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Nemesis Star Theory; Does the Sun Have an Evil Twin?
Many people remain anxious about the threat posed from a hidden nemesis planet, known as Nibiru, that has been prophesied to collide with Earth. Though many of the proposed dates for this collision have come and gone, there is another celestial body that may be more likely to lead to an apocalyptic event: The Nemesis Star.
Clues of the Sun's Twin
The Nemesis Star Theory
Binary star systems occur frequently and are actually more common than single stars. At least that’s what we thought, until a recent hypothesis proposed the possibility that every star starts out as a binary pair or multi-pair system. While the theory hasn’t been confirmed, there is significant evidence that our Sun likely has a twin, an evil twin.
The majority of stars in the galaxy are red dwarfs, which are a fifth of the size of the sun and up to 50 times fainter. These types of stars are pretty commonly paired with another star in a binary system, leading astronomers to believe that Nemesis would be the Sun’s red dwarf star companion. But due to the small size and faintness of these stars, they can be hard to find, making Nemesis all the more elusive.
This star is thought to be responsible for 12 cyclical extinction events on Earth, including the one that killed the dinosaurs. The Nemesis Star Theory’s roots can be traced to two paleontologists, David Raup and Jack Sepkoski, who noticed that there was a periodicity to major die-outs throughout Earth’s history, occurring in 26 million year intervals. This led to a number of astrophysicists and astronomers, postulating their own Nemesis Star hypotheses.
So how would the sun’s twin be responsible for mass extinctions? The Nemesis Star Theory proposed the idea that the Earth’s binary twin must be in a large 1.5 light-year orbit, retaining just enough gravitational pull between it and the Sun so as not to drift off. But the issue with the orbit of Nemesis is the possibility that it occasionally passes through a cloud of icy debris on the fringe of our solar system, known as the Oort Cloud.
Don’t Perturb the Oort
The Oort Cloud is a theoretical sphere that is believed to orbit our solar system, consisting of planetesimals, the small icy building blocks of planets, comets, and asteroids. These planetesimals are sticky and collide with each other until they become large enough to have a significant gravitational pull, eventually becoming as large as a moon or a planet. They also create asteroids and comets which can be knocked out of orbit and sent hurtling toward the center of the solar system, crashing into planets.
There is a binary star system that once passed close enough to nearly perturb the Oort, and it was likely visible from Earth. Scholz’s Star made a flyby some 70,000 years ago, at a distance of 50,000 astronomical units (AU), with one AU being the distance from Earth to the Sun. The Oort is thought to extend from anywhere between 5,000 and 100,000 AUs and is believed to contain up to two trillion celestial objects. Astronomers are 95% certain that Shulz’s star passed within half of a light year of us, possibly perturbing the Oort, though apparently not enough to cause a mass extinction event.
Comets are believed to exist within the Oort and are the product of a thief model, a give-and-take of celestial bodies between stars when they’re formed. In this process comets get pulled back and forth between the gravitational field of stars. It was for this reason that the Oort was theorized, due to the number of comets coming from it, there had to have been a sibling star that pulled them out to the Oort.
Astronomers also found a dwarf planet in the Kuiper Belt, a region just before the Oort that also contains icy, celestial bodies. This planet, named Sedna, orbits the Sun in a long, drawn-out elliptical path and is one of potentially hundreds. Sedna may help to explain the Nemesis star theory, in that its far-flung orbit was likely caused by our Sun’s twin, pulling it out as it drifted off into the depths of space. Imagine if instead of 9 planets in our solar system, there were a few hundred?
So where is this Nemesis star? Several years ago, the E.U. launched the wonderfully named, Gaia satellite, to map out the stars in the Milky Way and look specifically at stars that have had a close encounter with our solar system or that might come close in the future. But whether or not Nemesis will be found is unknown; it’s possible that it could make a return for the next mass extinction, or it is possible that it drifted off, perturbing the Oort of another star. | 0.896259 | 3.529244 |
Shining Light on "Dark Matter"... Feb 7, 2006 7:38:50 GMT -6
Post by Chicago Astronomer Joe on Feb 7, 2006 7:38:50 GMT -6
Dark matter comes out of the cold
Astronomers have for the first time put some real numbers on the physical characteristics of dark matter.
This strange material that dominates the Universe but which is invisible to current telescope technology is one of the great enigmas of modern science.
That it exists is one of the few things on which researchers have been certain.
But now an Institute of Astronomy, Cambridge, team has at last been able to place limits on how it is packed in space and measure its "temperature".
"It's the first clue of what this stuff might be," said Professor Gerry Gilmore. "For the first time ever, we're actually dealing with its physics," he told the BBC News website.
Science understands a great deal about what it terms baryonic matter - the "normal" matter which makes up the stars, planets and people - but it has struggled to comprehend the main material from which the cosmos is constructed.
Astronomers cannot detect dark matter directly because it emits no light or radiation.
Its presence, though, can be inferred from the way galaxies rotate: their stars move so fast they would fly apart if they were not being held together by the gravitational attraction of some unseen material.
Using the biggest telescopes in the world, including the Very Large Telescope facility in Chile, the group has made detailed 3D maps of the galaxies, using the movement of their stars to "trace" the impression of the dark matter among them and weigh it very precisely.
With the aid of 7,000 separate measurements, the researchers have been able to establish that the galaxies contain about 400 times the amount of dark matter as they do normal matter.
"If this temperature for the dark matter is correct, then it has huge implications for direct searches for these mysterious particles (it seems [science] may be looking in the wrong place for them) and for how we thought the galaxies and clusters of galaxies evolve in the Universe.
"Having 'hotter' dark matter makes it harder to form the smallest galaxies, but does help to make the largest structures. This result will generate a lot of new research."
"It turns out the Milky Way is more massive than we thought," said Professor Gilmore. "It now looks as though the Milky Way is the biggest galaxy in the local Universe, bigger even than Andromeda. It was thought until just a few months ago that it was the other way around."
Read the full story here from the BBC: news.bbc.co.uk/2/hi/science/nature/4679220.stm
I wonder what mysteries will be found within the dark matter. | 0.866055 | 3.669452 |
The popular notion of a black hole is as a space mouth, gobbling up anything and turning it into nothing. Scientists know that’s not actually how these phenomena work. Black holes often spew out jets of interstellar matter brighter than stars. But the mechanism by which a spinning black hole can generate these blasts of energy has always been a mystery.
Magnetic fields have been long thought to play a significant role, and new findings published Thursday in the journal Science seem to confirm this. Researchers at the Harvard-Smithsonian Center for Astrophysics have just detected the presence of magnetic fields at the Milky Way galaxy’s central black hole, Sagittarius A-star.
“These magnetic fields have been predicted to exist, but no one has seen them before,” Shep Doeleman, a co-author of the study, said in a statement. “Our data puts decades of theoretical work on solid observational ground.”
The CfA team found the magnetic fields protruding just outside the event horizon of the black hole, thanks to the Event Horizon Telescope — a conglomerate of radio telescopes around the world that operate together to observe and identify features in outer space — like the size of the golf ball on the moon.
That’s critical, because a black hole is pretty much the most compact object that exists in the universe. Sir A weighs 4 million times more than our own Sun, but has an event horizon that’s smaller than Mercury’s orbit.
When the CfA team began observing Sgr A, they noticed a polarized light was emitted. They traced the source back to electrons spiraling around what have to be magnetic field lines, and a larger magnetic field structure.
This particular magnetic field is actually a dynamic mess. The black hole is surrounded by a ton of interstellar junk, causing the magnetic field to show up as disordered loops and whorls in certain spots. Other, more organized ares could be signs of where jets of matter and energy are being expelled. The study helps researchers get closer to answering a question that, as Doelerman puts it, has mystified astronomers for decades now: “Why are black holes so bright?”
Perhaps it’s time to start considering a name change. | 0.914285 | 3.792659 |
On Monday, a spacecraft called InSight will arrive at Mars and, if all goes well, land on the surface. Insight is the latest in a long line of probe that have been investigating the planet, carrying instruments that will build on what earlier spacecraft have discovered.
But this satellite isn't alone. Its mission is not only redefining what humanity knows about Mars, it is breaking new ground in the way our species explores the solar system.
When InSight launched on May 5, 2018, two briefcase-sized vehicles were tucked off to the side of the lander—a pair of Cubesats called Mars Cube One, or MarCO. “Once InSight got deployed of a launch vehicle, each of the two MarCO's got deployed as well,” Tim Linn, the InSight deputy program manager for Lockheed Martin, tells Popular Mechanics. “So basically all three spacecraft were basically all flying in basically the same direction, toward Mars.”
Now that the trio of spacecraft has arrived at Mars, it’s official: The small satellite revolution we’ve been seeing in Earth orbit has reached other parts of the solar system.
The two CubeSats proved themselves just by getting this far. Their list of accomplishments include becoming the first CubeSats to provide images of Earth, the Moon, and Mars; proving out radios, high-gain antennas, and propulsion; and performing the first trajectory correction maneuvers by CubeSats when they steered toward Mars. In short, they proved this class of small, affordable spacecraft can survive in deep space.
Now it’s time for the pair of small sats to do the job they came to do: relay data from InSight as it enters the Martian atmosphere and lands. NASA says this “could represent a new kind of communication capability.”
Probes that travel with their own small data relays are obviously more self-sufficient as one-off missions. Linn says it’s now possible to imagine future missions in which the main spacecraft acts as a sort of mothership, carrying CubeSats that it deploys once it reaches the destination.
"It's Still Terrifying"
Even with the pair of helper telemetry sats in tow, the landing outcome for Mars InSight will be uncertain for a full frightening eight minutes, due to the lag time of the communication at long distances. “It’s still terrifying,” Linn says.
No conversation with engineers involved in Mars landings is complete without a warning about how hard it is. There is a large percentage of failures, worldwide, when it come to landing on the Red Planet.
Mars has a thin atmosphere, just 1 percent of Earth’s, and that leaves little friction to slow down InSight during the landing. “When we enter this 80-mile-point above the surface, we’re going at about 13, 000 miles per hour,” Linn says. “When we touch down, we’re going at about five miles per hour.”
The high speed is a necessary evil. The process is determined by the location of the landing site and constrained by physics. InSight has an “Entry Flight Path Angle” of minus 12 degrees. If it comes in too steep, it will burn up. Too shallow, it will skip out of the Martian atmosphere.
NASA says that only about 40 percent of the missions ever sent to Mars by any space agency have been successful, but notes that the U.S. is the only nation whose missions have survived. Those probes—like InSight, built by Lockheed—have provided some useful lessons. The spacecraft shares a real engineering heritage with the Mars Phoenix Lander, which landed a decade ago. But no landing is identical, and Insight has more mass and a very different landing angle than its Mars-proven ancestor.
“We’re leveraging as much from Phoenix as we can for these kind of missions, but because of the unique nature of what we're doing on InSight, there are a lot of things that we’ve had to modify,” Linn says.
The vehicle will use various tricks to stay safe during the trip to the surface, using a parachute to slow down. “We have a heat shield to slow us down, to take out most of the energy, and we have a parachute to take out a lot more, and keep us stable as we go supersonic to subsonic,” Linn says. “And then we have the last 45 seconds, where 12 large thrusters will fire to really set ourselves down softly on the surface.”
The heat shield is a critical piece of hardware, and is the chief way to slow the probe down. But the proven heat shield used on earlier Mars missions wasn’t going to be tough enough to handle this entry, and the main reason is dust.
“We’re also actually landing in dust season, because of when we launched and where we wanted to arrive,” Linn says. “So we had to actually increase the thickness of the heat shield. As we’re reentering, that dust can peel off a lot of our thermal protection system. We get sandblasted by these dust storms.”
Linn calls it a dance in which every step has to be correct. “That’s what make it kinda unique,” he says. ”And it all has to go right. We can’t accommodate a hiccup in any of the systems.”
The Discoveries to Come
Once the probe lands, the science can begin. InSight carries a slew of sensors to measure things like seismic activity, wind velocity, and the planet’s magnetic field. The most groundbreaking experiment really does crack the planet’s surface—a drill that will twist 5 meters into the surface to take the first measurements of Mars’ geothermal heat flux.
And that’s what all this extreme engineering is about: finding out why two neighboring planets that should be so similar are so different. One is vibrant with life, the other a place where life didn’t gain purchase, has died off, or is hiding in extremophile clusters.
“Unlike Earth, which has gone through a lot of plate tectonics, Mars has preserved a lot of that information,” Linn says. “So we’re trying to look on the inside, trying to understand from core to crust, what Mars looks like.” | 0.806322 | 3.300831 |
In astronomy, Aries is one of the 12 original constellations of the zodiac—the band of constellations that lies along the ecliptic, the apparent yearly path of the sun across the sky. Aries, which is Latin for “ram,” is a relatively faint constellation of the Northern Hemisphere. Its chief stars are arrayed in a V shape, which ancient skywatchers likened to a crouching ram. The zodiacal constellations are Aquarius, Aries, Cancer, Capricornus, Gemini, Leo, Libra, Pisces, Sagittarius, Scorpius, Taurus, and Virgo.
Aries lies between the constellations Taurus and Pisces. It is visible in both the Northern and Southern hemispheres from September through February. The head of the ram is marked by the first bright star due west of the Pleiades (a cluster of seven stars in Taurus). This star is Alpha Arietis, known as Hamal (from the Arabic for “lamb”). Just to the southwest lie two bright stars, Beta and Gamma Arietis, or Sheratan and Mesarthim, which represent the ram’s horns. To the northeast of Hamal is a somewhat dimmer star that marks the ram’s back, and southeast of that point is Delta Arietis, or Botein, which represents the tail. Aries is one of the oldest and most revered constellations. The chief traditional significance of Aries is its role as the first sign of the zodiac. At the time that astrology first developed, more than 2,000 years ago, one of the two points where the ecliptic intersects the celestial equator (the imaginary line formed by the projection of the Earth’s equator onto the sky) was located in Aries. This point marks the vernal equinox, or the beginning of spring in the Northern Hemisphere. However, because of a phenomenon known as precession, the slow change of orientation of the Earth’s axis with respect to the stars, the vernal equinox has since moved into the constellation Pisces. In spite of this, Aries retains its symbolic position as the first sign of the zodiac, and the vernal equinox is still known as the first point of Aries.
Hamal, the brightest star in Aries, is a yellow giant of magnitude 2.0 lying 75 light-years away from Earth. Sheratan, 52 light-years away from Earth, is a white star of magnitude 2.6. Mesarthim is a white double star whose components are magnitude 4.7 and 4.6. Although Mesarthim lies 120 light-years away from Earth, its individual stars are easily resolvable with a small telescope. In 1665, British astronomer Robert Hooke became the first person to notice that Mesarthim was a double star. It was one of the first double stars to be discovered. Botein is a magnitude 4.4 star about 254 light-years away from Earth.
Aries also contains a number of galaxies. A cluster of several galaxies visible through a low-power telescope lies immediately to the north of Sheratan. The Arietids, a meteor shower occurring every October, takes place in Aries. This shower is a daytime shower and can be observed only by radio astronomy.
The ancient Egyptians associated Aries with Amon-Re, the ram-headed supreme sun god who symbolized power and fertility. The Mesopotamians’ name for the constellation meant a military leader or prince. In Hebrew tradition, the ram represented the death-defying blood of the lamb wiped on the doorways as part of the original Passover, which preceded the Hebrew Exodus from Egypt. The Greeks related Aries to the story of the golden fleece, the hide of the flying ram that Jason—with the help of his beloved Medea—spirited away from the serpent in the Grove of Aries. The Greek poet Aratus mentioned Aries in his work Phaenomena, which dates from the 3rd century bc. Ptolemy, the great astronomer who lived and worked in Egypt during the 2nd century ad, cataloged the constellation. The present name of the constellation came from the Romans, who adopted their mythology from the Greeks.
Critically reviewed by James Seevers | 0.832329 | 3.857126 |
New pulsar systems suggest that nature is more creative than previously thought
Two astronomers from Bonn have proposed a new path for the formation of a newly discovered class of millisecond pulsars with similar orbital periods and eccentricities. In the scenario of Paulo Freire and Thomas Tauris, a massive white dwarf star accretes matter and angular momentum from a normal companion star and grows beyond the critical Chandrasekhar mass limit. However, it does not collapse immediately into a neutron star because it is rotating very fast and is thus sustained by centrifugal forces.
After the mass transfer ceases, this massive white dwarf loses rotational energy and eventually collapses directly into a millisecond pulsar, without the need for further accretion. The associated instantaneous release of gravitational binding energy is expected to produce the characteristic eccentricities observed in such systems. The new hypothesis makes several testable predictions about this recently discovered sub-class of millisecond pulsars. If confirmed, it opens up new avenues of research into the physics of stars, in particular the momentum kicks and mass loss associated with accretion induced collapse of massive white dwarfs.
The paper appears as a Letter in Monthly Notices of the Royal Astronomical Society.
Neutron stars can spin very fast – with a record value of 716 rotations per second. Such extreme objects are known as millisecond pulsars. Ever since their first discovery in 1982, it has been thought that they are old dead neutron stars that are lucky enough to be in binary star system. As the companion evolves, it starts transferring matter onto the neutron star, spinning it up. This sort of system is known as an X-ray binary. Eventually the companion evolves into a white dwarf star, accretion stops and the neutron star becomes a millisecond pulsar, detectable through its radio pulsations. The orbits of these systems have very low eccentricities, meaning their orbits are extremely close to being perfect circles. This is a consequence of the tidal circularization that happens during the mass transfer stage. Such a scenario has been confirmed both in theoretical work and in the discovery of several systems in different stages of their evolution from X-ray binaries to millisecond pulsars.
However, recent discoveries like PSR J1946+3417 are hinting at the possibility of different formation paths to millisecond pulsars. This source is among 14 new pulsars recently discovered with the Effelsberg 100-m radio telescope. Spinning 315 times per second, this is clearly a millisecond pulsar; however, its orbital eccentricity is 4 orders of magnitude larger than other systems with a similar orbital period. Its companion mass is about 0.24 solar masses, most likely a helium white dwarf. Interestingly enough, at about the same time, two systems with similar parameters were discovered using the Arecibo 305 m radio telescope.
It is quite possible that these binary systems started their evolution as triple systems which became dynamically unstable, as in the case of PSR J1903+0327, the first millisecond pulsar with an eccentric orbit. However, this process generates a wide variety of orbital periods, eccentricities and companion masses, quite unlike the three new discoveries, which are in everything very similar.
The new hypothesis includes the collapse of a massive white dwarf after accretion has terminated. It explains not only the similarity of eccentricities and companion masses, but also their values. "I was surprised when we looked at the calculated orbital periods and eccentricities predicted by our model", says Thomas Tauris, affiliated with both, Argelander-Institut für Astronomie & Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn. "It gives an exact match with the observations! Thus I knew then we were on to something, although small number statistics could still be at work."
The new theory builds on previous extensive computational work lead by Tauris. It makes a prediction for the new type of systems: they should have orbital periods between 10 and 60 days, but with a concentration towards the middle of that range, almost exactly as observed for the new systems.
"Our new approach is very elegant", says the lead author, Paulo Freire from MPIfR. "But whether Nature is really making millisecond pulsars this way is not known yet.''
For the next few years, the pulsar team at the Fundamental Physics In Radio Astronomy Group at MPIfR will be involved in testing the predictions of this scenario, particularly by doing optical follow-up studies and by making precise mass measurements of the pulsars and their companions, a key feature of this study. They will also attempt to find more of these pulsar systems using the Effelsberg radio telescope.
"The neat thing is that if the theory passes these tests, it will allow us to learn much more about the kicks and mass loss associated with accretion induced supernovae, and even about the interiors of neutron stars. It might thus be an extremely useful piece of understanding", concludes Paulo Freire. | 0.822538 | 3.976406 |
Astronomers believe supermassive black holes probably lurk in the centers of most large galaxies. These gargantuan black holes can gather swirling disks of material around them as their gravity attracts stars and gases. In some cases, these disks can emit vast amounts of light and even shoot huge jets of matter into space. The centers of such an eventful galaxy is called an active galactic nucleus, or AGN.
Our own Milky Way seems to have a relatively calm center, but astronomers suspect this wasn’t always the case.
Some clues suggest that a flare of energetic radiation burst from our galaxy’s center within the last few million years. Now, in a new study, a team of researchers describe another piece of evidence that the Milky Way burped out such a flare. The research also points to the supermassive black hole in our galaxy’s center, called Sagittarius A* or Sgr A*, as being responsible.
The team also estimated when this event occurred. They put the outburst at 3.5 million years ago, give or take a million years. That would mean that the Milky Way’s center transitioned from an active to a quiet phase pretty recently in Earth’s history, possibly when early human ancestors were roaming the planet. The researchers describe their findings in an upcoming paper in The Astrophysical Journal.
Following the Trail
Clues to the Milky Way’s active history include giant bubbles of gas ballooning out from the disk of the galaxy. The bubbles, which emit high-energy X-ray and gamma-ray radiation, could have formed when jets of matter shot out from the galaxy center.
This new piece of evidence comes from examining a stream of gas that arcs around the Milky Way. This stream of gas is like a trail that two dwarf galaxies, called the Large and Small Magellanic Clouds, leave as they orbit the Milky Way. The research team studied ultraviolet light coming from this gas trail, called the Magellanic Stream.
The characteristics of the UV light indicate that gases in some sections of the stream are in an excited state. Only a very energetic event, like a beam of radiation from an active galactic nucleus, could have done this, according to Jonathan Bland-Hawthorn, a University of Sydney astrophysicist and lead author of the study. This means that our own home galaxy had an active galactic nucleus phase in the past.
“I think AGN flickering is what goes on for all of cosmic time,” Bland-Hawthorn said via email. “All galaxies are doing this,” he said, like volcanoes that can lie quietly for long stretches of time but suddenly erupt.
Learning more about the central black hole of our galaxy is an exciting area of research, he added.
“I think Sgr A* is the future of astrophysics, like searching for life signatures around planets,” Bland-Hawthorn said. “I am excited by what we will learn over the next 50 years.” | 0.842966 | 4.032338 |
Gibbous ♑ Capricorn
Moon phase on 13 June 2033 Monday is Full Moon, 15 days old Moon is in Sagittarius.Share this page: twitter facebook linkedin
Moon rises at sunset and sets at sunrise. It is visible all night and it is high in the sky around midnight.
Lunar disc appears visually 1.5% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1861" and ∠1889".
The Full Moon this days is the Strawberry of June 2033.
There is high Full Moon ocean tide on this date. Combined Sun and Moon gravitational tidal force working on Earth is strong, because of the Sun-Earth-Moon syzygy alignment.
The Moon is 15 days old. Earth's natural satellite is moving through the middle part of current synodic month. This is lunation 413 of Meeus index or 1366 from Brown series.
Length of current 413 lunation is 29 days, 9 hours and 30 minutes. It is 1 hour and 36 minutes shorter than next lunation 414 length.
Length of current synodic month is 3 hours and 14 minutes shorter than the mean length of synodic month, but it is still 2 hours and 55 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠46°. At beginning of next synodic month true anomaly will be ∠74.1°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
7 days after point of apogee on 6 June 2033 at 10:13 in ♎ Libra. The lunar orbit is getting closer, while the Moon is moving inward the Earth. It will keep this direction for the next 7 days, until it get to the point of next perigee on 21 June 2033 at 01:28 in ♈ Aries.
Moon is 385 210 km (239 358 mi) away from Earth on this date. Moon moves closer next 7 days until perigee, when Earth-Moon distance will reach 369 518 km (229 608 mi).
5 days after its ascending node on 7 June 2033 at 22:45 in ♎ Libra, the Moon is following the northern part of its orbit for the next 7 days, until it will cross the ecliptic from North to South in descending node on 21 June 2033 at 08:42 in ♈ Aries.
5 days after beginning of current draconic month in ♎ Libra, the Moon is moving from the beginning to the first part of it.
At 04:17 on this date the Moon is meeting its South standstill point, when it will reach southern declination of ∠-18.723°. Next 12 days the lunar orbit will move in opposite northward direction to face North declination of ∠18.717° in its northern standstill point on 26 June 2033 at 03:12 in ♊ Gemini.
The Moon is in Full Moon geocentric opposition with the Sun on this date and this alignment forms Sun-Earth-Moon syzygy. | 0.847411 | 3.128211 |
Meteors are small interplanetary objects that cause visible streaks of light in the sky when they collide with the Earth’s atmosphere. Before this visible collision, the object in space is called a meteoroid, and if any pieces of the object survive to land on the surface of Earth they are called meteorites. Meteoroids are considered to range from roughly the size of a peppercorn up to about a metre across. Larger objects are generally called asteroids, while smaller ones are micrometeoroids or space dust.
Most meteoroids are made of various types of rock, but a small percentage are mostly iron or iron-nickel alloy, and a few are icy. There are vast numbers of these objects in orbit around the sun, and many million enter the Earth’s atmosphere every day, although only a small fraction of those are large enough to produce a meteor trail visible to the human eye. Meteoroids originate from the asteroid belt, or as broken off parts of comets. These small objects are very easily perturbed by the gravity of large objects in the solar system, which effectively randomises their orbits. So in any region of the solar system, the positions and velocities of meteoroids is more or less random.
From an observation point on Earth, we can watch for meteors. Better than counting by eye, we have built specialised radar systems that can detect meteors with greater sensitivity, including during daylight hours, and we can set them up counting meteors all day, every day. Every time the radar detects a meteor, it can record where in the sky it was, what direction it moved, and what time the event occurred. Thinking about the time in particular, we can count how many meteors arrive during any given hour, and average this over many days to produce an hourly rate of meteor events. Many experiments do just this.
Let’s consider what time of day meteors arrive, and if the hourly rate of meteors is the same at all times, or if it varies with time. If the Earth were flat, how might we expect the hourly rate of meteors to behave? Is there any reason to think that the hourly rate of meteors might be different at, say, 8pm, compared to 4am? Or midnight? If the Earth is flat, then… meterors should probably arrive at the same rate all the time. There’s no obvious reason to think it might vary at all.
What happens in reality?
There are several published studies showing measurements of the hourly arrival rate of meteors versus the time of day. Here are some graphs from one such paper (reference ):
These graphs show the average number of meteors observed arriving during each hour of the day as observed by a meteor-detecting radar station at the Esrange Space Centre near Kiruna in Sweden. The numbers on the vertical axis are normalised so that the 24 hourly bins add up to 1. As shown earlier in the paper, the total number of meteors observed per day is roughly 2000 to 5000, for an overall average of approximately 150 per hour. The times on the horizontal axis are in Universal Time, but Sweden’s time zone is UTC+1, so local midnight occurs at 23 on the graph. Notice that the number of meteors observed per hour is not constant throughout the day, but varies in a systematic pattern. Hmmm.
Here’s another set of data (reference ):
This shows the hourly arrival rate of meteors for a single day as recorded by the American Meteor Society Radiometer Project stations in the southern USA. Again, the times shown are UTC, but the time zone is UTC-6, so local midnight occurs at 6 on the graph.
For good measure, here’s one more (reference ):
These plots show the hourly arrival rate of meteors at three separate SKiYMET meteor observation sites, at latitudes 69°N, 22°S, and 35°S respectively. The times shown on the horizontal axis here are all local times.
Now, notice how in all of these graphs that the hourly arrival rate of meteors varies by time of day. In particular, in every case there is a maximum in the arrival rate at around 6am local time (to within 2 or 3 hours), and a minimum at around 6pm local time. This pattern, once you notice it, is striking. What could be the cause?
The Earth is moving in its orbit about the sun. In other words, it is sweeping through space, in an almost circular path around the sun. Now, remember that the distribution of meteoroid locations and velocities in space is essentially random. If the Earth is moving through this random scattering of meteoroids, it should sweep up more meteors on the side of the planet that is moving forwards, and fewer on the side that is trailing. And the Earth is also rotating about its axis, this rotation being what causes the daily variation of night and day – in other words the times of the day.
The side of the Earth that is moving forwards is the side where the rotation of the Earth is bringing the dark part of the Earth into the light of the sun, at the dawn of a new day. We call this the dawn terminator. In terms of the clock and time zones, this part of the Earth has a time around 6am. The trailing side of the Earth is the sunset terminator, with a time around 6pm. There will be some variation, up to a couple of hours or so at moderate latitudes, caused by the seasons (the effect of the tilt in the Earth’s rotation axis relative to its orbit).
In other words, if the Earth is a rotating sphere in space, orbiting around the sun, we should expect that the dawn part of the Earth, where the local time is around 6am, should sweep up more meteors than the sunset part of the Earth, where the local time is around 6pm. And if the Earth is a sphere, this variation should be sinusoidal – the distinctive smooth shape of a wave as traced out by points rotating around a circle.
And this is exactly what we see. The variation in the hourly arrival rate of meteors, as observed all across the Earth, matches the prediction you would make if the Earth was a globe. One consequence of the Earth being a globe is that if you want to see meteors – other than during one of the regular annual meteor showers – it’s much better to get up before dawn than to stay up late.
Younger, P. T.; Astin, I.; Sandford, D. J.; and Mitchell, N. J. “The sporadic radiant and distribution of meteors in the atmosphere as observed by VHF radar at Arctic, Antarctic and equatorial latitudes”, Annales Geophysicae, 27, p. 2831-2841, 2009. https://doi.org/10.5194/angeo-27-2831-2009
Meisel, D. D.; Richardson, J. E. “Statistical properties of meteors from a simple, passive forward scatter system”. Planetary and Space Science, 47, p. 107-124, 1999. https://doi.org/10.1016/S0032-0633(98)00096-8
Singer, W; von Zahn, U; Batista, Paulo; Fuller, Brian; and Latteck, Ralph. “Diurnal and annual variations of meteor rates at latitudes between 69°N and 35°S”. In The 17th ESA Symposium on European Rocket and Balloon Programmes and Related Research, Sandefjord, Norway, 2005, ISBN 92-9092-901-4, p. 151-156. https://www.researchgate.net/publication/252769360_Diurnal_and_annual_variations_of_meteor_rates_at_latitudes_between_69N_and_35S | 0.847872 | 3.880203 |
One of the greatest benefits to come from space telescopes and ground-based observatories that take advantage of advanced imaging techniques is their ability to see farther into space (and hence, further back in time). In so doing, they are revealing things about the earliest galaxies, which allows astronomers to refine theories of how the cosmos formed and evolved.
For example, new research conducted by the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) has found a “ring galaxy” that existed 11 billion years ago (about 3 billion years after the Big Bang). This extremely rare structure, which the team describes as a “cosmic ring of fire,” is likely to shake up cosmological theories of how the cosmos has changed over time.
Continue reading “Rare “Ring Galaxy” Seen in the Early Universe”
Today, on Saturday, May 30th, NASA and SpaceX successfully launched the Crew Dragon to space with two astronauts for the first time. Far from just a demonstration, this launch signaled the restoration of domestic launch capability to US soil! From this day forward, NASA astronauts will no longer be dependent on foreign launch providers (like Roscosmos) to send astronauts to the International Space Station (ISS).
Continue reading “NASA and SpaceX Make History with Successful Crew Dragon Launch!”
Oh Planet Nine, when will you stop toying with us?
Whether you call it Planet Nine, Planet X, the Perturber, Jehoshaphat, “Phattie,” or any of the other proposed names—either serious or flippant—this scientific back and forth over its existence is getting exhausting.
Is this what it was like when they were arguing whether Earth is flat or round?
Continue reading “Maybe the Elusive Planet 9 Doesn’t Exist After All”
Earlier today (Friday, May 29th), at 01:49 p.m. local time (02:49 p.m. EDT; 11:49 PDT), SpaceX Starship prototype (SN4) exploded on the company’s test pad near Boca Chica, Texas. The explosion occurred two minutes after ground crews commenced a static fire test of its Raptor engine. This test was intended to test the Raptor and the Starship design once more in preparation for a major milestone – a 150 m (500 ft) hop test – this summer.
Continue reading “SN4, We Hardly Knew You. Another Starship Prototype Lost!”
On Wednesday, May 27th, NASA and SpaceX geared up for what was sure to be a historic event! After years of hard work, the Crew Dragon capsule developed through NASA’s Commercial Crew Program would dock with the ISS for the first time. This launch would effectively restore domestic-launch capability to the United States, something it lost in 2011 with the retiring of the Space Shuttle. Unfortunately, the weather didn’t get the memo!
Less than 15 minutes before the Crew Dragon was to launch atop a Falcon 9 rocket from Launch Complex 39A at NASA’s Kennedy Space Center in Florida, mission controllers scrubbed the flight because the weather was not clearing up. As a result, NASA and SpaceX pushed the launch of the Crew Dragon to their two backup launch opportunities, both of which will be happening this weekend.
Continue reading “Due to Weather Delay, NASA & SpaceX Push Historic Launch to Saturday”
Even though Earthling scientists are studying Mars intently, it’s still a mysterious place.
One of the striking things about Mars is all of the evidence, clearly visible on its surface, that it harbored liquid water. Now, all that water is gone, and in fact, liquid water couldn’t survive on the surface of the Red Planet. Not as the planet is now, anyway.
But it could harbour water in the past. What happened?
Continue reading “Mars Doesn’t Have Much of a Magnetosphere, But Here’s a Map”
For the child inside all of us space-enthusiasts, there might be nothing better than discovering a new type of explosion. (Except maybe bigger rockets.) And it looks like that’s what’s happened. Three objects discovered separately—one in 2016 and two in 2018—add up to a new type of supernova that astronomers are calling Fast Blue Optical Transients (FBOT).
Continue reading “A New Kind of Supernova Explosion has been Discovered: Fast Blue Optical Transients”
If we ever intend to send crewed missions to deep-space locations, then we need to come up with solutions for how to keep the crews supplied. For astronauts aboard the International Space Station (ISS), who regularly receive resupply missions from Earth, this is not an issue. But for missions traveling to destinations like Mars and beyond, self-sufficiency is the name of the game!
This is the idea behind projects like BIOWYSE and TIME SCALE, which are being developed by the Centre for Interdisciplinary Research in Space (CIRiS) in Norway. These two systems are all about providing astronauts with a sustainable and renewable supply of drinking water and plant food. In so doing, they address two of the most important needs of humans performing long-duration missions that will take them far from home.
Continue reading “How to Make the Food and Water Mars-Bound Astronauts Will Need for Their Mission”
The closest star to the Sun is a small red dwarf star known as Proxima Centauri. It is only 4.2 light-years away and is now known to have an Earth-sized planet in its habitable zone. That doesn’t mean there is life orbiting the nearest star, but its proximity should help us understand the possibilities.
Continue reading “Powerful Telescope Confirms There’s an Earth-Sized World Orbiting Proxima Centauri”
One of the most striking features on Earth are the curious flows of lava as it cools, forming undulating ropes of rock known by the Hawaiian word pahoehoe. New research simulating conditions on Mars now reveals that the red planet has its own kind of pahoehoe…but made of mud.
Continue reading “On Mars, mud flows like lava” | 0.901335 | 3.051331 |
The eerie glow of a dead star, which exploded long ago as a supernova, reveals itself in this NASA Hubble Space Telescope image of the Crab Nebula. But don’t be fooled. The ghoulish-looking object still has a pulse. Buried at its centre is the star’s telltale heart, which beats with rhythmic precision.
The “heart” is the crushed core of the exploded star. Called a neutron star, it has about the same mass as the Sun but is squeezed into an ultra-dense sphere that is only a few miles across and 100 billion times stronger than steel. The tiny powerhouse is the bright star-like object near the centre of the image.
This surviving remnant is a tremendous dynamo, spinning 30 times a second. The wildly whirling object produces a deadly magnetic field that generates an electrifying 1 trillion volts. This energetic activity unleashes wisp-like waves that form an expanding ring, most easily seen to the upper right of the pulsar. The nebula’s hot gas glows in radiation across the electromagnetic spectrum, from radio to X-rays. The Hubble observations were taken in visible light as black-and-white exposures. The Advanced Camera for Surveys made the observations between January and September 2012. The green hue has been added to give the image a Halloween theme.The Crab Nebula is one of the most historic and intensively studied supernova remnants. Observations of the nebula date back to 1054 A.D., when Chinese astronomers first recorded seeing a “guest star” during the daytime for 23 days. The star appeared six times brighter than Venus. Japanese, Arabic, and Native American stargazers also recorded seeing the mystery star. In 1758, while searching for a comet, French astronomer Charles Messier discovered a hazy nebula near the location of the long-vanished supernova. He later added the nebula to his celestial catalogue as “Messier 1,” marking it as a “fake comet.” Nearly a century later British astronomer William Parsons sketched the nebula. Its resemblance to a crustacean led to M1’s other name, the Crab Nebula. In 1928 astronomer Edwin Hubble first proposed associating the Crab Nebula to the Chinese “guest star” of 1054.
The nebula, bright enough to be visible in amateur telescopes, is located 6,500 light-years away in the constellation of Taurus. | 0.847696 | 3.719805 |
NASA scientists on the trail of mystery molecules
(PhysOrg.com) -- Space scientists working to solve one cosmic mystery at NASA's Ames Research Center, Moffett Field, Calif., now have the capability to better understand unidentified matter in deep space. Using a new facility so sensitive that it can recognize the molecular structure of particles in space, researchers now are able to track unidentified matter seen for the last century absorbing certain wavelengths of light from distant stars.
Astronomers suspect that one family of carbon-containing compounds, called polycyclic aromatic hydrocarbons (PAHs), are the long-sought matter that produces holes in astronomical observations from multiple wavelengths. Researchers compared laboratory data of PAHs, measured in this unique facility that simulates space-like conditions, with an extensive set of high-resolution optical astronomical data. With this approach, they were able to survey the mysterious spectral signatures seen in both light absorption and emission that are common throughout interstellar space and determine the abundance of PAHs.
"It is important to understand how PAHs absorb stellar radiation, and how they emit it back, because it contributes to the global energy balance in space," said Farid Salama, a space science researcher in the Astrophysics Branch at Ames. "Now, we can offer a clear and unambiguous explanation for the presence (or the absence) of specific PAH molecules in the interstellar medium." This research will be presented today at the American Astronomical Society meeting in Boston, Mass.
The research helps solve a problem scientists have struggled with for most of the century. They have detected more than 500 interstellar absorption lines in the spectra (range of frequencies or color) of starlight approaching Earth. Absorption lines are discrete colors of light absorbed by intervening matter; this absorption leaves holes or "lines" in the spectra. The lines are called diffuse interstellar band.
"PAHs are excellent candidates to account for the infrared emission bands seen in the interstellar medium," said Salama. "But their signature also must be seen in the visible and ultraviolet. This evidence was missing until now, because of the lack of relevant laboratory data."
PAHs are very stable and thought to be ubiquitous in the interstellar medium. They are flat molecules of carbon and hydrogen that form hexagons their skeleton looks like chicken wire. On Earth, they can be found in coal, soot, and automobile exhaust.
By mimicking realistic interstellar conditions in the laboratory, Salama and his colleagues measured the spectra (fingerprints of molecules) of large PAHs and ions in the ultraviolet and visible light bands and compared the data to high-resolution astronomical data from the Ultraviolet and Visual Echelle Spectrograph instrument of the Very Large Telescope at the European Southern Observatory.
To achieve these results, Salama and his team used a unique specialized facility, called the Cosmic Simulation Chamber (COSmIC), which integrates a variety of state-of-the-art instruments to allow scientists to form, process and monitor simulated space conditions for interstellar materials in the laboratory. The chamber recreates the extreme conditions in space, where average temperatures can be as low as 100 Kelvin (less than -170 degree Celsius), densities are quadrillionths of Earth's average atmospheric density at sea level, and interstellar molecules and ions are bathed in stellar ultraviolet and visible radiation. Interstellar molecules and ions must be stable enough to survive in this harsh environment. | 0.844944 | 3.860736 |
Searching for Ancient Life on Mars
John P. Grotzinger
Fletcher Jones Professor of Geology, Ted and Ginger Jenkins Leadership Chair, Division of Geological and Planetary Sciences, Caltech
SIMONS IMAX THEATRE, NEW ENGLAND AQUARIUM
Thursday, October 11, 2018, 7-9 PM
By: Fatima Husain | EAPS News
In 2018, millions around the world caught glimpses of the planet Mars, discernible as a bright red dot in the summer’s night skies. Every 26 months or so, the red planet reaches a point in its elliptical orbit closest to Earth, setting the stage for exceptional visibility. This proximity also serves as an excellent opportunity for launching Mars missions, the next of which will occur in 2020 when a global suite of rovers will take off from Earth.
While Mars hid behind the drizzling Boston sky on October 11th, 2018, an audience gathered at the New England Aquarium for the 8th annual John Carlson Lecture featuring Mars expert John Grotzinger, the Fletcher Jones Professor of Geology at the California Institute of Technology and a former professor in the MIT Department of Earth, Atmospheric and Planetary Sciences (EAPS). In his talk, Grotzinger gave audiences a different perspective of Mars, taking them through a journey of its geologic history as well as the current search for life on the planet.
Specializing in sedimentology and geobiology, Grotzinger has made significant contributions to understanding the early environmental history of the Earth and Mars and their habitability. In addition to involvement with the Mars Exploration Rover (MER) mission and the High Resolution Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter (MRO), Grotzinger served as project scientist of the Mars Science Laboratory mission, which operates the Curiosity roving laboratory. Curiosity explores the rocks, soils and air of Gale Crater to find out whether Mars ever hosted an environment that was habitable for microbial life in its nearly 4.6-billion-year history. “What I’d like to do is give you a very broad perspective of how we as scientists go about exploring a planet like Mars, with the rather audacious hypothesis that there could have been once life there,” he said. “This is a classic mission of exploration where a team of scientists heads out into the unknown.”
“Simple one-celled microorganisms we know have existed on Earth for the last three-and-a-half billion years — a long time. They originated, they adapted, they evolved, and they didn’t change very much until you had the emergence of animals just 500 million years ago,” Grotzinger said. “For basically 3 billion years, the planet was pretty much alone with microbes. So, the question is: Could Mars have done something similar?”
Part of the research concerning whether or not Mars ever hosted ancient life involves identifying the environmental characteristics necessary for the survival of living organisms, including liquid water. Currently, the thin atmosphere around Mars prevents the accumulation of a standing body of water, but that may not always have been the case. Topographic features documented by orbiters and landers suggest the presence of ancient river channels, deltas and possibly even an ocean on Mars, “just like we see on Earth,” Grotzinger said. “This tells us that, at least, for some brief period of time if you want to be conservative, or maybe a long period of time, water was there [and] the atmosphere was denser. This is a good thing for life.”
To describe how scientists search for evidence of the past habitability on Mars, Grotzinger told the story of stratigraphy — a discipline within geology that focuses on the sequential deposition and layering of sediments and igneous rocks. The changes that occur layer-to-layer indicate shifts in the environmental conditions under which different layers were deposited. In that manner, interpreting stratigraphic records is simple: “It’s like reading a book. You start at the bottom and you get to the first chapter, and you get to the top and you get to the last chapter,” Grotzinger said. “Sedimentary rocks are records of environmental change…What we want to do is explore this record on Mars.”
While Grotzinger and Curiosity both continue their explorations of Mars, scientists from around the world are working on pinpointing new landing sites for future Mars rovers which will expand the search for ancient life. This past summer, the SAM (Sample Analysis on Mars) instrument aboard the Curiosity rover detected evidence of complex organic matter in Gale Crater, a discovery which further supports the notion that Mars may have been habitable once.
“We know that Earth teems with life and we have enough of a fossil record to know that it’s been that way since we get to the oldest, well-preserved rocks on Earth. But yet, when you go to those rocks, you almost never find evidence of life,” Grotzinger said, leaving space for hope. “And that’s because, in the conversion of the sedimentary environment to the rock, there are enough mineralogic processes that are going on that the record of life gets erased. And so, I think we’re going to have to try over and over again.”
Following the lecture, members and friends of EAPS attended a reception in the main aquarium that featured some of the research currently taking place in the department. Posters and demonstrations were arranged around the aquarium’s cylindrical 200,000-gallon tank simulating a Caribbean coral reef, and attendees were able to chat with presenters and admire aquatic life while learning about current EAPS projects. EAPS graduate student, postdoc and research scientist presenters included Tyler Mackey, Andrew Cummings, Marjorie Cantine, Athena Eyster, Adam Jost, and Julia Wilcots from the Bergmann group; Kelsey Moore and Lily Momper from the Bosak group; Eric Beaucé, Ekaterina Bolotskaya, and Eva Golos from the Morgan group; Jonathan Lauderdale and Deepa Rao from the Follows group; Sam Levang from the Flierl group; Joanna Millstein and Kasturi Shah from the Minchew group; and Ainara Sistiaga, Jorsua Herrera, and Angel Mojarro from the Summons group.
The John H. Carlson Lecture series communicates exciting new results in climate science to general audiences. Free of charge and open to the general public, the annual lecture is made possible by a generous gift from MIT alumnus John H. Carlson to the Lorenz Center in the Department of Earth, Atmospheric and Planetary Sciences, MIT.
To join the invitation list for next year’s Carlson Lecture, please contact Angela Ellis: [email protected].
About the Speaker
John Grotzinger is a professor of geology and geobiology, and the division chair for Geological and Planetary Sciences at the California Institute of Technology (Caltech). He received his B.S. from Hobart College, M.S. from the University of Montana and Ph.D. from Virginia Polytechnic Institute and State University (Virgina Tech), and was a postdoctoral fellow at Columbia University. Prior to moving to Caltech in 2005, he spent 18 years as a member of the faculty at the Massachusetts Institute of Technology, where he was named Waldemar Lindgren Distinguished Scholar and Robert R. Shrock Professor of Geology.
At Caltech, his research group studies the co-evolution of surficial environments on Earth and Mars. Field-mapping studies are the starting point for more topical laboratory-based studies involving geochemical, geologic and geochronological techniques. He served as the chief scientist for the Mars Curiosity rover mission from 2007 to 2015. He is a member of the National Academy of Sciences and a recipient of NASA’s Distinguished Public Service Medal, and he received the Charles Doolittle Walcott Medal in 2007 for the elucidation of ancient carbonates and the stromatolites they contain and for meticulous field research that has established the timing of early animal evolution. | 0.841713 | 3.264457 |
Well the weather is getting a little better for some astronomical observations, but this week we follow up on early galaxy formation as pickles rather than spheroids and then look back into the past discoveries of x-ray objects, look at Maxwell's faithful friend and the 100 year centennial of the measurement of bending of light observed during the total solar eclipse of May 29, 1919.
Now, when Visionary Physicist Dr. Don, alerted us to the upcoming UCI seminar presentation by Dr. Joel Primack, UCSC, we knew we had to get this seminar on our schedule. Readers of this blog will of course know that three previous blogs posts of November 1, 2017, November 26, 2017 and June 8, 2018 all had some reference to Dr. Primack's work or books as he has been such a leading scientist and cosmologist. Thanks for the alert, Don!
In this UCI seminar presentation entitled "Comparing Galaxy Formation Simulations and Observations with Machine Learning", Dr. Primack described how the early formation of galaxies really began as more "pickle" shaped than spheroidal. In the introductory slide below you can see how as galaxies start to form the amount of gas decreases, because it is being tied up in stars, and the amount of initial dark matter just increases slightly as more and more material is falling in towards the gravitational potential well. Dr. Primack mentioned that when he was studying galaxy formation it was almost common knowledge that they must have started as spheroidal collections of gas, even though many early observations had clearly shown the more prolate or pickle shape.
|Joel Primack, UCSC, discusses prolate structure of early galaxies at UCI Seminar (Source: Palmia Observatory)|
So, now why is the pickle shape the new standard form used to describe galaxy formation? In the figure below, taken from the published paper, you can see the various shapes under consideration. If the dimensions of the two axes are about the same value, then the shape is considered spheroidal, but if one axis is much longer than the other, then the shape is more pickle like or prolate as it says here. So, if we were to measure the dimensions of galaxies along these two dimensions, a and b, and compare these measurements along with the redshift of the galaxies, which corresponds to the age of the galaxies, we can see what the shape of the early galaxies was.
|The Evolution of Galaxy Shapes: From Prolate to Oblate (Primack+, 1805.12331v1, 31 May 2018)|
The study makes use of galaxy images collected using the HST in the large datasets produced in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). An example of a galaxy image, taken from Figure 15 of the paper, is shown below.
So, after reviewing many images of galaxies at various redshifts the results can be plotted as shown below. You can see here that the older the galaxy is, that is the more redshifted in shows up in the image, the more prolate the structure. So, even though many of us grew up with the image of galaxies forming as a spherical ball of collapsing gas, the real picture and history is more complicated and the original shape is now thought to be more prolate or pickle shaped.
Primack discussed the formation of early galaxies along the filaments of dark matter in the early universe. Afterwards, I found this simulation image of dark matter filaments. Yes, the filaments are long narrow structures, so why wouldn't early galaxies sort of form like pickles on a wire? Thanks to Dr. Primack for very interesting presentation!
|Simulation of expected cosmic web filaments of dark matter forming after the big bang (Source: Wikipedia)|
After the UCI seminar there was few spare minutes to catch up on studying the emission of radiation from neutron stars. In the previous blog of May 26, we saw that material falling into black holes result in emission over a wide frequency spectrum. In searching for the spectrum from neutron star pulsars, I saw a reference to the first detection of x-rays from an extra-solar source outside the solar system. Hmm, let's follow up on this discovery from 1962 and look a bit more into the history and details of the discovery.
The image below is from a 1962 paper published in Physical Review Letters by Riccardo Giacconi, et al, titled "Evidence for x-rays from sources outside the solar system." The image shows the raw data taken from x-rays sensors aboard an Aerobee rocket that was launched so that the sensors were above the Earth's atmosphere, which would have blocked and absorbed the x-ray radiation. You can see a peak in the collected data, but what source outside the solar system does this come from?
|Evidence for x-rays from sources outside the solar system (Giacconi+, Physical Review Letters, Dec 1, 1962)|
Well given the orientation of the rocket and sensors and an indication of the azimuth and the time of observations, we can calculate where on the sky the sensors were pointing. So, in the plot below you can see that Giacconi identified the x-ray source as located in the constellation Scorpio. Pretty neat! It turns out that that x-ray source, now called Sco X-1, is one of the brightest x-ray sources in the sky and now there are hundreds if not thousands of known x-ray sources. Sco X-1 is now recognized as a binary star system composed of a neutron star and low mass companion star.
Now, I worked on guided missile autopilots in the 70's, so I imagined the early experimenters would have used accelerometers and such instruments to monitor the position of the rocket during flight so that the orientation of the x-ray detectors could be traced back to identify where in the sky the sensors were pointed. It turns out in 1962 the x-ray data was taken during just the straight vertical rise of the rocket. The rocket was uncontrolled and did not rely on feedback control systems with gyros and accelerometers, but relied only on aerodynamic fins to help stabilize the flight which rotated at 2 revolutions per second. The three x-ray sensors were mounted symmetrically around the rocket, oriented to point upwards at about 55 degrees. Then some (unspecified) optical alignment device identified the azimuth orientation of the rocket and so from that and the rotation rate and assumed vertical position, the sky location can be calculated. The paper goes into more of the details and even says that one of the three x-ray sensors malfunctioned and was not used in the analysis. Also just in case you were wondering, the x-ray sensors were covered with material so that the sensors would not be affected by visible or UV sunlight.
|Aerobee Rocket (Source: White Sands Missile Range Museum)|
So, with the clouds out and about, it was more time to watch some livestreamed presentations at the Institute of Advanced Studies (IAS) in Princeton. Math Whiz Dave had alerted us to watch for this livestreamed event and I'm glad I tuned in on it. The topic of the presentations was "The Universe Speaks in Numbers" and I sat down to watch some of the presentations with Astronomer Assistants Ruby and Danny. Thanks for the alert, Dave, all of us enjoyed the presentations!
Graham Farmelo talked about how James Clerk Maxwell described how the universe speaks in numbers though the now famous Maxwell Equations of Electromagnetism. One of his slides shows a portrait of Maxwell, with wife Katherine, who also was a physicist in her own right, and the faithful dog. At this point, Astronomer Assistants Ruby and Danny wanted to know more about the dog. What is the dog's name?
|James C. Maxwell, Wife Katherine, and faithful friend (Source: G. Farmelo, IAS Presentation, May 29, 2019)|
Well the name of the dog was not included in that presentation, but some independent searching on the internet came up with some more information. Check out this image of the Maxwell statue in Edinburgh, Canada. Now Resident Astronomer Peggy and I visited Edinburgh maybe 20 years ago now and I sort of remember seeing some statue like this but could not find any photographs of it. But the point is to notice that included in this statue is not the wife, but the faithful dog, not that the wife was not faithful. Anyway James Rautio published a little article in the IEEE Microwave Magazine with more details about the statue and the dog's name.
|Statue of Maxwell in Edinburgh (Source: J. Rautio, IEEE Microwave Magazine)|
Here you can see a larger view of the dog faithfully laying at Maxwell's side. Well it turns out the dog's name is Toby. So there you go, Ruby and Danny, the dog's name is Toby!
|Statue of Maxwell in Edinburgh includes his faithful dog, Toby (Source: J. Rautio, IEEE Microwave Magazine)|
Separately, another way the universe speaks in numbers is through astronomical predictions. It turns out that May 29 is the centenary of the famous total solar eclipse expedition that was to verify the bending of light by the gravity, as observed for starlight passing close to the edge of the sun. Hmm, I wonder if our modern sky location tools will be able to show the location of the sun and moon back on May 29, 1919? Yep, it seems to work ok. Take a look at this Sky Safari Pro screenshot with the date set to May 29, 1919 and the location set to Principe Island, off the coast of West Africa. We modern day observers have it so easy compared to the early explorers from whom we have learned so much. What a 100 years of progress have achieve!
|Sky Safari Pro screenshot for total solar eclipse at Principe on May 29, 1919 (Source: Palmia Observatory)| | 0.883167 | 3.961285 |
In 1859, a massive burst of energy from the sun slammed into Earth. It caused telegraph wires to explode in sparks, which gave some telegraph operators electric shocks. People could see auroras — the northern lights — as far south as Cuba and Hawaii.
If such a powerful burst, called a solar flare, were to hit our planet today, it could disrupt modern civilization. The energy could zap satellites, fry computer systems and knock out power grids. So when can we expect the next “super flare” to strike?
That’s the question Steven Saar has been trying to answer. He is one of many scientists trying to better understand our sun.
Of all the bodies in the universe, the sun seems one of the most familiar. After all, by the time you turn 20, you’ll have seen it rise and set some 7,300 times. But there’s still a lot that science does not yet know about the star at the center of our solar system. What causes solar flares and can they be predicted? Why is the sun’s atmosphere more than a million degrees hotter than its surface? How does the sun actually work?
Our star is still full of mysteries. And here are three scientists who are working to crack the case.
Sampling other suns
Saar is an astronomer studying at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., who studies stars. He wanted to know how often the sun produces a super flare like the one in 1859. There was just one problem: it had only happened once in recorded history. That made it mathematically impossible to predict how often it might occur.
To get a larger sample, Saar had to look outside our solar system. “The sun is a star,” he says. “So one can go out and try to find other stars that are as similar to the sun as possible.”
Using data from NASA’s Kepler space telescope, he looked for these “sun twins.” He turned up 84 sun-like stars and observed them for around four years. He wanted to see how often they released bursts of energy at least as powerful as the 1859 flare. Then he combined all of these data to get an average.
The stars he studied were younger and more active than our sun. That meant they had more flares. When he adjusted the results for an older, quieter star, he got his answer. A star like our sun should produce a super flare once every 200 to 480 years. His best guess: probably close to 350 years.
Saar was excited. “Getting an estimate for the sun itself, that was the holy grail, the key question,” he says.
Hooked on stars
Saar has loved astronomy since he was a child. While he explored other sciences as a student, astronomy was always his favorite. Eventually he decided to become an astronomer. In graduate school, galaxies were a popular subject. Saar wanted to do something different. A mentor suggested he look at sun-like stars. And with that, he was hooked.
“The sun is obviously really important to us,” he says. “It’s actually an area of astronomy that has relevance for our daily life. So it’s interesting and important to understand how the sun works, how it can change over time and what it can do.”
Saar saw that the key to understanding some of the sun’s biggest mysteries might actually be in looking at other stars.
“Although we can study the sun in great detail, it’s only a single example,” he says. “The idea is that if you study a lot of stars that are maybe similar to the sun, you might learn how the sun works.” In this case, it will be “indirectly, by looking at other examples.”
