "growth spurt" called inflation. For decades, cosmologists have suggested that the universe went through an extremely rapid growth phase within the first trillionth of a second it existed. WMAP's observations support the notion that inflation did occur, and its detailed measurements now rule out several well-studied inflation scenarios while providing new support for others.
"It never ceases to amaze me that we can make a measurement that can distinguish between what may or may not have happened in the first trillionth of a second of the universe," says Bennett.
WMAP was the first spacecraft to use the gravitational balance point known as Earth-Sun L2 as its observing station. The location is about 930,000 miles or (1.5 million km) away.
"WMAP gave definitive measurements of the fundamental parameters of the universe," said Jaya Bapayee, WMAP program executive at NASA Headquarters in Washington. "Scientists will use this information for years to come in their quest to better understand the universe."
Launched as MAP on June 30, 2001, the spacecraft was later renamed WMAP to honor David T. Wilkinson, a Princeton University cosmologist and a founding team member who died in September 2002.
Image Caption: This image is the detailed, all-sky picture of the infant universe created from seven years of WMAP data. The image reveals 13.7 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies. Credit: NASA
On the Net: | 0.804895 | 3.827657 |
Earth, Moon and Planets, 74 (1996), No. 3, 223 – 230.
KAZIMIERZ M. BORKOWSKI
Torun Radio Astronomy Observatory, PL 87-100 Toruń, Poland
(Received 10 October 1996, accepted 10 November 1996)
|Abstract. Using the analytical theory of the motion of the Earth around the Sun the times of the vernal (Spring) equinox has been calculated over the period from the Hijra (AD 622) to AD 3800. These data alone allow to decide whether a particular Persian (or Jalaali) calendar year is common or leap. Presented analysis shows that an algorithm implemented in the so called Khayam program is valid for the years 1799 to 2256 (1178 to 1634 Jalaali). A concise algorithm has been worked out that reconstructs the pattern of leap years over time span of about 3000 years. FORTRAN routines for conversion between the Jalaali, Gregorian and Julian calendars and the Julian Day Number are presented.|
The Persian or Jalaali calendar is officially used in Iran and surrounding areas. It is a solar calendar closely following the astronomical seasons, thus requires the knowledge of exact times of the vernal (Spring) equinox.
The rules of the Jalaali calendar are quite simple. Years of 12 months are reckoned from the era of the Hijra, commemorating the migration of the Prophet and his followers from Mecca to Medina in AD 622. A Jalaali year begins on the first day of astronomically determined spring or on the day following it according to whether the exact moment of the equinox occurs before or after, respectively, 12:00 of the Teheran mean time. The first 6 months all have 31 days and the last 6 manths all have 30 days in leap years. In common years the last month has 29 days. Thus every season is associated with three consecutive months.
As expected, roughly every fourth year in the Persian calendar is the leap one. This is the well known regularity in solar calendars. However, normally after every 32 (sometimes after 28 or 36) years follows an extra common year making four consecutive 365-day years instead of the usual three. Currently the leap years go smoothly in the 33-year cycles and specifically they are those years that after dividing by 33 leave a remainder of 1, 5, 9, 13, 17, 22, 26 and 30. E.g., the Jalaali year 1375 that begun on March 20, 1996 has the remainder of 22 and thus is the leap year. These rules are implemented in the so called Khayam program of Ali Moayedian and Mash Cheragh-Ali, which is available on the Internet. Unfortunately this simple behaviour will not last indefinitly and the 33-year cycle is sure to break sometimes. Hossein Bagherzadeh Rafsanjani in his introduction to the program suggests that a break may occur `early in the next century Hijra' and that the program should be correct until early 2050's of Gregorian calendar. It is the purpose of this paper to determine exactly how long the above rule of remainders will be valid and to establish the rules for the Jalaali calendar as far into future as is presently practical.
In general, to determine if a Persian year is leap or common it is necessary to
find the date and time of the vernal equinox at the beginning of that year and
at the beginning of the next year. To this end I have employed an analytical
theory of the motion of the Earth around the Sun (Bretagnon et al.1986),
which is accurate to about 2′′
in the angular coordinates of the Sun as
viewed from the Earth. The theory has been used in a converging process to
find the Terrestrial Time (TT or Ephemeris Time) of the epoch at which the
celestial longitude of the Sun equalled 0. The TT of the equinox has been
then converted to the Universal Time (UT1) using past estimates, measurements,
and future predictions of the difference
ΔT = TT –
UT1 = 32.184 –
(UT1 – TAI), where TAI is the atomic time scale of BIPM.
For past years and far future predictions I have used essentially
tabular data and formulae of Stephenson and Morrison (1984):
In Table I we present partial list of vernal equinoxes given in the Universal Time that might be of general interest. As a final step, the mean time of Teheran has been calculated by adding its geographic longitude, 3.425 hours, to the UT1 of the equinoxes.
A full list of equinoxes comprising the years AD 550 to 3800, referred to the Teheran time has been used to identify the leap years of the Jalaali calendar. The pattern of leap years is quite regular: they come every 4 years in groups of 28, 32 or 36 years with each group supplemented with an extra common year. Usually these are 32+1 year groups and the few occasional exceptions, called here breaks, can be used in a practical procedure to reconstruct the entire sequence of leap years. In Table II the Jalaali years represent the first year (leap) of a new cycle (mostly the 33-year cycle) after a break (i.e. after the 4-th common year closing the 28 or 36 year group).
|Table II: The years of the Gregorian calendar (Gy) that mark the end of a 29- or 37-year period which breaks the 33-year rule validity. Around 20 March Gy ends the 4th common year and begins the Jalaali leap year Jy|
As can be seen from Table II, the 33-year cycle operates continuously between 1831 and 2256. Closer examination shows that in fact it operated from 1799, since 1831 marks just the end of the 29-year period, and would not appear here if the previous break would fall four years earlier. This is thus the time span of validity of the Khayam algorithm. There is however a possibility that it will not be as good as that and the upper limit may fall on AD 2124. I shall return to this question when discussing errors.
The proposed algorithm is based on the described list of the breaking years in which the fourth common Jalaali year occurs after 28 or 36 (and not 32) years of 4-year periods since the previous occurence of four common years in succession. During 3000 years there are only about 20 such breaking years, and they allow for an easy reconstruction of a complete sequence of Jalaali leap years.
To determine whether a Jalaali year is common or leap, one finds the number,
say N, of years that have passed since the last breaking year of
Table II. With one exception, the year of interest
is leap if –1 plus the remainder of (N + 1)/33 is
evenly divisible by 4, or
Using the integer arithmetic this algorithm reduces to just two FORTRAN lines (apart of searching the list for the required breaking years). For the common years the remainder of division by 4, i.e. lp, tells how many years have passed since the last leap year. E.g. the remainder of 1 (2 or 3) means that the leap year was the previous one (2 or 3 years ego). Obviously, it is also possible to tell whether the considered year is the 4-th common one. The case occurs when N + 1 (or N + 1 ± 4 if it is the exceptional situation), is evenly divisible by 33.
To relate the Jalaali calendar to the Gregorian one it is necessary to
find the number of leap years since an initial epoch in both these calendars.
In the Jalaali calendar, the number of leap years between two adjacent break
years of Table II, say between yi and yj is
This algorithm has been encoded in the FORTRAN integer arithmetic subroutine (Table III) JalCal(Jy,leap,Gy,March), which for a given Jalaali year Jy returns information on the leap year in the leap variable, which assumes values 0 to 4, as described above. The routine returns also the Gregorian date of the first day of the Jalaali year in the variables Gy (Gregorian year) and March (day of March). Thus it can be directly used to relate the beginning of the Persian calendar for any year within about 3000 years to the Gregorian calendar.
Such a procedure can be employed for full date conversion from the Persian
calendar if we note that until the Jalaali date m (month) and d (day)
Practical programs were written and tested for convertion of Jalaali calendar, first into the Julian Day number (JD), and then into the Gregorian or Julian calendar, and also for reverse conversion of these calendars to the Persian one. The following procedures in FORTRAN serving this purpose are available from the author (see this complete coversion program listing and the DOS executable):
Due to approximate nature of the ephemeris the results of the equinox time may be in error of about 1 minute of time. Uncertainty of ΔT adds to the error of the final result. This parameter is very well known from direct observations only back to about AD 1630.
|Table IV: Critical years in the Jalaali calendar most likely to alter the sequence of breaking years. The first four columns give Gregorian date in March, the Teheran mean time (in hours and minutes) of the vernal equinox, and the value of ΔT = TT – UT1. Then there is the day in March of the first day of the Jalaali year (Farvardin the 1st) and the year itself. The last column shows possible additions (+) to and subtractions (–) from the breaking years list of Table II.|
The past breaking years, as being purely astronomical and based on contemporary knowledge, may not coincide with the actual Jalaali calendar, used then for astronomical purposes only. Also, the future breaking years of Table II may disappear altogether or new ones will have to be introduced depending on real rotation of the Earth (the behaviour of the ΔT value). The most critical years are listed in Table IV, where the date in March (Gregorian calendar) and the predicted Teheran mean time are given along with the assumed ΔT value. The table contains all the cases that the equinox time is removed from 12:00 Teheran time by less than (1 + ΔT/10) minutes, where the 1 minute is due to uncertainty of the equinox determination and the other term is intended to account for 10% error in ΔT (an ad hoc error estimate). The Jalaali years indicated in Table IV are leap years if the equinox time is less than 12:00, otherwise the previous year is leap. The expected change to be introduced to the list of breaking years in case the actual equinox time shifts across the noon point (12:00) due to combined effect of the ephemeris error and a change in ΔT, is shown in the last column of this table.
It will be noted, that the discussed change affects only the year in question (shifting it by one day relative to e.g. Gregorian calendar) and the last day of the previous Jalaali year. Thus the algorithm in the form presented may lose its validity only for some of the future Jalaali years given in Table IV. In the worst case, if my estimates of ΔT are systematically low, the 10 critical years with equinox greater than 12:00 of that table may drop to less then 12:00 and thus the corresponding Jalaali years would shift by one day into the previous year, themeselves becoming the leap years. Should the ΔT be systematically high instead, there would be only 7 future years of Table IV endangered by an opposite shift.
2124 is the nearest doubtful year. The Teheran times of the vernal equinox indicate that in this year the 1503 Jalaali year starts on 21 March and not on 20 March just because the calculated equinox time was only about one third of a minute past 12:00 (see Table IV). Thus if ΔT will be greater by some 20 seconds than predicted in this analysis, this year will become an additional breaking point to be added to the presented algorithm along with another one 37 years later (1540 Jalaali). | 0.834019 | 3.514687 |
New Exomoon Hunting Technique Could Find Solar System-like Moons
Among the most sought-after prizes in astronomy these days are “exomoons,” or moons orbiting exoplanets. Although astronomers have detected more than a thousand exoplanets, any exomoons they might harbor have so far eluded capture. However, judging by our own Solar System, where moons greatly outnumber planets, scientists believe that hordes of exomoons are indeed out there.
To find these exomoons hiding in plain view, a new technique has just been proposed. Described in a study recently accepted in The Astrophysical Journal, the new approach relies on a particular eclipsing effect of moons when viewed against the background radiance of their host stars.
Unlike traditional exomoon hunting techniques, the new method has the advantage of being able to find natural satellites on the scale of the moons here in the Solar System. Other methods can probably only yield exomoons several times the mass of the biggest moon known, Jupiter’s Ganymede — in other words, unprecedentedly monstrous moons.
“This technique is the first method that has been demonstrated to allow detection of moons akin to those in the Solar System,” said study author René Heller, a postdoctoral fellow in astronomy at McMaster University, in Ontario, Canada. “Four hundred years after Galileo Galilei discovered four moons orbiting Jupiter, the first moons we knew of besides our moon, we now have the technologies and methods available to go find ‘alien’ moons beyond our Solar System.”
Additionally, the new method can distinguish multi-moon systems, whereas standard techniques focus on solo exomoons. A third benefit is that existing data from the Kepler spacecraft should suffice for identifying exomoons. That’s in contrast to some other proposed methods which would require new technologies and force exomoon hunters to await future generations of telescopes.
Intriguingly, the method could tease out the presence of exomoons orbiting planets in the so-called habitable zones of red dwarf stars and orange dwarfs. The habitable zone is the not-too-close, not-too-far-away band around a star wherein residing worlds could have liquid water.
To date, the most common planets found in habitable zones are not Earth-sized (though a substantial number of earthly twins could emerge from Kepler data yet to be analyzed). Rather, habitable zone-dwellers are often “super-Earths” and gas giants. The latter certainly, and some have argued the former, cannot serve as abodes for life. But their moons could be a different story.
“Super-Earths and giant planets have been observed to be much more abundant in the stellar habitable zones than truly Earth-sized planets,” said Heller. “While super-Earths and giants may not be habitable, their moons might be. Hence, habitable moons may be much more common than habitable planets.”
Scouring for exomoons in a new way
The new technique comes at a good time. Researchers have already thrown the proverbial kitchen sink at the problem of exomoon catching, trying out about a dozen different methods without a confirmed detection. Some methods include looking for the tiny amount of infrared light a giant, hot exomoon emits, or a one-off, gravitational-light-warping effect of a background star’s light as a planet and its moons pass in front of the star.
The concept behind the new method, observing “transits,” is not in of itself new. Spotting transits, the mini-eclipses caused when an exoplanet (or an exomoon) crosses the face of its star respective to our viewing angle here on Earth, has been used to find hundreds of exoplanets with Kepler, CoRoT and other telescopes. A prominent exomoon-finding project, Hunting Exomoons with Kepler (HEK), as well as other efforts, seeks slight variations in transit timings or durations. These hiccups to an orderly, planetary transit might be the handiwork of a moon blocking out just a little extra starlight.
What the new method, called the orbital sampling effect, does is consider these exomoon transits from a clever statistical perspective. Picture a planet and moon system viewed edge-on in silhouette, where the moon orbits around the planet’s equatorial midline (as is typical in the Solar System). The moon orbits in “front” of the planet, slightly nearer to us, and then completes the orbital circle behind the planet.
Imagine taking a snapshot every now and then of this setup and superimposing the pictures. The moon’s positions in the front and back of the orbit overlap, though where the moon is directly in front of or behind the planet, the moon’s shadow is not seen. What the moon does form, though, looks like two “wings” sticking out of the planet’s sides, made up of dotted lines. The dots represent the moon’s position at any particular, random moment as it progresses through its orbit.
The insight Heller had is that the dots in the wings will not appear evenly plotted over time. The wings will look lighter at their inner edges, nearer the planet, and darker at their outer edges, farther from the planet. That’s because when the moon reaches the extent of its orbit and then starts circling back around the planet, its positions overlap more in a tighter space. As such, the “wingtips” look darker; that is, there is increased eclipsing of background starlight at the moon’s farthest apparent positions from the planet.
For this effect to emerge, an observer must stare at a star constantly over a significant period of time. The moon cannot be glimpsed once or twice in isolation. Instead, the moon must complete quite a number of orbits, and be witnessed doing so, in order for its light-blocking effect to preferentially stack up at the wingtips. Fortunately, the Kepler spacecraft was designed to do just this, having patiently stared at around 150,000 stars for four years before suffering an equipment failure last summer.
“Such observations have already been taken by Kepler, and they are publicly accessible,” said Heller. “So there’s no need to wait for future technology.”
One moon or many
When an exoplanet transits a star as seen by Kepler or another transit-registering telescope, there occurs a single drop in the amount of starlight received (only around a thousand parts per million for a gas giant planet). Using the orbital sampling method with Kepler data, averaged over time, the signature of an exoplanet sporting an exomoon would look like as follows.
First, there would be two small dips in the amount of light collected, one preceding and one following the comparatively much bigger dip in light by the host planet as the transit gets under way. This initial sequence is small dip, big dip, then an additional small dip. The sequence then reverses itself, with a slight lightening, followed by a relatively big increase in illumination, and a final small increase in the star’s brightness as the planet and moon combo, averaged-over-time, emerges from the transit. In other words, small bump, big bump, and a final small bump in brightness.
The upshot of all this: astronomers (or computers) can look through Kepler data for the tell-tale “pre-darkening” and “post-darkening” of an exoplanet’s regular transit to discover an exomoon.
As a bonus, the orbital sampling method can pick out multiple moons. Rather than the simple step-wise darkening just described for one moon, complex steps could point to more than one moon adding in its own, additional shadowy signature shifted in time.
What it might find
Based on the data collected by Kepler, Heller’s study shows that moons about the size of Ganymede should be findable in the habitable zone of red dwarf stars. The advantage with small stars is that their planets have short orbits, with “years” lasting only weeks or days. Accordingly, these worlds racked up a lot of transits over Kepler’s operational lifetime. More transits, of course, mean more exomoon positioning data for review with the orbital sampling method.
Red dwarf stars present some habitability issues, so better candidates for illuminating life-friendly worlds are the next stellar class up — the bigger, warmer orange dwarfs. In these stars’ habitable zones, the Heller technique could potentially discover exomoons about ten times Ganymede’s mass (but still smaller than Earth), which are the traditional quarry for current exomoon hunting methods, again using Kepler observations.
Unfortunately, moons around exoplanets in the habitable zones of still bigger and hotter Sun-like, yellow-dwarf stars will still remain unobtainable. Exoplanets revolving around stars like the Sun did not pile up enough transits in the Kepler observation window to apply the orbital sampling method. However, future telescopes with sharper cameras will give a leg-up to other exomoon-seeking techniques and will also provide Heller’s method a boost in sensitivity.
The orbital sampling effect is much simpler than the elaborate exomoon detection mechanisms developed by other teams. Heller hopes that fellow researchers might go and try his technique to find extrasolar satellite systems.
“This paper was not planned to serve my own ambitions towards an exomoon detection,” Heller said. “But if someone uses this new effect to find a moon outside the Solar System, I’d feel flattered.” | 0.910957 | 3.857144 |
Hugh Ross, in his famous book The Fingerprint of God (Whitaker House, 1989), summarized several important questions related to modern science:
(1) Is our universe finite or infinite in size and content?
(2) Has this universe been here forever or did it have a beginning?
(3) Was the universe created?
(4) If the universe was not created, how did it get here?
(5) If the universe was created, how was this creation accomplished, and what can we learn about the agent and events of creation?
(6) Who or what governs the laws and constants of physics?
(7) Are such laws the products of chance or have they been designed?
(8) How do the laws and constants of physics relate to the support and development of life?
(9) Is there any knowable existence beyond the apparently observed dimensions of the universe?
(10) Do we expect the universe to expand forever, or is a period of contraction to be followed by a big crunch?
While answers to some of these questions lie outside of the territory of chemistry, chemistry should help answering some of the last questions where molecules should play an important role. It is generally accepted that almost all present-day knowledge about the structure and properties of molecules comes via studies of their spectra. Although laboratory measurements are usually considered to be the prime sources for the relevant information, there are a number of occasions where theory has played, and will continue to play, a central role in the understanding of properties of molecules and their spectra. Cutting-edge studies in spectroscopy help to answer more mandane questions than those raised above but these questions and answers are still highly interesting to those studying nature.
Astronomical environments, such as those found in interstellar medium, are very different from those on Earth. This dissimilarity leads to a fundamentally different chemistry and to the production of species that can be hard to create in the laboratory. Theory can play an important role in predicting main features of spectra of such species or looking for possible spectral matches in other solar systems and in the atmospheres of exoplanets. The detailed understanding of the chemistry taking place in astronomical environments is central to understand a couple of less grand but still important questions:
(1) How did the solar systems form?
(2) Will the understanding of chemistry on earth help to understand chemistry in diverse astronomical objects?
(3) How did the building blocks of life form on earth and outside of earth?
(4) How did life begin on earth?
(5) Would understanding of the origin of life on earth help to understand the origin of life and its building blocks in other solar systems and on exoplanets?
Theoretical high-resolution molecular spectroscopy offers important contributions toward answering at least some parts of these questions.
Studies of potential energy and property hypersurfaces
Even when laboratory spectra have been recorded for a particular species, this data may only be partial. One such situation, which is particularly common for unstable or reactive species, is that wavelengths can be measured to high accuracy but there is no or extremely limited information on transition probabilities and line strengths. To understand these one needs to compute potential energy (PES) and property (like the dipole moment surface, DMS) hypersurfaces which can be obtained with modern techniques of electronic structure theory. Computing accurate and global PESs and DMSs is still a considerable challenge for polyatomic systems.
A. G. Császár, W. D. Allen, Y. Yamaguchi, and H. F. Schaefer III, Ab Initio Determination of Accurate Potential Energy Hypersurfaces for the Ground Electronic States of Molecules, in Computational Molecular Spectroscopy, 2000, eds. P. Jensen and P. R. Bunker, Wiley: New York.
A. G. Császár, G. Tarczay, M. L. Leininger, O. L. Polyansky, J. Tennyson, and W. D. Allen, Dream or Reality: Complete Basis Set Full Configuration Interaction Potential Energy Hypersurfaces, in Spectroscopy from Space, edited by J. Demaison, K. Sarka, and E. A. Cohen (Kluwer, Dordrecht, 2001), pp. 317-339.
Computational molecular spectroscopy
It must be realized that many modelling applications are particularly demanding on spectroscopic data. For example, to model the role of triatomic species, such as H2O or [H,C,N], which are important components of O-rich and C-rich cool stars, respectively, may require up to a billion vibration-rotation transitions. The laboratory measurement and analysis of a dataset of transitions of this size is completely impractical. Computational molecular spectroscopy, with its fourth-age quantum chemical techniques, come to the rescue and allows the straightforward determination of huge molecular linelists.
A. G. Császár and V. Szalay, Molekularezgések elméleti vizsgálata, in: Kémia Újabb Eredményei, Vol. 83, Akadémiai Kiadó: Budapest, 1998, pp. 213–353 (in Hungarian).
O. L. Polyansky, A. G. Császár, S. V. Shirin, N. F. Zobov, P. Barletta, J. Tennyson, D. W. Schwenke, and P. J. Knowles, High-Accuracy Ab Initio Rotation-Vibration Transitions of Water, Science 2003, 299, 539-542.
A. G. Császár, C. Fábri, T. Szidarovszky, E. Mátyus, T. Furtenbacher, and G. Czakó, Fourth Age of Quantum Chemistry: Molecules in Motion, Phys. Chem. Chem. Phys. 2012, 14(3), 1085-1106. | 0.80459 | 3.331053 |
The structure of an atmosphere may be discussed in one of two ways -- in terms of the way that its density changes as you go upward or downward in the atmosphere, or in terms of the way that its temperature changes as you go upward or downward. For all planets the density structure is similar, in that the density steadily increases as you go downward and steadily decreases as you go upward; only the rate at which the density changes differs. But the temperature structure, though similar in some ways, is different for the Earth than for any other planet (though it was recently discovered that Pluto's atmospheric structure may be more like ours than previously thought). For all planets there is a relatively rapid temperature increase as you go downward at the bottom of the atmosphere, and a relatively rapid temperature increase as you go upward at the top of the atmosphere; but for most planets the middle atmosphere is relatively cold, while for the Earth, the lower middle atmosphere and upper lower atmosphere contains a heat source due to absorption of ultraviolet light by our ozone layer which makes that region much warmer than it would otherwise be. There is another object in the Solar System -- Titan, the largest moon of Saturn -- which has a similar temperature structure (in its case due to absorption of ultraviolet light by methane), but since Titan is classified as a moon (or natural satellite), the Earth is essentially unique among the planets in this respect.
As you go downward in an atmosphere its density steadily increases, and if you go upwards the atmospheric density steadily decreases. That is, the air becomes denser and denser (or thicker and thicker) as you go downwards, and less and less dense (or more rarified) as you go upwards.
The rate at which the density changes is normally expressed in terms of the "scale height", which is the height that the atmosphere would have if it were the same density everywhere as it has at the bottom. In the case of the Earth the scale height is about 5 miles, but for all the other planets the scale height is substantially larger, varying from around 10 to 15 miles for Venus, Mars and (when it has an atmosphere) Pluto, to 20 to 30 miles for the Jovian planets. Of course as already stated, the density is not the same everywhere, but steadily increases or decreases with height; so instead of representing the actual depth of the various atmospheres, the scale height represents the distance in which, as you go up (or down), the density decreases (or increases) by a factor of e, the base of natural logarithms, or (approximately) 2.71828. Thus, in the case of the Earth, to observe a change in the density by this factor you'd have to go about 5 miles upward or downward, while in the case of Venus, Mars and Pluto, you'd have to go two to three times as far to observe a similar change in density, and in the case of the Jovian planets four to six times as far. In this sense, we could say that the Earth's atmosphere is more compressed toward the surface of the planet by two to six times more than the atmospheres of the other planets.
Mathematicians and meteorologists (people who study atmospheres) love the number e, because it makes the mathematics they use to discuss atmospheres simpler than if they were to use some other ratio of densities. But for non-mathematicians, e seems a cumbersome number, so in the discussion below I consider the change in height required to cause a change in density of a factor of two. Since 2 is less than e, the height involved is less than the numbers previously shown for the various planets. For the Earth, the distance required to change the density by a factor of two is a little over 3 miles; while for Venus, Mars and Pluto it is 6 to 10 miles, and for the Jovian planets, 12 to 18 miles.
A Trip to the Top of the Atmosphere
To see how this works, imagine that you start at the surface of the Earth and climb up a mountain, such as Mount Whitney, which is about 3 miles high. As you rise the air gradually becomes more and more rarefied, until at the top of the mountain, it is only about half as dense as at sea level. This is enough of a change in density that most people, if exposed to such a change in a short period of time, feel somewhat ill. The effects involved, which are due partly to the smaller amount of oxygen in the "thinner" air, and partly to the lower atmospheric pressure, are referred to as altitude sickness; and in rare cases, can be severe or even fatal. For this reason, airplanes which rise above two miles altitude are usually "pressurized" so that the air inside the airplane is the same density as at eight to ten thousand feet altitude, regardless of how high the airplane flies and how low the density of the outside air becomes.
If you had no difficulty with such a change in atmospheric density, and could continue to climb to an altitude of six miles above sea level (as at the top of Mount Everest), you would experience atmospheric densities which are only half those at three miles altitude, and a quarter of the density at sea level. At this low density the oxygen content of the atmosphere is so low that even well-acclimated climbers (people who have lived for some time at high altitude) have difficulty taking even a single step without some kind of oxygen "assist"; and for all practical purposes this is the greatest height (and the lowest density for ordinary air) which can sustain human life. (Of course our atmosphere only contains 20% oxygen, so we could reduce the effects of very thin air by using oxygen assistance of some sort, and many Himalayan climbers have resorted to such methods to allow them to exceed their normal physical limitations.)
But let's suppose that instead of expiring in one way or another, you had no difficulty in rising still further; then you would find as you rise, mile after mile, that the density of the atmosphere continues to decrease at about the same rate of halving the density each three or so miles higher. So at nine miles altitude, the air is only about 1/8th as dense as at sea level and at twelve miles altitude, only 1/16th as dense. And if you continued to rise until you were thirty miles (or ten times three miles) above the surface, you would find that the atmospheric density had dropped by a factor of two ten times over, making it only a thousandth as dense as at sea level.
For all practical purposes, at thirty miles altitude you would be at the "top" of the atmosphere, as very few airplanes or ballooons can rise to such heights, as the thin air provides too little "lift" to support an airplane and too little "buoyancy" to support a balloon. But thin though it is there is still air there, and you have to go much higher to reach the actual "top" of the atmosphere, such as it is. Another thirty miles height reduces the atmospheric density another thousand times, to only a millionth of the density at the surface, and another thirty miles another thousand times, to only a billionth of the surface density. But even at that height (ninety miles), a spacecraft returning from orbit or extraterrestrial travel, entering the atmosphere at speeds of 18 to 25 thousand miles an hour, would experience so much frictional heating that its surface (and the surrounding air) would be heated to temperatures hot enough to vaporize virtually all known materials. It is in fact such frictional heating of extraterrestrial objects called meteoroids that causes the phenomenon we call meteors, or "shooting stars". Grains of extraterrestrial material, usually the size of a grain of sand or a small pebble, heat the air surrounding them to distances several times greater than the size of the object, to temperatures of thousands or even tens of thousands of degrees (depending upon how fast the particles are moving). Thus, a 1/10th inch-wide meteoroid might heat a column of air an inch in diameter and tens of miles long as it plunges into the atmosphere, until it is vaporized by the heat of its passage.
If you were to go another thirty or sixty miles higher, the air would become even thinner -- millions of millions of times thinner than at sea level at 120 miles altitude, and millions of billions of times thinner than at sea level at 150 miles altitude -- and as a result friction, even for rapidly moving objects such as the International Space Station or manned spacecraft, is reduced to negligible values. This is why we don't say that a spacecraft is "in orbit" until it is at such altitudes, even if it has enough speed to "be in orbit" at lower altitudes. At lower altitudes the gases in the upper atmosphere would not only heat it but also rob it of some of its speed, causing it to gradually spiral into lower orbits where it would encounter denser air, which would cause even greater frictional heating and slowing, so that within a relatively short period of time it would either "burn up" or fall to the surface of the Earth.
How Scale Height Is Related to Various Factors
(brief notes from an earlier version of this page, to be updated and enlarged in the next iteration of the page)
The Scale Height of a planet's atmosphere depends upon three factors:
(1) how strong the planet’s gravity is. A high gravity will compress the gas towards the surface, and as a result any change in the atmosphere will occur over smaller distances.
(2) how much each particle of gas ‘weighs’ (or, more accurately, how much mass it has). A light gas like hydrogen doesn't weigh as much, so gravity can’t compress it toward the surface as much as a heavier gas, like carbon dioxide.
(3) temperature. If the gas is hot it will tend to expand, if cold it will tend to contract.
Scale Height is proportional to temperature / mass per particle / gravity.
On the Earth, the Scale Height is about 5 miles, when defined in a particular way which mathematicians love -- a way in which as you go up or down one Scale Height the atmosphere increases or decreases its density by 2.71828 times (e, the base of natural logarithms). They like to do it this way for two reasons -- first, it makes the calculus easier, and secondly, the Scale Height, when defined in this way, is the height that the atmosphere would have if it were all the same density as at the surface.
But the density is NOT the same everywhere, as discussed in detail above. It decreases as you go up, according to the Law of Hydrostatic Equilibrium and the Gas Law:
The Law of Hydrostatic Equilibrium says that there is a strict relationship between the weight compressing a fluid, and the pressure inside it, namely:
P = W
(pressure at some point in a fluid = weight pressing down on it from above)
This relationship is directly related to the law of buoyancy as discovered by Archimedes, two millennia ago.
The (Ideal) Gas Law:
Pressure = density (times) temperature (ignoring all conversion constants)
Insofar as the temperature in the atmosphere is roughly constant as you go up, this means that the density has to change, as the weight compressing the gas changes. (And as it turns out temperature is ‘roughly’ constant for the first 100 miles up from the surface of the Earth, so virtually all the change in pressure is accomplished by changing the density as descibed in "A Trip to the Top of the Atmosphere", above.)
When talking about the structure of an atmosphere, all of the planets have one thing in common -- as you go up or down the density changes at some rate. It changes more quickly if the gas is heavy, and more slowly if it is light and expands into space, but all of the planets’ atmospheres get thinner and thinner as you go up, and thicker and thicker as you go down.
The differences in different planets' atmospheric structure primarily have to do with temperature. There are various heat sources in a planet’s atmosphere, and where you have them it is warm, and where you don’t it is cold.
In general, it is ‘warm’ at the surface. For most of the planets because that’s where the sunlight falling on the planet is absorbed. Either the light is reflected away by clouds or it goes through the atmosphere, and is absorbed at the surface, heating it up. The lowest part of the atmosphere is warmed by its contact with the surface, and as a result is warmer than the layers above.
In addition, for the Jovian planets (particularly Jupiter and Saturn) there is a lot of heat coming out of the inside because the interiors of all the planets are hot, and being liquid heat can easily flow from the cores of these planets to the surface. So despite its great distance from the Sun and its very lower temperature at the cloud-tops and in most of its atmosphere, as you go down into Jupiter (and to a lesser extent, Saturn) it gets very hot.
Also, for every planet there are very high temperatures (1000 Celsius, typically) at the top of the atmosphere. This is because of bombardment by Solar Wind particles. There’s not much gas hitting the upper atmosphere in this way, but it is going very fast and has a lot of energy per particle, so it substantially heats up the upper atmosphere. In our case the amount of heating is fairly large because we’re fairly close to the Sun. In Jupiter’s case, because it’s so far away from the Sun, you’d expect the amount of energy being delivered in this way to be much less, but the immense magnetic field of Jupiter traps a huge number of Solar Wind particles, so its upper atmosphere is actually just as hot as ours.
Other planets, depending upon their distance from the Sun and how efficiently they trap Solar Wind particles (or merely run into them) may have cooler upper atmospheres or warmer ones, but the upper atmosphere will always be much hotter than deep down in the atmosphere, where this heat source cannot penetrate.
As a result, a typical planetary atmosphere temperature structure would be hot at the top and the bottom, and cold in between. (This is called a cold trap, which sounds like it's something unusual, but actually it's the "normal" situation.)
The structure of Jupiter's atmosphere
In the diagram above "neutrally stratified atmosphere" means that the lower portion of Jupiter's atmosphere has a temperature gradient (the rate of temperature increase as you go downward) that is on the verge of causing vertical mixing, or convection. If the temperature gradient were to increase even a little (by reducing the temperature at greater height or increasing the temperature at depth), strong vertical mixing would occur, as in a thunderstorm. This would carry heat upward, increasing the temperature at high altitudes, which would reduce the temperature gradient and cut off the mixing. Over a period of time the temperature gradient increases and decreases, allowing mixing and cutting if off, but always remaining close to the gradient which is just barely stable against mixing. The same thing happens in the lower portion of the Earth's atmosphere, or troposphere, as shown in the diagram below. As a result, it might be just as appropriate, and less confusing for beginning students, to call the "neutrally stratified" portion of Jupiter's lower atmosphere its troposphere, as in the case of the Earth.
The structure of the Earth's atmosphere
In the Earth’s atmosphere, there is an extra heat source (to be discussed below), so the middle part of the atmosphere is much warmer, and you don’t have a cold trap.
The heat source in the ‘middle’ of our atmosphere is due to the absorption of ultraviolet radiation by the gases. There are different kinds of ultraviolet radiation, which are given different names -- UVA, UVB, UVC and so on -- according to how far they are from the visible. The further you go into the ultraviolet the more energy each photon of radiation has (refer to chapter on light and matter, if you haven’t done so, and don’t recognize this discussion). The UVA particles have more energy than visible-light photons, but not as much as UVB, which have less than UVC.
All of the common gases in atmospheres (and in fact, most common molecules) can be torn apart by the absorption of UVC and shorter-wavelength, higher-energy kinds of radiation. This process is called photodissociation if it tears molecules apart, or photoionization if it tears atoms apart.
This process causes the upper atmosphere to have a large number of ‘pieces’ of atoms and molecules, many of which are electrically charged, leading to the term ionosphere to describe the region, because a charged particle is called an ion.
At the same time particles are being broken down by absorbing UVC, they are recombining to make whole atoms and molecules, by running into each other. This happens fastest at the bottom of the atmosphere where the gas is thicker and the particles are closer together, and slower at the top, where the particles are further apart because the gas is so rarified.
In the upper stratosphere particles recombine over times measured in minutes or seconds. But if you go up 10 miles (3 times 3) the air is about 10 times thinner, and particles collide 100 times less frequently, so recombination takes hours. Go up another 10 miles, and it would take days.
During the day sunlight pours into the atmosphere, allowing UVC to tear apart molecules and atoms in the upper and middle atmosphere, but in the lower middle atmosphere the particles are rapidly recombining, and it takes all of the UVC to keep things ‘as they are’, and none of it makes it into the lower atmosphere. But further up you can maintain a continual dissociation of the molecules, because it takes longer than the Sun is down for the particles to recombine.
The Ozone Layer
Ozone is created by the photodissociation of oxygen molecules by UVC. Oxygen and other molecules are being torn apart, and although the other molecules are not part of this story, they also dissociate.
For oxygen, we’re interested in one particular result:
O2 --> O + O (only caused by UVC and ‘harder’ radiation)
O + O2 --> O3 (= ozone)
This process of turning part of the oxygen into free atoms and ozone occurs throughout the part of the atmosphere (from its "top", downward to the middle stratosphere) where UVC is tearing apart molecules.
Now, ozone can do something interesting.
As mentioned above there are various kinds of UV. They are defined according to their wavelengths, or the energy per photon of the radiation, and the way in which that interacts with common molecules. UVA cannot affect the structure of most atmospheric molecules, although it is capable of disrupting sensitive organic molecules (causing tanning, sunburn and skin cancer, among other things). UVC can do this and also tear apart any atmospheric molecule. UVB, which is ‘in-between’, can do more than UVA but not as much as UVC. It can disrupt ‘sensitive’ atmosperic molecules, but not ‘normal’ ones; and in particular, it can destroy ozone:
O3 + UVB (or UVC) --> O2 + O (UVA cannot do this)
Sunlight contains far more UVB than UVC, so as the ozone absorbs UVB and the energy associated with it, it heats up the part of the atmosphere that we call the ‘ozone layer’ far more than it would if it could only absorb UVC.
ALL planetary atmospheres absorb UVC, and there is a small amount of heating in the middle atmosphere of each planet in this way. But if you can absorb UVB as well, since there is a lot more of it, the atmosphere heat up a lot more. And ozone can do that, so if you can have ozone the part of the atmosphere where it is common gets a lot hotter than it would otherwise be; but to make ozone you have to combine free oxygen atoms with oxygen molecules, and that’s not going to happen unless you have a lot oxygen floating around. And only the Earth's atmosphere contains significant amounts of oxygen, so that only occurs in the atmosphere of the Earth.
Ozone can be destroyed in two ways -- by chemical interactions (molecule runs into other molecules which are willing to take the ‘extra’ oxygen atom), and by the absorption of UVB. During the day both of these are at work, but at night only the chemical interaction is at work. During the day, when both of them are at work, absorption of UVB is more important in the upper part of the ozone layer, where the gas is ‘thinner’ and collisions (and chemical reactions) are less frequent, and chemical reactions are more important in the lower part, where the gas is thicker and collisions are more frequent.
In the upper part of the ozone layer, where UVB is the primary way that ozone is destroyed, we can to a first approximation ignore chemical reactions.
But in the lower part, where chemical reactions are more important, IF THOSE REACTIONS GO FASTER THAN NORMAL the amount of ozone will decrease. And we can make the reactions go faster by putting halogen gases (fluorine, chlorine, bromine and the like) into the stratosphere, because they eagerly interact chemically with other materials in general, and ozone in particular.
The main way we destroy ozone is with refrigerants containing halogen gases such as freon or halon. Halon happens to be a fairly light gas, and as a result it diffuses up/down in the stratosphere pretty easily. Remember, the stratosphere is ‘stratified’ because, being an inversion layer, you cannot have vertical mixing or convection. HOWEVER, you can have diffusion -- a random motion of gas particles through collisions, back and forth, forth and back, which gradually moves molecules throughout a region. Light molecules diffuse more rapidly and heavy molecules more slowly. Freon molecules are very heavy so they diffuse up or down in the stratosphere over decades. Halon molecules, because they are lighter, do it in years.
Because of this the freon now in the stratosphere is a result of freon gas being released over the last half century, still gradually diffusing throughout the upper stratosphere. And now that it is there, it will stay there, even if ALL FREON IN THE LOWER ATMOSPHERE DISAPPEARED, for another fifty to one hundred years. But because it diffuses more rapidly the amount of halon can go up/down in just years, and in fact has significantly declined in the decade or so since halon use was (mostly) banned.
Fortunately, since it will be a century or more before the freon is gone, it doesn’t do much damage to the ozone layer in most places. It just makes the breakdown of ozone go a little faster, so the percentage of ozone which is in equilibrium (being made by UVC and broken down by UVB and chemical reactions) is a little smaller than usual -- typically, about 5 to 10% smaller. And that’s within ‘normal’ geological and historical ranges, so although we might feel a bit chagrined at our actions and their results, it’s not a really big deal.
But there are places where things get quite drastic -- such as near the Poles, resulting in ozone "holes". (end of the 'quick and dirty' discussion noted above; to be further addressed in the next iteration of this page.) | 0.847951 | 4.061567 |
Published time: February 17, 2015 05:11
Mysterious plumes over 150 miles high have been recorded erupting on Mars by amateur astronomers – and the strange discovery has scientists stumped.
The bright flares have now died away, but they were spotted on two occasions – lasting for 10 days each time – by amateur astronomers in 2012. The dusty plumes were seen rising to altitudes of 155 miles (250km) and spread out over a region measuring 300-600 miles wide.
— StarTalk (@StarTalkRadio) February 17, 2015
Scientists have captured plumes erupting from Mars before by the Hubble Telescope and on databases of amateur images, but none of them reached such heights – the maximum previously recorded was 62 miles.
“At about 250 km, the division between the atmosphere and outer space is very thin, so the reported plums are extremely unexpected,” said Agustin Sanchez-Lavega of the Universidad del Pais Vasco in Spain, the lead author of the paper, reporting the finding in the journal Nature.
Amateur astronomer Wayne Jaeschke, who spends about 100 nights a year watching the heavens, was looking at footage of Mars he had captured in his private observatory when he noticed the plumes. He shared the images with friends and then it was circulated among amateur and professional astronomers.
Scientists are using the Hubble data along with amateur images to find out what the plumes are made of and what might be causing them to occur. The announcement about a week after NASA’s Maven Spacecraft arrived to study Mars’ upper atmosphere.
“One idea we’ve discussed is that the features are caused by a reflective cloud of water-ice, carbon dioxide-ice or dust particles, but this would require exceptional deviation from standard atmospheric circulation models to explain cloud formations at such high altitudes,” Agustin said.
Still, Agustin said the theory of a dazzling Martian aurora, like the Northern Lights on Earth, couldn’t explain the enormous size of the clouds.
Another scientist is cautious about the claims.
“I don’t think it’s real…basic physics says this can’t occur,” Todd Clancy, planetary scientist at the Space Science Institute, told USA Today, adding that Mars’ upper atmosphere doesn’t supply the necessary ingredients for clouds. | 0.842711 | 3.349666 |
This image shows some of the dunefields of Mars.
Click on image for full size
This is an example of the dunefields of Mars. They are located in the southern hemisphere. They are evidence of planetary resurfacing by wind.
Sand dunes were also seen at equatorial regions by Mars Pathfinder and also by the Viking I lander in the Chryse Planitia Basin (check the large topographic map of Mars for the distances between these two landing sites).
The prevelance of sand dunes is an indication of the importance of wind to the erosion of the Martian landscape.
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The Naked-Eye Universe
Men at some time are masters of their fates:
The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings.
– Cassius, from Julius Caesar (Act I, Scene ii) by William Shakespeare
If you live in a big city, you have no doubt heard talk of stars. Next time you are driving across country at night or any time you are away from the city lights, stop for a while and take a good look at the sky. How many stars do you think you can see? Generally speaking, if you are in a dark enough location, you should be able to see around 1000 stars at any given time. As the Earth rotates throughout the night and stars rise in the east and others set in the west, you can increase your count to 2000, then 2001 when the Sun rises. The total number will grow further over the course of a year, with the slow motion of the Earth around the Sun. With a visit to other latitudes to see objects otherwise hidden below the horizon, the total would come to around 6000, depending on how good your eyesight is. Some of these ‘stars’ are in fact nebulae or even one of the five planets visible to the naked eye. The total number of objects is only slightly increased by throwing in one Moon and three galaxies. Including the odd comet and closely passing asteroid, the rare supernova, the occasional Earth-orbiting satellite, that’s the entire list of objects beyond the Earth you can hope to see with the naked eye.
Given that our galaxy alone has some 10 billion stars in it, you might think that we are missing out on a lot. But our eye is doing a remarkable job even to present this view of our universe, and it is the result of much evolutionary modification. It has been theorised that the development of vision was responsible for the Cambrian evolutionary explosion some 540 million years ago. For around 3.5 billion years, life on Earth developed into just three phyla (a taxonomic grouping of plants or animals). Then, after a burst of evolutionary development lasting possibly as little as 5 million years, there were 38 phyla (which later extinctions reduced to the 35 we see today). It just so happens that natural light-sensitive receptors began to develop around this same period. Vision provides a huge selective pressure on animals to detect predators, prey, food, mates and the surrounding environment. Not surprisingly, then, eyes have developed in many different forms. Some animals are sensitive to ultraviolet or infrared radiation that we cannot see, while others have eyes specially designed for low light levels or polarised light. Even the different structures of eyes demonstrate a wide diversity: from the multi-lensed fly to the lobster, which produces images by reflection. Some creatures have zoom lenses, others have scanning optics while yet others have simple eyes which act like pinhole cameras. The eye is a remarkable piece of natural engineering, and in the case of humans, by far the most powerful of our senses.
The human eye has many parts, but the basic design can be broken down into four major sections, as shown in Figure 1.1. There is a cornea for protection, an iris to alter the amount of incoming light and a focusable lens which forms an image onto the light-sensitive retina. The retina has two types of light-sensitive receptors, namely cones and rods. There are about 5 million colour-sensitive cones, predominantly located within a 1.5-mm diameter region called the fovea. These provide sharp imaging over a small field of view under good lighting conditions. The 100 million rods are distributed over the rest of the retina and while not able to distinguish colours, provide most of our peripheral and low-light vision.
Overall the eye is able to image at wavelengths of light (in effect defining the ‘visible spectrum’) from around 400 nm (violet) to 700 nm (red).1 Individual cones are sensitive to a narrow range of colours centred approximately over the violet-blue, green and greenish-yellow portions of the spectrum. The actual colour of incoming light is inferred by the amount of activity triggered in each type of cone. For example, if the brain senses an equal output signal from neighbouring blue- and green-sensitive cones, then a colour lying midway between the two (something like aqua or turquoise) would be what the brain ‘sees’. The cones are separated by about 2.5 micrometres (2.5 μm) in the fovea, so the smallest angle we can resolve under ideal conditions is around 1 arcminute (or around a thirtieth of the angle subtended by the full Moon). To put it another way, this means we should just be able to make out two distinct headlights on a car around 3 km away.
As a slight diversion at this point, it is often said that the Great Wall of China is the only man-made object visible from space. This is complete nonsense, as can easily be demonstrated. From the height of the International Space Station (350 km), an angle of 1 arcminute translates to 100 m on the ground. There are, of course, a multitude of structures larger than this. For example, the Great Pyramid of Giza, at 230 m on a side would be easily visible and appear quite separate to other pyramids nearby. On the other hand, the Great Wall is a little less obvious and most astronauts, including Chinese astronaut Yang Liwei, have said it was not visible. We will address this issue in greater detail later on, but the fact that the wall is quite long (over 6000 km) means nothing – the more important factor is that it is only 15 m wide. Under the right lighting conditions, it may show up against the background, just as we see stars at night but cannot resolve them.
This leads to another property of the eye which is truly remarkable – its sensitivity to a wide range of light levels. The eye’s response to luminous flux is logarithmic, which permits us to accommodate both very bright and very dim scenes, often without even being aware of the difference. For example, you can comfortably read this book in direct sunlight, or by the light of a half-full Moon – a reduction in light levels by a factor of one million! By comparison, manufacturers of photographic film are happy with a film which can accommodate a range one thousand times smaller. Even the most advanced digital sensors would find it difficult to accommodate these extremes. Of course, the human eye cheats a little by using cones for bright light and rods for low light levels. For astronomy then, rods are the more important detector in the retina, and they lie outside our direct field of vision (the fovea). This means that to see the faintest stars it is often best to use averted vision. That is, you should look to one side of the star so that the light does not fall on the fovea, which is predominately populated with less sensitive cones. The problem with rods, of course, is that they have no colour sensitivity. This is fairly evident when you look at a nighttime scene dimly lit by the Moon, where everything loses its colour and the scene appears in shades of grey. The colours are still there – you simply can’t see them.
Beyond just collecting light, the human eye forms images of distant objects. These images are produced on the retina by the lens, in precisely the same way as a camera lens forms images on film. We’ll come back to the concept of imaging later, but for now we should note that by changing the tension in muscles surrounding the lens of our eye, the shape of the lens can be stretched or compressed in order to maintain focus over a wide range of viewing distances. The retinal image is actually produced upside down, but the brain does its own correction to this unreal situation and inverts everything back to normal. The brain then combines the light from two eyes which look at a scene from slightly different angles (parallax) to give us a sense of three dimensions. In summary, the human eye can be used to detect colours, shades, shapes, dimensions and distances. From an engineering point of view, the eye is a truly remarkable instrument; even more so given that it is the result of millions of years of random trial and error.
Of course, the human eye does have some limitations. We cannot see radio waves, microwaves, infrared, ultraviolet, X-rays or gamma-rays. The refresh rate of the visual signal processing (called persistence) is around 20 times a second and changes occurring faster than this cannot be seen. At the same time, we cannot brighten the image of a dim object by staring at it for a long period of time in the same manner as a time-lapse exposure on film. Another difference between the eye and cameras is that there is no way of recording our retinal views on a permanent medium for others to see. The eye is susceptible to fatigue, disease and aging, which can affect resolution, focusing and sensitivity. On top of this, the eye (or more correctly, the brain) can also be confused and fooled by certain arrangements of objects. In spite of these limitations, though, the eye is a remarkably versatile instrument.
Often when considering a telescope, people will be prompted to ask: ‘Just how far can it see?’ Later in this book it will become clear just how meaningless this question is, but for now consider applying the same question to our eye. You can see objects sitting right in front of your face, but at the same time you can see a mountain dozens of kilometres away. Alpha Centauri is around 40 trillion kilometres away, and Andromeda Galaxy, also visible to the naked eye in dark skies, is nearly a million times more distant than this. So really, whether the eye can see an object comes down to how big and bright the object is, not how far away it is. Of course, seeing light from a star is not the same as forming an image of it – after all, a point of light is not an illuminated disk, so this is where it becomes meaningless to consider these sorts of issues. In fact, it is because we cannot see any of their details that cosmic objects have always held such a fascination for us.
As you look at the stars, try to imagine yourself as an Egyptian sailor on the Mediterranean Sea some four-and-a-half thousand years ago. From an early age, you would have been taught how to find the dim star Thuban. Throughout the entire night, it would serve as an unwavering beacon by which to navigate. Even after the most disorientating of storms, this star always lay to the north. It is no wonder, then, that Pharaoh Khufu aligned his Great Pyramid to this most important of stars. It is in contemplating the history of naked-eye observations of the sky that we begin to appreciate why such observations have had such a powerful effect on mankind throughout the ages.
Every star (except the Sun) rises and sets around four minutes earlier every night. Over 365 days, this amounts to a complete day, so the rising or setting of a particular star at a particular time can be used as a measure of a year. The same Egyptian sailor, as a long-time observer of the heavens, would know that the rising of certain groupings of stars at dusk indicates the onset of particular seasons. This knowledge could be used to anticipate the annual flooding of the Nile and for planning harvests and plantings. To nomadic civilisations, accurate timekeeping was equally important for following migratory animals and preparing for the harsh environmental conditions of particular seasons. As civilisations developed, crop rotations and agricultural storage requirements were determined by a ‘calendar’ which was essentially a measure of the motion of the stellar sphere.
Naturally it was easy to believe that these groupings of stars were not simply passive markers of time, but exerted an active influence over life on Earth. These groupings (asterisms or constellations) were associated with physical objects or gods as long ago as 4000 BCE, and from there it was a small step to anthropomorphising their forms. The constellations thus became powerful gods influencing our lives, which inevitably led to religious and superstitious rituals and beliefs. Temples were built and offerings and sacrifices were made to influence the gods to provide bountiful harvests and improve living conditions. These gods were regarded as powerful enough to control human existence, so they were not to be trifled with. The intertwining of superstitions and religion continued even into the modern era. For example, the Catholic Church used astrological charts until well into the eighteenth century.
While many people still believe in astrology today, it clearly makes no sense. The constellations used for astrological ‘signs’ are merely apparent groupings of stars which are actually unrelated and lie at completely different distances. They have no physical existence – you could never ‘visit’ a constellation. Furthermore, there are three planets which are used in present-day astrology whose existence was not even known before the eighteenth century, so those who purport to be using ‘ancient mystical knowledge’ are relying more on the gullibility of the uneducated than on any secrets of civilisations past. It is also worth mentioning that there are in fact 13 Zodiacal constellations, with Ophiuchus lying between Libra and Sagittarius.
While the stars appear to move around us, their motions are really only telling us where we are and what time it is.
The Chinese, well aware of the ‘clockwork’ nature of the celestial sphere, used the apparent motions of the Moon and the Sun as the basis of their calendar. A Chinese year can have 353, 354, 355, 383, 384 or 385 days on a cycle which repeats every 60 years. It may seem a little confusing and cumbersome at first, but it works. Proof of this is the fact that the Western year 2006 CE is year 4703 in the Chinese calendar. In fact, it is the longevity of this calendar which has made it possible for historians to examine Chinese records to determine accurately the precise dates of ancient events, both celestial and social. Likewise, the Jewish and Muslim faiths have, for centuries, used the cycles of the Moon for daily observances and calendrical measurement. The Hebrew calendar date for 2006 CE is 5766 AM (Anno Mundi – in the year of the world). By comparison, the Gregorian calendar seems positively newfangled. It also puts into perspective all the superstitious fuss that went along with the dawning of the third millennium.
I was once observing a transit of Mercury across the Sun with a student who remarked on the amazing punctuality of the event. Quite the opposite, I pointed out, she should be more amazed that our clocks are timed with such precision to celestial events. After all, this is where we get our system of time measurement. In fact, measurements of the passage of certain stars across a ‘fixed’ point or line in space were used to determine the length of what would become our Gregorian calendar year. While the actual tropical year is determined by the Sun, a rough approximation can be made by measuring the time between successive transits of a given star across an arbitrary north-south line in the sky at a certain time of the day. For example, if you have a telescope aligned north-south, and Vega is centred in your view at exactly 9 pm, then it will be centred again at the same time a year later.
An example of the clockwork precision of celestial motions was never more evident than at the turn of the sixteenth century. While on his fourth voyage to the New World, Christopher Columbus became stranded in Jamaica. At first, Columbus and his crew were well received by the locals, who fed and housed them while they waited for a rescue party. However, as the months passed, he and his badly behaving crew became increasingly unpopular with the indigenous population. Relations degraded to such an extent that there was a distinct possibility of a bloody confrontation. Sensing this, Columbus invited the chiefs to a meeting with him on 29 February 1504. Columbus stated that God was unhappy with their treatment, and threatened to remove the Moon from the sky. That night, as Columbus well knew, there was to be a lunar eclipse. Sure enough, as foretold, the Moon began to darken and redden. The natives, understandably impressed and more than a little terrified, begged Columbus to get his God to return the Moon. Columbus ‘pondered’ their request for a while and eventually agreed to do so (he could afford to play it slow as a lunar eclipse can last for hours). From this point onwards the locals pretty much did his bidding until the rescue party arrived several weeks later.
Astrometry, the measurement of stellar positions, is also essential for navigation. Throughout the course of the night, the stars in the sky will rotate about the celestial pole. In the Northern Hemisphere, this point in the sky is very close to Polaris (the North Star or Alpha Ursae Minoris). Taking a long-exposure photo of the night sky towards either pole will demonstrate this, as shown in Figure 1.2. The Earth also has a slight wobble, which causes its axis of rotation to precess (describe a circle) over a period of 25,800 years. Around 4500 years ago, the north celestial pole lay near a star called Thuban, but today it is close to Polaris. In fact, precession will continue to narrow the angle between them until 2106. But even now, Polaris serves as a much better guide to true north than magnetic north measured by a compass. This relationship is quite fortuitous (and unlikely) and in the Southern Hemisphere there is no bright star close to the south celestial pole.
While navigators can get their bearings (compass orientation) from the celestial poles, knowing your current location on the Earth is also critical for navigation. For this we can use the celestial poles once again. Quite simply: the angle of the pole above the horizon is your latitude. Live in Oslo? Since your latitude is 60 degrees North, Polaris is 60 degrees above the horizon, or a third of a way around the sky. Longitude is much trickier to determine. In order to know how far you are east or west of the Greenwich meridian, you essentially need two clocks – one telling you the local time, and one telling you the time it is in London. For each hour’s difference between the two clocks, you are a further 15 degrees removed from zero degrees longitude. So, if your local time is four in the afternoon and it is noon in London, then your longitude is 60 degrees East.
For millennia, navigators had been able to measure latitude, but it was not until towards the end of the eighteenth century that John Harrison developed a sufficiently accurate timepiece for longitude measurements at sea. For accurate navigation today, we mostly use the Global Positioning System that consists of 24 or so satellites in precisely known locations. GPS uses the relative timing of signals from atomic clocks on these satellites to determine position (latitude, longitude and even altitude) on the ground. These days there are international organisations that exist to take care of the details and help us better define time and location to the nth decimal place. Before the invention of the telescope, however, people had to rely on less scientific authorities to determine such things in their lives.
At the turn of the sixteenth century in Europe, the Catholic Church had pretty much determined the way things were in the universe. Following a strict Ptolemaic doctrine, there were several assertions which were not up for debate. The Earth was the centre of the universe (by virtue of it being the ultimate work of God), and the planets and Sun all rotated around it in circular orbits. All bodies in the universe were perfectly spherical and except for the odd comet, the celestial sphere was permanent and unchanging. Over much of the Dark Ages, this simple arrangement was immutable. But as measurements of planetary positions improved, adjustments had to be made to make doctrine agree with reality. For example, the planets simply refused to move in precisely circular orbits about the Earth. In order to correct for this, some planets were permitted to travel in small circles about a point which itself moved in orbit about the Earth. This stopgap measure worked up to a point, but it was becoming clear that further improvements were required. So it was that in 1540 Nicholas Copernicus published De Revolutionibus with the primary tenet being that the Sun, not the Earth, was the centre of the universe.
The Sun-centred model solved many nagging problems associated with planetary motions but was still far from perfect and often required as much tweaking as had the Earth-centred model. Fortunately for Copernicus (depending on how you look at it) he died within days of the publication of this work, and so did not have to answer for any of the subsequent controversy. While it was not widely read, the main thesis was discussed widely around Europe. For the most part, the Church largely ignored it or at least treated it as an annoying work of fiction. After all, there were no gross errors in the motions of nighttime objects that could seriously threaten the basic canonical law and besides, the Sun-centred model was not new, but had in fact been suggested by Aristarchus (and reported by Archimedes) at some time during the third century BCE. Since the Church was able to ignore this for nearly a millennium, the resurgence of the idea was no great cause for concern.
Tycho Brahe2 is perhaps one of the last of the pre-Enlightenment ‘scientists’. His life work consisted almost entirely of observations and cataloguing of phenomena without much effort to devising an underlying theoretical framework to describe the ‘why’ behind the phenomena or making predictions for testing these theories. However, this should not diminish his achievements in any way – far from it. In fact, his observations were of such a high quality that they were used by his assistant to devise the first laws of motion of planetary bodies, which are still used today. And he did all this without the aid of a telescope.
Brahe was born in Skane, Denmark (now in Sweden) and raised by his aristocrat uncle in an environment which emphasised education and critical study. Early on, perhaps as the result of observing a partial eclipse in Copenhagen, Brahe became intrigued with celestial observations and the ability of astronomers to predict such events well in advance. Throughout his early life, he studied at various universities, eagerly pursuing a future in the sciences. In his day, most astronomy was actually astrology, and Brahe made a name for himself when he used a lunar eclipse of 1566 to correctly ‘predict’ the death of Suleiman the Magnificent, ruler of the Ottoman Empire. Since Suleiman was 72 years old, it may be said that this ‘prediction’ was not much of a stretch, and it was even less impressive when it was later discovered that Suleiman had actually died a few weeks before the eclipse – but word of this had failed to reach the Danish court. A further significant event in Brahe’s early life occurred when the tempestuous young man got into a duel that resulted in him losing a portion of his nose. For the rest of his life he covered up this disfigurement with a prosthesis of gold and silver. Much of his early work is fairly unremarkable, except perhaps for the fact that his studies gave him a good knowledge of the heavens. This would prove to be instrumental in a discovery that would bring him his fame.
On the evening of 11 November 1572, Brahe noticed a new star in the Constellation Cassiopeia. Over the next few months, he continued to observe the star and eventually published his findings in De Nova Stella (About The New Star). While others had observed the star, Brahe made the bold assertion, on the basis of his measurements, that this was indeed a new object and not a new comet or meteor which were the only other known objects that could appear in the sky. His revelation should be viewed in the context of the time in which he lived. It has already been mentioned that the Catholic Church had held steadfast to the view that the heavens were perfect and unchanging. Brahe’s new star challenged this prevailing doctrine and could not be ignored. Such was the impact of this work that today we still refer to similar events as ‘novas’ (and supernovas, which is in fact what Brahe’s new star was). For Brahe personally, the acclaim the work received had more immediate financial benefits, when he managed to parlay it into a Royal tenure. The King of Denmark gave him a generous income and support for the creation of Uraniborg observatory, which Brahe built on Hven, an island near Copenhagen. While not quite what we think of as an observatory in today’s terms (as there was no telescope), it was a site for observing and documenting the heavens in a consistent manner.
To aid his observations, Brahe constructed a fine quadrant which could measure the altitude of stars above the horizon to great precision. For the rest of his life he made copious measurements of the positions of celestial objects and it is for these measurements that Brahe should be noted. While to most people they resemble a tedious catalogue of numbers, they far surpassed the accuracy of any previous measurements. Most were good to a couple of arc minutes, and some to better than a quarter of this – something which can be compared to the size of the printed words on this page on the other side of a large room. It was as a direct result of these unprecedented observations that his assistant, Johannes Kepler, was able to formulate his laws of planetary motion.
Kepler was a long-time supporter of the Copernican Sun-centred universe theory but lacked the eyesight for the high-quality observations required to evaluate the theory. Over many years he sought to work with Brahe (or rather, his data) and was eventually hired as his assistant early in 1601. Brahe was very protective of his measurements and would only allow Kepler to look at limited portions of it. This all changed when he died later that year and Kepler inherited the valuable catalogues. With his gift for mathematics, Kepler was able to use the data to formulate three laws of planetary motion (published in 1609) which went a huge way to legitimising the Copernican universe. The three laws are:
- The orbits of planets are ellipses, with the Sun at one focus of the ellipse.
- As the planet moves in orbit about the Sun, the line joining the planet to the Sun sweeps out an equal area in an equal time.
- The ratio of the squares of the orbital periods of two planets is equal to the ratio of the cubes of their semi-major axes.
The underlying physical reason for these laws being the way they are was not really understood until Newton formulated his Theory of Gravitation some50 years later. However, these simple laws made it possible to accurately predict the motion of planets, and are still used today for all but the highest precision orbital calculations. Kepler’s work was incredibly important, and began a gradual change in opinion away from the Earth-centred universe theory, and from the unquestioned acceptance of religious dogma. Alone it would have caused an upheaval in the way the world viewed the universe. However, even as it was being prepared for publication, an optical worker in Holland had invented a device which would dramatically increase the pace of inquiry into the physical universe and usher in the Enlightenment.
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File created: 8/7/2007
Questions and comments to: [email protected]
Princeton University Press | 0.944452 | 3.484991 |
posted on Jun, 16 2004 @ 07:17 AM
well dont forget this from1998 so alot of universe is gone AND we cant actually see whats taken its place till millions or bilions of years from now,
so deff some are gone and destroyed........
May 6, 1998
Web posted at: 8:37 p.m. EDT (0037 GMT)
WASHINGTON (CNN) -- Astronomers are mystified by the most powerful explosion ever witnessed, an enormous burst of gamma ray energy 12 billion light
years from Earth that in one second released almost as much energy as all the stars of the universe.
The explosion was too far away to affect the Earth or the sun, but the astronomers say they are astounded by the might of the blast and baffled about
what might have caused it.
"The energy released by this burst in its first few seconds staggers the imagination," said Shrinivas Kulkarni, a professor of astronomy at
California Institute of Technology and leader of a team that helped calculate the explosion size.
Kulkarni is co-author of a study being published Thursday in the journal Nature. He and others appeared at a Washington news conference Wednesday.
"For about one or two seconds, this burst was as luminous as all the rest of the entire universe," said Caltech professor George Djorgovski, another
member of the team. "In a region about a hundred miles across, the burst created conditions like those in the early universe, about one millisecond
after the Big Bang."
"I was astounded when I heard these results," said Stan Woosley, a professor of astronomy at the University of California, Santa Cruz, and an expert
on astronomical explosions. "At first I could hardly believe them, but now I'm convinced they're true, and it makes the universe bigger and more
exciting than I ever thought before."
'Brightest documented explosion in history'
The gamma ray explosion came from a faint galaxy known as GRB 971214 and was first seen December 14. It is about 12 billion light years from Earth. A
light year is the distance light travels in a year at 189,000 miles a second, or about 5.9 trillion miles.
Gamma ray bursts are common, occurring once or twice a day, but the rays are invisible and can be detected only by satellites orbiting above the
Since a burst lasts only seconds, astronomers rarely are able to focus telescopes on the source and measure the light necessary to calculate the size
of the explosion or pin down its location.
But on the night of December 14, an Italian team detected the gamma ray burst with the BeppoSAX orbiting observatory and quickly alerted David J.
Helfand, a Columbia University astronomer. Helfand relayed the information to astronomers operating telescopes at Kitt Peak near Tucson, Arizona, who
were able to photograph the burst.
Later, the Hubble Space Telescope and others photographed the explosion's afterglow. Kulkarni and others analyzed the energy and light released from
the object and concluded it was a very faint and distant galaxy about 12 billion light years away.
That it occurred so far away, Kulkarni said, indicated that the explosion was immensely powerful.
The arrow shows the galaxy where the explosion occurred
"This was the brightest documented explosion in history," said Woosley.
Power released is almost unimaginable
Woosley said the energy released was equal to about 5 billion supernovae, the explosion of dying stars that, until this explosion, had provided the
most powerful documented sudden releases of energy.
In visible light alone, Woosley said, the gamma ray burst energy was equal to about 1,000 supernovae.
By some calculations, the gamma ray burst release equaled as much energy in one second as all of the 10 billion trillion stars in the universe
Woosley said it is difficult to relate the power in common terms.
For instance, he said, if all of the nuclear weapons ever made were exploded at once, the energy released would equal about 1/100,000 of a second of
the energy from Earth's sun. Yet over its 10 billion-year history, Woosley said, the sun will produce only about 1 percent of the energy of the
Gamma ray bursts were unknown until the launch of U.S. military satellites designed to detect radiation from the explosion of atomic bombs. Later,
scientific satellites were launched to study the bursts, but astronomers were still at a loss to explain them.
"We had no idea where they came from or what was responsible for them," said Alan Bunner, a science program director at NASA.
Theoretical models can't explain it
More than 2,000 gamma ray bursts have been recorded, but astronomers were unable until recently to pinpoint their location or measure their distance
from Earth. Only three have been pinpointed so far.
Kulkarni said that all of the bursts have been located in dusty regions where stars form, suggesting that the massive explosions may play a role in
the birth of new stars.
NASA animation showing an exploding star
Woosley and others speculate that such an explosion may occur when a black hole swallows a neutron star. A black hole is a collapsed object that is so
dense that its gravity permits not even light to escape; a neutron star is a massive collapsed star.
Astronomers believe the immense explosion sent matter, such as neutrons and electrons, streaking outward at near the speed of light. About a day
later, the matter smashed into gas and dust particles, and the violence and heat of the collisions created gamma rays, X-rays, and then visible light.
It was these energy sources that were detected by the orbiting instruments and later by the telescopes.
"Most of the theoretical models proposed to explain these bursts cannot explain this much energy," Kulkarni said, adding that it might have come
from a rotating black hole.
"On the other hand, this is such an extreme phenomenon that it is possible that we are dealing with something completely unanticipated and even more | 0.834068 | 3.01003 |
Comet Swift-Tuttle to Reveal Its Showering Achievement in Mid-August
Sunday, July 27, 2008
The annual Perseid meteor shower -- perfectly punctual specks of cosmic dirt puncturing Earth's atmosphere at high speed -- peaks the night-early morning of Aug. 11-12. Barring cloudy skies, these shooting stars are best seen in the wee hours of the morning.
The evening of Aug. 11 begins with Jupiter and the gibbous moon loitering in the eastern heavens. The bright moon sets about 1:51 a.m. in the west Aug. 12, according to the U.S. Naval Observatory. This makes the night sky dark enough to enjoy meteors.
Get away from city lights, says Bill Cooke of NASA's Meteoroid Environment Office at Marshall Space Flight Center. He says sky gazers might see a few Perseid meteors at nightfall Aug. 11 because the constellation Perseus-- from which the meteors appear to originate -- rises in the east. These few early meteors skim off Earth's atmosphere, he says, making them long, slow and colorful.
The American Meteor Society says a good time for meteor hunting might be between 4 and 5 a.m. Aug. 12. Dark locations are best, but in metropolitan areas, the visibility rate can be as low as 25 meteors an hour -- probably giving sky watchers only a handful to view in an hour.
Meteors occur when the Earth cuts through the dirty old paths of comets. In this case, Earth slices through Comet Swift-Tuttle's trail. The specks strike Earth's atmosphere and burn up, creating brilliant streaks of light. The comet's co-discoverer, astronomer Horace Tuttle, died in 1923 and is buried in an unmarked grave near Seven Corners in Falls Church.
Jupiter, the planetary king of the solar system, is high in the southeast sky at dusk and spends next month hanging out in the constellation Sagittarius. Early in August, it sets about 3 a.m. The large gaseous planet gleams at a brilliant negative second magnitude, making it easy to find from urban locations. To the naked eye, Jupiter looks like a bright, white object.
Busier than the Beltway at rush hour, the western sky at dusk is full of planets next month: Mars, Saturn and Venus meet. Lining up single-file along the sun's apparent path in the sky, the planets entertain sky gazers for less than an hour after sunset. At the beginning of August, dim Mars is the highest, then Saturn, and Venus sits closest to the sun.
By mid-August, Saturn and Venus convene low on the western horizon, if you can see it at all. Mercury joins the ringed Saturn and Venus to form a tight-knit group in mid-August. By the end of the month, Venus, long since past Saturn, nudges closer to Mars. Use binoculars to find these planets, but be careful. Look for them after sunset. Never use binoculars to view the sun.
· Saturday-- The heavens are filled with planets, stars and cosmic objects in "Exploring the Sky" at Rock Creek Park, held by the National Park Service and the National Capital Astronomers. Meet near the nature center in the field south of Military and Glover roads NW. 8:30 p.m. Information: 202-895-6070.
· Aug. 5-- Astronomer Rosemary Killen talks about "Tenuous Atmospheres: Neutrals, Ions and Dust in the Solar System" at an open house, University of Maryland observatory, College Park. See the heavens after, weather permitting. 9 p.m. Information: 301-405-6555; http:/ | 0.925061 | 3.518328 |
Now that Cassini has gone off on a new trajectory taking it above and below the equatorial plane of Saturn, we’re back to getting some fantastic views of the rings — the likes of which haven’t been seen in over two and a half years!
The image above shows portions of the thin, ropy F ring and the outer A ring, which is split by the 202-mile (325-km) -wide Encke gap. The shepherd moon Pan can be seen cruising along in the gap along with several thin ringlets. Near the A ring’s outer edge is a narrower space called the Keeler gap — this is the home of the smaller shepherd moon Daphnis, which isn’t visible here (but is one of my personal favorites!)
The scalloped pattern on the inner edge of the Encke gap downstream from Pan and a spiral pattern moving inwards from that edge are created by the 12.5-mile-wide (20-km-wide) moon’s gravitational influence.
Other features that have returned for an encore performance are the so-called propellers, spiral sprays of icy ring material created by tiny micro-moons within the rings. Individually too small to discern (less than half a mile in diameter) these propeller moons kick up large clumps of reflective ring particles with their gravity as they travel through the rings, revealing their positions.
The three images above show a propeller within the A ring. Nicknamed “Sikorsky” after Russian-American aviator Igor Sikorsky, the entire structure is about 30 miles (50 km) across and is one of the more well-studied propellers.
Scientists are eager to understand the interactions of propellers in Saturn’s rings as they may hold a key to the evolution of similar systems, such as solar systems forming from disks of matter.
“One of the main contributing factors to the enormous success we on the Cassini mission have enjoyed in the exploration of Saturn is the capability to view the planet and the bodies around it from a variety of directions,” Cassini Imaging Team Leader Carolyn Porco wrote earlier today. “Setting the spacecraft high into orbit above Saturn’s equator provides us direct views of the equatorial and middle latitudes on the planet and its moons, while guiding it to high inclination above the equator plane affords the opportunity to view the polar regions of these bodies and be treated to vertigo-inducing shots of the planet’s glorious rings.”
Image credits: NASA / JPL / Space Science Institute. | 0.851887 | 3.683091 |
Hubble telescope spots new class of planet: a steamy 'waterworld'
The planet GJ 1214b is a watery planet covered in a thick, steamy atmosphere, a new study of Hubble data suggests.
Scientists have discovered a new type of alien planet — a steamy waterworld that is larger than Earth but smaller than Uranus.
The standard-bearer for this new class of exoplanet is called GJ 1214b, which astronomers first discovered in December 2009. New observations by NASA's Hubble Space Telescope suggest that GJ 1214b is a watery world enshrouded by a thick, steamy atmosphere.
"GJ 1214b is like no planet we know of," study lead author Zachory Berta of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., said in a statement. "A huge fraction of its mass is made up of water."
Adding to the diversity
To date, astronomers have discovered more than 700 planets beyond our solar system, with about 2,300 more "candidates" awaiting confirmation by follow-up observations.
These alien planets are a diverse bunch. Astronomers have found one planet as light and airy as Styrofoam, for example, and another as dense as iron. They've discovered several alien worlds that orbit two suns, like Luke Skywalker's home planet of Tatooine in the "Star Wars" films. [The Strangest Alien Planets]
But GJ 1214b, which is located 40 light-years from Earth in the constellation Ophiuchus (The Serpent Bearer), is something new altogether, researchers said.
This so-called "super-Earth" is about 2.7 times Earth’s diameter and weighs nearly seven times as much as our home planet. It orbits a red-dwarf star at a distance of 1.2 million miles (2 million kilometres), giving it an estimated surface temperature of 446 degrees Fahrenheit (230 degrees Celsius) — too hot to host life as we know it.
Scientists first reported in 2010 that GJ 1214b's atmosphere is likely composed primarily of water, but their findings were not definitive. Berta and his team used Hubble's Wide Field Camera 3 to help dispel the doubts.
Hubble watched as GJ 1214b crossed in front of its host star, and the scientists were able to determine the composition of the planet's atmosphere based on how it filtered the starlight.
"We’re using Hubble to measure the infrared color of sunset on this world," Berta said. "The Hubble measurements really tip the balance in favor of a steamy atmosphere."
Berta and his colleagues report their results online in the Astrophysical Journal.
A watery world
Since astronomers know GJ 1214b's mass and size, they're able to calculate its density, which turns out to be just 2 grams per cubic centimeter (g/cc). Earth's density is 5.5 g/cc, while that of water is 1 g/cc.
GJ 1214b thus appears to have much more water than Earth does, and much less rock. The alien planet's interior structure is likely quite different from that of our world.
"The high temperatures and high pressures would form exotic materials like 'hot ice' or 'superfluid water,' substances that are completely alien to our everyday experience," Berta said.
GJ 1214b probably formed farther out from its star, where water ice was plentiful, and then migrated in to its current location long ago. In the process, it would have experienced more Earth-like temperatures, but how long this benign phase lasted is unknown, researchers said.
Because GJ 1214b is so close to Earth, it's a prime candidate for study by future instruments. NASA's James Webb Space Telescope, which is slated to launch in 2018, may be able to get an even better look at the planet's atmosphere, researchers said. | 0.818032 | 3.635434 |
New research has identified a cradle of young stars 2.4 billion light years away as the source of mysterious fast radio bursts detected on Earth.
These bursts – which each lasted just a few milliseconds – come from dense neutron stars just 20 kilometres (12 miles) across in the constellation Auriga.
Initially experts were baffled where these strange bursts of energy were coming from with some speculating it could be a sign of alien life trying to contact us.
However, researchers now believe the young stars are 6,200 light years from the centre of the small galaxy called FRB 121102.
Researchers from the Netherlands Institute for Radio Astronomy in Dwingeloo have used the Hubble Space Telescope to study the small galaxy in detail never seen before.
‘The Hubble observations allow us to get a very sharp image’, researcher Shriharsh Tendulkar of McGill University in Montreal told New Scientist.
‘There is a very bright spot of star formation, and this FRB [fast radio burst] lies bang inside it.’
Scientists believe the nursery of stars lies on the edge of the galaxy, which has a diameter of around 20,000 light years.
The giant nursery is itself 4,400 light years across, astronomers believe.
Researchers believe these FRBs are caused by flares from the dense core of a young neutron star left behind when the mother star explodes.
The waves were first detected by researchers from McGill University in Montreal, using the Green Bank Telescope in West Virginia, and at the Arecibo Observatory in Puerto Rico in December last year.
In their paper, published in The Astrophysical Journal, the researchers, led by Paul Scholz, wrote: ‘We have detected six additional radio bursts from this source: five with the Green Bank Telescope at 2 GHz, and one at 1.4 GHz with the Arecibo Observatory, for a total of 17 bursts from this source.’
The detection follows 11 previously recorded outbursts from the same location in the small FRB 121102 galaxy.
This is the only known repeater of fast radio bursts (FRBs) – radio emissions that appear temporarily and randomly.
The researchers added: ‘Whether FRB 121102 is a unique object in the currently known sample of FRBs, or all FRBs are capable of repeating, its characterisation is extremely important to understanding fast extragalactic radio transients.’
Previously when waves have been detected, astronomers have also asked Seti (Search for Extraterrestrial Intelligence) to take a closer look at whether they could be a message from ET.
But it is unclear if the McGill researchers will ask Seti to help this time.
If there are any intelligent alien life forms out there, Stephen Hawking thinks we’re playing a dangerous game by trying to contact them.
Source: The Mail | 0.843203 | 3.771297 |
December 11, 2009
VISTA Telescope Starts Work
A new telescope "” VISTA (the Visible and Infrared Survey Telescope for Astronomy) "” has just started work at ESO's Paranal Observatory and has made its first release of pictures. VISTA is a survey telescope working at infrared wavelengths and is the world's largest telescope dedicated to mapping the sky. Its large mirror, wide field of view and very sensitive detectors will reveal a completely new view of the southern sky. Spectacular new images of the Flame Nebula, the center of our Milky Way galaxy and the Fornax Galaxy Cluster show that it is working extremely well.
VISTA is the latest telescope to be added to ESO's Paranal Observatory in the Atacama Desert of northern Chile. It is housed on the peak adjacent to the one hosting the ESO Very Large Telescope (VLT) and shares the same exceptional observing conditions. VISTA's main mirror is 4.1 meters across and is the most highly curved mirror of this size and quality ever made "” its deviations from a perfect surface are less than a few thousandths of the thickness of a human hair "” and its construction and polishing presented formidable challenges.VISTA was conceived and developed by a consortium of 18 universities in the United Kingdom led by Queen Mary, University of London and became an in-kind contribution to ESO as part of the UK's accession agreement. The telescope design and construction were project-managed by the Science and Technology Facilities Council's UK Astronomy Technology Centre (STFC, UK ATC). Provisional acceptance of VISTA was formally granted by ESO at a ceremony at ESO's Headquarters in Garching, Germany, attended by representatives of Queen Mary, University of London and STFC, on 10 December 2009 and the telescope will now be operated by ESO.
"VISTA is a unique addition to ESO's observatory on Cerro Paranal. It will play a pioneering role in surveying the southern sky at infrared wavelengths and will find many interesting targets for further study by the Very Large Telescope, ALMA and the future European Extremely Large Telescope," says Tim de Zeeuw, the ESO Director General.
At the heart of VISTA is a 3-tonne camera containing 16 special detectors sensitive to infrared light, with a combined total of 67 million pixels. Observing at wavelengths longer than those visible with the human eye allows VISTA to study objects that are otherwise impossible to see in visible light because they are either too cool, obscured by dust clouds or because they are so far away that their light has been stretched beyond the visible range by the expansion of the Universe. To avoid swamping the faint infrared radiation coming from space, the camera has to be cooled to -200 degrees Celsius and is sealed with the largest infrared-transparent window ever made. The VISTA camera was designed and built by a consortium including the Rutherford Appleton Laboratory, the UK ATC and the University of Durham in the United Kingdom.
Because VISTA is a large telescope that also has a large field of view it can both detect faint sources and also cover wide areas of sky quickly. Each VISTA image captures a section of sky covering about ten times the area of the full Moon and it will be able to detect and catalogue objects over the whole southern sky with a sensitivity that is forty times greater than that achieved with earlier infrared sky surveys such as the highly successful Two Micron All-Sky Survey. This jump in observational power "” comparable to the step in sensitivity from the unaided eye to Galileo's first telescope "” will reveal vast numbers of new objects and allow the creation of far more complete inventories of rare and exotic objects in the southern sky.
"We're delighted to have been able to provide the astronomical community with the VISTA telescope. The exceptional quality of the scientific data is a tribute to all the scientists and engineers who were involved in this exciting and challenging project," adds Ian Robson, Head of the UK ATC.
The first released image shows the Flame Nebula (NGC 2024), a spectacular star-forming cloud of gas and dust in the familiar constellation of Orion (the Hunter) and its surroundings. In visible light the core of the object is hidden behind thick clouds of dust, but the VISTA image, taken at infrared wavelengths, can penetrate the murk and reveal the cluster of hot young stars hidden within. The wide field of view of the VISTA camera also captures the glow of NGC 2023 and the ghostly form of the famous Horsehead Nebula.
The second image is a mosaic of two VISTA views towards the center of our Milky Way galaxy in the constellation of Sagittarius (the Archer). Vast numbers of stars are revealed "” this single picture shows about one million stars "” and the majority are normally hidden behind thick dust clouds and only become visible at infrared wavelengths.
For the final image, VISTA has stared far beyond our galaxy to take a family photograph of a cluster of galaxies in the constellation of Fornax (the Chemical Furnace). The wide field allows many galaxies to be captured in a single image including the striking barred-spiral NGC 1365 and the big elliptical galaxy NGC 1399.
VISTA will spend almost all of its time mapping the southern sky in a systematic fashion. The telescope is embarking on six major sky surveys with different scientific goals over its first five years. One survey will cover the entire southern sky and others will be dedicated to smaller regions to be studied in greater detail. VISTA's surveys will help our understanding of the nature, distribution and origin of known types of stars and galaxies, map the three-dimensional structure of our galaxy and the neighboring Magellanic Clouds, and help determine the relation between the structure of the Universe and the mysterious dark energy and dark matter.
The huge data volumes "” typically 300 gigabytes per night or more than 100 terabytes per year "” will flow back into the ESO digital archive and will be processed into images and catalogues at data centers in the United Kingdom at the Universities of Cambridge and Edinburgh. All data will become public and be available to astronomers around the globe.
Jim Emerson of Queen Mary, University of London and leader of the VISTA consortium, is looking forward to a rich harvest of science from the new telescope: "History has shown us some of the most exciting results that come out of projects like VISTA are the ones you least expect "” and I'm personally very excited to see what these will be!"
The VISTA Consortium is led by Queen Mary, University of London and consists of: Queen Mary, University of London; Queen's University of Belfast; University of Birmingham; University of Cambridge; Cardiff University; University of Central Lancashire; University of Durham; The University of Edinburgh; University of Hertfordshire; Keele University; Leicester University; Liverpool John Moores University; University of Nottingham; University of Oxford; University of St Andrews; University of Southampton; University of Sussex and University College London.
ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organization in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious program 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 organizing 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 VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-meter European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".
Image 1: This image, the first to be released publicly from VISTA, the world's largest survey telescope, shows the spectacular star-forming region known as the Flame Nebula, or NGC 2024, in the constellation of Orion (the Hunter) and its surroundings. In views of this evocative object in visible light the core of the nebula is completely hidden behind obscuring dust, but in this VISTA view, taken in infrared light, the cluster of very young stars at the object's heart is revealed. The wide-field VISTA view also includes the glow of the reflection nebula NGC 2023, just below center, and the ghostly outline of the Horsehead Nebula (Barnard 33) towards the lower right. The bright bluish star towards the right is one of the three bright stars forming the Belt of Orion. The image was created from VISTA images taken through J, H and Ks filters in the near-infrared part of the spectrum. The image shows about half the area of the full VISTA field and is about 40 x 50 arcminutes in extent. The total exposure time was 14 minutes. Credit: ESO/J. Emerson/VISTA. Acknowledgment: Cambridge Astronomical Survey Unit
Image 2: With this remarkable VISTA mosaic we look deep into the dusty heart of our own Milky Way galaxy in the constellation of Sagittarius (the Archer). About one million stars are revealed in this picture, most of them not seen in visible light pictures. As well as absorbing light, the dust also scatters blue light from the distant stars and makes the central part of this huge starscape appear very red. This image is a mosaic created from VISTA images taken through Y, J and Ks filters in the near-infrared part of the spectrum. The image is about 2 degrees by 1.5 degrees in extent. The total exposure time for this mosaic was only 80 seconds. Credit: ESO/VISTA. Acknowledgment: Cambridge Astronomical Survey Unit
On the Net: | 0.867673 | 3.340621 |
Cosmic Flow: In The Rainforest
A workshop on large scale structure inferred from velocity fields for 30-50 participants
Cosmic flow refers to any coherent motion in the universe including the common Hubble flow due to the expansion. It can be used to probe the dynamics of our local universe as well as provide new insights into cosmology and gravitational theory. Local flows are particularly useful for studies of dark energy, since models of gravity that can explain the acceleration of the expansion of the universe may fail in explaining the growth of structure within it.
It is an area of research that is now seeing a resurgence of interest, and one in which Australia is particularly active. The 6 degree Field Galaxy Survey (6dFGS) has been undertaking a project to measure the peculiar velocities of around 10,000 galaxies and will soon be releasing their results. The WiggleZ dark energy survey recently reported their measurement of the rate of growth of structure in the universe, which confirmed that general relativity remains the best theory of gravity and vacuum energy remains the leading contender for dark energy. Meanwhile, new Australian facilities such as SkyMapper and ASKAP are now coming online that will make excellent peculiar velocity measurements over the next few years.
This meeting is a follow up to our Cosmic CoMotion Conference in September 2010 and the purpose of this meeting is to gather together the Australian community and international experts on cosmic flows to maximise the output from existing data sets such as 6dFGS and WiggleZ as well as optimise upcoming experiments and plan the analyses that are necessary to make the greatest scientific impact from these exciting new windows on the universe. It will largely be discussion based. We encourage interaction between observers and theorists and we are looking to include at least one theory specific session. Simulations of the expanding Universe will be showcased throughout this meeting.
Each half-day will consist of a series of short talks followed by a panel discussion (or similar) about the topics raised. There will also be free time for discussion and collaboration.
Day 1: Redshift space distortions and BAO
Day 2: Peculiar velocity surveys
Day 3: Future work (half day only) | 0.819658 | 3.475296 |
No matter where you look in the fields of astronomy and planetary science, humankind’s exploration of our Solar System’s largest planet has been a centrepiece for new discoveries and new insights into our place in the universe. What shaped the architecture of our Solar System, allowing the formation of rocky terrestrial worlds close to the Sun and cold, giant planets at greater distances? Jupiter. What might control the distribution of planetary debris left over from formation, and the bombardment of Earth by comets and asteroids? Jupiter’s massive gravitational influence. Where might we find the perfect conditions for habitable environments? Jupiter’s icy moons and their hidden, liquid oceans are the ideal place to look. Which planet serves as the archetype for the complex, dynamic atmospheres of giant planets, both in our Solar System and around other stars? You guessed it, Jupiter again. And where might we look for the Solar Systems largest natural particle physics laboratory? That would be Jupiter’s powerful magnetosphere, and the beautiful aurora that it creates. Jupiter, Jupiter, Jupiter.
It is little surprise, then, that the exploration of Jupiter is at the top of everyone’s list, from NASA in the USA to ESA in Europe. And excitement for new Jovian discoveries is once again building, with the imminent arrival of NASA’s newest mission to Jupiter: the Juno spacecraft. Early in the morning of Tuesday, July 5th, the Juno spacecraft will fire its main engines to enter orbit around the giant planet after a five-year interplanetary cruise. The solar-powered spacecraft carries a suite of new instruments to explore the planet’s interior, atmosphere and magnetosphere, revealing the inner workings of Jupiter like never before. At the same time, Earth and space-based observatories are engaged in an unprecedented international campaign to support Juno’s science.
Juno is led by Scott Bolton of the Southwest Research Institute (San Antonio, Texas), and is managed by the Jet Propulsion Laboratory. Lockheed Martin Corporation built the spacecraft. The University of Leicester is home to the UK’s only formal co-investigator of this NASA-led mission, Professor Stan Cowley of the Physics and Astronomy Department, and a team of Leicester’s planetary scientists are engaged in a wide variety of Juno-related science. Leicester’s expertise, honed over decades of involvement with the Cassini mission to Saturn, extends from the churning cloud-decks, through the upper atmosphere and aurora, and into the enormous magnetosphere.
The Leicester team are all members of the Radio and Space Plasma Physics Group (RSPP) in the Department of Physics and Astronomy, shown in the attached photograph. Professor Stan Cowley, Professor Emma Bunce and Dr. Gabrielle Provan use magnetic field data and theoretical modelling to explore the plasma environment of the Jovian magnetosphere and its coupling to the ionosphere. Dr. Jonathan Nichols, Dr. Tom Stallard and Rosie Johnson use Earth- and space-based facilities (including the Hubble Space Telescope) to explore Jupiter’s beautiful auroras and their interaction with the upper atmosphere. Finally, Dr. Leigh Fletcher and Dr. Henrik Melin exploit infrared and ultraviolet observations to explore the variability of Jupiter’s climate, and the origin and formation of the giant planet.
We hope that this blog will help tell the story of the Juno mission from Leicester’s perspective, sharing new discoveries and insights as they are revealed. You’ll find articles about specific aspects of our research, the history and challenges of the mission, our use of ground- and space-based observatories to support Juno, and introductions to the Leicester scientists working on this project. We’ll start with an introduction to the spacecraft itself, and what to expect for Juno’s imminent arrival. Thanks for reading!
For more details:
Mission Juno website: https://www.missionjuno.swri.edu/
Juno fact sheet: http://www.nasa.gov/pdf/541929main_JunoFactSheet2011.pdf
Wikipedia entry: https://en.wikipedia.org/wiki/Juno_(spacecraft)
Leicester’s RSPP Group: http://www2.le.ac.uk/departments/physics/research/rspp | 0.915501 | 3.451361 |
Our first talk was an overview of giant planet atmospheric dynamics by Adam Showman.
Giant planet atmospheres are rotationally dominated, resulting in east-west jets. Jupiter and Saturn’s upper atmospheres exhibit a large number of zonal bands, whereas Uranus and Neptune have only very few thick bands. The size and shape of the jets depend on the radius of the planet compared to the characteristic scales at which vortices form. For Hot Jupiter exoplanets the characteristic scales of the vortices are comparable to the size of the planet.
As for Jupiter’s jets, it is unclear whether they are shallow or deep. The upcoming Juno mission hopes to answer this question.
The second part of the talk then discussed observations. Measured phase curves show that different hot Jupiters have a range of temperature differences between their day and night sides. Observations also hinted at a blueshifted atmospheric line in the HD 209458b transmission spectrum, maybe due to km/s atmospheric winds.
The second speaker was Fran Bagenal, who talked about planetary magnetic fields. A key component of this talk was the discussion of the mechanism for transporting plasma from Io (released from volcanism) into Jupiter’s orbit, which leads to an expansion of the magnetosphere. She showed a nice movie of observations of the plasma torus around Jupiter at different wavelengths, where you can see the wobble due to the 10 degree misalignment between the magnetic pole and the rotation axis.
One interesting observation is that magnetic fields are very diverse within our solar system. Mercury’s field is so small that the planet and the magnetosphere together will fit within the Earth. Earth and its magnetic field will then fit inside Jupiter. Venus and Mars have no magnetic field, although Mars likely used to. She also mentioned the MAVEN mission, which will examine the planet’s upper atmosphere.
We were also shown beautiful pictures of the aurorae around Jupiter and Saturn.
Our third speaker was Emily Rauscher, who discussed some of the observable effects of magnetic drag in planetary atmospheres. In short, for stronger magnetic fields, the ohmic heating increases, which can be a contributory factor in radius inflation. Also, the magnetic drag lowers the wind speeds in the atmosphere. This is observable in the phase curve of a transiting exoplanet. Fast winds mean that the hottest point is offset from the substellar point, and magnetic drag will decrease this offset.
Our final speaker, Andrew Youdin, continued on the theme of inflating hot Jupiters by discussing two theories: ohmic dissipation and the mechanical greenhouse.
In the theory of ohmic dissipation, surface winds induce currents, which then dissipate and get converted into heat. He also pointed out that the high speed winds required for this are damped by large magnetic fields, which is a potential flaw for this scenario as an explanation of radius inflation.
In the mechanical greenhouse model, the outer radiative zones of hot Jupiters are turbulent due to the intense heating from the star. This then drives eddies downwards into the interior of the planet, acting in reverse to convection.
Feature image: NASA, Hubble website | 0.910479 | 3.942075 |
Monday, May 2, 2016
3 Earth-Like Planets Discovered By Astronomers In ‘Habitable Zone’ Of Star
The star, known as TRAPPIST-1, is only slightly larger than Jupiter, Detroit Free Press reports. But it’s only 38.8 light years from Earth, which is relatively close. Some “exoplanets” are more than 13,000 light years away.
The 3 Earth-like planets discovery in constellation Aquarius involves planets that might be just the right distance from their host star to have surface water. Fewer than 40 of these so-called “Goldilocks” worlds are known to exist.
Advances in technology have enabled scientists to find about 2,000 planets beyond our solar system since the 1990s, and there’s some evidence for roughly 4,700 more, the Business Insider reported.
This also is the first time that scientists have found planets orbiting a comparatively small, faint object known as ultracool dwarf star, according to an international research team that includes UC San Diego, NASA, the University of Liege in Belgium and other institutions. The team reported its findings Monday in the journal Nature.
“This is almost certainly the first of many planets (that will) be found around these cool stars, because up to now their faintness made it risky to invest time and resources to monitor large numbers of them,” said Adam Burgasser, a UC San Diego astronomer who led the group that characterized TRAPPIST-1.
“The kind of planets we’ve found are very exciting from the perspective of searching for life in the universe beyond Earth.”
The 3 Earth-like planets were found using a variety of methods. One involves looking for stars that wobble a bit. The wobble can be produced by the gravitational influence of a planet that’s hidden by the glare of the star.
But the most common technique involves using a telescope to study whether a star’s brightness briefly dips. Those dips can be caused by a planet passing in front of the star, as seen from Earth. That is how scientists found the three planets in Aquarius. The phenomenon was observed late last year from La Silla Observatory in Chile.
Subsequent work with larger telescopes revealed that the planets appear to be roughly the size of Earth. The planet closest to the star completes an orbit every 1.5 days. The second does so in 2.4 days. The speed of the third, outer planet, has yet to be clearly determined, but may have an orbital period that lasts up to 73 days.
The research team was led by Michael Gillon of the University of Liege, who said in a statement, “With such short orbital periods, the planets are between 20 and 100 times closer to their star than the Earth to the Sun. The structure of this planetary system is much more similar in scale to the system of Jupiter’s moons than to that of the Solar System.”
The Discover Magazine said the 3 Earth-like planets “puts them just inside the habitable zone for this system, an orbital ring of distances at which surface water is likely to be liquid and life as we know it most likely. | 0.924525 | 3.462043 |
According to Astronomy Now, the most powerful solar storm was recorded in 1859. It was known as the Carrington Flare in honour of the English Astronomer Richard Carrington who observed it at the Colaba Observatory in India. Thanks to this solar storm, auroras (or the Northern Lights) were seen at latitudes as low as Madrid and even the Caribbean Sea. And more importantly, the solar storm caused power outages and fires at telegraph facilities all over Europe and North America.
Ever since, geomagnetic storms caused by the sun pose a serious threat to a society that is increasingly reliant on technology by directly affecting power and communication networks.
Recently (10 October 2015), NASA's orbiting Solar Dynamics Observatory has mapped an enormous coronal hole – a gap in the Sun's outer layer and magnetic field – which is the size of 50 earths and is releasing an extra-fast solar wind in Earth's direction.
The gap lets out a stream of particles travelling at up to 800 kilometres per second that if aimed towards Earth, could result in a geomagnetic storm, a phenomenon that can affect power and navigation for satellites orbiting the Earth as well as radio communication. Newspaper reports don’t say how big the impact might be. Could it shut down the Internet or telephone networks?
But it says as the coronal hole continues its slow march westward on the sun's surface (to the right, from earth's perspective), solar winds will stay strong, according to US National Oceanic and Atmospheric Administration (NOAA).
As far as I can understand, our life is dependent on huge cosmic forces over which we have NO control. (And I don’t mean the positions of the so-called planets on your astrological chart). What would happen if the coronal hole was the size of 500 Earths instead of 50? What if it was 5000?