Saar looks for stars that are similar to our sun in mass, temperature, age, chemical composition and other properties. Sometimes it’s useful to look at stars that are similar to the sun in every way but one. “What if the sun was a little bit heavier?” Saar asks. “What would that change? And what does it tell you about the sun itself?”
Next, Saar would like to add more stars to his sample. That would let him predict the frequency of super flares more precisely. He also plans to look at his original data again. He wants to remove any other bursts of energy or activity near a star that may have been mistaken for a flare. That might lower the estimate slightly, getting it closer to results announced by Japanese scientists working on the same question. They had predicted a super flare once every 500 to 600 years. “I think we’re homing in on a good number,” Saar says.
A powerful new telescope
At the top of a 10,000-foot mountain on the Hawaiian island of Maui, the world’s most powerful solar telescope is under construction. When completed, the Daniel K. Inouye Solar Telescope will be able to see objects on the sun’s surface as small as 18 miles across.
Solar physicist Thomas Schad is helping design one of the five main tools that will be used in the telescope. He is a scientist with the University of Hawaii’s Institute for Astronomy in Pukalani. His instrument will analyze the makeup of the sun’s light.
Every element reflects light at a different wavelength. By splitting a beam of light into these wavelengths, scientists can learn about the sun’s properties. These include such things as what chemicals it is made of and how hot they are.
This split light is referred to as a spectrum. Studying it doesn’t just tell scientists about how the sun works. It also gives them a close-up look at some of the physics that might also be happening in more distant stars. Because the sun is so close, they can study it in much greater detail.
“We’re looking at features you’ll never see on another star,” Schad explains.
Schad got interested in solar physics while he was in college. He had taken part in a research program. The scientist who supervised him handed him data on the light spectra from explosions in the sun. Schad was asked to use those data to learn more about the explosions.
“It’s amazing just how much information we can pull out from the sun by analyzing the spectrum,” Schad now observes.
When what you need does not exist
As he began studying the sun, Schad realized that some of the tools he needed did not yet exist. He was excited to build them himself. “That’s how science moves forward. You know what the questions are, and you come up with ways you might answer them.” Plus, he adds, “I’ve always liked tinkering with things.”
The instrument Schad is helping to build for the new solar telescope will analyze infrared light. It is called the Diffraction Limited Near Infrared Spectropolarimeter (SPEK-trow-po-ler-IM-eh-tur) — or DL-NISP, for short. Many of the most important elements in the sun reflect light at infrared wavelengths. When the telescope first sees light in 2019, the DL-NISP will be used to study magnetic fields at the sun’s surface and in its lower atmosphere.
Schad must study the instrument’s design and make sure it has all the parts that it will need to do its job. He sends guidelines to the people producing its lenses and mirrors. Then he orders other special parts. When all of the pieces are completed, he must test each one to make sure they meet the telescope’s strict requirements. Then he will start putting them together.
In all, the telescope will have 21 lenses, 15 mirrors, three cameras and 21 motors. “We basically are building a big robot,” he says.
Solving a solar mystery
If you took a stroll on the surface of the sun, the temperature would be a relatively cool 6,000° Celsius (11,000° Fahrenheit). But move up into the sun’s atmosphere and it gets much toastier — around 2 million degrees. Why is the sun’s atmosphere so much hotter than its surface? And where does all that heat come from? These are among the biggest mysteries in solar science.
Some physicists think the heating of the solar atmosphere, or corona, is related to the sun’s magnetism. They think that waves of magnetic energy vibrate. These waves might move energy from the sun’s interior out into the corona, where it would be released as heat. But they’re not sure exactly how that might work.
Patrick Antolin wanted to test this theory. He is a solar physicist at the National Astronomical Observatory of Japan in Tokyo. He also is part of a team that worked with two space-based telescopes.
Japan’s Hinode telescope observed how the sun’s magnetic waves moved from side to side. NASA’s IRIS telescope measured their twisting motion. Combining both sets of data gave the scientists a complete picture of the movement.
With this, they saw the first direct evidence that coronal heating is caused by magnetic resonance. That’s when two magnetic waves vibrate in sync with one another, causing one of the waves to get stronger.
Antolin’s team then used a supercomputer to run a numerical simulation. It showed how this movement created an unusual form of turbulence — a bumpy swirling of gases — not seen on Earth. It also showed how this turbulence released energy into the atmosphere.
Antolin was excited. And part of that was because this finding was such a surprise. When they started the project, his team didn’t think it would work. True, his model predicted magnetic resonance would cause heating. But previous observations didn’t seem to support the theory. Still, the physicist says: “I was unwilling to give up so easily.”
When his group finally put all of the data together for the first time, these scientists were able to show how it worked. They realized magnetic resonance was not acting alone. It was accompanied by that strange turbulence. “The combination of both these mechanisms was producing exactly what was being observed,” he says.
What’s next for his research? Antolin’s team only looked at magnetic resonance in solar prominences (large loops of gas). That’s one type of structure in the sun. Next, they want to see if it also happens in another type of structure called spicules (little jets of gas).
If they can show that their model explains heating in many parts of the sun, it may someday solve the coronal mystery once and for all. And along with research by Saar and Schad, such findings will bring us a little closer to understanding our nearest star — our sun.
This is one in a series on careers in science, technology, engineering and mathematics made possible with generous support from Alcoa Foundation.
Word Find (click here to enlarge for printing) | 0.839133 | 3.889849 |
The image above shows a near true color picture of the C-type (carbonaceous) asteroid 1 Ceres, the first asteroid ever to be discovered, and the biggest object in the asteroid belt. With a diameter of 945 km (587 miles), it is also the largest of the minor planets within the orbit of Neptune, and the 33rd biggest object in the solar system overall, accounting for about 33% of all the mass in the asteroid belt.
For a considerable time after its discovery by Giuseppe Piazzi in 1801 it was considered to a be proper planet, until many other objects were found in similar orbits, leading to its reclassification as an asteroid in the mid-1800”s. Although Ceres is reasonably easy to spot from Earth with binoculars and small to medium sized telescopes, its brightness varies from 6.7 to 9.3 over a period of 15-16 months.
• Aphelion: 2.9773 AU
• Perihelion: 2.5577 AU
• Eccentricity: 0.075823
• Orbital period: 4.60 years (1,681.63 days)
• Equatorial rotation velocity: 92.61 m/sec
• Average orbital speed: 17.905 km/sec
• Mean proper motion: 78.193318 degrees/year
• Dimensions: 945 km (Diameter)
• Volume: 421,000,000 cubic kilometres
• Mass: 9.393 ± 0.005 × 1020 kilograms
• Surface area: 2,770 000 square kilometres
• Mean density: 2.161±0.009 gram/cubic centimetre
• Escape velocity: 0.51 km/sec
• Apparent magnitude: Variable from 6.64 to 9.34
Due to its mass and size, it is likely that Ceres is a surviving protoplanet remnant. Current models of how the solar system formed suggest that while all lunar to Mars-sized bodies had either been incorporated into the rocky planets, or been ejected from the solar system by Jupiter and/or the other gas giants, Ceres had survived the formation of the solar system relatively unscathed. However, a competing theory holds that Ceres had formed in the Kuiper belt and migrated inwards as the large planets moved outwards into the Kuiper belt, since the presence of ammonia salts in the Occator crater on Ceres suggests that it (Ceres) had not formed in the inner solar system.
Ceres is the only object in the asteroid belt that is known to be in hydrostatic equilibrium, meaning that it is the only asteroid belt body whose own gravity has caused it to be roughly spherical in shape. This was confirmed after detailed analysis revealed that this was not the case with 4 Vesta. Ceres is also the smallest known body that is confirmed to be in hydrostatic equilibrium after Saturn’s satellite Rhea, which is 600 km bigger and more than twice as massive as Ceres.
Ceres is composed mainly of ice and rock, and its slightly oblate shape is the result of its internal structure, which is partially differentiated. In terms of its structure, Ceres consists of a large rocky core that is overlaid by a 100-km-thick icy mantle that is estimated to hold about 200 million cubic kilometres of water.
If this estimate turns out to be accurate, it would mean that Ceres contains more water than all the fresh water on Earth, which is supported by several observations made with the Keck telescope in 2002, as well as by complex evolutionary models. Moreover, studies have shown that a liquid water ocean under a thick layer of water ice may have persisted to present times. However, recent studies have suggested that Ceres could possibly have a small inner iron-rich core due to partial differentiation of the rocky fraction of its core.
Although the surface of Ceres is largely similar to those of most other C-type asteroids in terms of chemical composition, there are some significant differences. For instance, some persistent and ubiquitous features in Ceres’ infrared spectrum indicate the presence of hydrated materials that include iron-rich clay minerals such as cronstedtite, and carbonate minerals such as dolomite and siderite, all of which are common in carbonaceous chondrite meteorites. The presence of these materials requires that relatively large amounts of water be present in the asteroid’s interior, which is absent in the spectra of most other C-type asteroids. For this reason, Ceres is sometimes classified as a G-type asteroid.
Studies based on Hubble Space Telescope-derived data have also revealed the presence of graphite, sulphur dioxide, and sulphur on Ceres’ surface. While the exact origins of these materials remain somewhat unclear, the presence of graphite is almost certainly the result of space weathering on some of Ceres’ older surfaces, while the latter two are volatile under Cerean conditions. As such, sulphur, and sulphurous compounds released by recent geological activity on the surface either would have escaped rapidly, or would have become trapped in cold spots on the asteroid.
In terms of surface features, the Dawn spacecraft found that, the asteroid’s surface is heavily cratered, although the total number of large impact craters was lower than was expected by most investigators. However, a relatively large number of large craters have central pits, likely as the result of cryovolcanic or other geological process, while many other craters have prominent central peaks. Ceres also has one prominent mountain, a cryovolcanic structure named Ahuna Mons, which is estimated to be no more than a few hundred million years old, based on the relative absence of impact craters on the mountain.
A recent computer simulation has also suggested that other ice volcanoes may have existed on Ceres at various times, but that these have become indistinguishable from the surrounding terrain through the process of viscous relaxation. In simple terms, this means that the surface of Ceres is partially viscous (fluid), and that fluid motions continually mould and shape the surface so that some features are destroyed while others are created.
Surface temperatures on Ceres are relatively high. With the Sun at the zenith, the maximum surface temperature (based on Ceres’ position on 5 May 1991) was estimated be in the region of 235K (-38 °C, -36 °F). At this temperature, ice is unstable, which could explain the dark surface of the asteroid since minerals mixed into the ice would remain on the surface when the ice fraction sublimates.
Based on data obtained from the Herschel Space Observatory in 2014, it appears that Ceres has a tenuous atmosphere consisting primarily of water vapor. The origin of the water vapor has been shown to derive from several localized sources of water vapor in mid-latitudes, that each releases about 3 kilograms of water second.
Possible mechanisms include the sublimation of exposed water ice over a surface area of about 0.6 square km, although cryovolcanic eruptions resulting from radiogenic internal heat is likely to produce more vapor than sublimation of surface ice. In fact, observations made by the Dawn spacecraft provide strong evidence that ongoing geological activity is a major contributor to the water vapour in Ceres’ atmosphere, since the asteroids’ atmosphere appears to be reasonably stable. If sublimation of surface ice were the main source of water vapor, the density of the atmosphere would vary according to the asteroid’s position relative to the Sun. | 0.866064 | 3.926987 |
Two instruments aboard NASA’s Spitzer Space Telescope – the Infrared Array Camera and the Multiband Imaging Photometer, or MIPS – have captured a spectacular image of the Cat’s Paw Nebula showing bright green clouds of gas and huge reddish bubbles. The green areas show areas where radiation from hot young stars causes molecules known as polycyclic aromatic hydrocarbons to fluoresce. The reddish bubbles likely are caused by gas and dust in the nebula being heated up by recently-born stars, expanding to create the giant structures.
Some of the bubbles many eventually burst, creating U-shaped features more easily visible in a Spitzer image below, taken by the telescope’s Infrared Array Camera alone. The MIPS instrument captures the warm dust visible in the upper image.
The Cat’s Paw Nebula is located 4,500 to 5,500 light years away. It stretches 80 to 90 light years across. | 0.817967 | 3.275959 |
This week, ESA’s Integral space observatory celebrates ten years since launch on 17 October 2002. To mark the occasion, we present a slideshow of artist’s impressions depicting some of Integral’s most important discoveries.
Integral, short for International Gamma-Ray Astrophysics Laboratory, is equipped with two gamma-ray telescopes, an X-ray monitor and an optical camera. All four of Integral’s instruments point simultaneously at the same region of the sky to make complementary observations of high-energy sources.
Integral is often bathed in gamma-ray bursts, the death cries of massive stars that have burned up their fuel and exploded as a dramatic supernova, blasting high-energy radiation through the Solar System on a near-daily basis.
The satellite has also discovered objects that are much subtler than exploding stars. Highly absorbed X-ray binaries shrouded in material streaming off a high-mass companion star are too faint to be seen in optical and ultraviolet wavelengths, but high-energy X-ray and gamma-ray radiation can escape from that environment, detectable by Integral.
Meanwhile, supergiant fast X-ray transients display X-ray and gamma-ray outbursts that last only a few tens of minutes to hours. These objects comprise a neutron star – the dead core of a normal star which ended its life through a supernova – grabbing material from the clumpy wind emitted by its supergiant stellar neighbour.
A strange breed of pulsar with super-strong magnetic fields has also been uncovered by Integral. A pulsar is a rotating neutron star that appears to emit beams of radiation like a lighthouse.
Integral is also capable of all-sky surveys and has for the first time mapped the entire sky at the specific energy produced by the annihilation of electrons with their positron anti-particles.
The power released by the annihilating particles corresponds to over six thousand times the luminosity of our Sun.
Integral has also made the first unambiguous discovery of highly energetic X-rays coming from the galaxy cluster known as Ophiuchus. The emission is thought to originate from giant shockwaves rippling through the cluster’s gas as two galaxies collide and merge.
Integral has also been probing the feeding habits of active galaxies and black holes, which lurk in the bellies of most galaxies, including our own.
Many supermassive black holes are surrounded by thick dust discs, which Integral can peer through to identify the black hole hidden within.
Read more about Integral’s decade-long contribution to high-energy astrophysics in our special anniversary article coming up on Wednesday. | 0.890123 | 3.918213 |
When it comes to searching for life, we’ve usually assumed that all parts of our galaxy are equally likely contenders.
Maybe not, according to Cardiff University astronomers Jane Greaves and Phil Cigan, who presented some new findings at the European Week of Astronomy and Space Science (EWASS) in Liverpool last week.
The astronomers found that the Crab Nebula, a giant cloud of dust and gas left over from a supernova that was observed by Chinese astronomers in the year 1054, is very low in phosphorus – a vital component in DNA. This suggests planetary systems that form in the region will have a hard time supporting life.
Phosphorus – along with hydrogen, carbon, nitrogen, oxygen and sulfur – is one of six elements essential for life on Earth. It is produced when massive stars, more than eight times the size of the Sun, explode as supernovae. The phosphorus and other stellar shrapnel are ejected and disperse out into space to form a supernova remnant.
It was only in 2013 that phosphorus was directly detected in a supernova remnant. In that remnant, Cassiopeia A, researchers found the ratio of phosphorus to iron was as much as 100 times the average ratio found throughout the Milky Way.
However, the amount of phosphorus measured in Cassiopeia A was at odds with the predictions of some computer models. And that got Greaves thinking: “I wondered what the implications were for life on other planets if unpredictable amounts of P [phosphorus] are spat out into space and later used in the construction of new planets.”
So the Cardiff team used the UK’s William Herschel Telescope to observe infrared light from phosphorus and iron in the Crab Nebula. They found that the Crab Nebula contains far less phosphorus than Cassiopeia A, although the exact abundances are still to be measured.
The comparison suggests that the balance of elements in material ejected into space during supernovae can vary dramatically. Although it is still uncertain exactly how planets in the cosmos get their phosphorus, if supernovae are responsible, “the route to carrying phosphorus into new-born planets looks rather precarious,” remarks Greaves.
Lucky regions of the cosmos “could potentially ‘hit the jackpot’ and be showered with plentiful phosphorus,” says Cigan. On the other hand, planets born near phosphorus-poor supernova might struggle. Cigan cautions, however, that more observations are needed to ensure that their preliminary results are representative of the Crab Nebula as a whole. The team also hope to extend their phosphorus inventory across the galaxy by studying other supernova remnants.
Cigan is pleased with the study’s reception at the meeting last week: “They said [the findings were] very cool.”
Vhairi Mackintosh is a scientific educator, writer and researcher based in Melbourne who holds a PhD in earth sciences.
Read science facts, not fiction...
There’s never been a more important time to explain the facts, cherish evidence-based knowledge and to showcase the latest scientific, technological and engineering breakthroughs. Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science. Financial contributions, however big or small, help us provide access to trusted science information at a time when the world needs it most. Please support us by making a donation or purchasing a subscription today. | 0.861422 | 3.911118 |
Planet Mercury a result of early hit-and-run collisions
Planet Mercury‘s unusual metal-rich composition has been a longstanding puzzle in planetary science. According to a study published online in Nature Geoscience July 6, Mercury and other unusually metal-rich objects in the solar system may be relics left behind by collisions in the early solar system that built the other planets.
The origin of planet Mercury has been a difficult question in planetary science because its composition is very different from that of the other terrestrial planets and the moon. This small, innermost planet has more than twice the fraction of metallic iron of any other terrestrial planet. Its iron core makes up about 65 percent of Mercury’s total mass; Earth’s core, by comparison, is just 32 percent of its mass.
How do we get Venus, Earth and Mars to be mostly “chondritic” (having a more-or-less Earth-like bulk composition) while Mercury is such an anomaly? For Arizona State University professor Erik Asphaug, understanding how such a planet accumulated from the dust, ice and gas in the early solar nebula is a key science question.
There have been a number of failed hypotheses for Mercury’s formation. None of them until now has been able to explain how Mercury lost its mantle while retaining significant levels of volatiles (easily vaporized elements or compounds, such as water, lead and sulfur). Mercury has substantially more volatiles than the moon does, leading scientists to think its formation could have had nothing to do with a giant impact ripping off the mantle, which has been a common popular explanation.
To explain the mystery of Mercury‘s metal-rich composition, ASU’s Asphaug and Andreas Reufer of the University of Bern have developed a new hypothesis involving hit-and-run collisions, where proto-Mercury loses half its mantle in a grazing blow into a larger planet (proto-Venus or proto-Earth). One or more hit-and-run collisions could have potentially stripped away proto-Mercury’s mantle without an intense shock, leaving behind a mostly-iron body and satisfying a number of the major puzzles of planetary formation – including the retention of volatiles – in a process that can also explain the absence of shock features in many of the mantle-stripped meteorites.
Asphaug and Reufer have developed a statistical scenario for how planets merge and grow based on the common notion that Mars and Mercury are the last two relics of an original population of maybe 20 bodies that mostly accreted to form Venus and Earth. These last two planets lucked out.
“How did they luck out? Mars, by missing out on most of the action – not colliding into any larger body since its formation – and Mercury, by hitting the larger planets in a glancing blow each time, failing to accrete,” explains Asphaug, who is a professor in ASU’s School of Earth and Space Exploration. “It’s like landing heads two or three times in a row – lucky, but not crazy lucky. In fact, about one in 10 lucky.”
By and large, dynamical modelers have rejected the notion that hit-and-run survivors can be important because they will eventually be accreted by the same larger body they originally ran into. Their argument is that it is very unlikely for a hit-and-run relic to survive this final accretion onto the target body.
“The surprising result we have shown is that hit-and-run relics not only can exist in rare cases, but that survivors of repeated hit-and-run incidents can dominate the surviving population. That is, the average unaccreted body will have been subject to more than one hit-and-run collision,” explains Asphaug. “We propose one or two of these hit-and-run collisions can explain Mercury’s massive metallic core and very thin rocky mantle.”
According to Reufer, who performed the computer modeling for the study, “Giant collisions put the final touches on our planets. Only recently have we started to understand how profound and deep those final touches can be.”
“The implication of the dynamical scenario explains, at long last, where the ‘missing mantle’ of Mercury is – it’s on Venus or the Earth, the hit-and-run targets that won the sweep-up,” says Asphaug.
The duo’s modelling has revealed a fundamental problem with an idea implicit to modern theories of planet formation: that protoplanets grow efficiently into ever larger bodies, merging whenever they collide.
Instead, disruption occurs even while the protoplanets are growing.
“Protoplanets do merge and grow, overall, because otherwise there would not be planets,” says Asphaug. “But planet formation is actually a very messy, very lossy process, and when you take that into account, it’s not at all surprising that the ‘scraps,’ like Mercury and Mars, and the asteroids are so diverse.”
These simulations are of great relevance to meteoritics, which, just like Mercury’s missing mantle, faces questions like: Where’s all the stripped mantle rock that got removed from these early core-forming planetesimals? Where are the olivine meteorites that correspond to the dozens or hundreds of iron meteorite parent bodies?
“It’s not missing – it’s inside the mantles of the planets, ultimately,” explains Asphaug. “It got gobbled up by the larger growing planetary bodies in every hit-and-run series of encounters.” | 0.856632 | 3.863398 |
Beyond Pluto: Spacecraft to fly by distant space rock 'Ultima Thule' on New Year's Day
Talk about far out.
NASA's unmanned New Horizon spacecraft, now zooming into outer space beyond Pluto, will fly by a small space rock known as Ultima Thule on New Year's Day.
The flyby will "provide NASA researchers with valuable images and science data of a world we know practically nothing about," according to CNet. If successful, it will be the most distant flyby in human history, at about 4 billion miles from Earth.
"New Horizons will map Ultima, determine how many moons it has and find out if it has rings or even an atmosphere, " said the mission's principal investigator Alan Stern of the Southwest Research Institute. "It will make other studies, too, such as measuring Ultima's temperature and perhaps even its mass. In the space of one 72-hour period, Ultima will be transformed from a pinpoint of light – a dot in the distance – to a fully explored world. It should be breathtaking!" Stern said.
With the inelegant official name of "2014 MU69," Ultima Thule was first discovered in 2014 by astronomers using the Hubble Space Telescope. Scientists believe it's an ancient relic of the formation of our solar system, the Planetary Society said.
"We don’t have much idea what 2014 MU69 is going to look like," said Emily Lakdawalla of the Planetary Society. "It seems to have a very irregular shape."
At about 19 miles in diameter, the object is a bit larger than Manhattan. The rock is located in the Kuiper Belt, a massive, doughnut-shaped region of icy bodies beyond the orbit of Neptune.
"The Kuiper Belt is a scientifically rich frontier. Its exploration has important implications for better understanding comets, small planets, the solar system as a whole," NASA said.
Objects such as Ultima Thule are believed to be the building blocks of planets.
The New Horizons spacecraft was launched from Earth 13 years ago and flew by Pluto in 2015. The craft will come three times closer to Ultima Thule than it did Pluto, according to NASA.
NASA said the nickname Ultima Thule means "beyond the borders of the known world." | 0.892267 | 3.046463 |
In this VIS image, taken by the NASA - Mars Odyssey Orbiter on July, 31st, 2002, and during its 3.415th orbit around the Red Planet, we can see, jointly with countless Unnamed Impact Craters of various age and sizes, a number of Windstreaks (one of the most common Aeolian Features of Mars) which are located on the Floor of the very well known Gusev Crater (the last and sandy home of the now decomisssioned NASA - Mars Exploration Rover - or "MER", for short - "Spirit").
Very interesting, in our opinion (as IPF), is the truly remarkable color difference of the Floor which exists between the Northern Portion of this area of Gusev Crater, as compared to the Southern one (in fact, we go from a brown/orange color - North - to a dark gray - South, with light gray nuances in the middle).
A definitive explanation of this color difference cannot be given, however (always in our humble opinion), the action of the strong Dominant Winds which blow all over Gusev Crater could, most likely, be the main reason - and certainly not the only one - of such a contrast.
Latitude (centered): 14,1644° South
Longitude (centered): 175,4240° East
This image (which is an Original Mars Odyssey Orbiter false colors and Map-Projected frame published on the NASA - Planetary Photojournal with the ID n. PIA 19020) has been additionally processed, magnified to aid the visibility of the details, contrast enhanced and sharpened, Gamma corrected and then re-colorized in Absolute Natural Colors (such as the colors that a normal human eye would actually perceive if someone were onboard the NASA - Mars Odyssey Orbiter and then looked down, towards the Surface of Mars), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. | 0.851421 | 3.517524 |
Astronomers Discover that Stars Produce Sounds Similar to a Human Heartbeat
The universe now knows a star that exhibits a pulse-like rhythm like a human heartbeat, thanks to NASA's TESS. Astronomers were able to see and pass through the consistent noise the universe makes and have discovered that a specific star exhibits a steady pulse-like rhythm, with reference as close to the human heartbeat.
The Delta Scuti
The Delta Scuti, a type of star, baffled astronomers for years. It's bigger in mass compared to the Sun and is confirmed to be 1.5-2.5 times bigger than the Sun. However, because of its different properties from the Sun, it functions differently from the Sun. According to NASA, The Sun takes about 27 days to rotate.
For a Delta Scuti star, on the other hand, it only takes one full day to rotate. It can even spin on its axis twice on a single day. Because of its high-speed rotation, the poles of Delta Scuti stars tend to flatten out. This makes it difficult for astronomers to examine the inner workings of Delta Scuti stars.
This specific star is believed to be the exhibitor of the pulse-like rhythm that is very much like a human heartbeat because of recent news from NASA.
The Analogy of Geology and Astronomy
Geologists understand the way the Earth was structured by understanding first the seismic waves coming from earthquakes. Analogy-wise, astronomers use this way to understand the inner structure of stars. They first examine the inner workings of a star and then work their way out from there.
Essentially, sound waves go through the interior of a star at various speeds. This results in sporadic depth change within a star. Because of the sporadic changes within a star, there exists a series of fluctuations within a star. This causes a star to give off sounds from within it.
According to NASA's TESS (Transiting Exoplanet Survey Satellite), stars of the Delta Scuti class have always exhibited pulse-like sounds; however, there was no specific pattern within the sounds. Now, NASA recently just discovered that stars do exhibit a specific sound pattern. Delta Scuti stars are under surveillance and monitoring.
Moreover, astronomers discovered that these pulse-like sounds are actually sound waves within the stars. It's not only the Delta Scuti stars that exhibit pulse-like rhythms but also 60 other stars that exist close to the Milky Way galaxy and, evidently, our solar system.
The data that came from NASA's TESS enabled astronomers to get past the noise of the universe and observe patterns and a sense of order within the internal sounds of stars.
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Just as the Earth and other planets rotate around our Sun, our solar system has a rotation trajectory around our galaxy Milky Way. And I must say…before I leave this plane of existence, I feel confident future research will show our galaxy, along with neighboring galaxies, will also have a periodicity rotation with cyclical parameters…rotating around what is yet to be discovered.
The Earth is regularly exposed to cosmic rays as it oscillates upward through the galactic disc. Every 60 million years or so, astronomers believe that our Sun and planets cycle northward in the galactic plane. Just as the Earth has her magnetic field, Milky Way has its own. Without the galactic plane’s magnetic field shielding our solar system, we would be at even higher risk of radiation exposure. It is hypnotized that the closer our solar system travels to the galactic center, we note a correlation between this cyclical motion and partial to mass extinctions happening with a fair amount of regularity on Earth over the past 500 million years.
Some scientists have surmised we are in the midst of a sixth mass extinction of plants and animals. An assemblage of researchers have noted the cycle we are currently experiencing may be a high ratio of species die-offs since. Although extinction is a natural phenomenon, it occurs at a natural “background” rate of about one to five species per year. Scientists estimate we’re now losing species at 1,000 to 10,000 times the background rate. However, to keep things in perspective – researchers currently know of about 1.2 million species to be recorded by science. What’s left to be discovered however is very interesting. The number of species that scientists think are left to be discovered is around 8.7 million. Still, new discoveries can change a scenario, and so can the numbers.
I have re-written this article and ones coming 3 or 4 times because of its importance. Some of you might remember an importance decision I made concerning the direction of my research. I had such a strong pull to go beyond the study of our Sun-Earth connection and peeking around the corner to see what’s next. What I hope to show you is that I am finding a very similar pattern of cause and effect, symbiotic relationship between each level of co-existence. I hope you agree and perhaps catch a flavor of my enthusiastic venturous demeanor. If so, pledge your donation to match renewed devotion to this work. If you happen to know Bill Gates, or his neighbor, give him a call.
Coming Next: Part III – First Will Come Reversal Excursions Then the Flip | 0.867664 | 3.160815 |
By Zach Royer
Seventy million years ago, the earth was inhabited by giant reptiles: gigantic lizards, colossal saurains, who slithered, swam, flew. Their reign lasted one hundred million years - whereas, according to the most optimistic estimates, man has had barely six million years.
This means that these species of reptiles had in order to become adapted and to evolve, an infinitely longer time than man. Furthermore, it is impossible to pretend that they represented an evolutionary failure: any species that lasts a hundred million years must be considered to be fully adapted. Yet few species that were contemporaries of those reptiles survive -- for example, certain crabs, which have not changed in three hundred million years. In fact, in less than one million years the giant reptiles entirely disappeared.
How and Why?
We can scarcely maintain that it was because a change in climate; for even when the climate changes, the oceans hardly vary, and many of these reptiles lived in the oceans.
It is impossible to believe that a higher form of life was able to exterminate them. This would have required a considerable army, whose traces we would certainly have found.
One amusing hypothesis is that our ancestors, the mammals, might have fed on dinosaur eggs. But it is only that: an amusing hypothesis: the icthyosaurs deposited their eggs in the oceans, out of their adversaries' reach.
It has been said that the grasses changed, and that the new grasses were too tough for the big reptiles. A completely unlikely hypothesis: large numbers of vegetation types have survived, on which they could have fed perfectly well. The giant tortoises of the Galapagos Islands, the ones that interested Darwin so much, did not die of hunger.
One could say that species grow old, become senile, and die. But this is bad logic: the preservation of the genetic code prevents a species from dying out. And why haven't those species that are still living after several hundred millions of years, such as crabs and cockroaches, become senile too?
None of these hypotheses hold. But something happened. What then? An ingenious hypothesis has been outlined by two Soviet scientists, V. I. Krasovkii and I. S. Chklovski, both of whom are eminent astrophysicists -- especially the latter, who is the author of some extremely important works in astrophysics and radio astronomy. It was Chklovski, in fact, who studied synchotron radiation and showed that relatively rapid and extremely violent events can be produced at the center of galaxies as well as in space in general.
(AA) Youtuber MrMBB333 gives us a run down of today's weird and strange weather events including a giant lightning storm and two possible tornadoes in the Mid-west. Visit our WEATHER WATCH and SKY WATCH pages to follow weather and other anomalies in your area.
Have you ever looked up and spotted a long contrail extending across the sky? Have you ever noticed that sometimes they disappear instantaneously or sometimes they spread out and create a cloud cover? Google the terms "Chemtrails" or "Geoengineering" and learn how many methods are used today to create or prevent certain weather patterns, with unknown consequence.
The document "Weather as a Force Multiplier - Owning the Weather by 2025" created for the United States Air Force by military officials outlines the use of weather for military applications:
Posted by Jason A. in Earth Changes, Human Interest
(AA) PROPHETIC EVENTS the past week or so with signs of the times. Worldwide bible prophecy, end times, extreme weather events, wildfires and more on the world news.
Send your links, photos, videos and news tips to [email protected]
(AA) In the wake of the recent string of solar flares, some Americans--particularly Gulf Coast residents--may be wondering whether there are places in the U.S. that are safe from such natural disasters. The short answer? No. The Midwest may not be vulnerable to hurricanes, but twisters drop in regularly. Major earthquakes don't tend to strike New England, but strong winds can peel the roof off a northeastern house and snowstorms can shut down cities.
"Every location in the country is exposed to one disaster or another," says Wendy Rose, spokeswoman for the Institute for Business & Home Safety, a Tampa, Fla.-based nonprofit insurance industry group that aims to reduce losses from natural catastrophes.
Still, some places are less susceptible than others to natural hazards. To get an idea where they might be, we partnered with Sperling's Best Places ( www.bestplaces.net), a data collection company based in Portland, Ore. Sperling's has compiled weather and disaster data for 331 metropolitan statistical areas in the U.S., and we used the information to discern the safest--and least safe--areas in which to live.
By Martin Gray
Early in the spring of 1986 I began a year-long pilgrimage around Europe by bicycle. Over four seasons I cycled through eleven countries to visit, study and photograph more than 135 holy places. In succeeding years I traveled to Europe several additional times, visiting other countries and their sacred sites. These travels took me to the sacred places of Megalithic Greek and Celtic cultures as well as to the pilgrimage sites of medieval and contemporary Christianity. For many thousands of years our ancestors have been visiting and venerating the power places of Europe. One culture after another has often frequented the same power places. The story of how these magical places were discovered and used is filled with myths of cosmic and cometary induced world destroying cataclysms, astronomers and sages, and nature spirits and angels. Misconceptions about the so-called Ice Age and its glacier coverage Before beginning our discussion of the megalithic use of power places in ancient Europe we should first address certain misconceptions regarding the cause of the transition between the Paleolithic and Neolithic eras. According to conventional beliefs (deriving from incorrect assumptions of the Uniformitarian theory of Charles Lyell and the Ice Age or glacial theory of Louis Agassiz in the early 1800's) enormous glaciers once covered vast regions of the northern hemisphere. These conventional beliefs state that the levels of the world's oceans were lower during the glacier age because of all the water supposedly frozen up in the polar ice cap. Between 13,000 and 8000 BC the vast glaciers melted and the levels of the world oceans rose by 120 meters. The effect of this glacial melting and sea level rise on archaic European life marked the end of the Paleolithic and the beginning of the Neolithic.
This idea of a so-called Ice Age, with enormous glaciers covering vast areas of the northern hemisphere, has been debated by numerous scientific studies in the fields of geology, paleontology, biology, zoology, climatology, anthropology and mythology. Readers interested in learning more about these studies and their revelations regarding the Ice Age and its less-than-previously-assumed glacier coverage, as well as alternative dates for the occurrence of the Ice Age, will enjoy the books Cataclysm: Compelling Evidence of a Cosmic Catastrophe in 9500 BC, by Allan & Delair and Ice Age Civilizations, by James Nienhuis. The factual material presented in this scholarly book is slowly making its way into university courses and text books around the world, thereby rewriting our understanding of early Neolithic times.
Cosmic and cometary induced cataclysms - 9500, 7640, 3150 and 1198 BC Prior to embarking on a discussion regarding the discovery and use of power places by humans during Neolithic times there is another - and critically important - matter that must be explored first. This concerns the pass-by and actual impact of cosmic and cometary objects at four distinct periods in the prehistoric past. To begin to explore this matter let us first refer to the enigmatic writings of the 4th century BC Greek philosopher Plato. In the Timaeus dialogues, these being a record of discussions between the Greek statesman Solon and an Egyptian priest, Plato report the following:
"You Greeks are all children. You have no belief rooted in the old tradition and no knowledge hoary with age. And the reason is this. There have been and will be many different calamities to destroy mankind, the greatest of them by fire and water, lesser ones by countless other means. You remember only one deluge, though there have been many."
What might these calamities be which Plato's Egyptian informants are referring to? Evidence has accumulated from a variety of scientific disciplines which demonstrate that a massive cosmic object (probably a portion of an astronomically-near supernova explosion) passed close by the earth in approximately 9500 BC. This cosmic event caused a worldwide cataclysm of enormous proportions, including massive shifting of the earth's surface, devastating volcanic activity, mega-tsunami waves, subsidence of regional landmasses, and mass extinctions of both animals and humans. In this regard it is vitally important to note that many of the geological and biological effects previously attributed to the hypothesized glacier movements of ice age times could NOT have been caused by the slow movement of ice but were in fact caused by the rapid and vast displacement of oceanic bodies of water (this being caused by the irresistible gravitational pull of the enormous cosmic object passing by the earth). Additionally, the species-wide animal extinctions caused by this event occurred far beyond the geographical boundaries set for the 'Ice Age glaciations' by orthodox theorists.
The shifting of the earth's surface, termed crustal displacement by its primary theorist, Charles Hapgood, was also studied by Einstein who reported, "One can hardly doubt that significant shifts of the earth's crusts have taken place repeatedly and within a short time."
To read more about the cosmic object pass-by and the ensuing crustal displacement of 9500 BC, refer to Cataclysm by D.S. Allan & J.B. Delair, The Atlantis Blueprint by Colin Wilson and Rand Flem-Ath, and Catastrophobia by Barbara Hand Clow.
Approximately 2000 years later, in roughly 7640 BC, a cometary object sped towards the earth. This time, however, rather than passing by the earth as the cosmic object of 9500 BC had done, the cometary object actually entered the atmosphere, broke into seven pieces, and impacted the earth at known locations on the planet's oceans. The following map shows the general location of each of the seven impacts.
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The “Comet of the Week” this week is Comet IRAS-Araki-Alcock 1983d, which passed just 0.031 AU (4.68 million km, or 12.2 lunar distances) from Earth on May 11, 1983 – the closest confirmed cometary approach to Earth during the 20th Century, and the fifth-closest confirmed such approach in all of recorded history. Within this context, it is perhaps appropriate to examine some of the other very close approaches of comets to Earth.
The comet that has made the closest confirmed approach to Earth was discovered on June 14, 1770 by the renowned French comet-hunter Charles Messier. At that time it was located in Sagittarius and perhaps close to 5th or 6th magnitude, but it brightened rapidly over the subsequent couple of weeks as it approached Earth. On July 1 it passed just 0.0151 AU (2.26 million km, or 5.9 lunar distances) from Earth, and according to Messier and other observers of that time was as bright as 1st or 2nd magnitude and exhibited a coma up to 2½ degrees in diameter (although apparently without any appreciable tail). Within about three days after its closest approach it disappeared into sunlight; Messier later recovered it in the morning sky on August 3 and followed it for the next two months before it faded from view.
According to orbital calculations performed by Swedish mathematician Anders Lexell – for whom the comet was eventually named – the comet was a short-period object with a period of only 5.6 years, and had been placed into that orbit as a result of a very close approach to Jupiter (0.02 AU) in 1767. After being missed due to poor viewing geometry in 1776, Comet Lexell passed even closer to Jupiter (0.0015 AU) in 1779, with the results of that encounter being very difficult to predict; it is possible that the comet was placed into a much-longer period orbit (a few centuries) or perhaps even ejected from the solar system altogether. A re-examination of Comet Lexell’s orbit in 2018 by Chinese-American astronomer Quan-Zhi Ye and his colleagues suggests that the Apollo-type asteroid (529668) 2010 JL33 might possibly be a remnant of Comet Lexell, although it is not possible to establish a definite linkage. (This object passed just 0.043 AU from Earth in late 2010 and became as bright as 13th magnitude, but does not come close again until a moderately close approach of 0.12 AU in December 2045.)
The 20 closest cometary approaches to Earth in recorded history are listed in the following table:
|Rank||Comet||Approach date||Distance (AU)|
|1.||Lexell 1770 I||1770 July 1||0.015|
|2.||5P/Tempel-Tuttle||1366 October 26||0.023|
|3.||PANSTARRS P/2016 BA14||2016 March 22||0.024|
|4.||289P/Blanpain P/2003 WY25||2003 December 11||0.025|
|5.||IRAS-Araki-Alcock 1983d||1983 May 11||0.031|
|6.||1P/Halley||837 April 10||0.033|
|7.||252P/LINEAR||2016 March 21||0.036|
|8.||3D/Biela 1806 I||1805 December 9||0.037|
|9.||Grischow 1743 I||1743 February 8||0.039|
|10.||7P/Pons-Winnecke 1927c||1927 June 26||0.039|
|11.||Comet of 1014 (C/1014 C1)||1014 February 24||0.041|
|12.||Comet of 1702 (C/1702 H1)||1702 April 20||0.044|
|13.||Comet of 1132 (C/1132 T1)||1132 October 7||0.045|
|14.||Comet of 1351 (C/1351 W1)||1351 November 29||0.048|
|15.||Comet of 1345 (C/1345 O1)||1345 July 31||0.048|
|16.||209P/LINEAR||2014 May 29||0.055|
|17.||Comet of 1499 (C/1499 Q1)||1499 August 17||0.059|
|18.||45P/Honda-Mrkos–Pajdusakova||2011 August 15||0.060|
|19.||73P/Schwassmann-Wachmann 3 1930d||1930 May 31||0.062|
|20.||Sugano-Saigusa–Fujikawa 1983e||1983 June 12||0.063|
Comet 1P/Halley is discussed in a previous “Special Topics” presentation, and Comet 55P/Tempel-Tuttle, the parent comet of the Leonid meteor shower, is discussed in a future “Special Topics” presentation. Comet 3D/Biela, which no longer exists, is a previous “Comet of the Week.” Comet Grischow in 1743 is possibly a short-period comet, but it has never been seen since. The comet of 1702 is not the same object as a bright comet seen earlier that year (X/1702 D1) that may have been a Kreutz sungrazer. The comet of 1499 is possibly identical to Comet Levy 1991q, which was found to be a Halley-type comet with an orbital period of 51 years, and when that object returns in 2042 it should be possible to confirm (or disprove) that identity.
In a similar fashion, the following table lists the 20 closest cometary approaches during the “Ice and Stone 2020” era, i.e., within the past 50 years – coincident with the period of time that I have been actively observing comets.
|Rank||Comet||Approach date||Distance (AU)|
|1.||PANSTARRS P/2016 BA14||2016 March 22||0.024|
|2.||289P/Blanpain P/2003 WY25||2003 December 11||0.025|
|3.||IRAS-Araki-Alcock 1983d||1983 May 11||0.031|
|4.||252P/LINEAR||2016 March 21||0.036|
|5.||209P/LINEAR||2014 May 29||0.055|
|6.||45P/Honda-Mrkos–Pajdusakova||2011 August 15||0.060|
|7.||Sugano-Saigusa–Fujikawa 1983e||1983 June 12||0.063|
|8.||46P/Wirtanen||2018 December 16||0.077|
|9.||73P/Schwassmann-Wachmann 3||2006 May 12||0.079|
|10.||45P/Honda-Mrkos–Pajdusakova||2017 February 11||0.083|
|11.||107P/Wilson-Harrington P/1979 VA||1979 October 30||0.091|
|12.||289P/Blanpain||2020 January 11||0.091|
|13.||252P/LINEAR P/2000 G1||2000 March 4||0.097|
|14.||Hyakutake C/1996 B2||1996 March 25||0.102|
|15.||300P/Catalina P/2005 JQ5||2005 June 27||0.103|
|16.||Suzuki-Saigusa-Mori 1975k||1975 October 31||0.104|
|17.||103P/Hartley 2||2010 October 20||0.121|
|18.||Catalina P/2009 WX51||2009 December 25||0.147|
|19.||169P/NEAT||2005 August 7||0.147|
|20.||6P/d’Arrest 1976e||976 August 12||0.151|
The lone “Great Comet” on this list is Comet Hyakutake C/1996 B2, which is a previous “Comet of the Week.” Comet 103P/Hartley 2 was encountered by the EPOXI mission (rescaled from the Deep Impact spacecraft) around the time of its 2010 approach to Earth, and an image from this encounter is featured in a previous “Special Topics” presentation.
The top entry on this list and the Number 3 entry on the “recorded history” list, Comet PANSTARRS P/2016 BA14, was a very dim object which appeared almost stellar and never was brighter than 13th magnitude despite its close distance, however radar studies with the DSN tracking antenna at Goldstone, California suggested that its nucleus is close to 1 km in diameter, indicating that it is only very weakly active. Its orbit bears a striking similarity to that of Comet 252P/LINEAR, which passed close to Earth at the same time, and which despite having a smaller nucleus was much brighter (close to 4th or 5th magnitude). This comet was much brighter intrinsically in 2016 than during its discovery return in 2000, when it also came close to Earth (although it wasn’t discovered until over a month later); it makes another close approach in 2032 (see below).
Comet 73P/Schwassmann-Wachmann 3, which had passed close to Earth during its discovery return in 1930 (Number 19 on the “recorded history” list) had split up in the mid-1990s, with over 60 fragments being detected during the close approach in 2006; some of these were bright enough to be visually detectable, and passed even closer to Earth than the primary fragment (which the distance in the above table refers to). An infrared image of the comet, with several of these fragments, taken by the Spitzer Space Telescope is included in a previous “Special Topics” presentation.
Comet 289P/Blainpain was discovered as far back as 1819 and was an obvious comet then, but had been lost ever since. At its re-discovery in 2003 it initially appeared asteroidal and was never brighter than 15th magnitude, however in March 2004 a faint coma was detected with large telescopes. It experienced an apparent outburst in 2013 over a full year before its perihelion passage but was not seen again on that return. On its most recent return it was duly recovered last year, but despite its close approach to Earth this past January it remained a tiny and faint object, never brighter than about 17th magnitude.
Comet 107P/Wilson-Harrington was discovered in November 1949 during the course of the National Geographic-Palomar Observatory Sky Survey being conducted with the recently-built 1.2-meter Schmidt telescope; it exhibited an obvious tail (although no apparent coma) on both the red and blue discovery plates, but not on plates taken on subsequent nights. It was only followed for four nights and then subsequently lost. It was re-discovered by Eleanor Helin from Palomar in November 1979 but appeared completely asteroidal, and in fact was considered to be an “ordinary” Apollo-type asteroid and later assigned the number (4015); the identity with the lost Comet Wilson-Harrington was not established until 1992. It has never exhibited cometary activity outside of its discovery images, and its true physical nature remains unclear. It will pass close to Earth again in 2039 (see below).
There are some objects that I am excluding from the above lists. The LASCO coronagraphs aboard the SOlar and Heliospheric Observatory (SOHO) spacecraft have detected numerous comets – with some of these perhaps better being described as “apparent comets” – some of which have been found to be traveling on short-period orbits. One of these is P/1999 J6, which is a member of a group the existence of which was first pointed out by Brian Marsden, and which has an orbital period close to 5.5 years and which has been seen (in LASCO images) on two returns since then. Orbital calculations indicate it would have passed just 0.013 AU from Earth on June 12, 1999, one month after perihelion passage (when it appeared in the LASCO images); nothing had been recorded in any of the survey programs operating at the time, although it’s fair to point out that its existence wasn’t detected until a year later. Another of these “comets,” now designated as 323P/SOHO, would have passed 0.058 AU from Earth on January 13, 2000, again one month after it was discovered in LASCO images. Although these are called “comets,” their appearance is basically stellar in the LASCO images, and they have never been detected from the ground; their exact physical nature is unclear.
During the late 19th and early 20th Centuries there were several reports of various fast-moving diffuse objects that, in theory at least, could have been small comets passing very close to Earth. The validity of these reports is difficult to evaluate, and the fact that there haven’t been any such reports over the past several decades (when modern equipment and observing techniques are being utilized) is worrisome, but on the other hand some of the reports were made by experienced and capable observers of the time, and the intrinsic brightnesses of these supposed “comets” are reasonably consistent with the dimmer comets that are being discovered nowadays. Julius Franz, then-Director of the observatory at Breslau University (now the University of Wroclaw in Poland) reported seeing such an object in July 1911, and Estelle Glancy and Charles Perrine of the Cordoba Observatory in Argentina reported another such object in May 1916. (Perrine, then-Director of the Cordoba Observatory, had previously worked at Lick Observatory in California, where he discovered nine comets as well as Jupiter’s sixth and seventh moons.) It is perhaps conceivable that the Glancy-Perrine object was an example of the aurora-like phenomenon now called STEVE (Strong Thermal Emission Velocity Enhancement) that has only become recognized within recent years. In any event, in the absence of any confirming information I am excluding these objects from the above lists.
Also excluded from these lists are the objects usually described as “active asteroids” (which are the subject of a future “Special Topics” presentation). Although in some contexts these can perhaps be considered as “comets” – and, indeed, one of them is a previous “Comet of the Week” – the activity they have been seen to exhibit is, in general, due to mechanisms other than sublimation of volatile substances. (3200) Phaethon, which is generally considered as being the parent “comet” of the Geminid meteor shower, and which in fact has exhibited weak cometary activity around some of its perihelion passages, passed 0.121 AU from Earth on December 10, 2007 and 0.069 AU from Earth on December 16, 2017. NASA’s OSIRIS-REx mission, presently in orbit around the near-Earth “asteroid” (101955) Bennu, detected several bursts of jetting activity from that object in early 2019 when it was near perihelion; Bennu passed 0.015 AU from Earth on September 22, 1999 (a week and a half after its discovery) and 0.033 AU from Earth on September 20, 2005.
Finally, these lists do not include apparent “asteroids” that might be “extinct” or possibly “dormant” comets. (These objects are discussed in a future “Special Topics” presentation.) Several such objects have passed close to Earth from time to time; the closest such approach was by 2015 TB145, which passed only 0.00325 AU (486,000 km, or 1.27 lunar distances) from Earth on October 31, 2015. (This object was popularly called names like the “Skull Asteroid” since radar images showed two surface indentations remarkably similar to the appearance of eye sockets on a human skull, and since its approach to Earth took place on Halloween.) The Damocloid 1999 XS35 (orbital period 75 years) had passed 0.045 AU from Earth on November 5, 1999, four weeks before its discovery.
Comets will, of course, continue to approach Earth from time to time in the future; I have pointed out in a previous “Special Topics” presentation that Comet 1P/Halley will pass just 0.096 AU from Earth during its 2134 return, and meanwhile Comet 109P/Swift-Tuttle – the parent comet of the Perseid meteor shower, and a future “Comet of the Week” – will make moderately close approaches to Earth during both of its next two returns (in 2126 and 2261). In the near term, while for obvious reasons any forthcoming close approaches by as-yet-undiscovered comets cannot be predicted, we can certainly determine when already-known short-period comets will be coming close by. The following table lists those short-period comets that will be passing within 0.2 AU of Earth during the next two decades.
|Comet||Approach date||Distance (AU)|
|364P/PANSTARRS||2023 April 7||0.121|
|249P/LINEAR||2029 November 3||0.057|
|252P/LINEAR||2032 March 15||0.058|
|15P/Finlay||2034 August 13||0.185|
|289P/Blanpain||2035 November 6||0.082|
|300P/Catalina||2036 June 9||0.051|
|141P/Machholz 2||2036 December 19||0.125|
|Catalina P/2009 WX51||2037 April 18||0.052|
|107P/Wilson-Harrington||2039 October 31||0.108|
“Active asteroids” and potential “extinct” comets that will be making close approaches to Earth during this same interval include: (14827) Hypnos, 0.078 AU on June 2, 2024; (2101) Adonis, 0.036 AU on February 7, 2036; (101955) Bennu, 0.099 AU on February 11, 2037; 2015 HX176, 0.099 AU on April 1, 2038; (16960) 1998 QS52, 0.081 AU on June 10, 2039; and (2201) Oljato, 0.100 AU on December 16, 2040.
Earth certainly isn’t the only planet that comets pass close to; the other planets get their occasional cometary visitors as well. Jupiter has comets passing by all the time – often significantly affecting their orbits in the process – and, of course, we have already seen one comet strike Jupiter (Comet Shoemaker-Levy 9, in 1994; this is a future “Comet of the Week”). Just two examples of many comet/planet encounters that have taken place in recent years include an approach to Mars of 0.072 AU by Comet ISON C/2012 S1 – a future “Comet of the Week” – on October 1, 2013, and an approach to Mercury of only 0.025 AU by Comet 2P/Encke – another future “Comet of the Week” – on November 18 of that same year. The ultimate “near-miss” encounter took place in October 2014 and involved Mars and Comet Siding Spring C/2013 A1; this event will be described in that comet’s “Comet of the Week” presentation. | 0.819744 | 3.831055 |
The black hole in the above image resides at the centre of Messier 87 (M87), around 16.4 million parsecs (53 million light-years) from Earth, and part of the Virgo galactic cluster of about 12,000 galaxies. It marks the first time we have directly imaged a black hole – and it is a remarkable achievement for a number of reasons.
Thanks to Hollywood, we’re all very probably familiar with the idea of black holes: a point is space where matter is so compressed that it creates a gravity field from which not even light can escape. However, black holes come in a variety of forms, of which the most unusual might well be those that exist at the centre of many galaxies – including our own. Referred to as “supermassive black holes” on account of their extreme mass, they on a scale many times larger than your typical stellar black hole (which, despite being referred to as “massive” – a reference to their gravitational attraction.
We don’t actually understand how galactic black holes like the one at the heart of M87 – and called M87*) formed, but being able to examine them directly could answer some fundamental questions about the nature of the universe and physics, as well as helping us to understand the role they play in the evolution of galaxies. The problem is, actually directly imaging any black hole is actually very hard simply because they are – well, black, and thus not the easiest of things to see against the blackness of space.
Fortunately, there is a way around this problem: black holes are not alone. Their massive gravity means they attract dust and gas, which forms an accretion disk around the black hole, spinning around them at enormous speeds and producing radiation in a range of wavelengths including radio, optical and infra-red. Given given the right capabilities, we can image a black hole against the radiation from this accretion disk.
But even with an accretion disk to shed light around a galactic black hole has its own set of issues. To image the one at the centre of our own galaxy, for example, is the equivalent of trying to stand in New York’s Times Square and being able to count the dimples on a golf ball 4,000 km (2,450 mi) away; and this despite the fact that the black hole at the centre of our galaxy is thought to be at least 60 million kilometres across.
Nor is trying to image them optically particularly helpful. They need to be imaged across a range of wavelengths – the problem here being that to do so, you need a radio telescope effectively the size of the Earth.
To achieve this, and following an idea first put forward 26 years ago by German radio-astronomer Heino Falcke, the idea of the Event Horizon Telescope (EHT) was developed. This involves linking numerous radio telescopes together so they can jointly examine a single target and gather data on it.
To image M87*, eight of the world’s most powerful radio telescopes and telescope arrays were linked together. Over a period of about a week in 2017, they were used to gather 4 petabytes of data about the light from M87* in the millimetre wavelength. The drives containing this data were then physically shipped from the observatories to the Haystack Observatory and the Max Planck Institute for Radio Astronomy, where they were plugged into a grid computer made from about 800 CPUs linked through a 40 Gbit/s network, with the data processed by four independent teams using a series of tested algorithms to ascertain the reliability of the results. The final processing run was completed using the two most established algorithms to produce the image seen here.
This is in fact only the first galactic black hole image to b released. As well as studying M87*, the global EHT array has also gathered data on the black hole at the centre of our galaxy (and called Sagittarius A*), and at least two other supermassive black holes. However, imaging our own galactic black hole proved much harder, and delays in getting the physical hardware containing the data captured by the South Pole Telescope shipped from Antarctica to the Haystack Observatory has meant that processing the data is still in progress.
According to theoretical physics – such as Einstein’s theory of relativity – scientists already knew what the image should look like: the aforementioned glowing accretion disk and the shadow of the black hole at its centre (so beloved of sci-fi films that feature black holes). However, simply seeing an image that matches what we believe we should be theoretically seeing helps further confirm Einstein’s theories about the nature of the universe around us.
From the actual image on M87*, scientists have already been able to confirm Einstein’s general theory of relativity under extreme conditions – notably the prediction of a dark shadow-like region, caused by gravitational bending and capture of light. They have also confirmed the shadow is consistent with expectations for that of a spinning Kerr black hole, which Einstein again predicted. Further, by combining the asymmetric nature of the accretion disk with the angle of the relativistic plasma jet created by M87* (not actually visible in the black hole image), astronomers believe M87* is spinning in a clockwise direction.
Further, the image has refined estimates of M87*’s size – 40 billion km across the event horizon (that’s 270 AU or 0.0042 light years; roughly 2.5 times smaller than the shadow circle shown in the image) – and its mass, estimated at 6.5 billion solar masses (± 0.7 billion).
We have taken the first picture of a black hole. This is an extraordinary scientific feat accomplished by a team of more than 200 researchers.
– Sheperd S. Doeleman, EHT project director
The image itself is shown in false colour to indicate the intensity of the emissions from the accretion disk. Yellow represents the most intense emissions, dropping to red as the lower intensity emissions, and black for little or no emissions. Were we able to see M87* with the naked eye, the colours would lightly be white, perhaps slightly tainted with blue or red. And while it has yet to be 100% confirmed, the colour bias towards yellow on the southern arc of the ring, together with its asymmetry, is thought to be the result of the gases in that region moving more in our general direction.
While this image has already revealed much, there are numerous questions we have yet to fathom. We may now know the nature of M87*, but we still don’t know how it was formed, or why so many galaxies have black holes at their centres. Nor do we as yet understand why some (like M87*) produce the great plumes of relativistic gas while others, such as the black hole at the centre of our galaxy do not. So expect more to come as a result of studies arising from the work of EHT.
Launched on February 21st, Israel’s Beresheet lunar lander mission, was lost as it attempted to make its Moon landing on April 11th.
The vehicle, originally built by the SpaceIL team to compete in the (ultimately cancelled) Google Lunar X-Prize, was attempting to land in the Mare Serenitatis region of the Moon, having spiralled its way from Earth to lunar orbit during March, and then spending a week orbiting the Moon.
Initially, things went well with the landing: the main engine fired, slowing the vehicle sufficiently to start its decent, and Beresheet returned an image of its landing region from an altitude of 22 km.
However, at 14 km above the Moon’s surface, the lander began to suffer what SpaceIL later referred to as a “chain of events” that resulted in the vehicle’s loss. These started with a problem with an inertial measurement unit on the spacecraft (which was noted by mission control during the descent) and culminated in an initial failure of the vehicle’s main engine to restart in order to slow its final descent and cushion the landing. While the motor was successfully restarted, it was too late. The final telemetry received from Beresheet indicated that at a height of 150m above the Moon, it was descending at 500 km/h – much too fast for a controlled soft landing.
But this is not game over for SpaceIL. Following the cancellation of the Google Lunar XPrize, the company teamed with Israel’s government-owned aerospace company Israel Aerospace Industries to complete the project, and both have already confirmed they will be trying again.
We’re going to actually build a new halalit – a new spacecraft. We’re going to put it on the moon, and we’re going to complete the mission … The work on Beresheet 2.0 will begin immediately. The team is meeting this weekend to start planning the new project.
– Billionaire Morris Kahn, SpaceIL Chairman
That work is liable to involve a comprehensive post-mortem on the original mission, not just because of the final failure, but because Beresheet suffered multiple issues during its six-week voyage from Earth to the Moon – all of which it recovered from, but which may have been the results of compromises inherent in the design as a result of it taking a piggyback ride into orbit aboard another mission. In the meantime, the X-Prize organisation offered a small sweetener to SpaceIL: a US $1 million bonus award.
I think they managed to touch the surface of the moon, and that’s what we were looking for [with] our Moonshot Award.
– X-Prize CEO Anousheh Ansari
Beresheet’s loss sits as a reminder that landing on the Moon isn’t necessarily easy – something NASA planners will likely be keeping in mind given the pressure they are under to return humans to the surface of the Moon by 2024, and yet to have a confirmed method (and vehicle) capable of doing so.
Falcon Heavy Thunders
On Thursday, April 11th, 2019, SpaceX completed the second launch of its mighty Falcon Heavy rocket. It was something of a milestone in the vehicle’s evolution, being its first commercial launch, and the first with the rocket in its “Block 5” configuration, using the cores stages from the most powerful variant of the Falcon 9 booster.
The launch was a resounding success on all fronts: following a picture-perfect lift-off, the vehicle climbed to “first stage” separation – the point at which the two Falcon 9 side boosters separated, leaving the central core stage pushing the upper stage and its 6.4-tonne Arabsat 6A communications satellite towards orbit. The two side boosters they performed their “burn back” manoeuvres, flying back to Florida to make near synchronous landings at Cape Canaveral Air Force Station 8 minutes after launch.
Following its separation two minutes after the side boosters, the core stage also made a burn back manoeuvre but, having travelled a much greater distance, descended to make a successful landing on the autonomous drone ship Of Course I Still Love You, almost 1,000 km off the Florida coast. This marked another first for SpaceX: the recovery of all three core stages from a single launch (the core stage used for the vehicle’s test flight in February 2018 failed to make a successful at-sea landing).
Nor did it end there. Following their jettisoning from the upper stage and satellite, the rocket’s payload fairings fell back to a watery landing at sea, and were safely recovered.
With successful delivery of Arabsat 6A to orbit, SpaceX indicated that the two Falcon boosters will be re-used on the next Falcon Heavy mission, the launch of the US Air Force / NASA STP-2 flight in June, while the payload fairings will be used on a Falcon 9 launch of more of the company’s Starlink global broadband satellites.
The “Roc” Flies
On Saturday, April 13th, Stratolaunch, the private launch company founded by the late billionaire Paul Allen, successfully completed the first flight of the world’s largest aircraft by wingspan.
Dubbed the “Roc”, the Scaled Composites Model 351 is a six-engined, “twin-hulled” behemoth, designed to be an aerial launch platform for up to three Pegasus XL rockets per flight. Originally rolled-out in March 2017, the aircraft has more recently completed several months of taxi tests, which included “rotation authority manoeuvres”, design to simulate everything up to the point of take-off.
The first flight for the aircraft, which uses two heavily modified 747 fuselages, commenced as it rolled down the runway at Mojave Air and Space Port in California at 06:58 local time and completed a full rotation. Lifting clear of the runway, the “Roc” entered a 2.5 hour test flight and reached an altitude of 4,570 m (15,000 ft), before returning to base and making a perfect landing.
I honestly could not have hoped for more on a first flight, especially of an aeroplane of this complexity and this uniqueness. Really, for a first flight, it was spot on.
– Evan Thomas, Scaled Composites test pilot, after the flight
Despite the success of the flight, Stratolaunch has refused to comment on when “Roc” might next take to the air. There are also questions on the viability of the system. While Stratolaunch have settled on the idea of carrying three Pegasus XL launch craft per flight, the Pegasus programme has itself struggled to win customers in recent years. As such, doubts exist about the cmpany’s ability to attract either commercial or military customers. | 0.939328 | 4.091501 |
Researchers supported in part by the NASA Astrobiology program are providing new insight into the late stages of solar system formation. The team developed empirical relationships to understand the processes behind accretion and erosion when large planetary bodies of varying compositions collide – including bodies that are rich in water. The study also focuses on the fine line between collisions where two bodies merge together, and those that result in a ‘hit-and-run’ scenario. The results indicate that hit-and-run collisions occur across a wider range of impact angles than previously thought. The team provides an algorithm for incorporating their model into N-body planet formation simulations.
The study, “Gravity-dominated Collisions: A Model for the Largest Remnant Masses with Treatment for “Hit and Run” and Density Stratification,” was published in The Astrophysical Journal. The work was supported by the Nexus for Exoplanet System Science (NExSS). NExSS is a NASA research coordination network supported in part by the NASA Astrobiology Program. This program element is shared between NASA’s Planetary Science Division (PSD) and the Astrophysics Division. This research is a critical part of NASA’s work to understand the Universe, advance human exploration, and inspire the next generation. As NASA’s Artemis program moves forward with human exploration of the Moon, the search for life on other worlds remains a top priority for the agency.
Reference: “Gravity-dominated Collisions: A Model for the Largest Remnant Masses with Treatment for “Hit and Run” and Density Stratification” by Travis S. J. Gabriel, Alan P. Jackson, Erik Asphaug, Andreas Reufer, Martin Jutzi and Willy Benz, 24 March 2020, The Astrophysical Journal. | 0.878042 | 3.063591 |
Disks of space dust (debris disks) surround many stars. The dust can be detected because it absorbs ordinary starlight and re-emits it as infrared radiation. Even if the dust particles have a total mass well less than that of Earth, they can still have a large enough total surface area that they outshine their parent star in infrared wavelengths.
The Hubble Space Telescope is capable of observing dust disks with its NICMOS (Near Infrared Camera and Multi-Object Spectrometer) instrument. Even better images have now been taken by its sister instrument, the Spitzer Space Telescope, and by the European Space Agency's Herschel Space Observatory, which can see far deeper into infrared wavelengths than the Hubble can. Dust disks have now been found around more than 15% of nearby sunlike stars.
The dust is believed to be generated by collisions among comets and asteroids. Radiation pressure from the star will push the dust particles away into interstellar space over a relatively short timescale. Therefore, the detection of dust indicates continual replenishment by new collisions, and provides strong indirect evidence of the presence of small bodies like comets and asteroids that orbit the parent star. For example, the dust disk around the star tau Ceti indicates that that star has a population of objects analogous to our own Solar System's Kuiper Belt, but at least ten times thicker.
More speculatively, features in dust disks sometimes suggest the presence of full-sized planets. Some disks have a central cavity, meaning that they are really ring-shaped. The central cavity may be caused by a planet "clearing out" the dust inside its orbit. Other disks contain clumps that may be caused by the gravitational influence of a planet. Both these kinds of features are present in the dust disk around epsilon Eridani, hinting at the presence of a planet with an orbital radius of around 40 AU (in addition to the inner planet detected through the radial-velocity method). These kinds of planet-disk interactions can be modeled numerically using collisional grooming techniques.
Read more about this topic: Transiting Extrasolar Planets, Detection of Extrasolar Asteroids and Debris Disks | 0.895584 | 4.006448 |
Lafcadio Adams has over 10 years of experience teaching fellow Earthlings, ages 4 to 400 about the stars using this step-by-step method. Over 40 original diagrams and photographs are included to help you begin to unravel the secrets of the universe.
Designed as a comprehensive introduction for the beginner and those who want to find out more, How to Identify the Night Sky covers everything that can be seen with the naked eye and binoculars, as well as what is visible using a small telescope.
There are sections on how to observe and understand the objects that comprise the night sky, the moon, the movements of the stars and planets throughout the year and astronomical events.
The constellations are given a comprehensive treatment. For each one there is a chart, a photograph, a description of its features and history, the best dates and times of visibility, the mythological representation and a list of interesting objects.
Sir Patrick introduces the wonders of the night sky to absolute beginners in his characteristically entertaining and informative style. The Moon, the planets, the Sun and the stars are explained in non-technical language, while the constellations are described with the help of star maps and tables.
The four main chapters in Philip's Guide to the Night Sky are devoted to what's on view in each season of the year. The information is appropriate for observers in Britain and Ireland, northern Europe and Canada; it will also be helpful a little outside these latitudes. Using prominent patterns, such as the Plough and Orion, Sir Patrick teaches the reader to 'star-hop' from constellation to constellation, thus learning to navigate the night sky. Star maps and photographs illustrate and clarify what will be on view.
Philip's Guide to the Night Sky is an ideal introduction to stargazing, suitable for all ages and with no need for anything more technical than the naked eye.
Most books on stargazing claim to be for beginners, but by page 12 are talking about celestial equators and sidereal months. No wonder so many people have planispheres but no idea how to use them.
Working at the planetarium in Greenwich, Anton has met hundreds of enthusiastic but utterly bemused beginners of all ages, and has made sense of the night sky for them. In this book he introduces the night sky just as if he were by your side, pointing everything out. And contrary to popular belief, you don't need any expensive equipment to start skygazing. Anton takes you through all the things you can discover with just the naked eye.
The book is suitable for use in the northern and southern hemispheres – two sections give equal coverage to where to start and what you can see wherever you are in the world, whenever.
From planets and stars to black holes and the Big Bang, take a journey through the wonders of the universe. Featuring topics from the Copernican Revolution to the mind-boggling theories of recent science, The Astronomy Book uses flowcharts, graphics, and illustrations to help clarify hard-to-grasp concepts and explain almost 100 big astronomical ideas. Covering the biographies of key astronomers through the ages such as Ptolemy, Galileo, Newton, Hubble, and Hawking, The Astronomy Book details their theories and discoveries in a user-friendly format to make the information accessible and easy to follow.
In Wonders of the Solar System – the book of the acclaimed BBC TV series – Professor Brian Cox will take us on a journey of discovery where alien worlds from your imagination become places we can see, feel and visit.
The Wonders of the Solar System – from the giant ice fountains of Enceladus to the liquid methane seas of Titan and from storms twice the size of the Earth to the tortured moon of Io with its giant super-volcanoes – is the Solar System as you have never seen it before.
In this series, Professor Brian Cox will introduce us to the planets and moons beyond our world, finding the biggest, most bizarre, most powerful natural phenomena. Using the latest scientific imagery along with cutting edge CGI and some of the most spectacular and extreme locations on Earth, Brian will show us Wonders never thought possible.
Employing his trademark clear, authoritative, yet down-to-earth approach, Brian will explore how these previously unseen phenomena have dramatically expanded our horizons with new discoveries about the planets, their moons and how
they came to be the way they are.
With his proven techniques and using examples from his own highly successful experiences, Dyer will convince you that you can make your most impossible dreams come true. You’ll See It When You Believe It demonstrates that through belief you can make your life anything you with it to be. Learn practical steps such as how to set real goals and achieve them; turn obstacles into opportunities; rid yourself of guilt and inner turmoil; develop a strong inner-confidence; dramatically improve relationships; spend every day doing the things you love to do, and so much more.
Go beyond self-help to self-realization with this accessible and uplifting manual. | 0.903015 | 3.458498 |
Astronomers believe that planets such as Jupiter shield us from spacecraft that would otherwise slam into the ground. Now, they are closer to learning about giant planets acting as guardians of solar systems elsewhere in the galaxy.
A UCR-led team has discovered two Jupiter-sized planets about 1
"We believe that planets such as Jupiter have greatly influenced the progress of life on Earth. Without them, humans may not be here to get this conversation," says Stephen Kane, senior study author and UCR lecturer in planetary astrophysics. "Understanding how many other stars have planets such as Jupiter could be very important to learn about the planets life in these systems."
Along with floating waters, Kane said astronomers believe that such planets have the ability to act as "slingshots" & # 39; drag objects such as meteors, comets, and asteroids out of their paths toward battle with small rocky planets.
Many larger planets have been found close to their stars. But they are not so helpful in learning about the architecture of our own solar system, where the giant planets, including Saturn, Uranus and Neptune, are far away from the sun. Large planets far from their stars have so far been more difficult to find.
A recent study accepted for publication in Astronomical Journal describes how Kane's team succeeded in a new approach that combines traditional detection methods with the latest technologies.
A popular method for searching for exoplanet planets in other solar systems – involves monitoring stars for "wobble", where a star moves toward and away from the ground. Wobble is probably caused by gravity pulling a nearby planet exercising on it. When a star is angled, it is a sign that there may be an exoplanet nearby.
When the planet is far from its star, gravity traits are weaker, making wobble smaller and harder to detect. The other problem with using the wobble detection method, Kane said, is that it just takes a long time. The earth only takes a year to pave the sun. Jupiter takes 12, Saturn takes 30, and Neptune takes an amazing 164 years.
The larger exoplanets also take many years to encircle their stars, which means observing a complete trajectory could engulf an astronomer's entire career. To speed up the process, Kane and his team combined the wobble method with direct imaging. In this way, if the team believed that a planet could cause wobble, they could confirm it by sight.
Obtaining a direct image of a planetary quadrangle of miles away is not a simple task. It requires the largest possible telescope, one that is at least 32 meters long and very sensitive. Even from this distance, the light of the star can overexpress the image and obscure the target planets.
The team overcomes this challenge by learning to recognize and eliminate the patterns in their images created by starlight. Removing the starlight gave Kane's team the opportunity to see what was left.
"Direct imaging has come a long way, both in terms of understanding the patterns we find and in terms of the instruments used to create the images, which is much higher resolution than they have ever been," Kane said. . "You see this every time a new smartphone is released. The camera detectors are always improved and so is in astronomy."
In this project, the team used the combination of wobble and imaging method for 20 stars. In addition to the two being bound by giant jupiter-like planets that had not been discovered earlier, the team also discovered a third previously observed star with a giant planet in its system.
In the future, the team continues to monitor 10 of the stars where planetary escorts could not be ruled out. In addition, Kane is planning a new project to measure how long it takes these exoplanets to complete rotations toward and away from their stars that are not currently being measured.
Kane's team is international with members of the Australian Astronomical Observatory, the University of Southern Queensland, the University of New South Wales and Macquarie University in Australia, as well as at the University of Hertfordshire in the United Kingdom. They are also spread across the United States at the National Observatory Astronomy Observatory in Tucson, AZ, Southern Connecticut State University, NASA Ames Research Center and Stanford University in California and the Carnegie Institution of Washington in DC
"This discovery is an important piece of the puzzle, because it helps us understand the factors that make a planet habitable and whether it is common or not, "Kane said. "We quickly gather answers to this question that the last 3,000 registered years of history could only wish they had made them available."
Five planets revealed after 20 years of observation
Detection of planetary and star comrades for neighboring stars via a combination of radial velocity and direct image technology, arXiv: 1904.12931 [astro-ph.EP] arxiv.org/abs/1904.12931
Meteor magnets in outer space study find extinct giant planets (2019, May 24)
May 25, 2019
This document is subject to copyright. Besides any fair trade for private study or research, no
part can be reproduced without written permission. The content is for informational purposes only. | 0.910796 | 3.67414 |
Electron particles are flying away from Saturn’s polar region. Image credit: University of Cologne. Click to enlarge
Auroras on Earth happen when the solar wind interacts with our planet’s magnetic field; electrons are accelerated downwards into the atmosphere, and we see the pretty lights in the sky. On Saturn; however, this process also goes in reverse. Most electrons are accelerated down, but others go in the opposite direction, away from the planet.
Polar lights are fascinating to look at on Earth. On other planets, they can also be spectacular. Scientists from the Max Planck Institute for Solar System Research in Katlenberg, Lindau, Germany, have now observed Saturn’s polar region using the particle spectrometer MIMI, on the Cassini Space Probe. They discovered electrons not only being accelerated toward the planet, but also away from it (Nature, February 9, 2006).
We can see polar lights on Earth when electrons above the atmosphere are accelerated downwards. They light up when they hit the upper atmosphere. Some years ago, researchers discovered that electrons inside the polar region can also be accelerated away from the Earth – that is, “backwards”. These anti-planetary electrons do not cause the sky to light up, and scientists have been puzzled about how they originate.
Until now it has also been unclear whether anti-planetary electrons only occur on Earth. An international team led by Joachim Saur at the University of Cologne have now found electrons on Saturn that are accelerated “backwards” – that is, in an anti-planetary direction. These particles were measured using “Magnetospheric Imaging Instruments” (MIMI) on NASA’s Cassini Space Probe. One of these instruments’ sensors, the “Low Energy Magnetospheric Measurement System” (LEMMS), was developed and built by scientists at the Max Planck Institute for Solar System Research.
The rotation of the space probe helped the researchers to determine the direction, number, and strength of the electron rays. They compared these results with recordings of the polar region and a global model of Saturn’s magnetic field. It turned out that the region of polar light matched up very well with the lowest point of the magnetic field lines in which electron rays were measured.
Because the electron ray is strongly focussed (with an angle of beam spread less than 10 degrees), the scientists were able to determine where its source lies: somewhere above the polar region, but inside a distance of maximum five radii of Saturn. Because the electron rays measured on the Earth, Jupiter, and Saturn are so similar, it appears that there must be some fundamental process underlying the creation of polar lights.
Doing these measurements, Norbert Krupp and his colleagues Andreas Lagg and Elias Roussos from the Max Planck Institute for Solar System Research worked closely with scientists from the Institute for Geophysics and Meteorology at the University of Cologne and the Applied Physics Laboratory of Johns Hopkins University in Baltimore. US scientists led by Tom Krimigis are responsible for service and coordination of the instrument on the Cassini Space Probe.
Original Source: Max Planck Society | 0.869579 | 3.992275 |
The finding suggests large structures in the cosmic web are magnetized
By MARIA TEMMING, JUNE 6, 2019
MAGNETIC CONNECTION Two distant galaxy clusters, Abell 0399 (left) and Abell 0401 (right), are connected by magnetic fields containing high-energy electrons. X-rays from the cluster cores are shown in purple, and radio emission from the magnetic bridge forms the blue-toned smear in between.
For the first time, astronomers have sighted magnetic fields between two galaxy clusters — a find that suggests some of the largest scale structures in the universe are magnetized.
The fields run between the galaxy clusters Abell 0399 and Abell 0401, which are beginning to merge about 1 billion light-years from Earth, researchers report in the June 7 Science. Radiation from electrons zipping through the magnetic fields revealed this magnetism inside the gaseous filament that connects the clusters in the cosmic web (SN: 3/8/14, p. 8). The source of those high-speed particles, however, remains a mystery.
“So far, magnetic fields have been measured in [specific] objects, like in clusters, or in galaxies,” says Nabila Aghanim, a cosmologist at the Institute for Space Astrophysics in Orsay, France, not involved in the work. In the cosmic web, filaments stretch between galaxy clusters to form a sort of celestial mesh full of cavernous voids. If magnetic fields also pervade the gaseous throughways between galactic hubs, they may have influenced the properties and evolution of gas throughout the cosmos, she says.
Researchers examined the 10-million light-year gap between Abell 0399 and Abel 0401 using the Low-Frequency Array radio telescope network, or LOFAR, based mainly in the Netherlands. Observations of the space between these galaxy clusters uncovered a faint band of radiation called synchrotron emission — a kind of illumination produced by high-speed electrons spiraling around magnetic field lines.
Computer simulations indicate that weak shock waves from the early stages of this galaxy cluster merger can’t accelerate normal electrons in the gaseous filament enough to generate the synchrotron emission observed. Instead, the filament must already have contained high-energy electrons that are being reaccelerated by merger shock waves.
“We still don’t know where this preexisting population [of electrons] comes from,” says study coauthor Federica Govoni, a radio astronomer at the Cagliari Observatory in Selargius, Italy. “They may have been ejected in the past by [nearby] galaxies or by explosions of supernovae.”
Another lingering question is whether other filaments in the cosmic web are also threaded with magnetic fields. “This is a filament that’s kind of modest, in terms of its size,” Aghanim says. She’s curious whether magnetic fields could go the distance between cosmic filaments tens of millions of light-years long.
F. Govoni. A radio ridge connecting two galaxy clusters in a filament of the cosmic web. Science. Vol. 364, June 7, 2019, p. 981. doi: 10.1126/science.aat7500. | 0.887509 | 3.987124 |
Geoffrey Burbidge (born Chipping Norton, 24 September 1925; died La Jolla, California, 26 January 2010) was an English astrophysicist. For many years he was professor at the University of California, San Diego. In 1957 he published a famous paper, together with three other physicists, about the origin of elements. Many scientists disagreed with ideas that he had later in his life, because he did not believe in the Big Bang theory.
Education and early career[change | change source]
He started to study history at the University of Bristol, but soon changed to physics because he could then get financial help from the government (World War II was on, so science was very important to the government). He went to London and got a doctorate from University College London in 1951. He met the astronomer Margaret Peachey. He became very interested in astronomy and he married her in 1948. From then on they always worked together in several places. They worked at Harvard, the University of Chicago and Cambridge University. Then Margaret got work at the California Institute of Technology, while Geoffrey worked at the Mount Wilson Observatory and Palomar Observatory. They both got jobs at the University of California, San Diego, in 1962.
The B2FH paper[change | change source]
In 1957 he and his wife, together with William Fowler, the American physicist, and Fred Hoyle, the British astronomer, wrote a 104-page paper about stellar nucleosynthesis. The paper became known as the B2FH (because of their initials). It talked about nuclear reactions inside stars, showing how these reactions tear apart blocks of matter and put it together again differently. It was a similar idea to what Charles Darwin had written about 100 years earlier in the “Origin of Species”, where he had described how creatures had evolved. Scientists saw this paper as the most important paper ever written about astrophysics.
Later career[change | change source]
Later in his career Burbidge refused to accept the Big Bang theory which describes the start of the universe. Quasars are very bright objects with a very high redshift. The Big Bang theorists say that they come from places extremely far away in the universe. But Burbidge thought that quasars come from nearby galaxies, travelling near the speed of light, which explains their redshift. He thought they produced new matter as old matter was destroyed by reactions.
Although many scientists disagree with Burbidge’s later ideas, he is still thought of as an extremely important scientist. He was given many honours. In 2005 he and his wife were awarded the British Royal Astronomical Society Gold Medal.
References[change | change source]
- ”Geoffrey Burbidge- Obituary” in The Independent 24 April 2010 p. 51 | 0.863947 | 3.220243 |
When spacecraft pass the Earth, they get a buzz from it and this sudden boost makes them speed up. But what’s causing it? The answer is that nobody seems to know. Even researchers at NASA’s Jet Propulsion Laboratory have thrown up their hands, hoping that the world’s physicists would come up with an answer. That solution doesn’t seem to have arrived yet, although we’ve come to expect what we refer to as the flyby anomaly.
It first happened when the Jupiter-bound Galileo spacecraft broke into a sprint when it swung by our planet in 1990 and 1992, followed by NEAR in early 1998 and then Cassini in 1999. The Rosetta spacecraft, which reached its destination at comet 67P/Churyumov–Gerasimenko, also experienced the same boost back in 2005. All crafts were using the Earth’s gravitational assistance to catapult themselves into the Solar System.
The most obvious boost in speed, which changed a good 13 millimetres per second more, was recorded for the Near Earth Asteroid Rendezvous – Shoemaker (NEAR Shoemaker) spacecraft. Scientists figured that the anomaly was much too big to be explained by Einstein’s general theory of relativity. However, arming themselves with a variety of suggestions, some experts think that they might have the answer. Perhaps, they investigate, that the anomaly could be due to the Earth’s spin on its axis, or there could be some type of dark matter halo around our planet. The possibilities are coming, but we need to choose the one that fully fits.
Image Credit: ESA | 0.874586 | 3.203902 |
The Leonid meteor shower (so named because the meteor trails trace back to a radiant point in the constellation Leo the Lion) will likely peak locally after 12:00 am the night of November 16th-17th. The constellation Leo will be located directly south of the Big Dipper’s bowl and, as an added bonus, Jupiter should be glowing brightly nearby. The Moon will be a small crescent so the sky should be fairly dark. The Leonid meteors streak at a very high speed so they often generate fireballs.
The Rosetta spacecraft has been traveling to Comet 67P/Churyunov-Gerasimenko for ten years and the European Space Agency will broadcast a live landing on the comet Wednesday evening, November 12th, at 9:00 pm on the Science Channel. Both the Rosetta spacecraft and its robotic lander, Philae, will accompany the comet as it orbits around the Sun reaching perihelion (minimum) in August 2015. Comet 67P is a member of the Jupiter family of comets and its orbit carries it from approximately 5.8 au (an astronomical unit is is a unit of length, roughly the distance from the Earth to the Sun) to 1.7 au.
The planet Jupiter (and its four bright moons) rises around midnight on November 1st and two hours earlier by the end of the month and shines brightly in the constellation Leo the Lion. The best viewing time, of course, is a couple of hours after it rises higher in the sky. Venus and Saturn are too close to the Sun to see in November. Mars remains the brightest object in the southwestern sky as it hovers near the Sagittarius Teapot asterism and sets more than three hours after the Sun early in the month.
Two excellent binocular objects almost directly overhead in November are the Andromeda Galaxy (M31) and the Pinwheel Galaxy (M33), both members of the Local Group that includes our Milky Way Galaxy. Start at the Square of Pegasus (directly overhead) and proceed to its northeastern corner where two arms of stars project out to the northeast from this corner. The Andromeda Galaxy will appear as a hazy oval blur just north of the second star on the most northern arm of stars. The Pinwheel Galaxy will appear southeast of the second star in the most eastern arm of stars. The Andromeda Galaxy is roughly twice the size of our Milky Way Galaxy and the Pinwheel Galaxy is roughly one-half the size of the Milky Way. | 0.853326 | 3.249522 |
Authors: Alexander L. DeSouza and Shantanu Basu
First Author’s Institution: Department of Physics and Astronomy, University of Western Ontario
Status: Accepted by MNRAS
A major goal for the next generation of telescopes, such as the James Webb Space Telescope (JWST) is to study the first stars and galaxies in the universe. But what would they look like? Would JWST be able to see them? Recent studies have suggested that even the most massive specimens of the very first generation of stars, known as Population III stars, may be undetectable with JWST.
But not all hope is lost–one of the reasons why Population III stars are so hard to detect is that, unlike later generations of stars, they are believed to form in isolation. Later generations of stars (called Population I and Population II stars) usually form in clusters, from the fragmentation of large clouds of molecular gas. On the other hand, cosmological simulations have suggested that Population III stars would form from gas collected in dark matter mini-halos of about a million solar masses in size which would have virialized (reached dynamic equilibrium) by redshifts of about 20-50. Molecular hydrogen acts as a coolant in this scenario, allowing the gas to cool enough to condense down into a star. Early simulations showed that gravitational fragmentation would eventually produce one massive fragment–on the order of about a hundred solar masses–per halo. This molecular hydrogen, however, could easily be destroyed by the UV radiation from the first massive star formed, preventing others from forming from the same parent cloud of gas. While Population III stars in this paradigm are thought to be much more massive than later generations of stars, they would also be isolated from other ancient stars.
However, there is a lot of uncertainty about the masses of these first stars, and recent papers have investigated the possibility that the picture could be more complicated than first thought. The molecular gas in the dark matter mini-halos could experience more fragmentation before it reaches stellar density, which may lead to multiple smaller stars, rather than one large one, forming from the same cloud of gas. These stars could then evolve relatively independently of each other. The authors of today’s paper investigate the idea that Population III stars could have formed in clusters and also study the luminosity of the resulting groups of stars.
The authors of today’s paper begin by arguing that the pristine, mostly atomic gas that collects in these early dark matter mini-halos could fragment by the Jeans criterion in a manner similar to the giant molecular clouds that we see today. This fragmentation would produce small clusters of stars that are relatively isolated from each other, so they are able to model each of the members in the cluster independently. They do this by using numerical hydrodynamical simulations in the thin-disk limit.
Their fiducial model is a gas of 300 solar masses, about 0.5 pc in radius, and at a temperature of 300 K. They find that the disk that forms around the protostars (the large fragments of gas that have contracted out of the original cloud of gas) forms relatively quickly, within about 3 kyr of the formation of the protostar. The disk begins to fragment a few hundred years after it forms. These clumps can then accrete onto the protostar in bursts of accretion or get raised to higher orbits.
Most of the time, however, the protostar is in a quiescent phase and is accreting mass relatively smoothly. The luminosity of the overall star cluster increases during the bursts of accretion, and it also increases as new protostars are formed. The increasing luminosity of the stellar cluster can make it more difficult to detect single accretion events. For clusters of a moderate size of about 16 members, these competing effects result in the star cluster spending about 15% of its time at an elevated luminosity, sometimes even a 1000 times the quiescent luminosity. The star clusters can then have luminosities approaching and occasionally exceeding 108 solar luminosities. Population III stars with masses ranging from 100-500 solar masses on the other hand, are likely to have luminosities of about 106 to 107.
These clusters would be some of the most luminous objects at these redshifts and would make a good target for telescopes such as ALMA and JWST. We have few constraints on the star formation rates at such high redshifts, and a lot of uncertainty in what the earliest stars would look like. So should these exist, even if we couldn’t see massive individual population III stars, we may still be able to detect these clusters of smaller stars and gain insight into what star formation looked like at the beginning of our universe. | 0.866007 | 4.109365 |
Do any of the posted answers take account of the planet's inertia?
I'm certainly NOT about to be the first poster to say that the Earth does accelerate towards us. Because plenty of the previous posters have said exactly that, while mentioning that in practice the effect would be too small to notice or to measure.
I am going to complain about the answer that the Moon can accelerate toward the Earth, because it is fairly widely known that the Moon is in orbit, and as frame-dragging effects caused by the Earth's gravitational field accelerate any orbiting object, that effect causes the Moon to move away from the Earth at a continuously accelerating rate, which I have a memory from childhood of being a rate of approx one inch per century (or metric equivalent).
If it were in a retrograde orbit, it would at least be capable of decreasing its distance from the Earth over time, since then the frame-dragging effect would be decelerating it, instead of accelerating it.
My actual answer is more down-to-earth -- :)
Since the Earth has a large mass, and since one fairly well established property of mass is inertia, I'm willing to go half-way, and say that the Earth doesn't accelerate toward us: because it doesn't move at all. If I perform the jumping experiment (with a mass of 180 lbs x 1), or even if I get all the men in China to (180 lbs x 1 billion), the Earth is held in place in spacetime by the inertia associated with its mass.
It's approximately equivalent to throwing a tennis ball at an approaching freight train and expecting to derail it, or to halt or delay the train, even temporarily: mathematically, a calculation might be done that demonstrates there is a calculable effect (as some on here have done); but such calculations tend to ignore the inertial component (quite large, for a body of planetary mass).
If I had some significant fraction of the mass of the Moon, and then jumped, I might reasonably expect that a measurable effect would result. But the Earth is massive enough for its position to remain unaffected below a limit determined by Kepler's laws of planetary motion.
Again, I have a memory about Newtonian conservation of momentum, but which I suspect won't apply within a closed system: me plus the Earth.
But in relation to does the Earth accelerate towards the Moon, well the answer is it does! Well, it does in part, at least. It's called the tide, and at any point on the Earth's equator that has open sea, you'll experience high tide once a day when the Moon is more or less overhead.
This is due to planetary inertia! If the Earth had no inertial component to its mass, when the tidewater moved 4 ft closer to the Moon at local noon, so would the Earth: in that case you would not notice a change in the tidal level, because both ocean and seashore would have moved by an equivalent amount.
The fact that you do notice the tide rising and falling each day is a proof of the existence of inertia (the Earth has it, so the seashore has it), but the sea has very much less of it. | 0.892866 | 3.632804 |
Future Observations of Cosmic Magnetic Fields with the SKA and its Precursors
The origin of magnetic fields in the Universe is an open problem in astrophysics and fundamental physics. Polarization observations with the forthcoming large radio telescopes, especially the Square Kilometre Array (SKA), will open a new era in the observation of magnetic fields and should help to understand their origin. Low-frequency radio synchrotron emission, to be observed with LOFAR, MWA and the SKA, traces low-energy cosmic ray electrons and allows us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in halos and relics of galaxy clusters and in the Milky Way. Polarization at higher frequencies (1–10 GHz), to be observed with the SKA and its precursors ASKAP and MeerKAT, will trace magnetic fields in the disks and central regions of galaxies and in cluster relics in unprecedented detail. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources with ASKAP (project POSSUM) and the SKA are dedicated to measure magnetic fields in intervening galaxies, clusters and intergalactic filaments, and will be used to model the overall structure and strength of magnetic fields in the Milky Way. “Cosmic Magnetism” is key science for LOFAR, ASKAP and the SKA.
The Square Kilometre Array (SKA) is the most ambitious radio telescope ever planned. With a collecting area of about one square kilometer, the SKA will be about ten times more sensitive than the largest single dish telescope (305 m diameter) at Arecibo (Puerto Rico), and fifty times more sensitive than the currently most powerful interferometer, the Expanded Very Large Array (EVLA, at Socorro/USA). The SKA will continuously cover most of the frequency range accessible from ground, from 70 MHz to 10 GHz in the first and second phases, later to be extended to at least 25 GHz. The third major improvement is the enormously wide field of view, ranging from 200 square degrees at 70 MHz to at least 1 square degree at 1.4 GHz. The speed to survey a large part of the sky, particularly at the lower frequencies, will hence be ten thousand to a million times faster than what is possible today. The SKA is dedicated to constrain fundamental physics on the dark energy, gravitation and magnetism.
2 Technical design of the SKA
The SKA will be a radio interferometer and consist of many antennas which are spread over a large area to obtain high the resolving power. The three separate SLA core regions of 5 km diameter each will contain about 50% of the total collecting area and comprise dish antennas and the two types of aperture arrays (Fig. 4). The mid-region out to about 180 km radius from the core comprises dishes (Fig. 2) and sparse aperture array antennas (Fig. 2) aggregated into stations distributed on a spiral arm pattern. Remote stations with about 20 dish antennas each will spread out to distances of at least 3000 km from the core and located on continuations of the spiral arm pattern. The overall extent of the array determines the angular resolution, which will be about 0.1\arcsec at 100 MHz and 0.001\arcsec at 10 GHz.
To meet the ambitious specifications and keep the cost to a level the international community can support, planning and construction of the SKA requires many technological innovations such as light and low-cost antennas, detector arrays with a wide field of view, low-noise amplifiers, high-capacity data transfer, high-speed parallel-processing computers and high-capacity data storage units. The enormous data rates of the SKA will demand online image production with automatic software pipelines.
The frequency range spanning more than two decades cannot be realized with one single antenna design, so this will be achieved with a combination of different types of antennas. Under investigation are the following designs for the low and mid-frequency ranges:
1. An aperture array of simple dipole antennas with wide spacings (a “sparse aperture array”) for the low-frequency range (about 70–450 MHz) (Fig. 2). This is a software telescope with no moving parts, steered solely by electronic phase delays. It has a large field of view and can observe towards several directions simultaneously.
2. An array of several thousand parabolic dishes of about 15 meters diameter each for the medium-frequency range (about 450 MHz–3 GHz), each equipped with a wide-bandwidth single-pixel “feed” (Fig. 2). The surface accuracy of these dishes will allow a later receiver upgrade to higher frequencies.
As an “Advanced Instrumentation Programme” for the full SKA, two additional technologies for substantially enhancing the field of view in the 500–1000 MHz range are under development: aperture arrays with dense spacings, forming an almost circular station 60 m across (Fig. 4) and phased-array feeds for the parabolic dishes (see below).
3 Technical developments
Technical developments around the world are being coordinated by the SKA Science and Engineering Committee and its executive arm, the SKA Project Office. The technical work itself is funded from national and regional sources, and is being carried out via a series of verification programs. The global coordination is supported by funds from the European Commission under a program called PrepSKA, the Preparatory Phase for SKA, whose primary goals are to provide a costed system design and an implementation plan for the telescope by 2012.
A number of telescopes provide examples of low frequency arrays, such as the European LOFAR (Low Frequency Array) telescope, with its core in the Netherlands, the MWA (Murchison Widefield Array) in Australia, PAPER (Precision Array to Probe the Epoch of Reionization), also in Australia, and the LWA (Long Wavelength Array) in the USA. All these long wavelength telescopes are software telescopes steered by electronic phase delays (phased aperture array). Examples of dishes with a single-pixel feed are under development in South Africa (MeerKAT, Karoo Array Telescope).
Dense aperture arrays comprise up to millions of receiving elements in planar arrays on the ground (Fig. 4) which can be phased together to point in any direction on the sky. Due to the large reception pattern of the basic elements, the field of view can be up to 250 square degrees. This technology can also be adapted to the focal plane of parabolic dishes. Prototypes of such wide-field cameras are under construction in Australia (ASKAP, Australian SKA Pathfinder), the Netherlands (APERTIF) and in Canada (PHAD).
The data from all stations have to be transmitted to a central computer and processed online. Compared to LOFAR with a data rate of about 150 Gigabits per second and a central processing power of 27 Tflops, the SKA will produce much more data and need much more processing power - by a factor of at least one hundred. Following “Moore s law” of increasing computing power, a processor with sufficient power should be available by the next decade. The energy consumption for the computers and cooling will be tens of MegaWatts.
4 SKA timeline
The detailed design for low and mid frequencies will be ready until 2013. The development of technologies for the high-frequency band will start in 2013. Construction of the SKA is planned to start in 2016. In the first phase (until about 2020) about 10% of the SKA will be erected (SKA) (Garrett et al. ), with completion of construction at the low and mid frequency bands (SKA) by about 2024, followed by construction at the high band.
The members of the SKA Organisation agreed on a dual site solution for the SKA with two candidate sites fulfilling the scientific and logistical requirements: Southern Africa, extending from South Africa, with a core in the Karoo desert, eastward to Madagascar and Mauritius and northward into the continent, and Australia, with the core in Western Australia. The dishes of SKA will be built in South Africa, combined with the MeerKAT telescope, and further dishes will be added to the ASKAP array in Australia. All the dishes and the mid-frequency dense aperture array for SKA will be built in Southern Africa. The low-frequency sparse aperture array of dipole antennas for SKA and SKA will be built in Australia.
5 Key science projects
Apart from the expected technological spin-offs, five main science questions (Key Science Projects) drive the SKA (Carilli & Rawlings ).
Probing the dark ages
The SKA will use the emission of neutral hydrogen to observe the most distant objects in the Universe. The energy output from the first energetic stars and the jets launched near young black holes (quasars) started to heat the neutral gas, forming bubbles of ionized gas as structure emerged. This is called the Epoch or Reionization. The signatures from this exciting transition phase should still be observable with help of the HI radio line, redshifted by a factor of about 10. The lowest SKA frequency will allow us to detect hydrogen at redshifts of up to 20, to search for the transition from a neutral to an ionized Universe, and hence provide a critical test of our present-day cosmological model.
Galaxy evolution, cosmology, and dark energy
The expansion of the Universe is currently accelerating, a not understood phenomenon, named “dark energy”. One important method of distinguishing between the various explanations is to compare the distribution of galaxies at different epochs in the evolution of the Universe to the distribution of matter at the time when the Cosmic Microwave Background (CMB) was formed. Small distortions in the distribution of matter, called baryon acoustic oscillations, should persist from the era of CMB formation until today. Tracking if and how these ripples change in size and spacing over cosmic time can then tell us if one of the existing models for dark energy is correct or if a new idea is needed. A deep all-sky SKA survey will detect hydrogen emission from Milky Way-like galaxies out to redshifts of about 1. The galaxy observations will be “sliced” in different redshift (time) intervals and hence reveal a comprehensive picture of the Universe’s history.
The same data set will give us unique information about the evolution of galaxies, how the hydrogen gas was concentrated to form galaxies, how fast it was transformed into stars, and how much gas did galaxies acquire during their lifetime from intergalactic space. The HI survey will simultaneously give us the synchrotron radiation intensity of the galaxies which is a measure of their star-formation rate and magnetic field strength.
Tests of General Relativity and detection of gravitational waves
Pulsars are ideal probes for experiments in the strong gravitational field around black holes have yet been made. We expect that almost all pulsars in the Milky Way will be detected with the SKA (Fig. 6) plus several 100 bright pulsars in nearby galaxies. The SKA will search for a radio pulsar orbiting around a black hole, measure time delays in extremely curved space with much higher precision than with laboratory experiments and hence probe the limits of General Relativity.
Regular high-precision observations with the SKA of a network of pulsars with periods of milliseconds opens the way to detect gravitational waves with wavelengths of many parsecs, as expected for example from two massive black holes orbiting each other with a period of a few years resulting from galaxy mergers in the early Universe. When such a gravitational wave passes by the Earth, the nearby space-time changes slightly at a frequency of a few nHz (about 1 oscillation per 30 years). The wave can be detected as apparent systematic delays and advances of the pulsar clocks in particular directions relative to the wave propagation on the sky.
The cradle of life
The SKA will be able to detect the thermal radio emission from centimeter-sized “pebbles” in protoplanetary systems which are thought to be the first step in assembling Earth-like planets. Biomolecules are observable in the radio range. Prebiotic chemistry - the formation of the molecular building blocks necessary for the creation of life - occurs in interstellar clouds long before that cloud collapses to form a new solar system. Finally, the SETI (Search for Extra Terrestrial Intelligence) project will use the SKA to find hints of technological activities. Ionospheric radar experiments similar to those on Earth will be detectable out to several kpc, and Arecibo-type radar beams, like those that we use to map our neighbor planets in the solar system, out to as far as a few 10 kpc.
Origin and evolution of cosmic magnetism
Synchrotron radiation and Faraday rotation revealed magnetic fields in our Milky Way, nearby spiral galaxies, and in galaxy clusters, but little is known about magnetic fields in the intergalactic medium. Furthermore, the origin and evolution of magnetic fields is still unknown. The SKA will measure the Faraday rotation towards several tens of million polarized background sources (mostly quasars), allowing us to derive the magnetic field structures and strengths of the intervening objects, such as, the Milky Way, distant spiral galaxies, clusters of galaxies, and in intergalactic space – see below.
From the five Key Science Projects two major science goals have been identified that drive the technical specifications for the first phase (SKA):
Origins: Understanding the history and role of neutral hydrogen in the Universe from the dark ages to the present-day.
Fundamental Physics: Detecting and timing binary pulsars and spin-stable millisecond pulsars in order to test theories of gravity.
6 Future magnetic field observations
Next-generation radio telescopes will widen the range of observable magnetic phenomena. At low frequencies, synchrotron emission will be observed from aging electrons far away from their places of origin. Low frequencies are also ideal to search for small Faraday rotation measures from weak interstellar and intergalactic fields (Arshakian & Beck ) and in steep-spectrum cluster relics (Brunetti et al. ). The recently completed LOFAR (operating at 10–240 MHz), followed by the MWA and the LWA (both under construction), are suitable instruments to search for weak magnetic fields in outer galaxy disks, galaxy halos and cluster halos. First LOFAR results have been presented at this conference (Anderson et al., Mulcahy et al., this volume).
LOFAR will detect all pulsars within 2 kpc of the Sun and discover about 1000 new nearby pulsars, especially at high latitudes (van Leeuwen & Stappers ). Most of these are expected to emit strong, linearly polarized signals at low frequencies. This will allows us to measure their RMs and to derive the magnetic field structure near to the Sun.
Deep high-resolution observations at high frequencies, where Faraday effects are small, require a major increase in sensitivity of continuum observations, to be achieved by the EVLA and the SKA. The detailed structure of the magnetic fields in the ISM of galaxies, in galaxy halos, cluster halos and cluster relics will be observed. The magnetic power spectra can be measured (Vogt & Enßlin ). Direct insight into the interaction between gas and magnetic fields in these objects will become possible. The SKA will also allow to measure the Zeeman effect of weak magnetic fields in the Milky Way and in nearby galaxies.
Detection of polarized emission from distant, unresolved galaxies will reveal large-scale ordered fields (Stil et al. ), to be compared with the predictions of dynamo theory (Arshakian et al. ). The SKA will detect Milky-Way type galaxies at (Murphy ) and their polarized emission at (assuming 10% polarization). Cluster “relics” are highly polarized (van Weeren et al. ) and will also be detectable at large redshifts.
Bright starburst galaxies are not expected to host ordered fields. Unpolarized synchrotron emission from starburst galaxies, signature of turbulent magnetic fields, will be detected with the SKA out to large redshifts, depending on luminosity and magnetic field strength (Fig. 6), and from cluster halos. However, for fields weaker than 3.25 G , energy loss of cosmic-ray electrons is dominated by the inverse Compton effect with CMB photons, so that the energy appears mostly in X-rays, not in the radio range. On the other hand, for strong fields the energy range of the electrons emitting at a 1.4 GHz drops to low energies, where ionization and bremsstrahlung losses become dominant (Murphy ). In summary, the mere detection of synchrotron emission of galaxies at high redshifts will constrain the range of allowed magnetic field strengths.
If polarized emission from galaxies, cluster halos or cluster relics is too weak to be detected, the method of RM grids towards background QSOs can still be applied and allows us to determine the field strength and pattern in an intervening galaxy. This method can be applied to distances of young QSOs (). Regular fields of several G strength were already detected in distant galaxies (Bernet et al. , Kronberg et al. ). Mean-field dynamo theory predicts RMs from evolving regular fields with increasing coherence scale at (Arshakian et al. ). (Note that the observed RM values are reduced by the redshift dilution factor of .) A reliable model for the field structure of nearby galaxies, cluster halos and cluster relics needs RM values from a large number of polarized background sources, hence large sensitivity and high survey speed (Krause et al. ).
The POSSUM all-sky survey at 1.1–1.4 GHz with the ASKAP telescope (under construction) with about 30 deg field of view will measure about 100 RMs of extragalactic sources per square degree within 10 h integration time.
The SKA Magnetism Key Science Project plans to observe a wide-field survey (at least deg) around 1 GHz with 1 h integration per field which will detect sources of 0.5–1 Jy flux density and measure at least 1500 RMs deg. This will contain at least 1.5 RMs from compact polarized extragalactic sources at a mean spacing of (Gaensler et al. ). This survey will be used to model the structure and strength of the magnetic fields in the Milky Way, in intervening galaxies and clusters and in the intergalactic medium (Beck & Gaensler ). The SKA pulsar survey will find about 20,000 new pulsars which will mostly be polarized and reveal RMs (Fig. 6), suited to map the Milky Way’s magnetic field with high precision. More than 10,000 RM values are expected in the area of the galaxy M 31 and will allow the detailed reconstruction of the 3-D field structure. Simple patterns of regular fields can be recognized out to distances of about 100 Mpc (Stepanov et al. ) where the polarized emission is far too low to be mapped. The evolution of field strength in cluster halos can be measured by the RM grid method to redshifts of about 1 (Krause et al. ).
If the filaments of the local Cosmic Web outside clusters contain a magnetic field (Ryu et al. ), possibly enhanced by IGM shocks, we hope to detect this field by direct observation of its total synchrotron emission (Keshet et al. ) and possibly its polarization, or by Faraday rotation towards background sources. For fields of G with 1 Mpc coherence length and cm electron density, Faraday rotation measures between 0.1 and 1 rad m are expected which will be challenging to detect even with LOFAR. More promising is a statistical analysis like the measurement of the power spectrum of the magnetic field of the Cosmic Web (Kolatt ) or the cross-correlation with other large-scale structure indicators like the galaxy density field (Stasyszyn et al. ).
If an overall IGM field with a coherence length of a few Mpc existed in the early Universe and its strength varied proportional to , its signature may become evident at redshifts of . Averaging over a large number of RMs is required to unravel the IGM signal. The goal is to detect an IGM magnetic field of 0.1 nG, which needs an RM density of sources deg (Kolatt ), achievable with the SKA. Detection of a general IGM field, or placing stringent upper limits on it, will provide powerful observational constraints on the origin of cosmic magnetism.
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Image credit: UW-Madison
A new telescope lodged in the ice of Antarctica has completed the first map of the high-energy neutrino sky. AMANDA II consists of 677 glass detectors in the shape of a cylinder sunk into the Antarctic ice at a depth greater than 500 metres. It actually looks down, through the entire Earth to view the Northern sky for neutrinos, which move at high velocity and pass through almost all matter unhindered. AMANDA II has discovered neutrinos with 100 times the energy of any produced in laboratory experiments on Earth.
A novel telescope that uses the Antarctic ice sheet as its window to the cosmos has produced the first map of the high-energy neutrino sky.
The map, unveiled for astronomers here today (July 15) at a meeting of the International Astronomical Union, provides astronomers with their first tantalizing glimpse of very high-energy neutrinos, ghostly particles that are believed to emanate from some of the most violent events in the universe – crashing black holes, gamma ray bursts, and the violent cores of distant galaxies.
“This is the first data with a neutrino telescope with realistic discovery potential,” says Francis Halzen, a University of Wisconsin-Madison professor of physics, of the map compiled using AMANDA II, a one-of-a-kind telescope built with support from the National Science Foundation (NSF) and composed of arrays of light-gathering detectors buried in ice 1.5 kilometers beneath the South Pole. “To date, this is the most sensitive way ever to look at the high-energy neutrino sky,” he says.
The ability to detect high-energy neutrinos and trace them back to their points of origin remains one of the most important quests of modern astrophysics.
Because cosmic neutrinos are invisible, uncharged and have almost no mass, they are next to impossible to detect. Unlike photons, the particles that make up visible light, and other kinds of radiation, neutrinos can pass unimpeded through planets, stars, the vast magnetic fields of interstellar space and even entire galaxies. That quality – which makes them very hard to detect – is also their greatest asset because the information they harbor about cosmologically distant and otherwise unobservable events remains intact.
The map produced by AMANDA II is preliminary, Halzen emphasizes, and represents only one year of data gathered by the icebound telescope. Using two more years of data already harvested with AMANDA II, Halzen and his colleagues will next define the structure of the sky map and sort out potential signals from statistical fluctuations in the present map to confirm or disprove them.
The significance of the map, according to Halzen, is that it proves the detector works. “It establishes the performance of the technology,” he says, “and it shows that we have reached the same sensitivity as telescopes used to detect gamma rays in the same high-energy region” of the electromagnetic spectrum. Roughly equal signals are expected from objects that accelerate cosmic rays, whose origins remain unknown nearly a century after their discovery.
Sunk deep into the Antarctic ice, the AMANDA II (Antarctic Muon and Neutrino Detector Array) Telescope is designed to look not up, but down, through the Earth to the sky in the Northern Hemisphere. The telescope consists of 677 glass optical modules, each the size of a bowling ball, arrayed on 19 cables set deep in the ice with the help of high-pressure hot-water drills. The array transforms a cylinder of ice 500 meters in height and 120 meters in diameter into a particle detector.
The glass modules work like light bulbs in reverse. They detect and capture faint and fleeting streaks of light created when, on occasion, neutrinos crash into ice atoms inside or near the detector. The subatomic wrecks create muons, another species of subatomic particle that, conveniently, leaves an ephemeral wake of blue light in the deep Antarctic ice. The streak of light matches the path of the neutrino and points back to its point of origin.
Because it provides the first glimpse of the high-energy neutrino sky, the map will be of intense interest to astronomers because, says Halzen, “we still have no clue how cosmic rays are accelerated or where they come from.”
The fact that AMANDA II has now identified neutrinos up to one hundred times the energy of the particles produced by the most powerful earthbound accelerators raises the prospect that some of them may be kick-started on their long journeys by some of the most supremely energetic events in the cosmos. The ability to routinely detect high-energy neutrinos will provide astronomers not only with a lens to study such bizarre phenomena as colliding black holes, but with a means to gain direct access to unedited information from events that occurred hundreds of millions or billions of light years away and eons ago.
“This map could hold the first evidence of a cosmic accelerator,” Halzen says. “But we are not there yet.”
The hunt for sources of cosmic neutrinos will get a boost as the AMANDA II Telescope grows in size as new strings of detectors are added. Plans call for the telescope to grow to a cubic kilometer of instrumented ice. The new telescope, to be known as IceCube, will make scouring the skies for cosmic neutrino sources highly efficient.
“We will be sensitive to the most pessimistic theoretical predictions,” Halzen says. “Remember, we are looking for sources, and even if we discover something now, our sensitivity is such that we would see, at best, on the order of 10 neutrinos a year. That’s not good enough.”
Original Source: WISC News Release | 0.876607 | 4.097763 |
Orbital mayhem around a red dwarf
In the collective imagination, planets of a solar system all circle in the equatorial plane of their star. The star also spins, and its spin axis is aligned with the spin axes of the planetary orbits, giving the impression of a well-ordered system. But nature is capricious, as an international team led by researchers from the University of Geneva (UNIGE), Switzerland, has detected a planetary system turned upside down. This discovery is published this week in the prestigious journal Nature.
GJ436 is a star that hosts a planet nicknamed "the hairy planet," which evaporates like a comet. In this study, researchers at UNIGE showed that in addition to its huge cloud of gas, the planet GJ436b also has a very special orbit. It is polar: Instead of orbiting in the equatorial plane of the star, the planet passes almost above the stellar poles.
The orbital inclination of this plane is the last piece of a puzzle that has baffled astronomers for 10 years. Unlike the planets of our solar system, whose orbits almost form perfect circles, tGJ436 forms a very flat or strongly eccentric ellipse—that is, its distance to the star varies along its orbit. "This planet is under enormous tidal forces because it is incredibly close to its star, barely 3 percent of the Earth-sun distance," explains Vincent Bourrier, researcher at the Department of Astronomy of the UNIGE Faculty of Science. "The star is a red dwarf whose lifespan is very long, and the tidal forces it induces should have since circularized the orbit of the planet, but this is not the case," he says.
Orbital architectures of planetary systems are fossil records that tell us how they have formed and evolved. A planet disturbed by the passage of a nearby star or by the presence of other massive planets in the system will keep track of it in its orbit. "Even if we have already seen misaligned planetary orbits, we do not necessarily understand their origin. This is the first time we've measured the architecture of a planetary system around a red dwarf," says Christophe Lovis, a UNIGE researcher and co-author of the study.
The existence of an unknown, more massive and more distant disturbing planet would explain why GJ436b is not on a circular orbit: "If that is true, then our calculations indicate that not only would the planet not move along a circle around the star, as we've known for 10 years, but it should also be on a highly inclined orbit. That's exactly what we just measured," says Hervé Beust, who did the orbital calculations.
These same calculations also predict that the planet has not always been so close to its star, but might have come near it recently (on a cosmic scale). Thus, the "evaporating planet" would have been pushed towards the star by the gravity of a yet-undetected companion. For Vincent Bourrier, the hunt continues: "Our next goal is to identify the mysterious planet that has upset this planetary system." | 0.907263 | 3.976704 |
Ever watch the Moon cover up a star? There’s a great chance to see just such an event this coming weekend, when the waxing gibbous Moon occults (passes in front of) the bright star Aldebaran for much of North America on Saturday night, March 4th.