Surely, there is a tipping point. If the hole goes beyond that point, it might lead to the end of the world as we know it. And this is just one aspect of the sun. There would be thousands of other cosmic phenomena that might kill everyone on earth, everyone, irrespective of whether they eat beef, pork, or just vegetables.
India has been one of the oldest civilisations on earth that nurtured rationality and intellectual openness. It produced Boudhayana, who had propounded the "Pythagorean Theorem" 200 years before Pythagoras, the same Boudhayana and Aryabhatta who discovered irrational numbers, and finally, Brahmagupata, who introduced the decimal system with place values in 628 AD, the one revolutionary concept that changed the future of maths, accounting, and science – yet, in the same country, THE RAGING DEBATE TODAY IS WHETHER THE VEDAS APPROVE OF LYNCHING A MAN WHO MIGHT HAVE EATEN BEEF.
In the last fortnight or so, three innocent law-abiding Indians like you or me have been brutally murdered in three states in India merely on the suspicion that they had eaten beef or killed a cow. Shame and disgust are bloody inadequate words for what our ruling party, the BJP and its armies of goons are systematically doing to our polity, or even at a more fundamental societal level. If this violent march of unreason and hatred continues, India will be destroyed as a country long before any solar flare destroys the earth.
Let’s respect everyone’s right to eat what they wish, to do what they wish, as long as it doesn’t harm others. Let me accept that you have the right to have an opinion different from mine. Let everyone accept that intolerance to others’ views or beliefs or life-style is unacceptable in the civilised world. The moment we start tolerating intolerance, we too begin our inexorable journey towards being a Taliban or IS perhaps with a different religious tag.
And certainly, the time has come when everyone must stand up and protest against irrationality and bigotry that kill others. One must protest against the not-so-hidden agenda of turning India into a Hindu Pakistan.
PLEASE STAND UP NOW AND PROTEST!
If you agree with my views, the least you can do is to share this post and spread the message to a wider audience. Today. Because tomorrow may be too late.
If you disagree, you are welcome to enter a civilised debate here. Will you?
Bengaluru / Monday, 19 October 2015 | 0.813698 | 3.211444 |
The planetary clock is moving inexorably closer to the year 2012. Prophecies about “the End of the World” and the inevitable destruction of the greater part of the human race have become the most discussed topic on our TV screens and in the media generally.
In the scenarios most often suggested the Earth’s future is presented as a succession of planetary-scale catastrophes, in the face of which a considerable portion of humanity helplessly awaits “the End”. But the “End of the World” is not coming and the vast majority of the Earth’s population will not perish, although serious trials and tribulations do lie ahead for humanity.
Coming events will unfold in close connection with processes taking place on the Sun which will really begin in late December 2012, when solar activity reaches its peak. Between 16 and 28 December (the phase of the winter solstice) the planet’s core will begin to radiate a flow of energies that, overlying the solar radiation, will stimulate the activity of processes in the Earth’s bio- and geospheres. Super-powerful coronal discharges will bring our planet magnetic storms of unprecedented force that will cause climatic and shorter-term weather anomalies, floods, earthquakes, tsunamis, fires, diseases and local conflicts.
The map shows in general outline the zones of high and relatively high instability on the Earth’s surface that will last several decades from 2013. Although the coming events hold nothing good in store for humanity, the future of civilization is not as hopeless as the ancient prophecies foretell. The Earth’s human population is capable of influencing the future in a practical way, moderating the gravity of coming events and moving from passive expectation to positive action.
The technology for exerting such an influence was known and used effectively in the very remote past. It is interesting and useful to us, because it is capable of reducing the impact and consequences of the approaching cataclysms. To employ this technology we will need to undertake a series of practical steps to create a means (tool) of influence.
To understand the mechanism by which future events might be influenced, let us begin with the premise that unprecedentedly powerful solar and magnetic storms will cause a sharp surge in the intensity of the Earth’s magnetic field and increased tension in the planet’s energy system (the conductivity of its energy channels). The Earth is a living cosmic organism that reacts with great sensitivity to external factors. At the end of the first decade of the new millennium that organism is profoundly “ill” due to humanity’s immoral industrial and economic activity. When the Earth as an organism initiates self-healing and self-cleansing processes, the planet is subject to earthquakes and anomalous weather conditions that are a part of the functioning of its immune system. This condition will be compounded by influences from outer space. Now let us turn our attention to the wisdom of the ancients, drawing certain parallels. This will help us to understand the logic of that wisdom and to see the way to solve our problem…
When human beings fall seriously ill, their body temperature rises and their general condition worsens. The organism is in a state of stress. Zones of excess energy appear in the energy system. Any external influence causes unhealthy reactions, shaking of the body, pains and even convulsions… When exposed to negative factors (such as solar and magnetic storms), the heightened tension in the Earth’s magnetic field causes corresponding immune reactions: a worsening of the physical condition and even agony. In such cases people in the East have traditionally resorted to a method of combating the illness by inserting needles into specific acupuncture points on the human body that act something like lightning conductors, discharging the excess energy in a particular area, after which the illness goes into recession and the organism calms down.
The ancient wisdom tells us that human beings and the Earth are constructed similarly. The human being has a physical body and so does the Earth. A person has 7 energy bodies and a system of energy channels and the Earth has the same arrangement. It also has acupuncture points on its surface – the “places of power” that are associated with geological faults (channels carrying energy). But in the case of the Earth, the “needles” that should be used are pyramids, the energy flow from which penetrates deep into the Earth’s energy system and is capable of influencing its structure, alleviating tension and local excess build-ups. This idea was one of the main reasons established in deep antiquity that led to the creation of pyramid complexes in a belt around the Earth from East to West. Many of those pyramids have not survived.
Subsequent generations of pyramids were also constructed at particular sites in order to influence the planet’s energy system, to alleviate tensions arising in the crust and thus reducing potential natural and social cataclysms to a minimum. Note that all the pyramid and temple complexes that have come down to us today are located in the zone of maximum energy and seismic tension – the belt of high instability. These enduring monuments to ancient wisdom precisely demonstrate and indicate what we need to do to diminish future cataclysms and their consequences. In some rare instances it may even be possible to avert disastrous phenomena altogether.
Functioning as both and energy lens and a resonator, the pyramid acts like a funnel, gathering and amplifying cosmic energies in a particular wave range. As a result a column (flow) of energy forms along its vertical axis. Radar installations operating in the centimetre range that are located 60, 32 and 30 kilometres from the 22-metre pyramid constructed in the village of Khitino near Ostashkovo in Russia were used to scan the area around the pyramid. These studies revealed the presence of an energy formation -- a column up to 1,200 metres high and 500m in diameter centred on the vertical axis of the pyramid.
On rare occasions this energy column can be seen with the naked eye. This photograph clearly shows the ray of energy above the Khitino pyramid in Russia. Although this shot was taken at night, the film recorded a glow running upwards from the pyramid.
The pyramid's energy flow is directed both up and down. The upward flow pulsates and can reach a height of 1,200 metres. The same kind of flow runs downwards from the pyramid. It is like an acupuncture needle penetrating the Earth’s crust and influencing the energy processes that take place there.
Therefore to influence the energy processes in the Earth’s crust and energy system we need to begin building pyramids in particular places to alleviate future disasters in the areas where they will be most severe in the coming years. There are places on Earth from which energy channels extend even as far as neighbouring countries. The best thing would be to use places of power that have regional significance, because the installation of a pyramid in northern Italy or southern Germany, for example, would diminish future catastrophes not only in those countries, but also in their European neighbours. In brief: the means by which we can exert an influence over the coming catastrophes is complexes of special pyramids that should be constructed according to a particular pattern.
This will of course involve considerable financial outlay. In order for the construction of such installations to be economically viable, even profitable, the pyramids should be surrounded by hotel complexes where anyone who wants can come and stay with the family, in a group or as an individual. The New Atlantis project could become a turning point in the history of Earthly civilization. It will inspire great following across a whole range of fields: medicine, philosophy, art, business, sport, spiritual improvement… and bring it millions of tourists, making it a new centre of pilgrimage on the world map.
Today the world has nothing like the proposed hotel complexes. But bearing in mind humanity’s tremendous interest in pyramids and the influence that they have on people and the environment, we can confidently predict that this kind of complex will be fully occupied all year round!
Pyramids are able like nothing else to exert a positive influence on human health and the human immune system, to stimulate spiritual growth and to transform the world around them. Years of research into the ancient texts and scientific experiments to study the effect of the pyramid field on animate and inanimate objects have made possible a number of highly important conclusions.
The pyramid is:
- a powerful cosmic antenna;
- a model in stone of the energy structure of the human being and of the universe, using the latter’s energy mechanism;
- a very powerful generator of cosmic energies operating on various planes.
Pyramidal energy structures, whose positioning should be decided with reference to the energy qualities of the location, open up the following possibilities:
1... Tapping into natural flows of cosmic energy, the organisation and stimulation of evolutionary processes in the biosphere and in human consciousness.
2... Tapping into natural flows of cosmic energy, the organisation and stimulation of evolutionary processes in the biosphere and in human consciousness. In the immediate area of the pyramid harmonization will take place, a retardation of internal biological time and, as a result a slowing of the aging processes and the prolongation of life.
3... A positive influence on the immune and nervous systems, leading to their improvement.
4... An improvement of mankind’s energo-ecological environment, an increase and improvement of the energy state at the pyramid’s location.
5…as a consequence of the spread of pyramidal structures throughout the world, a reorganisation of the planet’s energy structure within the next 10–15 years.
Pyramids have many beneficial properties that will play a special role in humanity’s development, but the most important for us is that they are capable of reducing the coming problems of 2012 to a minimum, giving humanity a real chance of coming safely through the tough trials that are on their way and preserving the world for our children. | 0.850287 | 3.074731 |
Nasa researchers found the first gamma-ray binary star system in another galaxy, and the most luminous one, for the first time using the Fermi Gamma-ray Space Telescope.
A cyclic flood of gamma rays was observed by the scientists, which is the outcome of an interaction between a crushed stellar core and a massive star that is a part of the dual-star system referred to as LMC P3. LMC stands for Large Magellanic Cloud, a small galaxy in which the binary star system has been found.
"Fermi has detected only five of these systems in our own galaxy, so finding one so luminous and distant is quite exciting," lead researcher Robin Corbet at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said.
"Gamma-ray binaries are prized because the gamma-ray output changes significantly during each orbit and sometimes over longer time scales. This variation lets us study many of the emission processes common to other gamma-ray sources in unique detail," Corbet added.
These rare systems comprise a black hole or neutron, which emits energy in the form of gamma rays. The LMC P3 is so far the second dual star system that has been discovered by the Fermi Gamma-ray Space Telescope.
The LMC P3 is located amid the increasing fragments of a supernova explosion in the galaxy, said to be 163,000 light years away. Researchers using Nasa's sophisticated telescope, the Chandra X-ray Observatory, in 2012 found a source of strong X-ray within the supernova remnant and figured out that it was a young and hot orbiting star.
The mass of this star was found to be many times greater than that of the sun. It was concluded that this object was either a black hole or a neutron star. This system was classified as a high-mass X-ray binary (HMXB).
The team led by Corbet started searching for new gamma-ray binaries in Fermi data by hunting for the periodic changes characteristic of these systems in 2015.
The scientists made the following discoveries: The LMC underwent a 10.3 day cyclic change which centred near one out of many gamma-ray point sources. It was also found that one of the gamma ray sources — P3 — was located near the HMXB and was not related to any of the wavelengths.
Further investigations were made by Corbet's team using NASA's Swift satellite.
"They observed the binary in X-rays , at radio wavelengths with the Australia Telescope Compact Array near Narrabri and in visible light using the 4.1-meter Southern Astrophysical Research Telescope on Cerro Pachón in Chile and the 1.9-meter telescope at the South African Astronomical Observatory near Cape Town," according to a statement released by Nasa on September 29.
The Swift satellite had also found the same phenomenon of the 10.3-day emission cycle. The brightest X-ray emission was found occurring opposite the gamma-ray peak.
"The optical observations show changes due to binary orbital motion, but because we don't know how the orbit is tilted into our line of sight, we can only estimate the individual masses," said Jay Strader, a team member and an astrophysicist at Michigan State University in East Lansing.
"The star is between 25 and 40 times the sun's mass, and if we're viewing the system at an angle midway between face-on and edge-on, which seems most likely, its companion is a neutron star about twice the sun's mass. If, however, we view the binary nearly face-on, then the companion must be significantly more massive and a black hole," Strader added.
The surface at the heart of LMC P3 was found to have a temperature more than 60,000 degrees Fahrenheit (33,000 degrees Celsius), or more than six times hotter than the sun. The star was extremely luminous and the light's pressure drove materials from the surface, and created very speedy particle outflows. The speed of these outflows is estimated to be several million miles per hour.
"It is certainly a surprise to detect a gamma-ray binary in another galaxy before we find more of them in our own," said Guillaume Dubus, a team member at the Institute of Planetology and Astrophysics of Grenoble in France.
"One possibility is that the gamma-ray binaries Fermi has found are rare cases where a supernova formed a neutron star with exceptionally rapid spin, which would enhance how it produces accelerated particles and gamma rays," Dubus concluded. | 0.889592 | 4.035533 |
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Escaping Pulsar Breaks Speed Records.
Astronomers have found a fast moving pulsar on a trajectory that'll take it completely out of the Milky Way. The object, called B1508+55, is located about 7,700 light-years from Earth. The incredibly sharp radio vision of the continent-wide Very Long Baseline Array (VLBA) has tracked this pulsar moving at approximately 1,100 km/s (670 miles/s). By tracking its position back, the Astronomers have calculated that it started out in the constellation Cygnus. A powerful nearby supernova explosion probably kicked it into its current trajectory.
A speeding, superdense neutron star somehow got a powerful "kick" that is propelling it completely out of our Milky Way Galaxy into the cold vastness of intergalactic space. Its discovery is puzzling Astronomers who used the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope to directly measure the fastest speed yet found in a Neutron star.
The neutron star is the remnant of a massive star born in the constellation Cygnus that exploded about two and a half million years ago in a titanic explosion known as a supernova. Ultra-precise VLBA measurements of its distance and motion show that it is on course to inevitably leave our Galaxy.
"We know that supernova explosions can give a kick to the resulting Neutron star, but the tremendous speed of this object pushes the limits of our current understanding," said Shami Chatterjee, of the National radio astronomy Observatory (NRAO) and the Harvard-Smithsonian Center for Astrophysics. "This discovery is very difficult for the latest models of supernova core collapse to explain," he added.
Chatterjee and his colleagues used the VLBA to study the pulsar B1508+55, about 7700 light-years from Earth. With the ultrasharp radio "vision" of the continent-wide VLBA, they were able to precisely measure both the distance and the speed of the pulsar, a spinning neutron star emitting powerful beams of radio waves. Plotting its motion backward pointed to a birthplace among groups of giant stars in the constellation Cygnus - stars so massive that they inevitably explode as supernovae.
"This is the first direct measurement of a Neutron star's speed that exceeds 1,000 kilometers per second," said Walter Brisken, an NRAO astronomer. "Most earlier estimates of neutron-star speeds depended on educated guesses about their distances. With this one, we have a precise, direct measurement of the distance, so we can measure the speed directly," Brisken said. The VLBA measurements show the pulsar moving at nearly 1100 kilometers (more than 670 miles) per second - about 150 times faster than an orbiting Space Shuttle. At this speed, it could travel from London to New York in five seconds.
In order to measure the pulsar's distance, the Astronomers had to detect a "wobble" in its position caused by the Earth's motion around the Sun. That "wobble" was roughly the length of a baseball bat as seen from the Moon. Then, with the distance determined, the scientists could calculate the pulsar's speed by measuring its motion across the sky.
"The motion we measured with the VLBA was about equal to watching a home run ball in Boston's Fenway Park from a seat on the Moon," Chatterjee explained. "However, the pulsar took nearly 22 months to show that much apparent motion. The VLBA is the best possible telescope for tracking such tiny apparent motions."
The star's presumed birthplace among giant stars in the constellation Cygnus lies within the plane of the Milky Way, a spiral galaxy. The new VLBA observations indicate that the neutron star now is headed away from the Milky Way's plane with enough speed to take it completely out of the Galaxy. Since the supernova explosion nearly 2 and a half million years ago, the pulsar has moved across about a third of the night sky as seen from Earth.
"We've thought for some time that supernova explosions can give a kick to the resulting Neutron star, but the latest computer models of this process have not produced speeds anywhere near what we see in this object," Chatterjee said. "This means that the models need to be checked, and possibly corrected, to account for our observations," he said.
"There also are some other processes that may be able to add to the speed produced by the supernova kick, but we'll have to investigate more thoroughly to draw any firm conclusions," said Wouter Vlemmings of the Jodrell Bank Observatory in the UK and Cornell University in the U.S.
The observations of B1508+55 were part of a larger project to use the VLBA to measure the distances and motions of numerous pulsars. "This is the first result of this long-term project, and it's pretty exciting to have something so spectacular come this early," Brisken said. The VLBA observations were made at radio frequencies between 1.4 and 1.7 GigaHertz.
Chatterjee, Vlemmings and Brisken worked with Joseph Lazio of the Naval Research Laboratory, James Cordes of Cornell University, Miller Goss of NRAO, Stephen Thorsett of the University of California, Santa Cruz, Edward Fomalont of NRAO, Andrew Lyne and Michael Kramer, both of Jodrell Bank Observatory. The scientists presented their findings in the September 1 issue of the Astrophysical Journal Letters.
The VLBA is a system of ten radio-telescope antennas, each with a dish 25 meters (82 feet) in diameter and weighing 240 tons. From Mauna Kea on the Big Island of Hawaii to St. Croix in the U.S. Virgin Islands, the VLBA spans more than 5,000 miles, providing Astronomers with the sharpest vision of any telescope on Earth or in space.
The National radio astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreeement by Associated Universities, Inc.
Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists organized into seven research divisions study the origin, evolution, and ultimate fate of the universe.
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Here on Earth, we tend to take air resistance (aka. “drag”) for granted. We just assume that when we throw a ball, launch an aircraft, deorbit a spacecraft, or fire a bullet from a gun, that the act of it traveling through our atmosphere will naturally slow it down. But what is the reason for this? Just how is air able to slow an object down, whether it is in free-fall or in flight?
Because of our reliance on air travel, our enthusiasm for space exploration, and our love of sports and making things airborne (including ourselves), understanding air resistance is key to understanding physics, and an integral part of many scientific disciplines. As part of the subdiscipline known as fluid dynamics, it applies to fields of aerodynamics, hydrodynamics, astrophysics, and nuclear physics (to name a few).
By definition, air resistance describes the forces that are in opposition to the relative motion of an object as it passes through the air. These drag forces act opposite to the oncoming flow velocity, thus slowing the object down. Unlike other resistance forces, drag depends directly on velocity, since it is the component of the net aerodynamic force acting opposite to the direction of the movement.
Another way to put it would be to say that air resistance is the result of collisions of the object’s leading surface with air molecules. It can therefore be said that the two most common factors that have a direct effect upon the amount of air resistance are the speed of the object and the cross-sectional area of the object. Ergo, both increased speeds and cross-sectional areas will result in an increased amount of air resistance.
In terms of aerodynamics and flight, drag refers to both the forces acting opposite of thrust, as well as the forces working perpendicular to it (i.e. lift). In astrodynamics, atmospheric drag is both a positive and a negative force depending on the situation. It is both a drain on fuel and efficiency during lift-off and a fuel savings when a spacecraft is returning to Earth from orbit.
Calculating Air Resistance:
Air resistance is usually calculated using the “drag equation”, which determines the force experienced by an object moving through a fluid or gas at relatively large velocity. This can be expressed mathematically as:
In this equation, FD represents the drag force, p is the density of the fluid, v is the speed of the object relative to sound, A is the cross-section area, and CD is the the drag coefficient. The result is what is called “quadratic drag”. Once this is determined, calculating the amount of power needed to overcome the drag involves a similar process, which can be expressed mathematically as:
Here, Pd is the power needed to overcome the force of drag, Fd is the drag force, v is the velocity, p is the density of the fluid, v is the speed of the object relative to sound, A is the cross-section area, and Cd is the the drag coefficient. As it shows, power needs are the cube of the velocity, so if it takes 10 horsepower to go 80 kph, it will take 80 horsepower to go 160 kph. In short, a doubling of speed requires an application of eight times the amount of power.
Types of Air Resistance:
There are three main types of drag in aerodynamics – Lift Induced, Parasitic, and Wave. Each affects an objects ability to stay aloft as well as the power and fuel needed to keep it there. Lift induced (or just induced) drag occurs as the result of the creation of lift on a three-dimensional lifting body (wing or fuselage). It has two primary components: vortex drag and lift-induced viscous drag.
The vortices derive from the turbulent mixing of air of varying pressure on the upper and lower surfaces of the body. These are needed to create lift. As the lift increases, so does the lift-induced drag. For an aircraft this means that as the angle of attack and the lift coefficient increase to the point of stall, so does the lift-induced drag.
By contrast, parasitic drag is caused by moving a solid object through a fluid. This type of drag is made up of multiple components, which includes “form drag” and “skin friction drag”. In aviation, induced drag tends to be greater at lower speeds because a high angle of attack is required to maintain lift, so as speed increases this drag becomes much less, but parasitic drag increases because the fluid is flowing faster around protruding objects increasing friction. The combined overall drag curve is minimal at some airspeeds and will be at or close to its optimal efficiency.
Wave drag (compressibility drag) is created by the presence of a body moving at high speed through a compressible fluid. In aerodynamics, wave drag consists of multiple components depending on the speed regime of the flight. In transonic flight – at speeds of Mach 0.5 or greater, but still less than Mach 1.0 (aka. speed of sound) – wave drag is the result of local supersonic flow.
Supersonic flow occurs on bodies traveling well below the speed of sound, as the local speed of air on a body increases when it accelerates over the body. In short, aircraft flying at transonic speeds often incur wave drag as a result. This increases as the speed of the aircraft nears the sound barrier of Mach 1.0, before becoming a supersonic object.
In supersonic flight, wave drag is the result of oblique shockwaves formed at the leading and trailing edges of the body. In highly supersonic flows bow waves will form instead. At supersonic speeds, wave drag is commonly separated into two components, supersonic lift-dependent wave drag and supersonic volume-dependent wave drag.
Understanding the role air frictions plays with flight, knowing its mechanics, and knowing the kinds of power needed to overcome it, are all crucial when it comes to aerospace and space exploration. Knowing all this will also be critical when it comes time to explore other planets in our Solar System, and in other star systems altogether!
We have written many articles about air resistance and flight here at Universe Today. Here’s an article on What Is Terminal Velocity?, How Do Planes Fly?, What is the Coefficient of Friction?, and What is the Force of Gravity?
We’ve also recorded many related episodes of Astronomy Cast. Listen here, Episode 102: Gravity. | 0.898633 | 3.900641 |
We live in or on many places — a town or city, a region, a country, even a planet. We live on planet Earth, but there are seven other planets that are all a part of our solar system. These planets have a special relationship to each other because they all revolve around the sun.
More About the Solar System
Our solar system has:
- One central star called the Sun
- Eight planets:
- Mercury (closest to the sun)
- Neptune (farthest from the sun)
- More than 60 moons
- Millions of rocky asteroids
- Billions of icy comets
- Four dwarf planets:
Questions and Anwsers
How old is the solar system? About 4.6 billion years old.
How was it formed? All of the solar system except the sun are loose particles left over from the formation of the Sun. Find out more at Amazing Space.
How big is the solar system? The Oort Cloud, a collection of comets orbiting the solar system, is considered the boundary between our solar system and deep space. It lies about 50,000 astronomical units (or almost one light-year) away from the sun.
Do the planets have the same shaped orbit? No! All the planets have their own unique paths around the sun.
Can you see the planets? You can see Mercury, Venus, Mars, Jupiter and Saturn without a telescope but not Uranus or Neptune.
Where do the planet names come from? Every planet, except for Earth, was named for an ancient Roman god or goddess.
Wasn't Pluto once called a planet? Yes, but scientists reclassified it as a dwarf planet in 2006. Read about why at this Library of Congress Q&A page.
What Is An Orbit?
An orbit is the path followed by an object in space as it moves moves around another object. Read more about orbits from NASA!
Earth takes 365 days to go around the sun, while Neptune takes 164 years.
The Rocky Planets
The Rocky Planets are small and similar in composition to Earth — they all have a solid, rocky surfaces and hot, molten cores. They do not have rings. Earth and Mars have moons.
A look at how the early solar system formed will help explain how the inner, rocky planets came to differ from the outer, gaseous ones.
The Gaseous Planets (or Gas Giants)
The Gas Giants are much larger than the rocky planets and are made mostly of hydrogen, helium, frozen water, ammonia, methane and carbon monoxide. They all have rings and moons.
Jupiter and Saturn contain the largest percentages of hydrogen and helium. Uranus and Neptune contain largest shares of ices — frozen water, ammonia, methane, and carbon monoxide.
Mercury has almost no atmosphere and can be very, very hot and very, very cold.
The Messenger space probe orbited Mercury from 2011–2015 and helped us learn more about the closest planet to the sun.
Check out this gallery of Mercury images.
Venus is the hottest planet and the brightest object in the sky after the Sun and the Moon.
The Soviet space program landed 10 probes on Venus. Pictures taken by these landers can be seen here.
Check out this gallery of Venus images.
Earth is the only planet with liquid water and the only planet that has life!
Earth has one moon . . . but Jupiter has 60!
We use spacecraft to learn about Earth in much the same way we explore other planets.
Check out this gallery of Earth images.
We've been sending spacecraft to Mars since 1960. Explore the many missions humans have sent to the Red Planet.
Check out this gallery of Mars images.
Check out this gallery of Jupiter images.
Saturn has the most spectacular and complex set of rings in the solar system. The rings are made of chunks of ice and rock, are very thin sheets, and there are lots of them!
The Cassini-Huygens Mission to Saturn launched in 1997 and is still (as of 2015) orbiting the planet and sending back spectacular images and data!
Check out this gallery of Saturn images.
The Voyager Two spacecraft has provided us with our best information about Uranus to date.
Check out this gallery of Uranus images.
Each season on Neptune lasts 40 years. Its blue color is caused by methane in its atmosphere.
Neptune has dark spots, which are anti-cyclones in the planet's freezing clouds.
After it flew by Uranus, the Voyager Two spacecraft went past Neptune. It is the only human-made object to have flown by this planet.
Check out this gallery of Neptune images.
Past Neptune there are a class of objects known as the trans-Neptunians. The most well-known of these is the dwarf planet, Pluto. But there are at least two more dwarf planets, Eris and Makemake, and a possible third, Sedna. This NASA site will show some of the objects we know about.
Pluto is so small that some moons in the solar system are bigger than this dwarf planet. Pluto is usually farther away from the sun than Neptune, but its unique orbit sometimes brings it closer than the eighth planet. Pluto's surface is covered by ice made from frozen nitrogen.
In July, 2015, the New Horizons spacecraft visited Pluto, the first human spacecraft to do so.
Pluto was changed from a planet to a dwarf planet on August 24, 2006.
Check out this gallery of Pluto images.
Kuiper Belt and Beyond
Pluto is just one of the many thousands of objects that make up the Kuiper Belt. These are the icy remnants of the solar system's formation 4.5 billion years ago.
Astronomers believe that past the Kuiper Belt is the Oort Cloud, a collection of icy debris that surrounds the solar system at almost a light-year away. This marks the edge of our solar system.
Did You Know . . . ?
“When the Cassini-Huygens spacecraft arrived at Saturn on July 4, 2004 it was traveling so fast that engineers had to burn the spacecraft's engines for 97 minutes to slow it down. If mission engineers didn't do this, the spacecraft would have kept on going instead of entering the orbit around Saturn.”
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Big Bang dustup
In March this year, the US BICEP team of astronomers claimed to have found the long-sought evidence for cosmic inflation - one of the mechanisms that underpin what happened in a fraction of a second after the Big Bang when the Universe began. Inflation has been theorised for decades and the results caused a big stir in the scientific community, with talk of Nobel prizes being awarded to the American astronomers. But, just this week, these findings have been called into question, as Europe's Planck satellite published data suggesting the BICEP results could have been caused by cosmic dust contamination. Graihagh Jackson has been looking at this story and told Chris Smith the latestdevelopments...
Chris - So, what's first of all the background to this?
Graihagh - As you mentioned already, inflation was a theory developed in the 80s to help explain what happened in the first trillionth of a trillionth of a trillionth of a second after the Big Bang, and what happened in inflation is that space expanded very, very fast, faster than the speed of light from something the size of a proton, so, smaller than an atom, all the way to what we now see as the observable universe and this happened all in the fraction of a second. So, according to this theory, the expansion would have caused a sort of ripple in space and time, waves of gravity, and these waves and ripples have left like a pattern on the sky, so to speak, that we could potentially now see and this is what BICEP have claimed to have seen. This polarised cosmic micro background radiation or CMB.
Chris - So, if these waves are there, then it lends credence to the theory of inflation. It tells us what must have happened in the early epoch of the universe during those very, very early times when it was growing rapidly.
Graihagh - Precisely, yeah. It puts us that much closer to seeing the origins of our universe and how it came to be, and I've heard about physicists talking about this could be, you know, discovery of their lifetime sort of thing. So, it's caused a really big stir in the scientific community.
Chris - A ripple even.
Graihagh - A ripple. Yes, precisely!
Chris - It's not just in space-time. And what has Planck now done, because to put this into perspective, Planck is a satellite mission that launched from the European Space Agency 2009, I think it was, wasn't it, to try and probe some of these and other questions. So, what is the Planck probe saying?
Graihagh - It's worth just stepping back a little bit here and talking about what BICEP did. So, BICEP looks at a very small sections of sky and is looking at one frequency or color and that's what they were monitoring in the sky, whereas Planck looks at a huge area in the sky and is looking at multiple frequencies, and these frequencies that the Planck is looking at are much more sensitive to things like cosmic dust, the dust in the sky from asteroids, comets, and when stars explode. So, what Planck have now done is they've looked at exactly the same area of sky that BICEP have looked at and they now think that actually, there's much more dust than they previously thought, and this dust is imitating the polarised CMB.
Chris - The shortfall of the BICEP mission - we actually had them on this program at the beginning of the year when they made this announcement - was that they looked at just this one discreet frequency because we asked them why didn't you look at others, and they said, well our instrument's set up to look at that particular color of light. Planck now say, they've looked at other colors, you're saying, and that actually you may be able to explain those initial observations on the basis of dust. So, what do the BICEP people say about it?
Graihagh - BICEP have always been wanting to corroborate these results. It's just only that now that the Planck satellites come available to actually look at this segment of the sky. So, they haven't commented on it, so to speak, it's always been in the pipeline that they're going to come together and look at results together to see whether actually it is this sort of cosmic dust that's causing this, this signature in the sky or whether actually we really are seeing a signature of the beginning of our universe.
Chris - Ironic, that the guys who discovered the Cosmic Microwave Background radiation, and it won them a Nobel prize in the 1960s, this is Wilson and Penzias. And they actually first of all thought that pigeon poo on their antenna was the cause of this funny signal they were seeing, and it turned out that was the after-glow of the Big Bang. Now these guys might actually done the reverse and claimed to have seen something that is caused by the space equivalent of pigeon poo, cosmic dust. So what does this actually mean then, in real time terms? Are they now saying we're going to go and do some more studies or what?
Graihagh - So the Planck people and BICEP people are now coming together to look at results because as I said before they're quite different data sets, apples and oranges if you like, so they're now looking to put these results together, see what the results are, and we should actually see something coming out at the end of the year. Whether really, it was dust or whether we are seeing the beginning of our universe.
Chris - So there may still be a Nobel prize up for grabs. Graihagh, thank you very much. Graihagh Jackson. And Planck's data that Graihagh was describing was published just this Monday in the online journal Archive. | 0.803747 | 3.715123 |
- Education and Science
Astronomy; The Planet Mercury - Facts and Photos
Credit To Nasa
All photos on this page are credited to Nasa.
My thanks to Nasa - without these spectacular images, this webpage would not have been possible.
This is the first of a series of pages in which I will look at the major objects which make up the solar system - the local group of planets and moons, asteroids and comets which orbit our star, the Sun. In this page I look at the planet which is closest of all to the Sun - the planet Mercury.
Of all the planets, Mercury has been among the most neglected, as it seems superifically at least to be among the less interesting. At first glance it really resembles nothing more closely than our own Moon - a barren rocky world strewn with craters and little else. But there is a bit more to Mercury than meets the eye.
And the planet has recently become the focus of much attention as a Nasa probe entered orbit around Mercury - a mission which, no doubt, will add much to our sparse knowledge of this world.
VISIBILITY OF MERCURY IN THE NIGHT SKY
It may come as a surprise to many, but Mercury - largely unnoticed by the majority of casual observers of the night sky - is potentially easily visible to the naked eye. I say 'potentially' because its maximum brightness is comparable to the very brightest objects in the sky (the scale which is employed by astronomers to measure this is called 'apparent magnitude' and Mercury's apparent magnitude varies from +5.7 (barely visible in the clearest of skies) to -2.3 (the sixth brightest object after the Sun, Moon, Venus, Jupiter and Mars).
However, because Mercury is the closest of all planets to the Sun, it never strays more than 28 degrees from the Sun in our line of sight, and this means that it rises and sets on the horizon more or less with the Sun, and is usually lost in the star's overwhelming glare. Even if visible at dawn or dusk, (when the Sun is diminished in brilliance), the planet is so low on the horizon that heavy atmospheric turbulence impedes clear vision.
When viewed through a telescope, Mercury can often appear as a crescent. This is because we often see the planet to one side of the Sun; we therefore see only the sunlit side of Mercury, just as we often only see the sunlit side of our Moon resulting in its familiar crescent shape.
THE HISTORY OF OUR KNOWLEDGE ABOUT MERCURY
Despite the difficulty of viewing a planet so close to the Sun, Mercury is one of five planets (and Earth) which were known to the ancients. Indeed, it was known at least as long ago as 3000 BC. But for many centuries the planet was believed to be two distinct bodies - one which appeared in the hours around dawn, and another which appeared in the hours around dusk. The early Greeks had separate names for these 'two' planets - Apollo and Hermes respectively. Later Greek scientists however knew full well that Apollo and Hermes were, in fact, just one planet (and some even figured that it probably revolved around the Sun, and not the Earth (a theory which was only proven to be fact in 1639 by Italian astronomer Giovanni Zupus).
Hermes was the Greek Messenger of the Gods, and his Roman equivelant was Mercury, and it is this name by which we now know the closest planet to the Sun. (The Gods Hermes and Mercury were swift-footed, and the planet Mercury has the most rapid motion of all planets across the sky and around the Sun, and this is probably the reason for the Roman association between the God and the planet).
THE CURRENT MISSION TO MERCURY
The ongoing Messenger mission to Mercury has meant that the planet has received much more attention in recent years than previously. Our knowledge of the planet will be greatly increased as a result of this mission, and about 75,000 images including many improved colour photos should be received from the surface, superceding some of the older black and white pictures on this page.
Eventually I will either revise this page, or compile a second page detailing the new information, though it will be some months before all of the information transmitted from the Messenger mission is fully analysed and interpreted.
MODERN EXPLORATION OF MERCURY
Although it was first observed with a telescope by Galileo, this planet is not easily viewed with ground-based instruments, and apart from the phases of the planet as described above, little else of interest could be discerned about the surface features of the planet until the 1960s.
(At this point can I offer the hopefully needless warning about viewing Mercury through binoculars or telescopes? The proximity of the planet to the Sun makes such viewing a potentially disastrous exercise without proper filtration of the light. Catch the Sun in the field of view, and blindness may be the result).
There have been just two space missions to investigate this small world. In 1974-5 the Mariner 10 space probe made the first visit to Mercury. 40-45% of the planet was mapped during three fly-bys, revealing much data about the surface features.
Another 30 years passed before America commenced its second big mission to Mercury. The orbiting probe Messenger launched on 3rd August 2004. It reached Mercury in 2008 and over the next two years made three photographic fly-bys. Messenger finally assumed an orbit around the planet in March 2011, and began to intensively map the surface, taking more than 100,000 images. Data has also been collected by the probe about the interior structure and magnetic field and much else.
BASIC FACTS AND FIGURES
DISTANCE FROM SUN - This varies from about 46 million kilometres to 70 million kilometres. The average distance is 58 million kilometres (36 million miles). Mercury has the most elliptical orbit of any planet.
DIAMETER - 4878 kilometres (3000 miles). Mercury is the smallest of all the 8 currently recognised planets. The surface area is about 14% as big as the Earth, but Mercury is rather larger than our Moon.
GRAVITY - Gravity is about 40% as strong as it is on Earth.
LENGTH OF YEAR - 88 Earth days.
LENGTH OF SIDERIAL DAY (Period of rotation) - 59 Earth days.
LENGTH OF SOLAR DAY (Sunrise to Sunrise) - 176 Earth days.
THE MOVEMENTS OF MERCURY WITHIN THE SOLAR SYSTEM
Mercury rotates on its own axis, with the smallest axial tilt of any planet, in about 59 Earth days, This is a rotational period (also known as a 'siderial' day) slower than that of any other planet except Venus. Revolution around the Sun takes just 88 Earth days which is the shortest year of any planet. It is also a highly eccentric revolution; at times Mercury is 70 million km (43 million miles) distant from the Sun, but at its closest approach is a mere 46 million km (29 million miles) distant. At its closest approach the Sun is about 3 times bigger in the Mercurian sky than it is here on Earth.
The relationship between the period of rotation and the period of revolution is quite interesting. Simple mathematics shows that a 59 Earth day rotation on its axis, and a revolution of 88 Earth days means that Mercury rotates exactly 3 times in 2 of its years. The consequence of this is that although a rotation or 'siderial day' is 59 Earth days in length, the actual interval between one sunrise and the next is closer to 176 Earth days, and the same face is directed towards the Sun's heat, (or shielded from it on the dark side) for 88 Earth days.
(For a diagrammatic representation of this complex rotation/revolution and siderial day/actual day relationship, follow the Mercuryenchantedlearning link)
THE SURFACE FEATURES OF MERCURY
This planet is much more similar in appearance to our own Moon than it is to any of the other planets in the Solar System. Like the Moon, Mercury is a dark world reflecting just 6% of the light it receives. Also like the Moon the geography of the surface comprises large cliffs and escarpments, great flat plains, and huge numbers of craters. The cliffs and escarpments, some of which are hundreds of kilometres in length, and as high as 2000m, may result from contraction of the planet's surface crust, and from the upheavals caused by meteor impact. The origin of the comparatively featureless plains is unknown, but it is possible that they may result from ancient volcanic activity. There are even more craters on Mercury than on the Moon, and in the areas so far imaged, they are more evenly distributed. Mercury has virtually no atmosphere (see below); as a result, small meteors do not burn up as they do when they approach the Earth, and therefore far more will hit the surface creating impact craters. A lack of atmosphere also means a lack of wind or water erosion, so it is possible for craters to survive for millions - even billions - of years intact.
Probably the most famous feature on Mercury is the huge Caloris Basin, bigger than the State of Texas. It's origin is unknown; there has been speculation that It may have been formed by a massive meteor impact early in the history of the Solar System, though volcanic lava flows also seem to be a possibility. If it is indeed a meteor impact crater, then it is the largest of its kind known in the Solar System.
One of the most surprising revelations of recent years is the possible detection of water ice on Mercury. Initially it was Earth-based radar in the 1990s which made this discovery, but recent images from Messenger appear to confirm it. This water ice, if it does exist, is not of course to be found in regions exposed to the intensely hot sunlght, but may be present in craters near the North and South Poles where the floor beneath the crater rim is permanently shielded from the Sun. If ice exists here, it probably originates from cometary or meteor collisions. Another possibility is that water vapour buried deep inside the interior has escaped and frozen at the surface.
At the time of writing this is pretty much all that is known about the surface of Mercury, although the current Messenger mission is already imaging parts of the planet never seen before. Much more information will be forthcoming from Nasa's planetary scientists in due course.
THE GEOLOGY OF MERCURY
The geology of Mars is not particularly well understood, but it is known to be the second most dense planet or moon in the Solar System (second only to our own planet Earth). Although smaller than Ganymede and Titan (the great moons of Jupiter and Saturn), Mercury is more than twice as massive, or heavy. The reason for this great density and mass is that Mercury possesses a substantial iron core. Indeed Mercury's core is proportionately much larger than that of the Earth, and has for some time been believed to exceed half the diameter of the planet. Recent evidence from Messenger suggests the core may amount to substantially more than this - an extraordinary 85% of the planet.
Mercury has a small but significant magnetic field, about 1% as powerful as Earth's magnetic field. For a magnetic field to exist around a planet, convection currents emanating in the core, and a rapid rotation of the planet on its axis, are normally required. In the case of Mercury, planetary rotation is very slow, and would be expected to have a negligible effect. Therefore, convection currents are assumed to be responsible for the magnetosphere. However, convection requires fluidity, and it had long been assumed that the small size of Mercury would have led to the core cooling and solidifing long ago. The presence of even a weak magnetosphere indicates that the core is at least partially molten, though scientists are unsure how such a small planet could have retained a molten core over billions of years.
By contrast to the massive core, the rocky outer mantle and particulate silica crust of Mercury seems to be relatively thin at only 500 to 600 kilometres (300-370 miles) thick. (The Earth's mantle and crust is more than 3000 kilometres thick, and our Moon is composed almost entirely of this rocky matter). It remains to be discovered why Mercury's core is so thick, its crust is so thin, and its geological make-up is so different to the other inner planets of the Solar System.
The role of volcanism on Mercury is also unclear. As already indicated, ancient volcanic lava flows may be responsible for some of the surface features of the planet, and data from Mariner 10 even suggests that recent volcanism may have taken place, but this is far from being proven. The presence of so many intact craters on Mercury somewhat contradicts this, as intact craters are evidence of a lack of disruptive geological activity.
THE ATMOSPHERE AND CLIMATE OF MERCURY
Mercury is the closest planet to the Sun, and the the sunlight here is about 7 times as intense as it is on Earth. Unsurprisingly this planet is extremely hot on the Solar side (albeit not quite so hot as Venus which suffers from a runaway greenhouse effect). However, the very peculiar relationship between the planet's revolution around the Sun and it's rotation on its own axis, means that one side of the planet is shielded from the Sun's heat for a full year at a time, and this results in Mercury having the greatest temperature range in the Solar System, from minus 183 °C (-297°F) to plus 427 °C (800 °F).
There is effectively no atmosphere on Mercury. There is, however, an extremely thin 'exosphere', which consists only of atomic particles of various elements blasted from the surface dust by the Solar wind or by striking meteors. In the extreme temperatures of Mercury, these particles quickly escape the planet's low gravitational pull, but then the processes which liberate these particles, also regularly replace them.
SUMMARY OF INTERESTING FACTS ABOUT MERCURY
Mercury has the longest period of daylight of any planet in the Solar System.
Mercury has the most elliptical (least circular) of all planetary orbits.
Mercury has proportionately, the largest iron core of any planet.
Mercury and Venus are the only planets without attendant moons.
Mercury has the most extreme temperature range in the Solar System.
Mercury - like all the planets of the Solar System - is blessed with so many unique features. However it seems, without doubt, a barren world. It is also a planet which lacks a moon of its own, so it travels through space alone - or at least it did until March 2011 when the Messenger orbiter became a temporary, artificial attendant. Mercury does not feature on the Wonders of the Solar System discussion linked to this page as there are worlds with more obviously diverse atmospheres and geologies than exist here. However, there is no such thing as a dull world, and the current Messenger mission will undoubtably reveal some extraordinary new facts about this enigmatic planet of eccentric orbits, mysterious internal geology, and extreme temperatures.
For up to date information about the Messenger mission, you may find it useful to go to the official Nasa page, by following the highlighted link.
IF YOU WISH TO LEARN MORE ABOUT MERCURY ...
LINKS TO MY OTHER ASTRONOMY PAGES
- Astronomy; Links to my Articles - A Greensleeves Hom...
This is the home page to my astronomy articles on HubPages. The page includes a brief description of the various aspects of astronomy which make this such a fascinating subject to study for both professionals and amateurs alike. This page will also i
- The Planet Venus - A Greensleeves Page
Venus was long considered as Earth's twin, and compared by the ancients to the Goddess of Beauty and Love. However the truth has proved to be very different. Venus is the personification of Hell.
- The Geology and Climatology of Planet Venus - A Gree...
The planet Venus has a complex geological history, and an alien climatology. This page gives a basic explanation of our current state of knowledge about Venus's geology and climate, and how it may have developed
- Astronomy; A Beginner's Guide to the Night Sky - A G...
One of four pages presenting a basic guide to the night sky, and what can be seen with the naked eye or binoculars. This page identifies the different kinds of objects you can see when you look at the night sky
- Astronomy; A Beginner's Guide to the Moon - A Greens...
This is a beginner's guide to the surface structures on the Moon. There is more that can be seen on the Moon with a pair of binoculars, than in the whole of the rest of the sky put together. This guide tells you what to look for.
- Astronomy; A Beginner's Guide to the Stars - A Green...
This is the third page in a series of guides for anyone who wants to learn a little more about our night sky. This page looks at those most numerous of all objects visible in the night sky - the stars
- Astronomy; A Beginner's Guide to Naked Eye and Binoc...
In this fourth page of a series of guides to the night sky for beginners, I look at the most prominent objects other than our Moon and the stars which can be easily seen in the night sky.
- Wonders of the Solar System - A Greensleeves Page
Some time ago on British television, Professor Brian Cox presented an excellent series in which he described his personal list of the greatest wonders of our solar system. This is an alternative list, but it's a list with a bit of a difference ...
- Neil Armstrong; A Tribute - A Greensleeves Page
Neil Armstrong died in 2012. This is a brief tribute to a man who played a central role in one of the greatest moments of human history, and a man who very possibly will one day become the most famous human being in history | 0.880959 | 3.680593 |
The surface of Ceres just got more dazzling. This psychedelic map of the mysterious dwarf planet located in the asteroid belt could hold the secrets of its composition.
The view was built up from images captured by NASA’s Dawn spacecraft while orbiting the dwarf planet at high altitude in August and September. The rainbow-coloured surface was created thanks to the use of infrared filters, which highlighted subtle differences in hue that wouldn’t be visible naturally. The technique can give clues about the minerals that make up the surface as well as the age of different features.
Another view, shown below, zooms in on the Occator crater. This contains the brightest spots on the dwarf planet, possibly caused by water spewing into space.In this case, the colours represent elevation, with the lowest areas shown in blue and the highest in brown. Scientists are interested in the irregular shape of the crater and how it came about.
From October to December, the Dawn spacecraft will descend into its lowest and final orbit, hovering 375 kilometres above Ceres. It will continue to send back images to Earth as well as the most-detailed data ever captured.
The mission is hoping to answer some big questions about the tiny world, including whether life could be lurking in its icy volcanoes.
The maps are being discussed at the European Planetary Science Congress in Nantes, France, this week. | 0.858631 | 3.192556 |
Any model of Solar System formation must explain the following facts:
- 1. All the orbits of the planets are prograde (i.e. if seen from above the North pole of the Sun
they all revolve in a counter-clockwise direction).
- 2. All the planets (except Pluto) have orbital planes that are inclined by less than 6 degrees with respect
to each other (i.e. all in the same plane).
- 3. Terrestrial planets are dense, rocky and small, while jovian planets are gaseous and large.
I. Contraction of insterstellar cloud
- Solar system formed about 4.6 billion year ago, when gravity pulled together
low-density cloud of interstellar gas and dust (called a nebula)(movie).
The Orion Nebula, an interstellar cloud in which star
systems and possibly planets are forming.
- Initially the cloud was about several light years across. A small overdensity in the cloud caused the
contraction to begin and the overdensity to grow, thus producing a faster contraction -->
run away or collapse process
- Initially, most of the motions of the cloud particles were random, yet the nebula had a
As collapse proceeded, the rotation speed of the cloud was gradually increasing due
to conservation of angular momentum.
Going, going, gone
- Gravitational collapse was much more efficient along the spin axis, so the rotating ball collapsed into thin disk
with a diameter of 200 AU (0.003 light years) (twice Pluto's orbit),
aka solar nebula (movie),
with most of the mass concentrated near the center.
- As the cloud contracted, its gravitational potential energy was
converted into kinetic energy of the individual gas particles.
Collisions between particles converted this energy into heat (random motions).
The solar nebula became hottest near the center where much of the mass was collected to
form the protosun(the cloud of gas that became Sun).
- At some point the central temperature rose to 10 million K. The
collisions among the atoms were so violent that nuclear reactions began,
at which point the Sun was born as a star, containing 99.8% of the total mass.
- What prevented further collapse? As the temperature and density increased toward
the center, so did the pressure causing a net force pointing outward. The Sun
reached a a balance between the gravitational force and the internal pressure, aka as hydrostatic equilibrium,
after 50 million years.
- Around the Sun a thin disk gives birth to the planets, moons, asteroids and comets. Over
recent years we have gathered evidence in support of this theory.
Close-up of the Orion Nebula obtained with HST, revealing what seem to be disks of dust
and gas surrounding newly formed stars. These protoplanetary disks span about 0.14 light years and are probably similar
to the Solar Nebula.
II. The structure of the disk
- The disk contained only 0.2% of the mass of the solar nebula with particles moving in circular orbits.
The rotation of the disk prevented further collapse of the disk.
- Uniform composition: 75% of the mass in the form of hydrogen, 25% as helium, and all other elements comprising only 2% of the total.
- The material reached several thousand degrees near the center due to the release of gravitational energy --> it
was vaporized. Farther out the material was primarily gaseous because H and He remain gaseous even at very low T.
The disk was so spread out that gravity was not strong enough to pull material and form planets.
- Where did solid seeds for planet formation come from? As the disk radiated
away its internal heat in the form of infrared radiation (Wien's law) the temperature dropped and the heaviest molecules
began to form tiny solid or liquid droplets, a process called condensation.
- There is a clear relation between the temperature and the mass of the particles that become solid (Why?).
Near the Sun, where the T was higher, only the heaviest compounds condensed forming heavy solid grains, including compunds of aluminum, titanium, iron, nickel, and, at somewhat cooler temperatures, the silicates.
In the outskirts of the disk the T was low enough that hydrogen-rich
molecules condensed into lighter ices, including water ice,
frozen methane, and frozen ammonia.
- The ingredients of the solar system fell into four categories:
- Metals: iron, nickel, aluminum. They condense at T~1,600 K and comprise only 0.2% of the disk.
- Rocks: silicon-based minerals that condense at T=500-1,300 K (0.4% of the nebula).
- Ices: hydrogen compounds like methane (CH4), ammonia (NH3), water (H2O) that condense at T~150 K
and make up 1.4% of the mass.
- Light gases: hydrogen and helium that never condensed in the disk (98% of the disk).
- The great temperature differences between the hot inner regions and the cool outer regions of the disk
determined what of condensates were available for planet formation at each location from the center. The
inner nebula was rich in heavy solid grains and deficient in ices and gases. The outskirts are rich in
ice, H, and He.
- Meteorites provide evidence for this theory.
A piece of Allende meteorite showing white inclusions. The inclusions
are aluminum-rich minerals that formed first in the solar nebula. The inclusions are surrounded by
material with lower condensation temperatures which aggregated later. | 0.851776 | 3.975868 |
Eta Ursae Majoris (η UMa, η Ursae Majoris) is a star in the constellation Ursa Major. It has the traditional names Alkaid (or Elkeid) and Benetnash (Benetnasch). Alkaid is the most eastern (leftmost) star in the Big Dipper (Plough) asterism. However, unlike most stars of the Big Dipper, it is not a member of the Ursa Major moving group. With an apparent visual magnitude of +1.84, it is the third brightest star in the constellation and one of the brightest stars in the night sky.
From My own backyard. Attached to my Orion 120. Shot at F2.8 a 1.9 Second exposure at iso3200
The Cats Eye Nebula
The Cat's Eye Nebula (NGC 6543, Caldwell 6) is a planetary nebula in the constellation of Draco. Structurally, it is one of the most complex nebulae known, with high-resolution Hubble Space Telescope observations revealing remarkable structures such as knots, jets, bubbles and sinewy arc-like features. In the center of the Cat's Eye there is a bright and hot star; around 1000 years ago this star lost its outer envelope, producing the nebula.
It was discovered by William Herschel on February 15, 1786, and was the first planetary nebula whose spectrum was investigated by the English amateur astronomer William Huggins in 1864. The results of the latter investigation demonstrated for the first time that planetary nebulae consist of hot gases, but not stars. Currently the nebula has been observed across the fullelectromagnetic spectrum, from far-infrared to X-rays.
Modern studies reveal several mysteries. The intricacy of the structure may be caused in part by material ejected from a binary central star, but as yet, there is no direct evidence that the central star has a companion. Also, measurements of chemical abundances reveal a large discrepancy between measurements done by two different methods, the cause of which is uncertain. Hubble Telescope observations revealed a number of faint rings around the Eye, which are spherical shells ejected by the central star in the distant past. The exact mechanism of those ejections, however, is unclear
The Cats Eye Nebula F2.8 4 second exposure at ISO3200 | 0.857741 | 3.751432 |
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Meteor Shower - The Perseids
One of the delights of dark skies is to see a sudden brief shining streak across the sky. They're commonly known as shooting stars and many ancient cultures thought they were souls ascending to heaven.
“Shooting stars” are correctly known as meteors, bits of space debris burning up in the Earth's atmosphere. The word meteor comes from a Greek word referring to atmospheric phenomena. Greek philosopher Aristotle (384 BC – 322 BC) thought they were related to the atmosphere and weather. This is how meteorology came to be the study of weather rather than meteors.
Meteoroids are bits of space debris that orbit the Sun. Most of them are small, though their sizes range from tiny particles to great boulders. Some meteoroids are material thrown into space by collisions involving other Solar System bodies. Others are leftovers from the formation of the Solar System. Still others, as we'll see, come from comets.
When a meteoroid enters the Earth's atmosphere, we call it a meteor. Friction with the air heats it to 3000 degrees Fahrenheit (1650 degrees Celsius), vaporizing it and leaving behind glowing gases and particles. This is what creates the meteor trail, which does look like a bright star shooting across the sky. It usually lasts for no more than a second or so.
Most incoming debris simply burns up in the atmosphere, but some pieces are large enough to reach the ground. These remnants are called meteorites. Since very little extraterrestrial material has been collected by astronauts or space probes, meteorites are of great interest to astronomers.
Yet sometimes there is a not only a noticeable increase in meteor activity, but of meteors originating from the same region of the sky. This is a meteor shower and the apparent point of origin is called the radiant. The meteoroids that create these showers come from comets.
When a comet comes near the Sun, it warms up. The warming comet ejects gases and a lot of debris, which it leaves as a trail along its orbit. When our orbit takes us through this debris, a meteor shower occurs. They recur on the same dates every year.
One of the best known meteor showers is the Perseids. A meteor shower is called after the location of its radiant and the Perseids seem to come from the constellation Perseus, named for the Greek hero who saved Princess Andromeda from the sea monster.
The Perseids occur in mid-August and records of heightened August meteor activity go back over two thousand years, with the earliest accounts by Chinese astronomers.
The Perseids were the first meteor shower to be connected to a specific comet. Late nineteenth century Italian astronomer G.V. Schiaparelli made calculations relating them to comet Swift-Tuttle. Since then the same has been done for the other main meteor showers.
Earth can encounter debris from Swift-Tuttle from mid-July on through the third week in August, with the peak activity occurring somewhere in the period August 9-14. Sometimes the Perseids are known as the "tears of St Lawrence" since his feast day, the 10th of August, is within this peak period.
People in the northern hemisphere get the best view of the Perseids because in the southern hemisphere the radiant is below the horizon. Nonetheless southern hemisphere observers can see a worthwhile number of meteors coming up from the horizon.
As the Earth turns, the radiant gets higher in the sky. The higher the radiant the more meteors you'll see, so watching after midnight is worthwhile. The very best time is an hour or two before dawn.
Although it's called a shower, don't expect meteors cascading like raindrops. At best, under clear, dark skies and with an unobstructed horizon, you might see two or three a minute, but there will also be gaps of several minutes in which nothing seems to be happening. The brightest of them will outshine the brightest stars. As well as the meteors streaking away from Perseus, you may see some random meteors going in a completely different direction. These are not part of the shower.
Also there is a good chance of seeing meteors before and after the predicted peak, so it's worth looking on more than one evening if you can, although the numbers will be lower.
In choosing a viewing place, the darker the better. Be sure to tape some red cellophane over your flashlight so that you can see without ruining your eyes' dark adaptation. A reclining lawn chair or camping mattress is useful to avoid getting a stiff neck while trying to get a good view of the sky. Even though it's August, remember to take some warm clothing.
By the way, you don't need binoculars or a telescope. You get a wider view of the sky without them. Let your eyes relax – your dark-adapted eyes are very sensitive to motion.
Give yourself plenty of time. Be patient and with any luck, you'll see one of the sky's loveliest light shows.
(1) Sharpton, Virgil L. "Meteor." World Book Online Reference Center. 2005. World Book, Inc. http://www.nasa.gov/worldbook/meteor_worldbook.html
(2) Kronk, Gary W."What Is a Meteor Shower?" http://meteorshowersonline.com/ [accessed 2010-08-01]
There are images relating to this article at Asteroids & Meteors.
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20 August 1977: Voyager 2 was launched from Launch Complex 41 at the Kennedy Space Center, Cape Canaveral, Florida, aboard a Titan IIIE-Centaur launch vehicle. It was placed on an orbital trajectory that would take it on a journey throughout the Solar System and beyond.
Nearly two years later, 9 July 1979, Voyager 2 made its closest approach to Jupiter, passing within 350,000 miles (570,000 kilometers) of the planet. Many dramatic images as well as scientific data were transmitted back to Earth.
The probe continued outward to Saturn, Neptune and Uranus, continuously transmitting images and data. In 1990, the space probe passed beyond the limits of the Solar System.
Voyager 2 is now approaching interstellar space. It is still transiting the heliosheath, where “solar wind” is slowed by the pressure of interstellar gas. (10,706,654,718 miles, or 17,230,690,530 kilometers, from the Sun, as of 17:22:00 hours, PDT, 19 August 2017) and is still operating, 40 years after it was launched.
20 August 1975: The Viking 1 space probe was launched from Kennedy Space Center, Cape Canaveral, Florida, aboard a Titan IIIE/Centaur rocket. For the next ten months it traveled to Mars, the fourth planet of the Solar System. Once there, it was placed in orbit and began sending telemetry data back to Earth. A Viking Lander descended to the planet’s surface, landing at Chryse Planitia.
This was the first time that a spacecraft had landed on another planet. The orbiter continued to operate over the course of 1,485 orbits. As it ran low on fuel, mission controllers boosted it into a higher orbit to prevent it falling to the planet. Orbiter operations were terminated 17 August 1980. The lander operated for 6 years, 116 days, before the mission was terminated by a faulty transmission which resulted in a loss of contact, 11 November 1982.
19–20 August 1957: At 9:22 a.m., CDT (1422 UTC), 19 August 1957, Major David G. Simons, M.D., United States Air Force, lifted off aboard a helium-filled balloon at an open pit mine near Crosby, New Hampshire. This was the second flight of Project MANHIGH, MANHIGH II. This was a series of experiments to investigate the physiological effects of extreme high altitude flight. The balloon and its 1,648 pound (748 kilogram) gondola were deployed from the bottom of Portland Mine as protection from wind while it inflated.
After 2 hours, 18 minutes, Major Simon had reached 100,000 feet above the surface of the Earth. The peak altitude was a record-setting 101,516 feet (30,942 meters). While at altitude, Dr. Simon performed 25 aeromedical experiments.
32 hours, 10 minutes after lift off, at 5:32 p.m., CDT (2232 UTC), 20 August, the MANHIGH II gondola touched down 10 miles northwest of Frederick, South Dakota. Major Simons was awarded the Distinguished Flying Cross.
Prof. Dr. Dr. h.c. David G. Simons, M.D., Ph.D., Hon., was a world leading authority on chronic and myofascial pain. He died in 2010.
20 August 1955: Colonel Horace A. Hanes, United States Air Force, flew the first North American Aviation F-100C-1-NA Super Sabre, 53-1709, to Mach 1.246 at 40,000 feet (12,192 meters), setting a new Fédération Aéronautique Internationale (FAI) speed record of 1,323.312 kilometers per hour (822.268 miles per hour) over a measured 15/25-kilometer course at Edwards Air Force Base, California.¹
This was the first supersonic world speed record. It was also the first speed record set at high altitude. Previously, all speed records were set very close to the ground for measurement purposes, but with ever increasing speeds this practice was becoming too dangerous.
For his accomplishment, Colonel Hanes was awarded the Mackay Trophy.
After being used in Air Force testing at Edwards AFB, 53-1709 was transferred to the NASA High Speed Test Station, also at Edwards AFB. It was identified as NASA 703, and assigned civil registration N703NA. At some point its tail surfaces were upgraded to those of the F-100D series.
Today, the FAI record setting F-100C is displayed at the Castle Air Museum, marked as F-100D 55-2879.
Horace Albert Hanes was born at Fayette, Illinois, 1 March 1916, the first of two children of Albert Lee Hanes, a farmer, and Martha Elizabeth Jones Hanes. Hanes grew up in Bellflower, Illinois. He attended Normal Community High School at Normal, Illinois, graduating in 1933, and then Illinois State Normal University, also located in Normal. He participated in basketball and track and field. He graduated in 1938 with a bachelor of arts degree in education. He worked as a teacher and athletic coach.
Hanes married Miss Virginia Kumber, a school teacher, in Covington, Indiana, 9 October 1937. The ceremony was officiated by Rev. Lawrence P. Green.
Horace Hanes entered the U.S. Army Air Corps as an aviation cadet, 8 October 1938. He graduated from flight training 25 August 1939 and was commissioned as a second lieutenant, Air Reserve. Lieutenant Hanes was assigned to the 18th Pursuit Group at Wheeler Field, Oahu, Territory of Hawaii, which was equipped with Curtiss-Wright P-36 Hawk and P-40 Warhawk “pursuits.”
Hanes was commissioned as a second lieutenant, Air Corps, United States Army, 1 July 1940. While retaining his permanent rank of second lieutenant, Hanes advanced to the rank of first lieutenant, Army of the United States (A.U.S.), 10 October 1941. He returned to the United States and served with the Air Training Command.
Lieutenant Hanes was promoted to captain, A.U.S. (A.C.), 1 March 1942, and placed in command of a P-47 Thunderbolt squadron based in Florida, the 312th Fighter Squadron, 338 Fighter Group. On 26 November 1942, Hanes was promoted to the rank of major, A.U.S. On 1 July 1943, Hanes was promoted to the permanent rank of first lieutenant, Air Corps, United States Army. He retained this permanent rank until after the war.
Major Hanes was deployed to Europe in August 1943, commanding the 71st Fighter Squadron (Twin Engine), 1st Fighter Group, at Mateur Airfield, Tunisia. The 71st had been the first operational P-38 squadron. After flying 30 combat missions, Major Hanes’ P-38 went down over Yugoslavia in January 1944. For the next three months he evaded capture. Hanes returned to the United States in April 1944 and was assigned to command Punta Gorda Army Airfield, a fighter training base on the western coast of Florida.
Hanes was promoted to lieutenant colonel, A.U.S., 1 August 1944, and to colonel, A.U.S., 23 October 1945. In January 1946, Colonel Hanes assumed command of the 31st Fighter Group, which deployed to Giebelstadt Army Airfield in southwest Germany. The group operated P-51D Mustangs and the new Lockheed P-80B Shooting Star jet fighter. In 1947, Colonel Hanes took command of the 67th Tactical Reconnaissance Group at March Air Force Base, Riverside, California. The 67th was equipped with the Douglas RB-26 Invader and the Lockheed RF-80 Shooting Star.
From January to July 1949, Colonel Hanes attended the Armed Forces Staff College, and then was assigned as Chief of the Air Defense Division within the Directorate of Research and Development, Headquarters, U.S. Air Force. From July 1952 to June 1953, he attended the Air War College, Maxwell Air Force Base, Montgomery, Alabama, and then became Director of Flight Test at the Air Force Flight Test Center, Edwards Air Force Base. It was while at Edwards that Colonel Hanes set the world speed record. He remained at the AFFTC for four years.
Hanes took command of the 58th Fighter-Bomber Wing at Osan Air Base, Republic of South Korea, July 1957. The 58th flew the North American Aviation F-86F Sabre. He then spent three years in Japan as Deputy Chief of Staff, Operations, Fifth Air Force.
In July 1964, Brigadier General Hanes took command of the 9th Aerospace Defense Division at Ent Air Force Base, Colorado Springs, Colorado. On 24 September 1964, Hanes was promoted to the rank of major general, with his date of rank retroactive to 1 April 1960. After two years, Hanes returned to Europe as Assistant Chief of Staff, Operations, Supreme Headquarters, Allied Powers Europe.
Major General Hanes’ final assignment was as Vice Commander, Aerospace Defense Command. He retired from the United States Air Force in 1973.
During his military Career, Major General Horace Albert Hanes, United States Air Force, was awarded the Distinguished Service medal, the Silver Star, Legion of Merit with oak leaf cluster (two awards), the Air Medal with five oak leaf clusters (six awards), the Air Force Commendation medal and the Air Force Outstanding Unit Award ribbon.
Major General Hanes died at his home in Bloomington, Indiana, 3 December 2002. He was buried alongside his wife, Virginia (who died in 1996) at the United States Air Force Academy Cemetery, Colorado Springs, Colorado.
20 August 1947: At Muroc Dry Lake in the high desert of southern California, Commander Turner Foster Caldwell, Jr., United States Navy, flew the first of three Douglas D-558-I Skystreaks, Bu. No. 37970, to a Fédération Aéronautique Internationale (FAI) World Record for Speed Over a 3 Kilometer Straight Course.¹
Four passes were made over the course at an altitude of 200 feet (61 meters) or lower. Two runs were made in each direction to compensate for any head or tail winds. The official speed for a record attempt was the average of the two best consecutive passes out of the four.
Commander Caldwell’s average speed was 1,031.178 kilometers per hour (640.744 miles per hour). He was awarded his second Distinguished Flying Cross for this flight.
The D-558 Program was intended as a three-phase test program for the U.S. Navy and the National Advisory Committee on Aeronautics (NACA) to investigate transonic and supersonic flight using straight and swept wing aircraft powered by turbojet and/or rocket engines. The Douglas Aircraft Company designed and built three D-558-I Skystreaks and three D-558-II Skyrockets. The Phase I aircraft were flown by Douglas test pilot Gene May and Navy project officer, Commander Turner Caldwell.
The D-558-I Skystreak was a single-engine, turbojet-powered airplane. It was built of magnesium and aluminum for light weight, but was designed to withstand very high acceleration loads. It was 35 feet, 8 inches (10.871 meters) long with a wingspan of 25 feet (7.62 meters) and overall height of 12 feet, 1¾ inches (3.702 meters). The airplane had retractable tricycle landing gear. Its empty weight was approximately 7,500 pounds (3,400 kilograms), landing weight at the conclusion of a flight test was 7,711 pounds (3,498 kilograms). The maximum takeoff weight was 10,105 pounds (4,583.6 kilograms). The aircraft fuel load was 230 gallons (870.7 liters) of kerosene.
The D-558-I was powered by a single Allison J35-A-11 turbojet engine. The J35 was a single-spool, axial-flow turbojet with an 11-stage compressor section, 8 combustion chambers and single-stage turbine. The J35-A-11 was rated at 5,000 pounds of thrust (22.24 kilonewtons). The engine was 12 feet, 1.0 inches (3.683 meters) long, 3 feet, 4.0 inches (1.016 meters) in diameter and weighed 2,455 pounds (1,114 kilograms). The J35-A-11 was a production version of the General Electric TG-180, initially produced by Chevrolet as the J35-C-3. It was the first widely-used American jet engine.
The D-558-I had a designed service ceiling of 45,700 feet (13,930 meters). Intended for experimental flights of short duration, it had a very short range and took off and landed from the dry lake at Muroc. (After 1949, this would be known as Edwards Air Force Base.) The experimental airplane was not as fast as the more widely known Bell X-1 rocketplane, but rendered valuable research time in the high transonic range.
Gene May did reach Mach 1.0 in 37970, 29 September 1948, though he was in a 35° dive. This was the highest speed that had been reached up to that time by an airplane capable of taking off and landing under its own power.
The three D-558-I Skystreaks made a total of 229 flights and Bu. No. 37970 made 101 of them. After the Douglas test program was completed, -970 was turned over to NACA as NACA 140, but it was quickly grounded after the crash of the number two aircraft, and was used for spare parts for number three.
Today, 37970 is in the collection of the National Naval Aviation Museum at Naval Air Station Pensacola, Florida. The other surviving Skystreak, Bu. No. 37972, is at the Carolinas Aviation Museum, Charlotte-Douglas International Airport, Charlotte, North Carolina.
Turner Foster Caldwell, Jr., was born 17 November 1913 at Narbeth, Pennsylvania. He was the first of four children of Lieutenant Turner Foster Caldwell and Eleanor Polk Owings Caldwell. The senior Caldwell was a graduate of Yale University, New Haven, Connecticut, and was commissioned as an ensign, United States Navy, through the Reserve Officers Training Corps (R.O.T.C). Commander Caldwell was assigned to the U.S. Naval Academy, Annapolis, Maryland, 1 September 1930, and was promoted to the rank of captain, 1 October 1930. He retired from the Navy 1 August 1940.
Turner Foster Caldwell, Jr., entered the United States Naval Academy as a midshipman, 12 June 1931. He graduated and was commissioned an Ensign, United States Navy, 6 June 1935.
Ensign Caldwell was promoted to the rank of Lieutenant (Junior Grade), with date of rank 6 June 1938. He was assigned as a flight instructor at NAS Pensacola, Florida. On that same day, Lieutenant (j.g.) Caldwell married Miss Helen Adele Glidden of Coronado, California, at Yuma, Arizona. They would have four children.
By 1940, Lieutenant (j.g.) Caldwell was assigned to Scouting Squadron Five (VS-5). On 7 December 1941, VS-5 was aboard USS Yorktown (CV-5) at Norfolk Virginia.
Caldwell was promoted to Lieutenant, 1 January 1942. He was a Douglas SBD-3 Dauntless scout bomber bomber pilot with Scouting Squadron Five (VS-5) aboard U.S.S. Yorktown (CV-5) and commanded the squadron with its 18 SBD-3s aboard U.S.S. Enterprise (CV-6) during the occupation of Guadalcanal and the Battle of the Eastern Solomons.
Between March and September 1942 he was three times awarded the Navy Cross, the U.S. Navy’s second-highest award for valor after the Medal of Honor. He was promoted to lieutenant commander (temporary) 1 May 1943, and to commander, 1 March 1944. (He retained the permanent rank of lieutenant until after the war.)
Later he commanded a night fighter group of F6F Hellcats and TBM Avengers, CVLG(N)-41, assigned to USS Enterprise (CV(N)-6). For his actions during that period he was awarded his first Distinguished Flying Cross and the Legion of Merit.
After the war, Caldwell commanded Carrier Air Group 4 (CVG-4) aboard USS Franklin D. Roosevelt (CVB-42). He was promoted to the rank of captain, 1 July 1954. Captain Caldwell commanded the “long-hull” Essex-class aircraft carrier USS Ticonderoga (CVA-14), from 5 September 1959 to 24 August 1960.
Captain Caldwell was promoted to the rank of rear admiral, 1 April 1963. He rose to the rank of Vice Admiral, 1 November 1967, and served as Director of Anti-Submarine Warfare Plans. Admiral Caldwell retired from the Navy in May 1971. He died at Kilmarnock Hospital, Rappahannock, Virginia, 12 October 1991. | 0.876783 | 3.154886 |
What is EPIC?
EPIC (Earth Polychromatic Imaging Camera) is a 10-channel spectroradiometer (317 – 780 nm) onboard NOAA’s DSCOVR (Deep Space Climate Observatory) spacecraft. EPIC provides 10 narrow band spectral images of the entire sunlit face of Earth using a 2048x2048 pixel CCD (Charge Coupled Device) detector coupled to a 30-cm aperture Cassegrain telescope (Figure 1).
The DSCOVR spacecraft is located at the Earth-Sun Lagrange-1 (L-1) point giving EPIC a unique angular perspective that will be used in science applications to measure ozone, aerosols, cloud reflectivity, cloud height, vegetation properties, and UV radiation estimates at Earth's surface.
The ten channels are listed in Table 1 along with their primary applications for the data that will be obtained for the entire globe (sunrise to sunset) every 60 to 100 minutes.
Field of view that EPIC sees
The EPIC instrument has a field of view (FOV) of 0.62 degrees, which is sufficient to image the entire Earth, which has a nominal size of 0.5 degrees. Because of the tilted (Lissajous) orbit about the L‐1 point, the apparent angular size of the Earth changes during the 6-month orbital period from 0.45 to 0.53 degrees.
EPIC Wavelengths and main data products
The first image released to the public (Figure 3) shows Africa, Middle East, India and China, it also shows the size of the Earth relative to EPIC’s field of view (black area). The pixel size projected onto the Earth near the equator is 8x8 km squared with an optical resolution of about 12x12 km squared for visible wavelengths. The projected pixel size of images increases with distance from the equator, doubling by latitude of 60 degrees. To reduce the amount of data transmitted from DSCOVR, four pixels are averaged onboard the spacecraft yielding downloaded images of 1024 x1024 elements at an estimated optical resolution of approximately 24x24 km squared.
A technical schematic of EPIC
A technical schematic of the telescope (Figure 4) shows the primary and secondary mirrors, focusing or Field Lens Group (FLG), and the filter wheel location just in front of the CCD. In addition to focusing the image on the CCD, the FLG reduces the aberrations inherent in a Cassegrain design. In the EPIC system, the FLG is physically located between the primary mirror and the filter wheels. Along with new narrow-band wavelength filters with improved antireflection coatings, the original FLG was replaced with an improved design to reduce stray light. The optical efficiency of the telescope permits between 70 to 80% of the photons entering the telescope to reach the CCD detector.
DSCOVR Earth science instruments
The DSCOVR spacecraft with the DSCOVR Earth Science instruments NISTAR and EPIC are shown in Figure 5 relative to the size of persons working with them. The National Institute of Standards and Technology (NIST) Advanced Radiometer (NISTAR) is on the left side at the top of the spacecraft. It measures the absolute "irradiance" as a single pixel integrated over the entire sunlit face of the Earth. On the right side at the top of the spacecraft, EPIC is shown with the circular door closed. The door was opened when the spacecraft achieved orbit at L-1 in June 2015.
Double Filter Wheel
Inside the EPIC telescope is a double filter wheel with 12 spaces for 10 filters plus 2 open holes (Figure 6) arranged with six holes in each wheel. The filters are positioned by computer controlled stepper motors in a pre-¬‐determined sequence that can be altered by ground commands.
Rotating shutter and exposure times
In front of the filterwheels there is a rotating shutter wheel mechanism (Figure 7) showing 3 slots. The narrow slot is intended for exposures less than 10 milliseconds, the medium slot is used for exposures of 10 to 46 milliseconds, and the wide slot is used for exposures > 46 ms. For 10 to 46 ms exposures, the shutter blade is moved so that the middle sized slot crosses the light path in a single motion. For exposures longer than 46 ms, the wide slot is used. To obtain the various exposures, the blade slows down, then speeds up to complete the exposure. For an exposure longer than about 60 ms, the blade comes to a complete stop in the open position prior to closing. . In the refurbished design, the filter widths were adjusted so that the narrowest slot is not used so as to improve the uniformity of exposure across the CCD.
The focal plane contains a 2048x2048 pixel backside thinned CCD that is hafnium coated to optimize sensitivity (quantum efficiency) down to 300 nanometers. The CCD is passively cooled to approximately ‐20°C (-4°F) to reduce the zero-light noise (dark current) and other noise effects. In normal operation, the CCD will be read out from one of the opposite corners at 500 kHz. Since the entire array can be read out from either side, it provides some measure of redundancy. The CCD characteristics are summarized in Table 2. The CCD quantum efficiency shown in Figure 8 illustrates a reasonable response at both ends of the desired spectrum, 317 nanometers (80%) and 780 nanometers (50%).
Table 2. CCD Characteristics
EPIC Mirrors and Telescope Components
The composition of the mirrors and structures are specifically made to minimize thermal expansion. Specifically, the mirrors are built from Zerodur with an aluminum coating overcoated with silicon dioxide SiO2 coating on the primary mirror and aluminum overcoated with Magnesium Flouride MgF2 on the secondary mirror. The structure maintaining the optical separation between the primary and secondary mirrors (metering tube) is a graphite composite cylinder designed to exhibit near-zero CTE (Coefficient of Thermal Expansion). The mechanical structure supporting the primary and secondary mirrors (between the mirrors and the metering tube) is Invar 36, also selected to minimize thermal expansion properties.
The EPIC filters were refurbished to have improved antireflection coatings and better out of band rejection (light from other wavelengths). Out of band leakage is very small (0.04 percent for 325 nanometers). The mean filter transmission functions are shown in Figure 9. For most science products, the measurements from each filter are combined in pairs as a ratio or difference. An exception is for estimating cloud reflectivity using 340 or 388 nanometers, where a single channel is used.
Corrections applied to images
A series of corrections must be applied before either realistic color images or science data products can be obtained. The major corrections are for “flat‐fielding” and stray light. “Flat-fielding” is based on measurements with a uniform light source to measure the differences in sensitivity for each of the 4 million pixels. The resulting correction map is applied to the measured counts from the CCD. Stray light was measured in the laboratory using a series of small diameter light sources entering the telescope and imaged on the CCD. A similar set of measurements has been performed on orbit using the moon. The illumination of pixels outside the main diameter of the light source was measured to produce a detailed matrix map of the entire stray light function (the effect of light directed at each pixel affecting every other pixel). The stray light correction is applied to every image. Other corrections are also applied based on laboratory measurements. For wavelengths longer than 550 nm there are back to front interference effects in the partially transparent CCD (etaloning) that must also be removed from the measured radiances.
User guide and a description for EPIC is available at https://avdc.gsfc.nasa.gov/pub/DSCOVR/DSCOVR-EPIC-Description.pdf | 0.84676 | 3.605651 |
Right now, about 500,000 pieces of human-made debris are whizzing around space, orbiting our planet at speeds up to 17,500 miles per hour. This debris poses a threat to satellites, space vehicles and astronauts aboard those vehicles.
What makes tidying up especially challenging is that the debris exists in space. Suction cups don't work in a vacuum. Traditional sticky substances, like tape, are largely useless because the chemicals they rely on can't withstand the extreme temperature swings. Magnets only work on objects that are magnetic. Most proposed solutions, including debris harpoons, either require or cause forceful interaction with the debris, which could push those objects in unintended, unpredictable directions.
To tackle the mess, researchers from Stanford University and NASA's Jet Propulsion Laboratory (JPL) have designed a new kind of robotic gripper to grab and dispose of the debris, featured in the June 27 issue of Science Robotics.
"What we've developed is a gripper that uses gecko-inspired adhesives," said Mark Cutkosky, professor of mechanical engineering and senior author of the paper. "It's an outgrowth of work we started about 10 years ago on climbing robots that used adhesives inspired by how geckos stick to walls."
The group tested their gripper, and smaller versions, in their lab and in multiple zero gravity experimental spaces, including the International Space Station. Promising results from those early tests have led the researchers to wonder how their grippers would fare outside the station, a likely next step.
"There are many missions that would benefit from this, like rendezvous and docking and orbital debris mitigation," said Aaron Parness, MS '06, PhD '10, group leader of the Extreme Environment Robotics Group at JPL. "We could also eventually develop a climbing robot assistant that could crawl around on the spacecraft, doing repairs, filming and checking for defects."
Creating a gecko gripper
The adhesives developed by the Cutkosky lab have previously been used in climbing robots and even a system that allowed humans to climb up certain surfaces. They were inspired by geckos, which can climb walls because their feet have microscopic flaps that, when in full contact with a surface, create a Van der Waals force between the feet and the surface. These are weak intermolecular forces that result from subtle differences in the positions of electrons on the outsides of molecules.
The gripper is not as intricate as a gecko's foot - the flaps of the adhesive are about 40 micrometers across while a gecko's are about 200 nanometers - but the gecko-inspired adhesive works in much the same way. Like a gecko's foot, it is only sticky if the flaps are pushed in a specific direction but making it stick only requires a light push in the right direction. This is a helpful feature for the kinds of tasks a space gripper would perform.
"If I came in and tried to push a pressure-sensitive adhesive onto a floating object, it would drift away," said Elliot Hawkes, MS '11, PhD '15, a visiting assistant professor from the University of California, Santa Barbara and co-author of the paper. "Instead, I can touch the adhesive pads very gently to a floating object, squeeze the pads toward each other so that they're locked and then I'm able to move the object around."
The pads unlock with the same gentle movement, creating very little force against the object.
The gripper the researchers created has a grid of adhesive squares on the front and arms with thin adhesive strips that can fold out and move toward the middle of the robot from either side, as though it's offering a hug. The grid can stick to flat objects, like a solar panel, and the arms can grab curved objects, like a rocket body.
One of the biggest challenges of the work was to make sure the load on the adhesives was evenly distributed, which the researchers achieved by connecting the small squares through a pulley system that also serves to lock and unlock the pads. Without this system, uneven stress would cause the squares to unstick one by one, until the entire gripper let go. This load-sharing system also allows the gripper to work on surfaces with defects that prevent some of the squares from sticking.
The group also designed the gripper to switch between a relaxed and rigid state.
"Imagining that you are trying to grasp a floating object, you want to conform to that object while being as flexible as possible, so that you don't push that object away," explained Hao Jiang, a graduate student in the Cutkosky lab and lead author of the paper. "After grasping, you want your manipulation to be very stiff, very precise, so that you don't feel delays or slack between your arm and your object."
Testing in zero-G
The group first tested the gripper in the Cutkosky lab. They closely measured how much load the gripper could handle, what happened when different forces and torques were applied and how many times it could be stuck and unstuck. Through their partnership with JPL, the researchers also tested the gripper in zero gravity environments.
In JPL's Robodome, they attached small rectangular arms with the adhesive to a large robot, then placed that modified robot on a floor that resembled a giant air-hockey table to simulate a 2D zero gravity environment. They then tried to get their robot to scoot around the frictionless floor and capture and move a similar robot.
"We had one robot chase the other, catch it and then pull it back toward where we wanted it to go," said Hawkes. "I think that was definitely an eye-opener, to see how a relatively small patch of our adhesive could pull around a 300 kilogram robot."
Next, Jiang and Parness went on a parabolic airplane flight to test the gripper in zero gravity. Over two days, they flew a series of 80 ascents and dives, which created an alternating experience of about 20 seconds of 2G and 20 seconds of zero-G conditions in the cabin. The gripper successfully grasped and let go of a cube and a large beach ball with a gentle enough touch that the objects barely moved when released.
Lastly, Parness's lab developed a small gripper that went up in the International Space Station (ISS), where they tested how well the grippers worked inside the station.
Next steps for the gripper involve readying it for testing outside the space station, including creating a version made of longer lasting materials able to hold up to high levels of radiation and extreme temperatures. The current prototype is made of laser-cut plywood and includes rubber bands, which would become brittle in space. The researchers will have to make something sturdier for testing outside the ISS, likely designed to attach to the end of a robot arm.
Back on Earth, Cutkosky also hopes that they can manufacture larger quantities of the adhesive at a lower cost. He imagines that someday gecko-inspired adhesive could be as common as Velcro.
Additional Stanford co-authors are Matthew A. Estrada, Srinivasan A. Suresh, Amy K. Han, Shiquan Wang and Christopher J. Ploch. Christine Fuller and Neil Abcouwer of NASA JPL are also co-authors. Cutkosky is also a member of Stanford Bio-X and the Stanford Neurosciences Institute.
Source and top image: Stanford University | 0.820871 | 3.068866 |
Modeling the universe: ISU physicist designs computer code to understand quantum world
A jumble of letters and numbers fills the computer screen. To an untrained onlooker, the lines may look like gibberish, but it is actually a computer code key to understanding the smallest pieces of the universe.
Allison Harris, an assistant professor of physics at Illinois State University, is the author of the code. Harris researches quantum physics by studying atomic collisions. Her work deals with the tiniest particles—those on the atomic and subatomic levels.
All matter is composed of atoms. Atoms are so tiny that a cube of sugar has as many atoms as there are stars in the universe. An atom is the smallest amount of matter that retains the properties of an element. Think of it as the smallest known building block of hydrogen that is still recognizable as hydrogen.
But atoms are not the most fundamental pieces of matter. They are composed of even smaller—subatomic—particles. Atoms have a nucleus surrounded by electrons (negatively charged particles). Inside the nucleus are protons (positively charged particles) and neutrons (particles with no electric charge).
How these particles interact, or more precisely, what happens when a single one of these charged particles collides with an atom, is what fascinates Harris. “My job is to make predictions. If you shoot a proton at an atom, where does the proton go?” said Harris.
To help people grasp what she is studying on a subatomic scale, Harris uses a much, much larger example of the forces at work. “NASA scientists can launch a rocket that has a rover on it and land it on an asteroid. We’ve seen them do it, and it’s really amazing,” said Harris.
“They deal with the gravitational forces that are pulling on the rocket—from the nearby planets and moons, and from the asteroid itself. They all impact the rocket’s path.”
On a much smaller scale, it’s not gravity that affects a charged particle as it flies into an atom, but instead it’s the electric force. “Take a charged particle, like a proton, and shoot it at an atom of helium or hydrogen. Now you have multiple charged particles interacting,” Harris said. “I try to answer the fundamental questions. What is going to happen when that particle collides with the atom?”
Harris works with complex calculations that generate possible paths a free-flying proton might take when it slams into an atom. Glancing at the screen of code, Harris gives a slightly sheepish smile. “I work in Fortran language for coding, which would make computer programmers laugh because it is so old, but it works great for science computation,” she said.
The code she and her undergraduate students generate is fed into one of the 64-processor units in the Department of Physics (a laptop generally has two processors). From there, they analyze and share the results of their computer simulations. Her theoretical computations are used in collaboration with experiments performed in laboratories in China, Germany, Australia, and the United States. Last fall she presented her work in Germany, and her work has been published in international scientific journals, such as the Journal of Physics and Physical Review. Her research is funded by a $100,000 National Science Foundation grant.
“This is a methodology that has been used very successfully in high-energy physics but is new to atomic collisions,” said Department of Physics Chair Dan Holland. “Proof of the novelty and potential for the idea is that the National Science Foundation has awarded her a three-year grant.”
Harris’ development of the theory and the code are unique in her field. Previously, similar types of calculations have been used in high-energy quantum physics, where man-made collisions happen at crushing speeds at locations such as CERN (European Organization for Nuclear Research) and the Fermilab (Fermi National Accelerator Laboratory). “The people at colliders like CERN are interested in smashing nuclei together and blowing them apart—which is very cool,” Harris said with a smile. “But I’m more interested in the path tiny particles take when they collide at much slower speeds.”
No matter the pace of particle collisions, the world of quantum physics throws a lot of curveballs that complicate predictions. “It’s funny. We know more about how to crash that rocket into an asteroid than we do about the dynamics of particles at the atomic scale,” said Harris.
For one thing, working on the atomic scale means that the peculiarities of quantum mechanics come into play. “There is something called the uncertainty relationship, which tells us that in quantum mechanics you cannot know an object’s position and momentum at the same time,” said Harris. That means a scientist may know where a particle is located at a certain point in time but cannot know how fast it is moving, or vice versa.
Therefore, the calculations Harris and her students perform are based on the idea that in quantum mechanics, particles behave very differently than they do in the classical world.
Related Article: Allison Harris was a recipient of the University's Research Initiative Award.
For example, scientists can track the exact path that a rocket takes as it approaches an asteroid. But in the quantum world, there is no way to know the exact path a tiny particle takes as it collides with an atom. Instead, all possible paths from one point to another must be included in the calculation. As part of her computations, Harris creates graphs showing the potential paths of particles. “We try to predict which way they will go.”
Her research is the building block upon which applied science can be done. One area of application involves plasmas—gases consisting of charged particles. Plasmas are important in many industrial applications, such as plasma etching, which is used to make integrated circuits for computers. “Understanding what happens during a single collision can help the scientists who need to predict what will happen with countless collisions as the plasma is formed and interacts with the material being etched,” said Harris.
The National Science Foundation grant is geared toward Harris providing opportunities for her students. “The work we do on quantum physics is trying to understand the fundamental forces of the universe—the very tiny parts anyway,” said Harris. “And NSF wants us to inspire and train the next generation of scientists to continue that work.”
One inspired scientist was Thomas Esposito, an engineering physics major who has published four papers in scholarly journals and presented at several conferences. “It was an absolute pleasure to work with Dr. Harris, who enabled me to talk to large crowds of people on a topic that can be very technical. At conferences, I learned to answer tough questions with composure.”
The grant will allow Harris to expand her current work tracking particle trajectories with her own “Harris code,” and also look at what happens in more complex collisions. “I want to build on the code and start to get a better overall picture of the collisions. We’re here to answer the fundamental questions.”
Rachel Hatch can be reached at [email protected]. | 0.812635 | 3.893852 |
If we ever travel to the nearest solar system, it would be good to know the kind of planets to expect. Now we have the best hint yet.
The Alpha Centauri dual star system is thought to host rocky Earth-mass worlds, but this assumes they could form in the turbulent conditions associated with the opposing gravitational tugs of paired star systems.
Rocky planets are created from the merger of moon-sized planetary embryos which, in turn, form from the accretion of kilometre-sized planetesimals. However, there is no guarantee that such embryos could form in turbulent conditions.
To find out, Jian Ge of the University of Florida in Gainesville and colleagues built a computer simulation of Alpha Centauri, which showed that moon-sized protoplanets could indeed form after about a million years. No gas giants would be created though, as any gas would be dispersed by the turbulent conditions.
Phillipe Thebault of the Observatory of Paris in France describes the work as interesting, but says the issue is still far from settled. It is impossible to numerically study the planet accretion process in a turbulent system, such as Alpha Centauri, without some simplification, he says.
Journal reference: arxiv.org/abs/1001.2614
More on these topics: | 0.872773 | 3.319568 |
Earth-Moon-Earth, also known as moon bounce, is a radio communications technique which relies on the propagation of radio waves from an earth-based transmitter directed via reflection from the surface of the moon back to an earth-based receiver.
The use of the Moon as a passive communications satellite was proposed by Mr. W.J. Bray of the British General Post Office in 1940. It was calculated that with the available microwave transmission powers and low noise receivers, it would be possible to beam microwave signals up from Earth and reflect off the Moon. It was thought that at least one voice channel would be possible. The “moon bounce” technique was developed by the United States Military in the years after World War II, with the first successful reception of echoes off the Moon being carried out at Fort Monmouth, New Jersey on January 10, 1946 by John H. DeWitt as part of Project Diana. The Communication Moon Relay project that followed led to more practical uses, including a teletype link between the naval base at Pearl Harbor, Hawaii and United States Navy headquarters in Washington, DC.
- The Moon is typically around 384.400 Kilometers away from Earth.
- The moon’s Diameter is 3.476 Kilometers.
- The Moon only takes up 0.52 of one degree out of the full 180 degrees of sky.
- The fact that the Moon appears larger at moonrise and moonset is only an optical illusion.
- The Moon rotates around the Earth every 27 days 7 hours 43 minutes.
- The Moon goes from New Moon to New Moon every 29 days 12 hours 44 minutes.
- With my antenna (22dBi and 16°/-3dB angle) only 0,1% of total radiated energy hit the Moon (99,9% pass beside the Moon and go to the Space)
- The Moon only reflects back about 7 % of the signal during a Moonbounce Contact
- The average loss in decibels for the Earth-Moon-Earth path is 252,5dB (assuming a Moon reflectivity of about 7%, and calculated for my 144MHz (2m) frequency band)
- The path loss will wary approximately ±1dB during each month (as range to the Moon changes).
- If the receiver antenna array is linearly polarized (like my – horizontally), due to rotation of polarization into upper layers of atmosphere (ionosphere; Faraday fading), addition of attenuation can be expected between 20 to 30db
- Below about 1000MHz, cosmic noise is the dominant factor and varies with the portion of the galaxy observed. For 2m band it is between 150 to 7000°K. For successful EME contact on 144MHz, sky noise in direction of the Moon has to be less or equal 500°K.
- It takes approximately 2.52 seconds for a radio wave to travel from Earth to the Moon and back to Earth again.
- The Phase of the Moon has little to no effect on the EME Signals.
Spatial Polarization Loss: The signal loss in dB’s as a result of polarization differences between two stations across the EME signal path. Imagine that you are on the Moon and you have a horizontal beam looking down at the Earth. If one station is on one side of the Earth and another station is on another side of the Earth, the signal polarizations of those stations will not be the same because of the curvature on the Earth. It is this difference of polarizations that will cause a loss of signal strength. This is the Spatial Polarization Loss. If both stations are at the same latitude, then the loss will be just about nothing.
Faraday Rotation: The rotation of the polarization of the signal path caused by the earth’s magnetic field. This normally is a great contributor to signal QSB on EME Signals. It is more pronounced on the lower EME Bands.
Libration Fading: Fading of EME Signals due to the reflected characteristics of the signal. This is due to the rough surface of the Moon. The Moon actually wabbles in its orbit so when signals are reflected off the Moon, they are reflected across the rough terrain on the moon’s surface causing the reflected signals to be inconsistent. This fading becomes extremely pronounced on the higher EME bands (like 1296MHz and above) and is barely noticeable on the lower bands.
Doppler Shift: The frequency offset from the transmitted signal due to velocity factor. The velocity factor is determined by the rate of change in the EME Signal Path Distance. The Earth and Moon are constantly moving, sometimes closer to each other and other times farther away from each other. The greater the change in distance rate, the greater the Doppler Shift will be. Also, the higher the EME Frequency Band is, the greater the Doppler Shift will be also. Another thing to keep in mind is that the Doppler Shift will be higher from the original frequency when the distance becomes closer and the will become lower when the distance becomes farther.
Antenna Temperature (Ta): The Noise Temperature of the signal being received from the antenna. This noise comes from not only the main front lobe of the antenna, but also all the minor lobes and rear of the antenna as well. The combined noise of all these sources becomes the total Noise Temperature of the antenna or Antenna Temperature. One example is that the Moon normally runs at a temperature of around 210 degrees Kelvin. If this is all the antenna was seeing, then 210 degrees would be the Antenna Temperature. This becomes a critical parameter when designing a good antenna for EME use. The idea is to design an antenna that will not contribute noise from other directions that will add to degradation of the signal received off the Moon.
G/T or (Antenna Gain over System Noise Temperature): This is the Ratio of Antenna Gain over System Noise Temperature. Signal to Noise Ratio is comparable to this ratio and are related. This is also a very important parameter when designing a good EME station. A simple way to describe this is to make the Antenna Gain as high as possible and the Noise figure as low as possible to increase the Signal to Noise Ratio. The higher the G/T is, the better. When looking at the G/T of an antenna by itself, it is the factors of Antenna Temperature, Gain, and the antenna pattern that make up the G/T of an antenna.
Declination: The term used to describe the moon’s position relative to the equator of the Earth. If the Declination is minus 8 degrees, then the Moon would be 90 degrees elevation overhead at 8 degrees south latitude on Earth.
GHA or Greenwich Hour Angle: The term to describe the moon’s Position in relations to earth’s Longitude. If the moon’s GHA was at 20 degrees, then the Moon would be located directly overhead 20 degrees West Longitude.
EME Degradation: Basically, it is the amount of degradation in dB’s due to the Sky Temperature, moon’s Distance and Declination. Typically from 0dB’s to -2.5dB’s maximum. Most would agree that the smallest degradation loss would be with the lowest Sky Noise, highest Declination and Moon at Perigee.
Moon Perigee: When the Moon is at its closest Distance from the Earth.
Moon Apogee: When the Moon is at its farthest Distance from the Earth.
Sky Noise: This is the term to describe the background noise behind the Moon or Noise Temperature at and around the Moon. It is measured in degrees Kelvin. If the Moon is located at or near a high noise area such as the Milky Way or the Sun, then the Sky Noise would be high compared to the area in the sky which has the lowest Noise Temperature which is known as “Cold Sky “.
Elevation of the Moon: The term used to describe the height of the Moon at the observer’s location relative to the horizon. An elevation of 10 degrees would mean that the Moon at the observer’s location is 10 degrees above the horizon. 90 degrees elevation would be directly overhead.
Phase of the Moon: The term used to describe the Illumination of the Moon by the Sun. A full Moon would mean that the entire disk of the Moon is illuminated at the observer’s location. A New Moon would mean that the moon’s disk is completely dark at the observers location. The Phase of the Moon DOES NOT have any effect on EME Propagation. | 0.876224 | 3.488354 |
When Cassini/Huygens was launched from Cape Canaveral on 15 October 1997, the 5.6 t, 6.8 m-high spacecraft carried a suite of scientific sensors to support 27 investigations probing the mysteries of Saturn's system. In addition to a fascinating atmosphere and interior, the vast system contains the most spectacular of the four planetary ring systems, numerous icy satellites with a variety of unique surface features, a huge magnetosphere teeming with particles interacting with the rings and moons, and the intriguing moon Titan - slightly larger than the planet Mercury and with a hazy atmosphere denser than Earth's.