Shining at magnitude +0.85, Aldebaran is the brightest star that lies along the Moon’s path in the current epoch, and is one of four +1st magnitude stars that the Moon can occult. The other three are Regulus, Antares and Spica. This is the 29th in a series of 49 occultations of Aldebaran worldwide spanning from January 29th, 2015 to September 3rd, 2018, meaning Aldebaran hides behind the Moon once every lunation as it crosses through the constellation Taurus and the Hyades open star cluster in 2017. Like eclipses belonging to the same saros cycle, successive occultations of bright stars shift westward by about 120 degrees westward longitude and slowly drift to the north. Europe saw last month’s occultation of Aldebaran, and Asia is up next month on April 1st.
All of the contiguous ‘lower 48 states’ except northern New England see Saturday night’s occultation, and under dark skies, to boot. It’s a close miss for Canada. Mexico, central America and the Caribbean will also witness the event under dark skies. Hawaii will see the event under daytime skies. We can attest that this is indeed possible using binocs or a telescope, as we caught Aldebaran near the daytime Moon during last month’s event.
Occultations give us a chance to see a split second magic act, in a Universe that often unfolds over eons and epochs. The motion you’re seeing is mostly that of the Moon, and to a lesser extent, that of the Earth as the star abruptly ‘winks out’.
Observers in northern tier states might witness an additional spectacle, as Aldebaran grazes the northern limb of the Moon. This can make for an unforgettable sight, as the star successively winks in at out from behind lunar peaks and valleys. The graze line for Saturday night follows the U.S./Canadian border from Washington state, Idaho and Montana, then transects North Dakota, Minnesota just below Duluth and northern Wisconsin, Michigan and New York and Connecticut. Brad Timerson over at the international Occultation Timing Association has a good page set up for the circumstances for the grazing event, and the IOTA has a page detailing ingress (start) and egress times for the event for specific cities.
You’ll be able to see the occultation of Aldebaran with the unaided eye, no telescope over binocular needed, though it will be fun to follow along with optics as well. The ingress along the leading dark limb of the Moon is always more dramatic, while reemergence on the bright limb is a more subtle affair.
A simple video aimed afocally through a telescope eyepiece can easily capture the event. We like to run WWV radio on AM shortwave in the background while video recording so as to get a good time hack of the event on audio. Finally, set up early, watch those battery levels in the frigid March night, and be sure to balance out your exposure times to capture both Aldebaran and the dazzling limb of the Moon.
Anyone Live-casting the event? It’ll be a tough one low to the horizon here in central Florida, but a livestream would certainly be possible for folks westward with Aldebaran and the Moon high in the sky. Let us know of any planned webcasts, and we’ll promote accordingly.
The Moon also occults several other bright stars this week, leading up to an occultation of Regulus on March 10th favoring the southern Atlantic. Read all about occultations, eclipses, comets and more in our free e-book, 101 Astronomical Events for 2017 from Universe Today.
Don’t miss Saturday night’s stunning occultation, and let us know of your tales of astronomical tribulation and triumph.
-Send those astro-images in to Universe Today’s Flickr forum, and you might just see ’em featured here in a future article. | 0.859103 | 3.477569 |
From: NASA HQ
Posted: Thursday, August 18, 2011
NASA spacecraft observations and new data processing techniques are giving scientists better insight into the evolution and development of solar storms that can damage satellites, disrupt communications and cause power grid failures on Earth.
The solar storms, called Coronal Mass Ejections (CMEs), are being observed from NASA's twin Solar Terrestrial Relations Observatory, or STEREO, spacecraft launched in 2006. The duo represents a key component within a fleet of NASA spacecraft that enhance the capability to predict solar storms.
Previous spacecraft imagery did not clearly show the structure of a solar disturbance as it traveled toward Earth. As a result, forecasters had to estimate when storms would arrive without knowing the details of how they evolve and grow. New processing techniques used on STEREO data allow scientists to see how solar eruptions develop into space storms at the Earth.
"The clarity these new images provide will improve the observational inputs into space weather models for better forecasting," said Lika Guhathakurta, STEREO program scientist at NASA Headquarters in Washington.
CMEs are billion-ton clouds of solar plasma launched by the same sun explosions that spark solar flares. When they sweep past Earth, they can cause auroras, radiation storms that can disrupt sensitive electronics on satellites, and in extreme cases, power outages. Better tracking of these clouds and the ability to predict their arrival is an important part of space weather forecasting.
Newly released images from cameras on the STEREO-A spacecraft reveal detailed features in a large Earth-directed CME in late 2008, connecting the original magnetized structure in the sun's corona to the intricate anatomy of the interplanetary storm as it hit the planet three days later. When the data were collected, the spacecraft was more than 65 million miles away from Earth.
The spacecraft's wide-angle cameras captured the images. They detect ordinary sunlight scattered by free-floating electrons in plasma clouds. When these clouds in CMEs leave the sun, they are bright and easy to see. However, visibility is quickly reduced, as the clouds expand into the void. The clouds are about one thousand times fainter than the Milky Way, which makes direct imaging of them difficult. That also has limited our understanding of the connection between solar storms and the coronal structures that cause them.
"Separating these faint signals from the star field behind them proved especially challenging, but it paid off," said Craig DeForest, scientist at the Southwest Research Institute in Boulder, Colo. and lead author of an Astrophysical Journal article released online yesterday. "We have been drawing pictures of structures like these for several decades. Now that we can see them so far from the sun, we find there is still a lot to learn."
These observations can pinpoint not only the arrival time of the CME, but also its mass. The brightness of the cloud enabled researchers to calculate the cloud's gas density throughout the structure, and compare it to direct measurements by other NASA spacecraft. When this technique is applied to future storms, forecasters will be able to say with confidence whether Earth is about to be hit by a small or large cloud, and where on the sun the material originated.
STEREO's two observatories orbit the sun, one ahead of Earth and one behind. They will continue to move apart over time. STEREO is the third mission in NASA's Solar Terrestrial Probes program. The program seeks to understand the fundamental physical processes of the space environment from the sun to Earth and other planets.
The STEREO spacecraft were built and are operated for NASA by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the mission, instruments and science center. The STEREO instruments were designed and built by scientific institutions in the U.S., UK, France, Germany, Belgium, Netherlands, and Switzerland.
For more information and images, visit: http://www.nasa.gov/sunearth
For more information about the STEREO mission and instruments, visit: http://stereo.gsfc.nasa.gov/
// end // | 0.838243 | 3.644027 |
Life Beyond the Solar System: From Science Fiction to Science
by Michaël Gillon, Senior Research Associate of the FRS-FNRS at the STAR (Space Sciences, Technologies and Astrophysics) Institute of the University of Liège, Belgium. Dr. Gillon is known for leading the team that discovered a planetary system around the star TRAPPIST-1.
The conference will take place on Wednesday, October 24, 2018 at 7:30 pm, at the University of Montreal, at Pavillon Jean-Brillant, room B-2325.
No prior knowledge is necessary. IREx conferences are for anyone who wants to learn about exoplanets and astronomy, regardless of age or scientific knowledge.
Since the dawn of time, the existence of other inhabited worlds has fascinated human beings. Until the Copernican revolution, this pluralistic hypothesis remained purely mythological or philosophical. Only with the understanding that our Earth, far from being the center of the universe, is only one of many planets orbiting the Sun, which is itself nothing more than a star similar in every respect to the stars lining the celestial vault, did cosmic pluralism become a dominant notion defended by many scholars and philosophers. Later, astronomy taught us that there are hundreds of billions of stars in the Milky Way, our galaxy, and that there are hundreds of billions of galaxies in our expanding Universe. Faced with such immensity, it is very tempting to hypothesize the existence of other inhabited planets, and even other advanced civilizations, somewhere beyond our solar system. Indeed this hypothesis captivated the public during the second half of 20th century, with the help of countless science fiction stories, novels and movies. Over the past two decades, this fascination has become even stronger, this time thanks to science instead of science fiction. Indeed, in the 90s, astronomers detected the first exoplanets, that is to say the first planets orbiting another star than the Sun. Since these historical discoveries, more than 3000 exoplanets have been detected at an ever-accelerating pace. A few dozens of these are “potentially habitable”, that is to say they could be rocky worlds harboring oceans of water on their surface, like our Earth. From there, imagining complex forms of life on some of these planets is but a small step away, one that is happily crossed by many. But our imagination will soon be replaced by real scientific measures, because, in the next decade, our most powerful telescopes will be able to probe the atmospheric compositions of some of these extrasolar worlds, and possibly even find chemical traces of life there. If successful, our view of Cosmos will change forever…
Born on January 24, 1974 in Liège, Belgium, Michaël Gillon is a FRS-FNRS Senior Research Associate at the STAR (Space Sciences, Technologies and Astrophysics) Institute at the University of Liège, Belgium. At the age of 24, after seven years in the Belgian army, he began studying sciences at the University of Liège. From there he obtained a Bachelor degrees in Biology (2000) and Physics (2003), and a Masters in Biochemistry (2002) and Astrophysics (2006). After these studies, he did a doctoral thesis on the detection of exoplanets which he defended in 2006 in Liège. He then joined the Observatory of the University of Geneva (Switzerland) as a postdoctoral researcher as part of the team of Michael Mayor and Didier Queloz, the two discoverers of the first exoplanet in 1995. He returned to Liège in 2009, notably to initiate and lead the TRAPPIST and SPECULOOS exoplanet projects.
Michaël Gillon has made several major contributions to the detection and characterization of exoplanets. He notably led the first size measurement of a Neptune sized exoplanet (2007) and the first detection of the emission of a rocky exoplanet (2012). He is also the principal discoverer of the famous planetary system TRAPPIST-1 (2016, 2017) composed of seven Earth-sized planets orbiting a small nearby star, many of which are potentially habitable and well adapted for follow-up detailed atmospheric studies. The importance of his contributions to the study of exoplanets and to the search for life elsewhere in the Universe earned him one of the prestigious Balzan Awards in 2017, and to be nominated as one of the 100 most influential personalities in the world by the Times magazine.
The Pavillon Jean-Brillant at the Université de Montréal is at 3200 Jean-Brillant. It is easily accessible by subway, through Côte-des-Neiges metro station on the blue line. Walk on Chemin de la Côte-des-Neiges towards the Oratoire Saint-Joseph and turn left on Jean-Brillant street. The building will be less than 5 minutes away, on your right. Directions to the room will then be clearly visible. | 0.892355 | 3.500394 |
Kepler is NASA’s 10th Discovery mission. It is designed specifically to detect Earth-size planets orbiting in the habitable zone of solar-like stars. The telescope will stare continuously at over 100,000 stars in one region of the sky for 3 1/2 or more years looking for transits of planets, when they block a bit of light from their parent stars. From the amount of light blocked during the transit, scientists can calculate the size of the planet. Measuring the time between the transits , scientists can calculate the orbital period. Using Kepler’s Third Law of planetary motion, scientists then can calculate the distance the planet is from its star. The distance from the star largely determines the temperature of the planet and whether it may be habitable. | 0.87312 | 3.309748 |
Astronomers recorded the most powerful explosion of energy in the Universe since the Big Bang. Some experts compare the opening in significance with the discovery of the first dinosaur bones. This writes Lenta.Ru.
The explosion occurred near the supermassive black hole at the center of the galaxy, remote from Earth 390 million light years and is located in the Ophiuchus cluster. The release of energy was so strong that it punched a giant hole in the plasma surrounding the cluster. In this cavity could fit 15 galaxies of the milky Way.
Scientists had previously observed a gap through the x-ray telescopes, however, they rejected the idea that the phenomenon is explosive in nature. This hypothesis was confirmed during observations, using telescopes and other instruments, sensitive to different wavelengths: x-ray Chandra, XMM-Newton, ESA, antenna Murchison Widefield Array (MWA) in Western Australia and the radio telescope Giant Metrewave Radio Telescope (GMRT) in India.
“Before, we saw the flash in the centers of galaxies, but it is really massive. And we don’t know why it’s so big,” said Professor Melanie Johnston-Hollit, writes Hromadske.
She said that the explosion occurred very slowly, “like an explosion in slow motion, which lasted for hundreds of millions of years”.
According to her, the explosion occurred, the release of energy, which is five times the previous record.
The first hint of this giant explosion actually came in 2016. Then, astronomers saw a strange curved edge in Ophiuchus. However, scientists did not anticipate the eruption, given the amount of energy needed, writes UNIAN.
Researchers are still unknown the reason of such a strong explosion. In the future will be conducted a more thorough observations using 4096 instead of 2048 of the MWA antennas. | 0.828664 | 3.435897 |
A new Johns Hopkins University study suggests dark matter may have existed before the Big Bang.
Researchers believe dark matter makes up about 80% of the universe’s mass, but its origins and composition remain among the most elusive mysteries in modern physics.
A new mathematical model suggests dark matter may have been produced before the Big Bang during cosmic inflation.
The study, published in _Physical Review Letters, presents a new idea of how dark matter was created and how it might be identified during astronomical observations.
Tommi Tenkanen, a postdoctoral fellow in JHU’s Department of Physics and Astronomy and the study’s author, said:
“The study revealed a new connection between particle physics and astronomy. If dark matter consists of new particles that were born before the Big Bang, they affect the way galaxies are distributed in the sky in a unique way. This connection may be used to reveal their identity and make conclusions about the times before the Big Bang, too.
If dark matter were truly a remnant of the Big Bang, then in many cases researchers should have seen a direct signal of dark matter in different particle physics experiments already.”
While not much is known about its origins, astronomers have shown that dark matter plays a crucial role in the formation of galaxies and galaxy clusters. Though not directly observable, scientists know dark matter exists by its gravitation effects on how visible matter moves and is distributed in space.
For a long time, researchers believed that dark matter must be a byproduct of the Big Bang. Scientists have long sought this kind of dark matter, but so far all experimental searches have been unsuccessful.
Using a new, simple mathematical framework, the study shows that dark matter may have been produced before the Big Bang during an era known as the cosmic inflation when space was expanding very rapidly. The rapid expansion is believed to lead to copious production of certain types of particles called scalars. So far, only one scalar particle has been discovered, the famous Higgs boson.
Image credit NASA’s Goddard Space Flight Center/CI Lab
source Johns Hopkins University | 0.848127 | 3.907269 |
In February 2017, Julien de Wit ’14 was a member of the international team, led by University of Liège colleague Michaël Gillon, that announced the discovery of seven temperate Earth-sized planets orbiting the red dwarf star TRAPPIST-1. Soon afterward, the team found evidence bolstering the supposition that the outer planets in the system could hold significant stores of water. “It’s amazing how quickly our perspective on this [system] has changed,” de Wit— then a postdoc in the group of Sara Seager, Class of 1941 Professor of Physics and Planetary Science—told MIT News in 2017. “It’s a steep learning curve that is really exciting.” In July 2018, de Wit began a faculty appointment as assistant professor in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS).
De Wit now leads the effort to characterize the atmospheres of the newly discovered TRAPPIST-1 planets. So far, using the Hubble Space Telescope, his team has ruled out the presence of hydrogen-dominated atmospheres (which would be typical of inhospitable, gaseous planets such as Neptune) for the five innermost planets of the system. These results strengthen the case that Earthlike conditions could potentially exist within the system, and lay the groundwork for more targeted observations via NASA’s James Webb Space Telescope, scheduled to launch in 2021.
De Wit is also involved in the effort to establish an observatory in the Northern Hemisphere (part of a project whimsically dubbed SPECULOOS, after a popular cookie from de Wit’s native Belgium). This new network of telescopes will expand upon the TRAPPIST prototype, continuing the search for new potentially habitable systems.
According to de Wit, “The door now stands open to expanding our understanding of planetary systems, habitats, life, and ultimately our own planet, through the discovery and study of new terrestrial exoplanets that can be characterized in-depth. This has the potential to be paradigm-shifting.” | 0.86728 | 3.494596 |
When I was 14 years old, I was interested in science—fascinated by it, excited to learn about it. And I had a high school science teacher who would say to the class, "The girls don't have to listen to this." Encouraging, yes. I chose not to listen—but to that statement alone.
So let me take you to the Andes mountains in Chile, 500 kilometers, 300 miles northeast of Santiago. It's very remote, it's very dry and it's very beautiful. And there's not much there. There are condors, there are tarantulas, and at night, when the light dims, it reveals one of the darkest skies on Earth. It's kind of a magic place, the mountain. It's a wonderful combination of very remote mountaintop with exquisitely sophisticated technology.
And our ancestors, for as long as there's been recorded history, have looked at the night sky and pondered the nature of our existence. And we're no exception, our generation. The only difficulty is that the night sky now is blocked by the glare of city lights. And so astronomers go to these very remote mountaintops to view and to study the cosmos. So telescopes are our window to the cosmos.
It's no exaggeration to say that the Southern Hemisphere is going to be the future of astronomy for the 21st century. We have an array of existing telescopes already, in the Andes mountains in Chile, and that's soon to be joined by a really sensational array of new capability. There will be two international groups that are going to be building giant telescopes, sensitive to optical radiation, as our eyes are. There will be a survey telescope that will be scanning the sky every few nights. There will be radio telescopes, sensitive to long-wavelength radio radiation. And then there will be telescopes in space. There'll be a successor to the Hubble Space Telescope; it's called the James Webb Telescope, and it will be launched in 2018. There'll be a satellite called TESS that will discover planets outside of our solar system.
For the last decade, I've been leading a group—a consortium—international group, to build what will be, when it's finished, the largest optical telescope in existence. It's called the Giant Magellan Telescope, or GMT. This telescope is going to have mirrors that are 8.4 meters in diameter—each of the mirrors. That's almost 27 feet. So it dwarfs this stage—maybe out to the fourth row in this audience. Each of the seven mirrors in this telescope will be almost 27 feet in diameter. Together, the seven mirrors in this telescope will comprise 80 feet in diameter. So, essentially the size of this entire auditorium. The whole telescope will stand about 43 meters high, and again, being in Rio, some of you have been to see the statue of the giant Christ. The scale is comparable in height; in fact, it's smaller than this telescope will be. It's comparable to the size of the Statue of Liberty. And it's going to be housed in an enclosure that's 22 stories—60 meters high. But it's an unusual building to protect this telescope. It will have open windows to the sky, be able to point and look at the sky, and it will actually rotate on a base—2,000 tons of rotating building.
The Giant Magellan Telescope will have 10 times the resolution of the Hubble Space Telescope. It will be 20 million times more sensitive than the human eye. And it may, for the first time ever, be capable of finding life on planets outside of our solar system. It's going to allow us to look back at the first light in the universe—literally, the dawn of the cosmos. The cosmic dawn. It's a telescope that's going to allow us to peer back, witness galaxies as they were when they were actually assembling, the first black holes in the universe, the first galaxies.
Now, for thousands of years, we have been studying the cosmos, we've been wondering about our place in the universe. The ancient Greeks told us that the Earth was the center of the universe. Five hundred years ago, Copernicus displaced the Earth, and put the Sun at the heart of the cosmos. And as we've learned over the centuries, since Galileo Galilei, the Italian scientist, first turned, in that time, a two-inch, very small telescope, to the sky, every time we have built larger telescopes, we have learned something about the universe; we've made discoveries, without exception. We've learned in the 20th century that the universe is expanding and that our own solar system is not at the center of that expansion. We know now that the universe is made of about 100 billion galaxies that are visible to us, and each one of those galaxies has 100 billion stars within it.
So we're looking now at the deepest image of the cosmos that's ever been taken. It was taken using the Hubble Space Telescope, and by pointing the telescope at what was previously a blank region of sky, before the launch of Hubble. And if you can imagine this tiny area, it's only one-fiftieth of the size of the full moon. So, if you can imagine the full moon. And there are now 10,000 galaxies visible within that image. And the faintness of those images and the tiny size is only a result of the fact that those galaxies are so far away, the vast distances. And each of those galaxies may contain within it a few billion or even hundreds of billions of individual stars. Telescopes are like time machines, so the farther back we look in space, the further back we see in time. And they're like light buckets—literally, they collect light. So larger the bucket, the larger the mirror we have, the more light we can see, and the farther back we can view.
So, we've learned in the last century that there are exotic objects in the universe—black holes. We've even learned that there's dark matter and dark energy that we can't see. So you're looking now at an actual image of dark matter. You got it. Not all audiences get that.
So the way we infer the presence of dark matter—we can't see it—but there's an unmistakable tug, due to gravity. We now can look out, we see this sea of galaxies in a universe that's expanding.
What I do myself is to measure the expansion of the universe, and one of the projects that I carried out in the 1990s used the Hubble Space Telescope to measure how fast the universe is expanding. We can now trace back to 14 billion years. We've learned over time that stars have individual histories; that is, they have birth, they have middle ages and some of them even have dramatic deaths. So the embers from those stars actually then form the new stars that we see, most of which turn out to have planets going around them.
And one of the really surprising results in the last 20 years has been the discovery of other planets going around other stars. These are called exoplanets. And until 1995, we didn't even know the existence of any other planets, other than going around our own sun. But now, there are almost 2,000 other planets orbiting other stars that we can now detect, measure masses for. There are 500 of those that are multiple-planet systems. And there are 4,000—and still counting—other candidates for planets orbiting other stars. They come in a bewildering variety of different kinds. There are Jupiter-like planets that are hot, there are other planets that are icy, there are water worlds, and there are rocky planets like the Earth, so-called "super-Earths," and there have even been planets that have been speculated diamond worlds.
So we know there's at least one planet, our own Earth, in which there is life. We've even found planets that are orbiting two stars. That's no longer the province of science fiction. So around our own planet, we know there's life, we've developed a complex life, we now can question our own origins. And given all that we've discovered, the overwhelming numbers now suggest that there may be millions, perhaps, maybe even hundreds of millions of other planets that are close enough, just the right distance from their stars that they're orbiting, to have the existence of liquid water and maybe could potentially support life. So we marvel now at those odds, the overwhelming odds, and the amazing thing is that within the next decade, the GMT may be able to take spectra of the atmospheres of those planets, and determine whether or not they have the potential for life.
So, what is the GMT project? It's an international project. It includes Australia, South Korea, and I'm happy to say, being here in Rio, that the newest partner in our telescope is Brazil.
It also includes a number of institutions across the United States, including Harvard University, the Smithsonian and the Carnegie Institutions, and the Universities of Arizona, Chicago, Texas-Austin and Texas A&M University. It also involves Chile.
So, the making of the mirrors in this telescope is also fascinating in its own right. Take chunks of glass, melt them in a furnace that is itself rotating. This happens underneath the football stadium at the University of Arizona. It's tucked away under 52,000 seats. Nobody know it's happening. And there's essentially a rotating cauldron. The mirrors are cast and they're cooled very slowly, and then they're polished to an exquisite precision. And so, if you think about the precision of these mirrors, the bumps on the mirror, over the entire 27 feet, amount to less than one-millionth of an inch. So, can you visualize that? Ow! That's one five-thousandths of the width of one of my hairs, over this entire 27 feet. It's a spectacular achievement. It's what allows us to have the precision that we will have.
So, what does that precision buy us? So the GMT, if you can imagine—if I were to hold up a coin, which I just happen to have, and I look at the face of that coin, I can see from here the writing on the coin; I can see the face on that coin. My guess that even in the front row, you can't see that. But if we were to turn the Giant Magellan Telescope, all 80-feet diameter that we see in this auditorium, and point it 200 miles away, if I were standing in São Paulo, we could resolve the face of this coin. That's the extraordinary resolution and power of this telescope. And if we were—if an astronaut went up to the Moon, a quarter of a million miles away, and lit a candle—a single candle—then we would be able to detect it, using the GMT. Quite extraordinary.
Here's an image. This is a simulated image of a cluster in a nearby galaxy. "Nearby" is astronomical, it's all relative. It's tens of millions of light-years away. This is what this cluster would look like. So look at those four bright objects, and now lets compare it with a camera on the Hubble Space Telescope. You can see faint detail that starts to come through. And now finally—and look how dramatic this is—this is what the GMT will see. So, keep your eyes on those bright images again. This is what we see on one of the most powerful existing telescopes on the Earth, and this, again, what the GMT will see. Extraordinary precision.
So, where are we? We have now leveled the top of the mountaintop in Chile. We blasted that off. We've tested and polished the first mirror. We've cast the second and the third mirrors. And we're about to cast the fourth mirror. We had a series of reviews this year, international panels that came in and reviewed us, and said, "You're ready to go to construction." And so we plan on building this telescope with the first four mirrors. We want to get on the air quickly, and be taking science data—what we astronomers call "first light," in 2021. And the full telescope will be finished in the middle of the next decade, with all seven mirrors.
So we're now poised to look back at the distant universe, the cosmic dawn. We'll be able to study other planets in exquisite detail. But for me, one of the most exciting things about building the GMT is the opportunity to actually discover something that we don't know about—that we can't even imagine at this point, something completely new. And my hope is that with the construction of this and other facilities, that many young women and men will be inspired to reach for the stars. Thank you very much. Obrigado.
Thank you, Wendy. Stay with me, because I have a question for you. You mentioned different facilities. So the Magellan Telescope is going up, but also ALMA and others in Chile and elsewhere, including in Hawaii. Is it about cooperation and complementarity, or about competition? I know there's competition in terms of funding, but what about the science?
In terms of the science, they're very complementary. The telescopes that are in space, the telescopes on the ground, telescopes with different wavelength capability, telescopes even that are similar, but different instruments—they will all look at different parts of the questions that we're asking. So when we discover other planets, we'll be able to test those observations, we'll be able to measure the atmospheres, be able to look in space with very high resolution. So, they're very complementary. You're right about the funding, we compete; but scientifically, it's very complementary.
Wendy, thank you very much for coming to TEDGlobal. | 0.839233 | 3.509656 |
“When you point a telescope at a black hole, it turns out you don’t just see the swirling sizzling doughnut of doom formed by matter falling in,” reports the New York Times. “You can also see the whole universe.”
Light from an infinite array of distant stars and galaxies can wrap around the black hole like ribbons around a maypole, again and again before coming back to your eye, or your telescope. “The image of a black hole actually contains a nested series of rings,” said Michael Johnson of the Harvard-Smithsonian Center for Astrophysics, not unlike the rings that form around your bathtub drain.
Dr. Johnson was lead author of a study, describing the proposed method that would allow our telescopes to pry more secrets from the maw of any black hole, that was published in the March 18 edition of the journal Science Advances. He and other authors of the paper are also members of the team operating the Event Horizon Telescope, a globe-girding network of radio telescopes that made that first image of a black hole. Their telescope saw these rings, but it didn’t have enough resolution to distinguish them, so they were blurred into a single feature…. Andrew Strominger, a Harvard theorist and co-author of the paper, said, “Understanding the intricate details of this historic experimental observation has forced theorists like myself to think about black holes in a new way…”
As Peter Galison of Harvard, another E.H.T. collaborator said, “As we peer into these rings, we are looking at light from all over the visible universe, we are seeing farther and farther into the past, a movie, so to speak, of the history of the visible universe.” | 0.812728 | 3.283366 |
A new image of a mysterious nebula has been revealed and has gained an interesting nickname. The astronomers working with Europe’s Very Large Telescope have been calling the photo that was captured the “Mouth of the Beast.” While scientists and astronomers aren’t entirely sure what this giant mass of cloudy gas is, or what it’s forming – astronomers and scientists have labeled it a “cometary globule.” The event is happening nearly 1,300 light years away from Earth and is embedded in the Puppis constellation.
While the European Southern Observatory’s image shows some really impressive colors – researchers have warned that it isn’t actually as bright as it appears in the photo. It’s a fairly massive cloud, too, encompassing some-1.5 light years across. Interestingly though, the globule is forming new stars – while simultaneously being destroyed by stars around it. Those studying the globule have also noted that several stars the size of the sun could be produced from the amount of gas that is inside the cloud.
Some have speculated what it might be, and alternatively to the “Mouth of the Beast” namesake that it has gathered – it’s also being called the “Hand of God” by others. There are two popular theories behind this cloud and how it formed. One theory is that stellar winds caused the cloud to form while another theory suggests that it might be the result of a massive supernova explosion that happened nearby. Scientists expect to learn more as they dive deeper into the findings and the images that were captured, but ultimately more research will need to be done before any final assumptions can be made.
Either way, the cloud is an interesting conversation starter in the science community that will give those individuals researching the gas cloud an opportunity to understand what might have formed the cloud to begin with. Interestingly, this is likely only the beginning of the cloud – as it’s unclear right now how quickly it will dissipate. Scientists believe that while it provides the energy and gas to create other stars within the cloud – that it could begin to unlock some of the mysteries around space science, and the formation of stars. | 0.875582 | 3.04503 |
The way it really is: little-known facts about radiometric dating
Long-age geologists will not accept a radiometric date unless it matches their pre-existing expectations.
Many people think that radiometric dating has proved the Earth is millions of years old. That’s understandable, given the image that surrounds the method. Even the way dates are reported (e.g. 200.4 ± 3.2 million years) gives the impression that the method is precise and reliable (box below).
However, although we can measure many things about a rock, we cannot directly measure its age. For example, we can measure its mass, its volume, its colour, the minerals in it, their size and the way they are arranged. We can crush the rock and measure its chemical composition and the radioactive elements it contains. But we do not have an instrument that directly measures age.
Before we can calculate the age of a rock from its measured chemical composition, we must assume what radioactive elements were in the rock when it formed.1 And then, depending on the assumptions we make, we can obtain any date we like.
It may be surprising to learn that evolutionary geologists themselves will not accept a radiometric date unless they think it is correct—i.e. it matches what they already believe on other grounds. It is one thing to calculate a date. It is another thing to understand what it means.
So, how do geologists know how to interpret their radiometric dates and what the ‘correct’ date should be?
A geologist works out the relative age of a rock by carefully studying where the rock is found in the field. The field relationships, as they are called, are of primary importance and all radiometric dates are evaluated against them.
For example, a geologist may examine a cutting where the rocks appear as shown in Figure 1. Here he can see that some curved sedimentary rocks have been cut vertically by a sheet of volcanic rock called a dyke. It is clear that the sedimentary rock was deposited and folded before the dyke was squeezed into place.
By looking at other outcrops in the area, our geologist is able to draw a geological map which records how the rocks are related to each other in the field. From the mapped field relationships, it is a simple matter to work out a geological cross-section and the relative timing of the geologic events. His geological cross-section may look something like Figure 2.
Clearly, Sedimentary Rocks A were deposited and deformed before the Volcanic Dyke intruded them. These were then eroded and Sedimentary Rocks B were deposited.
The geologist may have found some fossils in Sedimentary Rocks A and discovered that they are similar to fossils found in some other rocks in the region. He assumes therefore that Sedimentary Rocks A are the same age as the other rocks in the region, which have already been dated by other geologists. In the same way, by identifying fossils, he may have related Sedimentary Rocks B with some other rocks.
Creationists would generally agree with the above methods and use them in their geological work.
From his research, our evolutionary geologist may have discovered that other geologists believe that Sedimentary Rocks A are 200 million years old and Sedimentary Rocks B are 30 million years old. Thus, he already ‘knows’ that the igneous dyke must be younger than 200 million years and older than 30 million years. (Creationists do not agree with these ages of millions of years because of the assumptions they are based on.2)
Because of his interest in the volcanic dyke, he collects a sample, being careful to select rock that looks fresh and unaltered. On his return, he sends his sample to the laboratory for dating, and after a few weeks receives the lab report.
Let us imagine that the date reported by the lab was 150.7 ± 2.8 million years. Our geologist would be very happy with this result. He would say that the date represents the time when the volcanic lava solidified. Such an interpretation fits nicely into the range of what he already believes the age to be. In fact, he would have been equally happy with any date a bit less than 200 million years or a bit more than 30 million years. They would all have fitted nicely into the field relationships that he had observed and his interpretation of them. The field relationships are generally broad, and a wide range of ‘dates’ can be interpreted as the time when the lava solidified.
What would our geologist have thought if the date from the lab had been greater than 200 million years, say 350.5 ± 4.3 million years? Would he have concluded that the fossil date for the sediments was wrong? Not likely. Would he have thought that the radiometric dating method was flawed? No. Instead of questioning the method, he would say that the radiometric date was not recording the time that the rock solidified. He may suggest that the rock contained crystals (called xenocrysts) that formed long before the rock solidified and that these crystals gave an older date.3 He may suggest that some other very old material had contaminated the lava as it passed through the earth. Or he may suggest that the result was due to a characteristic of the lava—that the dyke had inherited an old ‘age’.
The error is not the real error
The convention for reporting dates (e.g. 200.4 ± 3.2 million years) implies that the calculated date of 200.4 million years is accurate to plus or minus 3.2 million years. In other words, the age should lie between 197.2 million years and 203.6 million years. However, this error is not the real error on the date. It relates only to the accuracy of the measuring equipment in the laboratory. Even different samples of rock collected from the same outcrop would give a larger scatter of results. And, of course, the reported error ignores the huge uncertainties in the assumptions behind the ‘age’ calculation. These include the assumption that decay rates have never changed. In fact, decay rates have been increased in the laboratory by factors of billions of times.1 Creationist physicists point to several lines of evidence that decay rates have been faster in the past, and propose a pulse of accelerated decay during Creation Week, and possibly a smaller pulse during the Flood year.2
- Woodmorappe, J., Billion-fold acceleration of radioactivity demonstrated in laboratory, TJ 15(2):4–6, 2001. Return to text.
- Vardiman, L., Snelling, A.A. and Chaffin, E.F., Radioisotopes and the age of the Earth, Institute for Creation Research, El Cajon, California and Creation Research Society, St. Joseph, Missouri, USA, 2000. Text is available at icr.org/rate Return to text.
What would our geologist think if the date from the lab were less than 30 million years, say 10.1 ± 1.8 million years? No problem. Would he query the dating method, the chronometer? No. He would again say that the calculated age did not represent the time when the rock solidified. He may suggest that some of the chemicals in the rock had been disturbed by groundwater or weathering.4 Or he may decide that the rock had been affected by a localized heating event—one strong enough to disturb the chemicals, but not strong enough to be visible in the field.
No matter what the radiometric date turned out to be, our geologist would always be able to ‘interpret’ it. He would simply change his assumptions about the history of the rock to explain the result in a plausible way. G. Wasserburg, who received the 1986 Crafoord Prize in Geosciences, said, ‘There are no bad chronometers, only bad interpretations of them!’5 In fact, there is a whole range of standard explanations that geologists use to ‘interpret’ radiometric dating results.
Why use it?
Someone may ask, ‘Why do geologists still use radiometric dating? Wouldn’t they have abandoned the method long ago if it was so unreliable?’ Just because the calculated results are not the true ages does not mean that the method is completely useless. The dates calculated are based on the isotopic composition of the rock. And the composition is a characteristic of the molten lava from which the rock solidified. Therefore, rocks in the same area which give similar ‘dates’ are likely to have formed from the same lava at about the same time during the Flood. So, although the assumptions behind the calculation are wrong and the dates are incorrect, there may be a pattern in the results that can help geologists understand the relationships between igneous rocks in a region.
Contrary to the impression that we are given, radiometric dating does not prove that the Earth is millions of years old. The vast age has simply been assumed.2 The calculated radiometric ‘ages’ depend on the assumptions that are made. The results are only accepted if they agree with what is already believed. The only foolproof method for determining the age of something is based on eyewitness reports and a written record. We have both in the Bible. And that is why creationists use the historical evidence in the Bible to constrain their interpretations of the geological evidence.
What if the rock ages are not ‘known’ in advance—does radio-dating give coherent results?
Recently, I conducted a geological field trip in the Townsville area, North Queensland. A geological guidebook,1 prepared by two geologists, was available from a government department.
The guidebook’s appendix explains ‘geological time and the ages of rocks.’ It describes how geologists use field relationships to determine the relative ages of rocks. It also says that the ‘actual’ ages are measured by radiometric dating—an expensive technique performed in modern laboratories. The guide describes a number of radiometric methods and states that for ‘suitable specimens the errors involved in radiometric dating usually amount to several percent of the age result. Thus … a result of two hundred million years is expected to be quite close (within, say, 4 million) to the true age.’
This gives the impression that radiometric dating is very precise and very reliable—the impression generally held by the public. However, the appendix concludes with this qualification: ‘Also, the relative ages [of the radiometric dating results] must always be consistent with the geological evidence. … if a contradiction occurs, then the cause of the error needs to be established or the radiometric results are unacceptable’.
This is exactly what our main article explains. Radiometric dates are only accepted if they agree with what geologists already believe the age should be.
Townsville geology is dominated by a number of prominent granitic mountains and hills. However, these are isolated from each other, and the area lacks significant sedimentary strata. We therefore cannot determine the field relationships and thus cannot be sure which hills are older and which are younger. In fact, the constraints on the ages are such that there is a very large range possible.
We would expect that radiometric dating, being allegedly so ‘accurate,’ would rescue the situation and provide exact ages for each of these hills. Apparently, this is not so.
Concerning the basement volcanic rocks in the area, the guidebook says, ‘Their exact age remains uncertain.’ About Frederick Peak, a rhyolite ring dyke in the area, it says, ‘Their age of emplacement is not certain.’ And for Castle Hill, a prominent feature in the city of Townsville, the guidebook says, ‘The age of the granite is unconfirmed.’
No doubt, radiometric dating has been carried out and precise ‘dates’ have been obtained. It seems they have not been accepted because they were not meaningful.
- Trezise, D.L. and Stephenson, P.J., Rocks and landscapes of the Townsville district, Department of Resource Industries, Queensland, 1990. Return to text.
References and notes
- In addition to other unprovable assumptions, e.g. that the decay rate has never changed. Return to text.
- Evolutionary geologists believe that the rocks are millions of years old because they assume they were formed very slowly. They have worked out their geologic timescale based on this assumption. This timescale deliberately ignores the catastrophic effects of the Biblical Flood, which deposited the rocks very quickly. Return to text.
- This argument was used against creationist work that exposed problems with radiometric dating. Laboratory tests on rock formed from the 1980 eruption of Mt St Helens gave ‘ages’ of millions of years. Critics claimed that ‘old’ crystals contained in the rock contaminated the result. However, careful measurements by Dr Steve Austin showed this criticism to be wrong. See Swenson, K., Radio-dating in rubble, Creation 23(3):23–25, 2001. Return to text.
- This argument was used against creationist work done on a piece of wood found in sandstone near Sydney, Australia, that was supposed to be 230 million years old. Critics claimed that the carbon-14 results were ‘too young’ because the wood had been contaminated by weathering. However, careful measurements of the carbon-13 isotope refuted this criticism. See Snelling, A.A., Dating dilemma: fossil wood in ‘ancient’ sandstone, Creation 21(3):39–41, 1999. Return to text.
- Wasserburg, G.J., Isotopic abundances: inferences on solar system and planetary evolution, Earth and Planetary Sciences Letters 86:129–173, 150, 1987. Return to text. | 0.839223 | 3.266791 |
On March 9th we can see the second “supermoon” of this year, and the last full moon of winter in the northern hemisphere, (summer in the south).With the collaboration of the EELabs project, coordinated by the Instituto de Astrofísica de Canarias, sky-live.tv will broadcast live, from the Teide Observatory, the rise of the “supermoon” which will be aligned in the evening with the shadow of the volcano which tops the summit of Tenerife.
The term “supermoon” was coined only a few decades ago. The diameter of the Moon observed from the Earth varies, because its orbit is not a circle but an ellipse. It looks smaller when it is at its apogee, when its distance from Earth is a maximum, and bigger when it is at perigee, when its distance from Earth is a minimum. The “supermoon” is seen when the full Moon phase occurs at the time when the Moon is near its perigee. Its apparent diameter is then 14% bigger than its value at apogee, and its brightness up to 30% more. During the next “supermoon” its size and brightness will be greater by 12% and 29.2% respectively, compared to apogee. Using a specific number, on Monday 9th March the Earth-Moon distance will be 357, 404km compared to its maximum at apogee in 2020 of 406,690 km.
The reason that all “superlunas” are not the same is because the parameters of the Moon’s orbit are not perfectly constant, but vary due to the gravitational influence of the Sun, and to a much small degree the planets. So its period, of around 28 days, and the distances from the Earth of its apogee and perigee are continually subject to small variations over the years.
By the definition of a “supermoon” this is produced if full Moon occurs close to lunar perigee. So during this year 2020 we will have up to four “supermoons”, in February, March, April, and May. In fact this astronomical phenomenon is so usual that in general there are between three and five “supermoons” per year.
Alignment with the shadow of Teide and live broadcast
The live broadcast from the Teide Observatory will start on Monday March 9th from 18:45 UT. The astronomer of the Instituto de Astrofísica de Canarias (IAC) and administrator of the Teide observatory, Miquel Serra-Ricart will guide us through this astronomical event, during which we will see the full Moon aligned with the shadow of the volcano, just at sunset.
If we are at the summit of a mountain, close to sunset (or at dawn) it is possible to see its shadow along the line towards the Sun, but in the opposite direction. In the first moments the shape of the shadow reproduces the silhouette of the peak of the mountain, and as time passes the length of this shadow will grow as the height of the Sun over the horizon decreases, and its projection in the atmosphere ends up triangular.
Teide, because of its height, and because from its peak all the horizons are clear, is one of the best places to observe the formation and the evolution of the shadow of a mountain.
I the full moon and solar twilight are close together we can observe the shadow of Teide and the full Moon. And if in addition the time of full Moon coincides with sunset or dawn we can see a (close) alignment between the shadow of Teide and the natural satellite of the Earth, which we will see on Monday 9th.
EELabs (eelabs.eu) is a project funded by the Programme INTERREG V-A MAC 2014-2020, cofinanced by FEDER (European Fund for Regional Development) of the European Union, under contract number MAC2/4.6d/238. Five centres in Macaronesia (IAC, ITER, ULPGC, SPEA-Azores and SPEA-Madeira) work in EELabs. The objective of EELabs is to build laboratories to measure the energy efficiency of the artificial night lighting in protected natural areas in Macaronesia (the Canaires, Madeira, and the Azores).
Images and more audiovisual content about "Supermoons"
Teide shadow images and videos:
EELabs (eelabs.eu) is a project financed by the INTERREG V-A MAC 2014-2020 Programme, co-financed by the FEDER (European Regional Development Fund) of the European Union, under contract number MAC2/4.6d/238. Five centres in Macaronesia work in EELabs (IAC, ITER, UPGC, SPEA-Azores, SPEA-Madeira).
Initiation of the European project EELabs. The recent visit of the Mayor of Gúímar to the Teide Observatory sees the start of the Energy Efficiency Laboratories project, coordinated by the Instituto de Astrofísica de Canarias, for the protection of night-time ecosystems through energy efficiency.
Canaries is the best place in Europe from which to view this astronomical event
Imágenes de la SuperLuna del 10 de agosto de 2014 tomadas desde diferentes localizaciones próximas al Observatorio del Teide, en Tenerife (Islas Canarias) | 0.839649 | 3.64177 |
Astronomers have found one of the best pieces of evidence for the existence of dark matter, a mysterious quantity that pervades our Universe.
They have identified what appears to be a ghostly ring in the sky which is made up of this enigmatic substance.
Using the Hubble Space Telescope, the scientists have established that the ring formed long ago after a colossal smash-up between two galaxy clusters.
Details of the research are to appear in the Astrophysical Journal.
As the name suggests, dark matter does not reflect or emit detectable light, yet it accounts for most of the mass in the Universe.
Astronomers have long suspected the existence of this invisible "stuff" as the source of additional gravity that holds together galaxy clusters.
The clusters would fly apart if they were reliant only on the gravity from their visible stars.
No one knows what dark matter is made of, but it is thought to be a type of elementary particle found throughout the cosmos.
Researchers from Johns Hopkins University and the Space Telescope Science Institute - both in Baltimore, US - spotted the ring unexpectedly while they were mapping the distribution of dark matter within the galaxy cluster Cl 0024+17.
This cluster lies 5 billion light-years from Earth; its ring of dark matter measures 2.6 million light-years across.
Because astronomers cannot see dark matter, they must infer its existence by studying how its gravity bends the light of more distant, background galaxies.
This powerful trick, called gravitational lensing, allows astronomers to map the distorted light to deduce the cluster's mass and how dark matter is distributed in the cluster.
At first, team members thought the ring was an illusion - or artefact - in the data. But repeated attempts to make the ring disappear met with failure. Finally, the astronomers became convinced that it must be a real feature.
Ripples in a pond
In August 2006, US astronomers identified the gravitational signature of dark matter in another merging galaxy cluster. But the ring structure in Cl 0024+17 is exceptional.
"Although the invisible matter has been found before in other galaxy clusters, it has never been detected to be so largely separated from the hot gas and the galaxies that make up galaxy clusters," said co-author Myungkook James Jee of Johns Hopkins University.
"By seeing a dark-matter structure that is not traced by galaxies and hot gas, we can study how it behaves differently from normal matter."
Computer simulations of galaxy cluster collisions show that when two clusters smash together, the dark matter falls to the centre of the merged cluster and sloshes back out.
As the dark matter seeps outward, it begins to slow down under the pull of gravity and gathers together like a traffic pile-up.
Luckily, astronomers had a head on view of this collision because it occurred along the Earth's line of sight.
"It's like looking at the pebbles on the bottom of a pond with ripples on the surface. The pebbles' shapes appear to change as the ripples pass over them," Dr Jee explained.
"So, too, the background galaxies behind the ring show coherent changes in their shapes due to the presence of the dense ring."
Team member Holland Ford, also of Johns Hopkins, said: "By studying this collision, we are seeing how dark matter responds to gravity.
He added: "Nature is doing an experiment for us that we can't do in a lab, and it agrees with our theoretical models." | 0.823896 | 4.042817 |
Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have revealed extraordinary details about a recently discovered far-flung member of our Solar System, the planetary body 2014 UZ224, more informally known as DeeDee.
At about three times the current distance of Pluto from the Sun, DeeDee is the second most distant known trans-Neptunian object (TNO) with a confirmed orbit, surpassed only by the dwarf planet Eris. Astronomers estimate that there are tens-of-thousands of these icy bodies in the outer solar system beyond the orbit of Neptune.
The new ALMA data reveal, for the first time, that DeeDee is roughly 635 kilometers across, or about two-thirds the diameter of the dwarf planet Ceres, the largest member of our asteroid belt. At this size, DeeDee should have enough mass to be spherical, the criteria necessary for astronomers to consider it a dwarf planet, though it has yet to receive that official designation.
“Far beyond Pluto is a region surprisingly rich with planetary bodies. Some are quite small but others have sizes to rival Pluto, and could possibly be much larger,” said David Gerdes, a scientist with the University of Michigan and lead author on a paper appearing in the Astrophysical Journal Letters. “Because these objects are so distant and dim, it’s incredibly difficult to even detect them, let alone study them in any detail. ALMA, however, has unique capabilities that enabled us to learn exciting details about these distant worlds.”
Currently, DeeDee is about 92 astronomical units (AU) from the Sun. An astronomical unit is the average distance from the Earth to the Sun, or about 150 million kilometers. At this tremendous distance, it takes DeeDee more than 1,100 years to complete one orbit. Light from DeeDee takes nearly 13 hours to reach Earth.
Gerdes and his team announced the discovery of DeeDee in the fall of 2016. They found it using the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile as part of ongoing observations for the Dark Energy Survey, an optical survey of about 12 percent of the sky that seeks to understand the as-yet mysterious force that is accelerating the expansion of the universe.
The Dark Energy Survey produces vast troves of astronomical images, which give astronomers the opportunity to also search for distant solar system objects. The initial search, which includes nearly 15,000 images, identified more than 1.1 billion candidate objects. The vast majority of these turned out to be background stars and even more distant galaxies. A small fraction, however, were observed to move slowly across the sky over successive observations, the telltale sign of a TNO.
One such object was identified on 12 separate images. The astronomers informally dubbed it DeeDee, which is short for Distant Dwarf.
The optical data from the Blanco telescope enabled the astronomers to measure DeeDee’s distance and orbital properties, but they were unable to determine its size or other physical characteristics. It was possible that DeeDee was a relatively small member of our solar system, yet reflective enough to be detected from Earth. Or, it could be uncommonly large and dark, reflecting only a tiny portion of the feeble sunlight that reaches it; both scenarios would produce identical optical data.
Since ALMA observes the cold, dark universe, it is able to detect the heat – in the form of millimeter-wavelength light – emitted naturally by cold objects in space. The heat signature from a distant solar system object would be directly proportional to its size.
“We calculated that this object would be incredibly cold, only about 30 degrees Kelvin, just a little above absolute zero,” said Gerdes.
While the reflected visible light from DeeDee is only about as bright as a candle seen halfway the distance to the moon, ALMA was able to quickly home in on the planetary body’s heat signature and measure its brightness in millimeter-wavelength light.
This allowed astronomers to determine that it reflects only about 13 percent of the sunlight that hits it. That is about the same reflectivity of the dry dirt found on a baseball infield.
By comparing these ALMA observations to the earlier optical data, the astronomers had the information necessary to calculate the object’s size. “ALMA picked it up fairly easily,” said Gerdes. “We were then able to resolve the ambiguity we had with the optical data alone.”
Objects like DeeDee are cosmic leftovers from the formation of the solar system. Their orbits and physical properties reveal important details about the formation of planets, including Earth.
This discovery is also exciting because it shows that it is possible to detect very distant, slowly moving objects in our own solar system. The researchers note that these same techniques could be used to detect the hypothesized “Planet Nine” that may reside far beyond DeeDee and Eris.
“There are still new worlds to discover in our own cosmic backyard,” concludes Gerdes. “The solar system is a rich and complicated place.” | 0.900555 | 4.010297 |
The great astronomers of the past formulated theories and developed new ideas with simple lenses in their telescopes. Eventually, science and industrial communities partnered to develop more complex systems like the Hubble Telescope, which just celebrated 25 years of breathtaking images and discovery.
Today’s researchers can gaze farther across the universe than ever before. Telescopes, satellites, exploratory spacecraft, and manned shuttles all contribute to our study of the solar system and beyond. We’re able to spot supernovae, comb the surface of a comet, even uncover the inner workings of our own sun, and many of these missions are made possible in part by one integral component: glass.
Critical to advanced telescopes are the advanced glass components used in telescopes and aboard rovers and satellites are engineered with low thermal expansion, high chemical stability, and long-term durability, helping researchers and astronomers better understand our universe. Glass with enhanced optical properties solved the light refraction problems that Galileo and Isaac Newton couldn’t answer, and made the night sky clear for observation.
Here are just a few ways glass is key to investigating our solar system and beyond.
Eyeing the heart of our solar system: Though solar flares create beautiful visuals, the radiation they emit can disrupt communication and radar systems on Earth. Across the globe, solar telescopes equipped with ZERODUR® glass-ceramic mirror blanks keep a watchful eye on the sun to detect these bursts of energy. ZERODUR® glass-ceramic has extremely low thermal expansion, allowing giant telescopes, including the Daniel K. Inouye Solar Telescope in Hawaii, Big Bear Solar Observatory in California, and GREGOR telescope in Teneriffa, Spain, to observe the sun throughout the day without image deterioration.
Peering far beyond our solar system: Modern telescopes can detect objects and details light years farther away than early astronomers could ever see. The Keck telescope array on Mauna Kea in Hawaii includes the world’s largest optical and infrared telescopes, which also employ ZERODUR® glass-ceramic mirror blanks to observe exploding stars, measure the distance to a nearby galaxy, and capture eruptions on celestial bodies near Earth.
ZERODUR® glass-ceramic is also used for the primary mirror in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) in China. Rather than capture visual images, this telescope focuses on spectroscopic scanning of millions of stars and galaxies outside the Milky Way, and will help create large-scale models of the universe.
Interference filters also play a vital role in space discovery. For example, these filters were recently implemented in the Observatorio Astrofisico de Javalambre in Spain to assist in space observation. These extremely narrow bandpass filters enable to analyze narrow spectral regions of starlight while accurately blocking out unwanted wavelengths. Furthermore, the filters are conceived for low wavefront errors, and therefore deliver extremely high image quality.
Another glass type plays a role in the search for the most mysterious force in space — dark energy. BOROFLOAT® floated borosilicate glass — with excellent optical properties and a low thermal expansion coefficient — is an important component in the 156 spectrographs used in the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) in Texas. The spectrographs will 3-D map the universe, calculate the speed of its expansion, and reveal the composition of celestial objects. Researchers hope to uncover the underlying physics of the universes’ rapid expansion.
Shielding astronauts during blastoff and re-entry: While achieving escape velocity is an achievement in itself, doing so safely is the most important consideration for scientists and astronauts. In order to protect astronauts, space shuttles must resist the extreme heat created when leaving and entering the Earth’s atmosphere. Porous glass, like SCHOTT’s established CoralPor® 1000 glass, is one proven way to protect shuttles. It is used as the base for the NASA-developed coating that protects space shuttles — and the astronauts inside them — from harm.
Zooming in on celestial bodies from space: Photographs from space capture our imagination, from Neil Armstrong’s first photos on the Moon to the Pale Blue Dot to Curiosity’s panoramas of Mars. Cameras installed on satellites and rovers must be equipped with high-performance lenses to withstand the extreme conditions of space, which include freezing temperatures, high doses of radiation, and vacuum conditions. Special optical glass is used for the optical, infrared, and radiation-resistant lenses that allow these cameras to capture the entire light spectrum, offering researchers a more comprehensive view of the planets, stars, and solar systems near and far.
In 1969, Apollo 11’s Neil Armstrong recorded footage from the surface of the Moon with a video camera equipped with four pieces of SCHOTT optical glass. More recently, advanced camera systems took photos of Comet 67P/Churyumov-Gerasimenko during the Rosetta mission. The cameras aboard the Philae lander travelled to Comet 67P equipped with 28 specialty glass lenses that SCHOTT engineered to resist cosmic radiation during the craft’s 10-year journey from Earth.
Continuing our exploration of space with assistance from glass
The vastness of space sparks our natural curiosity and desire to understand everything around us. Generations of technological breakthroughs have increased the power and capabilities of our telescopes, and we’re able to take a deeper look at the constellations and the space far beyond them with manned missions, telescopes, and satellites. We even safely put a man on the moon, and photographed and broadcast its surface — a feat nearly unimaginable even a decade prior. Specialized glass designed for the final frontier will allow researchers to continue gazing into the vastness of space and support new missions that unravel the mysteries of the cosmos. | 0.906644 | 3.810003 |
On a flat, red mulga plain in the outback of Western Australia, preparations are under way to build the most audacious telescope astronomers have ever dreamed of – the Square Kilometre Array (SKA). Next-generation telescopes usually aim to double the performance of their predecessors. The Australian arm of SKA will deliver a 168-fold leap on the best technology available today, to show us the universe as never before. It will tune into signals emitted just a million years after the Big Bang, when the universe was a sea of hydrogen gas, slowly percolating with the first galaxies. Their starlight illuminated the fledgling universe in what is referred to as the “cosmic dawn”.
“It is the last non-understood event in the history of the universe,” says Stuart Wyithe, a theoretical astrophysicist at the University of Melbourne in Australia.
Like any dream, realisation is the hard part. In 2018, when the first of 130,000 Christmas-tree-like antennae is deployed on the sandy plains of Murchison, an almost uninhabited district of 50,000 square kilometres, it will mark 28 years since its conception.
Epic battles have brought the project to this point – most famously the six-year contest between countries to host the telescope. Australia and South Africa ended up sharing the prize. The SKA’s telescope in South Africa will be built on another flat, red flat plain – the Karoo region of the North Cape. It has somewhat less lofty ambitions – its dishes will probe only halfway to the edge of the universe. Its moniker, SKA-mid, denotes the mid-range frequencies of radio waves stretched across this distance.
Australia’s SKA-low, by contrast, will tune into the low frequencies emanating from the extremities of the cosmos. Together the two telescopes will represent “the largest science facility on the planet,” says SKA director-general and radio astronomer Phil Diamond, who is based at Jodrell Bank Observatory in the UK.
The game-changing technology that will allow us to hear the whispers of newborn stars against the cacophony of the universe doesn’t involve grinding mirrors to atom-thin smoothness or constructing dishes the size of sports fields. The disruptive technology here is supercomputing.