The Cassini/Huygens mission is an international venture between NASA, ESA, the Italian Space Agency (ASI) and several separate European academic and industrial partners. The mission is managed for NASA by the Jet Propulsion Laboratory (JPL) in Pasadena, California. After an interplanetary voyage of 6.7 years, the spacecraft will arrive at Saturn on 1 July 2004, where it will brake into orbit around the planet. ESA's 318 kg Huygens Probe will execute its mission in November 2004, at the end of the first of Cassini's many orbits about Saturn. Having relayed the Huygens data, the Orbiter will then continue its intensive exploration of the system through June 2008.
Cassini/Huygens was launched atop a Titan-4B/Centaur from Launch Complex 40 at the US Air Force Cape Canaveral Air Station in Florida. Though under the primary control of the USAF 45th Space Wing, launch operations also involved the efforts of many other agencies, technical centres and contractors. Once injected into space and acquired by the Deep Space Network (DSN) tracking antennas, mission control shifted to the Mission and Science Operations (MSO) teams at JPL, with Probe support from ESA's European Space Operations Centre (ESOC) in Darmstadt, Germany (see the article by Sollazzo et al. in this issue).
On reaching Saturn in mid-2004, Cassini will swing to within 20 000 km of the cloud tops (an altitude only 1/6th the diameter of Saturn) to begin the first of 74 planned orbits. In late 2004, Cassini will release the Huygens Probe for a descent of up to 2.5 h through Titan's dense atmosphere. The instrument-laden Probe will beam its findings to the Orbiter for storage and then relay to Earth. The Huygens portion of the mission is covered in detail in the Lebreton & Matson and Hassan & Jones articles in this issue.
What we know about Titan is certainly tantalising. Its brownish-orange, hazy atmosphere of nitrogen, methane and complex array of carbon-based molecules hides a frigid surface that may contain subsurface reservoirs or perhaps even lakes of liquid ethane and methane. Much of Titan's interior and surface is probably frozen water ice, with perhaps thin patches of overlying frozen methane and ammonia. As high-energy particles and ultraviolet radiation bombard the nitrogen and methane molecules in the atmosphere, these and further reactions create a variety of organic molecules that clump together and rain slowly down. Whether this material collects on the surface or sinks into surface pores is not known. In many ways, Titan's environment may resemble the chemical factory of primordial Earth. Though the extreme cold makes the possibility of life unlikely, Titan may still provide valuable clues to the chemistry of early Earth.
The Orbiter will execute 50 close flybys of the moons, including more than 40 of Titan. In addition, there will be more than 25 distant flybys of the icy moons. Cassini's orbits will also allow it to study Saturn's polar and equatorial regions.
Throughout the mission, costs will be contained and efficiency enhanced by streamlined operations. The Cassini Project uses simplified organisational groups to make decisions. Flight controllers will take advantage of high- level building blocks of spacecraft action sequences to carry out mission activities. New technology includes powerful new computer chips, solid-state recorders, gyroscopes with no moving parts, and solid-state power switches.
Cassini requires several planetary swingbys to gain sufficient Sun- relative speed to reach Saturn almost 7 years after launch. (Courtesy of JPL)
Delivering Cassini and its large complement of scientific instruments to Saturn and Titan produced a spacecraft launch mass of 5548 kg, more than half of which is propellant for trajectory changes. Not even the powerful Titan-4B/Centaur can reach Saturn directly with this payload, but it can provide sufficient energy for a direct trajectory to Venus. Here, the great velocity gains from a gravity assist must be used to reach Saturn 6.7 years after launch, by flying by Venus twice and Earth and Jupiter once each - the so-called 'VVEJGA trajectory' (Venus-Venus-Earth-Jupiter Gravity Assist).
As the Jupiter-Saturn connection is only available for one 3-year period every 20 years (Voyager used the 1976-1978 equivalent), it turns out that departures later than Cassini's primary launch period (6 October - 4 November 1997, with contingency days available through 15 November) lose the energy gain available from Jupiter and must endure much longer flight times if they are to make it to Saturn with sufficient performance to attempt a minimum tour mission. For the VVEJGA route, the Sun-relative speed gains for each of the four swingbys are roughly 6, 7, 6 and 2 km/s, respectively. For the secondary launch period from 28 November 1997 to 11 January 1998, the speed gains from the VEEGA route are about 6 km/s for each of the three swingbys, with arrival at Saturn some 2.3 years later than the preferred arrival date of 1 July 2004, for the primary mission.
Cassini begins the Saturn Orbit Insertion (SOI) burn on 1 July 2004 (Courtesy of David Seal/JPL)]
The primary arrival date is favourable from three points of view. It allows a close flyby (52 000 km) of the moon Phoebe (likely a captured asteroid in a distant, retrograde orbit) some 19 days before Saturn Orbit Insertion (SOI). The tilt of Saturn's rings is more favourable for imaging and radio-science observations than it is for later arrivals. Finally, the spacecraft power available during the tour from the Radioisotope Thermal Generators (RTGs) is higher than it would be after the longer journey times of the later launches.
Daily launch windows from Cape Canaveral opened at 09:38 UT on 6 October and lasted for up to 140 min each launch day, moving earlier by about 6 min daily. During the cruise to Saturn, activities are limited primarily to engineering and science instrument maintenance and calibrations, navigation data collection, trajectory corrections and gravitational-wave searches during 40-day periods around solar oppositions beginning in December 2001.
The probability of accidental entry during the >1000 km altitude Earth swingby will be controlled to 10-6 through measures such as trajectory aim-point biasing, precision navigation, robust spacecraft design against propulsion- and micrometeoroid-induced failures, and rigorous flight-team training. Scientific observations will be made of the Saturnian system during the late cruise phase as Cassini approaches. Present funding and project planning do not allow for scientific data to be collected during the earlier planetary swingbys.
On arrival at Saturn, Cassini will make its closest approach to the planet, passing only 20 000 km above the cloud tops. It will fire one of its two redundant engines on 1 July 2004 for 96 min to slow its speed by 622 m/s for SOI; braking into a 1.33x178 Saturn radii (RS), 148-day, 16.8° orbit will consume 830 kg of the main propellant supply. A 50-min, 335 m/s burn 13 days after apoapsis of the post-SOI orbit will raise periapsis to 8.2 RS to target Cassini for a Titan encounter and Huygens' entry on 27 November 2004. If any problem with the spacecraft or ground system prevents execution of the Probe mission on the first Titan pass, a decision can be made as late as a few days before Probe separation to delay until the second Titan encounter on 14 January 2005.
On 6 November 2004, 22 days before the first Titan flyby, the entire spacecraft will be manoeuvred into an impact trajectory with Titan. Two days later, the Orbiter will turn to orient the Probe to its entry attitude, spin it up to just over 7 rpm, and release it with a separation velocity of about 0.3 m/s. Two days after separation, the Orbiter Deflection Manoeuvre (ODM) of 45 m/s ensures that it will not follow the Probe into Titan's atmosphere (by aiming 1200 km off Titan's limb) and establishes the proper geometry (by slowing down) for the Probe Relay Link. Huygens is targeted for an entry angle of -64° and a dayside landing 18.4°N of Titan's equator and some 200°E of the sub-Saturn point.
After Huygens enters Titan's atmosphere at 6 km/s, decelerates to 400 m/s in less than 3 min, and deploys its series of parachutes, it will transmit its findings to the Orbiter for up to 2.5 h during descent, and possibly for another 30 min from the surface. The Orbiter will receive these data over its High-Gain Antenna (HGA) for redundant storage aboard its two Solid- State Recorders (SSRs), then turn later to play back these precious data to the waiting radio telescopes on Earth.
Cassini's tour phase begins after completion of Huygens' mission and ends four years after SOI. The baseline tour consists of 74 orbits of Saturn with various orientations, orbital periods ranging from 7 to 155 days, and Saturn-centred periapses ranging over about 2.6 - 15.8 RS. Orbital inclinations with respect to Saturn's equator range from 0° to 75°, providing opportunities for ring imaging, magnetospheric coverage and assorted Earth, Sun and stellar occultations by Saturn, Titan and the ring system. Most of the 43 Titan encounters have flyby altitudes of 950 - 2500 km. As a result of Titan's considerable mass, the Saturn-relative total gravity swingby gains amount to about 33 km/s (more than that gained during the interplanetary journey), easily enough to move the Saturn-relative orbits through a wide range of desired observational geometries. The baseline tour also contains seven close flybys within 1000 km of icy satellites, and 27 additional distant flybys of icy satellites within 100 000 km.
The tour designers have developed an elaborate sequence of Titan swingbys to achieve the many scientific remote-sensing and in-situ data-collection conditions requested by the scientists. It is crucial that the navigation accuracy for each swingby be very precise, because the total delta-V available for flying the entire 4-year tour is only 500 m/s, i.e. less than the average delta-V assist (770 m/s) from each Titan swingby. By using radiometric tracking data and optical navigation images of Titan and other satellites against a star background taken on each orbit, the Navigation Team predicts control errors at the 10 km level for the Titan swingbys, sufficient for the available propellant.
The mission designers are developing an integrated plan to allow the flight and ground systems to collect and return the desired science data, while Cassini remains 'on the tour'. Sequences of operational routines are used rather like building blocks to execute the necessary engineering support and scientific activities. These various 'operational modes', 'data modes' and 'templates' can be strung together to ensure that spacecraft subsystem and instrument capabilities are used to best advantage. As the three RTGs do not provide sufficient power to turn all the instruments on simultaneously, the various instruments must be operated in logically related subsets. Hence, such operational modes as 'Optical Remote Sensing', 'Radar/INKS' (Ion and Neutral Mass Spectrometer) and 'Downlink Fields/ Particles/ Waves' convey their intent.
The majority of the scientific instruments are body-mounted, making it is necessary to turn the entire spacecraft, point in different directions to perform the desired measurements, record these data on the two SSRs (which can hold 1.8 Gbit each), and finally turn to Earth to radio these data to the ground. During each orbit about Saturn, there are 4 to 7 days of 'high activity', with the remainder spent in 'low activity'. The former generally occurs near Saturn and the satellite flybys, with intensive data- collection periods lasting about 16 h daily, followed by 8 h of playback to either a 70 m antenna or a 34/70 m array, capturing up to 4 Gbit daily (by interleaving real-time and SSR data during each playback). During low activity, the Orbiter may simply roll to collect fields and particles data to broadcast to a smaller 34 m antenna each day, though off-Earth turns are still allowed as long as downlink data return levels do not exceed about 1 Gbit daily.
After delivering the Huygens Probe, the Orbiter will make 43 close gravity-assisted swingbys of Titan to achieve a variety of Saturn geometries for its 12 instruments (Courtesy of JPL)
Principal features of the Cassini/Huygens spacecraft (Courtesy of JPL)
The Cassini Orbiter is one of the largest and most complex robotic spacecraft ever built. Together with the Huygens Probe, it is twice the size of Galileo: 6.8 m tall and 4 m across. Carrying over half its mass in propellant (3132 kg), the total spacecraft with its instruments and Huygens weighs 5548 kg.
The Orbiter's main body is formed by a stack consisting of the lower equipment module, the propulsion module, the upper equipment module, and the High-Gain Antenna (HGA). Attached to this stack are the Remote-Sensing Pallet, the Fields and Particles Pallet, and the Huygens Probe. Some instruments, such as the Titan Radar and the Radio and Plasma Wave Subsystem (RPWS), are attached to the upper equipment module. The two equipment modules are also used for externally mounting the magnetometer boom and the three power- providing RTGs. The spacecraft electronics bus is part of the upper equipment module, supporting data handling (including the command and data subsystem and the radio-frequency subsystem), instruments and other spacecraft functions. During the inner Solar System cruise and science tour, the 4 m-diameter HGA communicates with the Deep Space Network at a maximum of 166 kbit/s, using its X-band transmitter and only 20 W power (19 W at end of mission). Two Low-Gain Antennas (LGAs) transmit data and receive commands when the HGA cannot be pointed at Earth.
Cassini's High-Gain Antenna (HGA) is able to operate at S-, X-, Ka- and Ku-band. In addition to communications (X-band with Earth and S-band with Huygens), radio-science measurements will probe Saturn and satellite gravity fields, rings, atmospheres and surfaces. This artist's concept illustrates the radar mapping of Titan's shrouded surface of Titan at Ku- band. Radar images will be taken at a typical resolution of 500 m. Altimetry and passive radiometry measurements will also made. Approximately 1% of Titan's surface can be mapped during a flyby. Full coverage will be accomplished by combining the high-resolution radar mapping with lower-resolution passive radiometry (Courtesy of JPL)
Once on its way to Saturn, the Orbiter uses two 445 N main engines and 16 smaller 0.5 N thrusters clustered in groups of four in redundant pairs for propulsion and manoeuvres. The primary and backup main engines have separate feed systems. A gimbal mechanism directs thrust through Cassini's centre of gravity and can swivel ±12.5° in two orthogonal axes. The main engines use the helium-pressurised hypergolic combination of monomethyl hydrazine (N2H3CH3) fuel and nitrogen tetroxide (N2O4) oxidiser. A separate 132 kg tank of hydrazine (N2H4) is used for the thrusters. In general, the main engines are used for all manoeuvres requiring a delta-V greater than 0.8 m/s. The thrusters can provide as little as 0.015 N/s for attitude control.
The Cassini Orbiter and Huygens Probe in the solar thermal vacuum test chamber (Courtesy of JPL)
The locations of the imaging science instruments on the Remote Sensing Pallet (Courtesy of JPL)
The locations of some of the fields and particles experiments on the Fields and Particles Pallet (Courtesy of JPL)
Mounted below the main engines is a retractable cover that protects them from micrometeoroids during cruise. The thin disilicide refractory ceramic coating on the inside of the engines is especially vulnerable to micrometeoroid damage: it could lead to burn-through and engine loss. The main engine cover can be extended and retracted many times and has a pyrotechnic ejection mechanism should there be a mechanical problem that interferes with main-engine operation. During cruise, the cover remains closed when the main engines are not in use.
Power is supplied to the spacecraft by three RTGs, providing about 700 W. Solar electric power generation is impractical so far from the Sun, as the enormous size of an effective solar array would be too massive and bulky to fit on any launch vehicle.
The Command and Data Subsystem (CDS) receives ground commands via the Radio Frequency Subsystem (RFS). The CDS then distributes the commands designated for other subsystems or instruments, executes those commands that are decoded as CDS commands, and stores sequence commands for later execution. There are two CDSs so that the mission can continue should one fail.
Cassini carries two identical 1.8 Gbit SSRs, each capable of transferring data at more than 470 kbit/s. Each CDS is linked to the SSRs such that each can communicate (read/write) with one SSR, but not both simultaneously. The CDS receives data destined for the ground on the data bus from other subsystems, processes it, formats it for telemetry and delivers it to RFS for transmission to Earth.
CDS software contains algorithms that provide protection for the spacecraft and the mission in the event of a fault. In the case of a serious fault, the spacecraft will be placed in a safe, stable, commandable state (without ground intervention) for at least two weeks to give the operations team time to solve the problem and send the spacecraft a new command sequence. It also automatically responds to a pre-defined set of faults (problems) needing immediate action.
The X-band RFS provides the telecommunications facilities for the spacecraft and is used as part of the radio-science instrument. The Ultra Stable Oscillator (USO), the Deep Space Transponder (DST), the X-band Travelling Wave Tube Amplifier (TWTA), and the X-band Diplexer are also used as part of the radio-science instrument.
The Attitude and Articulation Control Subsystem (AACS) provides dynamic control of Cassini's orientation. It keeps the spacecraft orientation fixed for HGA and remote-sensing pointing and performs target-relative pointing as well as repetitive motion required during imaging such as scans and mosaics. Spacecraft rotation during the Saturn tour that requires high pointing stability is normally controlled by the three main Reaction Wheel Assemblies (RWAs), although modes requiring faster rates or accelerations may use the thrusters. The AACS is capable of supporting a pointing accuracy of 1 mrad with a stability of 8 mrad/s, and rotation rates of 0.02 - 1°/s. The AACS also controls the main-engine gimbals.
The AACS uses Inertial Reference Units (IRUs) for angular-motion measurements about three orthogonal axes. Two of the three are operational at any one time, with one providing backup in case of equipment failure. Together with the Stellar Reference Unit (SRU) star tracker, the IRUs form the basis of Cassini's attitude-determination system.
The heart of each IRU is a set of four solid-state hemispherical resonator gyroscopes (HRGs) developed by the Delco Division of Hughes Aircraft Co. The inertially sensitive element in each HRG is a fused-silica shell, the hemispherical resonator. If a standing wave is established on the shell (much like making a wineglass 'sing' by sliding your finger around the rim) and the shell is rotated about its axis, the oscillating mass elements experience forces that cause the standing wave to precess with respect to the shell. The precession angle is a constant fraction of the angle through which the shell has rotated, allow precise measurement of angular motion in the axis of the HRG.
Each IRU weighs less than 8 kg. The units are designed to meet all performance requirements over 2500 h of testing and 30 000 h of in-flight operation. They must also meet requirements over 200 on/off cycles in testing and 500 on/off cycles in flight.
The SRU is a 15 deg-square field of view star tracker that provides three-axis attitude measurements. The redundant SRU can provide the AACS flight computer (AFC) with up to 50 000 pixels of information per second. AFC software algorithms can establish and maintain stellar reference by comparing incoming pixel frames to an onboard catalogue of some 5000 stars. Three to five stars are commonly tracked at any one time.
Cassini uses a digital Sun Sensor Assembly (SSA) to detect the Sun when it is in the sensor field of view. Following detection, the measured Sun location determines the spacecraft attitude to sufficient accuracy to facilitate star identification by the SRU. The SSA also provides Sun reference for spacecraft thermal 'safing' (i.e. shutdown in case of thermal overload). The SSA has 2-for-1 redundancy, and at least one SSA will be powered on at all times during the mission.
Thermal control is accomplished by several means, the most visible being the black-and-gold Multi-Layer Insulation (MLI). In addition to the automatically positioned reflective louvres covering the 12-bay electronics bus, strategically-placed heaters and radiators also help to provide thermal control for systems and instruments as Cassini travels between 0.61 and 10.1 AU from the Sun. The thermal-control elements must dissipate the waste heat from the RTGs, as well as the 700 W consumed by the various electronics subsystems. The majority of the electronics must be maintained within 5-50°C. In the case of VIMS and CIRS, where substantial thermal isolation from the platform and spacecraft is required, temperature control is provided as an integral part of the instruments themselves. The thruster clusters are temperature- controlled with Variable Radioisotope Heater Units (VRHUs) and catalyst bed electrical heaters. Electrical heaters are also used on the main engines. A heat shield protects the rest of the engine from radiant heating during and after main- engine firings.
Cassini's instruments are capable of observing from the infrared to the ultraviolet, as well as detecting charged particles, dust and magnetic fields. Its radar will pierce the clouds surrounding Titan to provide detailed images and measurements of its surface. During the four-year orbital tour of Saturn, hundreds of thousands of images in many frequencies will be sent back. The science instruments and their purposes are listed in Table 1.
Table 1. Cassini Orbiter instruments
Jean Dominique Cassini was born in Perinaldo, Italy on 8 June 1625, and given the name Gian Domenico Cassini; he changed his name in 1673 on becoming a French citizen. Christiaan Huygens was born to a prominent Dutch family in The Hague, The Netherlands on 14 April 1628. His family was deeply involved in the sciences, literature and music.
Jean Dominique Cassini with the Paris Observatory in the background (Painting by Duragel, courtesy of the Observatoire de Paris)
Cassini became the head of the Paris Observatory in 1668, and spent much of his time observing Saturn, its moons and rings. He was an excellent and assiduous observer, discovering the moons Iapetus, Rhea, Tethys and Dione between 1671 and 1684, as well as the large gap (1675) between the A and B rings now known as the Cassini Division. He also measured the rotation rate of Mars, determined the orbits of Jupiter's satellites, and created a complete and accurate map of the Moon.
Cassini had great skills as an organiser and in making science exciting to the public; he was also a first-class courtier in a patronage economy that valued novelty. In Bologna, he transformed a cathedral into an observatory, and in Paris he moved the Marly water tower to the Paris Observatory grounds for supporting very long telescopes. He personally supervised and participated in measuring the latitude and longitude of most French towns and villages. Though resistant to some new scientific ideas of his time, he and his sons and grandsons were a major presence at the Paris Observatory for almost 120 years.
Huygens, in addition to his cultural pursuits, also studied law and mathematics, and conducted experiments in mechanics and optics. Though his health was delicate, he was an accomplished dancer. Huygens discovered Saturn's large moon Titan in 1655, and was also the first to deduce (in 1656, but not reported until 1659) that Saturn was surrounded by a ring. He invented the pendulum clock, the first accurate time-keeping device, and was chosen as 'primus inter pares' ('first among equals') to organise the Academie Royale des Sciences in Paris when it was founded in 1666. Young scientists were often attracted by his brilliance, but Huygens preferred solitary contemplation to team efforts. His contributions to mathematics, astronomy, time measurement and the theory of light are considered to be of fundamental importance.
Christiaan Huygens (1629 - 1695) by Vaillant, (courtesy of Huygens museum Hofwyck, Voorburg, The Netherlands).
This view of Saturn's northern hemisphere, taken by Voyager-1 on 5 November 1980 from a range of 9 million km, shows a variety of cloud features. Small- scale convective clouds are visible in the brown belt; an isolated convective cloud with a dark ring is seen in the light brown zone; and a longitudinal wave is visible in the light-blue region. The smallest visible features are 175 km across. Such time-lapse sequences show how these storms evolve and allow the measurement of wind speeds. Winds blow mainly along lines of constant latitude on the gas giants. Near Saturn's equator, they blow eastward (with Saturn's rotation) at 500 m/s (Courtesy of JPL)
Although Saturn has been known since pre-historic times, its ring system was not discovered until the 17th Century, and much of what is now known came out of the Voyager flybys of 1980-81. Although its equatorial diameter is about 80% that of Jupiter, it has less than one third the mass, making it the only planet less dense than water (70%). Saturn's interior is suspected to be similar to Jupiter's, with a small rocky core, a liquid metallic hydrogen layer and a molecular hydrogen layer.
Saturn's hazy yellow hue is marked by broad atmospheric banding similar to, but less well defined than, that found on Jupiter. The atmosphere is primarily composed of hydrogen with a small amount of helium and traces of other gases (e.g. methane and ammonia). Near the equator, upper-atmosphere winds can reach 500 m/s, blowing mostly eastwards, but they appear to slow at higher latitudes. At latitudes beyond ±35*#176;, these winds can alternate east and west with increasing latitude.
Despite receiving only 1% or so of the sunlight that reaches the Earth, Saturn maintains a relatively high temperature. In fact, it radiates more heat than it receives. Some can be explained by Saturn's immense gravity compressing its interior (the Kelvin-Helmholtz mechanism), and by the condensation and 'raining out' of helium, which generates heat as the drops of liquid helium loose accumulated kinetic energy through friction with lower layers.
Saturn's northern hemisphere defined by bright features from 43 million km by Voyager-2 on 12 July 1981 (Courtesy of JPL)
Saturn Facts Mass (kg) 5.69x1026 Equatorial Diameter (km) 120 660 Mean density (kg/m3) 690 Escape velocity (m/s) 35 600 Average distance from Sun (AU) 9.539 Rotation period (length of day in Earth hours) 10.6 Revolution period (length of year in Earth years) 29.46 Obliquity (tilt of axis in degrees) 26.7 Orbit inclination (degrees) 2.49 Orbit eccentricity (deviation from circular) 0.056 Mean temperature (K) 88 (1 bar level) Core temperature (K) 12 000 Visual geometric albedo (reflectivity) 0.46 Atmospheric components 97% hydrogen 3% helium 0.05%methane
Saturn's system of rings and moons is vast, with rings labelled in order of discovery. The faint but far-reaching E-ring is many thousands of kilometres thick, but comprised mostly of micron-sized particles that are not a threat to Cassini (David Seal/JPL)
Though various discoveries have been made over the past 330 years, it was the remarkable images returned by Voyager-1 and 2 in 1980 and 1981 that really made a quantum leap forward in our understanding of the rings. Cassini will help to answer the many questions raised. Saturn's rings are a frigid cast of billions of particles and icebergs, ranging in size from that of fine dust to that of houses. The ring fragments are primarily loosely packed snowballs of water ice, but slight colourations suggest there to be small amounts of rocky material, possibly even traces of rust (iron oxide).
Although the distance from the inner edge of the C-ring to the outer edge of the A-ring is about 13 times the distance across the United States, the ring disc thickness is no more than 100 m (perhaps as small as 10 m!), with waves or 'corrugations' in this sheet rising and falling by a couple of kilometres. If a model of the ring sheet were to be made from material about the thickness of a coin, its diameter would need to be at least 15 km.
Numerous simple and complex patterns form within this rotating sea of icy fragments. They are variously described as circular rings, eccentric rings, clumpy rings, resonance gaps, spokes, spiral density waves, bending waves and shepherding moons. There are, no doubt, also tiny moonlets too small for the Voyager cameras to have detected. The elaborate choreography of this complex ring system of patterns is produced and orchestrated by the combined gravitational tugs from Saturn and its moons that lie beyond the ring sheet, as well as by the tiny tugs from and gentle collisions with neighbouring particles.
How did the rings form in the first place? If one could collect all of the ring particles and icebergs into a single sphere, its diameter would not exceed about 300 km - roughly midway between the sizes of the moons Mimas and Phoebe. Are the rings simply leftover material that never formed into larger bodies when Saturn and its moons condensed aeons ago? Or, as is believed from Voyager data, are they the relatively young (within the last 100 - 200 million years) shattered debris from one or more broken worlds? The subtle compositional variations suggest that more than one parent body was broken apart.
One explanation for the breakup argues that a body (either from within or outside of the Saturn system) passed close enough to the planet to be broken apart by tidal forces, but there would then need to be an energy-loss mechanism to allow the resulting fragments to be captured by Saturn. A more likely explanation attributes the breakup to impacts from meteoroids. If that theory is valid, small ring moons may still be awaiting disruption.
Numerous 'spoke' features appear in this Voyager-2 image of Saturn's rings. They are believed to arise from electromagnetic forces acting on charged dust grains that have been dislodged from ring bergs struck by meteoroids (Courtesy of JPL)
This view shows Titan's surface with Saturn dimly in the background through Titan's thick atmosphere of methane, ethane and (mostly) nitrogen. Cassini flies over with its HGA pointed at the Huygens Probe. Thin methane clouds dot the horizon and a narrow methane spring or 'methane fall' flows from the cliff at left and drifts mostly into vapour. Smooth ice features rise out of the methane/ethane lake and crater walls can be seen far in the distance (David Seal/JPL)
Titan is possibly the most unusual moon in the Solar System. Larger than Mercury, more massive than Pluto and only slightly less massive than Jupiter's largest moon Ganymede, it has an atmosphere for some reason yet unknown with a surface pressure 1.5 times that of Earth's at sea level. Although scientists had speculated that Titan had some sort of atmosphere, few were prepared for the layers of hazes and clouds that prevented Voyager from making detailed surface observations. The first hints of surface detail have come from the Hubble Space Telescope, which noted a relatively IR-bright region 4100 km across in the southern hemisphere.
Titan is denser than Saturn's other satellites, possibly due to gravitational compression. Its composition is not precisely known, although its density suggests mostly water ice. Whether it is differentiated into layers or whether there is a molten core is not yet known. No magnetosphere was discovered by Voyager, so Titan might be geologically inactive.
Titan's atmosphere is composed primarily of molecular nitrogen (as is Earth's) with no more than 1% argon and a few percent methane. There are also trace amounts of several other organic compounds (ethane, hydrogen cyanide, carbon dioxide, propane, acetylene, etc.). Other, more complex, chemicals in small quantities must be responsible for the orange colour as seen from space. It is suspected that the organics are formed as methane in the upper atmosphere is destroyed by sunlight. As high-energy particles and UV bombard the nitrogen and methane molecules in the upper atmosphere, these and further reactions could create a variety of organic molecules similar to the smog found over Earth's large cities, but much thicker. These molecules could then clump and rain slowly to the surface, where they may collect in pools, lakes or subsurface reservoirs.
In atmospheric terms, Titan is thought to represent conditions on the early Earth before life appeared. At the surface, Titan's temperature is a frigid 94 K. Water ice does not sublimate at this temperature and so any water at the surface should not be part of the atmospheric chemistry. Nevertheless, there appears to be some kind of complex chemistry going on. Though life in any form familiar to us is unlikely to exist, due to the extreme cold, Titan may still provide us with information that could apply to the chemistry of early Earth.
It has been speculated that methane clouds produce a rain of liquid methane, resulting in large bodies of a liquid ethane/methane mixture up to 1 km deep. However, recent ground-based radar and Hubble Space Telescope observations make it clear that such global oceans are unlikely.
This Voyager-2 photograph of Titan, taken on 23 August 1981 from 2.3 million km, shows some detail in the cloud systems. The southern hemisphere appears lighter in contrast, a well-defined band is seen near the equator, and a dark collar is evident at the north pole. All of these bands are associated with cloud circulation in Titan's atmosphere. The extended haze, composed of submicron-size particles, is seen clearly around the satellite's limb (Courtesy of JPL)
The bright surface of icy Enceladus. In the foreground, an ice geyser projects a vapour jet into space. Enceladus may be the source of the E-ring (which can be very faintly seen along Saturn's equatorial plane); icy geysers may sustain the ring's supply of micron-sized particles (David Seal/JPL)
All of Saturn's moons are likely primarily water ice with some rocky material, with the sizes and surface characteristics differing greatly, indicating widely ranging conditions during their formation and early existence. Some of the smaller irregular moons, such as Hyperion, might be the remnants of a larger satellite. Others inhabit the rings themselves, and might be leftovers from the cataclysms that created the rings.
Most of the moons for which the rotation rates are known orbit synchronously, keeping one face towards Saturn. This frequently leads to a dramatic difference between the leading and trailing hemispheres. Iapetus has an extremely dark leading hemisphere, and a brightly reflective trailing hemisphere. This dichotomy was first noted by Cassini, who observed that the satellite was visible only on one side of its orbit. Dione is remarkably free of large impact craters on its trailing hemisphere, probably due to a combination of being sheltered from impact gardening and the escape of icy fluids onto the surface through cracks in the crust, leaving the giant crisscrossing, wispy, bright marks observed by Voyager. Rhea shares many of Dione's characteristics.
Enceladus also shows the results of some kind of icy volcanism, with relatively smooth regions interrupting the otherwise cratered terrain. In addition, linear sets of grooves over 100 km long traverse the surface, probably due to faulting caused by crustal deformation, implying that Enceladus may have undergone relatively recent internal melting. Its relatively new surface makes it the brightest of Saturn's moons.
All of the moons show some level of impact cratering, with Mimas being perhaps the most dramatic example. The large impact crater Herschel on Mimas (130 km diameter) was the result of a collision that nearly shattered the moon. Tethys also boasts an immense (400 km) crater. Tethys must have been at least partly liquid to absorb the impact without breaking up. It is speculated that many of the moons may have been shattered and gravitationally reassembled many times in their early geological history. Tethys contains Ithaca Chasma, a huge trench, 100 km wide, stretching across three quarters of its circumference. This feature may have been formed when Tethys solidified and expanded, cracking the crust.
There are complex gravitational tidal resonances between some of Saturn's moons, each other and the ring system. The 'shepherding satellites' - Atlas, Prometheus and Pandora - appear to help keep the rings in place. Mimas may be responsible for the lack of material in the Cassini Division. Pan is in the Encke Gap. Tethys has Telesto and Calypso caught in the region of its Lagrange points. Helene orbits in Dione's leading Lagrange point. Janus and Epimetheus also nearly share an orbit, apparently switching places every four years or so.
Three pairs of moons - Mimas-Tethys, Enceladus-Dione and Titan-Hyperion - maintain stable relationships between their orbits, due to their gravitational interaction. The ratio of Mimas' orbital period to Tethys' is 2:1, as is Enceladus:Dione. Titan's and Hyperion's orbits are in a 3:4 resonance. These resonances can result in tidal heating of the moons, although it is not believed that this process alone could account for the icy volcanism that may exist on Enceladus.
While the majority of Saturn's moons orbit nearly in the plane of its equator, Iapetus' orbit is inclined almost 15°. Phoebe's orbit is upside down, with an inclination of almost 175°. It is possible that Phoebe may be a captured asteroid or a comet remnant.
In addition to the 18 named satellites, at least a dozen more have been reported and given provisional designations, although none has yet been confirmed.
Some of the interesting variety among Saturn's many known icy satellites is revealed in these Voyager-2 images. Enceladus' bright, relatively uncratered terrain is coated with water ice. The smooth areas suggest that internal heating has melted portions of the surface, possibly even leading to eruptions feeding Saturn's tenuous E-ring. Iapetus, on the other hand, has a leading face as dark as asphalt, while its trailing face is six times brighter. The dark side is presumably some type of carbon-based material, but was it swept up as the moon orbited Saturn or did it rise from the moon's interior? (Courtesy of JPL)
Saturn's magnetosphere and its major features (Courtesy of Univ of Michigan)
Saturn's magnetic field is probably generated by the planet's rotating layer of liquid metallic hydrogen. Equatorial ring currents as high as 107 A flow inside the resulting magnetosphere. The magnetic field is about 0.21 gauss at the cloud tops. Unlike most planets with magnetic fields, however, Saturn's dipole lies within 1° of its spin axis. This has important implications because dynamo theory requires some offset to permit regeneration of the magnetic field. Other Cassini objectives are to improve understanding of the source of the planet's intermittent radio bursts, as well as the many interactions among Saturn's magnetic field and the rings, moons and solar wind.
In this cover design for Cassini's DVD carrying 616400 signatures from 81 different countries, elements include flags, Earth, Saturn, Titan, spacecraft, probe, and Golden Eagle feathers (symbolic of the beauty and power of flight, as well as the quill pen used in writing for almost 14 centuries). Design by Charley Kohlhase (JPL)
The Cassini project maintains websites at http://www.jpl.nasa.gov/cassini/ and http://www.estec.esa.nl/spdww/huygens/html/. The sites also carry details of other material: videos, three 20-slide sets, a newsletter and an historical brochure and poster.
Educational products include a Teacher Guide (US grade levels 5-8), two interactive CD-ROMs (one on Saturn and the other on sensor 'ways of seeing'), a NASA special publication on what we know and hope to learn about the Saturnian system, and a 23-min computer animation depicting the journey of a photon from the Sun's core to Mimas, from there into Cassini's optics and through the spacecraft circuitry, and finally down to Earth where it is ultimately received by the brain of a young observer seeing this icy moon for the first time.
For community relations, the most dramatic product is the Digital Versatile Disk (DVD) containing over 616 400 signatures from 81 different countries. People of all ages mailed their signatures to JPL to be delivered to Saturn. ESA separately collected 100 000 signatures and messages for a CD-ROM attached to Huygens' Descent Module. | 0.856007 | 3.57742 |
The mundane facts of finance continue to threaten our far-flung Voyager spacecraft as NASA looks for dollars to keep the missions alive. Adding further significance to the issue is the upcoming news conference on May 24, in which Voyager scientists will present information that has led them to conclude Voyager 1 has reached the heliosheath — that area between 80 and 100 AU from the Sun just inside the boundaries of the heliosphere.
The heliosphere is that region carved out by the solar wind from the Sun within the larger interstellar medium. The ‘termination shock’ is the zone where the solar wind is slowed by interstellar gas, dropping abruptly from its 300 to 700 kilometer per second velocity (the solar wind seems to change in speed and pressure, causing the termination shock to expand and contract). Having apparently exited the termination shock, Voyager 1 is in the heliosheath, on its way to the outer boundary of the Sun’s magnetic field and solar wind.
What tells us that Voyager 1 has entered the heliosheath? On December 17, 2004, at a distance of 94 AU, the spacecraft noted an increase in the strength of the magnetic fields around it; particle beams in the area reversed direction and became steady in strength, markers of the passage. More on this on Tuesday, when we will also hear about “…some puzzling and unexpected aspects of these observations…” and predictions about what comes next. All this takes place within the context of the American Geophysical Union’s 2005 Joint Assembly, which runs from May 23 to 27 in New Orleans.
These findings, of course, are all the more reason we must find a way to sustain funding for the Voyagers. But the NASA budget crunch doesn’t stop here. NASA administrator Michael D. Griffin has sent a letter to Congress noting the agency’s $2 billion shortfall in the current year. Among the undesirable effects of the budget squeeze may be to stretch the timelines of both the Space Interferometry Mission (currently scheduled for 2011 launch) and Terrestrial Planet Finder (2012-2015).
The worst problem of all may be cutbacks and a delay in the launch of the James Webb Space Telescope, a 6.5-meter infrared observatory designed to study the earliest galaxies. The JWST is being jointly developed by NASA, the European Space Agency and the Canadian Space Agency. The delay would set the telescope’s launch back at least to 2012, with possible increases to mission costs also coming into the picture. The Webb telescope’s current budget is $3.5 billion.
Image: Artist’s conception of the James Webb Space Telescope. Credit: TRW and Ball Aerospace.
According to Sky & Telescope, NASA is now asking the project to consider a scaled-down JWST, perhaps a 4-meter telescope with fewer instruments. It is hard to see how such a minimized telescope could be justified, given the rapid increases in giant ground-based telescopes that could outperform it.
Science Magazine has a news feature on this story: “NASA Astronomy: New Space Telescope May Be Scaled Back,” Science 308 (2005), p. 935. And note this story from the Rocky Mountain News, seen through the eyes of JWST subcontractor Ball Aerospace & Technology. From the story:
“I’d say it is a crisis,” said John Mather, project scientist for the telescope at NASA’s Goddard Space Flight Center in Maryland.
“(NASA) headquarters just doesn’t have any more money for us,” Mather said. “Something’s got to give, but we don’t know what it’s going to be.”
Centauri Dreams‘ note: A panel of astronomers is to meet over the next two months to rank the JWST’s science priorities, but it’s hard to see how cutting deeply into the mission can avoid having a catastrophic effect on this successor to Hubble. Yes, it could still do good science, but its original mission goals (the study of galaxies that first appeared as early as 200 million years after the universe formed) would have to be abandoned because they’re based on the larger instrument. In what may now be seen as an ironic twist, the National Academy of Sciences has ranked the JWST as the most important NASA science project of the decade. Let’s hope it stays that way. | 0.888072 | 3.01724 |
After eight years of study, NASA has approved the construction of an unmanned satellite that will scan the entire sky in infrared light to reveal nearby cool stars, planetary "construction zones" and the brightest galaxies in the universe. Launch of the Wide-field Infrared Survey Explorer (WISE) -- the second phase of the WISE mission -- is scheduled for late 2009. The satellite will orbit the Earth and operate for at least seven months, with data expected a few times a day.
Edward L. (Ned) Wright, UCLA professor of physics and astronomy, is WISE's principal investigator. NASA's Jet Propulsion Laboratory in Pasadena will manage the mission, with JPL's William Irace as project manager.
Like a powerful set of night-vision goggles, WISE will survey the cosmos with infrared detectors 500 times more sensitive than those used in previous survey missions.
"This mission has incredible power for discovery," Wright said. "I expect that what we find will be amazing. There is still so much we don't know."
Wright said that 99 percent of the sky has not been observed yet with this kind of sensitivity, and that the survey should be able to find and observe at least 100 million galaxies and hundreds of nearby cool stars that are currently unknown.
"Approximately two-thirds of nearby stars are too cool to be detected with visible light," Wright said. "WISE will see most of them."
He added that proto-planetary discs around stars presumably condensing into a planetary system show up in the infrared. "Several have been detected, and we will be able to see many more in the Milky Way galaxy," Wright said. "In addition, we will be able to study star-forming regions in nearby galaxies and star formation in distant galaxies."
Such extensive sky coverage means that the mission will find and catalogue all sorts of celestial eccentrics, including perhaps elusive brown dwarfs close to the Earth. Brown dwarfs, the missing link between gas giant planets like Jupiter and small, low-mass stars, are failed stars about the size of Jupiter, with a much larger mass. They can be detected best in the infrared, but even within the infrared are very difficult to detect.
"Brown dwarfs are lurking all around us," said Peter Eisenhardt, project scientist for WISE and JPL. "We believe there are more brown dwarfs than stars in the universe, but we haven't found them because they are faint."
Galaxies in the distant, or early, universe were much brighter and dustier than our Milky Way galaxy. Their dusty coats light up in infrared wavelengths.
"It's hard to find the most energetic galaxies if you don't know where to look," Eisenhardt said. "We're going to look everywhere."
WISE will also provide a complete inventory of dusty planet-forming discs around nearby stars, and find colliding galaxies that emit more light, specifically infrared light, than any other galaxies in the universe. WISE is expected to produce more than 1 million images, from which hundreds of millions of space objects will be catalogued.
WISE may be able to confirm the existence of dark energy, which scientists believe comprises more than 70 percent of the universe, and which Albert Einstein postulated in 1917. Einstein later believed that to be a serious blunder, but it looks like he was correct, Wright said.
The cryogenic instrument will be built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft will be built by Ball Aerospace and Technologies Corporation in Boulder, Colo. Science operations and data processing will take place at the JPL/Caltech Infrared Processing and Analysis Center.
Wright; John Mather, chief scientist for the James Webb Space Telescope, and NASA's Cosmic Background Explorer (COBE) team were jointly awarded the 2006 Gruber Cosmology Prize in August for their research confirming that our universe was born in a hot Big Bang; Mather also shared the 2006 Nobel Prize in Physics. The instruments aboard COBE, launched in 1989, looked back over 13 billion years to the early universe. COBE showed that the young universe was hot, dense and almost uniform; that it contained weak fluctuations or lumps that grew into the galaxies and stars we see today; that these fluctuations were the consequence of a hot Big Bang, and that the universe is filled with diffuse radiation from previously unknown galaxies.
For more information about the WISE mission, visit wise.ssl.berkeley.edu/
Source: University of California - Los Angeles
Explore further: Photosynthesis under light conditions different from the Earth | 0.868141 | 3.875871 |
A planetary nebula is a nebula that is made up of gas and plasma. They are made by certain types of stars when they die. They are named this because they look like planets through small optical telescopes. They do not last for very long compared to a star, only tens of thousands of years.
At the end of a normal-sized star's life, in the red giant phase, the outside layers of a star are disposed of. Because the outside is gone, the star shines brightly and is very hot. The ultraviolet radiation given off by the center of the star ionizes the gas and plasma that was thrown out from the star. This is what causes a planetary nebula to look like it does.
Planetary nebulae are very special objects because they can help make more stars. When a star dies, the metals that were in the core of the star are sent to other places in the universe. The only place that these metals form are in stars. This is called nucleosynthesis.
The pictures of these nebulae show that they have very weird shapes. Scientists are not sure why they are not all spheres. There are many theories about why they are not. They think that binary stars, stellar winds and magnetic fields might be part of the reason they look so special.[source?]
Observations[change | change source]
Planetary nebula are not very bright. None of them are bright enough to see without a telescope. The first one discovered was the Dumbbell Nebula. To early astronomers they looked like gas giants. This is why people called them 'planetary nebula'. We still call them this even though we know they are not planets. Astronomers did not know what these objects were until the first spectroscopic experiments were done in the 1800's. William Huggins used a prism to look at galaxies. He noticed that they looked a lot like stars.
When he looked at the Cat's Eye Nebula, it did not look the same. He saw an emission line at a place that no one had seen before. This meant that it looked like an element that no one had ever seen before. Scientists thought it might be a new element. They decided to call it nebulium.
The stars in planetary nebulae are very hot. They are not very bright, though. This means that they must be very small. The only time that stars get that small is when they are dying. That means that they are one of the last steps in a star's death. Astronomers saw that all planetary nebula are expanding. This meant that they were caused by a star's outer layers being thrown into space at the end of its life.
Origins[change | change source]
Stars weighing more than 8 solar masses will supernova. Stars that weigh as much as the Sun will become planetary nebulae. After billions of years, a star will run out of hydrogen. This makes the star colder, and makes the core smaller. The sun's core is about 15 million degrees Kelvin. When it runs out of hydrogen, the smaller core will cause it to rise to about 100 million degrees Kelvin.
The outer layers of the star grow a lot because of the heat of the core, and become much cooler. The star becomes a red giant. The core gets even smaller and hotter. When its reaches 100 million K, helium begins to fuse into carbon and oxygen. When this happens, the core stops shrinking. Helium burning soon forms a core of carbon and oxygen, with both a helium and a hydrogen shell surrounding it.
Because helium in fusion reactions is not very stable, the core starts to grow and shrink very quickly. Strong Stellar winds blow the gas and plasma in the outer layer of the star outwards. These gases form a cloud around the core of the star. As more and more of the gas moves away from the star, deeper and deeper layers at higher and higher temperatures are sent out. When the gas heats up to around 30,000 degrees kelvin, the gas starts to glow. The cloud has then become a planetary nebula.
Numbers and where they are[change | change source]
We now know of about 3,000 of these nebulae in our galaxy, compared to 200 billion stars. Their very short lifetime compared to a star is why there are not that many compared to stars. They are found mostly in the plane of the Milky Way, and there are more and more the closer you get to the center of the Milky Way.
Shape[change | change source]
Only about twenty percent of planetary nebulae are spheres (like Abell 39). The rest of them have very weird shapes. The reason for all of these shapes is not understood, but it may be because of gravity with secondary stars if it is a binary star system. A second theory is that planets near the star might change how the nebula forms. A third theory is that magnetic fields cause the shapes. .
Problems[change | change source]
A big problem in studying planetary nebulae is that astronomers can not always figure out how far away they are. When they are close, astronomers use something called expansion parallax to figure out how far away they are, but this takes a long time. If they are not close, there is not a good way to figure out how far away they are yet.
Related pages[change | change source]
References[change | change source]
- Hubble Witnesses the Final Blaze of Glory of Sun-Like Stars, Hubblesite.org, 1997-12-17. Retrieved 2008-08-09
- Huggins W., Miller W.A. (1864). On the Spectra of some of the Nebulae, Philosophical Transactions of the Royal Society of London, 154, 437
- Bowen, I.S. (1927). The Origin of the Chief Nebular Lines, Publications of the Astronomical Society of the Pacific, 39, 295
- Parker Q.A, et al. (2006), The Macquarie/AAO/Strasbourg H-alpha Planetary Nebulae Catalogue: MASH, MNRAS, 373, 79
- Majaess D. J., Turner D., Lane D. (2007). In Search of Possible Associations between Planetary Nebulae and Open Clusters, PASP, 119, 1349
- Reed, D.S., Balick, B., Hajian, A.R. et al. (1999). Hubble Space Telescope Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution, Astronomical Journal, 118, 2430
Other websites[change | change source]
- Entry in the Encyclopedia of Astrobiology, Astronomy, and Spaceflight
- Press release on recent observations of the Cat's Eye Nebula
- Planetary Nebulae, SEDS Messier Pages
- The first detection of magnetic fields in the central stars of four planetary nebulae
- WWW Search for Galactic Planetary Nebulae
- Planetary Nebulae - Information and amateur observations
- Planetary nebula on arxiv.org | 0.895848 | 3.57687 |
After analyzing the data obtained with the Hubble space telescope and other space observatories, astrophysicists came to the conclusion that the observable Universe there are trillions of galaxies. Previously it was assumed that they, at least, ten times smaller — from 100 to 200 billion.
“Observed” refers to the part of the Universe, the radiation from which could reach Earth during the existence of the cosmos. That starry sky reports, not all its wealth, scientists have known since then as “the Hubble” found an incredible amount of dim galaxies are totally invisible to the less sophisticated devices. In the mid 90-ies of the last century, scientists came to the conclusion that the number of galaxies in the observable Universe hundreds of billions, but new data indicate that even these estimates are considered overly cautious.
The researchers compared the data obtained by modern space observatories, and compiled them with the help of special mathematical and three-dimensional models. As a result, scientists came to the conclusion that at the present stage of technology allows us to see only about 10 per cent of the observable Universe of galaxies, while the vast majority of them remain too dim to be discovered by mankind. Scientists suggest that in the future, more advanced telescopes will allow us to confirm their conclusions.
Telescope “Hubble” was launched from Cape Canaveral on 24 April 1990. According to some experts (in particular, NASA astronaut Tom Jones), this event, along with the launch of the International space station, can be considered one of the key events in the history of space exploration over the past few decades. Due to the lack of impact of the atmosphere resolution of the telescope is 7-10 times more than a similar telescope on the Earth. | 0.827366 | 3.429112 |
One of the newest fastest things in our universe was accidentally discovered in 2014, when astronomers were studying the M87 galaxy in the Virgo Cluster nearly 54 million light-years from our Milky Way home.
A little background: You'll remember, thanks to Edwin Hubble, that light from distant objects moving away from our galaxy appears red to us. That's because the universe's expansion, also a pretty speedy phenomenon, causes the wavelengths to elongate toward the red end of the spectrum (a redshift).