Once SKA-low is running, it will generate more data every day than the world’s internet traffic. Dealing with this deluge is a challenge being tackled by hefty global collaborations of academia and private enterprise – and it is by no means clear how it will be solved. “It’s a scale no one has attempted before,” says Peter Quinn, a computational astrophysicist at the University of Western Australia, and director of the International Centre for Radioastronomy Research (ICRAR) in Perth.
It will generate more data every day than the world’s internet traffic.
While international mega-science projects have been tackled before – think the European Organisation for Nuclear Research (CERN), which operates the world’s largest particle accelerator, the Large Hadron Collider – when it comes to the SKA, the potential world-changing spin-offs have never been so blazingly obvious.
CERN didn’t just find the Higgs boson – computer scientist Tim Berners-Lee created the World Wide Web to manage its information sharing. Wi-Fi was the spin-off when Australian CSIRO astronomers developed ways to realign scrambled radio signals from black holes.
Mega-corporations such as CISCO, Woodside, Chevron, Rio Tinto and Google are already positioned to collaborate with SKA astronomers around the world.
A science project of this grandeur, managed across 10 countries, involving dozens of specialist technical consortia and thousands of people, is challenging enough. The question of how to divvy up the pie for construction contracts and the commercial spin-offs that follow adds a whole new, complicated layer.
But astronomers have a great track record when it comes to teasing their way through gnarly collaborations to deliver triumphs such as the Hubble Space Telescope and the Atacama Large Millimeter Array. After nearly 25 years of wrangling, the signs are that the first binding SKA treaty will be signed early this year, committing the 10 member countries – Australia, Canada, China, India, Italy, New Zealand, South Africa, Sweden, the Netherlands and the UK – to funding and contracts for the 2018 rollout.
Even with the treaty, SKA will remain a confusing beast: not one telescope but two, located in two countries, with headquarters in a third – the UK. Despite the name, neither of the Phase 1 telescopes slated for construction actually boasts a square kilometre of collecting area. That won’t be realised until Phase 2 of the project, negotiations for which have yet to begin.
Nevertheless, as the gears of the vast project slowly grind into action, Australia is bracing to host its first global mega-science project. “It will be our CERN downunder,” says CSIRO astronomer Sarah Pearce, Australia’s science representative to the SKA board. But, she adds, “don’t expect a tour. It’s here precisely because there are very few people.”
An idea takes root
The curious thing about astronomy is that telescopes, as they grow more powerful, turn into time machines. When Galileo peered at Jupiter, he saw it as it appeared some 42 minutes earlier – the time it took for its light to reach him. Hubble’s iconic image of the Horsehead Nebula in the constellation of Orion is a snapshot of how it looked 1,500 years ago.
The astronomers who conceived the SKA had their sights set way beyond the 100,000-light-year dimensions of our own galaxy. The faint signals they seek began their journey more than 13 billion years ago, just a few million years after the Big Bang.
At that point, the hot plasma of electrons and protons had cooled enough to fuse and form the simplest atom – hydrogen. Except for a slight ripple here or there, our universe was a featureless sea of it. Today, things are different – the sea is dotted with galaxies. But how did these galactic islands form? To find out requires a telescope that can look back to the rippling hydrogen sea of 13 billion years ago. “That’s why the SKA was originally called the ‘hydrogen telescope’,” Quinn says.
Those who imagined the SKA had a lust for hydrogen. Their appetite had been whet by the Very Large Array (VLA), 27 dishes lying 80km west of Socorro, in New Mexico.
Now known as the Jansky VLA, the telescope generated some of the first detailed maps of atomic hydrogen. The bond between hydrogen’s electron and proton emits a unique 21-centimetre radio wave. Because the universe is expanding, the waves emitted from outer space have stretched by the time they reach us. The futher away, the greater the stretching; hydrogen waves emanating from the edge of the universe measure 1.5m by the time they reach Earth. It’s known as the Doppler effect; on Earth, we experience it when we hear the sound of an ambulance siren deepen as it speeds away, its sound wave stretching as it goes.
In 1990, on the 10th anniversary of the VLA, the world’s radio astronomers met to celebrate one of the New Mexico facility’s crowning achievements – mapping hydrogen in nearby galaxies. Ron Ekers, an Australian former director of the array, recalls that “everyone was on a high”.
Not content to rest on their laurels, a small group of visionary astronomers wondered how far the technology could be pushed. Egged on, Peter Wilkinson from the University of Manchester in Britain pitched the idea of reaching out to galaxies at the edge of the universe. A total collecting area of one square kilometre, he figured, should do the job.
The audacity of the proposal was amazing, Quinn says: “Most telescope improvements aim for a two-to-three-fold increase; this proposal represented a 10,000-fold increase.” That figure reflected a 50-fold increase in sensitivity multiplied by a 200-fold increase in field of view. “The goal was to see a milky way at the edge of the universe,” Quinn adds – and to scour the entire southern sky.
The breakthrough technology needed to enable this leap did not lie in fancy new telescope designs, but in the explosion of computing power and techniques able to handle massive amounts of data.
The receivers themselves could be little more than antennas. Tuned to radio wavelengths, they would pick up the extra-long waves of distant hydrogen – coincidentally the same wavelength used by many FM radio stations. “This is where the early universe is broadcasting,” says Quinn. “You just can’t hear it because it’s buried in the crackle.”
The more antennae, the greater the sensitivity – hence the planned one square kilometre of collecting surface. But the antennae don’t need to be all in one spot. Indeed, the more spread out they are, the sharper the focus.
How does a forest of radio antennae figure out where in the sky a signal has come from? Interferometry, a technique developed by British and Australian radio astronomers in the 1940s, is the key. It relies on the principle that each antenna in an array receives a signal at a slightly different time. For instance, radio waves coming from the easterly part of the sky hit the eastern-most antennae earlier than those lying further west. By electronically tweaking the delay on each, the entire forest could be made to point in a particular direction of the sky.
But using interferometry to tune into signals from the edge of the universe would have required filtering astronomical amounts of data; and that was a challenge yet to be mastered.
In 2000, a SKA steering committee led by Ekers invited proposals for a home for the telescope. Five countries responded. To help their bid, some built serious prototypes known as “pathfinders”. It resulted in an astronomical bonanza. Australia built the majestic dishes of the Australian Square Kilometre Array Pathfinder (ASKAP) and the antenna forest of the Murchison Widefield Array (MWA). South Africa built the seven dishes of KAT-7 and is building the larger MeerKAT. China began work on a prototype which paved the way for the Five-hundred-metre Aperture Spherical radio Telescope (FAST), the largest single radio dish in the world.
Geography worked against some of the contestants. The Chinese site wasn’t flat enough. The joint Brazilian-Argentinian bid was let down by a turbulent ionosphere – the uppermost layer of the atmosphere – which distorted the sought-after low frequency radio waves.
By 2006, Australia and South Africa were the last countries standing. Both laid claim to vast unpopulated regions, free of radio wave interference and with relatively placid ionospheres.
The South African site’s higher elevation was in its favour. Australia, on the other hand, had an impressive track record in radio astronomy. It boasted some of the world’s first interferometers, built in the 1940s at Dover Heights south of Sydney, and the iconic CSIRO Parkes telescope, operating since 1961.
algorithms developed to pursue SKA’s goals may be the next wi-Fi.
The contest was fierce, and for good reason: SKA’s benefits clearly stretched far beyond astronomy. “The devices and algorithms developed to pursue SKA’s goals may be the next Wi-Fi, the next multi-trillion dollar technology market,” says Steven Tingay, the former director of the MWA who now leads Italy’s SKA involvement. Whichever country hosted the SKA would be at the heart of the action, attracting and training the next generation of engineers and scientists in advanced manufacturing, telecommunications and high-performance computing.
Accompanied by the sort of media attention usually reserved for a football grand final, a competitive and secretive bidding process ensued.
In May 2012, members of the SKA organisation voted to split the array between the Australian and African sites. The South African telescope would observe radio waves from 350 MHz to 14 gigahertz, enabling it to detect signals up to six billion light-years away – a still sparse chapter in the universe’s life story. It would use dishes like those of the JVLA, but dramatically increase speed and sensitivity.
Australia’s array would detect frequencies in the range of 50 to 350 MHz – ideal for detecting hydrogen signals from the edge of the universe.
Both would rely on the development of disruptive new computation techniques.
“We believe we know how to do it, but I’m not hiding the fact that it’s a challenge,” Diamond says.
Getting to the Australian site of the SKA gives the words “isolation” and “quiet” whole new meanings. First, you make your way to Perth, itself one of the most isolated cities in the world. Then it’s another one-hour flight to the 35,000-strong port town of Geraldton. From there, bump around for four dusty hours in a four-wheel-drive until finally, on the horizon, you see a succession of towering white 12-metre telescope dishes.
You have arrived at the Murchison Radio-astronomy Observatory. The 36 dishes comprise ASKAP. Despite the name, they are not the prototype for SKA-low. That honour goes to the MWA, a rather less majestic affair that lies hidden in the nearby mulga scrub: 2,048 squat, wiry antennae, resembling a swarm of giant spiders. Unlike ASKAP, the MWA has no moving parts to point to different parts of the sky. That’s because this is a software telescope. It relies on a computer to program different delays into the antennae so signals from the same patch of sky are collected at the same time.
Amid great fanfare, MWA first came online in mid-2013. According to director Randall Wayth, it has blazed the trail for SKA-low. It is tuned to receive signals from the early universe within the bandwidth of 80 to 300 MHz. It does not have the sensitivity to detect features of the cosmic dawn, but its impressive 30-degree field of view allows it to map the entire visible sky over a few nights. The Galactic and Extragalactic All-sky MWA (GLEAM) survey, for instance, mapped bubbles of ionised hydrogen gas and quasars from up to six billion light years away.
Two trail-blazing aspects of its operation are key to SKA-low. The first is that it has pioneered methods to adjust for the distorting effects of the ionosphere above Murchison. “It’s like trying to see something at the bottom of a rippling pool,” explains Wayth. “Luckily for us, it’s usually just small ripples.”
Filtering out the ripples of the ionosphere is just one step in a multipronged data-processing operation whose ultimate aim is to deliver sharp images of the ancient universe.
Another early step reduces the noise inherent in the system. The heart of every radio telescope is an onsite computer known as a correlator. Developed through a partnership with IBM and Cisco, the MWA’s correlator compares signals from each of the 2,048 antennae. Noise is random; real signals are correlated. By accepting only correlated signals, this step reduces the data to a manageable 1% of the initial deluge.
The next phase takes place off-site. An 800 km optic fibre ferries the pre-filtered data from the desert to the Pawsey Supercomputing Centre in Perth. A mirror link also takes it to collaborators at the Massachusetts Institute of Technology in Boston, and Victoria University of Wellington in New Zealand, to be used by some 35 different science projects.
Just as a human brain must process vast amounts of data into a meaningful representation of the world, these supercomputers turn the MWA radio wave signals into pictures of the universe. There are data from across different regions of the sky, and across tens of thousands of frequencies. It is sifted by setting windows to extract “cubes” of information. Like pixels on a screen, they provide an image of the universe.
The MWA’s coarse resolution means its cubes can’t produce a sharp image. SKA, with its 100-fold greater sensitivity and 40-fold increase in resolution, will provide more cubes to show us what is actually there. But in order to do that, it must solve the data deluge problem.
Scaling up to SKA
The antenna design selected for SKA is not the MWA’s squat spider, but one that resembles a pine tree – the so-called log periodic design. Different rung lengths on the tree enable it to resonate in a wide range of frequencies – from 50 to 650 MHz. (MWA typically manages 80 to 300 MHz.) SKA will deploy 130,000 of them.
But that won’t deliver the eponymous square kilometre of collecting area. The €650 million (about US$690 million) funding for phase 1 will only deliver four-tenths of that. Nevertheless, it should have the sensitivity to detect primordial galaxies across large patches of sky.
The first phase of SKA-low will churn out raw data at a daily rate greater than the world’s internet traffic; impossible to store, or for human minds to process in real time. Ingenious algorithms will be needed to sift valuable nuggets from the deluge.
The University of Cambridge leads a consortium of 23 organisations, including Perth’s ICRAR, to develop new hardware and software systems for the task. One of ICRAR’s major software contributions goes by the name DALiuGE – an acronym for “data activated logical graph engine”. It’s also a bilingual play on the word deluge: “liu” is a Chinese character meaning “flow”.
Last June, an ICRAR team successfully ran the prototype of DALiuGE on the second-most powerful supercomputer in the world, Tianhe-2, in Guangzhou, China. Next, the team hopes to test it on the most powerful, Sunway TaihuLight in Wuxi, eastern China.
The computing challenges may be huge, but it’s not the first time the global community has taken on something so big. To solve CERN’s problem of distributed processing and information sharing, its researchers ended up developing the World Wide Web. “That changed our world forever,” Quinn says. “I suspect the SKA will do the same.”
THE WORLD WIDE WEB DEVELOPED BY CERN CHANGED THE WORLD FOREVER. ‘I SUSPECT THE SKA WILL DO THE SAME.’
SKA’s rewards are already reaching beyond science into industry. Besides CISCO and IBM, other big-name collaborators on the project include British-Australian mining giant Rio Tinto, international gas and oil company Chevron, Amazon and Intel. All are highly attuned to new ways of solving their big data problems – whether it is crunching data to make images of oil, gas and mineral deposits below the ground, or finding patterns in vast databases.
Construction in the middle of nowhere
The computational challenges of the SKA are formidable; so too are those involved in building and rolling out the infrastructure in the middle of the Australian outback. It’s a perfect job for a former army tank officer.
Tom Booler has been project manager for the MWA and part of the SKA-low team since 2011. His mission is to plan the construction and deployment of 130,000 antennas in the desert – absent a local workforce, with no construction equipment and no power grid. And that’s only the first phase of SKA-low. The second, slated for the mid-2020s pending funding, will see the number of antennas swell to about a million. The scale, cost and remoteness of the site make it one of the toughest science projects ever undertaken.
Supplying power is a major hurdle. The MWA is powered by a 1.6 MW hybrid solar-diesel power station, parts of which must be shielded to stop the radio waves it creates from interfering with the telescope. Phase 1 of SKA-low will need 2.25 MW. Phase 2 will need the power supply of a small city.
Extreme weather also has to be factored in. In 2015, nearby Milly Milly Station bore a year’s worth of rain in five months. While cattle grazers welcomed it, road closures disrupted plans at the observatory. Besides sudden downpours, Booler also has to reckon with temperatures soaring over 40 ºC in the summer months – and then there’s the desert death adder.
But one thing the shire of Murchison has going for it – and a reason it won the bid for the SKA – is the quiet. Population density is extremely low – just 115 people spread over an area the size of the Netherlands. There are no mobile phone towers or radio and television transmitters. The shire is also hushed by regulations enforced by the Australian Communications and Media Authority.
Within the observatory, every appliance gets stripped of wi-fi hardware before it arrives. The observatory control centre, which houses computers that crunch data from the existing telescopes, is the radio equivalent of an airlock, with radio-wave-proof double doors and no windows.
Inside a radius of 70km around the observatory authorities can order mobile phones be turned off. Out to 260km emissions are regulated in key radio frequency ranges.
The entire area is more than six times bigger than the US National Radio Quiet Zone, home to the Green Bank radio telescope and a population running into hundreds of thousands.
The quiet zones do not extend to high altitudes, so planes communicating with air traffic control could present a problem. To tackle that issue, CSIRO researchers have begun to investigate ways to measure the interference and remove it from the telescope observations.
As difficult as building the SKA will be, coming up with the money to bankroll it is trickier. Negotiations with the 10 participating governments for the first phase have been underway since late 2015.
But there’s a new sense of ease pervading the SKA community as it looks to an April 2017 sign-off on a binding treaty known as an International Government Organisation (IGO).
Once signed, ministers of each country will have a year to ratify it. Once ratified, researchers are confident things should roll out smoothly. There is a strong precedent: CERN is governed by an IGO, with 22 member states. “It’s a well-tested model,” says Pearce, who previously worked on computing challenges for the LHC as part of a multinational collaboration.
With SKA-low expected to come online in 2021, and be fully operational in 2024 astronomers are at last allowing themselves to get excited. “Until we can put a radio telescope on the moon, it will be the greatest advance in low-frequency radio astronomy,” says Elisabeth Mills, a radio astronomer at San José State University in California. “With such a great leap in technical capabilities, the most important advances from this telescope may be in areas we cannot even currently predict or imagine.”
Back to the cosmic dawn
We know something of the first few moments after the violent birth of our universe. A split second after the Big Bang, it was a tiny mushrooming fireball, 10 billion degrees hot and filled with a plasma of frenetic charged particles.
Over the next 380,000 years, the expanding universe cooled. Charged particles – electrons and protons – lost enough of their youthful energy to bond with each other and form the first hydrogen atoms. In this more staid universe, light from the Big Bang could at last move in uninterrupted straight lines. As space continued to expand, the light waves stretched to the length of microwaves – which we see today as the cosmic microwave background.
This much we know. The next episode remains a mystery.
At 380,000 years old, the universe was a peaceful sea of hydrogen. A billion years later, most of it was gone. We know a small percentage snowballed under the influence of gravity to form stars and galaxies. But the vast intergalactic sea of hydrogen gas disappeared, reionised into a plasma of protons and electrons. The era is known as “the epoch of reionisation”.
How did this happen? It turns out there are lots of theories, and they are almost completely unconstrained by data.
Traces of dark matter laid down in the Big Bang, slightly denser than their surrounds, may have triggered the snowballing of hydrogen into stars. But why did the intergalactic hydrogen disappear?
The leading theory is ultraviolet radiation from the first hot stars stripped the surrounding hydrogen of its electrons. But there is another contender: quasars. Quasars (quasi-stellar radio sources) are among the brightest and oldest objects in the universe. They are powered by black holes; the source of their light is the radiation emitted by accelerating gases as they are sucked towards the accretion disc. Quasars can be surprisingly ancient, appearing just 770 million years after the Big Bang.
“It’s controversial, but one exciting possibility is that it was quasars that reionised the universe,” says astrophysicist Stuart Wyithe, at the University of Melbourne, who specialises in trying to recreate this unknown period of the history of the universe. The theory also suggests that massive black holes may have played a far greater role in shaping our Universe than previously thought.
In Wyithe’s computer modelling, the ancient universe resembles Swiss cheese. The cheese is neutral hydrogen and the holes are where it has been eaten away, leaving an ionised plasma. Over a period of about 300 million years, the holes grow larger until, by about a billion years after the Big Bang, there’s almost no cheese left.
SKA-low is designed to supply theorists like Wyithe with hard data. It will have the resolution and the wide angle to map the distribution of hydrogen in the early universe and trace how it changed over time. He will combine these images with those from the Hubble telescope to try and detect what’s at the centre of those cheesy holes: stars or quasars.
Elizabeth Finkel is editor-at-large of Cosmos.
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Rendering Dark Energy Void
Dark energy observations may be explained within general relativity using an inhomogeneous Hubble-scale depression in the matter density and accompanying curvature, which evolves naturally out of an Einstein-de Sitter (EdS) model. We present a simple parameterization of a void which can reproduce concordance model distances to arbitrary accuracy, but can parameterize away from this to give a smooth density profile everywhere. We show how the Hubble constant is not just a nuisance parameter in inhomogeneous models because it affects the shape of the distance-redshift relation. Independent Hubble-rate data from age estimates can in principle serve to break the degeneracy between concordance and void models, but the data is not yet able to achieve this. Using the latest Constitution supernova dataset we show that robust limits can be placed on the size of a void which is roughly independent of its shape. However, the sharpness of the profile at the origin cannot be well constrained due to supernova being dominated by peculiar velocities in the local universe. We illustrate our results using some recently proposed diagnostics for the Friedmann models.
keywords:cosmology: observations cosmology: theory dark energy
An odd explanation for the dark energy problem in cosmology is one where the underlying geometry of the universe is significantly inhomogeneous on Hubble scales, and not homogeneous as the standard model assumes. These models are possible because we have direct access only to data on our nullcone and so can’t disentangle temporal evolution in the scale factor from radial variations. Such explanations are ungainly compared with standard cosmology because they revoke the Copernican principle, placing us at or very near the centre of the universe. Perhaps this is just because the models used – Lemaître-Tolman-Bondi (LTB) or Szekeres to date (Moffat & Tatarski, 1992, 1994; Mustapha et al., 1997; Sugiura et al., 1999; Alnes et al., 2006; Célérier, 2006; Vanderveld et al., 2006; Alexander et al., 2007; Célérier, 2007; Clifton et al., 2008; Garcia-Bellido & Haugbølle, 2008a; García-Bellido & Haugbølle, 2008b; Ishak et al., 2008; Yoo et al., 2008; Zibin et al., 2008; Bolejko & Wyithe, 2009; Célérier et al., 2009; Quercellini et al., 2009) – are very simplistic descriptions of inhomogeneity, and more elaborate inhomogeneous ones will be able to satisfy some version of the Copernican principle (CP) yet satisfy observational constraints on isotropy (e.g., a Swiss-Cheese model (Marra et al., 2007; Biswas & Notari, 2008; Marra et al., 2008) or something like that).111See Clarkson & Barrett (1999) and Barrett & Clarkson (2000) for examples of spacetimes which, although unrealistic, are globally inhomogeneous yet satisfy a version of the cosmological principle. We may instead think of these models as smoothing all observables over the sky and so compressing all inhomogeneities into one or two radial degrees of freedom (d.o.f.) centred about us – and so we needn’t think then as ourselves ‘at the centre of the universe’ in the standard way.222As argued by K. Bolejko and M.-N. Celerier, private communication. Whatever the interpretation, such models are at the toy stage, and have not been developed to any sophistication beyond understanding the background dynamics, and observational relations; in particular, perturbation theory and structure formation is more-or-less unexplored, though this is changing (Tomita, 1997; Zibin, 2008; Clarkson, Clifton & February, 2009). They should, however, be taken seriously because we don’t yet have a physical explanation for dark energy in any other form. Indeed, one could argue that these models are in fact the most conservative explanation for dark energy, as no new physics needs to be introduced.
Regardless of the details, these models raise an important question for cosmology, particularly so in the light of the dark energy problem: can we test the Copernican principle? While many would argue that it has effectively been done via the success and accuracy of the standard model, until we have a physical explanation for dark energy (and the inflaton for that matter) we are open to the accusation of having only phenomenological descriptions of two key observations in cosmology: accelerating expansion and scale-invariant initial conditions. Only a handful of tests have actually been proposed: the Goodman-Caldwell-Stebbins test, which looks at the Cosmic Microwave Background (CMB) inside our past lightcone (Goodman, 1995; Caldwell & Stebbins, 2008); and the ‘curvature test’, which checks if today’s value of the curvature parameter, , given by
yields the same answer regardless of the redshift of measurement (Clarkson et al., 2008; Uzan et al., 2008), as it must in any Friedmann-Lemaître-Robertson-Walker (FLRW) universe. A crucial issue for this test is that it requires two independent measurements: one for distances, from, e.g. Type Ia Supernovae (SNIa), and one for the Hubble rate, from, e.g. Baryon Acoustic Oscillations (BAO) or age estimates. However, recognising the difficulties posed by the requirement of independent observables that these tests require, it has recently been proposed instead that we can test the Copernican principle from SNIa alone (Clifton et al., 2008), thereby making the process much simpler than these other methods. If one demands that the void is suitably smooth at the centre, then, as argued in Clifton et al. (2008), this leads to inevitable differences from the cold dark matter () distance modulus which can be detected with future SNIa observations such as the SuperNova Acceleration Probe (SNAP). The essence of this argument is as follows. A generic LTB model has two radial functional d.o.f.. One of these is the bang time function, which controls any inhomogeneity of the big bang surface; the other may be chosen to be the radial curvature today. These functions can be chosen such that the observer at the centre observes distances and (or number-counts) exactly as one would in a model (Mustapha et al., 1997; Célérier et al., 2009). (In this scenario the curvature test would have to be performed using both radial and tangential Hubble rates – see below for definitions.) However, if the bang time function is not constant then this excites modes which are decaying (Silk, 1977); hence, if this is significant enough a factor at late times to affect these observables the models would have to be outrageously inhomogeneous at early times – this doesn’t rule them out a priori, but does mean such models would have to have their early time behaviour rigourously examined. One can argue on the basis of this that a ‘realistic’ LTB model has only one true d.o.f.. Now, if this d.o.f. is chosen to reproduce the distance modulus of a model, the void profile must be very spiky, and have a discontinuity at the origin. Although there is some debate as to whether this is unrealistic (Vanderveld et al., 2006) or not (Krasinski et al., 2009), Clifton et al. (2008) show that this, when combined with an assumption of asymptotic flatness, can be critical in deciding if SNIa contain enough information to test the Copernican principle: the distance modulus must differ significantly from the one.
In this paper we investigate this issue using the latest SNIa dataset, which includes SNIa at very low redshift (). The void profile can be made sufficiently differentiable by shaving off the spike in the void profile at any radius. Below , objects are not entirely in the Hubble flow and thus measurements are dominated by peculiar velocities, meaning that it is not possible to constrain cosmological models using the distance-redshift relation in this range. We introduce a simple void parameterisation which can reproduce the distance modulus to sub-percent accuracy, and which has a continuous parameterisation from a steep and spiky void mimicking to a smooth one. Thus we demonstrate stricto sensu that we can’t differentiate between and LTB voids using SNIa alone. However, the general gist of Clifton et al. (2008) is that the void must be very steep to mimic distances closely, and that this is unnatural. By fitting our parameterisation to the new data directly we can see if a steep void is preferred over a gentle Gaussian profile. If a steep void is preferred by the data, then, this would lend weight to . However, to fully break the degeneracy between and these void models another observable is required.
As suggested by the curvature test above, a good choice is . We use the ages of passively evolving galaxies to do this (Simon et al., 2005). This probe of the expansion rate of the Universe is still relatively new, and thus the data currently says little of significance. However, it has the benefit of being a relatively model independent method to reconstruct . In contrast to other works on this subject we don’t use tests like the BAO and the CMB. The reasoning for this is mainly that they are perturbative tests of the models and so test how perturbations evolve; this is particularly important for the BAO and small- CMB. The theory for this has not yet been worked out so we can’t say whether results we would obtain have any meaning. Although the ‘background’ part of the effect in LTB may be taken into account using the two Hubble rates in LTB (Garcia-Bellido & Haugbølle, 2008a; García-Bellido & Haugbølle, 2008b; Zibin et al., 2008; Bolejko & Wyithe, 2009), it has been assumed in previous works that the perturbations evolve as they do in FLRW – without any scale dependence in their late-time evolution – and so a comoving sphere at last scattering remains so at late times, modulo the distortion from the different Hubble rates in the radial and angular directions. However, background curvature enters the Bardeen equation for the gravitational potential, and this can vary significantly over a sphere of radius 150 Mpc in void models; this will add an important additional distortion which is not yet known, and may affect the BAO significantly.
Furthermore, in LTB models, perturbations are complicated (Clarkson, Clifton & February, 2009) because density perturbations couple to vector and tensor d.o.f.; how important this is in dissipating density fluctuations is also not known. Finally, we don’t consider CMB constraints partly for the reasons discussed for the BAO: the large-scale CMB has not been calculated. The small-scale CMB may be estimated, however, and intriguingly seems to favour a non-zero bang-time function and asymptotic curvature (Clifton et al., 2009). Though it is not yet clear how degenerate this result might be with the primordial power spectrum, which might be important because we don’t have an inflationary model for void models, this is a very interesting result. Here, however, we are really mainly concerned with what the local data tells us about the shape of the void, assuming that these voids can evolve out of perturbed FLRW, and we don’t consider CMB constraints further.
The paper is organized as follows. In §2, we describe the various void models based on the Lemaître-Tolman-Bondi metric and the kinematical quantities associated with them. Then in §3, we discuss the cosmological data that we have used to constrain the models presented in §2. §4 is devoted to the data analysis itself, and the interpretation of the results; in particular, we discuss the ability of data to constrain the smoothness and the size of the void, and a series of non-concordance diagnoses. Finally, we conclude in §5 with a summary of the main results and a sketch of future developments.
2.1 Lemaître-Tolman-Bondi models
We model the observable universe as an inhomogeneous void centered around us via the spherically symmetric LTB model with metric
where the radial () and angular () scale factors are related by
and a prime denotes partial derivative with respect to coordinate distance . The curvature is not constant but is instead a free function. We choose coordinates such that the angular scale factor is constant and . From these two scale factors we define two Hubble rates:
where an over-dot denotes partial differentiation with respect to . We denote their values today by etc. The analogue of the Friedmann equation in this space-time is then given by
where is another free function of , and the locally measured energy density is
which obeys the conservation equation
The acceleration equations in the transverse and radial directions are
We introduce dimensionless density parameters for the CDM and curvature, by analogy with the FLRW models:
using which, the Friedmann equation takes on its familiar form:
so . Integrating the Friedmann equation from the time of the big bang to some later time yields the age of the universe at a given :
(This integral can be given in closed form, but it’s rather ridiculous.)
We now have two free functional d.o.f.: and , which can be specified as we wish. However, if the bang time function is not constant this represents a decaying mode (Silk, 1977; Zibin, 2008); consequently we set throughout, which means that our model evolves from FLRW. As a result, the age of the universe is then a constant, and equal to the time today . So, by solving (11) for , we have that:
When we introduce the Hubble constant below, we shall use , which fixes in terms of , and .
2.2 Distance modulus and observables
In LTB models, there are several approaches to finding observables such as distances as a function of redshift. We refer to Enqvist (2008) for details of the approach we use here. On the past light cone a central observer may write the coordinates as functions of . These functions are determined by the system of differential equations
where , etc. The area distance is given by
and the luminosity distance is, as usual . Other observables can be calculated from these relations; in particular, the distance modulus is given by
where is the apparent magnitude of a source with intrinsic magnitude . The relative ages of galaxies may be calculated from Eq. (13) to give .
The algorithm for calculating functions of is as follows:
2.3 Void Profiles
For our main model we introduce a profile which is capable of reproducing the distance modulus to high accuracy, as well as being able to control the smoothness at the centre of the void via the parameter . The parameterization is given by (for and )
where and are the value of at the centre of the void at infinity, respectively. The parameter characterizes the size of the void, but a more useful quantity is the full width at half-maximum (FWHM), calculated by solving
for numerically. (We assume is even about so that .)
The parameter is chosen so that when is finite this function is at the origin (its first and second derivatives are well-defined and equal to zero at ). In the limit we have
which can give an extremely good fit to the distance modulus – at the expense of not being differentiable at the origin. The parameter gives us the power to control the sharpness of the void at the origin: the larger is, the steeper the void; the smaller is, the flatter the void is at the centre. Finally, note that the indeterminate form of at is only due to the form of the parameterization: we can analytically continue the function (17) to include :
In Fig. 1, we show this void for different values of .
In addition to the parameterization given by Eq. (17), we also considered the following void profiles:
Typically we will fix , so that the spacetime is asymptotically flat, in keeping with generic predictions from inflation. However, early-universe models which might produce a void of the kind we are considering have not been explored (although see Linde et al. (1995)). On the other hand, because we have set the bang time to , the models we consider evolve from a perturbed FLRW model at early times (the void has at last scattering), so this may conceivably be natural.
It is known that there exist LTB models which can give the FLRW distance modulus exactly for a central observer (Mustapha et al., 1997; Célérier et al., 2009; Yoo et al., 2008). Profile #1 is a void parameterisation which can accurately mimic to high precision. If we assume and perform a least-squares fit of the void to models for , then we find that all of the profiles given can reproduce the distance modulus of to sub-percent accuracy – see Fig. 2. Model #1 can produce a distance modulus to very high accuracy, which requires (a spiky void). The corresponding radial profiles for our 5 different best-fitting to void models, as well as their distance moduli and effective deceleration parameter (defined below by Eq. (24)) are shown in Fig. 3. For Model #1, even though the distance modulus is effectively the same as that of FLRW, the deceleration parameter is noticeably different; this is because the Hubble rates are different.
Finally, note that with , voids 2-5 have 3 parameters (including ), which is the same as a curved model, while #1 has 4. Note also that the parameter has dimensions of length, an issue we will return to.
2.4 Physical length scales and the distance modulus
In LTB models, subtleties arise concerning the relation between and the magnitude-redshift relation. In the FLRW case, since is just a magnitude offset related to the intrinsic (absolute) luminosity of a SNIa, it is usually removed from the analysis by marginalizing over it. The intrinsic absolute magnitude of SNIa’s is poorly constrained, and since this value and the value of are degenerate in , the Hubble constant is poorly measured by SNIa.
In an LTB model we have two length scales which are independent: the Hubble length, , associated with the expansion time, and the void scale depending on the physical ‘size’ of the underdensity. In the models considered here, this may be characterized by the parameter or the FWHM. The ratio of these two scales enters as a dimensionless number, and this must therefore have a physical significance. Thus, when we change keeping the void scale fixed this will be reflected in the distance modulus in a non-trivial way, namely, if one rescales the distance by , in the void profiles this becomes .
As a result, higher (lower) values of not only shifts the distance modulus curves down (up), but it also affects the overall shape too. This is shown in Fig. 4, where we can see that the shape of the function changes with . If were held fixed when is changed (for example by fixing in units of Mpc rather than Mpc, say), this would compensate for this effect and then would be a pure normalisation of the distances. However, linking the two independent scales in this way is rather restrictive.
This is an important issue, and, as far as we are aware, has not been previously considered. This means that the shape and size of our best fit void model is dependent on the value of we obtain when we fit the voids to data. With SNIa being able to poorly constrain the value of , this leads to an additional uncertainty in the best-fitting parameters obtained. The best-fitting value of as indicated by the latest supernova dataset is clearly not in agreement with other measurements, such as that found by the HST Key Project using Cepheid variables. However, we estimate that the additional uncertainty in void models is below the level, and as such does not play a significant role in the current error budget. Future studies of inhomogeneous models, be it globally LTB models as in our case, or mass-compensated ones in other cases (see e.g. Krasiński & Hellaby (2004), Alexander et al. (2007)), will need to consider the effect of on their results, possibly by fitting the supernova light-curves simultaneously with the model.
3 Cosmological Data
In this paper, we confront each of the 5 void models we introduced in the last section with the largest sample of SNIa to date; the Constitution dataset consisting of 397 SNIa (Hicken et al., 2009b), as well as the data (Simon et al., 2005), consisting of 10 points when we include the HST Key Project value of the Hubble constant, kmsMpc (Freedman et al., 2001).
The Constitution dataset of SNIa (Hicken et al., 2009b) is comprised of a large sample of nearby () objects (Hicken et al., 2009a) combined with the Union dataset (Kowalski et al., 2008) which covers a redshift range up to . This sample comprises 397 spectroscopically confirmed SNIa, making it the largest publicly available and uniformly analysed SNIa dataset to date. An additional intrinsic dispersion of = 0.12 is added to the errors of each supernova to better estimate the error due to the uncertainty in absolute magnitude of these events.
In §4 we consider several other supernova datasets. These samples do not include the large number of SNIa’s at low redshift that comprise a large proportion of the Constitution dataset. The Davis et al. dataset (Davis et al., 2007) combines SNIa’s discovered from the ESSENCE (Equation of State: SupErNovae trace Cosmic Expansion) survey with those from the High-Z release to produce a sample of 192 objects. The Union dataset (Kowalski et al., 2008) comprises 307 objects that have been combined from other publicly released datasets, whilst the ConstitutionT sample (Wei, 2009) uses the Constitution dataset described above, with 34 SNIa removed in order to make the sample be in better agreement with other SNIa datasets (not to mention the model!).
The expansion rate of the Universe, has been constrained using the differential ages of passively evolving galaxies as determined by fitting SED templates to their spectra. Using data from the Gemini Deep Survey (Abraham et al., 2004) and a sample of field early-type galaxies (Treu et al., 1999, 2001, 2002) along with two radio galaxies (Dunlop et al., 1996; Spinrad et al., 1997; Nolan et al., 2003), Simon et al. (2005) were able to constrain the evolution of for . In this analysis we include the measurement of the local value of as determined by Freedman et al. (2001) to make 10 data points, but note that a recent, more accurate measurement of (Riess et al., 2009) and additional points (Stern et al., 2009) have since been determined, and would place somewhat tighter contraints on the models considered in this work.
Thus this analysis uses two independent probes of the expansion history of the Universe. Other work, such as Zibin (2008), combine supernova datasets with other probes, such as BAOs and CMB measurements; however, these are not considered in this analysis, as explained in §1, since the growth of perturbations has not been properly explored in LTB cosmologies and thus approximations to relations may not be valid.
4 Data Analysis
4.1 Overview of Numerical and Statistical Method
We made use of the publically available easyLTB Fortran90 code provided by Garcia-Bellido & Haugbølle (2008a) to run through more than a million different parameter values, simultaneously computing , and the statistic for each model with the intent of finding the best-fitting parameters for the voids considered. The code is setup to compute for the SNIa (), BAO () and CMB data (), but we have left the testing of the LTB models against the last two for future work due to the fact that these quantities are affected by the growth of structure in the universe. On the other hand, we have added the Hubble rate data into our analysis, and we have used the longitudinal Hubble rate as our model prediction, since (Simon et al., 2005) determined via measurements, which in the LTB case (see Eq. (13)) is related to . The main reason for adding the data into our analysis is because, as shown in §2, all of our void parameterizations can mimic , making it impossible for us to distinguish between two such models if the data prefers ; so using in addition to the SNIa data (which we refer to as SNIa+H) allows us the further opportunity to find detectable differences between and LTB void models. The easyLTB code is not set up to compute models in which . For this analysis, we modified the code to allow to take on any value, as required by our oscillating voids, although for our main investigation we have fixed to 1.
Regarding the fitting of our void models to data, we computed the statistic, and associated reduced , , to determine the goodness of fit of the model to the data. Cases where indicate that the additional intrinsic dispersion added to the type Ia supernova error estimates is a conservative choice. On top of this, the confidence limits on each of the parameters was calculated using their likelihood distributions.
4.2 Pointy or Smooth?
As demonstrated earlier, void models that are pointy at the origin are capable of reproducing to arbitrary accuracy. However, what level of smoothness/sharpness at the origin do the SNIa data demand?
In Table 1, we show the best-fitting model parameters of void #1 when fitting to the samples described in §3. The Davis et al. sample (Davis et al., 2007) (A), the Union sample (Kowalski et al., 2008) (B), the original Constitution sample (Hicken et al., 2009b) (C), the Constitution sample with intrinsic dispersion added (D, our principle SNIa dataset) and finally the ConstitutionT sample (Wei, 2009) (E) are considered.
From these results we see that the best-fitting is different for different data sets. The reason is as follows: in the older data sets such as A and B, there are few to none low-redshift SNIa, so that is essentially meaningless, although, as shown in Table 1 and Fig. 5, the data sets given by A and B choose sharp voids naturally. On the other hand, with the abundant low-redshift SNIa in data sets C-E, can play an active role in determining the gradient of the profile around the origin, and, in particular, these data sets favour , corresponding to a void that is very smooth around the origin. This supports the claim by Clifton et al. (2008) that “realistic” voids should be smooth around the origin. Moreover, as Fig. 6 shows, void model #1 turns out to be flatter around the origin than the Gaussian model (#2). Note that even with the next generation of SNIa measurements, a very low distinction will not be realistic, since below SNIa are dominated by peculiar velocities and are not properly in the Hubble flow – indeed, a cosmological model becomes a bit meaningless on such small scales.
In Table 2 we show the best-fitting parameters for void models #2-5 after fitting them to the Constitution SNIa sample with intrinsic dispersion added (D). It is interesting to note that all of these models fit the SNIa data equally well compared to void model #1 – see Table 1. In addition, the FWHM of each void is roughly the same. Therefore, the simple void profiles such as the ones we have studied can all agree on the characteristic size that a void should be to fit the data, implying that one could effectively use any of these toy models in order provide a reasonable estimate of the physical size a typical void should be in order to fit the data. Comparing the ’s of the voids (model #1 included) with that of the model in Table 3 we obtain a similar (although slightly better) fit to the SNIa data as flat .
Given the difficulty of distinguishing LTB voids from using the SNIa data alone, we performed a combined analysis of the SNIa sample denoted D above with the data. In Table 4 we show the best-fitting parameters from SNIa+H data for each of our 5 void models, along with the corresponding ’s and FWHM. Notice again that the , and values for the voids are not only comparable to that of (see Table 3), but are slightly lower. In Fig. 7 we show the resulting void profiles for the best-fitting to SNIa+H data. The sizes (FWHM) of the voids are slightly larger (by roughly 1 Gpc) in this case compared to that of the fit to SNIa case. This is a result of the fact that the fit to by itself favours enormous voids (FWHM 65 Gpc!), and thus when combined to the SNIa data, we obtain bigger voids.
In Fig. 8 we show the best-fitting to SNIa+H data residuals (top panel) and Hubble rate (bottom panel) for each of our 5 different void models, as well as that of and EdS. In each case, the respective data points are overplotted (grey circles), along with 1- error bars. To illustrate the difficulty in distinguishing these voids from that of using SNIa data alone, in Fig. 9 we plot the magnitude difference between the two models after fitting our 5 different voids to the SNIa+H data.
4.3 Likelihood Contours
In this section, we explore the degeneracies between all the possible pairs of parameters by constructing joint-parameter likelihood contours, and also determine the likelihood distributions of each parameter from SNIa and SNIa+H constraints for void model #1.
Table 5 shows the marginalized best-fitting parameters for void model #1 with 95 per cent confidence limits, from fitting to SNIa and SNIa+H data, where the priors are also given. We see again that the main difference between the parameter values in the SNIa and SNIa+H cases is the value of : the SNIa+H case yields a higher value for , which arises from the fact that, when fitting void models to data only, extremely large () Gpc and empty () voids are the ones that give the minimum , so when combining with the fit to SNIa results which has a lower value for , it is only natural that is then larger in the fit to SNIa+H case than in the fit to SNIa case only. Notice in the column for the smoothness parameter (or log as shown), that the best-fitting values are roughly 3 orders of magnitude larger than that in the unmarginalized case (see Tables 2 and 4), indicative of sharp, spikier voids. Also note that there is no upper bound on , only a lower one, but we shall return to this topic in a moment.
In Fig. 10 we show the joint-parameter likelihood plots from SNIa+H constraints. The inner, red-filled regions represent the 68.3 per cent confidence level, the orange regions 95.4 per cent, and the off-yellow regions correspond to the 99.7 per cent level. The crosses indicate the positions of: the best-fitting to SNIa data (blue), the best-fitting to data (green), the best-fitting to SNIa+H data (cyan), and the best-fitting marginalized (black), parameters.
Let us quickly discuss the degeneracies that exist between the parameters. The strongest degeneracies are between all the possible pairs of , and , and can be interpreted as follows: in order to give the same , if one wants a larger void (larger ), then must decrease , and the void must be sharper at the origin (larger ), and vice versa. The degeneracies between those same parameters and are less obvious, but still present: emptier and sharper voids require a larger , whereas a larger void needs a lower in order to give similar , and vice versa.
In Fig. 11 we show the one-parameter likelihood distributions for each parameter from SNIa+H constraints. The vertical lines correspond to: the best-fitting to SNIa (blue, space-dashed), best-fitting to (green, dot-dashed), best-fitting to SNIa+H (cyan, solid) and marginalized best-fitting (black, dashed), parameters. Notice that and are fairly well constrained, whereas and, even more so, , are very poorly constrained individually owing to a degeneracy between them; taken together, however, the constraints in the plane are reasonable. Note that is not constrained from above because is the -void by construction.
4.4 Which model is most preferred?
According to the statistic, the void models considered here are, very slightly, favoured over . However, there are more sophisticated techniques applicable to model selection, such as the (corrected) Akaike information criterion (AIC) (Akaike, 1974)
where is the number of parameters and the number of data points, and the Bayesian information criterion (BIC) (Schwarz, 1978)
A lower AIC or BIC implies a more favoured model. In Table 6 we summarize the AIC and BIC values for each void model as well as that of .
Using the AIC criteria we can see that all models are more-or-less equally favoured, whilst the BIC, which heavily penalises additional parameters, moderately disfavours void model #1, in comparison to the remaining void models and .
4.5 Non-Concordance Diagnostics
Finally, we consider quantities that can serve as useful conceptual tools for distinguishing FLRW/ models from LTB models. Because the voids are really just toy models, constructing diagnostics from models allow us to visualize what our real constraints on are.
Consider the standard deceleration parameter in FLRW models which depends purely on the Hubble rate and the observable redshift:
In testing for acceleration in FLRW models, we would like to ideally constrain this function directly from data (Mörtsell & Clarkson, 2009). Now, using Eq. (13), we can define an effective deceleration parameter in void models as
We anticipate, given the results of Vanderveld et al. (2006), that models containing a weak-singularity would have , and models without the singularity would give .
In Fig. 12 we show the effective . These all have which is expected for smooth voids. It is interesting to note that Shafieloo et al. (2009) find for various classes of dark energy models within the FLRW paradigm when using the same datasets we consider here. In fact, it is worth comparing our with the form they find when they fit only SNIa – they are qualitatively very similar.
We may also consider an effective dark energy equation of state for the void models which we define as
where is the comoving angular diameter distance. This is the EOS which, in a flat FLRW dark energy model with energy density gives the comoving angular diameter distance . This gives us another nice way to visualize the differences between our voids and more standard dark energy functions used in the standard model. We show in Fig. 13 this function for our best-fitting void models. Note the apparent phantom behaviour for moderate redshift.
Finally we consider two tests which have recently been proposed. The first is a test for the flat scenario:
is zero in the concordance model (Zunckel & Clarkson, 2008).
The second test is a much more general test of a FLRW geometry (Clarkson et al., 2008).
should be constant for any FLRW dark energy model, and
should be zero. The utility of these tests is that they can be used independently of any model at all. Considering these functions in our void models helps us visualize the difference from FLRW in terms of observable functions. This is shown in Fig. 14. Note that for , our best-fitting voids produce a curve which is very similar to that found by Shafieloo et al. (2009) considering FLRW dark energy models.
In this work, we have discussed LTB void models as solutions to the dark energy problem, and have considered how to constrain them with cosmological data. Of particular interest is the steepness of the void near the centre of symmetry, as well as the need to combine independent data sets in order to distinguish voids from .
As far as SNIa and distance data are concerned, it is often claimed that to fit the data a spiky void near the centre is required; this is not the case. To reproduce the distance modulus exactly, one needs a void with a point at the origin; if one fits the actual data, and not a prediction of the model, smooth voids are perfectly compatible with observations, and their likelihoods make them indistinguishable from a scenario. By introducing a new parameterization we can smoothly parameterize away from the “-voids”, to test specifically how steep the void would have to be.
Moreover, we have included data in the hope of removing the degeneracy between a class of voids and the models. Unfortunately, current uncertainties on the age measurements do not yet allow for such a discrimination between the models, with only the void model with an additional parameter being moderately disfavoured by the BIC compared to . All other models are equally favoured by current datasets.
On the other hand, a careful look at the joint constraints from SNIa and data provides evidence for a robust estimation of the void size through the full width at half maximum. Indeed, in agreement with previous results, we have found that the size of the void is of order 6 Gpc. This estimation appears to be fairly independent on the parameterization of the void profile.
Finally, we have illustrated how our void models look when viewed in terms of standard FLRW functions. For example, the voids, interpreted through the lens of a flat dark energy fluid give a which has phantom behaviour at intermediate redshifts, and a deceleration parameter which is positive for low redshift. These profiles may be usefully considered as signatures of voids. Furthermore, we have also shown profiles for , which is constant only for flat , and which is constant in any FLRW model whatsoever. These will be very useful diagnostics in future studies of dark energy because they allow us to measure deviations from flat and FLRW models respectively in a model independent way. By seeing what they look like in void models, we understand further the range of non-concordance behaviour possible in these diagnostics. It is rather interesting to note, in fact, that the effective deceleration parameter, as well as the effective matter density predicted by LTB models look very similar to previous estimations of these quantites relying on a parameterization of the equation of state of Dark Energy (Shafieloo et al., 2009).
As a final remark, recent constraints on non-standard cosmologies were presented in Sollerman et al. (2009) using the first-year Sloan Digital Sky Survey-II (SDSS-II) supernova results (Frieman et al., 2008) in combination with other data, such as the latest BAO and CMB measurements. In particular, using a simple Gaussian void profile allowing to vary, Sollerman et al. (2009) demonstrate that with this new dataset LTB models are still capable of fitting the SNIa-only data better than the model.
However, Sollerman et al. (2009) do not find evidence that the additional d.o.f. they allow when compared to our Gaussian profile is supported by the latest dataset. This dataset contains new SNIa, which now fill in the gap around , but lack the recent low redshift supernovae that are included in the Constitution dataset. We note that their conclusion that LTB models are a worse fit than are as a result of using BAO/CMB data which we do not use here for the reasons discussed above. Thus, we expect that their new SNIa data will affect our conclusions only marginally.
This work strongly suggests the importance of testing LTB models with further observations such as CMB and BAO, jointly with SNIa and age measurements, in order to discriminate between models. Such analyses, however, will rely on a careful implementation of structure formation and CMB emission in an LTB background as initiated in Clarkson, Clifton & February (2009). This will be the topic of forthcoming studies.
We thank Timothy Clifton for very helpful discussions. CC is supported by the National Research Foundation (South Africa). MS is supported by SKA / KAT (South Africa). JL is supported by the Claude Leon Foundation (South Africa). SF is funded by the National Astrophysics and Space Science Programme (South Africa) and the SKA. The authors would also like to thank Seshadri Nadathur for pointing out minor corrections with a previous version of this manuscript.
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Image of the Sun taken from SOHO spacecraft
Today (2nd Dec 2010) marks the 15th anniversary of the launch of SOHO – the world’s largest and most successful solar space mission.
The Solar and Heliospheric Observatory (SOHO) mission, a joint programme between the European Space Agency (ESA) and NASA, studies the Sun’s interior, the Sun’s atmosphere and the solar wind.
SOHO moves in a halo orbit around the L1 Lagrange point, 1.5 million kilometres from the Earth. This location allows uninterrupted observation of the sun, with all SOHO instruments observing continuously, 24-hours a day.
Over 3,700 papers using SOHO data have been published in refereed journals since the launch, representing the work of over 3,000 individual scientists. Virtually every living solar physicist has had access to SOHO data.
The UK has very strong involvement in SOHO, primarily through the Coronal Diagnostic Spectrometer (CDS) which was built at the Rutherford Appleton Laboratory, including contributions from the UCL Mullard Space Science Laboratory and several foreign partners.
The CDS instrument is managed from the operations centre at RAL Space. The CDS team, led by the Principal Investigator, Dr Andre Fludra, receive and process observing requests from the world-wide research community, prepare daily science plans and send them to their instrument operators at NASA for uploading to the spacecraft. Over the 15 years, the RAL team have worked closely with UK research groups at 15 universities across the country, and also collaborated with 60 groups world-wide.
Dr Fludra, who has been involved in the SOHO CDS project for 16 years, including eight years at NASA Goddard Space Flight Center, said, “One of many things I enjoy in my PI role, is the opportunity to meet and interact with hundreds of users of the CDS instrument which include a significant fraction of the world-wide solar physics community. For many years, many of them were involved hands-on in preparing the observing plans for the instrument. A few years ago we streamlined the process and our project staff now do all the science planning.”
Recently, both NASA and ESA approved a further 2-year extension of SOHO operations. SOHO will continue to play a lead role in the early warning system for space weather, detecting mass ejections leaving the Sun’s corona and heading towards the Earth.
The UK instrument, CDS, remains as versatile as ever and continues observing all areas on the sun, often focusing on regions of concentrated magnetic field emerging on the Sun’s surface, which contain hot plasma emitting strong EUV radiation, and are seats of violent flares. The numbers of these ‘active regions’ are finally picking up after a mysteriously prolonged solar minimum that lasted a year longer than expected. The almost unbroken 15-year record of CDS observations will help unravel this mystery if extended for a little longer and aid understanding of the solar activity cycle. Two or three more years of observations are needed to catch the moment when the Sun’s magnetic fields will reverse their polarity again (this happens every 11 years) and the magnetic field in the entire heliosphere will respond accordingly. This response is seen in such unusual ways as, for example, modulated numbers of galactic cosmic rays reaching the Earth.
What is CDS?
The Coronal Diagnostic Spectrometer records emission from the solar corona which is the hottest part of the solar atmosphere. CDS is sensitive to very short wavelengths of light, called extreme ultraviolet. A spectrometer separates individual wavelengths and measures intensities and profiles of spectral emission lines.
What is a spectrometer?
The principle of observing the ultraviolet spectrum is similar to that when a prism separates white light into a rainbow of distinct colours. However, the extreme ultraviolet radiation is dispersed using reflective gratings instead of a prism. It is invisible to the human eye and can’t penetrate the Earth's atmosphere. It has to be observed from space. By analyzing ultraviolet emission, recorded by the CDS spectrometer, we can learn a huge amount of detail about the Sun’s atmosphere and derive the temperature, density, chemical composition, and motion of plasma in the various atmospheric layers.
For more information please contact: RAL Space Enquiries | 0.841487 | 3.085308 |
It’s pretty well-known these days that the spherical shape of the earth was discovered by ancient observers. As I wrote in an older post, the turning point seems to be a little before 400 BCE in Greece. Before that date, all reports have the earth as flat; after 400, round-earthers pop up quickly, and there are only a handful of flat-earthers. Flat-earthism has never been anything more than a fringe opinion since then, in any place that had access to their findings.
What’s obscure, though, is this: how exactly did the Greeks discover it? What was the key piece of evidence?
|A ship receding over the horizon. (NB: This is not how the ancients discovered the shape of the earth.) Notice the distortion caused by refraction. Source: ‘Mathias Kp’, preview image for ‘Ship sailing into the horizon’, YouTube, Feb. 2016.|
Ancient Greek philosophers argued earth was a sphere, on several grounds:The big myth here is the thing about ships going over the horizon. Weinberg’s first point is completely imaginary: ancient writers who discuss evidence for the earth’s shape talk about matter falling towards local minima in the earth’s surface, not about ‘perfection’. The second point, about ships, doesn’t appear in any ancient Greek source. It’s a distorted second-hand report of a low-quality Roman source who didn’t know what he was talking about. The third point isn’t precisely what the ancient sources say, but close enough. The fourth point is the most accurate: it does appear in surviving ancient accounts, Aristotle and Ptolemy.
- Sphere a "perfect" shape.
- Ships disappear over horizon.
- Positions of constellation above horizon change as one goes north or south.
- Earth casts round shadow on moon during a lunar eclipse.-- Prof. David Weinberg, Ohio State, A161 lecture notes
|Note: The lecture notes have some other errors too, especially in the bit about Eratosthenes. Most of them are copied from Carl Sagan’s inaccurate treatment in Cosmos (1980): I’ve dealt with that in an earlier post. The thing about the well is untrue. Two more specific points: the angular distance between Eratosthenes’ cities was 7.2°, not 7.5°; and his calculated circumference was ca. 46,600 km, not the 39,300 that Weinberg states. The standard Greek stadion was 185 m, plus or minus a metre. It’s true there’s some confusion over the length of the stadion, thanks to some variations, and some misreporting in the early 20th century, but the 185 m standard really is unproblematic: see here for more discussion. Anyway, Eratosthenes’ high figure comes from the fact that he didn’t have great figures for the distances between cities. His data seem to have been based on traditional measures of Egypt dating back to well over a thousand years before his lifetime.|
The problem is that it doesn’t actually work very well. Not because it’s false! Ships do indeed descend past the horizon.
It’s because human eyesight isn’t good enough. Sure, with a really good zoom, or a telescope, it’s possible to observe the phenomenon. But most people’s eyesight can’t resolve details that fine.
|A Nikon P900 can see this, but your eyes might not be up to the task: the schooner Denis Sullivan, photographed from Frankfort, Michigan, 2 July 2016. The ship is apparently about 18 km offshore, judging from how much of it is concealed. The height is 29 m. I assume that about a third of it is concealed by the horizon, and camera height at 2.5 m above sea level. At that distance, the angular size of what’s visible here would be about 0.06°, less than an eighth the diameter of the moon. According to Wikipedia, someone with 6/6 vision (20/20, for American readers) can discern contours 1.75 mm apart at a distance of 6 m. That’s an angular size of 0.0167°. The sails appear 3.6 times larger than that, so the feat is technically possible. But only about a third of people have 6/6 vision. Calculations are based on Walter Bislin’s Advanced Earth Curvature Calculator, and account for atmospheric refraction. Photo source: MLive.com.|
AristotleWhen Aristotle discusses empirical evidence for the earth’s shape, in On the sky 297a-298a, the evidence that he actually mentions is as follows:
- Gravity -- or as Aristotle puts it, ‘the nature of mass to be borne towards the centre’ (τὸ φύσιν ἔχειν φέρεσθαι τὸ βάρος ἔχον πρὸς τὸ μέσον) -- ensures that all parts of the earth come to rest at a local minimum, so the resulting shape must be roughly spherical.
- The earth’s shadow on the moon during a lunar eclipse is always circular, and only a sphere has a shadow that is invariably circular.
- Even a relatively short journey to north or south changes which stars are visible.
From all this, then, it is clear that not only is the earth’s shape curved, but also that it is not a huge sphere. Otherwise people would not be able to see it so quickly, when they move only a short distance. ... All the mathematicians who try to calculate the size of its circumference say that it is about 400,000 (stadia, i.e. 74,000 km).Even that figure is too high, obviously, and a century later Eratosthenes came closer.
-- Aristotle, On the sky 298a.6-8, 15-17
PtolemyPtolemy’s evidence for the earth’s shape, Almagest i.1.14-16 (ch. i.4), is a bit different:
- Lunar eclipses take place at the same time for all observers, but they are reported at an earlier hour by observers further east, and at a later hour by observers further west; and the difference in hour is proportional to the east-west distance separating the observers.
- Alternative shapes for the earth -- concave, plane, polyhedral, cylindrical -- are ruled out by various astronomical observations (omitted here).
- Travelling north or south changes which stars are visible in the sky, and the change is proportional to the north-south distance travelled.
- Observers on a ship moving towards a mountain see the mountain gradually rising up out of the sea as they approach.
|Samothraki seen from Thasos, 75 km away. Photo by Borislav Angelov. Source: Google Maps.|
The photo is taken from the edge of the shore, so let’s assume eye height at 2 m. A basic geometrical calculation would have it that the bottom 394 metres of the island are concealed by the earth’s curvature. However, we also need to account for atmospheric refraction. The vertical distortion from refraction actually reduces the effect of the earth’s curvature, so that distant objects are more visible.
|Diagram illustrating the relationship between a distant object’s actual location, and the place where it appears as a result of refraction. Source: Walter Bislin’s Calculator.|
Now, when I said mountains, you probably thought of Mt Olympus, the highest peak in Greece at 2917 m. Actually, Olympus doesn’t work well for this. But let’s do the calculation anyway.
|Mt Olympus seen from Sani, Halkidiki, 80 km away. Source: Sani Resort website.|
Basically, for best results, sail towards islands.
PlinyThere’s just one ancient writer who mentions the trope of ships going over the horizon: dear old Pliny the Elder.
It is the same reason why land is not seen from ships, but is visible from ships’ masts. Also, when a ship is sailing far away, if a shining light is attached to the top of the mast, it appears to go down gradually and is finally concealed.So, this line is the ultimate source of the myth. It isn’t hard to imagine that this is an experiment that someone might actually have tried.
-- Pliny, Natural history 2.164
But notice the difference. In the popular myth, you’re supposed to discern the contours of a distant ship, unaided. In Pliny’s version, it’s the light that you’re supposed to observe descending into the sea. That’s much easier to believe: a light-emitting source is way, way more visible than distant contours.
Still, I’m pretty sure Pliny isn’t the source that professors teaching the history of astronomy are getting it from. (If they were reading ancient sources, they’d know Aristotle doesn’t talk about spherical ‘perfection’.) I’m betting the modern myth is filtered through a much more recent source: Copernicus.
It is understood by sailors that waters also press down into the same shape (a sphere): for land which is not visible from (the deck of) a ship is regularly seen from the top of the mast. Conversely, if something shining is placed at the top of the mast as the ship is moved away, it seems to people remaining on shore to go down gradually, until at last it is hidden as if setting.Weirdly, Copernicus bases the structure of his introduction on Ptolemy, but his arguments are inspired by Pliny -- the worst possible choice, out of the three ancient sources we’ve looked at so far.
-- Copernicus 1543: 1b (ch. i.2)
Because Pliny is not a good source of evidence for the shape of the earth. OK, yes, he does say it’s a sphere. But most of his ‘evidence’ is ridiculous. He thinks mountains in the Alps are over 50 Roman miles high, that is 74 km (NH 2.162); he thinks the earth’s shape is demonstrated by the shape of drops of water; that a convex meniscus on a liquid surface is a consequence of the earth’s curvature; that heavy objects placed in a cup of liquid don’t cause it to overflow, because the surface acqures a convex curve (NH 2.163).
If you’re looking for empirical evidence for the earth’s shape, Pliny should not be your main resource. Copernicus, I’m afraid, gets C+ for treatment of textual evidence.
CleomedesCleomedes’ discussion of the earth’s shape is similar to Ptolemy’s, in that he spends time rejecting alternative shapes, then at the end he tacks on the appearance of mountains when approaching them by sea. This is slightly odd given that he never cites Ptolemy, but let’s not get into that. His exact arguments are (Circular motions of heavenly bodies 1.5, = pp. 72-86 Ziegler):
- The length of time between sunrise and sunset is different in different places.
- Eclipses are observed at different hours in different places.
- The celestial pole has a different azimuth in different places.
- Different stars appear in the sky depending on how far north or south you are.
- When you approach mountains by sea, they appear to gradually rise up out of the sea.
We still haven’t got to the root of the question. How did the person who worked out the earth’s shape do it?
One thing we can be absolutely sure of is this: they didn’t work it out by looking at ships or mountains. They were looking at the sky. All of the evidence cited by Aristotle, Ptolemy, and Cleomedes is based on astronomy, not geography. Ptolemy and Cleomedes only tack on the thing about mountains as an afterthought, to make it easier for readers to accept.
Here are two theories. First, Otto Neugebauer:
... [I]t seems plausible that it was the experience of travellers that suggested such an explanation for the variation in the observable altitude of the pole and the change in the area of circumpolar stars, a variation which is quite drastic between Greek settlements, e.g., in the Nile Delta and in the Crimea.And second, Dirk Couprie:
-- Neugebauer 1975: 576 (more generally see 575-578)
Several sources ascribe the discovery of the ecliptic (or the Zodiac) to Oenopides, who lived about one century after Anaximander and was a younger contemporary of Anaxagoras (DK 41A7). This makes Oenopides a serious candidate for the discovery of the sphericity of the earth as well, as the ecliptic must be thought of as inclined to the celestial equator, which is the projection of the equator of a spherical earth on the celestial sphere.Couprie’s theory about Oenopides and the ecliptic may take a little explaining.
-- Couprie 2011: 169 and 201-202
|Left: the ecliptic plotted on a celestial sphere. Right: the ecliptic plotted on a rectilinear map of the stars as seen from earth.|
Now, that’s the geocentric point of view. In reality, the ecliptic is the plane in which the earth and other planets revolve around the sun. The earth’s equator is at an angle to that plane, and that’s what produces the phenomenon.
Couprie’s idea is this. The astronomer Oenopides is said to have discovered the ecliptic, but we know that’s not true. It was well known to Babylonian astronomers a millennium earlier. However, the ecliptic implies a spherical geometry for the sky. So, Couprie thinks, what Oenopides really discovered is that that somehow implies a spherical geometry for the earth too.
It doesn’t imply that all by itself, mind. It does tend to imply that it’s the earth that’s rotating, not the stars -- but ancient testimony is pretty hostile to that theory (Aristotle On the sky 296a.26-27; Ptolemy Almagest i.1.24-25 = ch. i.7).
However, if you take it in conjunction with Neugebauer’s point about Greek colonists in Ukraine and Libya noticing different astronomical phenomena, then you get a line of reasoning that looks very similar to the opening chapters of Cleomedes’ work. Cleomedes doesn’t present the earth’s shape as a premise. He works his way up to it.
Cleomedes starts off by establishing the spherical geometry of the sky; he describes the celestial equator, tropics, and arctic and antarctic circles, and how these have corresponding zones on earth; then he moves on to the planets and their motion relative to the ecliptic, and how the ecliptic is at an angle to the celestial equator; and then he gets to the key point that
The Earth is spherical in shape, and thus [located] downwards from every part of the heavens; as a result its latitudes do not have an identical position relative to the zodiac, but different ones are located below different parts of the heavens.This is basically the conjunction of the spherical cosmology, the ecliptic, and Neugebauer’s point about the angle of the celestial sphere being different depending on how far north or south you are. Cleomedes carries on in exactly this way, talking about how ‘the heavens slope’. Only later on does he get into explicit arguments to support the earth’s sphericity.
-- Cleomedes 1.3 = p. 36.21-26 Ziegler (tr. Bowen and Todd)
It’s pretty likely that his manner of exposition is very close to the original reasoning. It isn’t a certainty. The ecliptic doesn’t come up in Aristotle’s or Ptolemy’s discussions of evidence for the earth’s shape. But I think the beginnings of the idea must have followed something like Cleomedes’ reasoning.
I want to add, as a postscript, that though Greek thinkers prior to 400 were all flat-earthers, including beloved names like Thales and Democritus, their work wasn’t a waste of time. Anaximander, in particular, can be credited with the important realisation that the earth isn’t the base of the cosmos, but is suspended in space. He was wrong about why it is suspended -- pre-Socratic philosophers thought it must be held up by air pressure -- but it was a crucial step. Without that notion, I doubt the spherical earth could have been discovered until many centuries later.
- Bowen, A. C.; Todd, R. B. 2004. Cleomedes’ lectures on astronomy. University of California Press.
- Copernicus, N. 1543. De revolutionibus orbium coelestium. Ioh. Petreius (Nürnberg).
- Couprie, D. L. 2011. Heaven and earth in ancient Greek cosmology. Springer.
- Neugebauer, O. 1975. A history of ancient mathematical astronomy (2 vols). Springer. | 0.85846 | 3.531603 |
Astronomers have been pondering the nature of our first interstellar visitor ever since its discovery. ‘Oumuamua is bizarre — not only is it from beyond the stars, but it’s also long and cigar-shaped. That led some to wonder if it wasn’t really an alien spacecraft, but past studies of ‘Oumuamua have suggested that it’s just a space rock. Now, a comprehensive analysis from scientists at the University of Maryland and other institutions has ruined our fun once and for all. ‘Oumuamua isn’t an alien spaceship.
While there have no doubt been alien objects in our solar system before, ‘Oumuamua was the first one we ever spotted. Astronomers at the Pan-STARRS observatory identified ‘Oumuamua in October 2017, but it was already on its way out of the solar system at that point. Its incredible speed and orbital eccentricity meant it could not have come from inside the solar system, but it was moving too fast for anything to catch up and take a closer look.
It didn’t take long after the discovery for people to start half-jokingly wondering if ‘Oumuamua was an alien ship. Even if we ignore that, it took scientists a few tries to properly identify the object. The initial assumption was that ‘Oumuamua had to be a comet because comets would be easier to eject from the edges of a solar system. However, scientists couldn’t see a cometary tail (or coma) on ‘Oumuamua. After labeling it an asteroid, further analysis of its trajectory found evidence of slight out-gassing. Astronomers finally decided ‘Oumuamua was likely a very old comet.
‘Oumuamua’s path through the solar system in 2017.
So, why is it definitely not an alien spaceship with a fuel leak or something? The team behind the new study included experts from a variety of fields to create a “big-picture summary” of ‘Oumuamua. They began with its origins, showing that there are several possible mechanisms by which an object like ‘Oumuamua could end up in interstellar space. Its behavior in our solar system, while strange, is also explainable with natural origins. In fact, its path around the sun matches a prediction published by one of the study authors six months before ‘Oumuamua’s discovery.
‘Oumuamua is strange, but the study concludes there’s nothing unexplainable going on here. Jumping to the conclusion that it’s an alien spacecraft is fun, but the evidence does not support that. Astronomers hope to get a look at more alien visitors in the future. Upcoming instruments like the Large Synoptic Survey Telescope (LSST) will make it easier to spot small objects passing through the solar system. If we can find a few dozen alien space rocks, we might find that ‘Oumuamua is very typical of visitors from beyond the stars.
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ExtremeTechExtreme – ExtremeTech | 0.886975 | 3.740569 |
NASA’s NEOWISE mission has recently discovered some celestial objects traveling through our neighborhood, including one on the blurry line between asteroid and comet. Another–definitely a comet–might be seen with binoculars through next week.
An object called 2016 WF9 was detected by the NEOWISE project on Nov. 27, 2016. It’s in an orbit that takes it on a scenic tour of our solar system. At its farthest distance from the sun, it approaches Jupiter’s orbit. Over the course of 4.9 Earth-years, it travels inward, passing under the main asteroid belt and the orbit of Mars until it swings just inside Earth’s own orbit. After that, it heads back toward the outer solar system. Objects in these types of orbits have multiple possible origins; it might once have been a comet, or it could have strayed from a population of dark objects in the main asteroid belt.
2016 WF9 will approach Earth’s orbit on Feb. 25, 2017. At a distance of nearly 32 million miles (51 million kilometers) from Earth, this pass will not bring it particularly close. The trajectory of 2016 WF9 is well understood, and the object is not a threat to Earth for the foreseeable future.
A different object, discovered by NEOWISE a month earlier, is more clearly a comet, releasing dust as it nears the sun. This comet, C/2016 U1 NEOWISE, “has a good chance of becoming visible through a good pair of binoculars, although we can’t be sure because a comet’s brightness is notoriously unpredictable,” said Paul Chodas, manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California.
As seen from the northern hemisphere during the first week of 2017, comet C/2016 U1 NEOWISE will be in the southeastern sky shortly before dawn. It is moving farther south each day and it will reach its closest point to the sun, inside the orbit of Mercury, on Jan. 14, before heading back out to the outer reaches of the solar system for an orbit lasting thousands of years. While it will be visible to skywatchers at Earth, it is not considered a threat to our planet either.
NEOWISE is the asteroid-and-comet-hunting portion of the Wide-Field Infrared Survey Explorer (WISE) mission. After discovering more than 34,000 asteroids during its original mission, NEOWISE was brought out of hibernation in December of 2013 to find and learn more about asteroids and comets that could pose an impact hazard to Earth. If 2016 WF9 turns out to be a comet, it would be the 10th discovered since reactivation. If it turns out to be an asteroid, it would be the 100th discovered since reactivation.
What NEOWISE scientists do know is that 2016 WF9 is relatively large: roughly 0.3 to 0.6 mile (0.5 to 1 kilometer) across.
It is also rather dark, reflecting only a few percent of the light that falls on its surface. This body resembles a comet in its reflectivity and orbit, but appears to lack the characteristic dust and gas cloud that defines a comet.
“2016 WF9 could have cometary origins,” said Deputy Principal Investigator James “Gerbs” Bauer at JPL. “This object illustrates that the boundary between asteroids and comets is a blurry one; perhaps over time this object has lost the majority of the volatiles that linger on or just under its surface.”
Near-Earth objects (NEOs) absorb most of the light that falls on them and re-emit that energy at infrared wavelengths. This enables NEOWISE’s infrared detectors to study both dark and light-colored NEOs with nearly equal clarity and sensitivity.
“These are quite dark objects,” said NEOWISE team member Joseph Masiero, “Think of new asphalt on streets; these objects would look like charcoal, or in some cases are even darker than that.”
NEOWISE data have been used to measure the size of each near-Earth object it observes. Thirty-one asteroids that NEOWISE has discovered pass within about 20 lunar distances from Earth’s orbit, and 19 are more than 460 feet (140 meters) in size but reflect less than 10 percent of the sunlight that falls on them.
The Wide-field Infrared Survey Explorer (WISE) has completed its seventh year in space after being launched on Dec. 14, 2009.
Data from the NEOWISE mission are available on a website for the public and scientific community to use. A guide to the NEOWISE data release, data access instructions and supporting documentation are available at:
Access to the NEOWISE data products is available via the on-line and API services of the NASA/IPAC Infrared Science Archive.
A list of peer-reviewed papers using the NEOWISE data is available at: | 0.869386 | 3.753896 |
Few educational hobbies provide as much universal fun as star-gazing. It’s an activity that kids and their families can get pleasure from together, and can be expanded as proficiency and skill increase. Also, it doesn’t require a lot of equipment to begin. All you need is a suitable pair of binoculars.
Many parents don’t realize that, like telescopes, binoculars work well to find and study things like nebulae, star clusters, comets and even distant galaxies. Some are surprised to learn that binoculars offer some definite benefits over the classic telescope, especially for children.
Binoculars are lighter than telescopes and don’t need to be set up. Just throw the binocular strap around your neck when the moods strikes, and go look at the stars. Binoculars are also made with unique prisms that permit the viewer to see the moon and other heavenly objects right side up, instead of upside down the way most telescopes do.
Binoculars have a wide field of vision, making it easier to see more of the sky. If you happen across a comet or a large constellation, the extra view makes it easier to see and follow them. Binoculars also have two lenses, which is easier for younger eyes to see through, and both smaller and lighter than a telescope, so kids can handle them more easily.
One of the biggest benefits to families on a budget is that binoculars are less expensive to than telescopes. Plus, they provide great opportunities for your children to participate in animal or bird watching, as well as using them when viewing sporting events or musical theater.
When buying a pair of binoculars for star-gazing, there are a few important features to consider.
: The diameter of the front lenses. They should be large enough to pick up the dim night-time light given off by the stars. Look for binoculars with no less than a 40 mm (millimeter) aperture. You can locate the aperture of a pair of binoculars by analyzing its number pairs. A 7X35 has an aperture of 35 mm while a 10x50 has an aperture of 50mm.
: As the word says, this measurement describes how close the object appears to be and is shown by the first number in the number pair. Binoculars for astronomy must have a magnification of between 7 (7x35) and 10 (10x50). Anything higher produces a fuzzy image and would require a tripod.
: Like the pupil in ones eye adjusts to the darkness of our surroundings, so binoculars can adjust how much light hits the user’s eye. As we age, our pupils lose the capacity to dilate easily as they did when we were younger. When binoculars allow more incoming light then our pupils can deal with, the view will be dimmer than it should be. The exit pupil measurement is found by dividing the aperture by the magnification. For young people and those in their mid thirties an exit pupil number of 6 or 7 will work best. For parents in their forties and older, an exit pupil number of 5 or 6 will allow for a brighter image.
Do all these numbers sound confusing? Don’t worry. If you choose a good astronomy or sporting goods store, their employees should be well trained in each model and brand of binocular they sell, and can help you find the binoculars that are right for you.
The very highest quality binoculars tend to be a little heavy for comfortable viewing. But that doesn’t have to be a problem. Field Optical Research carries several tripods
and accessories that allow you to enjoy the benefits of the larger binoculars without undue stress.
While you’re shopping, you might consider a pair of eyeShields. EyeShields
are made of soft pliable plastic and attach to the binocular eye-pieces to provide a more comfortable viewing experience while cutting eye irritants like wind and glare. They allow for better focus and improve night vision and increased comfort for both you and your children.
In this age of technical and digital entertainment, turn off the electronics and take your family outdoors. Explore the constellations in Orion’s belt, gaze at shadows in the moon’s craters, or get a close-up view of the Milky Way. Create lasting memories as you introduce your children to the wonders of the universe. | 0.893774 | 3.07237 |
When did these big galaxies first begin to dance? Really only four of the five of Stephan’s Quintet are locked in a cosmic tango of repeated close encounters taking place some 300 million light-years away. The odd galaxy out is easy to spot in this recently reprocessed image by the Hubble Space Telescope — the interacting galaxies, NGC 7319, 7318B, 7318A, and 7317 (left to right), have a more dominant yellowish cast. They also tend to have distorted loops and tails, grown under the influence of disruptive gravitational tides. The mostly bluish galaxy, large NGC 7320 on the lower left, is in the foreground at about 40 million light-years distant, and so is not part of the interacting group. Data and modeling indicate that NGC 7318B is a relatively new intruder. A recently-discovered halo of old red stars surrounding Stephan’s Quintet indicate that at least some of these galaxies started tangling over a billion years. Stephan’s Quintet is visible with a moderate sized-telescope toward the constellation of Winged Horse (Pegasus). | 0.901965 | 3.282465 |
Named for the Roman god of the sea, the solar system's eighth planet was discovered in 1846 by France's Urbain J.J. Leverrier and England's John Couch Adams, although they were working independently. The astronomers had observed that something was disturbing the orbit of Uranus, and mathematical calculations as to its location soon unveiled Neptune. Intriguingly, the planet was almost identified as early as 1612 by Galileo, but he mistakenly classified it as just another star.
Neptune has 13 known moons, but Triton is perhaps the most unique due to its unusual backward orbit. This odd orbital pattern, the only one known to occur in our entire solar system, has caused some astronomers to speculate that the moon was actually captured by the planet sometime in the distant past from Triton's original location in the Kuiper Belt, a collection of icy objects clustered in a disk shape on the extreme edge of our planetary system.
Neptune's rings are also unique in that unlike those around other planets, the ones circling Neptune seem to defy the laws of motion. The planet has three arcs named Liberty, Equality and Fraternity. What has puzzled scientists for years, though, is why the arcs haven't spread out to form a uniform ring. Astronomers now theorize that the gravitational forces from Galatea, one of Neptune's moons that lies closest to the rings, keep them narrow.
If the data received from probes of Neptune is correct, there is no solid surface on the planet. Instead, the rocky and icy core is completely surrounded by a liquid layer that in turn is smothered by dense gases. The atmosphere around the planet contains thick clouds that are blown around the sky by winds up to 700 miles per hour. Areas of swirling gases create features resembling giant hurricanes that can last for years. One of these supposed storms, the Great Dark Spot, was discovered by Voyager 2 in 1989, seemed to dissipate in 1994 and then appeared to be reforming a year later.
- earthview 01 image by Antony McAulay from Fotolia.com | 0.910189 | 3.371513 |
The Perseids, the most widely observed and dependable of the annual meteor displays, will peak during the overnight hours of Thursday, Aug. 11 into the morning of Friday, Aug. 12, and this year has all the earmarks of being a spectacular show.
First, there is the situation regarding the moon. At first glance, it appears that the viewing conditions aren't very good, as the peak night coincides with a waxing gibbous moon, 63-percent illuminated. Its bright light no doubt will wash out all but the very brightest of these swift streaks, which chiefly will emanate from out of the northeast part of the sky. However, there is some very good news: Early Friday morning (Aug. 12), the moon will set near 1:00 a.m. local time. Dawn breaks at about 4:20 a.m. around the mid-northern latitudes. Between those two times, there will be a nearly 3.5-hour "window" during which the sky will be totally dark.
Another reason the Perseids could put on a better-than-average show this year is a gravitational assist from Jupiter. [Perseid Meteor Shower 2016: When, Where & How to See It]
Most meteor showers evolve from comets. The cometary parent of the Perseids is a comet known as Swift-Tuttle. This comet takes approximately 130 years to make one trip around the sun. It was discovered in 1862 and last appeared in our skies in 1992. (It's due back in 2126.) Comets are composed chiefly of frozen gases, and meteoroids that are mixed in with that gas — the bits and pieces that have flaked off from the comet's solid center or nucleus.
Like all comets, Swift-Tuttle leaves behind streams of tiny particles ranging in size from large grains of sand to small pebbles, but with the consistency of cigar ash. They're invisible to people on Earth until, upon entering our atmosphere with immense velocity — 37 miles per second (60 kilometers per second) — they blaze up within the span of a heartbeat and streak across the sky in a brief, blazing finale. Comet Swift-Tuttle probably has passed the sun hundreds of times to produce the present stream of Perseid meteors.
The meteoroids have become distributed all around the comet's elongated elliptical orbit, which takes them out beyond the realms of Pluto and ultimately brings them back to intersect Earth's orbit at almost a right angle, producing a fairly predictable meteor display that lasts for several days in mid-August.
The Perseids intersect the orbit of Earth more or less directly, but on their way in toward the sun, they also pass other planets. In the case of the most massive planet in the solar system, Jupiter, there is no direct encounter; the dross of Comet Swift-Tuttle passes well above this giant world, never coming any closer than about 160 million miles (257 million km) at 11.8-Earth-year intervals — the time it takes for Jupiter to make a complete orbit around the sun.
But on those occasions when it's passing closest to Swift-Tuttle's trail of debris, Jupiter's powerful gravitational field can still slightly perturb the comet particles just enough to nudge them about 930,000 miles (1.5 million km) closer to Earth. The result is usually a noticeably brighter and stronger Perseid display, producing more than the usual complement of meteors.
Most years when the Earth encounters the Perseids, observers in areas where the sky is very dark and clear might count as many as 60 to 90 meteors per hour. (But here's a necessary disclaimer: If you live in an area where haze, smoke and bright city lights proliferate, or tall obstructions block large areas of the sky, you will likely see a lot fewer.)
When Jupiter has had an influence on the Perseid orbit, the meteor numbers tend to ramp up to above-normal levels. That's exactly what happened in 1921, 1945, 1968, 1980 and, most recently, in 2004.
As it turns out, Jupiter recently passed closest to the orbit of Comet Swift Tuttle in November 2014. But an additional 22 months must then pass for the meteoroid zone affected by Jupiter to arrive in the vicinity of Earth. That indicates that the 2016 Perseids could be another "prime year" for the Perseids; they could indeed prove to be unusually numerous. [Top 10 Perseid Meteor Shower Facts]
What do the Perseid pundits say?
In the 2016 edition of the "Observer's Handbook" of the Royal Astronomical Society of Canada, Margaret Campbell-Brown and Peter Brown noted that, "Some models predict an enhancement in activity from the Perseids in 2016 about 7 hours before the traditional peak, but this is from older trails unlikely to produce more than a moderate increase in rates." On their table of meteor showers for 2016, they highlighted the Perseids in bolddue to the possibility of this outburst.
The outburst in question is being forecast by French meteor expert Jeremie Vaubaillon. It shows the Earth moving along in its orbit and encountering a small, albeit concentrated, zone of comet material at around 1 a.m. EDT (0500 GMT) on Aug. 12 that would favor the eastern portions of the U.S. and Canada. But Vaubaillon is cautious. "This trail of material dates is over nine centuries old, making the forecast for a possible outburst less certain," he told me in an email. "Certainly I would look for it, but just keep in mind the uncertainties."
You can see a map charting that interaction here:
Another noted meteor expert, Mikhail Maslov of Russia, forecasts higher-than-normal Perseid meteor rates: "In 2016, Jupiter will cause a significant increase up to 160-180 meteors per hour. Earth will encounter the perturbed part of the Perseid stream, which was shifted closer to the Earth's orbit by Jupiter's gravitation. This means we have to expect heightened Perseid activity." His complete description, including more technical details, can be found here: http://feraj.narod.ru/Radiants/Predictions/Perseids2016eng.html
The "clumping effect"
This year is an auspicious occasion for me, as it marks the 50th summer in which I have watched out for the Perseids. What I (and others) have noted over the years is what some have called the "clumping effect" — that the Perseids appear to come in rapid succession; several or more within a minute or two, followed by a lull of several minutes before the sky suddenly bears fruit once again. Interestingly, while many observers have stated that the Perseids seem to come in bunches, when hourly Perseid observations have been carefully examined using the Poisson distribution formula (explained in statistics textbooks), it has been determined that, more often than not, a random distribution of arrival times has been inferred. Therefore, the "clumping" or bunches may be merely an illusion.
Have a Perseid party
Why not consider organizing a "Perseid party," and have a number of people watching different parts of the sky?
To observe the Perseids, you may need to dress warmly, bring a reclining chair and watch the sky. You need no other equipment. Find a dark observing spot, preferably with a low horizon, and look in any direction. Use this light-pollution map (http://tinyurl.com/zrk7qju) to find dark locations near you.
The Perseids get their name from their apparent radiation from the northern constellation of Perseus. At dusk, the uppermost part of this star pattern is grazing the northern horizon. Not until 11 p.m. local time is this group high enough in the northeast to be conspicuous. At 4 a.m., when Orion has risen, Perseus has reached a lofty perch and is nearly overhead; that's also when you're likely to see the most meteors.
But it is not necessary to continuously stare at Perseus itself if you are looking for these shooting stars. A Perseid may appear in any part of the sky, but its trail, if mentally traced backward, invariably leads back to Perseus.
Typically, they appear as bright, swift streaks. A few outstandingly bright meteors (fireballs) occasionally may be seen. Fainter meteors appear white or yellow; brighter ones green, orange or red. About one-third leave luminous trains, which may be spectacular and can persist for many seconds; the most outstanding meteors often end in flares or bursts (called "bolides") and are even capable of casting shadows! Those are the kind of meteors that tend to elicit screams of delight from Perseid watchers.
You can also contribute valuable observational data. If you decide to do so, use the techniques suggested by the International Meteor Organization (IMO) (http://www.imo.net/visual/major). This way, your data will be in a standard format, which can readily be used for analysis. Send your data to the IMO at http://www.imo.net/visual/report/electronic.
Good luck and here's to clear skies!
Editor's note: If you have an amazing photo of this year's Perseid meteor shower you'd like to share for a possible story or image gallery, please contact managing editor Tariq Malik at [email protected].
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com. | 0.885326 | 3.741863 |
Anyone who’s done some stargazing has probably noticed that the Sun and the Moon appear along nearly the same arc in the sky. This Sun’s arc, called the ecliptic, corresponds to the plane of the Earth’s orbit. Since all planets in the solar system share nearly the same orbital plane, they likewise hew close to this arc. It turns out that the ecliptic also coincides closely with the Sun’s equator.
The near alignment of all planetary orbits in the solar system is one of the most important clues to their formation – the solar system originated billions of years ago from a thin disk of gas and dust girding the young Sun’s belly like a hula hoop, an idea going back at least to Immanuel Kant in the 1700s called the Nebular Hypothesis.
Once it was accepted, this idea was so successful at explaining and predicting features of the solar system, astronomers believed all planetary systems in our galaxy would resemble our own – with small, rocky planets close to their stars and large, gassy planets farther away, but all sharing the same orbital plane.
The discoveries of thousands of exoplanets have turned all that on its head – planets around other stars have orbits oriented every which way. For example, the Upsilon Andromeda system has three Jupiter-like planets, all on orbits that are widely misaligned.
Although these topsy-turvy planetary orbits were initially puzzling, astronomers are starting to tease out the explanations for these systems. Planets probably do start out in well-aligned orbits, but, like kids in the backseat on a long car trip, jostling between the planets (due to mutual gravitational tugs) soon upsets this delicate arrangement and upends the orbits. In the case of Upsilon Andromeda, planets may even have been ejected from the system.
A recent study from Fei Dai and colleagues explored connections between orbital misalignment and the origins of one puzzling class of exoplanet – small, short-period planets. These planets range in size (and probably composition) from Neptune-like to smaller than Earth but inhabit orbits very close to their host stars, some taking only hours to circle the star. Many of these short-period planets also have sibling planets farther out, and the arrangement of these orbits might tell us how the planets got so close to their stars.
As for the Upsilon Andromeda system, the mutual inclination between the orbits, if its big, may point to a history of violence in the system. Such violence may explain how the short-period planets got so close to their stars – they could have started out far away and been thrown by their siblings toward the star. By contrast, a small mutual inclination could mean the system has always been relatively quiescent, and the short-period planets may have gently migrated inward from farther out.
By analyzing the transit light curves of the planets as observed by the Kepler spacecraft, Dai and colleagues found a pattern in the mutual inclinations for these systems. From their paper, the figure below shows that when the distance of the shortest-period planet in a system a/R* is larger, the mutual inclination ΔI between orbits tends to be less widely distributed.
What does this result mean? Since the short-period planets closest to their stars (small a/R*) also seem to have a very wide range of mutual inclinations, maybe they experience the same kind of gravitational jostling that took place in Upsilon Andromeda, while planets farther out, they were moved in more gracefully. | 0.926479 | 3.994375 |
New observations from NASA’s Swift and the Nuclear Spectroscopic Telescope Array, suggest that supermassive black holes send out beams of X-rays when their surrounding coronas shoot, or launch, away from the black holes.
The baffling and strange behaviors of black holes have become somewhat less mysterious recently, with new observations from NASA’s Explorer missions Swift and the Nuclear Spectroscopic Telescope Array, or NuSTAR. The two space telescopes caught a supermassive black hole in the midst of a giant eruption of X-ray light, helping astronomers address an ongoing puzzle: How do supermassive black holes flare?
The results suggest that supermassive black holes send out beams of X-rays when their surrounding coronas — sources of extremely energetic particles — shoot, or launch, away from the black holes.
“This is the first time we have been able to link the launching of the corona to a flare,” said Dan Wilkins of Saint Mary’s University in Halifax, Canada, lead author of a new paper on the results appearing in the Monthly Notices of the Royal Astronomical Society. “This will help us understand how supermassive black holes power some of the brightest objects in the universe.”
Supermassive black holes don’t give off any light themselves, but they are often encircled by disks of hot, glowing material. The gravity of a black hole pulls swirling gas into it, heating this material and causing it to shine with different types of light. Another source of radiation near a black hole is the corona. Coronas are made up of highly energetic particles that generate X-ray light, but details about their appearance, and how they form, are unclear.
Astronomers think coronas have one of two likely configurations. The “lamppost” model says they are compact sources of light, similar to light bulbs, that sit above and below the black hole, along its rotation axis. The other model proposes that the coronas are spread out more diffusely, either as a larger cloud around the black hole, or as a “sandwich” that envelops the surrounding disk of material like slices of bread. In fact, it’s possible that coronas switch between both the lamppost and sandwich configurations.
The new data support the “lamppost” model — and demonstrate, in the finest detail yet, how the light-bulb-like coronas move. The observations began when Swift, which monitors the sky for cosmic outbursts of X-rays and gamma rays, caught a large flare coming from the supermassive black hole called Markarian 335, or Mrk 335, located 324 million light-years away in the direction of the constellation Pegasus. This supermassive black hole, which sits at the center of a galaxy, was once one of the brightest X-ray sources in the sky.
“Something very strange happened in 2007, when Mrk 335 faded by a factor of 30. What we have found is that it continues to erupt in flares but has not reached the brightness levels and stability seen before,” said Luigi Gallo, the principal investigator for the project at Saint Mary’s University. Another co-author, Dirk Grupe of Morehead State University in Kentucky, has been using Swift to regularly monitor the black hole since 2007.
In September 2014, Swift caught Mrk 335 in a huge flare. Once Gallo found out, he sent a request to the NuSTAR team to quickly follow up on the object as part of a “target of opportunity” program, where the observatory’s previously planned observing schedule is interrupted for important events. Eight days later, NuSTAR set its X-ray eyes on the target, witnessing the final half of the flare event.
After careful scrutiny of the data, the astronomers realized they were seeing the ejection, and eventual collapse, of the black hole’s corona.
“The corona gathered inward at first and then launched upwards like a jet,” said Wilkins. “We still don’t know how jets in black holes form, but it’s an exciting possibility that this black hole’s corona was beginning to form the base of a jet before it collapsed.”
How could the researchers tell the corona moved? The corona gives off X-ray light that has a slightly different spectrum — X-ray “colors” — than the light coming from the disk around the black hole. By analyzing a spectrum of X-ray light from Mrk 335 across a range of wavelengths observed by both Swift and NuSTAR, the researchers could tell that the corona X-ray light had brightened — and that this brightening was due to the motion of the corona.
Coronas can move very fast. The corona associated with Mrk 335, according to the scientists, was traveling at about 20 percent the speed of light. When this happens, and the corona launches in our direction, its light is brightened in an effect called relativistic Doppler boosting.
Putting this all together, the results show that the X-ray flare from this black hole was caused by the ejected corona.
“The nature of the energetic source of X-rays we call the corona is mysterious, but now with the ability to see dramatic changes like this we are getting clues about its size and structure,” said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology in Pasadena, who was not affiliated with the study.
Many other black hole brainteasers remain. For example, astronomers want to understand what causes the ejection of the corona in the first place.
PDF Copy of the Study: Flaring from the supermassive black hole in Mrk 335 studied with Swift and NuSTAR | 0.871168 | 4.116987 |
Human beings have been observing the Moon for as long as they have walked the Earth. Throughout recorded and pre-recorded history, they have paid close attention to its phases and accorded them particular significance. This has played a major role in shaping the mythological and astrological traditions of every known culture.
With the birth of astronomy as a scientific discipline, how the Moon appears in the night sky (and sometimes during the day) has also gone long way towards helping us to understand how our Solar System works. It all comes down to the Lunar Cycle, the two key parts of this cycle involve the “waxing and waning” of the Moon. But what exactly does this mean?-day
First, we need to consider the orbital parameters of the Earth’s only satellite. For starters, since the Moon orbits Earth, and Earth orbits the Sun, the Moon is always half illuminated by the latter. But from our perspective here on Earth, which part of the Moon is illuminated – and the amount to which it is illuminated – changes over time.
When the Sun, the Moon and Earth are perfectly lined up, the angle between the Sun and the Moon is 0-degrees. At this point, the side of the Moon facing the Sun is fully illuminated, and the side facing the Earth is enshrouded in darkness. We call this a New Moon.
After this, the phase of the Moon changes, because the angle between the Moon and the Sun is increasing from our perspective. A week after a New Moon, and the Moon and Sun are separated by 90-degrees, which effects what we will see. And then, when the Moon and Sun are on opposite sides of the Earth, they’re at 180-degrees – which corresponds to a Full Moon.
Waxing vs. Waning:
The period in which a Moon will go from a New Moon to a Full Moon and back again is known as “Lunar Month”. One of these lasts 28 days, and encompasses what are known as “waxing” and “waning” Moons. During the former period, the Moon brightens and its angle relative to the Sun and Earth increases.
When the Moon starts to decrease its angle again, going from 180-degrees back down to 0-degrees, astronomers say that it’s a waning moon. In other words, when the Moon is waning, it will have less and less illumination every night until it’s a New Moon.
When the Moon is no longer full, but it hasn’t reached a quarter moon – i.e. when it’s half illuminated from our perspective – we say that it’s a Waning Gibbous Moon. This is the exact reverse of a Waxing Gibbous Moon, when the Moon is increasing in brightness from a New Moon to a Full Moon.
This is followed by a Third Quarter (or last quarter) Moon. During this period, 50% of the Moon’s disc will be illuminated (left side in the northern hemisphere, and the right in the southern), which is the opposite of how it would appear during a First Quarter. These phases are often referred to as a “Half Moon”, since half the disc is illuminated at the time.
Finally, a Waning Crescent is when the Moon appears as a sliver in the night sky, where between 49–1% of one side is illuminated after a Full Moon (again, left in the northern hemisphere, right in the southern). This is the opposite of a Waxing Crescent, when 1-49% of the other wide is illuminated before it reaches a Full Moon.
Even today, thousands of years later, human beings still look up at the Moon and are inspired by what they see. Not only have we explored Earth’s only satellite with robotic missions, but even crewed missions have been there and taken samples directly from the surface. And yet, it still possesses enough mystery to keep us inspired and guessing.
We have written many interesting articles about the Moon here at Universe Today. Here’s What is the Moon’s Real Name?, Does the Moon Have Different Names?, What are the Phases of the Moon?, Is the Moon a Planet?, What is the Distance to the Moon?, and Who Were the First Men on the Moon?
Want to know when the next waning gibbous moon is going to happen? NASA has a list of moon phases for a period of 6000 years.
You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From? | 0.837648 | 3.512211 |
– Space is a challenging place. We think of it as mostly empty, but that is not completely true. The vast sea of space in our solar system is filled with powerful radiation and bombarded with high-speed atomic particles. In addition, the Sun generates a continuous stream of particles that we call the “solar wind.”
The high energy radiation, the high energy particles, and the solar wind could prove dangerous to life here on Earth’s surface. Earth’s planetary shield — the Earth’s magnetic field working together with our atmosphere — protects us.
Every magnet generates a magnetic field. Several objects in our solar system also have their own massive magnetic fields: the Sun, Earth, Mercury, Jupiter, Saturn, Uranus, and Neptune. The magnetic field around a planet that extends into space is called a magnetosphere.
The magnetospheres of the planets interact with the particles from the Sun — the solar wind. Within the magnetosphere, charged particles spiraling along the Earth’s magnetic field toward the poles create beautiful aurorae, the northern and southern lights, when they interact with our atmosphere.
Magnetic fields can also create hazards. Magnetospheres trap high energy particles into radiation belts around planets.The distant gas giant planets do not need protection from the solar wind; instead, their powerful radiation belts create a serious hazard for spacecraft, as do our own Van Allen radiation belts here on Earth.
Earth’s magnetosphere does more than shield us from the constant barrage of high-energy particles. It also protects our atmosphere and oceans from the solar wind, which would otherwise gradually erode them away into space.
Mars’ lack of a magnetosphere may be partly responsible for the thinness of its atmosphere and absent oceans.
A magnetosphere on Venus could have prevented this planet’s primordial water from escaping into space.
Magnetism is a force in nature that is produced by electric fields in motion. This movement can involve electrons ‘spinning’ around atomic nuclei, flowing through a conducting wire or ions moving through space in an organized stream.
Earth’s magnetic field is familiar to us through its effects: our compasses point to the magnetic poles (north and south); it protects our atmosphere from the blast of the solar wind; and particles interact with it to produce the auroras, or northern and southern lights. Similarly, the magnetic fields of Mercury, Jupiter, Saturn, Uranus, and Neptune are detectable with compasses, and we have seen beautiful auroras on Jupiter and Saturn!Planetary magnetic fields originate from processes deep in each planet’s interior. Earth’s is generated from the electric current caused by the flow of molten metallic material within its outer core. Mercury’s may be generated from its liquid core.Jupiter and Saturn are composed of gases crushed to such incredible pressures that they are forced beyond the common states of liquid, solid, or gas that we find on Earth.
One such a layer inside Jupiter and Saturn is metallic hydrogen, and the electric current caused by swirling movements in this substance produces a magnetic field so large that the tail of Jupiter’s magnetic field reaches the edge of Saturn’s orbit!
Scientists map planetary magnetic fields with a more sophisticated version of a compass, called a magnetometer.
They also “listen” for the radio signals given off by charged particles as they move through the magnetic field, and measure the properties of ions and electrons directly with particle detectors.
This science visualization shows a magnetospheric substorm, during which, magnetic reconnection causes energy to be rapidly released along the field lines in the magnetotail, that part of the magnetosphere that stretches out behind Earth. This released energy is focused down at the poles and the resulting flood of solar particles into the atmosphere, causes the auroras at the North and South Poles. The Sun has a very large and complex magnetic field. It actually extends far out into space, beyond the furthest planet. The solar wind, the stream of charged particles that flows outward from the Sun, carries the Sun’s magnetic field to the planets and beyond.
While the basic shape of the Sun’s magnetic field is like the shape of Earth’s field, with a north and south pole, superimposed on this basic field is a much more complex series of local fields that vary over time.
Places where the Sun’s magnetic field is especially strong are called active regions, and often produce sunspots. Disruptions in magnetic fields near active regions can create energetic explosions on the Sun such as solar flares and coronal mass ejections. The exact nature and source of the Sun’s magnetic field are areas of ongoing research. Turbulent motions of charged plasmas in the Sun’s convective zone clearly play a role.
In spite of the low density, the solar wind and its accompanying magnetic fields are strong enough to interact with the planets and their magnetic fields to shape magnetospheres. A magnetosphere is the region surrounding a planet where the planet’s magnetic field dominates.
Because the ions in the solar plasma are charged, they interact with these magnetic fields, and solar wind particles are swept around planetary magnetospheres, as are particles from the planet’s atmosphere.
At Jupiter and Saturn, the plasma inside the magnetosphere is almost entirely from their moons. Robotic missions investigating these worlds are challenged by the energetic charged particles that are trapped in these planets’ magnetic fields as radiation belts.
The shape of the Earth’s magnetosphere is the direct result of being blasted by solar wind. Solar wind compresses its sunward side to a distance of only 6 to 10 times the radius of the Earth. Solar wind drags out the night-side magnetosphere to possibly 1,000 times Earth’s radius; this extension of the magnetosphere is known as the magnetotail. Many other planets in our solar system have magnetospheres of similar, solar wind-influenced shapes.
This gorgeous view of the aurora was taken from the International Space Station as it crossed over the southern Indian Ocean on September 17, 2011. The sped-up movie spans the time period from 12:22 to 12:45 PM ET. While aurora are often seen near the poles, this aurora appeared at lower latitudes due to a geomagnetic storm – the insertion of energy into Earth’s magnetic environment called the magnetosphere – caused by a coronal mass ejection from the sun that erupted.
Given these critical roles, it is not surprising that several missions are actively investigating these planetary shields. . The Solar Dynamics Observatory is monitoring the Sun and its magnetic field to explore its impact on the near Earth space environment. | 0.811895 | 3.712065 |
From: Brown University
Posted: Thursday, September 24, 2009
Brown University scientists have made a major discovery: The moon has distinct signatures of water. The discovery came from a paper published in Science detailing findings from the Moon Mineralogy Mapper (M3), a NASA instrument aboard the Indian spacecraft Chandrayaan-1. Carle Pieters, professor of geological sciences at Brown, is the principal investigator of the M3 instrument and the lead author of the Science paper.
PROVIDENCE, R.I. [Brown University] In a discovery that promises to reinvigorate studies of the moon and potentially upend thinking of how it originated, scientists at Brown University and other research institutions have found evidence of water molecules on the surface of the moon.
The molecules and hydroxyl a molecule consisting of one oxygen atom and one hydrogen atom were discovered across the entire surface of earths nearest celestial neighbor. While the abundances are not precisely known, as much as 1,000 water molecule parts-per-million could be in the lunar soil: harvesting one ton of the top layer of the moons surface would yield as much as 32 ounces of water, according to scientists involved in the discovery.
Carle Pieters, a planetary geologist at Brown, is the lead author of one paper this week in Science that reports evidence of water in the moons high latitudes greatly expanding current thinking about where water in any form was presumed to be located.
Weve made a very important step with this discovery, and now there are some very important steps to follow up on, Pieters said.
Carle Pieters: Professor of Geological Sciences Carle Pieters Professor of Geological Sciences Pieters is the lead investigator on the Moon Mineralogy Mapper (M3), a NASA instrument that was carried into space on Oct. 22, 2008, aboard the Indian Space Research Organizations Chandrayaan-1 spacecraft. She said the findings from M3 reveal interesting, new questions about where the water molecules come from and where they may be going. Scientists have speculated that water molecules may migrate from non-polar regions of the moon to the poles, where they are stored as ice in ultra-frigid pockets of craters that never receive sunlight.
If the water molecules are as mobile as we think they are even a fraction of them they provide a mechanism for getting water to those permanently shadowed craters, Pieters said.
She continued, This opens a whole new avenue [of lunar research], but we have to understand the physics of it to ultilize it.
The M3 team found water molecules and hydroxyl at diverse areas of the sunlit region of the moons surface, but the water signature appeared stronger at the moons higher latitudes. The M3 discovery was confirmed by data from two NASA spacecrafts the Visual and Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft and the High-Resolution Infrared Imaging Spectrometer on the EPOXI spacecraft. Data from those missions also are being published in separate papers in Science.
Pieters credited the Indian space agency for its role in the findings. If it werent for them, we wouldn't have been able to make this discovery, she said.
Other Brown members listed as contributing authors to the M3 paper include Brown planetary geology faculty James Head III and John Jack Mustard; postdoctoral research associates Rachel Klima and Jeffrey Nettles; and graduate student Peter Isaacson.
Isaacson said the M3 results were a huge surprise. There was no evidence that this was possible on such a broad scale, he said. This discovery turns a lot of the conventional thinking about the lunar surface on its head.
Mustard, who has had major findings of water-bearing minerals on Mars, said the moon discovery is intriguing, because it shows water on a planet that we werent anticipating, and its in a form thats mysterious. The finding may have implications for other planets, such as Mars, but it is different.
From its perch in lunar orbit, M3s state-of-the-art spectrometer measured light reflecting off the moons surface at infrared wavelengths, splitting the spectral colors of the lunar surface into small enough bits to reveal a new level of detail in surface composition. When the M3 science team analyzed data from the instrument, they found the wavelengths of light being absorbed were consistent with the absorption patterns for water molecules and hydroxyl.
For silicate bodies, such features are typically attributed to water and hydroxyl-bearing materials, Pieters said. When we say water on the moon, we are not talking about lakes, oceans or even puddles. Water on the moon means molecules of water and hydroxyl that interact with molecules of rock and dust specifically in the top millimeters of the moons surface.
The research was funded by NASA. Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.
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In this night scene from the early hours of November 14, light from a last quarter Moon illuminates clouds above the mountaintop domes of Kitt Peak National Observatory near Tucson, Arizona. Bright Jupiter is just left of the overexposed lunar disk with a streak of camera lens flare immediately to the right, but that's no fireball meteor exploding near the center of the picture. Instead, from the roadside perspective a stunningly bright moondog or paraselene stands directly over Kitt Peaks's WIYN telescope. Analogous to a sundog or parhelion, a paraselene is produced by moonlight refracted through thin, hexagonal, plate-shaped ice crystals in high cirrus clouds. As determined by the crystal geometry, paraselenae (plural) are seen at an angle of 22 degrees or more from the Moon. Compared to the bright lunar disk they are more often faint and easier to spot when the Moon is low. About 10 minutes after the photograph even this bright moondog had faded from the night.
How cold can it get on Earth? In the interior of the Antarctica, a record low temperature of -93.2 °C (-135.8 °F) has been recorded. This is about 25 °C (45 °F) colder than the coldest lows noted for any place humans live permanently. The record temperature occurred in 2010 August -- winter in Antarctica -- and was found by scientists sifting through decades of climate data taken by Earth-orbiting satellites. The coldest spots were found near peaks because higher air is generally colder, although specifically in depressions near these peaks because relatively dense cold air settled there and was further cooled by the frozen ground. Summer is a much better time to visit Antarctica, as some regions will warm up as high as 15 °C (59 °F).
Stars are sometimes born in the midst of chaos. About 3 million years ago in the nearby galaxy M33, a large cloud of gas spawned dense internal knots which gravitationally collapsed to form stars. NGC 604 was so large, however, it could form enough stars to make a globular cluster. Many young stars from this cloud are visible in the above image from the Hubble Space Telescope, along with what is left of the initial gas cloud. Some stars were so massive they have already evolved and exploded in a supernova. The brightest stars that are left emit light so energetic that they create one of the largest clouds of ionized hydrogen gas known, comparable to the Tarantula Nebula in our Milky Way's close neighbor, the Large Magellanic Cloud.
Where is the best place on Earth to find meteorites? Although meteors fall all over the world, they usually just sink to the bottom of an ocean, are buried by shifting terrain, or are easily confused with terrestrial rocks. At the bottom of the Earth, however, in East Antarctica, huge sheets of blue ice remain pure and barren. When traversing such a sheet, a dark rock will stick out. These rocks have a high probability of being true meteorites -- likely pieces of another world. An explosion or impact might have catapulted these meteorites from the Moon, Mars, or even an asteroid, yielding valuable information about these distant worlds and our early Solar System. Small teams of snowmobiling explorers so far have found thousands. Pictured above, ice-trekkers search a field 25-kilometers in front of Otway Massif in the Transantarctic Mountain Range during the Antarctic summer of 1995-1996. The week marks the 100th anniversary of humans first reaching the Earth's South Pole.
Created as planet Earth sweeps through dusty debris from mysterious, asteroid-like, 3200 Phaethon, the annual Geminid Meteor Shower should be the best meteor shower of the year. The Geminids are predicted to peak on the night of December 13/14, but you can start watching for Geminid meteors this weekend. The best viewing is after midnight in a dark, moonless sky, with the shower's radiant constellation Gemini well above the horizon - a situation that favors skygazers in the northern hemisphere. In this picture from the 2009 Geminid shower, a bright meteor with a greenish tinge flashes through the sky over the Mojave Desert near Barstow, California, USA. Recognizable in the background are bright stars in the northern asterism known as the Big Dipper, framing the meteor streak.
Many bright nebulae and star clusters in planet Earth's sky are associated with the name of astronomer Charles Messier, from his famous 18th century catalog. His name is also given to these two large and remarkable craters on the Moon. Standouts in the dark, smooth lunar Sea of Fertility or Mare Fecunditatis, Messier (left) and Messier A have dimensions of 15 by 8 and 16 by 11 kilometers respectively. Their elongated shapes are explained by an extremely shallow-angle trajectory followed by the impactor, moving left to right, that gouged out the craters. The shallow impact also resulted in two bright rays of material extending along the surface to the right, beyond the picture. Intended to be viewed with red/blue glasses (red for the left eye), this striking stereo picture of the crater pair was recently created from high resolution scans of two images (AS11-42-6304, AS11-42-6305) taken during the Apollo 11 mission to the moon.
At the center of our Milky Way Galaxy lies a supermassive black hole. Once a controversial claim, this conclusion is now solidly based on 16 years of observations that map the orbits of 28 stars very near the galactic center. Using European Southern Observatory telescopes and sophisticated near infrared cameras, astronomers patiently measured the positions of the stars over time, following one star, designated S2, through a complete orbit as it came within about 1 light-day of the center of the Milky Way. Their results convincingly show that S2 is moving under the influence of the enormous gravity of a compact, unseen object -- a black hole with 4 million times the mass of the Sun. Their ability to track stars so close to the galactic center accurately measures the black hole's mass and also determines the distance to the center to be 27,000 light-years. This deep, near-infrared image shows the crowded inner 3 light-years of the central Milky Way. Spectacular time-lapse animations of the stars orbiting within light-days of the galactic center can be found here.
What does the universe nearby look like? This plot shows over one and a half million of the brightest stars and galaxies in the nearby universe detected by the Two Micron All Sky Survey (2MASS) in infrared light. The resulting image is an incredible tapestry of stars and galaxies that provides limits on how the universe formed and evolved. Across the center are stars that lie in the plane of our own Milky Way Galaxy. Away from the Galactic plane, vast majority of the dots are galaxies, color coded to indicate distance, with blue dots representing the nearest galaxies in the 2Mass survey, and red dots indicating the most distant survey galaxies that lie at a redshift near 0.1. Named structures are annotated. Many galaxies are gravitationally bound together to form clusters, which themselves are loosely bound into superclusters, which in turn are sometimes seen to align over even larger scale structures.
Double, double toil and trouble; Fire burn, and cauldron bubble -- maybe Macbeth should have consulted the Witch Head Nebula. This suggestively shaped reflection nebula is associated with the bright star Rigel in the constellation Orion. More formally known as IC 2118, the Witch Head Nebula glows primarily by light reflected from bright star Rigel, located just off the upper right edge of the full image. Fine dust in the nebula reflects the light. The blue color is caused not only by Rigel's blue color but because the dust grains reflect blue light more efficiently than red. The same physical process causes Earth's daytime sky to appear blue, although the scatterers in Earth's atmosphere are molecules of nitrogen and oxygen. The nebula lies about 1000 light-years away.
In the center of star-forming region 30 Doradus lies a huge cluster of the largest, hottest, most massive stars known. These stars, known as the star cluster R136, and part of the surrounding nebula are captured here in this gorgeous visible-light image from the Hubble Space Telescope. Gas and dust clouds in 30 Doradus, also known as the Tarantula Nebula, have been sculpted into elongated shapes by powerful winds and ultraviolet radiation from these hot cluster stars. The 30 Doradus Nebula lies within a neighboring galaxy, the Large Magellanic Cloud, located a mere 170,000 light-years away.
An energetic jet from the core of giant elliptical galaxy M87 stretches outward for 5,000 light-years. This monstrous jet appears in the panels above to be a knotted and irregular structure, detected across the spectrum, from x-ray to optical to radio wavelengths. In all these bands, the observed emission is likely created as high energy electrons spiral along magnetic field lines, so called synchrotron radiation. But what powers this cosmic blowtorch? Ultimately, the jet is thought to be produced as matter near the center of M87 swirls toward a spinning, supermassive black hole. Strong electromagnetic forces are generated and eject material away from the black hole along the axis of rotation in a narrow jet. Galaxy M87 is about 50 million light-years away and reigns as the large central elliptical galaxy in the Virgo cluster.
From planet Earth, we view this strongly interacting pair of galaxies, cataloged as Arp 81, as they were only about 100 million years after their mutual closest approach. The havoc wreaked by gravity during their ominous encounter is detailed in this color composite image from the Hubble Space Telescope, showing twisted streams of gas and dust, a chaos of massive star formation, and a tidal tail stretching for 200 thousand light-years or so as it sweeps behind the cosmic wreckage. Also known as NGC 6622 (left) and NGC 6621, the galaxies are roughly equal in size but are destined to merge into one large galaxy in the distant future, making repeated approaches until they finally coalesce. Located in the constellation Draco, the galaxies are 280 million light-years away. The dark vertical band which seems to run through NGC 6621's location is a camera artifact.