As an object zips toward us, however, it has a blueshift. Now, to get to the fast part: Astronomers found a serious blueshift coming from M87, with the object moving toward us at a speed of 638 miles (1,026 kilometers) per second [source: Crosswell].
Scientists believe it's a star cluster shot out from M87's enormous black hole, which is 1,000 times more massive than the Milky Way's. But never fear: It's very unlikely that its trajectory will bring it close to us, and it'll probably end up just hanging out in a group of galaxies outside the Virgo Cluster. | 0.815966 | 3.210244 |
If there’s sibling rivalry in the nearby cosmos, the Moon must be feeling a lot of it these days. Last week, Mercury was the big story, with the discovery of ice and organic molecules on its sun-blasted surface. This week it’s Mars, thanks, maddeningly enough, to the non-discovery of signs of life by the Curiosity rover. Even the hoary Voyager 1 space probe, whose official mission ended three decades ago, is making news simply by leaving the building.
But now, finally, the Moon is getting some love. Three separate studies of Earth’s cratered companion are being published today in Sciencexpress, the online version of the journal Science, and they’re revealing the moon’s geography and geology (or more properly, selenology) with a precision that’s never been seen before — including a totally unsuspected web of subsurface cracks that crisscross the entire lunar body. It is, exults MIT’s Maria Zuber, lead author of the main paper, “absolutely transformative.”
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That transformation comes courtesy of the GRAIL lunar probe — or rather, probes, since the Gravity Recovery and Interior Laboratory is actually a pair of satellites, informally known as Ebb and Flow, which have been orbiting the Moon in tandem for almost a year now. When they fly over a larger mass of moon below — a mountain, say, or even even a dense concentration of rock beneath the surface — the excess gravity pulls the lead satellite a little harder, widening the gap between the two. When they come across a deficit of material, such as a crater, the lead satellite slows a bit and the gap shrinks.
These changes are almost absurdly tiny. “We’re measuring changes in velocity of .05 microns per second,” says Zuber, who serves as the mission’s principal investigator. “That’s five times better than we expected, and I calculated that it’s about 1/20,000th the speed of a snail.”
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The GRAILs whip across the Moon’s surface at an average altitude of 34 miles (55 km), and sometimes as low as six (9.7 km). Proximity to the ground lets the satellites make extraordinarily high resolution maps of the Moon’s surface features — and surprisingly, those features account for about 98% of the gravity anomalies the satellites picked up, with only 2% coming from subsurface density variations. “That’s unlike anything we’ve measured for other terrestrial [i.e., rocky] planets,” says Zuber.
What it suggests is that the Moon’s surface was so violently bombarded by asteroid impacts in the first billion years of the Solar System’s history that the crust was thoroughly pulverized and homogenized to a depth of several miles. “We knew it was a violent period,” says Zuber, “but now we can quantify that pretty precisely.” The same bombardment must have affected the Earth. “It makes your head spin,” she says, “thinking of the implications for the development of life [at around that time]. The more you look, the more respect you have for biology”
The 2% of underground gravity variation GRAIL saw was in large part due to a network of enormous subsurface cracks up to 300 miles (483 km) long and up to 25 miles (40 km) wide. “They’re amazingly straight,” says Jeffrey Andrews-Hanna of the Colorado School of Mines, lead author of the second paper. “We’ve never seen them in any other data set.”
The cracks, like the homogenous surface, are artifacts of the moon’s earliest days, but they formed in an entirely different way. According to the leading theory of our satellite’s origin, Earth was slammed by a Mars-size planetoid eons ago. The impact vaporized the smaller object along with a significant chunk of Earth’s surface, creating a ring of rocky material orbiting our young —and now wounded — planet.
As the Earth healed, the ring gradually coalesced to form the Moon — at first comparatively gently, as chunks of rock and dust banged into each other, but with increasing violence as the growing Moon’s gravity got stronger and stronger. The interior was relatively cool to start, while the collision-heated exterior was hot. But then the outside cooled and the core warmed up under the pressure of all that overlying rock. “The interior starts to expand,” says Andrews-Hanna, “and the exterior cracks.”
In a final formative step, the cracks filled with magma, which was denser than the surrounding rock and thus would have a different gravitational tug — a tug which would be detectable in the event that, four billion years later, a species on the nearby Earth sent up a pair of spacecraft to study such things. “We didn’t predict these at all,” says Andrews-Hanna. “That’s an important part of science — you don’t send out a probe to confirm what you know. You send it to be surprised. You expect to see what you don’t expect.”
It doesn’t always turn out that way, of course. The third paper in the trio uses GRAIL data to characterize the overall properties of the Moon’s crust, and here, the observations do confirm what planetary scientists think they know. The giant-impactor theory of the Moon’s formation implies that both Earth and Moon should be made of pretty much the same stuff. The Moon’s overall crustal density suggests that in fact they are.
Impressive as these findings are, these are likely to be just the first of many extraordinary discoveries GRAIL will be making. “We’re really just in the initial stages,” Zuber says. “Our understanding of the Moon is starting to fit together, and we’ve added something to the story. But there’s a lot to come.” | 0.891522 | 3.836171 |
left, in order of increasing distance from the planet, they
are Miranda, Ariel, Umbriel, Titania and Oberon. (Click
on the image for a larger view)
2 obtained clear, high-resolution images of each of the
five large moons of Uranus known before the encounter: Miranda,
Ariel, Umbriel, Titania and Oberon. The two largest, Titania
and Oberon, are about 1,600 kilometers (1,000 miles) in
diameter, roughly half the size of Earth's Moon. The smallest,
Miranda, is only 500 kilometers (300 miles) across, or just
one-seventh the lunar size.
10 new moons discovered by Voyager bring the total number
of known Uranian satellites to 15. The largest of the newly
detected moons, named Puck, is about 150 kilometers
(about 90 miles) in diameter, or larger than most asteroids.
analysis shows that the five large moons are ice-rock conglomerates
like the satellites of Saturn. The large Uranian moons appear,
in fact, to be about 50 percent water ice, 20 percent carbon-
and nitrogen-based materials, and 30 percent rock. Their
surfaces, almost uniformly dark gray incolor, display varying
degrees of geologic history. Very ancient, heavily cratered
surfaces are apparent on some of the moons, while others
show strong evidence of internal geologic activity.
for example, is marked by huge fault systems and canyons
that indicate some degree of geologic activity in its history.
These features may be the result of tectonic movement in
its crust. Ariel has the brightest and possibly the
geologically youngest surface in the Uranian moon system.
It is largely devoid of craters greater than about 50 kilometers
(30 miles) in diameter. This indicates that low-velocity
material within the Uranian system itself peppered the surface,
helping to obliterate larger, older craters. Ariel also
appears to have undergone a period of even more intense
activity leading to many fault valleys and what appear to
be extensive flows of icy material. Where many of the larger
valleys intersect, their surfaces are smooth; this could
indicate that the valley floors have been covered with younger
is ancient and dark, apparently having undergone little
geologic activity. Large craters pockmark its surface. The
darkness of Umbriel's surface may be due to a coating of
dust and small debris somehow created near and confined
to the vicinity of that moon's orbit.
outermost of the pre-Voyager moons, Oberon, also
has an old, heavily cratered surface with little evidence
of internal activity other than some unknown dark material
apparently covering the floors of many craters.
, innermost of the five large moons, is one of the strangest
bodies yet observed in the solar system. Voyager images,
which showed some areas of the moon at resolutions of a
kilometer or less, consists of huge fault canyons as deep
as 20 kilometers (12 miles), terraced layers and a mixture
of old and young surfaces. The younger regions may have
been produced by incomplete differentiation of the moon,
a process in which upwelling of lighter material surfaced
in limited areas. Alternatively, Miranda may be a reaggregation
of material from an earlier time when the moon was fractured
into pieces by a violent impact.
Miranda's small size and low temperature (-335 degrees Fahrenheit
or -187 Celsius), the degree and diversity of the tectonic
activity on this moon has surprised scientists. It is believed
that an additional heat source such as tidal heating caused
by the gravitational tug of Uranus must have been involved.
In addition, some means must have mobilized the flow of
icy material at low temperatures. | 0.878005 | 3.902834 |
Tonight – April 20, 2017 – the Lyrid meteor shower is picking up steam. We expect some Lyrid meteors to fly between late evening on Thursday, April 20 until dawn Friday, April 21. And we anticipate Friday night until dawn Saturday being even better. On both nights, try watching in the few hours before dawn. That’s when the radiant point – near the star Vega in the constellation Lyra – is highest in the sky. For that reason, it’s when you’re likely to see the most meteors.
Note for Southern Hemisphere observers: Because this shower’s radiant point is so far north on the sky’s dome, you’ll see fewer Lyrid meteors. But you might see some! Try watching between midnight and dawn on April 22.
On a dark night, this shower typically offers about 10 to 15 meteors per hour at its peak. Fortunately, in 2017, the waning crescent moon should enhance the show, more than it intrudes on it.
The shower’s radiant point is just to the right of beautiful blue-white Vega, which is the brightest light in the constellation Lyra the Harp. Vega will be bright enough to overcome the glare of some light-polluted cities. What’s a radiant point? If you trace the paths of these Lyrid meteors backward on the sky’s dome, you’ll find that they appear to originate from near Vega, which is the heavens’ 5th brightest star.
It’s from Vega’s constellation Lyra that the Lyrid meteor shower takes its name.
You don’t need to identify Vega in order to watch the Lyrid meteor shower. The meteors radiant from a point near this star, but they’ll appear unexpectedly, in any and all parts of the sky.
However, knowing the rising time of the radiant point helps you know when the shower is best in your sky. Assuming you’re in the Northern Hemisphere, Vega rises above your local horizon – in the northeast – around 9 to 10 p.m. local time. It climbs upward through the night.
The higher Vega climbs into the sky, the more meteors you’re likely to see. By midnight, Vega is high enough in the sky that meteors radiating from her direction streak across your sky. Just before dawn, Vega and the radiant point shine high overhead, and the meteors will be raining down from the top of the sky (assuming you’re in the Northern Hemisphere).
Why do the meteors radiate from a single part of the sky? The radiant point of a meteor shower marks the direction in space – as viewed from Earth – where Earth’s orbit intersects the orbit of a comet. In the case of the Lyrids, the comet is Comet Thatcher. This comet is considered the “parent” of the Lyrid meteors. Like all comets, it’s a fragile icy body that litters its orbit with debris. When the bits of debris enter Earth’s atmosphere, they spread out a bit before they grow hot enough (due to friction with the air) to be seen. So meteors in annual showers are typically seen over a wide area centered on the radiant, but not precisely at the radiant.
Only 10 to 15 meteors per hour doesn’t sound like many. But even an hour under a still, dark sky – raining down a dozen or so meteors – is a treat. Plus, the April Lyrids can surprise you. They’re known to have outburts of several times the usual number – perhaps up to 60 an hour or so – on rare occasions. Meteor outburts aren’t always predictable. So – like a fisherman – you’ll want your lawn chair, a thermos of something to drink, whatever other gear you feel you need – and then you need to wait. Not a bad gig.
Bottom line: On any clear night around April 20-23, 2017, the Lyrid meteor shower will kick off at late evening. In 2017, the peak numbers of Lyrid meteors are expected to light up the wee hours before dawn on April 22. | 0.853787 | 3.584214 |
Stephen Kane, a physics and astronomy professor at SF State, and his team have discovered and constructed a thermal image map of a new planet, named 55 Cancri. The new planet is the first of its kind to be discovered and draws striking similarities to Earth.
55 Cancri is a terrestrial planet, which means it has a rocky surface, and is slightly bigger than Earth. No other planet like that exists in our solar system. The new planet, not in our solar system, makes a complete rotation around its sun in 18 hours. As the planet circles swiftly around its sun, it does not tilt on an axis the way Earth does.
“It doesn’t actually rotate when it is going around the star,” Kane said. “It’s so close to its star that it’s tidally locked in the same way the moon is tidally locked to the Earth.”
Because 55 Cancri doesn’t spin as it orbits its sun, only one side of the planet is exposed at all times to the direct heat of its star. This makes one side of the planet significantly hotter than the other, even though the entire planet is more than 1,000 degrees Celsius.
NASA helped with the development of the animation used to represent the planet once Kane and his team created the thermal map. Once the imaging of the planet was complete studies of the composition revealed what the terrestrial planet had on its surface.
“The temperature difference (in the imaging) is actually a result of lava,” Kane said.
The thermal mapping of 55 Cancri also revealed that the planet at one time had an atmosphere. However the orbit of the star has since depleted it.
“Its atmosphere has literally been stripped away from it by the intense amount of energy it receives from its star,” Kane said. “The atmosphere has just been blown away.”
Patrizah Amil, an SF State microbiology major, was interested in the parallels between 55 Cancri and Earth, and the potential state of our atmosphere.
“I think it was really cool that Professor Kane was able to find and map a planet through thermal imaging,” Amil said. “Especially seeing how that can pertain to the planets that already exist, maybe we are headed in the same direction.”
Since there aren’t any other planets like this in our solar system, astronomers know little about terrestrial planets that are slightly bigger than Earth. The next planet that is larger than Earth is Neptune, and it’s a gaseous planet. The studying of 55 Cancri can help understand more about the universe.
“These kinds of planets are a big big mystery to us,” Kane said. “So it will tell us a lot about something for which we don’t have any analog in our own solar system. It tells us what happens if you move a planet very very close to the star that it’s orbiting.”
Students at SF State are excited to hear about the new planet and elated to hear that a professor from campus was a part of the discovery.
“I think that this is amazing, personally,” said Jordan Beaston, a microbiology major. “And I think it’s super cool that somebody on our faculty was involved.”
The discovery and imaging of this planet is a culmination of effort five years in the making. Analysis of the cause and effects of the atmosphere on 55 Cancri will aid in the understanding of the Earth’s atmosphere. According to Kane, since it has already lost its atmosphere and is evaporating, the planet will either be eroded or broken apart.
Watch a visualization of the atmosphere surrounding 55 Cancri here. | 0.829033 | 3.734392 |
When 100 years ago Einstein predicted gravitational waves, he was in a debate with himself. How would you prove something that is not only invisible, but so difficult to detect? Earlier this year, in 2016, scientists of LIGO (The Laser Interferometer Gravitational-Wave Observatory) announced to the world one of the major discoveries of the century: the existence of gravitational waves, which opened a new door into space exploration. Since 1998 scientists of ESA (The European Space Agency) have been working on a mission called LISA Pathfinder, which is designed to explore the technology to detect gravitational waves from space. The first spacecraft was launched on December 3, 2015, before LIGO's official announcement. This extraordinary mission inspired Ekaterina to create a ceramic sculpture.
At the essence of the LISA Pathfinder project are two perfect gold-platinum cubes that are free-falling through the fabric of space. With an ultra-precise laser measuring system on board of LISA Pathfinder, the slightest changes in the flow of the cubes caused by the solar wind, pressure of sunlight or other forces will be measured to determine how still they really can be in space. In a future space mission, such still cubes will be separated by millions of km so that any minute changes in their flow effected by the gravitational waves will be detected.
In this sculpture you will find gold cubes of the original size of the space mission (46 mm or 1.8”) that are floating on gravitational waves.
Study more: LISA Pathfinder sci.esa.int/lisa-pathfinder
Ceramic gold cubes are hand-built replicas of those found on the LISA Pathfinder spacecraft. To achieve the exact size of 46mm (1.8") per side was very challenging due to the nature of shrinking ceramics during firings.
Blog: working on the sculpture | 0.819392 | 3.101947 |
Astronomers from the University of Texas at Austin and Harvard University tested the main property of black holes, showing that the matter absorbed by them completely disappears. According to the results of the research, the general theory of relativity of Albert Einstein successfully withstood the next test for truth.
Most scientists agree that black holes, surrounded by the so-called event horizon, have such a strong gravity that no object will pass their “mouth.” When matter or energy approaches a black hole, it is inevitably absorbed by it. Although it is widely believed that the existence of the horizons of events is not proven.
“We want to turn the idea of the event horizon into experimental science and find out whether they really exist,” said Professor of Astrophysics Pavan Kumar.
It is believed that supermassive black holes lie in the heart of almost all galaxies. But some theorists suggest that instead of them there is something else – not a black hole, but an even more amazing supermassive object that somehow managed to avoid the gravitational collapse to a singularity, surrounded by the horizon of events. The idea is based on modified theories: the general theory of relativity and the theory of gravity of Einstein.
While the singularity does not have a surface, a collapsed object will have a hard surface. Thus, a material, for example a star, is drawn closer, but does not enter a black hole, but crashes into this hard surface and collapses.
Kumar, his graduate student Venbin Lou and Ramesh Narayan, a theorist at the Harvard-Smithsonian Center for Astrophysics, came up with a test to determine which of the ideas was correct.
“Our motive is not so much to establish that there is a solid surface, how much to expand our knowledge and to find concrete evidence of the existence of a horizon of events around black holes,” Kumar said.
The team found out that they would see the telescope when the star struck the solid surface of a supermassive object in the center of a nearby galaxy: the gas of the star would envelop the object and it would shine for months or maybe years.
As soon as they learned what to look for, they determined how often it can be observed in the neighboring universe if the theory of solid surfaces is correct. “We estimated the rate of stars falling to supermassive black holes. Almost every galaxy has one. We considered only the most massive, weighing about 100 million solar masses or more. About a million of them are several billion light-years from the Earth. ”
The team then studied the Pan-STARRS telescope in Hawaii, which recently completed a half-hemisphere study project. The telescope scanned the area for 3.5 years, fixing “transitory processes” – something that glows for a while, and then disappears. Their goal was to find such processes with the expected light signature of a star falling to a supermassive object and striking a hard surface.
“Given the speed of the falling stars to black holes and the degree of density of black holes in the neighboring universe, we calculated that the Pan-STARRS for 3.5 years of its operation should have detected more than 10 such processes if the theory of the solid surface is correct,” Lou explained. However, they found nothing.
“Our work implies that some or perhaps all black holes have horizons of events, and that the material really disappears from the observed universe when it is absorbed by these exotic objects, as we assumed for decades,” Narayan said. “The general theory of relativity has undergone yet another verification.”
Now the team intends to conduct research using the Large Synoptic Survey Telescope, which is now being built in Chile. Just like Pan-STARRS, LSST will perform repeated sky surveys in search of transient processes, but with much greater sensitivity.
The study is published in the Monthly Notices of the Royal Astronomical Society. | 0.877194 | 4.071761 |
Nearby earth-like planet may be just right for life
Nearby earth-like planet may be just right for life
Potentially habitable 'super-Earth' is prime target for atmospheric study
20 April, 2017, 09:27
A joint group of scientists from the European Southern Observatory announced on Wednesday that the group has found a planet 40 light years away from Earth that could potentially support life.
The newfound planet is described in a paper appearing in the April 20thissue of the journal Nature. NASA's Hubble Space Telescope will take a look soon to see how much high-energy radiation is pouring onto the exoplanet. It's not too hot and not too cold, it's just right - hence the term Goldilocks zone. And it may even have an atmosphere. Last year, a potentially habitable planet was found orbiting our nearest star, Proxima Centauri. "What really sets this planet apart from others that have been discovered is that we know the mass and the radius of the planet", said Jason Dittmann, a researcher at Harvard-Smithsonian Center for Astrophysics.
Super-Earths exist in between.
"The farthest we've ever sent humans is the Moon, 1 light second away", explained Charbonneau, "and the farthest we've sent spacecraft is the edge of the Solar System - about seven light hours".
A lot of planets that big are gaseous, but researchers say this one is rocky, made up of iron and silicates, just like Earth.
"This is the most exciting exoplanet I've seen in the past decade". It all started with the observation of a dip in the light of the star. But the smaller size of the star is offset by its proximity. That is proportional to the planet's mass. That's because they're the most abundant stars in the galaxy and some of the easier stars to capture transit signals from.
The exoplanet therefore lies in the middle of the habitable zone of the star, meaning it has numerous conditions needed to grow alien life.
For that duration, it would be easy for the planet to lose all of its potential water for good. For instance, astronomers may be able to measure oxygen molecules, which are key for life on our planet, Dittmann says. That's where lava comes in.
Exoplanet discoveries in the past decade have made it clear there are plenty of other solar systems, but in the previous year we've increasingly spotted new worlds that indicate there may be plenty of other Earths out there too.
Theresa May Calls General Election To Secure Brexit
Polls give May's Conservatives a double-digit lead on Labour, which is divided under left-wing leader Corbyn. A rift in Parliament will damage the government's ability to make a success of Brexit , she said.
There's been compelling evidence lately that some of these planets around red dwarfs could, in fact, retain an atmosphere.That's the case of GJ 1132b, a hellish world with Venus-like temperatures around an M-dwarf star that, despite all odds, seems to hold on to an atmosphere.
The boundaries of the habitable zone are critical. Think of it like holding an object too close to an open flame.
Red dwarfs are much smaller and cooler than the Sun and, although LHS 1140b is ten times closer to its star than the Earth is to the Sun, it only receives about half as much sunlight from its star as the Earth.
LHS 1140 b or TRAPPIST-1?
The star LHS 1140 is also a red dwarf, but it's old enough to have settled down. This affects the planet's ability to maintain an atmosphere, water and stable compounds.
However, since the planet is larger than Earth, it might have possessed a magma ocean on its surface for millions of years. The telescopes, part of the MEarth-South telescope array, saw the planet as it passed in front of its host star.
The James Webb Space Telescope is capable of observing large exoplanets and detecting starlight filtered through their atmosphere, which will enable scientists to determine the atmospheric composition and analyze them for gases that can create a biological ecosystem. But the hope is that by studying the atmosphere of all these planets in the habitable zone, we might find some of the biological signatures of living things.
The closest Earth-sized habitable-zone planet to us, circling Proxima Centauri, lies only 4.2 light years away, but does not transit in front of its star relative to our point of view, so we can not see the planet or its atmosphere.
If signs of life are found in the planet's atmosphere, it might be possible to send a probe to explore further. Both are ticks in the theoretical boxes for habitable worlds.
The announcement followed an inaugural meeting Tuesday of the U.S. -Japan Economic Dialogue in Tokyo chaired by visiting U.S. The trip so far has been dominated by US and allies' concerns about North Korea's nuclear and missile development efforts.
Last month Nintendo sold Switch units numbering more than 906,000 in the US , according to a press release issued by the company. Is it worth getting the Nintendo Switch? For more on upcoming games for the system, check out IGN's Nintendo Switch wiki .
Colton Sissons battled his way to the front of the net and took advantage of a rebound chance off a shot from Pontus Aberg. They have traditionally been an excellent road team. they should be confident... and the Predators need to remain wary.
He later went on to win the US Open that year, and finish in the top four in the British Open and PGA Championship. This perhaps explains why Paddy Power are offering 30/1 enhanced odds on McIlroy to win the US Masters.
The start of H-1B season was met with pointed reminders from the government that it is paying close attention to the visa. Non-premium visa petitions can take as much as eight months before they're approved, immigration lawyers say.
Although war is avoided, the threat to Japan and South Korea, which remain within range of North Korea's missiles, may continue. The Latest on the failed launch of a North Korean missile Sunday from the country's east coast (all times local): 9:44 a.m.
Trying for his first four-out save this year, Feliz (0-2) struck out Javier Baez to strand a runner on third in the eighth. Mike Montgomery , Pedro Strop , Koji Uehara and Wade Davis (2-0) combined for four scoreless innings, allowing two hits.
Pence will be diving into a tense standoff along the Korean Peninsula with visits to South Korea and Japan beginning Sunday. The Assembly merely reviewed the annual budget performance and the leader announced some personal appointments.
In South Florida, activists marched to Mr Trump's Mar-a-Lago resort, where the president stayed over the weekend. Spicer was asked if Trump would ever release his tax returns and replied, "I'd have to get back to you on that".
The unnamed calf weighed in at 133 pounds, posting an increase of 2 pounds during a period of 24 hours. The zoo, called Animal Adventure Park, is located about 200 kilometers northwest of New York City.
Jones wont especially with the traditional International Fight Week pay-per-view (PPV) card only three weeks earlier. Jones has fought once since his previous bout with Cormier, beating Ovince Saint Preux at UFC 197 in April 2016.
At least 26 dead as bus plunges into ravine in Philippines
Abad added the wounded, some of whom sustained critical injuries, were rushed to nearby hospitals. "The road is really risky". At least 40 passengers, including the dead and injured, were brought up to the side of the road, he said.
Rangers Bounce Back for Game 4 in Over Habs at The Garden
Reports from practice on Monday indicate that Nick Holden will draw back in for Game Four, playing alongside Marc Staal. But it was only a difference maker because the rest of his teammates followed suit with passionate play of their own.
Celtics clinch No. 1 seed in East, beat Bucks 112-94
The Bulls and Celtics are 2-2 in the regular season, but now this series determines who is the better team. The Celtics overcame a sluggish start to top the Milwaukee Bucks 112-94 on Wednesday night at TD Garden .
Hazard admits Chelsea striker may need summer transfer
He knows me better than I could imagine, I'm sure, and that's important: "it motivates you to work hard, train well". Hazard also believes he can become a world-class player without playing in the Ballon d'Or capital.
Schwab Rising on Quarterly Results
The Company's shares are trading -11.16% below their 50-day moving average and -0.97% below their 200-day moving average. The average estimate of 10 analysts surveyed by Zacks Investment Research was for earnings of 37 cents per share.
GALLERY: Easter egg drop in Iowa City
This was the first time the Recreation Commission held the Egg Hunt on the second Saturday of vacation week. Children scattered everywhere in a mad dash to gather the eggs with all those prizes hidden inside.
Boston Marathon Security Measures In Place
A year later, on the starting line of the 1973 Boston Marathon , the race official who had attacked Switzer gave her a kiss. The 121st Boston Marathon is on its way from Hopkinton to Boston . "You've reached it", said Lunenburg resident Kim Ortiz.
Mom accused of recording cruel abuse of 1-year-old son
Broadnax, who lives in Virginia, is Jaiden's aunt, and discovered the videos - 64 in all - on her brother's phone. Other videos showed Peterkin spitting on the baby and bending his hands back, according to the Chronicle.
Wells claws back $75 million from top execs in sales scandal
Tolstedt's lawyer, Enu Mainigi of the Washington firm Williams & Connolly, issued a statement challenging the board's findings. Stumpf already had agreed to give up $41 million in compensation, and Tolstedt had agreed to give up $19 million. | 0.887809 | 3.282109 |
The Flame Nebula, also called NGC 2024, is a region of dust and gas in the constellation Orion. Some of the dust and gas is in the process of condensing into stars. This photograph was taken in the infrared range of electromagnetic radiation. Infrared radiation has wavelenghts slightly longer than those of visible light.
Infrared Astronomy, the detection and study of infrared radiation emanating from objects in outer space. Infrared radiation is another form of electromagnetic energy, similar to visible light and radio waves, but differing by its wavelength (or frequency); all such waves travel at the speed of light in a vacuum. Infrared wavelengths begin around 0.0007 mm just beyond the reddest light that the human eye can detect, this is called the “near” infrared, and grow in size to about 0.35 mm in the “far” infrared. Wavelengths larger than this belong to the sub-millimeter, microwave, and radio parts of the electromagnetic spectrum.
Infrared observations are important in astrophysics for several reasons. Infrared radiation penetrates more easily through the vast stretches of interstellar gas and dust clouds than does visible and ultraviolet light, revealing regions hidden to normal telescopes. Young stars are surrounded by a cocoon of gas and dust which can make them invisible, but their heat warms the dust grains and produces infrared radiation which escapes to reveal their presence. Infrared radiation is also called “thermal” or heat radiation. Many molecules, such as carbon monoxide (CO) and hydrogen (H2), and tiny solid particles known as dust grains, are best studied at infrared wavelengths. Finally, the expansion of the universe changes (or redshifts) the visible light emitted by the most distant galaxies into red and infrared light.
INFRARED TELESCOPES AND DETECTORS
Infrared telescopes detect radiation that has wavelengths longer than the light that humans can see. Infrared radiation enters the telescope and reflects off of a large mirror on the bottom of the telescope, then off of a smaller mirror. Detectors and instruments beneath the mirrors record the radiation. Infrared telescopes must be kept at very low temperatures to prevent their own heat from producing infrared radiation that could interfere with observations.
Infrared telescopes look similar to normal optical telescopes. Light is collected and focused by a large curved mirror onto a smaller secondary mirror and then into the scientific instrument (camera or spectrometer) for analysis. Most often, the secondary mirror is very small and gold-coated because gold offers better reflectance in the infrared than the normal aluminized mirrors do. The secondary mirror is mechanized so that it can tilt back and forth rapidly, up to 20 times per second, allowing the detector in the science instrument to compare the signals from the source plus sky background and the sky background alone. This technique is called “chopping” and is very effective for detecting a faint signal against a very strong background. Infrared telescopes have an open structure, without the black tubes or baffles common to normal telescopes, since these emit infrared radiation. For an infrared telescope in space the baffles can be cooled to reduce infrared emissions. One of the largest telescopes dedicated to ground-based infrared astronomy is the 152-inch (3.8-m) United Kingdom Infrared Telescope (UKIRT) at the Mauna Kea Observatory in Hawaii, but many other telescopes possess infrared instruments, especially for near-infrared work. In recent years, infrared astronomy has been revolutionized by the introduction of tiny imaging devices called “infrared arrays” making it possible to take pictures at these invisible wavelengths and display them on computer screens.
Everything that is warm emits infrared radiation. A star like the Sun emits most of its radiant energy as visible (yellow) light. Redder and cooler stars at half the Sun’s temperature have a peak emission at near-infrared wavelengths. Merely warm objects, like telescopes and Earth’s atmosphere, don’t emit light but they give off profuse amounts of infrared radiation with a peak emission around a wavelength of 0.01 mm. Since they are much closer to the infrared camera or detector, these sources of infrared radiation swamp any signals from distant planets, stars, and galaxies. Likewise, the optical and mechanical parts of the scientific instrument will emit strong infrared radiation. The solution to this problem is to cool the detector, and all the optics, inside a vacuum chamber. Temperatures around that of liquid nitrogen (77 degrees Kelvin (K) above absolute zero) are needed for near-infrared detection whereas temperatures near liquid helium (only 4 K) are required for far-infrared detectors.
To eliminate the large, unwanted background of infrared radiation it would be necessary to cool down the entire telescope and remove Earth’s atmosphere. For a space-based telescope, however, there is no atmosphere and no problem of condensation and ice formation if the telescope itself is cooled. Ground-based infrared telescopes need to be located at very high, dry, and cold sites like Mauna Kea, Hawaii, to minimize the thermal background. This is effective for near-infrared work. Far-infrared observations are best done from space or from high-flying airplanes.
THE INFRARED UNIVERSE
Orion Nebula in Infrared
This image of the Orion Nebula was taken in infrared radiation—radiation with wavelengths longer than visible light—and given false visible colors. The Orion Nebula is a cloud of gas and dust that surrounds new stars. The young stars light up the nebula and cause it to glow.
Infrared radiation emanating from the outer planets and their moons reveals much about their temperatures and compositions. Jupiter emits more infrared radiation than expected from absorption of sunlight, indicating that it has an internal source of heat energy. Infrared observations of Jupiter’s moon Io show thermal hot spots caused by the active volcanoes on its surface.
Stars of lower mass than the Sun are less luminous and much cooler. They emit most of their energy at infrared wavelengths. While these red dwarf stars are much more plentiful than the rare and short-lived high-mass stars, the very lowest mass objects—called brown dwarfs—have been hard to find because they are so faint at visible light wavelengths. Infrared astronomy has played a key role in the search for these objects which lie on the boundary between true stars and giant Jupiter-like planets.
Although interstellar space is a vacuum, it is not completely empty. Tiny solid particles called dust grains can be found around and between the stars. These particles are formed from heavier elements (like silicon and iron) produced deep inside an earlier generation of massive stars. Dust grains absorb ultraviolet and visible light, making the most distant stars appear redder and fainter, while also heating the dust slightly above the temperature of space and causing it to glow at far-infrared wavelengths. Dust obscures our view of distant parts of our own Milky Way Galaxy, including the center of the galaxy. The central regions can only be observed at infrared and radio wavelengths. Recent ground-based and space-based observations of the center of the galaxy have revealed for the first time clear evidence of dynamic motion around a massive, invisible source believed to be a black hole with a mass over one million times that of the Sun. Dust also obscures our view of young, recently-formed stars. As a cloud of gas and dust contracts to form a star it tends to flatten into a disk due to rotation. Eventually the disk might dissipate or it may allow planets to form. The disk both hides the starlight and is heated by it. Infrared observations reveal the hidden source and provide knowledge of how stars and planetary systems form.
Spiral galaxies similar to our own contain lots of dust and star-forming regions making them difficult to study except with infrared instruments. Some classes of galaxies are exceptionally luminous in the infrared because they have so much dust and have absorbed so much ultraviolet energy from the central sources within the nucleus of the galaxy. Distant galaxies are fainter and redder than nearby ones. The reddening in this case is not caused by intergalactic dust but by the expansion of the universe discovered by Edwin Hubble. Traveling at 186,000 mi every second (300,000 km/s), it takes light billions of years to reach us from the most distant galaxies, and therefore we see these galaxies as they were when they were young and not as they are now. During this time space itself has expanded and the wavelength of the radiation has been stretched or “redshifted” by such a large amount that the galaxy is no longer readily detectable at visible light wavelengths because all its energy is now in the infrared.
HISTORY AND CURRENT RESEARCH
This infrared photo of the planet Saturn has been color coded to indicate the cloud level in Saturn’s atmosphere. Violet and blue represent areas in which Saturn’s atmopshere is clear down to the main cloud layer. Green and yellow show layers of haze above the main cloud layer (yellow represents thicker haze). Red and orange indicate the highest level of clouds, thicker than the haze. White areas are areas of the atmosphere with high levels of water vapor. The bright dots at the upper right and lower left of the picture are Saturn’s satellites Tethys and Dione, respectively. The Hubble Space Telescope took this image in 1998.
Modern infrared astronomy began in the 1950s when simple photoelectric detectors made from lead sulphide became available and were used to survey the sky at infrared wavelengths for new sources. Later, germanium detectors were used to open up the study of much longer infrared wavelengths with the aid of rocket, balloon, and airplane surveys. In the late 1970s, several large ground-based telescopes dedicated to infrared astronomy were built which included the 3.8-m United Kingdom Infrared Telescope (UKIRT) and the National Aeronautics and Space Administration (NASA) 3-m Infrared Telescope Facility (IRTF) both on Mauna Kea, Hawaii, at 14,000 ft above sea level. With the launch of the Infrared Astronomical Satellite (IRAS), by the United States, the United Kingdom, and The Netherlands in 1983, infrared astronomy took another leap forward. This mission surveyed the entire sky at wavelengths of 12, 25, 60, and 100 microns (1 micron is a millionth of a meter) until its onboard supply of liquid helium ran out. A short time later infrared astronomy was revolutionized by the first introduction of devices that could take infrared images. The advent of sensitive infrared cameras inspired many traditional observatories to convert for infrared work, especially in the near infrared where city lights don’t cause problems and the thermal background from the telescope is minimal.
Uranus and Its Rings
The planet Uranus rotates on an axis that is tilted nearly horizontal. Other planets in the solar system have axes that are more vertical. This infrared image taken by the Hubble Space Telescope shows Uranus's rings orbiting in the plane of the planet's tipped equator. The colors are not real and are used to bring out details such as clouds in the atmosphere and the shape of the rings. The white disks are moons.
Infrared astronomy from space received two boosts when the Infrared Space Observatory (ISO) was launched in December 1995 and when the Hubble Space Telescope was refurbished in 1997 with NICMOS, the Near Infrared Camera and Multi-Object Spectrograph. Both of these missions used infrared array detectors. Another important satellite which used infrared techniques for part of its mission was the Cosmic Background Explorer (COBE). The Spitzer Space Telescope, launched in 2003, is the largest and most sensitive infrared space telescope ever launched.
Future infrared missions include SOFIA, the Stratospheric Observatory for Infrared Astronomy. SOFIA is a modified Boeing 747 with a 2.5-m telescope on board, due for commissioning in 2004. | 0.873634 | 4.062913 |
- slide 1 of 5
A Star is Born
Stars are born when a swirling cloud of hydrogen gas and interstellar dust begins to coalesce into a distinct sphere. As the sphere grows, gravity compresses it more and more, and the temperature at the center rises. At some point, the gas and dust become compressed in the center to the point that the temperature is high enough to cause fusion to begin. A new star is born.
During this formative time, much more is going on. As the gas and dust coalesces, its central region begins to trap radiation so the temperature and pressure increases. A star with a mass about that of our sun, at this stage, will be much larger than the Sun, and as much as 1000 times brighter. But its temperature will be much lower than it eventually will be, as its heat at this point is supplied solely by gravitational contraction. However, it is producing light, and so is a protostar.
As the protostar continues to contract, the temperature and pressure at the core continues to increase until fusion begins. Temperatures increase further, and the core pressures increase to the point that they balance the gravitational contraction that has been pulling the gases toward the core. At this point the star is in hydrostatic equilibrium and is a full fledged star.
The basic fusion equation at work here is 2H+3H--->4He + 1n + energy, where n is a neutron.
This birth sequence holds true for stars of any mass above 0.08 solar masses, even giants many times larger than the Sun. A protostar with a mass as low as 0.08 solar masses never achieves nuclear fusion. Its heat and dim luminosity is created solely by gravitational contraction. It has a short life as a brown dwarf. Over a few thousand years it gradually cools and goes dark.
If the luminosity of a star is graphed against its temperature, all stars in their hydrogen burning phase will clump together in a long meandering grouping known as the Main Sequence. In the graph, below, (known as a Hertzsprung-Russel diagram) smaller stars are at the bottom right, and larger stars fall at the upper left of the diagram. The Sun, a fairly mid-size star, falls just about in the middle of the Main Sequence.
Notice as well, as you move through the Sequence, the color of the stars change. The smaller stars are red. Stars about the size of the Sun and up to about four solar masses are yellow. Stars larger become blue. This of course is a function of temperature.
Hydrogen burning stars larger than the small red stars at the lower end of the graph burn for billions of years, remaining in the Main Sequence throughout this period. Our Sun is expected to continue to burn its hydrogen for 10 billion years.
But eventually, all the hydrogen in the core is used up, transformed into helium. Then the star transforms.
- slide 2 of 5
After Hydrogen is Gone
When the hydrogen in the core is exhausted, radiation pressure cannot balance gravity, so the star contracts—but only slightly. This is because there is still hydrogen in the outer layers of the star, and it begins fusion. But fusion in these layers causes them to expand. The star becomes a Red Giant. Our Sun will go through this transformation 10 billion years from now, expanding out beyond the orbit of Mars. All inner planets, including Earth, will be scorched.
Hopefully mankind will have colonized at least our arm of the Milky Way by then, and the species will have a new home.
As the outer layers burn their hydrogen, the helium produced migrates to the core. Eventually, the helium builds up to a point that gravitational pressures and temperatures in the core cause the helium to begin fusion. The new energy produced by the core makes it expand. This reduces the fusion of the outer layers, so the total energy output of the star is reduced. This causes the star to contract again.
An important point about the helium cycle is the elements it produces. In stars up to about four solar masses, helium fusion first produces neon, then that fuses to oxygen and carbon. The planetary nebula surrounding the remnants of these former stars is filled with these vital elements.
This phase of a star’s life is extremely volatile. In this stage, it moves to the section of the graph to the right of the Main Sequence. During this period, the star undergoes violent pulsations and loses mass by ejecting material through powerful stellar winds. Eventually it will eject all its outer layers to form a planetary nebula. The star itself has collapsed to a dense small core in which the temperature is high enough to cause carbon to fuse. The star is now about 0.6 solar masses and only about the size of the Earth. It has become a white dwarf. It will continue life in this guise for billions of years.
But this is just the evolution of stars up to about four solar masses. More massive stars have a more explosive evolutionary tale.
- slide 3 of 5
Creation of Heavy Elements
Stars more massive than 40 solar masses have very strong stellar winds, and lose mass so rapidly they can’t expand into red giants. If the remaining core is no more than 1.4 solar masses, the fusion process continues as in less massive stars, except that the temperature is sufficient to fuse some of the neon into magnesium. The star eventually becomes a white dwarf.
If the core is more than about 2.5 solar masses, the oxygen begins to fuse into sulfur and silicon. As the core continues to collapse, the temperature becomes high enough to break down any nucleus. This forms alpha particles that fuse with other nuclei to form aluminum and sodium. If the star is too massive to form a white dwarf but not sufficiently massive to maintain the conversion of neon to oxygen and magnesium, it will collapse completely and explode as a supernova.
In even more massive stars, the fusion process continues until it produces iron. At this point, more energy is consumed producing iron than is generated, and the core undergoes a sudden, catastrophic collapse that overcomes the forces keeping nuclei apart and forces the electrons in the matter into the protons to form neutrons. The star becomes a very dense sphere of neutrons with a thin outer layer of iron.
It is a neutron star. It is only about 10 km in radius, and the compressed matter of which it is composed weighs 1015 grams per cubic cm. In the Hubble photo below of the Crab Nebula (M1), the bottom of the two stars, which are in a vertical line, slightly above and right of center, is the neutron star.
- slide 4 of 5
With a Bang and a Whimper
If the star is even more massive, the collapse is even more catastrophic, and the remaining protons and electrons in the collapsing outer layers also are compressed into neutrons. For an astronomical moment, the star releases the energy created by this transformation as a burst of neutrinos. The neutrinos bombard the iron core and create elements heavier than iron, up to and possibly beyond uranium.
There are four types of supernova—1a,1b, 1c and II. 1a supernova are rare, as they are white dwarfs that cannot maintain their plasma outer layers. These usually are in a binary system and pull off material from their companion. In their explosion, they reach an absolute magnitude of -19.5. Compare this with the magnitude of Venus, the brightest object in the sky, at -4.6. (Note that the minus in front of the magnitude number indicates a brighter object.) 1b and 1c supernova are more massive stars that have run out of fuel at their centers and have previously lost all their outer layers due to strong stellar winds. Their absolute magnitude is about -15.
In type II supernova the process is the same as described above, but the neutron core is about 30 km in diameter. It pulsates in a series of collapses and rebounds until it explodes in one final burst. Some of the material often falls back and coalesces. In stars originally of about 20 solar masses, the resultant remnant is a neutron star. If the original star was more than 20 solar masses, the remnant is a black hole.
It is possible for even more massive stars to go supernova without collapsing to a black hole, but that is rare. Generally, they collapse directly to a black hole without going supernova.
- slide 5 of 5
Main Sequence graph: Wikipedia http://upload.wikipedia.org/wikipedia/commons/7/78/H-R_diagram_-edited-3.gif
All star photos: NASA Hubble site http://hubblesite.org/gallery/album/entire/ | 0.904726 | 3.903469 |
Take a walk on the beach, holding a friend’s hand, and relax. Feel the sand squeezed between your toes and listen to the gently lapping waves. Peaceful, isn’t it?
Well, maybe not. Choose a different beach, and the surface might be sharp edges of volcanic rock, a foam frozen in time and cut by erosion to leave knife-edge broken bubbles. Or perhaps the beach is a long bank of rounded pebbles, tiring to walk on, like the 29-kilometer Chesil Beach in southern England. Each beach has its story, a varied history perhaps of fire and upheaval, or of shipwrecks and smugglers. But even a smooth, sandy beach has secrets. Life teems beneath your feet and the washed-up seaweed is home and food for numerous worms, crustaceans and arthropods. Come back in a few hours, and the broad swathe of sand might have disappeared so the waves pound the bottom of the cliff; the tide has come in.
The creatures of the beach face constant change, dominated by the twice-daily tide. Yet not quite: the major rhythm is every 12 hours, 25.2 minutes because the Moon orbits the Earth in the same direction as the Earth’s rotation. Beach creatures synchronise their activity with the tide, feeding when the food arrives and burrowing or hiding when necessary. Beach visitors, such as gulls, plovers, and curlews, time their visits by the tides too.
The size of the tides changes day by day, because the Sun’s gravity contributes to the tidal forces. When the Sun, Moon and Earth are lined up, at full moon and new moon, the forces combine and tides are largest, called spring tides. When the Moon is perpendicular to the Earth-Sun line, that is at the waxing half moon and waning half moon, the forces are opposed and the tides are smallest, called neap tides. Various creatures time their breeding to the tides, including paolo worms, salt marsh mosquitoes, grunions (a fish found on the Californian coast), and sea turtles. Usually, there is some perceivable benefit to the timing because the extra high tide allows the eggs to be laid further up the beach, or the tidal pools take longer to dry up.
Our coastal ancestors were also aware of the changes and could correlate them to the phases of the moon. The need to predict the tides, whether for safe food-gathering on mud flats or for navigation in shallow channels, probably contributed to the development of calendars. It has been claimed that both Stonehenge and the Pyramids were ancient astronomical calculators. They are certainly well-aligned with astronomical directions: the winter solstice and true north respectively, demonstrating that their builders made accurate observations. However, claims that they could be used to predict events such as eclipses are far less likely.
One ancient artifact does show very detailed astronomical knowledge. The Antikythera mechanism was found in a shipwreck off the Greek island of the same name in 1902. It was a lump of corroded bronze and wood, and an embedded gear wheel went unnoticed for two years. It was not until 1971 that x-ray and gamma-ray images of the device revealed its complexity. Now recognised as the earliest-known analogue computer, it was made about 87 BCE and is comprised of at least 30 gears. It was capable of predicting lunar and solar eclipses, with the varied gears calculating the orbits and precession of the celestial bodies. It even calculated the date of the ancient Olympic Games! The accuracy of the Antikythera mechanism could not be improved until the scientific theories about the motion of the planets were updated by Ptolemy in the 2nd century CE and Keppler in the 17th century.
Why the tides are correlated with the phases of the Moon was another problem. In ancient times, both in China and the West, the rise and fall of the tide was “explained” by the theory that the Earth inhaled and exhaled the seas. A 13th century Arabian scientist proposed that the Sun and Moon heated the waters, making them expand. Newton provided the basis of the explanation we use today: his theory of gravity says that every particle in the universe attracts every other particle with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. In his Principia he uses his theory to explain the twice-daily tides: the Moon’s gravity is strongest on the side of the Earth closest to the Moon, and weakest on the opposite side. Although the Sun is much more massive, its effect is less because it is further away.
Tides aren’t just affected by the Sun and Moon. Not far from Chesil Beach, the Isle of Wight is separated from the rest of England by the Solent, which is notable for having a doubly high tide. The effect is due to the shape of the coastline—the whole English Channel is like a long tank of water and the tide is the water sloshing back and forth. The Solent is in the middle of the tank, but the Cherbourg Peninsular on the other side of the Channel restricts the flow and sets up further oscillations. At Southampton, on the Solent, the result is a high tide, a slight dip and another high, extending the length of time that large ships can safely navigate the waters. On the other hand, currents around the Isle of Wight are strong and complicated, making the local knowledge of a good pilot important and explaining the large number of lifeboat stations in the area.
You could think of the ocean as the sound box of a huge musical instrument, the regular beat of the lunar tide sets the base note, but the complicated topography, the islands, inlets and channel depths, contribute different resonances so the final note is rich with many harmonics.
Your simple walk on the beach is part of a humming web of life and astronomy. | 0.860127 | 3.18717 |
Comet C/2016 U1 (NEOWISE) will reach its perihelion (the closest point on its orbit to the Sun) on Saturday 14 January 2017, when it will be approximately 0.32 AU from the Sun (i.e. 32% of the distance between the Earth and the Sun, inside the orbit of the planet Mercury). At this point it will also be at about its closest to the Earth, at a distance of 1.14 AU (1.14 times as far from us as the Sun). The comet will only be separated from the Sun by a distance of 15° seen from Earth (the entire sky, envisioned as a sphere around the Earth, being 360°), meaning that it is invisible from the Earth without fairly specialised viewing equipment (and attempting to view it with most amateur telescopes would be highly dangerous).
Image of C/2016 U1 (NEOWISE) seen taken from Jauerling in Austria on 23 December 2016. Michael Jäger/Universe Today.
C/2016 U1 (NEOWISE) was discovered on 21 October 2016 by the NEOWISE system on the Wide-field Infrared Survey Explorer satellite. The designation C/2016 U1 implies that it was the first comet (C/... 1) discovered in the second half of October 2016 (period 2016 U).
C/2016 U1 (NEOWISE) has an unknown period and a highly eccentric orbit that takes it from 0.32 AU from the Sun at perihelion (32% of the distance between the Earth and the Sun) to an unknown outer orbital point, somewhere beyond the Kuiper Belt, in the Oort Cloud. It is considered to be a hyperbolic comet, an object from the Oort Cloud (or possibly even the interstellar space beyond), that has been nudged onto a trajectory that takes it through the Inner Solar System by an encounter with another Oort Cloud body or possibly the gravity of another star or other extra-Solar System object. Such comets are not expected to make return visits to the Inner Solar System, but rather are thrown out of the Solar System altogether by a gravitational slingshot caused by their close encounter with the Sun.
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A series of new telescopes – a magnitude more powerful than the ones already in use – will allow humanity to detect alien life within decades, according to top NASA scientists.
“I think in the next 20 years we will find out we are not alone in the universe,” announced NASA astronomer Kevin Hand, during a public talk in Washington that showcased the US space agency’s top extra-terrestrial life specialists.
While the prediction may have seemed bold, it chimed with the utter certainty of all experts present, fueled by the already impressive work of the Kepler telescope – which is about to be superseded. In just five years, the space observatory has identified up to 5,000 planets, more than in the entire history of astronomy.
“What we didn’t know five years ago is that perhaps 10 to 20 percent of stars around us have Earth-size planets in the habitable zone. It’s within our grasp to pull off a discovery that will change the world forever,” said Matt Mountain, director and Webb telescope scientist at the Space Telescope Science Institute in Baltimore.
“Sometime in the near future, people will be able to point to a star and say, ‘that star has a planet like Earth’,” said Sara Seager, professor of planetary science and physics at the Massachusetts Institute of Technology.
While the Webb telescope is 6.5 meters long, more than twice the length of the Hubble launched back in 1990, the scientists agreed that a qualitative breakthrough could be achieved once a 20-meter telescope reaches the Earth’s atmosphere.
Such a project is currently limited by the payload restrictions of rockets currently in use. The Space Launch System, currently being perfected by NASA scientists, should be able to deliver a payload of 130 tons, more than ten times that of Russia’s popular Proton rocket.
And even if that is not enough, the alien-hunters still believe that finding a second Earth is just a matter of when, not if.
“Just imagine the moment, when we find potential signatures of life. Imagine the moment when the world wakes up and the human race realizes that its long loneliness in time and space may be over — the possibility we’re no longer alone in the universe,” said Mountain. | 0.845782 | 3.019377 |
I've read that the moon's (the Earth's that is) orbit is gradually enlarging, i.e. the moon is gradually moving away from Earth. The rate at which this is ocurring, I read, was about 2 inches per year. I know that the moon's orbit is an ellipse and that this figure must be an average rate. 1. Is it true that the moon is moving away from Earth?, and 2) if so what is causing the moon to move away from the Earth? I know it is the Earth's gravitational attraction that holds the moon in orbit. If the Earth's mass remains constant the gravitational attraction must remain the same. I also read that the Earth gains more mass than it losses due to the bombardment of space debris (asteroids and what not) and since the Earth is bigger than the moon it must be gaining mass more rapidly than the moon therefore Earth's gravitational influence to hold the moon in orbit must be increasing thereby 'gluing' the two bodies more tightly together. Please explain.
It's not a question of mass, but of energy! The tidal force exerted by the Moon on the Earth causes the oceans to bulge. The Earth rotates about its axis faster than the Moon revolves around the Earth, and this rapid rotation carries the tidal bulge of the oceans forward of the Moon in its orbit. So the tidal bulge on the Earth is always slightly ahead of the Moon's own position. This bulge is continuously tugging the Moon forward, increasing the Moon's total energy. Imagine a cowboy's lasso. As the cowboy spins the lasso faster and faster (increasing its total energy), the loop gets wider. The same thing essentially happens to the Moon. The tugging of the Earth's bulge lifts it into a wider orbit around the Earth.
The cowboy has to put some energy into the lasso to make the loop
wider. In the Moon's case, the energy comes from the Earth's
rotation. Friction between the oceans and the Earth's surface is
slowing the Earth's rotation by 0.002 seconds every 100 years. The
Earth's rotation will continue to slow, losing energy, until it's
rotating so that a solar day equals a lunar month. The Earth's tidal
bulge will point directly at the Moon, and the Moon will stop
spiraling away from the Earth. The Earth will then keep its same side
facing the Moon, just as the Moon presently keeps the same side facing
the Earth. This has already happened to Pluto and its Moon, Charon,
and is very common in the solar system.
Submitted by Peter (New Jersey, USA)
(May 29, 1998) | 0.866939 | 3.619069 |
With the forthcoming publication in the journal Nature on 12 January, it is estimated that there are more than 100 billion planets in our Milky Way galaxy. That means more than one planet per star, and results show that there are more rocky small Earth-like planets than giant Jupiter-size gas planets.
The conclusions in the Nature article are based on micro-lensing studies.
Recent results from the Kepler Observatory have shown the existence of three small, rocky planets around the star KOI-961, a red dwarf. These three planets, named KOI-961.01, KOI-961.02 and KOI-961.03, are 0.78, 0.73 and 0.57 times the radius of Earth. The smallest is about the size of Mars (see below). Follow-up observations were made by the Palomar Observatory, near San Diego, and the Keck Observatory atop Mauna Kea in Hawaii.
Since it is now clear that rocky planets exist around millions, if not billions, of stars, the question arises as to whether there is life on them, and whether it may resemble life on Earth.
Whether a planet exists in the “Goldilocks” region around a star depends on many factors. Three factors include the type of star, how far away from the star the planet resides and the atmospheric pressure of the planet. A red dwarf, such as Gliese 581, means the planet has to be closer than the Earth to our Sun. A white hot star means the planet has to be farther away. And if the atmosphere is low, like Mars, or to high, like Venus, liquid water is not likely.
A fourth factor is axial tilt. If a planet has no axial tilt (the spin axis is perpendicular to the plane of its orbit around the star) then the polar regions freeze and the equatorial regions bake. There is little exchange between these regions due to atmospheric circulation. Axial tilt, such as the Earth has, allows distribution of heat between the equator and the poles.
Even if a planet has axial tilt, a recent study shows that interaction at a close distance (within the “Goldilocks” region) with red dwarf will eliminate axial tilt in less than 100 million years. Bacteria on Earth required 1,000 million years to evolve. Theoretically, a planet with no axial tilt could possess bands between the equator and the poles where liquid water would exist. But, it is quite possible the atmosphere would collapse, with gases being driven off into space at the very hot equator, and freezing solid on the ground at the poles. Such a possibility faces the planets around KOI 961.
Systems with stars like our Sun present better possibilities. The “Goldilocks” conditions exist much farther out, and axial tilt is eliminated much more slowly, as our Earth is witness. Systems such as Kepler-22b are good candidates.
The conclusion drawn from these studies is that systems similar to our Solar System present the best opportunities for life. | 0.839218 | 3.797721 |
Jupiter now lies highest in the UK sky at sunset, but the Solar System’s largest planet and its four bright Galilean moons still provide plenty of observable events during June, as we reveal. If you’re uncertain which evening ‘star’ is Jupiter, the Moon conveniently passes by on the night of 3—4 June, a time when European skywatchers can also see the Moon occult (hide) bright double star Porrima.
On the night of 4-5 March 2017, UK observers with clear skies can see an occultation bonanza as the 6-day-old waxing crescent Moon passes in front of prominent members of the Hyades open cluster in Taurus. Some hours later, after the Moon has set in the British Isles, first-magnitude star Aldebaran is occulted across a large swathe of North America.
On the night of 12-13 December, the waxing gibbous Moon glides in front of the loose open star cluster known as the Hyades in the constellation of Taurus, culminating in the occultation of bright star Aldebaran around 5:24am GMT for observers in the British Isles. In North America, the event occurs at a more sociable hour late into the evening of 12 December.
The penultimate 2016 occultation of Neptune by the Moon occurs on 9 November for observers in Western Asia, Eastern Europe and northernmost Africa. In Western Europe, the nine-day-old waxing gibbous Moon merely brushes by the outermost planet, but the pair will be close enough to be seen within the same field of view of a typical binocular from the UK.
Observers up for an extreme observing challenge may care to make an attempt at viewing the almost full Moon pass in front of planet Neptune soon after 8pm BST on Thursday, 15 September. The planet’s disappearance occurs at a low altitude in twilight for the British Isles, but can also be seen from a large swathe of Europe and western Russia.
If the excitement of the Juno spacecraft’s arrival at Jupiter has prompted you to seek out the solar system’s largest planet, then the 5-day-old cresent Moon acts as a convenient celestial guide during the evening of Saturday, 9 July when it makes a close pass of the gas giant. Here’s our guide to where and when to see this beautiful celestial pairing.
If you have a clear western horizon from shortly before 9pm BST until midnight on Sunday, 10 April, don’t miss an opportunity to see a young crescent Moon glide slowly through the southern edge of the Hyades star cluster in Taurus, covering (or occulting) stars as it goes. All you need is a typical binocular or a small telescope to enjoy the show! | 0.895857 | 3.573582 |
Solar storms, space junk and the formation of the Universe are about to be seen in an entirely new way with the start of operations today by the $51 million Murchison Widefield Array (MWA) radio telescope.
The first of three international precursors to the $2 billion Square Kilometre Array (SKA) telescope, the MWA is located in a remote pocket of outback Western Australia. It is the result of an international project led by Curtin University and was officially turned on this morning by Australia’s Science and Research Minister, Senator Kim Carr.
Using bleeding edge technology, the MWA will become an eye on the sky, acting as an early warning system that will potentially help to save billions of dollars as it steps up observations of the Sun to detect and monitor massive solar storms. It will also investigate a unique concept which will see stray FM radio signals used to track dangerous space debris.
The MWA will also give scientists an unprecedented view into the first billion years of the Universe, enabling them to look far into the past by studying radio waves that are more than 13 billion years old. This major field of study has the potential to revolutionise the field of astrophysics.
“This collaboration between some of astronomy’s greatest minds has resulted in the creation of a groundbreaking facility,” Director of the MWA and Professor of Radio Astronomy at Curtin University, Steven Tingay said.
“Right now we are standing at the frontier of astronomical science. Each of these programs has the potential to change our understanding about the Universe.”
The development and commissioning of the MWA, the most powerful low frequency radio telescope in the Southern Hemisphere, is the outcome of nearly nine years’ work by an international consortium of 13 institutions across four countries (Australia, USA, India and New Zealand).
The detailed observations will be used by scientists to hunt for explosive and variable objects in the Milky Way such as black holes and exploding stars, as well as to create the most comprehensive survey of the Southern Hemisphere sky at low radio frequencies.
From today, regular data will be captured through the entirely static telescope which spans a three kilometre area at the CSIRO’s Murchison Radio-astronomy Observatory, future home to the SKA.
The data will be processed 800 kilometres away at the $80 million Pawsey High Performance Computing Centre for SKA Science, in Perth, carried there on a link provided by the NBN and enabled by AARNet. The MWA will be the Pawsey Centre’s first large-scale customer.
Nine major research programs were announced at the launch, with more than 700 scientists across four continents awaiting the information the telescope has now begun to capture.
“Given the quality of the data obtained during the commissioning process and the vast areas of study that will be investigated, we are expecting to see preliminary results in as little as three months’ time,” Professor Tingay said.
“This is an exciting prospect for anyone who’s ever looked up at the sky and wondered how the Universe came to be.
“The MWA has and will continue to lift the bar even higher for the SKA.”
Under Professor Tingay and fellow colleague Professor Peter Hall’s guidance, Curtin University has been awarded a $5 million grant by the Australian Government to participate in the SKA pre-construction program over the next three years, with the MWA’s unique insight being used to develop a low frequency radio telescope that is expected to be 50 times more sensitive.
The MWA has been supported by both State and Federal Government funding, with the majority of federal funding being administered by Astronomy Australia Limited.
The MWA project recognises the Wadjarri Yamatji people as the traditional owners of the site on which the MWA is built and thanks the Wadjarri Yamatji people for their support, as well as that of Astronomy Australia Limited.
The MWA launch event took place simultaneously at the Astronomical Society of Australia’s annual scientific meeting hosted at Monash University Melbourne and the Murchison Radio-astronomy Observatory in the Murchison, Western Australia.
Professor Steven Tingay, Director of the Murchison Widefield Array, will be available for media interviews on Tuesday 9 July, Wednesday 10 and Thursday 11 July.
Project leaders from the inaugural MWA research programs will also be available and will attend the ASA annual meeting:
Professor Rachel Webster, The University of Melbourne, Epoch of Reionisation (Highest ranked science).
Professor Martin Bell, University of Sydney, The MWA long-term radio sky monitor.
Still photography and pool vision
A range of still photography and pool vision is available as well as a selection of audio visual material to support this story.
These can be accessed directly via Dropbox and used with appropriate credits.
To arrange interviews or for further information please contact:
Tel: +61 (0)8 9421 3610
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Tel: +61(0)8 9421 3600
Mob: +61 (0)418 918 202 | 0.828868 | 3.24062 |
by Bob King
What strange creature is this flitting across the Moon? Several members of the European Space Agency’s Astronomy Center captured these views of the International Space Station near Madrid, Spain on January 14 as it flew or transited in front of the full moon. Credit: Michel Breitfellner, Manuel Castillo, Abel de Burgos and Miguel Perez Ayucar / ESA
One-one thou That’s how long it takes for the International Space Station, traveling at over 17,000 mph (27,300 kph), to cross the face of the Full Moon. Only about a half second! To see it with your own eyes, you need to know exactly when and where to look. Full Moon is best, since it’s the biggest the moon can appear, but anything from a half-moon up and up will do.
The photo above was made by superimposing 13 separate images of the ISS passing in front of the Moon into one. Once the team knew when the pass would happen, they used a digital camera to fire a burst of exposures, capturing multiple moments of the silhouetted spacecraft.
The ISS transits the Full Moon in May 2016
The ISS is the largest structure in orbit, spanning the size of a football field, but at 250 miles (400 km) altitude, it only appears as big as a modest lunar crater. While taking a photo sequence demands careful planning, seeing a pass is bit easier. As you’d suspect, the chances of the space station lining up exactly with a small target like the Moon from any particular location is small. But the ISS Transit Finder makes the job simple.
Click on the link and fill in your local latitude, longitude and altitude or select from the Google maps link shown. You can always find your precise latitude and longitude at NASA’s Latitude/Longitude Finder and altitude at Google Maps Find Altitude. Next, set the time span of your Moon transit search (up to one month from the current date) and then how far you’re willing to drive to see the ISS fly in front of the Moon.
This is a screen grab from the homepage of Bartosz Wojczy?ski’s most useful ISS Transit Finder. Credit: Bartosz Wojczy?ski
When you click Calculate, you’ll get a list of events with little diagrams showing where the ISS will pass in relation to the Moon and sun (yes, the calculator also does solar disk crossings!) from your location. Notice that most of the passes will be near misses. However, if you click on the Show on Map link, you’ll get a ground track of exactly where you will need to travel to see it squarely cross Moon or Sun. Times shown are your local time, not Universal or UT.
A beautiful ISS transit on June 19 2015 recorded at Biscarrosse, France. The photographer used CalSky, another excellent satellite site, to prepare a week in advance of the event. This composite image was made with a Canon EOS 60D. Notice how bright the space station appears against the moon due to the lower-angled lighting across the lunar landscape at crescent phase compared to full, when the ISS appears in silhouette. Credit: David Duarte
The map also includes Recalculate for this location link. Clicking that will show you a sketch of the ISS’ predicted path across the Moon from the centerline location along with other details. I checked my city, and while there are no lunar transits for the next month, there’s a very nice solar one visible just a few miles from my home on Feb. 8. Remember to use a safe solar filter if you plan on viewing one of these!
The ISS transits the Sun on May 3, 2016. Click for details on how the photo was taken. Credit: Szabolcs Nagy
While you might attempt to see a transit of the ISS in binoculars, your best bet is with a telescope. Nothing fancy required, just about any size will do so long as it magnifies at least 30x to 40x. Timing is crucial. Like an occultation, when the moon hides a background star in an instant, you want to be on time and 100% present.
Make sure you’re set up and focused on the moon or sun (with filter) at least 5 minutes beforehand. Keep your cellphone handy. I’ve found the time displayed at least on my phone to be accurate. One minute before the anticipated transit, glue your eye to the eyepiece, relax and wait for the flyby. Expect something like a bird in silhouette to make a swift dash across the moon’s face. The video above will help you anticipate what to expect.
The next lunar transit nearest my home is an hour and a half away in the small town of Biwabik, Minn. according to the ISS Transit Finder. On Jan. 30 at 8:00:08 p.m local time, the ISS will cross the crescent moon from there. Once you know the time of the prediction and the exact latitude and longitude of the location (all information shown in the info box on the map using the ISS Transit Finder), you can turn on the satellites feature in the free Stellarium program (stellarium.org), select the ISS and create a simulated, detailed path. Created with Stellarium
Even if you never go to the trouble of identifying a “direct hit”, you can still use the transit finder to compile a list of cool lunar close approaches that would make for great photos with just a camera and tripod.
The Transit Finder isn’t the only way to predict ISS flybys. Some observers also use the excellent satellite site, CalSky. Once you tell it your location, select the Lunar/Solar Disk Crossings and Occultations link for lots of information including times, diagrams of crossings, ground tracks and more.
I use Stellarium (above) to make nifty simulated paths and show me where the Moon will be in the sky at the time of the transit. When you’ve downloaded the free program, get the latest satellite orbital elements this way:
* Move you cursor to the lower left of the window and select the Configuration box
* Click the Plugins tab and scroll down to Satellites and click Configure and then Update
* Hover the cursor at the bottom of the screen for a visual menu. Slide over to the satellite icon and click it once for Satellite hints. The ISS will now be active.
* Set the clock and location (lower left again) for the precise time and location, then do a search for the Moon, and you’ll see the ISS path.
There you have it — lots of options. Or you can simply use the Transit Finder and call it a day! I hope you’ll soon be in the right place at the right time to see the space station pass in front of the Moon. Checking my usual haunts, I see that the space station will be returning next weekend (Jan. 27) to begin an approximately 3-week run of easily viewable evening passes.
Thanks to Bob and universetoday.com/ | 0.820074 | 3.41839 |
China's lunar probe Chang'e-3 was placed into an Earth-Moon transfer orbit on Monday by a Long March 3B launch vehicle from the Xichang Satellite Launch Centre. It has on board a lunar landing module, containing the Yu Tu (Jade Rabbit) lunar rover. If all continues to go well, on December 14 Chang'e-3 will land in Sinus Iridum on the Moon's northern hemisphere. It will be the first spacecraft to make a soft landing on the Moon in 37 years.
The Chang’e-3 mission incorporates two major components, a Lander and a Rover named Yu Tu, or Jade Rabbit, named after the companion of the Moon goddess Chang'e in Chinese mythology. The Lander is 0.83 m (33 in) high, the octagonal body is about 3.8 m (12.5 ft) across, and the four extendable landing legs span 4.76 m (15.6 ft). Fully fueled and carrying the Rover, the Lander has a mass of about 3,780 kg (8,300 lb), about 2,600 kg (5,700 lb) of which is fuel for the lunar descent and landing.
The three-stage Chang Zheng 3B (Long March 3B) launch vehicle used to send the Chang'e-3 probe to the Moon is roughly a functional equivalent of the SpaceX Falcon 9.
The Long March 3B is about 55 m (180 ft) in length, has a diameter of 3.35 m (11 ft), and weighs about 426 metric tons at liftoff. The first two stages and the booster rockets use a N2O4/UDMH (Nitrogen Tetroxide/Unsymmetrical DiMethylHydrazine) oxidizer/fuel combination, while the third stage has a cryogenic hydrogen/oxygen rocket engine. The 3B can lift 12 metric tons into low Earth orbit, 5.1 metric tons into a geostationary orbit, and 3.3 metric tons into an independent orbit around the Sun.
The third stage provides two crucial burns; the first occurs just after separation from the second stage. The purpose of this burn is to inject the third stage and the Chang'e-3 probe into a parking orbit. The rocket follows this parking orbit while the proper orientation is achieved for insertion into the translunar orbit.
A second burn of the third stage engines then pushed the Chang'e-3 into a highly elliptical translunar orbit. Taking the Chang'e-3 to an apogee of 368,000 kilometers, this maneuver was completed about 19 minutes after takeoff. Deployment of Chang'e-3's landing legs and two power-generating solar arrays also was carried out without a hitch. Now the probe will slumber for a few days, until it burns its own engines to enter lunar orbit on December 6.
Then will come the tricky bit, landing safely without any input from controllers on Earth. This requires a combination of inertial guidance, extremely precise range and velocity measurements, image recognition, and a pretty fast computer – not to mention a certain amount of luck.
Chang'e-3 will pass through several distinct stages during the landing procedure. Initially in a circular 100 x 100 km (63 x 63 mi) orbit, it will lower itself into an orbit whose closest approach to the lunar surface is 15 km (9.3 mi). The next step is to break out of that orbit, beginning the landing approach.
As the probe approaches the landing site, it begins to examine the area to look for unexpected hazards. Once over a good tract of land, Chang'e-3 will hover on its rockets, and do a thorough examination of the landing site. It will then avoid any hazards while slowly lowering itself toward the ground. The rockets will cut out when the craft is 4 meters (13 ft) above the soil, allowing it to free-fall until impact with the ground is absorbed by the landing legs. This may sound like harsh treatment, but in a fall of 4 meters under lunar gravity, the impact velocity is only 3.6 m/s, or about 8 mph.
Once landed, the Chang'e-3 lander will carry out some housekeeping tasks and then unload the Yu Tu rover. The lander uses a combination of solar panels and a radioactive thermoelectric generator to supply its power needs, both for operating electricity and for heating during the two week lunar nights. The rover uses only solar panels and batteries to operate during the days, and to store maintenance power for the nights.
Each wheel of the six-wheeled rover is powered by an independent brushless DC motor. When combined with a rocker-bogie suspension system similar to that used by the Mars rovers, the Yu Tu can travel at an amazing one-eighth of a mile per hour, climb 20 degree slopes, and roll over obstacles 20 cm (8 in) in size. The rover is steered by a control system that integrates local hazard analysis with teleoperation by controllers on Earth.
The lander comes equipped with a sophisticated assortment of scientific instrumentation. One is the Lunar Ultraviolet Telescope, or LUT. It is designed to act as a long-term astronomical observatory, the first ever placed on the Moon's surface. The vacuum environment and slow rotation of the lunar environment make an ideal location for near-UV observations that cannot be carried out from beneath the Earth's obscuring atmosphere. The LUT is a 15 cm (6 in) aperture Ritchey-Chretian telescope equipped by a CCD image sensor sensitive to light having wavelengths between 245 and 340 nanometers.
Another optical instrument is the Extreme Ultraviolet Camera intended to monitor the Earth's plasmasphere, which is a magnetically active region within the magnetosphere but above the ionosphere. It works by viewing light with a wavelength of 30.5 nm which is scattered from helium ions in the plasmasphere. The lander is also hosting several other cameras and a lunar soil probe.
Jade Rabbit is arguably fitted out with more sophisticated scientific equipment than any previous rover. Most notable is a powerful ground-penetrating radar capable of penetrating up to 30 meters (100 ft) of lunar soil or about 100 m (330 ft) of lunar crustal material, and analyzing the underlying structure.
The rover is also equipped with an Alpha Particle X-ray Spectrometer (APXS) installed with a sensor head on a robotic arm. The electronics inside remain protected within the rover. APXS, which comes equipped with a 30 millicurie radioactive alpha source, can use particle-induced X-ray emission and X-ray fluorescence to determine the abundance of elements within rock and soil samples, and can also find hidden materials, such as water of crystallization, which is otherwise difficult to detect remotely.
An imaging spectrometer that operates in the visible and near-infrared can quickly obtain data that can guide an initial guess for the identity of a mineral found during a lunar survey. The design that made its way onto the Yu Tu rover is particularly sophisticated, using an acoustic-optic tunable filter to control the imaging wavelengths. Again, there are additional stereo imaging and other special-purpose cameras.
The landing site for Chang'e-3 is in the general area of Sinus Iridum, the remains of a large impact crater which was subsequently flooded with basaltic lava. A precise location has not yet been announced, but speculation centers in the vicinity of crater Laplace A, a small crater that is nearly on the transition region between the lava floods and the more common crustal formations. An exciting prospect – we are likely to learn something new about the Moon in the next few weeks!
Source: NASA Spaceflight.com | 0.818721 | 3.063307 |
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Furthest known member of the solar system has been seen
V774104 is not an especially inspiring moniker, but this week it has gotten a lot of astronomers excited - it's the formal designation for the furthest member of our solar system ever to be seen. Out beyond the orbits of Uranus and Neptune is thought to lurk a whole collection of small, icy, weird worlds. Pluto was the first we've sent a space craft to, and others, like Sedna, are suspected to be foreigners from another solar system.
For now V774104 is just a distant spot of light - we know almost nothing about it except that it exists. “We don’t know anything about its orbit,” says Scott Sheppard of the Carnegie Institute of Washington, whose team discovered the new addition. “We just know it’s the most distant object known.”
But over the coming months Sheppard and other astronomers will be working hard to learn as much as they can about this new little world, and what it might teach us about the wider universe.
|Above: The Subaru telescope, which was used to find the new addition to the Sun's family. Courtesy of the National Astronomical Observatory of Japan.|
Cassini investigates odd red streaks on Tethys.
Scientists love a mystery - in fact that's at least 50% of the job definition - and the Saturn system is full of them. One that hasn't been investigated much until now is Saturn's moon Tethys. Although it looks like an unremarkable ball of cratered ice from a distance, closer inspection shows strange reddish streaks mottling its surface. This week the Cassini space probe performed a close flyby of Tethys to try and get a better look at them - hopefully some clues to what they can be found before the Cassini mission comes to an end in 2017.
|Above: Tethy's, an icy moon of Saturn with parts of its surface coated in faint red marks|
Asteroids seen being dismembered by dwarf star
A general rule of thumb in space exploration is that the more extreme the thing you're looking at is the more extreme you should expect its behaviour to be. White Dwarfs are up there with the most extreme things we know: They're the collapsed cores of dead suns. Incredibly dense and possessed of gravitational fields stronger than anything except a neutron star or a black hole, anything straying to close can expect a dramatic fate. For a collection of asteroids that strayed too close to the white dwarf called a SDSS1228+1040 their fate was to be ripped apart and smeared into an arc of dust and rock around the dead star.
Such is life in the universe, but for the first time the ring of debris has been imaged, using a technique called Doppler tomography. The new picture was taken by a team from the University of Warwick. Professor Boris Gänsicke of the University of Warwick’s Astrophysics Group described their find:
“When we discovered this debris disk orbiting the white dwarf SDSS1228+1040 back in 2006, we thought we saw some signs of an asymmetric shape. However, we could not have imagined the exquisite details that are now visible in this image constructed from twelve years of data - it was definitely worth the wait. Over the past decade, we have learned that remnants of planetary systems around white dwarfs are ubiquitous, and over thirty debris disks have been found by now. While most of them are in a stable state, just like Saturn’s rings, a handful are seen to change, and it is those systems that can tell us something about how these rings are formed.”
|Above: The image of the 'ring' of debris around the dwarf star. Although there had been hints in the past of it's irregular shape, this is the first time it has actually been seen. Courtesy of the University of Warwick.|
Indian Mars mission gets a look at Martian moon Deimos
The Indian space agency's Mars Orbiter Mission (MOM) has had a rare opportunity to get a look at the back side of the martian moon Deimos. Because its orbit is above that of most of the space craft orbiting the red planet, and because it is tidally locked to Mars, Deimos' back side is rarely able to be imaged.But MOM has a wider orbit than most, which crosses outside Deimos' orbit so it can photograph the tiny moon's unseen side. The pictures were taken from around four thousand kilometres away.
|Above: The backside of Deimos, as seen by MOM from around four thousand kilometres away. Courtesy of ISRO|
Archived press conferences for all the DPS announcements
Today is the last day of the Division of Planetary Science's 2015 conference. There's been a lot of interesting papers (here are a few of my favourites) and new discoveries announced, from scorching hot Mercury right near the Sun to frigid Pluto, all the way out on the edge of interstellar space. But it's been a busy week for us normal folk to, and the news outlets don't always catch everything. So, if you might have missed anything, here (the title link) is an archive of all the press releases from DPS this week.
Satellites to track planes worldwide
Following the the mysterious disappearance of flight MH370 in March 2014 representatives from countries across the world have met up at a conference run by the UN's International Telecommunication Union (ITU). To avoid such baffling tragedies as MH370 in future - where the lack of closur prevents many grieving relatives from moving on - the conference concluded that all aircraft would be tracked in future by satellites, allowing their positions to be known worldwide, in real time. Currently ground based radar is used to track aircraft, but this cannot follow an aircraft far out at sea, or flying below a certain altitude.
US Ambassador Decker Anstrom praised the deal, saying it would "enable better tracking and location of aircraft that otherwise could disappear from terrestrial tracking systems." | 0.934672 | 3.271554 |
4.37 light-years away lies the Alpha Centauri system. What lurks near our closest stellar neighbor? A big announcement last August revealed a planet in the habitable zone around the star. But its close orbit (just 11 days) means the chances of life on the planet are small. While the orbit might be temperate due to the nature of the Proxima Centauri (a red dwarf), the proximity means it’s probably being slammed by ultraviolet and X-ray flares from the star. A no-go for life. At least, as we know it.
But the discovery does make astronomers wonder what other chunks of rock are orbiting the three stars making up Alpha Centauri. The European Southern Observatory (ESO) agrees and plans to adapt the Very Large Telescope to conduct a more thorough search for planets in the star system in 2019.
The ESO and Breakthrough Initiatives entered into an agreement to modify the telescope to enhance its ability to discover planets around our nearest solar system.
Detecting planets in a habitable zone around another star is no easy feat. Because the habitable zones are often close to the star, the star’s blinding brightness makes it difficult to spot. Astronomers look at stars through the mid-infrared wavelength range to help tamp down the brightness from the star. Even then, the star can still be millions of times brighter than the planets.
That’s where the upgrade ESO and Breakthrough Initiatives comes into play. Using adaptive optics and a technique called coronagraphy (reduces the light from the star even more).
A coronagraph is a disc attached to a telescope that blocks the bright light from a star. Here’s how it looks when the Solar and Heliospheric Observatory looks at the sun.
Breakthrough Initiatives will provide most of the money for the tech upgrades while ESO provides the telescope and the time for the search. Among the new upgrades will be an instrument module, “which will host the wavefront sensor, and a novel detector calibration device.” A new coronagraph, like the one seen in the image above, is also being developed.
Alpha Centauri provides a unique opportunity for the ESO right now. The upcoming European Extremely Large Telescope (E-ELT) is designed to detect and study potentially habitable planets. But it won’t be ready until the mid-2020s. The Very Large Telescope isn’t as powerful as the E-ELT, but it has enough power to detect and study large planets around the closest star system to Earth.
The Very Large Telescope could find planets we don’t know about yet, but the E-ELT will be the one to watch for. The METIS (mid-infrared imager) on the E-ELT will be able to detect exoplanets the size of Mars orbiting Alpha Centauri, if they are out there.
The search for exoplanets like Earth will only heat up as more sophisticated telescopes are brought online. 2019 might not bring the announcement of a planet the size of Earth, but it could tell us the Alpha Centauri system has more planets than we know about right now.
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Ask Ethan: What should a black hole’s event horizon look like?
You might think that it should be all black, but then how would we see it?
“It is conceptually interesting, if not astrophysically very important, to calculate the precise apparent shape of the black hole… Unfortunately, there seems to be no hope of observing this effect.” -Jim Bardeen
Earlier this month, telescopes from all around the world took data, simultaneously, of the Milky Way’s central black hole. Of all the black holes that are known in the Universe, the one at our galactic center — Sagittarius A* — is special. From our point of view, its event horizon is the largest of all black holes. It’s so large that telescopes positioned at different locations on Earth should be able to directly image it, if they all viewed it simultaneously. While it will take months to combine and analyze the data from all the different telescopes, we should get our first image of an event horizon by the end of 2017. So what will it looks like? That’s the question of Dan Barrett, who’s seen some illustrations and is a bit puzzled:
Shouldn’t the event horizon completely surround the black hole like an egg shell? All the artist renderings of a black hole are like slicing a hard boiled egg in half and showing that image. How is it that the event horizon does not completely surround the black hole?
There are a few different classes of illustrations floating around, to be sure. But which ones, if any, are correct?
The oldest type of illustration is simply a circular, black disk, blocking out all the background light from behind it. This makes sense if you think about what a black hole actually is: a collection of mass that’s so great and so compact that the escape velocity from its surface is greater than the speed of light! Since nothing can move that quickly, not even the forces or interactions between the particles inside the black hole, the inside of a black hole collapses to a singularity, and an event horizon is created around the black hole. From this spherical region of space, no light can escape, and so it should appear as a black circle, from any perspective, superimposed on the background of the Universe.
But there’s more to the story than that. Because of their gravity, black holes will magnify and distort any background light, due to the effect of gravitational lensing. This is a more detailed and accurate illustration of what a black hole looks like, as it also possesses an apparent event horizon sized appropriately with the curvature of space in General Relativity.
Unfortunately, these illustrations are flawed, too: they fail to account for foreground material and for accretion around the black hole. Some illustrations, though, do successfully add these in.
Because of their tremendous gravitational effects, black holes will form accretion disks in the presence of other sources of matter. Asteroids, gas clouds, or even entire stars will be torn apart by the tidal forces coming from an object as massive as a black hole. Due to the conservation of angular momentum, and of collisions between the various infalling particles, a disk-like object will emerge around the black hole, which will heat up and emit radiation. In the innermost regions, particles occasionally fall in, adding to the mass of the black hole, while the material in front of the black hole will obscure part of the sphere/circle you’d otherwise see.
But the event horizon itself isn’t transparent, and you shouldn’t be able to see the matter behind it.
It might seem surprising that a Hollywood film — Interstellar — has a more accurate illustration of a black hole than many of the professional pieces of artwork created for/by NASA, but misconceptions abound, even among professionals, when it comes to black holes. Black holes don’t suck matter in; they simply gravitate. Black holes don’t tear things apart because of any extra force; it’s simply tidal forces — where one part of the infalling object is closer to the center than another — that does it. And most importantly, black holes rarely exist in a “naked” state, but rather exist in the vicinity of other matter, such as at the center of our galaxy.
So with all of that in mind, what are the hard-boiled-egg images that have been going around? Remember, we can’t image the black hole itself, because it doesn’t emit light! All we can do is look at a particular wavelength, and see a combination of the emitting light that comes from around, behind and in front of the black hole itself. The expected signal, indeed, does resemble a split hard-boiled egg.
This has to do with what it is we’re imaging. We can’t look in X-rays, because there are simply too few X-ray photons overall. We can’t look in visible light, because the galactic center is opaque it it. And we can’t look in the infrared, because the atmosphere blocks infrared light. But what we can do is look in the radio, and we can do it all over the world, simulataneously, to get the optimal resolution possible.
The black hole at the galactic center has an angular size of about 37 micro-arc-seconds, while the resolution of this telescope array is around 15 micro-arc-seconds, so we should be able to see it! At radio frequencies, the overwhelming majority of that radiation comes from charged matter particles being accelerated around the black hole. We don’t know how the disk will be oriented, whether there will be multiple disks, whether it will be more like a swarm of bees or more like a compact disk. We also don’t know whether it will prefer one “side” of the black hole, as viewed from our perspective, over another.
We fully expect the event horizon to be real, to be of a specific size, and to block all the light coming from behind it. But we also expect that there will be some signal in front of it, that the signal will be messy due to the messy environment around the black hole, and that the orientation of the disk with respect to the black hole will play an important role in determining what we see.
One side is brighter as the disk rotates towards us; one side is fainter as the disk rotates away. The entire “outline” of the event horizon may be visible as well, thanks to the effect of gravitational lensing. Perhaps most importantly, whether the disk is seen “edge-on” or “face-on” with respect to us will drastically alter the signal, as the 1st and 3rd panels below illustrate.
There are other effects we can test for, including:
- whether the black hole has the right size as predicted by general relativity,
- whether the event horizon is circular (as predicted), or oblate or prolate instead,
- whether the radio emissions extend farther than we thought,
or whether there are any other deviations from the expected behavior. This is a brand new frontier in physics, and we’re poised to actually test it directly. One thing’s for certain: no matter what it is that the Event Horizon Telescope sees, we’re bound to learn something new and wonderful about some of the most extreme objects and conditions in the Universe!
Send in your Ask Ethan questions to startswithabang at gmail dot com!
Starts With A Bang is based at Forbes, republished on Medium thanks to our Patreon supporters. Order Ethan’s first book, Beyond The Galaxy, and pre-order his next, Treknology: The Science of Star Trek from Tricorders to Warp Drive! | 0.889925 | 3.992615 |
NASA’s Neutron Star Interior Composition Explorer, or NICER, is an X-ray telescope launched on a SpaceX Falcon 9 rocket in early June 2017. Installed on the International Space Station, by mid-July it will commence its scientific work – to study the exotic astrophysical objects known as neutron stars and examine whether they could be used as deep-space navigation beacons for future generations of spacecraft.
What are neutron stars? When stars at least eight times more massive than the Sun exhaust all the fuel in their core through thermonuclear fusion reactions, the pressure of gravity causes them to collapse. The supernova explosion that results ejects most of the star’s material into the far reaches of space. What remains forms either a neutron star or a black hole.
I study neutron stars because of their rich range of astrophysical phenomena and the many areas of physics to which they are connected. What makes neutron stars extremely interesting is that each star is about 1.5 times the mass of the Sun, but only about 25km in diameter – the size of a single city. When you cram that much mass into such a small volume, the matter is more densely packed than that of an atomic nucleus. So, for example, while the nucleus of a helium atom has just two neutrons and two protons, a neutron star is essentially a single nucleus made up of 1057 neutrons and 1056 protons.
Exotic physics impossible on Earth
We can use neutron stars to probe properties of nuclear physics that cannot be investigated in laboratories on Earth. For example, some current theories predict that exotic particles of matter, such as hyperons and deconfined quarks, can appear at the high densities that are present in neutron stars. Theories also indicate that at temperatures of a billion degrees Celsius, protons in the neutron star become superconducting and neutrons, without charge, become superfluid.
The magnetic field of neutron stars is extreme as well, possibly the strongest in the universe, and billions of times stronger than anything created in laboratories. While the gravity at the surface of a neutron star may not be as strong as that near a black hole, neutron stars still create major distortions in spacetime and can be sources of gravitational waves, which were inferred from research into neutron stars in the 1970s, and confirmed from black holes by the LIGO experiments recently.
The main focus of NICER is to accurately measure the mass and radius of several neutron stars – and, although the telescope will observe other types of astronomical objects, those of us studying neutron stars hope NICER will provide us with unique insights into these fascinating objects and their physics. NICER will measure how the brightness of a neutron star changes according to its energy, and how it changes as the star rotates, revealing different parts of the surface. These observations will be compared to theoretical models based on properties of the star such as mass and radius. Accurate determinations of mass and radius will provide a vital test of nuclear theory.
A GPS for deep space
Another aspect of neutron stars that could prove important for future space travel is their rotation– and this will also be tested by NICER. Rotating neutron stars, known as pulsars, emit beams of radiation like a lighthouse and are seen to spin as fast as 716 times per second. This rotation rate in some neutron stars is more stable than the best atomic clocks we have on Earth. In fact, it is this characteristic of neutron stars that led to the discovery of the first planets outside our solar system in 1992 – three Earth-sized planets revolving around a neutron star.
The NICER mission, using a part of the telescope called SEXTANT, will test whether the extraordinary regularity and stability of neutron star rotation could be used as a network of navigation beacons in deep space. Neutron stars could thus serve as natural satellites contributing to a Galactic (rather than Global) Positioning System and could be relied upon by future manned and unmanned spacecraft to navigate among the stars.
NICER will operate for 18 months, but it is hoped that NASA will continue to support its operation afterwards, especially if it can deliver on its ambitious scientific goals. I hope so too, because NICER combines and greatly improves upon the invaluable capabilities of previous X-ray spacecraft – RXTE, Chandra, and XMM-Newton – that are used to uncover neutron stars’ mysteries and reveal properties of fundamental physics.
The first neutron star, a pulsar, was discovered in 1967 by Jocelyn Bell Burnell. It would be fitting to obtain a breakthrough on neutron stars in this 50th anniversary year. | 0.934842 | 3.97787 |
Eric Bell, an associate professor in astronomy, and Colin Slater, an astronomy Ph.D. student, found Andromeda XXVIII and XXIX---that's 28 and 29. They did it by using a tested star-counting technique on the newest data from the Sloan Digital Sky Survey, which has mapped more than a third of the night sky. They also used follow-up data from the Gemini North Telescope in Hawaii.
At 1.1 million and 600,000 light years from Andromeda, these are two of the furthest satellite galaxies ever detected. Invisible to the naked eye, the galaxies are 100,000 times fainter than Andromeda, and can barely be seen even with large telescopes.
The findings are published in the current Nov. 20 edition of Astrophysical Journal.
These astronomers set out looking for dwarf galaxies around Andromeda to help them understand how matter relates to dark matter, an invisible substance that doesn't emit or reflect light, but is believed to make up most of the universe's mass. Astronomers believe it exists because they can detect its gravitational effects on visible matter. With its gravity, dark matter is believed to be responsible for organizing visible matter into galaxies.
"These faint, dwarf, relatively nearby galaxies are a real battleground in trying to understand how dark matter acts at small scales," Bell said. "The stakes are high."
The prevailing hypothesis is that visible galaxies are all nestled in beds of dark matter, and each bed of dark matter has a galaxy in it. For a given volume of universe, the predictions match observations of large galaxies.
"But it seems to break down when we get to smaller galaxies," Slater said. "The models predict far more dark matter halos than we observe galaxies. We don't know if it's because we're not seeing all of the galaxies or because our predictions are wrong."
"The exciting answer," Bell said, "would be that there just aren't that many dark matter halos." Bell said. "This is part of the grand effort to test that paradigm."
The papers are titled, "Andromeda XXIX: A New Dwarf Spheroidal Galaxy 200 kpc from Andromeda," and Andromeda XXVIII: A Dwarf Galaxy more than 350 kpc from Andromeda."
The research is funded in part by the National Science Foundation.
For more information:Eric Bell: http://www.astro.lsa.umich.edu/~ericbell/
Abstract of Andromeda XXIX: A New Dwarf Spheroidal Galaxy 200 kpc from Andromeda: http://iopscience.iop.org/2041-8205/742/1/L15
Nicole Casal Moore | Newswise Science News
Tiny lasers from a gallery of whispers
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20.09.2017 | Physics and Astronomy | 0.85712 | 3.909574 |
“Earth is not round”
Earth is not round. Nor, for that matter, is it flat, rectangular, pyramidal, cubical or in the shape of any regular solid. Normally we think of it as being spherical, but that is really only a first impression. Of course the surface of the solid body of the planet has many variations, from tall mountain ranges to deep ocean trenches. But even if those variations are ignored, there are other variations. Some satellite data, for example, indicate a possible depression near the South Pole and a corresponding bulge near the North Pole. The most well known deviation, however, was theorized two centuries ago. It says that the Earth is slightly squashed, as if two great hands were pressing in on it at both poles. This effect is very slight and the shape is called an “oblate spheroid.” As the Earth rotates, a so-called “centrifugal force” causes the equatorial regions to be “flung out” slightly, in a manner similar to although much less noticeable than the way an uncooked pizza flattens out as it is spun. But the effect is small, making a diameter across the equator about 27 km (17 miles) greater than a diameter through the poles.
The sun is not “burning”
It is common to refer to the sun as “burning,” but this is a very big misconception. It is not burning in the common sense at all. When a lump of coal, a liter of gasoline or a piece of paper “burns,” it is a chemical reaction involving a rearrangement of the electrons in atom. It does not change the elements involved, but simply re-arranges the electrons in those elements. In the nuclear fusion process of our Sun and other stars, the very nature of the elements changes. In both cases, the mass of the end product versus the original product is less, and the mass lost is turned into energy via Einstein’s famous equation, E=MC2. However, in ordinary chemical burning (such as when you burn coal, gasoline or paper), only about one billionth of the mass is lost. Thus, a nuclear reaction such as that which occurs in the sun is a billion times more efficient. The sun is not “burning,” but it is converting about 4.5 million tons of matter into energy every second.
“There is lots of water and oxygen in space”
Water is a prime requisite for life as we know it, and although our Earth is the only place in the solar system with large oceans of it, water is the most common compound in the Universe. In fact, water molecules have been found in clouds in deep space. One recently discovered cache of water molecules, in one tiny corner of the universe, contains 140 trillion times the amount of water in all the Earth’s oceans.
“Oxygen is a metal”
Due to a now obscure astronomical definition, and element with more than two protons is considered a “metal.” Hydrogen and helium, having one and two protons respectively, are non-metals, but everything else including carbon, nitrogen and even oxygen is considered a “metal.” That being said, of course astronomers do not believe that oxygen and most of the other elements are metals in the ordinary sense. It is simply a strange use of the word.
Jupiter may have “metallic” hydrogen
Normally, astronomers consider hydrogen and helium to be the only two non-metals (see above). However, under enormous pressure, even hydrogen can be turned into a metal of sorts. This basically means that it has the electrical properties of a metal. Scientists have confirmed this in the laboratory, and there is good reason to such “metallic” hydrogen exists in the deep interiors of both Jupiter and Saturn.
“Jupiter also may have 35,000 degree ice”
Perhaps even stranger is the possibility that deep below the cloud tops of Jupiter is a region where the pressure is so great – millions of times the atmospheric pressure at the surface of the Earth – that water and other compounds can exist in a solid crystalline ice even at 35-40,000 degrees F! This would be true not just for Jupiter, but Saturn, Uranus and Neptune, too.
“Saturn has something in common with gasoline and wood”
Imagine a “drop” of gasoline (petrol) or a ball of maple wood, 9 times the size of Earth. What, pray tell, might these have in common with the planet Saturn? Density. Both gasoline and maple wood have a low density, approximately the same as the overall density of Saturn, and only about 70% that of water. It is often said that Saturn would float on water – the demonstration of which would be somewhat problematic – but that just means that its density is less than water. Gasoline floats on top of water, just a ball of maple wood does.
Some stars have more fuel than our sun, which is to say that they are more massive. Some stars have twice more, some 10 times more, and a relative few have 100 times more fuel as our sun. In fact, one “hypergiant” star designated as R136a1, is thought to be 265 times the mass of our sun. You might think that such stars, with such great mass, and such enormous reservoirs of fuel, would shine a very long time. But you would be wrong. In fact, very massive stars guzzle their nuclear fuel at prodigious rates, causing them to run out quickly. Our sun and similar stars have lifetimes of about 10 billion years, but a star 10 times more massive than the sun will “burn” for only about 30 million years, about one third of one percent as long!. A truly massive star 100 times more mass (and hence vastly more fuel) than our sun, may live only 100,000 years or so. If the sun’s lifetime were the same as the average human, a star 100 times as massive would live about six hours! And R136a1 would be gone in roughly the time it takes to watch a single episode of “The Big Bang Theory!”
“The hottest stars are the dimmest stars”
You might reasonably expect that the hottest stars would be the brightest. After all, a fireplace poker gets brighter as it gets hotter (at least in our experience). But there are two other factors. One is simply the fact that as a star gets hotter, more of its energy output moves beyond the visible light spectrum into ultra violet, X-rays and even gamma rays. Second is the fact that luminosity or total energy output (related to brightness) also depends on size. Smaller objects have less space from which to radiate electromagnetic energy, and hence are dim although hot. A newly formed white dwarf stars have surface temperatures of nearly 200,000 degrees F, but due to their small size (similar to Earth), are very dim. Smaller, hotter and dimmer still are neutron stars. A typical neutron star could easily fit between Dallas and Fort Worth, but can have a surface temperature of millions of degrees. In this case, the object is so small that its total energy output must also be small, and what energy it does radiate is mostly in shorter wavelength (non visible) ultraviolet and X-rays. Thus the hottest stellar mass objects in the universe are very, very dim (comparatively).
“Planetary Nebulae have nothing to do with planets”
When you see a spectacular telescope image it is not hard to see a resemblance to the Earth. In a telescope, some of these objects appear as faint, fuzzy greenish disks, resembling the planet Uranus “planetary nebulae.” The term “nebula” (“nebulae,” plural) is a Latin word for a cloud, a term applied to many dim, often ill-defined objects seen in early telescopes. In fact these objects have nothing to do with planets, but are the expanding clouds of gas and debris left over at the death of a sun-like star. They are vastly larger than any planet or star, averaging a light year or more across. | 0.897249 | 3.660684 |
The glowing region in this new image from the MPG/ESO 2.2-metre telescope is a reflection nebula known as IC 2631. These objects are clouds of cosmic dust that reflect light from a nearby star into space, creating a stunning light show like the one captured here. IC 2631 is the brightest nebula in the Chamaeleon Complex, a large region of gas and dust clouds that harbours numerous newborn and still-forming stars. The complex lies about 500 light-years away in the southern constellation of Chamaeleon.