Streaking high above diffuse clouds -- but well in front of distant stars -- are sand-sized bits of an ancient comet: meteors. These bits flaked off Comet Tempel-Tuttle during its pass through the inner Solar System about 150 years ago. Far in the background are stars toward the constellation of Ursa Major. The above image is digital combination of 12 exposures taken on the morning of November 19 from Florida, USA. Observers there reported a strong peak in faint meteors between 5:30 and 6:00 EST, with a particularly strong minute coming at 5:46 EST when 22 Leonid meteors were counted. The likely less impressive Geminid meteor shower will peak over the next three nights.
Venus, second planet from the Sun, appears above imaged for the first time ever in x-rays (left) by the orbiting Chandra Observatory. Chandra's smoothed, false-color, x-ray view is compared to an optical image (right) from a small earthbound telescope. Both show Venus illuminated by the Sun from the right, with only half the sunward hemisphere visible, but at least one striking difference is apparent. While the optical image in reflected sunlight is filled and bright at the center, Venus in x-rays is bright around the edge. Venus' x-rays are produced by fluorescence rather than reflection. About 120 kilometers or so above the surface, incoming solar x-rays excite atoms in the Venusian atmosphere to unstable energy levels. As the atoms rapidly decay back to their stable ground states they emit a "fluorescence" x-ray, creating a glowing x-ray half-shell above the sunlit hemisphere. More x-ray emitting material can be seen looking at the edge of the shell, so the edge appears brighter in the x-ray image.
The Omega Nebula is a massive, complex cloud of dust and gas from which new stars are continually forming. The similarity to the Greek letter capital Omega gives the molecular cloud its popular name, but the nebula is also known as the Swan Nebula, the Horseshoe Nebula, and M17. Detailed features such as thin filaments of emission by diffuse dust and dark clouds of absorption by dense dust are visible in this recently released picture. The image highlights infrared light emitted by large molecules known as polycyclic aromatic hydrocarbons (PAHs), a gas similar to car exhaust that traces carbon and interstellar dust. PAHs may be an intermediate step between smaller molecules and large interstellar dust grains. The origin of PAHs is currently unknown but thought by some astronomers to form in the cool atmospheres of young carbon stars and to be dispersed by their stellar winds.
The unassuming star centered in this sky view will one day be our next door stellar neighbor. The faint 9th magnitude red dwarf, currently 63 light-years away in the constellation Ophiucus, was recently discovered to be approaching our Solar System. Known in catalogs of nearby stars as Gliese 710 it is predicted to come within 1 light-year of the Sun ... a million years from now. At that distance this star, presently much too faint to be seen by the naked eye, will blaze at 0.6 magnitude - rivaling the apparent brightness of the mighty red giant Antares. Ultimately Gliese 710 poses no direct collision danger itself although its gravitational influence will likely scatter comets out of the Solar System's reservoir, the Oort cloud, sending some inbound. This future stellar encounter was discovered by researchers Joan Garcia-Sanchez and Robert Preston (JPL), and collaborators while studying stars in the solar neighborhood using data from the Hipparcos Astrometry Satellite. The star field shown is based on the Palomar Digitized Sky Survey and is 1/4 degree wide (about half the diameter of the full moon).
Each red speck indicated above is a powerful quasar estimated to be over 100 times brighter than a galaxy. Yet in these Sloan Digital Sky Survey discovery images the quasars appear faint because they are extremely distant. Their distances have been indirectly gauged by noting how much the light they emit has been stretched to longer wavelengths by the expansion of the Universe. Because red light has the longest wavelengths in the visible spectrum, this stretch has come to be called "redshift" - the greater the distance, the greater the redshift. Astronomers use a number known as "Z" to quantify this cosmological redshift and the quasar at the left, with a Z of 5, was just proclaimed the new quasar redshift champion (from left to right the measured Zs are 5.00, 4.90, 4.75). What's the actual distance to quasars with Zs of 5 or so? ... about 15 billion light-years, give or take a few billion light-years depending on your favorite cosmology!
Look closely. In this Mars Global Surveyor image of the Martian surface just south of Schiaparelli crater, dark lines appear to criss-cross light colored depressions. One tantalizing possibility is simply that the feature near the center is similar to a dried-up lake bed on planet Earth, where light colored mineral deposits are left as water evaporates and cracks are produced as the ground dries. This potential Martian lake bed is roughly 3/4 miles across and may provide further evidence that Mars once possessed surface water. Recently announced results from the Mars Pathfinder mission also point to a Martian past which included a denser atmosphere and surface water - conditions which could have supported life.
Where do stars form? A typical place is an area of dense nebular gas common to arms in spiral galaxies. Sometimes, however, a burst of star formation can occur with unusual geometry. Nearby galaxy NGC 1317 shows such an unusual ring of star formation surrounding its barred nucleus. In the above image, older stars appear more red and are more evident in the leftmost photograph in visible light. The rightmost photograph taken by the Ultraviolet Imaging Telescope is in ultraviolet and highlights stars which are younger and bluer and shows the starbirth ring. This unusual ring may be evidence of a gravitational encounter with another galaxy, causing a density wave to ripple out from the galaxy's center.
After a Sun-like star can no longer support fusion in its core, the center condenses into a white dwarf while the outer atmospheric layers are expelled into space and appear as a planetary nebula. This particular planetary nebula has a quite strange and chaotic structure. The inner part of this nebula contains an unusual expanding ring of gas that we see nearly edge-on. The exact mechanism that expels the planetary nebula gas is a current topic of astronomical speculation and research. | 0.956913 | 3.855081 |
The fun thing about astrophysicists is that they don’t only look 4 billion years into the future to see how our galaxy will get smashed up; they also like to look backward — 9 billion years ago, in this case — to see how it was formed in the first place.
Using NASA’s Hubble Space Telescope, a team of Hopkins researchers led by Steven Rodney (and his co-investigator, our fave Adam Riess), found an incredibly distant stellar explosion. That supernova, which they nicknamed SN Primo, is the last remnant of a white dwarf star that exploded 9 billion years ago. Now consider this: the cosmos itself is only 13.7 billion years old. By spectroscopic observations of SN Primo, the researchers hope to measure the expansion rate of the universe and to better understand dark energy, that mysterious force that’s making the universe accelerate in its expansion. | 0.871241 | 3.244717 |
A European space probe is due to land on a comet in November, and now scientists have identified five sites where it could touch down.
If successful, the touchdown of the Rosetta spacecraft's Philae lander on the target Comet 67P/Churyumov-Gerasimenko will be the first of its kind. Officials with the European Space Agency identified the potential comet landing sites after reviewing detailed images of the oddly-shaped 67P/C-G following Rosetta's arrival at the object on Aug. 6.
Comet 67P/C-G is littered with boulders the size of houses, craggy faces and jagged outcroppings, making the task of choosing a landing site for the 220-lb. (100 kilograms) lander somewhat complicated, according to ESA. The comet is also composed of three distinct parts: a "head," "neck" and body. Scientists originally picked 10 potential landing sites for Philae, but narrowed it down to five candidates over the last weekend. [See amazing photos taken by Rosetta]
"This is the first time landing sites on a comet have been considered," Stephan Ulamec, the mission's lander manager at the German Aerospace Center (DLR) said in a statement. "Based on the particular shape and the global topography of Comet 67P/Churyumov-Gerasimenko, it is probably no surprise that many locations had to be ruled out."
Ulamec said the science team picked the five candidates because they get six hours of daylight for each rotation of the comet, and have flat terrain that would be suitable for landing. And, Ulamec added, "of course, every site has the potential for unique scientific discoveries."
Philae needs a fair amount of sunlight in order to successfully recharge its batteries after its initial 64 hours of battery life runs out. However, too much sunlight could overheat the probe, so scientists need to choose a landing spot with a delicate balance, according to ESA officials. The landing spot also needs to be positioned so that the Rosetta spacecraft and its lander will be able to communicate with each other regularly.
Rosetta and Philae are designed to watch the comet as it makes its way toward a close approach with the sun in about a year. As the comet flies closer to the sun, Rosetta will make observations from orbit, while Philae takes measurements from the comet's surface to see how the activity of Comet 67P/C-G changes during its 6.5-year orbit.
The probe and the comet are currently flying about 324 million miles (522 million km) from the sun, but in about one year, the comet and spacecraft will fly about 115 million miles (185 million km) from the star, according to ESA.
"The comet is very different [from] anything we've seen before, and exhibits spectacular features still to be understood," Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument which is expected to take panoramic images of the comet's surface, said in a statement. "The five chosen sites offer us the best chance to land and study the composition, internal structure and activity of the comet with the 10 lander experiments."
Each of the landing sites chosen over the weekend have advantages and possible disadvantages, according to ESA:
Site A: This site is located on the larger "body" of the comet and provides a nice view of the smaller "head." Officials will need to investigate whether there are dangerous surface features that could damage the probe, ESA officials said.
Site B: Site B is inside a craterlike structure on the smaller lobe, ESA officials said. It's flat and seems somewhat safe for landing; however, more data is needed to discern whether lighting conditions are optimal for the landing.
Site C: This site on the larger "body" of the comet has plenty of light and some interesting features. Scientists still need to assess whether those depressions, cliffs and brighter material in the region could pose a hazard to Philae.
Site I: This flat area on the small lobe features some rough terrain and fresh material. However, sunlight abounds, and it could be an interesting area to land.
Site J: Site J and I are similar landing sites on the smaller "head" of the comet, according to ESA. Some boulders and other features could prove treacherous, so scientists need more high-resolution images to learn more about the area.
Officials still need to collect more data before a final landing area is chosen. ESA is planning to rank the five possible sites by Sept. 14, and a landing date is tentatively set for Nov. 11.
Rosetta launched in 2004 and arrived at the comet after a 10-year, 4 billion mile (6 billion km) trek across the solar system.
- Comet 'Cherry-Gerry' Landing Sites Narrowed To Five | Video
- European Spacecraft To Land On Comet In 2014 - Animation
- Comet Quiz: Test Your Cosmic Knowledge
- Rosetta Probe vs. Comet 'Cherry-Gerry' - Size Comparison | Video
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Supermoon of February 9, 2020
What is a Supermoon?
In recent years, the "Supermoon" has become more and more famous, and it attracts many people to observe enthusiastically every time it appears. The name "supermoon" was proposed by the American astrologer Richard Nolle in 1979. It is a phenomenon in which the new moon or full moon nearly coincides with perigee. When the moon is near the perigee, a new moon appears that is called super crescent; and if the moon is exactly the full moon when it is in the perigee, we call it super full moon. Because the moon orbits the earth in an elliptical orbit, the distance between the moon and the earth is constantly changing, the closer the moon is to the earth when the full moon occurs, the larger the full moon appear. Astronomy experts explained that the average distance between the moon and the earth is about 384,000 kilometers, the nearest is about 360,000 kilometers, and the furthest is about 400,000 kilometers. This change in the distance between the moon and the earth has caused the apparent diameter of the moon to change.
When is the Next One?
On February 9, there will be a supermoon. This is also the first of four supermoons for 2020. The Moon will be at its closest approach to the Earth and may look slightly larger and brighter than usual. At that moment, a full moon at perigee appears roughly 12.2% larger in diameter than at apogee. While the moon's surface luminance remains the same, because it is closer to the earth the illuminance is about 25.1% brighter than at its farthest point, or apogee (Depending on weather conditions). However, this change in size and brightness is actually not easy to detect by human eyes. You need to use a professional astronomical telescope to observe it. We recommend a popular saxon 6" DeepSky Dobsonian Telescope which comes with a light-grabbing aperture of 153mm and a focal length of 1200mm - perfect for viewing the Moon upclose as well as bright deep sky objects. | 0.836253 | 3.286243 |
NASA in a recent update has stated that the US space agency
is all set to launch a rocket to probe the Sun’s nanoflare using X-ray vision. Nanoflares are the tiny and highly intense eruptions that take place across the sun’s surface. These eruptions have resulted when the magnetic field lines of the sun’s atmosphere tangle up and stretch until they snap like a rubber band. The resultant energy released accelerates the particles to light speed and are responsible for heating up the solar atmosphere. The nanoflares are so tiny, that they are practically invisible to the naked eye. Christened as “FOXSI” OR Focusing Optics X-ray Solar Imager
, it is a sounding rocket mission that will fly 190 miles up in the earth’s atmosphere to scan the sun using x-ray vision in search of Nanoparticles. In a recent press release, NASA has stated that the mission is all set for its third flight from White Sands Mission Range in White Sands on September 7. Lindsay Glesener who is a space physicist at the University of Minneapolis is one of the principal investigators for the FOXIS mission. He stated, "FOXSI is the first instrument built specially to image high-energy X-rays from the Sun by directly focusing them.” NASA FOXSI rocket have benefits over other large-scale satellites due to its compact size and cheaper building costs. Also, being compact they travel at higher speed and can be built much faster than an average satellite, thus enabling scientists to study and map the space much more conveniently. FOXSI being a sounding rocket will make a short 15-minute journey up above the earth’s atmosphere
to collect data from the Sun’s Nanoflares, before falling back to the ground. X-rays from the sun cannot be easily captured. The rays are generally hard to focus and are mostly unaffected by the mirrors that are used in conventional telescopes. Designed by the FOXSI team, FOXSI lenses are generally hard, smooth surfaces tilted at a small angle(less than half a degree) that would converge the incoming x-ray lights to a point of focus. This third mission also includes a new telescope designed for imaging lower energy, termed as soft x-rays.
"Including the soft X-ray telescope gives us more precise temperatures" allowing the team to spot nanoflare signatures that would be missed with the hard X-ray telescopes alone - Glesener.
This will be NASA's FOXSI third flight since 2012. During its first journey, FOXSI had successfully captured a small solar flare in progress and its second in 2014, when it detected the best evidence at the time of X-ray emission from nanoflares.
India Coronavirus Cases Update
6,348 (2.8%) Deaths
109,462 (48.3%) Recovered
05 Jun 2020, 5:32 AM (GMT) | 0.800924 | 3.324828 |
eso1328 — Science Release
Three Planets in Habitable Zone of Nearby Star
Gliese 667C reexamined
25 June 2013
A team of astronomers has combined new observations of Gliese 667C with existing data from HARPS at ESO’s 3.6-metre telescope in Chile, to reveal a system with at least six planets. A record-breaking three of these planets are super-Earths lying in the zone around the star where liquid water could exist, making them possible candidates for the presence of life. This is the first system found with a fully packed habitable zone.
Gliese 667C is a very well-studied star. Just over one third of the mass of the Sun, it is part of a triple star system known as Gliese 667 (also referred to as GJ 667), 22 light-years away in the constellation of Scorpius (The Scorpion). This is quite close to us — within the Sun’s neighbourhood — and much closer than the star systems investigated using telescopes such as the planet-hunting Kepler space telescope.
Previous studies of Gliese 667C had found that the star hosts three planets (eso0939, eso1214) with one of them in the habitable zone. Now, a team of astronomers led by Guillem Anglada-Escudé of the University of Göttingen, Germany and Mikko Tuomi of the University of Hertfordshire, UK, has reexamined the system. They have added new HARPS observations, along with data from ESO's Very Large Telescope, the W.M. Keck Observatory and the Magellan Telescopes, to the already existing picture . The team has found evidence for up to seven planets around the star .
These planets orbit the third fainter star of a triple star system. Viewed from one of these newly found planets the two other suns would look like a pair of very bright stars visible in the daytime and at night they would provide as much illumination as the full Moon. The new planets completely fill up the habitable zone of Gliese 667C, as there are no more stable orbits in which a planet could exist at the right distance to it.
“We knew that the star had three planets from previous studies, so we wanted to see whether there were any more,” says Tuomi. “By adding some new observations and revisiting existing data we were able to confirm these three and confidently reveal several more. Finding three low-mass planets in the star’s habitable zone is very exciting!”
Three of these planets are confirmed to be super-Earths — planets more massive than Earth, but less massive than planets like Uranus or Neptune — that are within their star’s habitable zone, a thin shell around a star in which water may be present in liquid form if conditions are right. This is the first time that three such planets have been spotted orbiting in this zone in the same system .
“The number of potentially habitable planets in our galaxy is much greater if we can expect to find several of them around each low-mass star — instead of looking at ten stars to look for a single potentially habitable planet, we now know we can look at just one star and find several of them,” adds co-author Rory Barnes (University of Washington, USA).
Compact systems around Sun-like stars have been found to be abundant in the Milky Way. Around such stars, planets orbiting close to the parent star are very hot and are unlikely to be habitable. But this is not true for cooler and dimmer stars such as Gliese 667C. In this case the habitable zone lies entirely within an orbit the size of Mercury's, much closer in than for our Sun. The Gliese 667C system is the first example of a system where such a low-mass star is seen to host several potentially rocky planets in the habitable zone.
The ESO scientist responsible for HARPS, Gaspare Lo Curto, remarks: “This exciting result was largely made possible by the power of HARPS and its associated software and it also underlines the value of the ESO archive. It is very good to also see several independent research groups exploiting this unique instrument and achieving the ultimate precision.”
And Anglada-Escudé concludes: “These new results highlight how valuable it can be to re-analyse data in this way and combine results from different teams on different telescopes.”
The team used data from the UVES spectrograph on ESO’s Very Large Telescope in Chile (to determine the properties of the star accurately), the Carnegie Planet Finder Spectrograph (PFS) at the 6.5-metre Magellan II Telescope at the Las Campanas Observatory in Chile, the HIRES spectrograph mounted on the Keck 10-metre telescope on Mauna Kea, Hawaii as well as extensive previous data from HARPS (the High Accuracy Radial velocity Planet Searcher) at ESO’s 3.6-metre telescope in Chile (gathered through the M dwarf programme led by X. Bonfils and M. Mayor 2003–2010 described here).
The team looked at radial velocity data of Gliese 667C, a method often used to hunt for exoplanets. They performed a robust Bayesian statistical analysis to spot the signals of the planets. The first five signals are very confident, while the sixth is tentative, and seventh more tentative still. This system consists of three habitable-zone super-Earths, two hot planets further in, and two cooler planets further out. The planets in the habitable zone and those closer to the star are expected to always have the same side facing the star, so that their day and year will be the same lengths, with one side in perpetual sunshine and the other always night.
This research was presented in a paper entitled “A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone”, to appear in the journal Astronomy & Astrophysics.
The team is composed of G. Anglada-Escudé (University of Göttingen, Germany), M. Tuomi (University of Hertfordshire, UK), E. Gerlach (Technical University of Dresden, Germany), R. Barnes (University of Washington, USA), R. Heller (Leibniz Institute for Astrophysics, Potsdam, Germany), J. S. Jenkins (Universidad de Chile, Chile), S. Wende (University of Göttingen, Germany), S. S. Vogt (University of California, Santa Cruz, USA), R. P. Butler (Carnegie Institution of Washington, USA), A. Reiners (University of Göttingen, Germany), and H. R. A. Jones (University of Hertfordshire, UK).
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
- Research paper
- Description of HARPS
- Photos of the La Silla Observatory
- eso1214 — press release describing earlier observations of Gliese 667C by the HARPS team
- eso0939 — press release describing original observations of this star using HARPS
- Keck Observatory
- Las Campanas — Magellan telescopes
Institut fur Astrophysik, University of Göttingen
Tel: +49 0551 39 9988
Center for Astrophysics Reseach, Hertfordshire University
Tel: +44 01707 284095
Department of Astronomy, University of Washington
Tel: +1 206 543 8979
ESO education and Public Outreach Department
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591 | 0.819448 | 3.642584 |
The Gunlock Meteorite was discovered in 1982 in southwestern Utah. One of only 18 meteorite samples known from Utah (see geology.utah.gov/ surveynotes/gladasked/gladmeteorites.htm),the Gunlock Meteorite is an extremely rare and valuable find. Now, after 26 years in a private collection, a 18-pound piece of the Gunlock Meteorite has returned to Utah and found a new home at the UGS.
Meteorites are important because they are samples of asteroids, comets, or planets and are among the only rocks that provide geologists with “ground truth” information about the nature of solar-system bodies other than the Earth.
The Gunlock Meteorite is a chondrite, a particular group of stony meteorites that derives its name from the Greek word for “seeds.” The name alludes to the meteorites’ distinctive texture characterized by small grains called chondrules. Current theories concerning the origin of chondrites suggest they are related to the birth of the sun in a contracting disk of spinning interstellar dust and gas clouds called a solar nebula. As the sun ignited, interstellar dust in the nebula melted and condensed into droplets or chondrules of silicate minerals like olivine and pyroxene, which are also found in many igneous rocks on Earth.
As soon as the chondrules started forming they began clumping together with the remaining dust and gas in the solar nebula, forming a primitive cosmic sediment of silicate minerals, metals like iron and nickel, and simple organic compounds, as well as diamond dust and heavy elements seeded into the nebula by nearby exploding stars or novas. In time, this cosmic sediment grew from pebble-sized rocks to boulders, asteroids several hundred miles across, and occasionally into even larger objects like planets.
The present-day asteroid belt between Mars and Jupiter is a collection of leftover chondritic material that did not become part of a larger planet. Collisions between asteroids knock off pieces that occasionally fall to Earth as chondritic meteorites.
Chondritic meteorites are among the most exciting rocks available for scientific study. The age of chondrites, determined by the radioactive decay of constituent elements, is an amazing 4.5 billion years—older than any other known rocks on Earth. Although Earth probably formed about the same time, geologic processes have constantly recycled the rocks on its surface. Because chondrites retain their primitive texture and composition, they are the only rocks that can actually be traced back to the birth of the solar system.
Mr. Don Adair, of Boise, Idaho, discovered the Gunlock Meteorite on June 22, 1982, while mapping the geology of the Goldstrike mining district in Washington County. A quick survey of Padre Hill, where the meteorite was found, yielded a second meteorite fragment about 150 feet away. The two fragments fit together, indicating they were originally one piece. This past winter, Mr. Adair graciously donated one of the fragments to the UGS where it can be seen on permanent display in the Natural Resources Map & Bookstore. | 0.87177 | 3.834535 |
It takes your eyes about half an hour to fully adjust to the darkness. Little by little, everything comes into focus: The silhouettes of two Norfolk pines, stars glimmering between their branches. The moon, tracing a silver path across the sea, making the white barrel of the Dobsonian telescope glow. And above, stars like sand on the beach below; great drifts of them scattered across the darkness, condensing into a feathery cloud, like smoke suspended in the sky.
“What’s that?” I wonder aloud. “It’s a spiral arm of the Milky Way,” says star guide Deborah Kilgallon. Despite the darkness surrounding us, I can hear the smile in her voice. Her wellspring of enthusiasm for the night sky hasn’t been dimmed by her familiarity with it. The moon turns her blonde plait silver as she squints into the telescope, training its lens on a succession of individual stars. Until tonight, I had no idea stars had different textures and colours. Betelgeuse is soft and golden-orange, while Sirius is a sharp-edged, twinkling diamond.
“Sirius is the brightest star no matter where you are in the world,” says Kilgallon. “It’s only 8.6 light years away. Betelgeuse is a red supergiant, many thousands of times brighter than our sun, but it’s further away.” Using a laser pointer, Kilgallon connects the dots between seven stars in the shape of a saucepan. To me, this constellation looks like a pot, but to the ancient Greeks, it was the sword and belt of a giant: Orion. I tilt my head to the side in order to see him – he’s about to disappear head-first beneath the northern horizon. “A lot of the constellations in the Southern Hemisphere are viewed upside-down,” explains Kilgallon. “A bit later in the evening, I’ll show you Scorpius, which rises as Orion sets – it’s always chasing him across the sky.”
Eight cosy outdoor chairs, each one equipped with a pair of binoculars, are set up on the tussock verge above Medlands Beach, a crescent of sand located 10 minutes’ drive south of Claris, the airstrip on Great Barrier Island. I lean back into the cushions, trying to take it all in. Normally, you’d have to hike days into a national park to see a sky like this. The stars are hidden from most of us by the light of the cities we live in – 80% of humanity lives beneath light-polluted skies, while more than a third of the world’s population can’t see the cloud-like spiral arm of the Milky Way.
That’s what makes Great Barrier so special. It’s dark, but it’s inhabited by about 1,000 people. Being on the eastern edge of Auckland, it’s easy to reach. It’s part of the city, yet not quite, separated from it by 88km of ocean – far enough for Auckland’s bright lights to fade out. The island is long and narrow; you could drive across it in minutes, and top to bottom in a couple of hours, on winding roads that whisk you from view to view.
“The stars are hidden from most of us by the light of the cities we live in – 80% of humanity lives beneath light-polluted skies”
Here, every resident lives off the grid. The island has no traffic lights, no street lights, no commercial lighting, no reticulated electricity, no banks and no supermarket. It’s common for islanders to grow their own fruit and vegetables to supplement what’s available at the tiny store. There’s a sense of making do, of living carefully – with ingenuity and restraint – and of embracing nature. That means that when night enfolds the island, there’s nothing to drive it away.
In fact, Great Barrier is so unpolluted by light that it was recently declared a Dark Sky Sanctuary by the International Dark-Sky Association, which certifies places around the world in order to preserve the quality of their night skies. There are several levels of certification, and Great Barrier is the darkest – it’s one of only four destinations so far to achieve sanctuary status, and the only island at that.
Now people come here for the sole reason of getting a good look at the night sky – some for the first time in their lives. Locals, too, have gained a new appreciation for what’s in their backyard. These days, resorts host astrophotography workshops and Great Barrier residents form one of the largest amateur astronomy groups in New Zealand, with about 100 members or 10% of the island’s population.
The minute I arrive at my bed-and-breakfast, Medlands Beach Lodge, I notice the telescope tucked into the corner of the living room. “I think we have more telescopes per capita than anywhere else,” says Gendie Somerville-Ryan, an islander and one of the driving forces behind the creation of the sanctuary. She has a big smile, a silver-blonde bob and the air of a person who gets things done.
But it wasn’t always like this. Two years ago, Great Barrier had a perfectly ordinary number of telescopes. Gendie and her husband, Richard, had moved to the island after a career spent overseas consulting in developing countries. Returning home, both realised that Great Barrier’s sky was something special, and that it needed protecting. They joined forces with Auckland astronomer Nalayini Davies to measure exactly how special it was.
The trio pulled an all-nighter to take a series of readings with an electronic brightness meter designed for astronomers. The brightness of stars is classified according to magnitude, a system devised by the Greek astronomers Hipparchus and Ptolemy. The lower the magnitude, the brighter the star, and vice versa. How do you measure darkness? By determining the faintest star that can be detected – the one with the highest magnitude. That clear, moonless night confirmed what the group suspected: Great Barrier was very, very dark. Davies, who is on a personal quest to protect the sky from light pollution, was astonished. “All the night skies are deteriorating around the world,” she says. “[Great] Barrier is pristine.”
Next, the Somerville-Ryans wrote a report, convinced local businesses to reduce what little outdoor lighting they had, and arranged for 25 locals to receive astronomy training to become dark-sky ambassadors, with the idea that they’d pass on their knowledge to family, friends and visitors. Soon, the Dark Sky Sanctuary will become enshrined in law too. Richard tells me he’s working with the Auckland Council on legislation to ensure that any future development respects the island’s darkness. Amiable and chatty, he almost hums with enthusiasm, even when describing meetings with public officials. “Downtown Auckland, you’d be lucky to see 100 stars,” he says. “Great Barrier, on the same night, a very clear night, you could see maybe 5,000 stars – that’s the magnitude of difference we’re looking at.”
It’s a very clear night during my star tour, but the moon is waxing gibbous, like an inflating balloon, and my fellow astro-tourists and I cast sharply defined moon-shadows. Though the moon is barely three-quarters full, it’s bright enough to read by, and I understand why moonless nights are recommended for stargazing.
The waves on the beach below form a white-noise soundtrack as I peer through the telescope at Jupiter, a golden coin of a planet. I look at a star cluster called the Jewel Box, its central star a ruby-tinged flame, before sitting back to stare at the bright arm of the galaxy flung across the sky, like icing sugar dusting the night. It’s like looking back in time, I realise; by the time this light is reaching me, some of these stars are long dead. I’m witnessing astronomical ghosts.
Kilgallon points out the twin stars that form Gemini, then draws the crab, Cancer, and shows us our closest star, Alpha Centauri. It looks like one star, but it’s actually a binary system of two. “They’re sandwiched together like a double ice cream cone,” she says.
The island’s amateur astronomy group introduced Kilgallon to the stars. She loved learning about them so much that she became a dark-sky ambassador, and through the training, found two other women, Hilde Hoven and Orla Cumisky, who were equally enthusiastic. In 2017, they joined forces to form Good Heavens, the island’s first stargazing tour company.
Hoven is direct, yet carefully considered, and has her curly hair pulled back in a ponytail. Originally from the Netherlands, she arrived on Great Barrier in 1999, met a local and never really left, working as a translator, running a holiday home and leading star tours. For her, like the others, astronomy has opened up new worlds. “The sky had been something one-dimensional, two-dimensional, but this makes it three-dimensional,” she says.
I’m keen to put what I’ve learnt to the test. On my last night on the island, Mark Durling, the affable, laid-back proprietor of Medlands Beach Lodge, offers to set up his telescope outside for me, but I decide to take myself on a solo star tour instead, down at the beach. It’s only just become astronomical night – it takes about 90 minutes following sunset for the sun’s rays to fully disappear – but the sand still holds the heat of the day. When I lean back, the panoply of stars above is a scattered, confusing radiance, like an abstract painting of droplets. But soon, it begins to coalesce.
“Some [stars] shine like beacons, fresh and new. Others waver like firelight, in and out of being”
It’s as though I’m looking at the sketchbook of an artist who has jotted down only the tiniest gestures on the page – a curve of dots, an outline, a form. Some stars look old and faded, their polish worn. Some shine like beacons, fresh and new. Others waver like firelight, in and out of being. I can see Scorpius on the southern horizon, and the orange-red star pulsing at its heart, Antares. The bright “star” above it is actually Jupiter. I had looked at it up close through the Dobsonian the other night, and had seen the patches of its storms and three of its moons. I know which four-star kite is the Southern Cross, because I remember to look for the bright, identifying Pointers. Below the cross I see a patch of dark, blank space, and remember Kilgallon telling me that’s a dust cloud so thick that no starlight can get through.
For the first time, I have a map to the world above, not just the world below, and already I want to find out more. Hoven and Kilgallon had both warned me that this would happen. “The more you learn, the more you realise there is to learn,” said Kilgallon. “It just grows and grows and grows.”
– PHOTOGRAPHY BY TALMAN MADSEN
Singapore Airlines flies to Auckland daily. To book a flight, visit singaporeair.com
This article was originally published in the July 2018 issue of SilverKris magazine | 0.820899 | 3.47149 |
The news that an Earth-mass planet has probably been discovered in orbit around alpha Centauri B has a big impact on Project Icarus. If this news is confirmed, then it means our nearest stellar neighbor has at least one planet. Overnight, alpha Centauri has potentially become a more interesting target for Project Icarus.
Professor Ian Crawford, lead designer for Project Icarus science and target selection, has already written an article in which he favors alpha Centauri as a target (Which Exoplanet to Visit?). After the latest news was released, Crawford added:
“The alpha Centauri system was already the front runner as a Project Icarus target, because of the three different types of star it contains. So the discovery of a planetary system just reinforces the system’s priority as a target.
“Although this particular planet is too close to its star to be habitable, if the discovery is confirmed it is very likely that other planets exist at greater orbital distances. These could potentially be habitable and, if found to be present, would increase the priority of the system even more.”
Crawford sounds a note of caution:
“Clearly this was a very difficult measurement to make and the statistics, while formally good enough to claim a discovery, are not as great as one would like. It will be very interesting to see the results of follow-up observations. Hopefully these will confirm this detection.
“Moreover, it also appears that even these very sensitive radial velocity measurements are incapable of detecting Earth-mass planets in the alpha Centauri B habitable zone (HZ) — with the lowest mass detectable at HZ orbital distances being 4 Earth-mass super-Earths. Therefore, despite the very real cause for excitement about this detection, it may still be a long wait before we know whether or not this star also has Earth-mass planets in its habitable zone.”
So we proceed with Project Icarus bearing this caution in mind, but buoyed by the excitement of this potentially amazing discovery if it is confirmed.
Crawford’s paper Astronomical Considerations Relating To The Choice Of Target Star can be found in JBIS Vol 63 No 11/12 Nov/Dec 2010.
A list of Crawford’s publications can be found on his website. | 0.870944 | 3.389305 |
Two spacecraft are now beginning to study the moon’s environment as part of NASA’s ARTEMIS mission, whose principal investigator is Vassilis Angelopoulos, a UCLA professor of Earth and space sciences.
One of these satellites has been in the lunar environment since Aug. 25, and the second arrived Oct. 22, marking the start of the ARTEMIS mission to gather new scientific data in the sun-Earth-moon environment.
ARTEMIS is an acronym for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun.
For roughly six months, the two satellites will fly in orbits behind the moon but will not orbit the moon itself. This type of orbit relies on a precise balancing of sun, Earth and moon gravity. Then, in April 2011, the spacecraft are scheduled to make elliptical orbits around the moon, each providing data every second day for several years or longer.
ARTEMIS will use simultaneous measurements of particles and electric and magnetic fields from the satellites to provide the first three-dimensional perspective of how energetic particle acceleration occurs near the moon’s orbit, in the distant magnetosphere and in the solar wind. ARTEMIS will also make unique observations of the space environment behind the dark side of the moon — the greatest known vacuum in the solar system.
“We will study the space environment around the Earth and around the moon, which are not well understood,” Angelopoulos said. “ARTEMIS will provide unprecedented data and will go where no spacecraft have gone before.
“In collaboration with NASA’s Jet Propulsion Laboratory and UC Berkeley, we are flinging the satellites into interplanetary space to the point where the Earth’s gravity and moon’s gravity are approximately equal. ARTEMIS will also provide new operational data, which will help NASA plan future moon missions. NASA engineers and mission planners will gain valuable knowledge as a result.”
ARTEMIS is an offspring of the five-satellite NASA mission known as THEMIS (Time History of Events and Macroscale Interactions during Substorms), for which Angelopoulos is also the principal investigator. ARTEMIS, which redirects two of the THEMIS satellites to the moon, will study the space environment farther from Earth than THEMIS was ever designed to do, Angelopoulos noted.
“The space environment is very different that far away from the inner magnetosphere because it is not affected much by the Earth’s strong magnetic field,” he said. “It is a pure environment in which we can understand fundamental phenomena like magnetic reconnection, particle acceleration and turbulence, which are all very hard to study in the laboratory. Magnetic reconnection, particle acceleration and turbulence are important because they are a means of converting magnetic energy into particle energy, and they operate in many other environments, such as fusion machines and distant stars.
“In astrophysics, there are many places where magnetic reconnection, particle acceleration and turbulence take place. We can infer them only from the light they produce from some of the most violent explosions that occur in the universe — from X-rays and gamma rays in pulsars, for example. Magnetic fields interact and often create, through reconnection, the expulsion of jets releasing enormous amounts of energy away from black holes, into space.
“We expect to learn fundamentally how magnetic reconnection and turbulence work in three dimensions,” he added. “We need to understand the way particle interactions with electromagnetic fields take place in that pristine region of space. ARTEMIS is uniquely instrumented to study this problem.”
A vacuum is created behind the moon, Angelopoulos noted, as the solar wind goes by, and the solar wind is absorbed by the moon. ARTEMIS will study how magnetized bodies interact with the solar wind.
ARTEMIS represents a joint effort between UCLA; UC Berkeley; NASA’s Goddard Space Flight Center in Greenbelt, Md.; and the JPL. Several UCLA space scientists, from three separate departments, are involved in the mission.
The THEMIS mission has three additional satellites with electric, magnetic, ion and electron detectors that remain in carefully choreographed orbits around the Earth, as well as an array of 20 ground observatories with automated, all-sky cameras located in the northern U.S. and Canada that catch substorms as they happen.
As the THEMIS satellites are measuring the magnetic and electric fields of the plasma above Earth’s atmosphere and the ARTEMIS satellites record the distant effects of these phenomena as far as the moon, the ground-based observatories are continuing to image the auroral lights and the electrical currents in space that generate them.
THEMIS was launched Feb. 17, 2007, from Cape Canaveral, Fla., to impartially resolve the trigger mechanism of substorms. Themis was the blindfolded Greek goddess of order and justice. Artemis was the goddess of the moon in ancient Greek mythology. THEMIS and ARTEMIS are managed by the Explorers Program Office at NASA’s Goddard Space Flight Center.
Soon after their launch, the THEMIS probes discovered a cornucopia of previously unknown phenomena, including colliding auroras, magnetic spacequakes and plasma bullets shooting up and down Earth’s magnetic tail. This has allowed researchers to solve several longstanding mysteries of the aurora borealis, or “northern lights.”
In 2008, Angelopoulos and THEMIS colleagues identified the mechanism that triggers substorms in space, wreaking havoc on satellites, power grids and communications systems and leading to the explosive release of energy that causes the spectacular brightening of the aurora borealis.
UCLA is California’s largest university, with an enrollment of nearly 38,000 undergraduate and graduate students. The UCLA College of Letters and Science and the university’s 11 professional schools feature renowned faculty and offer more than 323 degree programs and majors. UCLA is a national and international leader in the breadth and quality of its academic, research, health care, cultural, continuing education and athletic programs. Six alumni and five faculty have been awarded the Nobel Prize.
For more news, visit the UCLA Newsroom or follow us on Twitter. | 0.869313 | 3.779381 |
For the first time, astronomers have discovered a class of exoplanets whose atmospheres have been seared away by heat, removing any doubts about what happens when a rocky object wanders too close to a star.
Theorists have long speculated that exoplanets snuggled right up next to their host stars would be subject to “stripping”, or erosion of the atmosphere by high-energy radiation. Now, using data collected by NASA’s Kepler Space Telescope, a team of astrophysicists at the University of Birmingham is reporting the very first observational evidence of these shriveled raisins. The findings are published today in Nature Communications.
“Our results show that planets of a certain size that lie close to their stars are likely to have been much larger at the beginning of their lives,” study co-author Guy Davies said in a statement. “For these planets it is like standing next to a hairdryer turned up to its hottest setting.”
The planets Davies and his co-authors studied are “super Earths”, rocky worlds larger than Earth but smaller than Neptune that are abundant in the cosmos but curiously absent from our own solar system (although that might change if and when astronomers discover Planet nine).
Despite how exotic these blistering hellscapes sound, they may foreshadow what’s to come in our own distant future. After all, as the Sun grows hotter and brighter over the next billion years, the extra radiation will start to cook our fragile biosphere, eventually boiling away the oceans and rendering the entire surface of the Earth uninhabitable. Whether our planet will eventually be stripped of its atmosphere too isn’t certain — but given the mounting evidence we’re beginning to see all over the galaxy, I don’t think we want to be around to find out.
Top: A planet having its atmosphere stripped by a star’s heat. Image: Peter Devine | 0.867773 | 3.747519 |
Olbers' paradox states that given the Universe is unbounded, governed by the standard laws of physics, and populated by light sources, the night sky should be ablaze with light. Obviously this is not so. However, the paradox does not lie in nature but in our understanding of physics. A Universe with a finite age, such as follows from big-bang theory, necessarily has galaxies of finite age. This means we can only see some of the galaxies in the Universe, which is the main reason why the night sky is dark. Just how dark can be calculated using the astrophysics of galaxies and stars and the dynamics of relativistic cosmology.
We know from the dynamics of individual galaxies and clusters of galaxies that the majority of matter that exerts gravitational forces is not detectable by conventional telescopes. This dark matter could have many forms, and candidates include various types of elementary particles as well as vacuum fluctuations, black holes, and others. Most of these candidates are unstable to decay and produce photons. So dark matter does not only affect the dynamics of the Universe, but the intensity of intergalactic radiation as well. Conversely, we can use observations of background radiation to constrain the nature and density of dark matter.
By comparing observational data with cosmological theory based on general relativity and particle physics, Dark Sky, Dark Matter reviews our present understanding of the universe and the astrophysics of the night sky and dark matter.
Table of Contents
The dark night sky
The modern resolution and energy
The modern resolution and spectra
The dark matter
Supersymmetric weakly interacting particles
Bolometric intensity integrals
Dynamics with a decaying vacuum
Absorption by galactic hydrogen
Overduin, J.M; Wesson, P.S
"Right after 'Why is the sky blue?,' 'Why is the sky dark?' is the next most commonly asked question kids, and non-kids, too, ask of parents, in particular, and science in general … the dilemma of the question actually became tougher to explain, resulting in what has become known as Olbers' paradox. Olbers, a Prussian astronomer, postulated in 1823, 'given that the Universe is unbounded, governed by the standard laws of physics, and populated by light sources of constant intensity, the simple cube law of volumes and numbers implies that the sky should be ablaze with light. Obviously, this is not so.' Dark Sky, Dark Matter takes this paradox and runs with it.
To the authors' credit, they begin the book with a remarkable history of Olbers and his paradox, explaining the variety of tactics people have used either to explain away the paradox or to support their own theories. The rest of the book delves into the astrophysical nature of the universe, structure of the stars and galaxies, radiation, and dark matter. The ancillary material includes three appendices that detail mathematical models and an adequate index.
This book utilizes advanced mathematics and physics appropriate for a graduate course in physics or astrophysics. Recommended for academic collections supporting physics (astrophysics) programs."
-Peggy Dominy, E-Streams
"The story of how all these exotic ingredients can be constrained by modern data is well told, and contains some interesting material. Overall, this book may well be consulted by graduate students seeking details of these topics."
-John Peacock, The Observatory, June 2003 | 0.821883 | 4.118298 |
The shock waves are still reverberating from BICEP2’s bombshell announcement that they’ve discovered the holy grail of cosmology: the telltale signature of gravitational waves from inflation. But what does this discovery really mean, and what impact will it have on cosmology?
About 13.8 billion years ago, merely 400,000 years after our Big Bang, everything in our observable universe was a hot plasma not too different from the surface of the Sun. Photos of this plasma, baby pictures of our universe around its 400,000th birthday, have already revolutionized modern cosmology and triggered two Nobel prizes. Now a team of astronomers has spent three years zooming in on about 1 percent of the sky from a state-of-the-art telescope at the South Pole, taking an even sharper photo of this plasma, including its polarization, and discovered that it’s distorted in a tantalizing way.
At the press conference, I met Alan Guth and Andrei Linde, whose theory of cosmological inflation had predicted this distortion, looking even happier than in the left-hand photo above. If they instead looked distorted as in the right-hand photo, you might wonder whether someone had slipped LSD into your morning coffee. Or whether gravitational waves – distortions in the very fabric of spacetime – were passing between you and them, bending the light rays that you see. BICEP2 has shown that humongous gravitational waves close to a billion light-years long are distorting their cosmic baby picture.
Making such strong gravitational waves requires extreme violence. For example, a cataclysmic collision of two black holes squeezing more than the Sun’s mass into a volume smaller than a city can create gravitational waves that the US-based LIGO experiment hopes to detect – but these waves are only about as big as the pair of objects creating them. So what could possibly have created the vast waves BICEP2 saw, given that our universe seems to contain no objects large enough to make them?
The answer to this question explains why Alan and Andrei were smiling: inflation! Their inflation theory in its simplest form predicts that our universe was once smaller than an atom, repeatedly doubling its size every 0.00000000000000000000000000000000000001 seconds or so, and this rapid doubling was precisely violent enough to create gravitational waves of the strength and length that BICEP2 has observed! Although it sounds like this repeated doubling of the inflating substance would violate the laws of energy physics (specifically energy conservation), it actually doesn’t, thanks to a loophole in Einstein’s theory of general relativity. I explain the physics of inflation and its aftermath in detail in chapter 5 of my new book Our Mathematical Universe in case you’re curious about how this works. When the inflating substance eventually decays into ordinary matter, the resulting hot plasma eventually cooled and clumped into the galaxies, stars and planets that adorn our universe today.
So how seriously should we take inflation? Inflation had emerged as the most successful and popular theory for what happened early on even before BICEP2, as experiments gradually confirmed one of its predictions after another: that our universe should be large, expanding and approximately homogeneous, isotropic and flat, with tiny fluctuations in the cosmic baby pictures that were roughly scale invariant, “adiabatic” and “Gaussian.” To me and many of my cosmology colleagues, the gravitational waves discovered by BICEP2 provide the smoking-gun evidence that really clinches it, because we lack any other compelling explanations for them. For example, the ekpyrotic and cyclic models of the universe that had emerged as the most popular alternatives to inflation are now suddenly ruled out because they cannot explain BICEP2’s gravitational wave detection.
This means that if the BICEP2 results hold up and we take inflation seriously, then we need to understand and take seriously also everything that inflation predicts - and these predictions form quite a long list! First of all, inflationary cosmology (“IC”) radically changes the answers to key questions given in the traditional cosmology (“TC”) textbooks I once studied:
Q: What caused our Big Bang?
TC: There’s no explanation – the equations simply assume it happened.
IC: The repeated doubling in size of an explosive subatomic speck of inflating material.
Q: Did our Big Bang happen at a single point?
IC: Almost: it began in a region of space much smaller than an atom.
Q: Where in space did our Big Bang explosion happen?
TC: It happened everywhere, at an infinite number of points, all at once, with no explanation for the synchronization.
IC: In that tiny region – but inflation stretched it out to about the size of a grapefruit growing so fast that the subsequent expansion made it larger than all the space that we see today.
Q: How could an infinite space get created in a finite time?
TC: There’s no explanation — the equations simply assume that as soon as there was any space at all, it was infinite in size.
IC: By exploiting a clever loophole in Einstein’s general relativity theory, inflation produces an infinite number of galaxies by continuing forever, and an observer in one of these galaxies will view space and time differently, perceiving space as having been infinite already when inflation ended.
Q: How big is space?
TC: There’s no prediction.
IC: Probably infinite.
Because of this last prediction, the BICEP2 discovery should cause dismay among multiverse skeptics – at least in this particular universe. This is because Alex Vilenkin, Andrei Linde, Alan Guth and others have shown that the space that inflation generically creates is not merely infinite, but uniformly filled with matter that forms infinitely many galaxies. This in turn means that no matter how unlikely it is that a galaxy will be indistinguishable from ours, containing someone whose life has so far been identical to yours, the probability is not zero since it clearly happened here. Which means that there must be duplicate copies of you far away in space, and indeed also similar versions of you living out countless variations of your life. Now it’s harder for skeptics to dismiss this by saying “inflation is just a theory” – first they need to come up with another compelling explanation for BICEP2’s gravitational waves.
I think that if the BICEP2 discovery holds up, it will go down as one of the greatest discoveries in the history of science. It has pushed our knowledge frontier back 38 orders of magnitude in time in a single giant leap, from the creation of Helium seconds after our Big Bang to inflation during the first few trillionths of a trillionth of a quadrillionth of that first second. This teaches us about physics at energies a trillion times greater than those produced in the Large Hadron Collider, of great relevance to string theory and other quests to unify the four fundamental forces into a single consistent theory.
Moreover, it’s a sensational breakthrough involving not only our cosmic origins, but also the nature of space: by producing the first-ever detection of Hawking/Unruh radiation (the process by which inflation's rapid doubling generates these gravitational waves), the BICEP2 team has found the first experimental evidence for quantum gravity.
So what lies ahead? Once the celebrations are over, we’ll look forward to seeing whether today’s announcement stands the test of time. The wait won’t be long since many other experiments have been racing against BICEP2 and will soon have the data to confirm or refute their findings. Many questions should get cleared up already in October, when the Planck satellite experiment is due to release its first polarized images of the cosmic plasma. Planck will produce the first good maps of polarized dust and establish whether its contaminating effect was as small as BICEP2 assumed. It will also produce an improved estimate of a parameter known as “tau” related to when the first stars ionized our universe. My personal guess is that they’ll find these stars to have formed later than currently assumed, which (for complex but well-understood reasons) will lower Plank’s estimate of how clumpy our universe is and will not only help bring the Planck constraints on gravitational waves up into better agreement with BICEP2’s detection, but also bring Planck’s predictions for the number of galaxy clusters down into agreement with what we observe.
If BICEP2 is proven correct, it should lead to at least one Nobel Prize. Further down the road, I bet that a first-ever satellite designed specifically to measure inflationary gravitational waves will get funded (now that we know there’s a signal for it to measure), which can determine how the cosmic doubling rate during inflation changed with time. This provides a great way to distinguish between specific inflation models and also to test any inflation competitors that may have gained credibility by then (for example, string gas models predict an increase whereas all inflation models predict a decrease).
But first, let’s celebrate one of the most exciting moments in the history of science! Above all, this feels like a great triumph for Occam’s razor: although countless complicated models for inflation emerged over the years, the BICEP2 data is beautifully fit by simple “classic’’ inflation, known in geek-speak as a single slow-rolling scalar field. And Andrei Linde looked particularly happy at the press conference, perhaps because two numbers have now been measured that act as a sort of fingerprint of inflation models: n=0.9608±0.0054 (reported by Planck, quantifying the ratio of small to large spots in the baby pictures) and r=0.16±0.05 (reported by BICEP2, quantifying the gravitational wave amplitude after correcting for galactic radio noise). These measurements agree tantalizingly well with the specific predictions of what’s arguably the simplest model of all: Andrei’s own favorite, whose potential energy curve is a simple parabola, which predicts n=0.96 and r=0.15. I think William of Occam would have been impressed! | 0.827011 | 4.037286 |
Exploration at the Edge of the Solar System
Telling the tale of Pluto’s discovery, the authors recount the grand story of our unfolding knowledge of the outer Solar System, from William Herschel’s serendipitous discovery of Uranus in 1781, to the mathematical prediction of Neptune’s existence, to Percival Lowell’s studies of the wayward motions of those giant planets leading to his prediction of another world farther out. Lowell’s efforts led to Clyde Tombaugh’s heroic search and discovery of Pluto—then a mere speck in the telescope—at Lowell Observatory in 1930.
Pluto was finally recognized as the premier body in the Kuiper Belt, the so-called third zone of our Solar System. The first zone contains the terrestrial planets (Mercury through Mars) and the asteroid belt; the second, the gas-giant planets Jupiter through Neptune. The third zone, holding Pluto and the rest of the Kuiper Belt, is the largest and most populous region of the solar system.
Now well beyond Pluto, New Horizons will continue to wend its lonely way through the galaxy, but it is still transmitting data, even today. Its ultimate legacy may be to inspire future generations to uncover more secrets of Pluto, the Solar System, and the Universe.
“This superb and timely book covers not only the New Horizons mission and its results, but also places the discovery of Pluto and the New Horizons mission in historical context, beginning with the discovery of Uranus in 1781.”—Society for the History of Astronomy Bulletin
“This authoritative, well-illustrated, and thoroughly-referenced book will be the ‘go-to’ tome for anyone interested in [Pluto] for many years to come.”—The Observatory Magazine
“Discovering Pluto is a beautiful book that will delight anyone interested in the Solar System.”—Sky at Night Magazine
“A comprehensive and authoritative account of the exploration of Pluto and its moons, providing a ringside seat to the exciting discoveries made during the New Horizons flyby. Here in one place is everything you need to know about the Plutonian system.”—Bonnie J. Buratti, Jet Propulsion Laboratory, California Institute of Technology
“Discovering Pluto offers a rare insider’s view, spanning the modern history of planetary science from early telescopic observations through the recent spectacular New Horizons flyby of Pluto.”—Keith Noll, Planetary Scientist | 0.882282 | 3.681335 |
Gibbous ♍ Virgo
Moon phase on 1 January 2089 Saturday is Waning Gibbous, 19 days old Moon is in Virgo.Share this page: twitter facebook linkedin
Previous main lunar phase is the Full Moon before 4 days on 28 December 2088 at 00:57.
Moon rises in the evening and sets in the morning. It is visible to the southwest and it is high in the sky after midnight.
Moon is passing about ∠14° of ♍ Virgo tropical zodiac sector.
Lunar disc appears visually 1.4% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1925" and ∠1951".
Next Full Moon is the Wolf Moon of January 2089 after 24 days on 26 January 2089 at 11:25.
There is low ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at big angle, so their combined tidal force is weak.
The Moon is 19 days old. Earth's natural satellite is moving from the middle to the last part of current synodic month. This is lunation 1100 of Meeus index or 2053 from Brown series.
Length of current 1100 lunation is 29 days, 19 hours and 26 minutes. This is the year's longest synodic month of 2089. It is 28 minutes longer than next lunation 1101 length.
Length of current synodic month is 6 hours and 42 minutes longer than the mean length of synodic month, but it is still 21 minutes shorter, compared to 21st century longest.
This lunation true anomaly is ∠160.8°. At the beginning of next synodic month true anomaly will be ∠185.7°. The length of upcoming synodic months will keep decreasing since the true anomaly gets closer to the value of New Moon at point of perigee (∠0° or ∠360°).
4 days after point of perigee on 28 December 2088 at 06:32 in ♋ Cancer. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 9 days, until it get to the point of next apogee on 11 January 2089 at 04:23 in ♑ Capricorn.
Moon is 372 359 km (231 373 mi) away from Earth on this date. Moon moves farther next 9 days until apogee, when Earth-Moon distance will reach 406 703 km (252 714 mi).
9 days after its descending node on 23 December 2088 at 02:43 in ♈ Aries, the Moon is following the southern part of its orbit for the next 3 days, until it will cross the ecliptic from South to North in ascending node on 4 January 2089 at 12:45 in ♎ Libra.
24 days after beginning of current draconic month in ♎ Libra, the Moon is moving from the second to the final part of it.
5 days after previous North standstill on 27 December 2088 at 04:20 in ♊ Gemini, when Moon has reached northern declination of ∠18.933°. Next 7 days the lunar orbit moves southward to face South declination of ∠-18.913° in the next southern standstill on 9 January 2089 at 11:54 in ♐ Sagittarius.
After 10 days on 11 January 2089 at 20:17 in ♑ Capricorn, the Moon will be in New Moon geocentric conjunction with the Sun and this alignment forms next Sun-Moon-Earth syzygy. | 0.848363 | 3.228797 |
Or it would be, if life was as fickle as the writers of popular science blogs.
The “Goldilocks Zone” comes up a lot when we talk about finding extraterrestrial life. This is the range of orbits around a star where the porridge is just right: temperatures will be roughly Earth-like, and ever-essential liquid water can exist. This lukewarm-porridge zone hugs a star closer if it’s dim, and remains farther out if it’s bright.
It’s a fairly narrow band, but not razor-thin. Scientists are generally aware that life on Earth can thrive both in arctic tundra and steamy jungles, so temperatures don’t have to be precisely Earth-norm. And to be fair, planets outside of this zone probably couldn’t have a biosphere that closely resembles Earth’s biosphere. But they could still have one.
In fact, they could have all kinds of different biospheres. Let’s look at five life-friendly but alien porridge bowls – er, worlds – in very different locations. And to take this one step further, let’s stay just close enough to home to make this thought experiment fun: some Earth-like life has to be able to live there. So we’ll keep liquid water as a criteria.
Boring Details: Why Water?
At the risk of sounding a bit Earth-centric here, water is an amazing solvent, and the best bet for life. Even if it’s not fair to say that water is required for life, it’s definitely impossible for organic, meat-based life to exist without SOME kind of liquid solvent – and water is both the most common compound in the universe, and liquid over a wide temperature range. The runner up here is ammonia: with lower temperatures and higher pressures, ammonia (or an ammonia/water mix) could be the solvent of life. But there’s less of it, it’s trickier to keep it liquid, and it’s generally a poorer solvent.
Regardless of the solvent used, it’s worth remembering that an atmosphere or ice cover is always required. The entire liquid phase of matter ceases to exist unless pressure is applied; on Earth, the atmosphere does double-duty of feeding you oxygen and keeping your water from boiling away. (Results may vary; see Mt. Everest for details.)
1. A Habitable Mercury
Let’s start out with Papa Bear’s porridge: it’s way too hot. We’re on a planet that’s practically in the fiery death-grip of its star, its years a scant few Earth months or even weeks long. Could we ever live here? Could we find life here at all?
Well, you probably see where this is going: yes. Yes we can. We even have options!