IC 2631 is illuminated by the star HD 97300, one of the youngest -- as well as most massive and brightest -- stars inits neighbourhood. This region is full of star-making material, which is made evident by the presence of dark nebulae noticeable above and below IC 2631 in this picture. Dark nebulae are so dense with gas and dust that they prevent the passage of background starlight.
Despite its dominating presence, the heft of HD 97300 should be kept in perspective. It is a T Tauri star, the youngest visible stage for relatively small stars. As these stars mature and reach adulthood they will lose mass and shrink. But during the T Tauri phase these stars have not yet contracted to the more modest size that they will maintain for billions of years as main sequence stars .
These fledging stars already have surface temperatures similar to their main sequence phase and accordingly, because T Tauri-phase objects are essentially jumbo versions of their later selves, they look brighter in their oversized youth than in maturity. They have not yet started to fuse hydrogen into helium in their cores, like normal main sequence stars, but are just starting to flex their thermal muscles by generating heat from contraction.
Reflection nebula, like the one spawned by HD 97300, merely scatter starlight back out into space. Starlight that is more energetic, such as the ultraviolet radiation pouring forth from very hot new stars, can ionise nearby gas, making it emit light of its own. These emission nebulae indicate the presence of hotter and more powerful stars, which in their maturity can be observed across thousands of light-years. HD 97300 is not so powerful, and its moment in the spotlight is destined not to last.
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 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. 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 a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become "the world's biggest eye on the sky".
- Images of the MPG/ESO 2.2-metre telescope at La Silla - http://www.
eso. org/ public/ images/ archive/ search/ ?adv= &subject_name= mpg
- Photos taken with the MPG/ESO 2.2-metre telescope at La Silla - http://www.
eso. org/ public/ images/ archive/ search/ ?adv= &facility= 15
ESO Public Information Officer
Garching bei München, Germany | 0.853955 | 3.876302 |
Image Credit: Tony Piro
In a couple of posts over the last few weeks (one on the "Death Star Pinwheel" and one on a very bright explosion), I've mentioned gamma ray bursts. But what is a gamma ray burst? Today, a little history, and tomorrow, the current hypothesis.
In the 1963, the US and Soviet Union entered into a treaty that prohibited the testing of nuclear weapons in the atmosphere, in outer space, or under water. The US decided that one way to verify that the Soviets were not testing weapons in space was to launch a satellite to look for gamma rays. Gamma rays are the most energetic form of light, and are released in copious quantities by nuclear reactions. The atmosphere blocks gamma rays, so the only way to look for them is in space.
So, the US launched a series of Vela satellites to look for short flashes of gamma rays -- and they found them! After a few tense weeks of detecting almost a flash a day, it was realized that the amount of nuclear material the Soviets would have to be using to test so many space weapons would be depleting their entire stockpile, which would not be a smart move, and the Soviets were not dumb. A little more research proved that the explosions were coming from deep space, and so were astronomical.
Most people though that gamma ray bursts must be material falling onto neutron stars in our galaxy causing small nuclear explosions. But in the the 1990s, the Compton Gamma Ray Explorer (the gamma-ray equivalent of the Hubble Space Telescope) found that gamma ray bursts do not come from the parts of the sky where the Milky Way galaxy is found -- they come from every direction. That is a strong indication that these gamma ray bursts come from the distant universe, which looks about the same in every direction. But if the events that caused gamma ray bursts sent gamma rays in every direction, the energies required were at least 10 times bigger than supernovae, the most powerful explosions in the Universe.
To further muddy the waters, the Compton Gamma Ray Observatory started to reveal evidence that there are two types of gamma ray bursts. One type, the short burst, has higher-energy gamma rays but only lasts a fraction of a second. The second type, or long burst, had lower-energy gamma rays but last ten to 30 seconds. I remember seeing some talks about this data when it was first emerging. Lots of people had lots of ideas as to what gamma rays were, why there might be two different types, and whether or not they actually believed any other theory. But we needed some more information, and that information came from an unexpected source: an Italian X-ray satellite called "Beppo-Sax."
To be continued... | 0.8395 | 3.94654 |
Ever since the days of Galileo and the first optical telescopes more than 400 years ago, astronomers have been looking for ways to cast their gaze farther into the heavens around us. Today, thanks to the earth-orbiting Hubble Space Telescope, that gaze extends to the very edges of the known universe.
On April 24, 1990, the U.S. space shuttle Discovery roared into orbit carrying the special instrument which would revolutionize our knowledge of the universe.
The Hubble Space Telescope was designed to orbit the earth - far above the obscuring haze of the earth’s atmosphere - observing planets, stars, galaxies and other distant celestial objects with unprecedented clarity.
The school bus-sized telescope, named after American astronomer Edwin P. Hubble, took 10 years to build at a cost of $1.5 billion. More than 10,000 people were involved in its design and construction.
Nancy Grace Roman is considered the “mother” of the Hubble. As the first chief astronomer at the U.S. space agency, NASA, Roman played a pivotal role in Hubble’s early planning and development.
She travelled around the country, talking with astronomers about what they needed in a new telescope.
“Astronomers had been wanting to get observations from above the atmosphere for a long time," says Roman. "Looking through the atmosphere is somewhat like looking through a piece of old, stained glass. The glass has defects in it, so the image is blurred from that.”
Roman set up a committee of astronomers, and NASA engineers to design a large and serviceable observatory that would orbit above the atmosphere and transmit clear images of the universe back to earth.
Ed Weiler, NASA’s current chief astronomer, worked with Roman and has been intimately involved with the Hubble program since he succeeded her in 1979.
“The Hubble, when it was launched, represented an increase in capability of other telescopes on the ground by a factor of 10," he says. "The last time in human history in astronomy that we leaped a factor of 10, in one step, was when Galileo stopped using his eye and put the first telescope to his eye.”
Despite an initial glitch with a defective mirror, Hubble’s mission of observation and discovery has been historic. The telescope’s wide-field camera has captured and transmitted stunning images of celestial objects back to earth, many of them more distant than anything seen before.
“The Hubble can see things that are billions of times fainter than your human eye can see, and it can resolve objects very, very much more clearly," says Weiler. "For instance, you can see a firefly on the moon with the Hubble, whereas you wouldn’t see that with your eye.”
Roman recalls how excited she was to see her first Hubble pictures.
“I think the image that to me was most striking was a picture of the center of a globular cluster," she says. "You could see each star individually, and see their color, and it was just a fantastic sight.”
Since its deployment more than 20 years ago, Hubble has expanded our knowledge of the universe a thousand-fold. The telescope has been upgraded in a series of space shuttle servicing missions. Its images of distant stars and galaxies have allowed astronomers to calculate that the universe was born about 14 billion years ago, a much more accurate measure than the old estimate of somewhere between 10 to 20 billion years.
Weiler says another of Hubble’s many scientific milestones was its confirmation of the existence of dark energy, a force that’s speeding the expansion of the universe. Hubble also proved that mysterious gravitational vortexes, known as black holes, exist at the center of most galaxies.
“Black holes were science fiction. "Star Trek," "Star Wars," "Black Holes"; nice theory but nobody believes in them right?" says Weiler. "Hubble proved they exist.”
On July 4 of this year, the Hubble Space Telescope completed its one millionth science observation; a spectrograph of an exoplanet 1,000 light-years away.
Today, the earth-orbiting observatory continues to perform what is widely hailed as one of the most successful space science missions in history.
As plans proceed for the launch of a new and even more powerful earth-orbiting telescope, Hubble is expected to remain in service for at least another decade, continuing to revolutionize astronomy and expand our knowledge of the universe. | 0.838157 | 3.764811 |
Physics Professor, Students Build Instruments to Study Cosmic Dust
April 27, 2017
When Fiona Breyer ’17 and Lunjun (Simon) Liu ’17 were teenagers looking at the night sky from their homes on two different continents, astrophysics seemed so exotic and exciting.
So the students were a bit nonplussed when their in-the-trenches experiences in astrophysics began not by looking up, but by drilling down — learning to use a milling machine, lathe, drill press and other important but rather unsexy pieces of equipment in the machine shops in the basement of the Center for Natural Science (CNS).
The two are among a half-dozen students contributing to a project led by Associate Professor of Physics Thushara Perera to design instrumentation that will help scientists learn more about cosmic dust. Once regarded as a nuisance by astronomers because it absorbs the visible light from objects, cosmic dust is now recognized for the role it plays in the evolution of galaxies, stars and planetary systems. Though not yet fully understood, cosmic dust is also thought to have an integral role in the chemical activity giving rise to complex molecules, some of which may be the precursors of amino acids, the building blocks of life.
Over his dozen-plus years in the field, Perera realized there is no one facility in the world dedicated solely to the study of cosmic dust candidates, or man-made items mimicking the dust’s chemical and physical properties. At large research facilities, an apparatus is rigged together for testing such candidates and then taken apart for other uses, said Perera, leading to systematic errors.
Perera reasoned that a dedicated system for studying cosmic dust — one that utilized the principles of observational cosmology — would greatly reduce such errors. “The whole goal of observational cosmology is to reduce systematic errors when you are looking at the sky,” he added. “So our system is built from a different perspective.” The National Science Foundation recognized the novelty of this approach and awarded Perera a grant for the project.
At the project’s center is a spectrometer. Its basic function is to take in light, break it into its spectral components, send those components through cosmic dust samples, record the amount of light transmitted through each sample as a function of wavelength, and display the data through a computer program.
One specific instrument Perera and his students are building is a Fourier Transform Spectrometer (FTS), which makes use of an innovative concept put forth by Dale Fixsen, a research scientist with NASA’s Goddard Space Flight Center. “I exchanged about three emails with Fixsen and we did the rest,” Perera said. When they are finished, Perera and his students will have constructed the world’s smallest FTS.
What’s most unique about the IWU project is the design — the compact FTS is coupled to a cryostat. Essentially a very cold refrigerator (indeed, Perera and his students refer to it as “the fridge”), the cryostat can cool samples to a temperature of 4 Kelvin, or –452 degrees Fahrenheit. The fridge can be used to match the temperatures of actual astronomical dust clouds (10-50 Kelvin). The structure that holds the fridge, along with the pumping/vacuum station, were mostly built and installed by Illinois Wesleyan physics students. So were most of the thermometers, associated cables and electronics, as well as special insulation within the fridge, which also includes a bolometer, or millimeter-wavelength light detector. This sensitive instrument measures radiant energy.
While Perera led the way in devising the spectrometer — from working out the mathematical formula to writing the source code to cut the metal for the ellipsoidal mirrors inside the spectrometer —his students made major contributions. Showing these components to a visitor, the professor ticks off some of the many advances made by past and current students:
- Kyle O’Shea ’16 took Perera’s CAD designs for the FTS and machined most of the necessary parts to high precision using IWU’s milling machine. He also implemented a system to control the FTS’s moving mirror, and used IWU’s 3D printers to make several items, including an adapter for the vacuum enclosure of the FTS. O’Shea is now a Ph.D. student in mechanical engineering at Michigan State University, where he’s working on new technology for 3D printing.
- Hansheng (Jason) Chen ’17 designed a robust optical window for the cryostat, so that a wide spectral range of light can pass into the fridge without compromising the vacuum within. After completing the design for the window — which was fabricated at the University of Illinois — Chen made changes and machined additional parts to help install the optical window. This fall, he will enter a graduate program in theoretical astrophysics at the University of California, Davis.
- Huy Do ’16 — now completing his 3:2 dual degree in electrical engineering at Washington University in St. Louis— was an early contributor to the project. Do’s work on the bolometer electronics and filter wheel mechanics built a foundation for the progress that has been made on the instrument thus far.
As the lead student on the spectrometer project this past year, Lunjun Liu played a major role in developing and testing a unique filter wheel housed in the fridge. This wheel holds and switches dust samples, allowing researchers to study up to eight different samples in one cooldown. Liu machined shafts, pulleys and dozens of other mechanical parts in the CNS machine shop, but his first challenge was to learn basic skills and safety protocols needed to work with the tools.
“I had no experience in any kind of building before coming to IWU,” said Liu, a native of Wuhan, China. “I was not expecting that would be something that would be necessary for an astrophysicist.” But as Liu was building the part, testing it, refining it, and testing it again in a seemingly endless process, he began to understand how important those routine tasks would be to the final outcome.
Liu believes his “in the trenches” experience in the IWU lab has given him an important advantage. Last summer he was selected for Caltech’s competitive Summer Undergraduate Research Fellowship. Because he was familiar with cryostats, detectors and electronics from his work at Illinois Wesleyan, Liu entered the Caltech lab confident of his abilities.
“At Caltech I observed other students not fully understanding the inner workings of the equipment, because they are not building things step by step, without understanding every concept of every device,” said Liu, who is returning to Caltech for a year to assist with deployment of one of his projects there before entering graduate school in astronomy at the University of Illinois. “I was able to provide my point of view to fine-tune a device, for example, to provide a better outcome.”
Getting it Right
“At temperatures this cold, so much can go wrong,” said Ronan Dorsey ’18, who joined Perera’s lab group in May 2016 and worked through the summer, spending much of that time machining parts for a “light pipe” within the cryostat that carries light from the outside to the dust samples inside the fridge.
“The machining can seem menial,” Dorsey admitted, “but it’s so important to take your time and just do it slow so you get it right. Or, at least, as much as you can before you test it. And then you go back to the machine shop when you figure out you did it wrong.”
Breyer’s introduction to the FTS project was equally unglamorous. When she joined the project in her sophomore year, she said her tasks involved screwing parts that had already been machined onto the body, or applying oil to keep the machining functioning smoothly. “I had no idea what I was doing at first,” she acknowledged with a laugh. “It takes a while to really understand the project.”
Soon, however, Perera tasked Breyer with logging the fridge’s temperature and detector data with LabVIEW, a graphical language used for data acquisition and instrument control. In the summer of 2015, Breyer worked in Perera’s lab to collect data as the spectrometer was being calibrated.
“My program would take data points every minute for something like 15 hours, store it and then we’d review it the next morning,” she said. According to Perera, Breyer also played a large role in structuring and organizing the inside of the cryostat. Breyer believes this lab research experience helped her secure a spot for a nationally competitive National Science Foundation Research Experiences for Undergraduates internship in 2016.
“Going into the summer research experience at the University of Wisconsin at Madison, I felt so much more confident about my abilities,” Breyer noted.
“Dr. Perera has always believed in me, even when I didn’t believe in myself, and he’s made me feel confident in my abilities to do lab work, to be a physicist, and to be successful,” she added.
Sharing with the World
The chance to work alongside a faculty member, building a device from the ground up in hopes of learning more about the origins of planetary systems, is not lost on the students.
“Spending four or five hours a day for a whole summer with Dr. Perera, working one-on-one on this project, is not something I would find at a big university,” Dorsey observed. “Working directly with a physicist of Dr. Perera’s caliber has been the most rewarding thing about this entire project.”
Dorsey has become the ‘go-to guy’ in day-to-day operations the past several months as Perera and his group have conducted three cooldowns in order to improve the bolometer’s performance. After a successful cooldown of the cryostat in February, the next step is to test and troubleshoot the entire system. Construction is scheduled for completion this summer, when the National Science Foundation grant’s funding cycle comes to a close.
Perera said that to his knowledge, there has been no other successful operation of a detector of this kind using a ‘dry’ cooling mechanism that employs gas pulses, rather than liquid helium, to cool. The only other FTS Perera knows of that’s remotely similar to the one at Illinois Wesleyan is housed in the lab of a colleague at the University of Michigan.
Despite the daily challenges and troubleshooting necessary to get a new instrument of such complexity up and running, Perera anticipates the satisfaction of soon being able to share the IWU group’s work with the world. First up is an academic paper on the project’s instrumentation, projected for later this year. And he looks forward to the day — soon, he hopes — when the device is fully functioning in its purpose to aid astronomers and astrophysicists in the quest to better understand the nature of cosmic dust.
“There is still much we don’t know about dust-obscured environments,” said Perera. “But knowing about the properties of the dust tells us how that dust was created, and that’s a piece of information about how a planetary system evolved or how a new planetary system was made.”
Perera noted the field of astronomy is currently preoccupied with asking the question of how life came to be, with the role of cosmic dust explored within that question. “I can understand that, because as a child in Sri Lanka, my interest in science was born, in part, that way as well,” he recalled. “Looking at the stars, and wondering if there was someone looking back from another planet.”
Perera and his students continue asking those questions and pursuing answers, but stand proud of what they believe their work will add to the growing body of knowledge for all those who still seek.
▷ RELATED STORY: Read how an IWU chemistry student replicated cosmic dust in the lab | 0.834852 | 3.84166 |
The work to be done by the VOlatiles, Regolith and Thermal Investigations Consortium for Exploration and Science (VORTICES) team will expand our understanding of the life cycle of volatiles and planetary regoliths as well as their interaction. Our NASA Lunar Science Institute Polar team, the predecessor to the VORTICES team, made great strides in understanding the processes that act on the surface of the Moon to form, deposit, modify and transport volatiles; to form and evolve a regolith; and to understand the geology of the poles. The goal of that team was to transform "Luna Incognita' into "Luna Cognita.' This increased understanding of how such processes operate on a large, low-gravity body with only a tenuous exosphere now places the VORTICES team in a position to extend that work in several directions including the deepening our understanding of the Moon, and addressing the first-order questions for Near Earth Asteroids (NEAs) and Phobos and Deimos, aka "small bodies' in the team's research.
The VORTICES team will expand the NLSI work by: determining whether H2O or OH is the dominant species on lunar and asteroidal surfaces; investigating the processes by which volatiles are created and destroyed; researching compositional dependencies on volatile production; understanding how volatiles are transported across and stored on and within regoliths; understanding the global surface and shallow subsurface thermal regimes on the Moon and small bodies that control volatile transport and storage processes; studying the manner in which regoliths form and evolve and the extent to which thermal fatigue can weaken and fracture rock to form a regolith; examining the space weathering effects of heating, simulated micrometeoroid bombardment, and radiation on the chemistry and spectral signature of regoliths through relevant lunar analogs and different meteorite types; assessing the potential for resource utilization and exploitation; and examining the Strategic Knowledge Gaps (SKG) for the Moon and small bodies and developing potential mission/instrument strategies that best addresses them.
The research is divided in to four themes: 1) Volatiles, 2) Regolith, 3) Resources, and 4) Strategic Knowledge Gaps. The first two themes contain tasks that are more science-centric, but the results will be of value to the exploration community. Similarly, themes 3 and 4 are more exploration focused but they, too, will yield important science. Themes 1 and 2 embody "science enables exploration' while Themes 3 and 4 represent "exploration enables science.' Our integrated research provides insight into the history of volatiles in the solar system; the manner in which regolith forms, evolves, and mixes with volatiles; and sets the stage, by providing fundamental information for the robotic and human exploration and exploitation of the Moon and small bodies.
|Research Themes||Research Tasks|
|1: Volatiles in the Solar System: Sources, Processes, Sinks||1: H Distribution on the Moon and Small Bodies
2: Modeling of Volatile Formation and Deposition
3: Experimental - Modeling of Volatile-Regolith Interaction
4: Thermal Characterization of the Surface and Near-Surface
5: Spectral Characterization of Volatile Species Interaction
|2: Regolith: Origin and Evolution on Airless Bodies||6: Regolith Generation by Thermal Fatigue
7: Lunar and Asteroidal Regolith Properties
8: Thermal and Irradiation Space Weather Processes
|3: Resources: Identification and Exploitation||9: Searching for Resources
10: Illumination Characterization for Surface Operations
|4: Closing Strategic Knowledge Gaps
||11: SKG Analysis
12: Instrument / Mission Concepts | 0.809919 | 3.447067 |
Gendler Rosette Nebula NGC 2244 Photo
Buy this Rosette Nebula NGC 2244 photo.
High quality Robert Gendler astronomy picture. Photographs are available in a wide variety of sizes.
Click to see selection as Astronomy Picture of the Day (APOD) - February 14, 2001
The Rosette Nebula is arguably one of the finest HII regions in the northern sky. Located in the constellation Monoceros, the nebula's center has been excavated centrally by the radiation pressure and powerful stellar winds of the massive OB stars belonging to its central cluster NGC 2244. The Rosette Nebula represents an ionization front along the edge of an enormous molecular cloud complex extending across 300 light years of winter sky called the Rosette molecular cloud (RMC). The RMC contains enough gas and dust to create over 100,000 suns. The hot stars of NGC 2244 are about 3 million years old (range of 0.3 to 6.4 Myr) and form the core cluster of the larger Monoceros OB2 stellar association. Monoceros OB2 contains at least three subassociations, the smallest being NGC 2244 at about 40 light years in diameter. Star formation is occurring along the edge of an expanding gas shell coincident with the interface of the Rosette Nebula with the surrounding RMC suggesting that sequentially triggered star formation is at work and progressing outward in the Rosette. The process by which massive molecular clouds transform themselves into clusters of stars is controversial. A likely explanation is that imbedded clusters form by compression of the molecular cloud by external shocks or triggering events. Triggering events can be supernova shock fronts, stellar winds from massive stars or expanding shells of neutral gas which all serve to compress and fragment the cloud into clumps which become the precursors of new stars.
The O and B type giants of the young open cluster NGC 2244 provide the excitation for the wreath-like emission cloud known as the Rosette Nebula. The cluster contains 30 OB type stars, including at least four O type giants (including a massive O4 type) and at least nine other massive stars earlier than B2 class, which all power the nebula. The winds from these powerful stars impart momentum to the ambient gas of the Rosette, expanding the nebula at about 4 kilometers per second. The Rosette HII region covers approximately 130 light years and contains some 10,000 solar masses of gas and dust.
The Rosette is undoubtedly a very active region of star formation. Herbig-Haro objects, Herbig Ae/Be stars, T Tauri stars, and Bok globules exist within the Rosette all pointing to the presence of infant stars imbedded within the nebulosity. Infant star clusters have been observed at infrared wavelengths (invisible optically) along the outer perimeter of the Rosette at its contact point with the RMC. Centrally in the Rosette the energy output of NGC 2244 creates a violent and tenuous environment which may serve to abort the formation of low mass stars and their planet progeny in close proximity to the massive hot stars. When the cold gases of a molecular cloud are heated too quickly by nearby hot stars the gases will evaporate off leaving insufficient material for star birth. Recent observations by the Chandra observatory have detected abundant x-ray emission deep within NGC 2244. The source of the x-rays is gas superheated to temperatures of almost 6 million degrees. The tremendous temperatures are believed to be generated when colliding shock fronts produced by the massive OB stars of NGC 2244 produce superheated gases which then emit high energy X-rays.
Dark filaments of dust appear to radiate towards the center of the Rosette and are sometimes referred to as "elephant trunks". The twisted helical pattern of these filaments is thought to be molded by the interplay of stellar winds, radiation, and electromagnetic forces. The resulting forces produce a double helix lining up along a magnetic field pointing towards the central cluster of hot young stars. Like other HII regions the Rosette will have a finite life of a few million years and will eventually disperse and disappear from view leaving behind the aging cluster NGC 2244.
Distance: 5000 light years
Right Ascension: 06 : 32.4 (hours : minutes)
Declination: +04 : 52 (degrees : minutes)
Image & Text Copyright Robert Gendler | 0.823783 | 3.516282 |
Smouldering several thousand light-years away in the constellation of Sagittarius (the Archer), the Trifid Nebula presents a compelling portrait of the early stages of a star’s life, from gestation to first light. The heat and “winds” of newly ignited, volatile stars stir the Trifid’s gas and dust-filled cauldron; in time, the dark tendrils of matter strewn throughout the area will themselves collapse and form new stars.
The French astronomer Charles Messier first observed the Trifid Nebula in June 1764, recording the hazy, glowing object as entry number 20 in his renowned catalogue. Observations made about 60 years later by John Herschel of the dust lanes that appear to divide the cosmic cloud into three lobes inspired the English astronomer to coin the name “Trifid”.
Made with the Wide-Field Imager camera attached to the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in northern Chile, this new image prominently displays the different regions of the Trifid Nebula as seen in visible light. In the bluish patch to the upper left, called a reflection nebula, dusty gas scatters the light from nearby, Trifid-born stars. The largest of these stars shines most brightly in the hot, blue portion of the visible spectrum. This, along with the fact that dust grains and molecules scatter blue light more efficiently than red light — a property that explains why we have blue skies and red sunsets — imbues this portion of the Trifid Nebula with an azure hue.
The gases and dust that crisscross the Trifid Nebula make up the third kind of nebula in this cosmic cloud, known as dark nebulae, courtesy of their light-obscuring effects. (The iconic Horsehead Nebula may be the most famous of these [ESO Press Photo 02/02]). Within these dark lanes, the remnants of previous star birth episodes continue to coalesce under gravity’s inexorable attraction. The rising density, pressure and temperature inside these gaseous blobs will eventually trigger nuclear fusion, and yet more stars will form.In the lower part of this emission nebula, a finger of gas pokes out from the cloud, pointing directly at the central star powering the Trifid. This is an example of an evaporating gaseous globule, or "EGG", also seen in the Eagle Nebula, another star-forming region. At the tip of the finger, which was photographed by Hubble, a knot of dense gas has resisted the onslaught of radiation from the massive star.
Dr. Henri Boffin | EurekAlert!
The material that obscures supermassive black holes
26.09.2017 | Instituto de Astrofísica de Canarias (IAC)
Creative use of noise brings bio-inspired electronic improvement
26.09.2017 | American Institute of Physics
Controlling electronic current is essential to modern electronics, as data and signals are transferred by streams of electrons which are controlled at high speed. Demands on transmission speeds are also increasing as technology develops. Scientists from the Chair of Laser Physics and the Chair of Applied Physics at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have succeeded in switching on a current with a desired direction in graphene using a single laser pulse within a femtosecond ¬¬ – a femtosecond corresponds to the millionth part of a billionth of a second. This is more than a thousand times faster compared to the most efficient transistors today.
Graphene is up to the job
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
26.09.2017 | Information Technology
26.09.2017 | Physics and Astronomy
26.09.2017 | Life Sciences | 0.812355 | 4.024045 |
Two black holes in nearby galaxies have been observed devouring their companion stars at a rate exceeding classically understood limits, and in the process, kicking out matter into surrounding space at astonishing speeds of around a quarter the speed of light.
The researchers, from the University of Cambridge, used data from the European Space Agency's (ESA) XMM-Newton space observatory to reveal for the first time strong winds gusting at very high speeds from two mysterious sources of x-ray radiation. The discovery, published in the journal Nature, confirms that these sources conceal a compact object pulling in matter at extraordinarily high rates.
When observing the Universe at x-ray wavelengths, the celestial sky is dominated by two types of astronomical objects: supermassive black holes, sitting at the centres of large galaxies and ferociously devouring the material around them, and binary systems, consisting of a stellar remnant - a white dwarf, neutron star or black hole - feeding on gas from a companion star.
In both cases, the gas forms a swirling disc around the compact and very dense central object. Friction in the disc causes the gas to heat up and emit light at different wavelengths, with a peak in x-rays.
But an intermediate class of objects was discovered in the 1980s and is still not well understood. Ten to a hundred times brighter than ordinary x-ray binaries, these sources are nevertheless too faint to be linked to supermassive black holes, and in any case, are usually found far from the centre of their host galaxy.
"We think these so-called 'ultra-luminous x-ray sources' are special binary systems, sucking up gas at a much higher rate than an ordinary x-ray binary," said Dr Ciro Pinto from Cambridge's Institute of Astronomy, the paper's lead author.
"Some of these sources host highly magnetised neutron stars, while others might conceal the long-sought-after intermediate-mass black holes, which have masses around one thousand times the mass of the Sun. But in the majority of cases, the reason for their extreme behaviour is still unclear."
Pinto and his colleagues collected several days' worth of observations of three ultra-luminous x-ray sources, all located in nearby galaxies located less than 22 million light-years from the Milky Way. The data was obtained over several years with the Reflection Grating Spectrometer on XMM-Newton, which allowed the researchers to identify subtle features in the spectrum of the x-rays from the sources.
In all three sources, the scientists were able to identify x-ray emission from gas in the outer portions of the disc surrounding the central compact object, slowly flowing towards it.
But two of the three sources - known as NGC 1313 X-1 and NGC 5408 X-1 - also show clear signs of x-rays being absorbed by gas that is streaming away from the central source at 70,000 kilometres per second - almost a quarter of the speed of light.
"This is the first time we've seen winds streaming away from ultra-luminous x-ray sources," said Pinto. "And the very high speed of these outflows is telling us something about the nature of the compact objects in these sources, which are frantically devouring matter."
While the hot gas is pulled inwards by the central object's gravity, it also shines brightly, and the pressure exerted by the radiation pushes it outwards. This is a balancing act: the greater the mass, the faster it draws the surrounding gas; but this also causes the gas to heat up faster, emitting more light and increasing the pressure that blows the gas away.
There is a theoretical limit to how much matter can be pulled in by an object of a given mass, known as the Eddington limit. The limit was first calculated for stars by astronomer Arthur Eddington, but it can also be applied to compact objects like black holes and neutron stars.
Eddington's calculation refers to an ideal case in which both the matter being accreted onto the central object and the radiation being emitted by it do so equally in all directions.
But the sources studied by Pinto and his collaborators are potentially being fed through a disc which has been puffed up due to internal pressures arising from the incredible rates of material passing through it. These thick discs can naturally exceed the Eddington limit and can even trap the radiation in a cone, making these sources appear brighter when we look straight at them. As the thick disc moves material further from the black hole's gravitational grasp it also gives rise to very high-speed winds like the ones observed by the Cambridge researchers.
"By observing x-ray sources that are radiating beyond the Eddington limit, it is possible to study their accretion process in great detail, investigating by how much the limit can be exceeded and what exactly triggers the outflow of such powerful winds," said Norbert Schartel, ESA XMM-Newton Project Scientist.
The nature of the compact objects hosted at the core of the two sources observed in this study is, however, still uncertain.
Based on the x-ray brightness, the scientists suspect that these mighty winds are driven from accretion flows onto either neutron stars or black holes, the latter with masses of several to a few dozen times that of the Sun.
To investigate further, the team is still scrutinising the data archive of XMM-Newton, searching for more sources of this type, and are also planning future observations, in x-rays as well as at optical and radio wavelengths.
"With a broader sample of sources and multi-wavelength observations, we hope to finally uncover the physical nature of these powerful, peculiar objects," said Pinto.
Sarah Collins | EurekAlert!
The material that obscures supermassive black holes
26.09.2017 | Instituto de Astrofísica de Canarias (IAC)
Creative use of noise brings bio-inspired electronic improvement
26.09.2017 | American Institute of Physics
Controlling electronic current is essential to modern electronics, as data and signals are transferred by streams of electrons which are controlled at high speed. Demands on transmission speeds are also increasing as technology develops. Scientists from the Chair of Laser Physics and the Chair of Applied Physics at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have succeeded in switching on a current with a desired direction in graphene using a single laser pulse within a femtosecond ¬¬ – a femtosecond corresponds to the millionth part of a billionth of a second. This is more than a thousand times faster compared to the most efficient transistors today.
Graphene is up to the job
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
26.09.2017 | Information Technology
26.09.2017 | Physics and Astronomy
26.09.2017 | Life Sciences | 0.845275 | 4.156836 |
Back in October, astronomers discovered a strange pattern of light near a distant star called KIC 8462852 that no one could explain. When a planet orbits a star, the star’s brightness will usually dip by just 1 percent, but KIC 8462852 has been experiencing dips of up to 22 percent, which suggests that something very, very big is zooming past.
The best explanation we had was that a huge mass of comets has been erratically orbiting KIC 8462852, kicking up enough dust to dim its light to such a degree. But a new analysis of the last 100 years of the star’s history has rendered this hypothesis just as implausible as any other. So... aliens then?
"Either one of our refutations has some hidden loophole, or some theorist needs to come up with some other proposal," astronomer Bradley Schaefer from Louisiana State University told Jacob Aron at New Scientist.
When KIC 8462852’s bizarre light patterns were announced last year, the team behind the discovery offered up what scientists have considered the most plausible explanation. We described the situation in October:
"The best explanation we have is that at one point, another star passed into KIC 8462852’s system and the disturbance of gravity caused a huge mass of comets to be pulled in towards it before being expelled again. And there just so happens to be another star close enough to KIC 8462852 to make this a possibility."
Based on what we knew about the star, the explanation made sense, theoretically, but it was an incredibly long shot. Not as unlikely as a light-harvesting alien megastructure called a Dyson Sphere, ripped straight out of science fiction by astronomers from Pennsylvania State University a month later, but the chances of us witnessing such an event were super thin.
"[It] would be an extraordinary coincidence, if that happened so recently, only a few millennia before humans developed the tech to loft a telescope into space. That’s a narrow band of time, cosmically speaking," Ross Andersen reported for The Atlantic at the time.
So what’s wrong with the comet swarm hypothesis?
When astronomer Tabetha Boyajian from Yale University and her colleagues first discovered that KIC 8462852 was giving off weird light patterns between 2009 and 2013, they checked 100 years worth of photographic plates held by the Harvard University archive to see if something similar had occurred around the star many years before. They come up with nothing.
Schaefer and his team from Louisiana State decided to check the data again using a different method of analysis, and noticed that the star dimmed very gradually by about 20 percent between 1890 and 1989. "The basic effect is small and not obvious," he told New Scientist.
Schaefer concluded that for the star to dim by about 20 percent over the course of an entire century, it would require some 648,000 comets - each about 200 kilometres wide - to have transited KIC 8462852, and that’s completely implausible, he said. "The comet-family idea was reasonably put forth as the best of the proposals, even while acknowledging that they all were a poor lot. But now we have a refutation of the idea, and indeed, of all published ideas."
So we’re back to the drawing board, and this time we don’t even have any remotely plausible explanations for wtf is going on with KIC 8462852.
Despite Schaefer insisting that a light-harvesting Dyson Sphere would be radiating heat that hasn’t appeared in infrared signals recorded from the star, the whole "Aliens…?!" thing is still probably going to follow KIC 8462852 to its grave.
But that’s no big deal, because what’s even cooler than the aliens non-event is the fact that we’ve got a front row seat to the scientific method in action, and what's more awesome than watching scientists try to explain possibly the weirdest star ever discovered? We can't wait to see what the next chapter of this story is going to be.
Schaefer's analysis has been published on the pre-print website, arXiv.org. | 0.830316 | 3.71717 |
Friday, July 20
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Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.
For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).
Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts effectively.
You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.
Can a computerized telescope replace charts? I don't think so not for beginners, anyway, and especially not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."
This Week's Planet Roundup
Mercury is out of sight in conjunction with the Sun.
Venus and Jupiter (magnitudes 4.6 and 2.1) shine dramatically in the east before and during dawn. They've widened to about 10° or 12° apart now, with Jupiter higher. Look for Aldebaran, much fainter, below or lower right of Jupiter. Also in Jupiter's starry background are the Hyades, and above it are the Pleiades.
The asteroids Ceres and Vesta, magnitudes 9.1 and 8.4, are in the area too! See article Predawn Treats for Early Risers for the naked-eye aspect, and to find the asteroids, Ceres and Vesta: July 2012 April 2013.
Mars (magnitude +1.0, in Virgo) glows orange low in the west-southwest at dusk, lower right of the Saturn-and-Spica pair by about 13°. It's heading their way; Mars will pass between Saturn and Spica in mid-August. In a telescope Mars is gibbous and very tiny, 6 arcseconds wide.
Saturn (magnitude +0.8, in Virgo) shines in the southwest as the stars come out. Below it by 4½° is Spica, nearly the same brightness but twinklier. After dark they move lower to the west-southwest.
Uranus (magnitude 5.8, at the Pisces-Cetus border) and Neptune (magnitude 7.8, in Aquarius) are high in the southern sky before the first light of dawn. Finder charts for Uranus and Neptune.
All descriptions that relate to your horizon including the words up, down, right, and left are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) equals Universal Time (also known as UT, UTC, or GMT) minus 4 hours.
Like This Week's Sky at a Glance? Watch our weekly SkyWeek TV short. It's also playing on PBS!
To be sure to get the current Sky at a Glance, bookmark this URL:
If pictures fail to load, refresh the page. If they still fail to load, change the 1 at the end of the URL to any other character and try again. | 0.845052 | 3.577101 |
Monday, May 02, 2016
The neutral hydrogen number density at a redshift of z=7 in slices of the simulations for different reionization models with large-scale ionized regions (bubble model), small-scale structures (web model), and both combined (web-bubble model). © MPA
This plot shows the cosmological fraction of neutral hydrogen (HI) in the diffuse intergalactic medium at various redshifts z. For earlier cosmic times (higher z), the universe is increasingly neutral. Constraints from previous work are shown with different symbols, the constraints from this work are shown as the orange regions. A late and rapid reionisation is clearly favoured. The solid line indicates the evolution of ionisation according to the models. © MPA
The intrinsic (black line) and observed differential Lyman alpha luminosity functions at z=7 as expected for the reionization models of figure 1. Several observed data points are also given. The observed Lyman alpha luminosity can be explained by completely different models.© MPA
In cosmology, one of the major challenges in next decades will be probing the epoch of reionization in the early universe. Scientists at MPA, the University of Oslo, and INAF have now used cosmological hydrodynamical, radiative transfer simulations to understand the impact of the complex distribution of neutral gas in the intergalactic medium on distant galaxies. Combining the simulations with observations of so-called Lyman alpha emitting galaxies they find that despite the uncertainty, the current simulation-calibrated measurements favour a late and rapid reionization history. The study also emphasizes that both the large-scale distribution of ionised gas regions and the small-scale structures of the intergalactic gas around galaxies must be understood to derive more robust constraints on the reionization epoch.
The epoch of reionization, when early galaxies or black holes drastically transformed the global state of the universe from neutral to an ionized plasma, is one of the major unsolved mysteries in modern extragalactic astronomy. Big questions remain unanswered: What was the history of reonization? Which sources were responsible for driving it?
One possibility to probe the physical state of the universe at very early times is by observing distant, high-redshift 'Lyman-alpha emitting galaxies'. These galaxies are emitting a strong Lyman alpha line, i.e. radiation from hydrogen gas in their interstellar medium. This strong emission line enables astronomers to observe these objects out to very far distances, at redshifts as high as 10. By now, hundreds of Lyman alpha galaxies have been found beyond redshift 6.
Observations show that the apparent demographics of Lyman alpha emitting galaxies changes over cosmic history. Beyond redshift 6, i.e. when the universe was less than 1 billion years old, the observed population of galaxies with Lyman alpha emission suddenly decreases. This is difficult to explain with galaxy formation alone. From medium to high distances (redshift 2 to 6), the fraction of star-forming galaxies that show a strong Lyman alpha emission increases, which is partly caused by less dust in these galaxies. Therefore, the sudden drop at very hight distances, beyond redshift 6, seems to indicate that something is blocking this kind of light. This drop is often interpreted as evidence of the gas in the universe being increasingly neutral at earlier cosmic times – this means the drop marks the time of reionization.
The idea to use Lyman alpha emitting galaxies as a probe of reionization is based on a simple idea. With more neutral gas along the line-of-sight to the galaxies, less Lyman alpha flux reaches the observer. The difference between the expected flux from a galaxy and the observed flux then tells us how much neutral gas exists along the line-of-sight.
Kakiichi and collaborators have used this method to infer the neutral hydrogen content of the universe at redshift 7. They used cosmological hydrodynamical, radiative transfer simulations of reionization (see Figure 1) to interpret observations of Lyman-alpha emitting galaxies. The observations are then compared with theoretical models of the apparent population of Lyman-alpha emitting galaxies. In this way, the neutral gas fraction can be inferred from the models that best fit the observations.
The new constraint this provides for the reionization history is shown in Figure 2, which shows that the universe is still very neutral at redshift 7. The present analysis therefore seems to suggest that reionization occurred late and rapidly around redshift 6 to 8.
This study also highlights an important uncertainty in this simulation-calibrated measurement of the neutral fraction. Figure 3 shows that completely different values of the neutral fraction combined with other 'topologies' of reionization work equally well in explaining the observed luminosity function (Figure 3). In fact, this leads to a systematic uncertainty in the inferred neutral fraction as high as an order of magnitude. Knowledge about the topology of reionization, namely both the large-scale distribution of ionized bubbles and the properties of small-scale self-shielded gas around galaxies, is crucial to robustly infer the reionization history. Only models containing both large and small-scale structures are able to coherently explain the observations of the Lyman alpha forest and Lyman alpha emitting galaxies from the reionization epoch to the post-reionized universe.
This difficultly, however, does not limit the scope of using Lyman alpha emitting galaxies as a probe of reionization. The uncertainties can be reduced by simultaneously using multiple statistics such as the luminosity function and the fraction of strong Lyman alpha line in Lyman Break Galaxies in surveys of Lyman alpha galaxies. New survey strategies search for early galaxies in the foreground of quasars at the reionization epoch, which will drastically increase the scope of this method because it allows astronomers to directly study both the state of the intergalactic gas and the properties of Lyman alpha emitting galaxies.
Together with the increasing capability of radiative transfer simulations, Lyman alpha emitting galaxies serve as important beacons to probe the state of the infant universe.
Lyman-Alpha Emitting Galaxies as a Probe of Reionization: Large-Scale Bubble Morphology and Small-Scale Absorbers | 0.832709 | 4.112072 |
Centaurus A is an active galaxy, meaning it gives off extraordinary amounts of radiation, most likely the result of a supermassive black hole. Somewhere inside these gas clouds and dust lanes, that black hole is creating unimaginable cosmic chaos.
This Hubble image shows off the central region of Centaurus A, which is a mix of red glowing gas, dark clumps of dust, and lots of bright blue star clusters. This particular image has been processed to appear in its natural colors, meaning this is basically how the galaxy would look to the human eye. Viewing it that way, however, obscures the presence of the supermassive black hole that is constantly showering this region in radiation.
To see the evidence of that, you have to look in a different part of the electromagnetic spectrum, as a NASA astronomer explains:
Infrared images from the Hubble have also shown that hidden at the center of this activity are what seem to be disks of matter spiraling into a black hole with a billion times the mass of the Sun. Centaurus A itself is apparently the result of a collision of two galaxies and the left over debris is steadily being consumed by the black hole. Astronomers believe that such black hole central engines generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies. But for an active galaxy Centaurus A is close, a mere 10 million light-years away, and is a relatively convenient laboratory for exploring these powerful sources of energy. | 0.845963 | 3.754105 |
Liquid Mirror Telescopes on the Moon
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October 9, 2008: A team of internationally renowned astronomers and opticians may have found a way to make "unbelievably large" telescopes on the Moon.
"It's so simple," says Ermanno F. Borra, physics professor at the Optics Laboratory of Laval University in Quebec, Canada. "Isaac Newton knew that any liquid, if put into a shallow container and set spinning, naturally assumes a parabolic shape—the same shape needed by a telescope mirror to bring starlight to a focus. This could be the key to making a giant lunar observatory."
Right: An artist's concept of a spinning liquid mirror telescope on the Moon. Credit: Univ. of British Columbia.
On Earth, a liquid mirror can be made quite smooth and perfect if it its container is kept exactly horizontal and rests on a low-vibration low-friction air bearing that is spun by a synchronous motor having one stable speed. "It doesn't need to spin very fast," says Borra. "The rim of a 4-meter–diameter mirror—the largest I've made in my lab—travels only 3 miles per hour, about the speed of a brisk walk. In the low gravity of the Moon, it would spin even slower."
Most liquid-mirror telescopes on Earth have used mercury. Mercury remains molten at room temperature, and it reflects about 75 percent of incoming light, almost as good as silver. The biggest liquid-mirror telescope on Earth, the Large Zenith Telescope operated by the University of British Columbia in Canada, is 6 meters across—a diameter 20 percent larger than the famous 200-inch mirror of the Hale telescope at Palomar Observatory in California. Yet when completed in 2005, the Canadian Palomar-class liquid-mirror telescope cost less than $1 million to build—only a few percent the cost of a solid-mirror telescope of the same diameter--and, for that matter, only a sixth of Palomar's original cost in 1948.
"Our study [with Borra] started when I was still an astronomy professor at the University of Arizona before I came to NASA in 2006," Worden recalls. "The real appeal of this approach is that we could get an unbelievably large telescope on the Moon."
Mercury is unworkable on the Moon: it's very dense and thus heavy to launch, it's very expensive, and it would evaporate quickly when exposed to the lunar vacuum. In recent years, however, Borra and his colleagues have been experimenting with a class of organic compounds known as ionic liquids. "Ionic liquids are basically molten salts," Borra explains. "Their evaporation rate is almost zero, so they would not vaporize in the lunar vacuum. They can also remain liquid at very low temperatures." He and his colleagues are now seeking to synthesize ionic liquids that remain molten even at liquid-nitrogen temperatures.
Below: The University of British Columbia's 6-meter Large Zenith Telescope uses a liquid mirror to scan the heavens. [more]
Much less dense than mercury, ionic liquids are only slightly denser than water. Although not highly reflective themselves, a spinning mirror of an ionic liquid can be coated with an ultrathin layer of silver just as if it were a solid mirror. Weirdest of all, the silver layer is so thin—only 50 to 100 nanometers—that it actually solidifies. In the vacuum of space, a liquid mirror coated with a thin solid layer of silver would neither evaporate nor tarnish.
A liquid mirror can't be tilted away from the horizontal because the fluid would pour out, destroying the mirror. But that does not mean a liquid mirror telescope cannot be pointed. Optical designers are now experimenting with ways of electromechanically warping secondary mirrors suspended above a liquid mirror—or even slightly warping the liquid mirror itself—to aim at angles away from the vertical. Similar techniques are used to point the great Arecibo radio telescope in Puerto Rico.
Furthermore, says Borra, "if the telescope is located anywhere other than exactly at the poles, with each rotation of Earth or Moon it would scan a circular strip of sky. And the rotational axis of the Moon wobbles with a period of 18.6 years; so over a period of 18.6 years, the telescope would actually look at a good-sized region of the sky."
Right: The 1000-ft Arecibo radio telescope in Puerto Rico cannot be moved, but it can still scan a wide swath of sky using movable secondary mirrors. A lunar liquid mirror telescope might employ similar techniques. [more]
Locating a major liquid-mirror telescope near the lunar poles is appealing. The telescope itself could reside near the bottom of a permanently shadowed crater where it would stay at cryogenic temperatures, desirable for the best infrared astronomy. Yet solar panels could be erected on nearby permanently illuminated mountain peaks to generate power to keep the mirror spinning.
The fact that a liquid-mirror telescope always looks straight up vastly simplifies its construction and reduces mass by eliminating heavy mounts, gearing, and pointing-control systems needed for a steerable telescope. "All you'd need is the liquid-mirror container, which might be an umbrella-like device that self-deploys, plus a nearly frictionless superconducting bearing and its drive motor," Borra says. Worden estimates that all the materials for an entire lunar telescope 20 meters across would be "only a few tons, which could be boosted to the Moon in a single Ares 5 mission in the 2020s." Future telescopes might have mirrors as large as 100 meters in diameter—larger than a football field.
"A mirror that large could peer back in time to when the universe was very young, only half a billion years old, when the first generation of stars and galaxies were forming," Borra exclaimed. "Potentially more exciting is pure serendipity: new things we might discover that we just don't expect."
Says Worden: "Putting a giant telescope on the Moon has always been an idea of science fiction, but it soon could become fact."
An article describing a potential lunar telescope 20 to 100 meters across is "Metal Films Deposited on Liquids and Implications for the Lunar Liquid Mirror Telescope," by Ermanno F. Borra, Omar Seddiki, Roger Angel, Daniel Eisenstein, Paul Hickson, Kenneth R. Seddon and Simon P. Worden Nature vol. 447 (2007), pp. 979-981.
This was not a new concept for Borra, who on May 20, 1991 published "The Case for a Liquid Mirror in a Lunar-Based Telescope" in The Astrophysical Journal (vol. 373, pp. 317–321). Borra, Worden, Roger Angel, and eight other experts co-authored another article called "A Lunar Infrared Telescope to Study the Early Universe," published in The Astrophysical Journal in 2008 (vol. 680, beginning p. 1582
An account of the Palomar-class 6-meter telescope built for only about half a million dollars appears in "The Large Zenith Telescope: A 6 m Liquid-Mirror Telescope," by Paul Hickson et al., in the Publications of the Astronomical Society of the Pacific in April 2007 (vol. 119, pp. 444–455). For an account of earlier attempts, see "Liquid Mirror Telescopes: History," by Brad K. Gibson, published in the Journal of the Royal Astronomical Society of Canada (vol. 85, no. 4, pp. 158–171, 1991).
Ground-based astronomers at the California Institute of Technology and at other international centers are pursuing concepts for ultralarge astronomical instruments on Earth using liquid-mirror telescopes. Among those is the International Liquid Mirror Telescope project.
Liquid mirror telescopes are a reality at last, New Scientist, June 2, 2008
NASA's Future: US Space Exploration Policy | 0.818459 | 3.826454 |
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