In our own solar system, Mercury is the planet closest to the Sun — almost three times as close as the Earth. It could probably never support life, but it does have two rather curious features that suggest life could exist much closer to a nuclear fireball than we’d expect. It has ice-filled craters at its poles, and at night its temperature is minus 173 degrees Celsius.
Let’s not go hunting for rich biospheres on Mercury anytime soon; it’s a bit on the small side for life anyway. But its lessons are important: on a hot world, we can still find water and cooler temperatures (MUCH cooler temperatures) if we stay in the shade. With just the right sort of thin, “greenhouse-gas-free” atmosphere, some of the heat could transfer from the hellishly hot day-side to the night-side or poles to produce something approaching a temperate climate belt. More importantly, some atmosphere allows water to be a liquid, and liquid water is a great heat-transfer and heat-storage medium. Boiling, evaporating day-side oceans could rain back down on the night side of the world. The permanent storms would be epic, but reasonably life-friendly – especially for underwater life.
2. A Habitable Mars or Europa
Mama Bear’s frosty porridge represents worlds orbiting too far from their sun – at a distance equivalent to Mars or beyond. Dimly lit and locked in ice, these worlds are frozen wastelands with no hope for… oh wait, let’s add some greenhouse gases. Okay, all better. Carbon dioxide makes a great blanket for cold planets, and there’s no shortage of it in the universe. If Mars had more a Earth-like gravity and magnetic field, it could have clung to its ancestral carbon dioxide atmosphere and liquid water.
If greenhouse gases aren’t enough to keep distant worlds warm and wet, life can always find a home in the oceans beneath the ice. Europa, a large moon orbiting Jupiter, is a great candidate for nearby extraterrestrial life – and its irrelevant surface is around -200 Celsius.
3. Goldilocks and the Very Small Oven
Have you ever stood around a campfire on a cold night, roasting in front and freezing in back? Well there are billions of porridge bowls – er, planets — out there that feel the same way.
If a planet orbits extremely close (where a year is like unto a day) to a small star, then the planet becomes tidally locked; like the Earth’s moon, it always displays just one face to its parent. This makes the whole sun-side / dark-side temperature-balance business easy, because it never changes. Instead, there would be a consistent band of “warm” at the horizon separating the permanent inferno and the permanent ice field.
When a planet is tidally locked, the concept of the goldilocks zone orbit makes even less sense. Instead, there’s a goldilocks zone on the planet itself: a ring of balmy terrain that’s closer to the sun side if the planet is farther away, and closer to the dark side if the planet orbits tightly. Life would generally prefer the side with sun (light for photosynthesis is handy) but all that really matters is keeping some water liquid — life will figure out the rest.
The life-friendly ring grows if the planet’s orbit is a bit eccentric, causing the sun to wobble in the sky and peek around to the cold side.* And if the orbit is close enough for a fast rotation (say, ten or fewer Earth days), it can still generate a magnetic field. It’s going to need it: red dwarf stars can spew some nasty flares, and life is going to want a good deflector shield or risk extinction-level auroras.
*Some scientists believe that librations caused by an eccentric orbit would cause too much tidal heating. This may not ruin the world for life, but it may cause some pesky supervolcano-related issues.
4. No star? No problem!
The resourceful Goldilocks, when trespassing in a bear-house containing only frozen porridge and no stove, will find some radioactive elements to heat the porridge to a nice, warm temperature.
Wait, what? No warm porridge and no oven? And… aren’t radioactive elements a problem?
Let’s step back and consider what this analogy means. The house Goldilocks has found is a planet floating in the void of space with no star – or orbiting so far from its star that it provides negligible energy. An alternative heat source is needed, because life as we know it (and even most life as we don’t) needs liquid water. Conveniently, there are multiple sources that can last billions of years: slow nuclear radiation from the heavy elements in a planet’s core, tidal stress as the planet interacts with its sun or moons, or even the remnant heat of the planet’s own formation trapped by a very thick atmosphere. Biospheres that entirely ignore Goldilock’s requirements wouldn’t look like Earth’s; they would be sparse, alien, predominantly aquatic, and nothing would have eyes. They may not be the universe’s prettiest biospheres, but they’re its most common.
5. No surface? Grab a moon.
Could we find life in the enormous, landless, sealess void of a gas giant?
It’s not impossible, just don’t expect to recognize anything. Life has an entirely different set of problems if it’s permanently airborne. But let’s not look at the big boring ball of gas like it’s a bowl of porridge (because ew, vaporized porridge sphere). It’s best to think of it as its own tiny oven, with small bowls of porridge orbiting it – and some of them could be delicious. The moons of giant planets could be great candidates for life, and planetary heating (tidal and reflective) could expand the classic Goldilocks zone. Large planets can have multiple large moons, all of which could have similar temperatures. Finding another habitable world on their doorstep would be a hell of an incentive for mooninite aliens to develop space travel.
And one more thing: remember the tidal locking problem that worlds have if they’re really close to a small star? It’s almost not a problem for a large moon in that system: the moon tidally locks to the planet, and the planet tidally locks to the star, but the star crosses the moon’s sky and doesn’t create permanent hot and cold sides. (It might form supervolcanoes due to tidal forces, but while civilization would hate those, life is more ambivalent.)
I cheated a bit: many of these ideas are from Chris Wayan’s Planetocopia. He has some astoundingly inspirational examples, and it’s definitely worth checking out – doubly so for skeptics.
Some might see his worlds, and this post in general, as overly optimistic. We’re not living in a Star Trek universe with its infestation of class-M planets; there are plenty of worlds that will NOT be life-friendly. The reasons could include hellish lava-tides, tiny size, massive radiation, constant comet bombardment or, always a classic, lack of atmosphere. Yet most of these problems aren’t related to a planet’s distance to its star. Life-hating worlds are by far the majority, but there are billions of worlds in our galaxy alone — if even a few percent are habitable, there is going to be a LOT of life out there. And for most of this life, if it spawns an intelligent civilization, the “goldilocks zone” will be known as “all planets with tidal forces or radiation strong enough to maintain a molten water-ocean below the ice crust that protects life from the deadly surface.” Not exactly catchy, but much more inclusive; there’s more than one good way to serve porridge.
P.S. Our bills are paid by our wonderful patrons. Could you chip in? | 0.881518 | 3.532689 |
As space agencies get ready for a new series of Mars missions dedicated to the search for life (the first of two European ExoMars missions launches next Monday) one important question is where they should land to have the best chance of finding biosignatures on the Martian surface. Thinking about this problem led me to a paper published several years ago that linked mineral composition in soils to life.
Based on their analysis of the mineral content of Martian soils, Tom Pike and co-authors concluded in a 2011 paper in Geophysical Research Letters that the Red Planet went through an extremely dry period that lasted hundreds of millions of years. The researchers looked at soil samples from the Phoenix landing site, which had almost no clay minerals or any other chemical or mineralogical markers suggesting the interaction of soil and water. Pike and colleagues concluded that the Martian soil at that location is Moon-like, and has been exposed to liquid water for a maximum of 5,000 years. Earlier assessments of the Phoenix site had focused on the soil’s low acidity, which was benign enough to grow asparagus, feeding speculation that the Phoenix site may be suitable for life.
The finding by Pike and colleagues harkened back to the Viking life detection experiments in 1976, particularly the Gas Exchange Experiment, which indicated that Martian soil was highly reactive chemically when exposed to liquid water. And the discovery of perchlorates, both at the Phoenix landing site and at the Curiosity site in Gale Crater, indicate extremely dry conditions on Mars today. This does not bode well for any putative Martian microbes that might have thrived on a wetter and warmer Mars about four billion years ago.
Whether these very dry conditions prevail only in some places on Mars or all over the planet is unclear at this time, but of critical importance. Although the planet’s wind patterns distribute sediment from one location to the other, resulting in mixing on a global scale, Mars is still a large and heterogeneous world, and we see evidence for a diversity of environments. Remote sensing images taken from Mars orbit support the notion that there are places on the surface with much different environmental conditions than we have observed at any of the landing sites to date. And there are many places we have not yet visited due to engineering constraints having to do with how high, or rough, or far from the equator a particular site is. No lander has yet touched down in the deep canyons of Valles Marineris, for example, or the Southern Highlands of Mars. And the so-called Special Regions of Mars, where water and life may be more likely, are subject to strict planetary protection requirements that drive up a mission’s costs. All of these factors make landing site selection as difficult as it is important. | 0.853859 | 3.903777 |
Scientists have long understood that in the course of cosmic evolution, galaxies become larger by consuming smaller galaxies. The evidence of this can be seen by observing galactic halos, where the stars of cannibalized galaxies still remain. This is certainly true of the Andromeda Galaxy (aka. M31, Earth’s closest neighbor) which has a massive and nearly-invisible halo of stars that is larger than the galaxy itself.
For some time, scientists believed that this halo was the result of hundreds of smaller mergers. But thanks to a new study by a team of researchers at the University of Michigan, it now appears that Andromeda’s halo is the result of it cannibalizing a massive galaxy some two billion years ago. Studying the remains of this galaxy will help astronomers understand how disk galaxies (like the Milky Way) evolve and survive large mergers.
Using computer models, Richard D’Souza and Eric Bell were able to piece together how a once-massive galaxy (named M32p) disrupted and eventually came to merge with Andromeda. From their simulations, they determined that M32p was at least 20 times larger than any galaxy that has merged with the Milky Way over the course of its lifetime.
M32p would have therefore been the third-largest member of the Local Group of galaxies, after the Milky Way and Andromeda galaxies, and was therefore something of a “long-lost sibling”. However, their simulations also indicated that many smaller companion galaxies merged with Andromeda over time. But for the past, Andromeda’s halo is the result of a single massive merger. As D’Souza explained in a recent Michigan News press statement:
“It was a ‘eureka’ moment. We realized we could use this information of Andromeda’s outer stellar halo to infer the properties of the largest of these shredded galaxies. Astronomers have been studying the Local Group—the Milky Way, Andromeda and their companions—for so long. It was shocking to realize that the Milky Way had a large sibling, and we never knew about it.”
This study will not only help astronomers understand how galaxies like the Milky Way and Andromeda grew through mergers, it might also shed light on a long-standing mystery – which is how Andromeda’s satellite galaxy (M32) formed. According to their study, D’Souza and Bell believe that M32 is the surviving center of M32p, which is what remained after its spiral arms were stripped away.
“M32 is a weirdo,” said Bell. “While it looks like a compact example of an old, elliptical galaxy, it actually has lots of young stars. It’s one of the most compact galaxies in the universe. There isn’t another galaxy like it.” According to D’Souza and Bell, this study may also alter the traditional understanding of how galaxies evolve. In astronomy, conventional wisdom says that large interactions would destroy disk galaxies and form elliptical galaxies.
But if Andromeda did indeed survive an impact with a massive galaxy, it would indicate that this is not the case. The timing of the merger may also explain recent research findings which indicated that two billion years ago, the disk of the Andromeda galaxy thickened, leading to a burst in star formation. As Bell explained:
“The Andromeda Galaxy, with a spectacular burst of star formation, would have looked so different 2 billion years ago. When I was at graduate school, I was told that understanding how the Andromeda Galaxy and its satellite galaxy M32 formed would go a long way towards unraveling the mysteries of galaxy formation.”
In the end, this method could also be used to study other galaxies and determine which were the most massive mergers they underwent. This could allow scientists to better understand the complicated process that drives galaxy growth and how mergers affect galaxies. This knowledge will certainly come in handy when it comes to determining what will happen to our galaxy when it merges with Andromeda in a few billion years.
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at dwarf elliptical galaxy known as Messier 32. Enjoy!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.
One of these objects is the dwarf elliptical galaxy known as Messier 32 (aka. NGC 221). Located about 2.65 million light-years from Earth, in the direction of the Andromeda constellation, this dwarf is actually a satellite galaxy of the massive Andromeda Galaxy (M31). Along with Andromeda, the Milky Way and the Triangulum Galaxy (M33) is a member of the Local Group.
M32 is an elliptical dwarf galaxy which contains about 3 billion solar masses. While it looks small compared to its massive neighbor, this little guy actually stretches across space some 8,000 light years in diameter. Once you pick it up, you’ll notice it’s really quite bright on its own – and with very good reason – its nucleus is almost identical to M31. Both contain about 100 million solar masses in rapid motion around a central supermassive object!
“M32 is the prototype for the relatively rare class of galaxies referred to as compact ellipticals. It has been suggested that M32 may be a tidally disturbed r1/4 elliptical galaxy or the remnant bulge of a disk-stripped early-type spiral galaxy reveals that the surface bightness profile, the velocity dispersion measurements, and the estimated supermassive black hole mass in M32 are inconsistent with the galaxy having, and probably ever having had, an r1/4 light profile. Instead, the radial surface brightness distribution of M32 resembles an almost perfect (bulge+exponential disk) profile; this is accompanied by a marked increase in the ellipticity profile and an associated change in the position angle profile where the “disk” starts to dominate. Compelling evidence that this bulge/disk interpretation is accurate comes from the best-fitting r1/n bulge model, which has a Sersic index of n=1.5, in agreement with the recently discovered relation between a bulge’s Sersic index and the mass of a bulge’s supermassive black hole.”
By probing deeply into Messier 32, we’ve learned this little galaxy is home to mainly mature red and yellow stars. And they’re good housekeepers, too… because there’s practically no dust or gas to be found. While this seems neat and tidy, it also means there isn’t any new star formation going on either, but there are signs of some lively doings in the not too distant past.
Because M32 has shared “space” with neighboring massive M31, the strong tidal field of the larger galaxy may have ripped away what once could have been spiral arms – leaving only its central bulge and triggering starburst in the core. As Kenji Bekki (et al) wrote in their 2001 study:
“The origin of M32, the closest compact elliptical galaxy (cE), is a long-standing puzzle of galaxy formation in the Local Group. Our N-body/smoothed particle hydrodynamics simulations suggest a new scenario in which the strong tidal field of M31 can transform a spiral galaxy into a compact elliptical galaxy. As a low-luminosity spiral galaxy plunges into the central region of M31, most of the outer stellar and gaseous components of its disk are dramatically stripped as a result of M31’s tidal field. The central bulge component on the other hand, is just weakly influenced by the tidal field, owing to its compact configuration, and retains its morphology. M31’s strong tidal field also induces rapid gas transfer to the central region, triggers a nuclear starburst, and consequently forms the central high-density and more metal-rich stellar populations with relatively young ages. Thus, in this scenario, M32 was previously the bulge of a spiral galaxy tidally interacting with M31 several gigayears ago. Furthermore, we suggest that cE’s like M32 are rare, the result of both the rather narrow parameter space for tidal interactions that morphologically transform spiral galaxies into cE’s and the very short timescale (less than a few times 109 yr) for cE’s to be swallowed by their giant host galaxies (via dynamical friction) after their formation.”
History of Observation:
M32 was discovered by Guillaume Le Gentil on October 29th, 1749 and became the first elliptical galaxy ever observed. Although it wasn’t cataloged by Charles Messier until August 3rd, 1764, he had also seen it some seven years earlier while studying at the Paris Observatory, but his notes had been suppressed. But no matter, for he made sure to include it in his notes with a drawing! As he wrote of the object:
“I have examined in the same night [August 3 to 4, 1764], and with the same instruments, the small nebula which is below and at some [arc] minutes from that in the girdle of Andromeda. M. le Gentil discovered it on October 29, 1749. I saw it for the first time in 1757. When I examined the former, I did not know previously of the discovery which had been made by M. Le Gentil, although he had published it in the second volume of the Memoires de Savans erangers, page 137. Here is what I found written in my journal of 1764. That small nebula is round and may have a diameter of 2 minutes of arc: between that small nebula and that in the girdle of Andromeda one sees two small telescopic stars. In 1757, I made a drawing of that nebula, together with the old one, and I have not found and change at each time I have reviewed it: One sees with difficulty that nebula with an ordinary refractor of three feet and a half; its light is fainter than that of the old one, and it doesn’t contain any star. At the passage of that new nebula through the Meridian, comparing it with the star Gamma Andromedae, I have determined its position in right ascension as 7d 27′ 32″, and its declination as 38d 45′ 34″ north.”
Later, Messier 32 would be examined again, this time by Admiral Symth who said:
“An overpowering nebula, with a companion about 25′ in the south vertical M32 … The companion of M31 was discovered in November, 1749, by Le Gentil, and was described by him as being about an eighth of the size of the principal one. The light is certainly more feeble than here assigned. Messier – whose No. 32 it is – observed it closely in 1764, and remarked, that no change had taken place since the time of its being first recorded. In form it is nearly circular. The powerful telescope of Lord Rosse is a reflector of three feet in diameter, of performance hitherto unequalled. It was executed by the Earl of Rosse, under a rare union of skill, assiduity, perseverance, and muniference. The years of application required to accomplish this, have not worn his Lordship’s zeal and spirit; like a giant refreshed, he has returned to his task, and is now occupied upon a metallic disc of no less than six feet in diameter. Should the figure of this prove as perfect as the present one, we may soon over-lap what many absurdly look upon as the boundaries of the creation.”
Locating Messier 32:
Locating M32 is as easy as locating the Andromeda Galaxy, but it will require large binoculars or at least a small telescope to see. Even under moderately light polluted skies the Great Andromeda Galaxy can be easily be found with the unaided eye – if you know where to look. Seasoned amateur astronomers can literally point to the sky and show you the location of M31, but perhaps you have never tried to find it.
Believe it or not, this is an easy galaxy to spot even under the moonlight. Simply identify the large diamond-shaped pattern of stars that is the Great Square of Pegasus. The northernmost star is Alpha, and it is here we will begin our hop. Stay with the northern chain of stars and look four finger widths away from Alpha for an easily seen star.
The next along the chain is about three more finger widths away… And we’re almost there. Two more finger widths to the north and you will see a dimmer star that looks like it has something smudgy nearby. Point your binoculars there, because that’s no cloud – it’s the Andromeda Galaxy!
Now aim your binoculars or telescope its way… Perhaps one of the most outstanding of all galaxies to the novice observer, M31 spans so much sky that it takes up several fields of view in a larger telescope, and even contains its own clusters and nebulae with New General Catalog designations. If you have larger binoculars or a telescope, you will be able to pick up M31’s two companions – M32 and M110. Messier 32 is the elliptical galaxy to the south.
Why not stretch your own boundaries? Go observing! Halton Arp included Messier 32 as No. 168 in his Catalogue of Peculiar Galaxies. It’s bright, easy and fun! And here are the quick facts on this Messier Object to help you get started:
Object Name: Messier 32 Alternative Designations: M32, NGC 221 Object Type: Type E2, Elliptical Galaxy Constellation: Andromeda Right Ascension: 00 : 42.7 (h:m) Declination: +40 : 52 (deg:m) Distance: 2900 (kly) Visual Brightness: 8.1 (mag) Apparent Dimension: 8×6 (arc min)
In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of the then-known 48 constellations. His treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come. Thanks to the development of modern telescopes and astronomy, this list was amended by the early 20th century to include the 88 constellation that are recognized by the International Astronomical Union (IAU) today.
Of these, Andromeda is one of the oldest and most widely recognized. Located north of the celestial equator, this constellation is part of the family of Perseus, Cassiopeia, and Cepheus. Like many constellation that have come down to us from classical antiquity, the Andromeda constellation has deep roots, which may go all the way back to ancient Babylonian astronomy.
What is up with these dwarf galaxies? A survey of thousands of galaxies using the Sloan Digital Sky Survey reveals something interesting, which was first revealed by looking at the massive Andromeda Galaxy nearby Earth: dwarf galaxies orbiting larger ones are often in disc-shaped orbits and not distributed randomly, as astronomers expected.
The finding follows on from research in 2013 that showed that 50% of Andromeda’s dwarf galaxies are in a single plane about a million light-years in diameter, but only 300,000 light-years thick. Now with the larger discovery, scientists suspect that perhaps there is a yet-to-be found process that is controlling gas flow in the cosmos.
“We were surprised to find that a large proportion of pairs of satellite galaxies have oppositely directed velocities if they are situated on opposite sides of their giant galaxy hosts,” stated lead author Neil Ibata of Lycée International in France.
“Everywhere we looked, we saw this strangely coherent coordinated motion of dwarf galaxies,” added Geraint Lewis, a University of Sydney physicist. “From this we can extrapolate that these circular planes of dancing dwarfs are universal, seen in about 50 percent of galaxies. This is a big problem that contradicts our standard cosmological models. It challenges our understanding of how the universe works, including the nature of dark matter.”
The astronomers also speculated this could show something unexpected in the laws of physics, such as motion and gravity, but added it would take far more investigation to figure that out.
M31 and M33 are two of the nearest spiral galaxies, and can form the basis for determining distances to more remote spiral galaxies and constraining the expansion rate of the Universe (the Hubble constant). Hence the relevance and importance of several new studies that employed near-infrared data to establish solid distances for M31 (Andromeda) and M33 (Triangulum) (e.g., Gieren et al. 2013), and aimed to reduce existing uncertainties tied to the fundamental parameters for those galaxies. Indeed, reliable distances for M31 and M33 are particularly important in light of the new Hubble constant estimate from the Planck satellite, which is offset relative to certain other results, and that difference hinders efforts to ascertain the nature of dark energy (the mysterious force theorized as causing the Universe’s accelerated expansion).
Gieren et al. remarked that, “a number of new distance determinations to M33 … span a surprisingly large interval … which is a cause of serious concern. As the second-nearest spiral galaxy, an accurate determination of [M33’s] distance is a crucial step in the process of building the cosmic distance ladder.” Concerning M31, Riess et al. 2012 likewise remarked that “M31, the nearest analogue of the Milky Way Galaxy, has long provided important clues to understanding the scale of the Universe.“
The new Gieren and Riess et al. distances are based on near-infrared observations, which are pertinent because radiation from that part of the electromagnetic spectrum is less sensitive than optical data to absorption by dust located along our sight-line (see the figure below). Properly accounting for the impact of dust is a principal problem in cosmic distance scale work, since it causes targets to appear dimmer. “different assumptions about [dust obscuration] are a prime source for the discrepancies among the various distance determinations for M33.” noted Gieren et al., and the same is true for the distance to M31 (see Riess et al.).
Gieren et al. observed 26 Cepheids in M33 and established a distance of ~2,740,000 lightyears. The team added that, “As the first modern near-infraredCepheid study [of] M33 since … some 30 years … we consider this work as long overdue …” Astronomers often cite distances to objects in lightyears, which defines the time required for light emitted from the source to reach the observer. Despite the (finite) speed of light being 300,000,000 m/s, the rays must traverse “astronomical” distances. Gazing into space affords one the unique opportunity to peer back in time.
The distances to M33 shown below convey seminal points in the evolution of humanity’s knowledge. The scatter near the 1920s stems partly from a debate concerning whether the Milky Way and the Universe are synonymous. In other words, do galaxies exist beyond the Milky Way? The topic is immortalized in the famed great debate (1920) featuring H. Shapley and H. Curtis (the latter argued for an extragalactic scale). The offset between the pre-1930 and post-1980 data result in part from a nearly two-fold increase in the cosmic distance scale recognized circa 1950 (see also Feast 2000). Also evident is the scatter associated with the post-1980 distances, which merely reinforces the importance of the new high-precision distance estimates.
Score another point for the National Science Foundation’s Green Bank Telescope (GBT) at the National Radio Astronomy Observatory (NRAO) in Green Bank. They have opened our eyes – and ears – to previously undetected region of hydrogen gas clouds located in the area between the massive Andromeda and Triangulum galaxies. If researchers are correct, these dwarf galaxy-sized sectors of isolated gases may have originated from a huge store of heated, ionized gas… Gas which may be associated with elusive and invisible dark matter.
“We have known for some time that many seemingly empty stretches of the Universe contain vast but diffuse patches of hot, ionized hydrogen,” said Spencer Wolfe of West Virginia University in Morgantown. “Earlier observations of the area between M31 and M33 suggested the presence of colder, neutral hydrogen, but we couldn’t see any details to determine if it had a definitive structure or represented a new type of cosmic feature. Now, with high-resolution images from the GBT, we were able to detect discrete concentrations of neutral hydrogen emerging out of what was thought to be a mainly featureless field of gas.”
So how did astronomers detect the extremely faint signal which clued them to the presence of the gas pockets? Fortunately, our terrestrial radio telescopes are able to decipher the representative radio wavelength signals emitted by neutral atomic hydrogen. Even though it is commonplace in the Universe, it is still frail and not easy to observe. Researchers knew more than 10 years ago that these repositories of hydrogen might possibly exist in the empty space between M33 and M32, but the evidence was so slim that they couldn’t draw certain conclusions. They couldn’t “see” fine grained structure, nor could they positively identify where it came from and exactly what these accumulations meant. At best, their guess was it came from an interaction between the two galaxies and that gravitational pull formed a weak “bridge” between the two large galaxies.
The animation demonstrates the difference in resolution from the original Westerbork Radio Telescope data (Braun & Thilker, 2004) and the finer resolution imaging of GBT, which revealed the hydrogen clouds between M31 and M33. Bill Saxton, NRAO/AUI/NSF Credit: Bill Saxton, NRAO/AUI/NSF.
Just last year, the GBT observed the tell-tale fingerprint of hydrogen gas. It might be thin, but it is plentiful and it’s spread out between the galaxies. However, the observations didn’t stop there. More information was gathered and revealed the gas wasn’t just ethereal ribbons – but solid clumps. More than half of the gas was so conspicuously aggregated that they could even have passed themselves off as dwarf galaxies had they a population of stars. What’s more, the GBT also studied the proper motion of these gas pockets and found they were moving through space at roughly the same speed as the Andromeda and Triangulum galaxies.
“These observations suggest that they are independent entities and not the far-flung suburbs of either galaxy,” said Felix J. Lockman, an astronomer at the NRAO in Green Bank. “Their clustered orientation is equally compelling and may be the result of a filament of dark matter. The speculation is that a dark-matter filament, if it exists, could provide the gravitational scaffolding upon which clouds could condense from a surrounding field of hot gas.”
And where there is neutral hydrogen gas, there is fuel for new stars. Astronomers also recognize these new formations could eventually be drawn into M31 and M33, eliciting stellar creation. To add even more interest, these cold, dark regions which exist between galaxies contain a large amount of “unaccounted-for normal matter” – perhaps a clue to dark matter riddle and the reason behind the amount of hydrogen yet to revealed in universal structure.
“The region we have studied is only a fraction of the area around M31 reported to have diffuse hydrogen gas,” said D.J. Pisano of West Virginia University. “The clouds observed here may be just the tip of a larger population out there waiting to be discovered.”
More of our readers had success in capturing the awesomeness of seeing Comet PANSTARRS encounter the Andromeda Galaxy (M31) in the night sky. Göran Strand sent us this absolutely gorgeous image, taken from 70 km north of Östersund, Sweden — a really dark site with no light pollution. “This photo is a 30 minute exposure through my 300mm/f2.8 lens using my full format Nikon D3s camera,” Göran said. “Besides seeing the comet and the galaxy, I also got to see 4 elks, 2 meteors, 1 bolide and 1 aurora. So all in all, it was a good night!”
That’s for sure!
See more images below of this great meet-up in the skies, and see our earlier post of our readers’ images here.
Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.
Cold rings of dust are illuminated in this image taken by Herschel’s Spectral and Photometric Imaging Receiver (SPIRE) instrument. Credit: ESA/NASA/JPL-Caltech/B. Schulz (NHSC)
Looking wispy and delicate from 2.5 million light-years away, cold rings of dust are seen swirling around the Andromeda galaxy in this new image from the Herschel Space Observatory, giving us yet another fascinating view of our galaxy’s largest neighbor.
The colors in the image correspond to increasingly warmer temperatures and concentrations of dust — blue rings are warmer, while pinks and reds are colder lanes of dust only slightly above absolute zero. Dark at shorter wavelengths, these dust rings are revealed by Herschel’s amazing sensitivity to the coldest regions of the Universe.
The image above shows data only from Herschel’s SPIRE (Spectral and Photometric Imaging Receiver) instrument; below is a mosaic made from SPIRE as well as the Photodetecting Array Camera and Spectrometer (PACS) instrument:
“Cool Andromeda” Credit: ESA/Herschel/PACS & SPIRE Consortium, O. Krause, HSC, H. Linz
Estimated to be 200,000 light-years across — almost double the width of the Milky Way — Andromeda (M31) is home to nearly a trillion stars, compared to the 200–400 billion that are in our galaxy. And within these cold, dark rings of dust even more stars are being born… Andromeda’s star-making days are far from over.
Herschel’s mission will soon be coming to an end as the telescope runs out of the liquid helium coolant required to keep its temperatures low enough to detect such distant heat signatures. This is expected to occur sometime in February or March.
Herschel is a European Space Agency cornerstone mission with science instruments provided by consortia of European institutes, and with important participation by NASA. Launched May 14, 2009, the telescope orbits the second Lagrange point of the Earth-Sun system (L2), located 1.5 million km (932,000 miles) from Earth. Read more from the Herschel mission here.
An ancient passing between two nearby galaxies appears to have left the participants connected by a tenuous “bridge” of hydrogen gas, according to findings reported Monday, June 11 by astronomers with the National Radio Astronomy Observatory (NRAO).
Using the National Science Foundation’s Green Bank Telescope in West Virginia — the world’s largest fully-steerable radio telescope — astronomers have confirmed the existence of a vast bridge of hydrogen gas streaming between the Andromeda galaxy (M31) and the Triangulum galaxy (M33), indicating that they likely passed very closely billions of years ago.
The faint bridge structure had first been identified in 2004 with the 14-dish Westerbork Synthesis Radio Telescope in the Netherlands but there was some scientific dispute over the findings. Observations with the GBT confirmed the bridge’s existence as well as revealed the presence of six large clumps of material within the stream.
Since the clumps are moving at the same velocity as the two galaxies relative to us, it seems to indicate the bridge of hydrogen gas is connecting them together.
“We think it’s very likely that the hydrogen gas we see between M31 and M33 is the remnant of a tidal tail that originated during a close encounter, probably billions of years ago,” said Spencer Wolfe of West Virginia University. “The encounter had to be long ago, because neither galaxy shows evidence of disruption today.”
Astronomers have known for years that our Milky Way and its closest neighbor, the Andromeda galaxy, (a.k.a M31) are being pulled together in a gravitational dance, but no one was sure whether the galaxies would collide head-on or glide past one another. Precise measurements from the Hubble Space Telescope have now confirmed that the two galaxies are indeed on a collision course, headed straight for a colossal cosmic collision.
No need to panic for the moment, as this is not going to happen for another four billion years. And while astronomers say it is likely the Sun will be flung into a different region of our galaxy, Earth and the solar system will probably just go along for the ride and are in no danger of being destroyed.
“In the ‘worst-case-scenario’ simulation, M31 slams into the Milky Way head-on and the stars are all scattered into different orbits,” said team member Gurtina Besla of Columbia University in New York, N.Y. “The stellar populations of both galaxies are jostled, and the Milky Way loses its flattened pancake shape with most of the stars on nearly circular orbits. The galaxies’ cores merge, and the stars settle into randomized orbits to create an elliptical-shaped galaxy.”
The simulations Besla was talking about came from precise measurements by Hubble, painstakingly determining the motion of Andromeda, looking particularly at the sideways motion of M31, which until now has not been able to be done.
“This was accomplished by repeatedly observing select regions of the galaxy over a five- to seven-year period,” said Jay Anderson of STScI.
Right now, M31 is 2.5 million light-years away, but it is inexorably falling toward the Milky Way under the mutual pull of gravity between the two galaxies and the invisible dark matter that surrounds them both.
Of course, the collision is not like a head-on between two cars that takes place in an instant. Hubble data show that it will take an additional two billion years after the encounter for the interacting galaxies to completely merge under the tug of gravity and reshape into a single elliptical galaxy similar to the kind commonly seen in the local universe.
Astronomers said the stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today.
There’s also the complication of M31’s small companion, the Triangulum galaxy, M33. This galaxy will join in the collision and perhaps later merge with the M31/Milky Way pair. There is a small chance that M33 will hit the Milky Way first.
The astronomers working on this project said that they were able to make the precise measurements because of the upgraded cameras on Hubble, installed during the final servicing mission. This gave astronomers a long enough time baseline to make the critical measurements needed to nail down M31’s motion.
The Hubble observations and the consequences of the merger are reported in three papers that will appear in an upcoming issue of the Astrophysical Journal.
First Row, Left: Present day.
First Row, Right: In 2 billion years the disk of the approaching Andromeda galaxy is noticeably larger.
Second Row, Left: In 3.75 billion years Andromeda fills the field of view.
Second Row, Right: In 3.85 billion years the sky is ablaze with new star formation.
Third Row, Left: In 3.9 billion years, star formation continues.
Third Row, Right: In 4 billion years Andromeda is tidally stretched and the Milky Way becomes warped.
Fourth Row, Left: In 5.1 billion years the cores of the Milky Way and Andromeda appear as a pair of bright lobes.
Fourth Row, Right: In 7 billion years the merged galaxies form a huge elliptical galaxy, its bright core dominating the nighttime sky. | 0.863536 | 3.954005 |
On Thursday, May 29th, Comet 209P/LINEAR will pass just 5 million miles (8 million km) from Earth, one of the closest comet approaches in history.[caption id="attachment_246599" align="alignright
Comet 209P/LINEAR moves rapidly south through the sky around its closest approach on May 29th.[/caption] Just 5 days earlier, early on the morning of May 24th, Earth is predicted to pass through the debris that lines the comet's orbit, causing a new and possibly spectacular meteor shower. But regardless of whether the meteor shower materializes, the comet itself is an appealing target for backyard astronomers.Comets are notoriously unpredictable. But with any luck, this one will shine at 10th magnitude from May 24th through June 2nd, making it an easy target through an 8-inch scope from a typical suburban backyard — or through a much smaller scope under dark skies. But the comet is moving rapidly southward through the sky, so it will be invisible from the Northern Hemisphere toward the end of that period.
At its closest approach, 209P will be moving almost almost a half degree per hour — the field of view of a telescope at medium-high power. So you need very detailed charts to locate it. Select one or more from the list below depending when you plan to observe. The times are plotted in Universal Time, which runs 4 hours ahead of Eastern Daylight Time and 7 hours ahead of Pacific Daylight Time. For example, 10 p.m. May 26th EDT is 2h May 27th Universal Time, so at that time you should look halfway between the ticks labeled 0h and 4h for May 27th. | 0.8299 | 3.071449 |
Crescent ♉ Taurus
Moon phase on 22 March 2015 Sunday is Waxing Crescent, 2 days young Moon is in Taurus.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 2 days on 20 March 2015 at 09:36.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing first ∠1° of ♉ Taurus tropical zodiac sector.
Lunar disc appears visually 0.8% wider than solar disc. Moon and Sun apparent angular diameters are ∠1940" and ∠1925".
Next Full Moon is the Pink Moon of April 2015 after 13 days on 4 April 2015 at 12:06.
There is low ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at big angle, so their combined tidal force is weak.
The Moon is 2 days young. Earth's natural satellite is moving from the beginning to the first part of current synodic month. This is lunation 188 of Meeus index or 1141 from Brown series.
Length of current 188 lunation is 29 days, 9 hours and 21 minutes. It is 5 minutes longer than next lunation 189 length.
Length of current synodic month is 3 hours and 23 minutes shorter than the mean length of synodic month, but it is still 2 hours and 46 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠9.9°. At beginning of next synodic month true anomaly will be ∠27.1°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
2 days after point of perigee on 19 March 2015 at 19:38 in ♓ Pisces. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 10 days, until it get to the point of next apogee on 1 April 2015 at 12:59 in ♍ Virgo.
Moon is 369 438 km (229 558 mi) away from Earth on this date. Moon moves farther next 10 days until apogee, when Earth-Moon distance will reach 406 012 km (252 284 mi).
1 day after its descending node on 21 March 2015 at 02:19 in ♈ Aries, the Moon is following the southern part of its orbit for the next 12 days, until it will cross the ecliptic from South to North in ascending node on 4 April 2015 at 03:17 in ♎ Libra.
14 days after beginning of current draconic month in ♎ Libra, the Moon is moving from the second to the final part of it.
8 days after previous South standstill on 14 March 2015 at 01:39 in ♐ Sagittarius, when Moon has reached southern declination of ∠-18.262°. Next 4 days the lunar orbit moves northward to face North declination of ∠18.241° in the next northern standstill on 26 March 2015 at 14:29 in ♊ Gemini.
After 13 days on 4 April 2015 at 12:06 in ♎ Libra, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.173736 |
A terrestrial planet, telluric planet, or rocky planet is a planet, composed of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun, i.e. Mercury, Venus and Mars; the terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth, as these planets are, in terms of structure, Earth-like. These planets are located between the asteroid belt. Terrestrial planets have a solid planetary surface, making them different from the larger gaseous planets, which are composed of some combination of hydrogen and water existing in various physical states. All terrestrial planets in the Solar System have the same basic type of structure, such as a central metallic core iron, with a surrounding silicate mantle; the Moon has a much smaller iron core. Io and Europa are satellites that have internal structures similar to that of terrestrial planets. Terrestrial planets can have canyons, mountains and other surface structures, depending on the presence of water and tectonic activity.
Terrestrial planets have secondary atmospheres, generated through volcanism or comet impacts, in contrast to the giant planets, whose atmospheres are primary, captured directly from the original solar nebula. The Solar System has four terrestrial planets: Mercury, Venus and Mars. Only one terrestrial planet, Earth, is known to have an active hydrosphere. During the formation of the Solar System, there were many more terrestrial planetesimals, but most merged with or were ejected by the four terrestrial planets. Dwarf planets, such as Ceres and Eris, small Solar System bodies are similar to terrestrial planets in the fact that they do have a solid surface, but are, on average, composed of more icy materials; the Earth's Moon has a density of 3.4 g·cm−3 and Jupiter's satellites, Io, 3.528 and Europa, 3.013 g·cm−3. The uncompressed density of a terrestrial planet is the average density its materials would have at zero pressure. A greater uncompressed density indicates greater metal content. Uncompressed density differs from the true average density because compression within planet cores increases their density.
The uncompressed density of terrestrial planets trends towards lower values as the distance from the Sun increases. The rocky minor planet Vesta orbiting outside of Mars is less dense than Mars still at, 3.4 g·cm−3. Calculations to estimate uncompressed density inherently require a model of the planet's structure. Where there have been landers or multiple orbiting spacecraft, these models are constrained by seismological data and moment of inertia data derived from the spacecraft orbits. Where such data is not available, uncertainties are higher, it is unknown. Most of the planets discovered outside the Solar System are giant planets, because they are more detectable, but since 2005, hundreds of terrestrial extrasolar planets have been found, with several being confirmed as terrestrial. Most of these are i.e. planets with masses between Earth's and Neptune's. During the early 1990s, the first extrasolar planets were discovered orbiting the pulsar PSR B1257+12, with masses of 0.02, 4.3, 3.9 times that of Earth's, by pulsar timing.
When 51 Pegasi b, the first planet found around a star still undergoing fusion, was discovered, many astronomers assumed it to be a gigantic terrestrial, because it was assumed no gas giant could exist as close to its star as 51 Pegasi b did. It was found to be a gas giant. In 2005, the first planets orbiting a main-sequence star and which show signs of being terrestrial planets, were found: Gliese 876 d and OGLE-2005-BLG-390Lb. Gliese 876 d orbits the red dwarf Gliese 876, 15 light years from Earth, has a mass seven to nine times that of Earth and an orbital period of just two Earth days. OGLE-2005-BLG-390Lb has about 5.5 times the mass of Earth, orbits a star about 21,000 light years away in the constellation Scorpius. From 2007 to 2010, three potential terrestrial planets were found orbiting within the Gliese 581 planetary system; the smallest, Gliese 581e, is only about 1.9 Earth masses, but orbits close to the star. An ideal terrestrial planet would be two Earth masses, with a 25-day orbital period around a red dwarf.
Two others, Gliese 581c and Gliese 581d, as well as a disputed planet, Gliese 581g, are more-massive super-Earths orbiting in or close to the habitable zone of the star, so they could be habitable, with Earth-like temperatures. Another terrestrial planet, HD 85512 b, was discovered in 2011; the radius and composition of all these planets are unknown. The first confirmed terrestrial exoplanet, Kepler-10b, was found in 2011 by the Kepler Mission designed to discover Earth-size planets around other stars using the transit method. In the same year, the Kepler Space Observatory Mission team released a list of 1235 extrasolar planet candidates, including six that are "Earth-size" or "super-Earth-size" and in the habitable zone of their star. Since Kepler has discovered hundreds of planets ranging
Gwendolyn Audrey Foster is an American scholar and filmmaker. Her work has focused on gender, ecofeminism, queer sexuality, eco-theory, class studies. From 1999 through the end of 2014, she was co-editor along with Wheeler Winston Dixon of the Quarterly Review of Film and Video. In 2016, she was named Willa Cather Endowed Professor of English at the University of Nebraska at Lincoln. Foster received a B. A. Degree in English from Douglass College, Rutgers University in 1983, earned a master's degree in 1992 and her doctorate at the University of Nebraska at Lincoln, in 1995. Foster teaches a broad variety of courses that reflect her diverse interests: Experimental Filmmakers, Queer theory and LGBTQ+ film, Apoco-tainment, Eco-Horror and Environmentalism in TV and Film, Italian Postwar Cinema, Challenging and Disruptive Films, Spectators as co-authors, Women Filmmakers in Film History, the films of Luis Buñuel, Chantal Akerman, Lucrecia Martel, Kelly Reichardt and Film Censorship and Marxist Approaches to Film, "Woman's Pictures" and Melodrama, Female Spectatorship, Queer Spectatorship, Race & Post/colonialism in Film, Social Class and Social Mobility in Film, Maids, & Sex Workers – Redefining Female Heroes in Film, Masculinity in Media, Ozu and Dreyer, Japanese and Asian Cinema, Latin American cinema, French Film Directors, Atomic anti-communist hysteria films and many other courses.
She has written about film-related topics such as eco-feminism, underground film, avant garde film, cultural studies and Marxist critical theory, women directors. Foster has made films including the 1991 documentary Women Who Made the Movies as well as the 1994 feature film Squatters, more a number of short films including the Gaia Triptych a series of short eco-horror and eco-feminist experimental films including Waste and Want Not. Foster's other short films include such Earth TV, Echo and Narcissus, Tenderness and Psyche, Pre-Raphaelite Falls, The Passenger, Pop. 1280 For Jim Thompson, Mirror and many other titles. Foster publishes in many journals such as Choice, Senses of Cinema, Film International, Quarterly Review of Film and Video, she writes and publishes extensively on film studies and cultural studies, along with her filmmaking and installation art projects. Foster and Wheeler Winston Dixon are coauthors of the popular film history textbook, A Short History of Film, they are Series Editors of "Quick Takes: Movies and Popular Culture," a series of books offering fresh perspectives on film and popular culture published by Rutgers University Press.
Her films have been screened at Outfest LA, Bi Arts Festival, The Nederlands Filmmuseum, Rice Museum, Collective for Living Cinema, Swedish Cinemateket, National Museum of Women in the Arts, DC, International Film Festival of Kerala, Films de Femmes, Créteil, Women's Film Festival of Madrid, Kyobo Center, Santa Barbara Museum of Art, Metropolitan Museum of Art, Université Laval, Forum Yokohama, Anthology Film Archives, Amos Eno Gallery, NY, SLA 307 Art Space, NY, Maryland Institute College of Art, NETV, Studio 44 Stockholm, X-12 Festival, UK, other museums and festivals around the world. In March and April 2018, the BWA Contemporary Art Gallery in Katowice, presented a month long retrospective of Foster's new video work. In May 2018, she presented a screening of her videos, along with the work of Bill Domonkos and Wheeler Winston Dixon at The Museum of Human Achievement in Austin, Texas. In the summer of 2018, she had a one woman show at Filmhuis Cavia in Amsterdam, her film Self Portrait was screened as part of NewFilmmakers at Anthology Film Archives on September 11, 2018.
Her one woman show, Queer Experimental Films was screened July/August 2018 on Salto Netherlands International TV, she had a one woman show at The Museum of The Future in Berlin, Germany on October 28, 2017. Foster's life partner is Wheeler Winston Dixon. Disruptive Feminisms: Raced and Classed Bodies in Film Hoarders, Doomsday Preppers, the Culture of Apocalypse 21st Century Hollywood: Movies in the Era of Transformation, co-written with Wheeler Winston Dixon, Rutgers University Press, 2011 A Short History of Film co-written with Wheeler Winston Dixon 3rd Edition, March, 2018. Class-Passing: Performing Social Mobility in Film and Popular Culture Performing Whiteness: Postmodern Re/Constructions Experimental Cinema: the Film Reader, co-edited with Wheeler Winston Dixon, London: Routledge, 2002 Troping the Body: Etiquette and Dialogic Performance Captive Bodies: Postcolonialism in the Cinema Women Filmmakers of the African and Asian Diaspora: Decolonizing the Gaze, Locating Subjectivity" Women Film Directors: An International Bio-Critical Dictionary.
Westport: Greenwood Press, 1995 Identity and Memory: The Films of Chantal Akerman Official website Gwendolyn Audrey Foster on IMDb Gwendolyn Audrey Foster at Vimeo Gwendolyn Audrey Foster at The Pythians Gwendolyn Audrey Foster at University of Nebraska–Lincoln
Lakeview is a census-designated place in Nassau County, New York, United States. The population was 5,615 at the 2010 census. Lakeview is located at west of Hempstead Lake State Park. According to the United States Census Bureau, the CDP has a total area of 1.2 square miles, of which, 1.0 square mile of it is land and 0.2 square miles of it is water. As of the census of 2000, there were 5,607 people, 1,525 households, 1,287 families residing in the CDP; the population density was 5,850.2 per square mile. There were 1,569 housing units at an average density of 1,637.1/sq mi. The racial makeup of the CDP was 6.90% White, 84.95% African American, 0.32% Native American, 0.48% Asian, 3.44% from other races, 3.91% from two or more races. Hispanic or Latino of any race were 6.94% of the population. There were 1,525 households out of which 37.8% had children under the age of 18 living with them, 51.6% were married couples living together, 26.5% had a female householder with no husband present, 15.6% were non-families.
11.3% of all households were made up of individuals and 5.5% had someone living alone, 65 years of age or older. The average household size was 3.59 and the average family size was 3.81. In the CDP, the population was spread out with 28.3% under the age of 18, 8.1% from 18 to 24, 27.5% from 25 to 44, 22.6% from 45 to 64, 13.5% who were 65 years of age or older. The median age was 36 years. For every 100 females, there were 82.6 males. For every 100 females age 18 and over, there were 75.6 males. The median income for a household in the CDP was $98,036; the per capita income for the CDP was $28,575. About 4.9% of families and 6.3% of the population were below the poverty line, including 6.4% of those under age 18 and 7.7% of those age 65 or over | 0.926675 | 3.88677 |
Mars may sport two different types of volcanoes, just like Earth.
The Red Planet has had plenty of "normal" lava-spewing volcanoes, one of which created the biggest mountain in the solar system: the 16-mile-high (25 kilometers) monster Olympus Mons. But some Mars volcanoes may erupt with mud rather than molten rock, a new study suggests.
Mars' northern hemisphere is dotted with tens of thousands of conical hills, some of which are topped with small craters. Some researchers have postulated that these features were created by mud volcanoes, but this hypothesis has been hard to assess. Scientists just don't know enough about how mud moves on the Red Planet, which is very cold and has an atmospheric pressure 150 times lower than that of Earth.
That's where the new study comes in. Researchers sent mud flowing down a sandy slope in a laboratory chamber that mimicked Mars conditions (except the Red Planet's gravity, which is just 40% as strong as Earth's).
The results were surprising, study team members said.
"Under the low atmospheric pressure of Mars, the mud flows behave in much the same way as 'pāhoehoe,' or 'ropy,' lava, which is familiar from large volcanoes on Hawaii and Iceland," lead author Petr Brož, of the Czech Academy of Sciences, said in a statement.
"Our experiments show that even a process as apparently simple as the flow of mud — something that many of us have experienced for ourselves since we were children — would be very different on Mars," Brož said.
The pāhoehoe-like behavior is driven largely by Mars' low pressure, which cannot support the existence of liquid surface water for long. As the water evaporates, it absorbs heat and cools the remaining mud. The mud freezes from the outside in, forming a crust around a gooey center, study team members. The unfrozen mud on the interior can break through the crust, forming a new lobe.
The new results don't conclusively demonstrate that Mars' northern hills are mud volcanoes. But they do bolster that interpretation, showing that such geological activity is possible on the Red Planet, study team members said.
And this information should be kept in mind when trying to understand geological features on worlds beyond Earth, they added.
"Once again, it turns out that different physical conditions must always be taken into account when looking at apparently simple surface features on other planets," study co-author Ernst Hauber, of the DLR Institute of Planetary Research in Berlin, said in the same statement. (DLR is the German acronym for the German Aerospace Center.) "We now know that we need to consider both mud and lava when analyzing certain flow phenomena."
Mud volcanoes could potentially be active today on Mars, as they are on Earth. After all, the Red Planet is thought to harbor large reservoirs of subsurface water, including, perhaps, a giant lake beneath its south pole.
The new study was published online today (May 18) in the journal Nature Geoscience.
- Weird volcanoes are erupting across the solar system
- 7 biggest mysteries of Mars
- An explosive volcano on Mars may have spawned this strange rock billions of years ago
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook. | 0.800104 | 3.873647 |
NGC 1542 - Spiral Galaxy
NGC 1542 is a Spiral Galaxy in the Taurus constellation. NGC 1542 is situated close to the celestial equator and, as such, it is at least partly visible from both hemispheres in certain times of the year.
Photometric information of NGC 1542
The following table lists the magnitude of NGC 1542 in different bands of the electomagnetic spectrum (when available), from the B band (445nm wavelength, corresponding to the Blue color), to the V band ( 551nm wavelength, corresponding to Green/Yellow color), to the J, H, K bands (corresponding to 1220nm, 1630nm, 2190nm wavelengths respectively, which are colors not visible to the human eye).
For more information about photometry in astronomy, check the photometric system article on Wikipedia.
The surface brightess reported below is an indication of the brightness per unit of angular area of NGC 1542.
Apparent size of NGC 1542The following table reports NGC 1542 apparent angular size. The green area displayed on top of the DSS2 image of NGC 1542 is a visual representation of it.
Digitized Sky Survey image of NGC 1542
The image below is a photograph of NGC 1542 from the Digitized Sky Survey 2 (DSS2 - see the credits section) taken in the red channel. The area of sky represented in the image is 0.5x0.5 degrees (30x30 arcmins).
NGC 1542 - Spiral Galaxy morphological classification
NGC 1542 - Spiral Galaxy is classified as Spiral (SAab) according to the Hubble and de Vaucouleurs galaxy morphological classification. The diagram below shows a visual representation of the position of NGC 1542 - Spiral Galaxy in the Hubble de Vaucouleurs sequence.
Celestial coordinates and finder chart of NGC 1542
Celestial coordinates for the J2000 equinox of NGC 1542 are provided in the following table:
The simplified sky charts below show the position of NGC 1542 in the sky. The first chart has a field of view of 60° while the second one has a field of view of 10°. | 0.839692 | 3.452749 |
Hot gas feeds spiral arms of the Milky Way
An international research team, with significant participation of astronomers from the Max Planck Institute for Astronomy (MPIA), has gained important insights into the origin of the material in the spiral arms of the Milky Way, from which new stars are ultimately formed. By analysing properties of the galactic magnetic field, they were able to show that the dilute so-called warm ionized medium (WIM), in which the Milky Way is embedded, condenses near a spiral arm. While gradually cooling, it serves as a supply of the colder material of gas and dust that feeds star formation.
The Milky Way is a spiral galaxy, a disc-shaped island of starsin the cosmos, in which most bright and young stars cluster in spiral arms. There they form from the dense interstellar medium (ISM), which consists of gas (especially hydrogen) and dust (microscopic grains with high abundances of carbon and silicon). In order for new stars to form continuously, material must be constantly flushed into the spiral arms to replenish the supply of gas and dust.
A group of astronomers from the University of Calgary in Canada, the Max Planck Institute for Astronomy (MPIA) in Heidelberg and other research institutions have now been able to show that the supply comes from a much hotter component of the ISM, which usually envelops the entire Milky Way. The WIM has an average temperature of 10,000 degrees. High-energy radiation from hot stars causes the hydrogen gas of the WIM to be largely ionised. The results suggest that the WIM condenses in a narrow area near a spiral arm and gradually flows into it while cooling.
The scientists discovered the dense WIM by measuring the so-called Faraday rotation, an effect named after the English physicist Michael Faraday. This involves changing the orientation of linearly polarised radio emissions when they pass through a plasma (ionised gas) traversed by a magnetic field. One speaks of polarised radiation when the electric field oscillates in only one plane. Ordinary light is not polarised. The magnitude of the change in polarisation also depends on the observed wavelength.
In the present study, recently published in The Astrophysical Journal Letters, astronomers were able to detect an unusually strong signal in a rather inconspicuous area of the Milky Way, which is located directly on the side of the Sagittarius arm of the Milky Way facing the Galactic Centre. The spiral arm itself stands out in the imaging data due to strong radio emissions generated by embedded hot stars and supernova remnants. However, the astronomers found the strongest shift in polarisation outside this prominent zone. They conclude from this that the increased Faraday rotation does not originate within this active part of the spiral arm. Instead, it originates from condensed WIM, which, like the magnetic field, belongs to a less obvious component of the spiral arm.
The analysis is based on the THOR survey (The HI/OH Recombination Line Survey of the Milky Way), which has been conducted at MPIA for several years now and in which a large area of the Milky Way is observed at several radio wavelengths. Polarised radio sources such as distant quasars or neutron stars serve as “probes” for determining the Faraday rotation. This allows astronomers not only to detect the otherwise difficult to measure magnetic fields in the Milky Way, but also to study the structure and properties of the hot gas. “We were very surprised by the strong signal in a rather quiet area of the Milky Way,” says Henrik Beuther from MPIA, who is leading the THOR project. “These results show us that there is still a lot to be discovered in studying the structure and dynamics of the Milky Way.”
Source:More information: R. Shanahan et al. Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm, The Astrophysical Journal(2019). DOI: 10.3847/2041-8213/ab58d4 | 0.891082 | 4.022157 |
The expression “Mercury Retrograde” is an astronomical phenomenon when Mercury seems to float through the sky from east to west, rather than its normal path from west to east. All of our planets do it at one time or another. The ancient Greeks thought it was because the planets wandered through the universe, but today we know that it is an optical illusion that occurs because other planets have different orbits than Earth does.
Some planetary orbits are faster or slower, shorter or longer. Because we are on Earth’s own elliptical orbit, our view of the path of the planets varies through time and place.
Mercury’s shorter and faster orbit causes the planet to appear to move eastward four times a year. Astrologers believe that while Mercury is in retrograde, it is in a resting or sleeping state, and that has a psychological effect on some people—you are more mercurial, in fact—and if you are born during one of those periods, your chances of being affected by Mercury’s fluctuations are more likely.
What Mercury Rules
In astrology, the planet Mercury rules all types of communications: Speaking, learning, reading, writing, researching, negotiations. Mercury describes our intelligence, our mind, and our memory; it rules our sense of humor, what fascinates us, how we speak write and otherwise communicate.
When moving in retrograde, though, the planet challenges us to act with greater wisdom but not necessarily back away from pursuing new goals. Leslie McGuirk suggests we should not blame Mercury retrograde for every failure, and that the study of astrology is about what it means to be human. Instead, understanding how the planets can affect ourselves and in our closest ones can help us to navigate through our lives.
Astrologer Bernie Ashman suggests that Mercury retrograde can bring positive changes, such as a deepening of communication skills, which might open doors for new job opportunities.
The Mercury Rx Club
About 25 percent of people on earth were born during a Mercury retrograde—you can check your own natal chart to see if you are one of those lucky few. Look for the Mercury glyph. If you see an Rx next to it, that means you were born in a retrograde time frame.
In astrology, Mercury affects your perceptive abilities, and if you know the effect that Mercury has on you, it can help you understand how you see things and thereby be more effective in the world. If you’ve got Mercury retrograde, you’ve got a very different mercurial make-up than other people. Understanding how you think can lessen the frustrations that go along with this kind of planetary influence.
Astrologer Jan Spiller connects people with Mercury retrograde to the trailing effect of past lives in which you were holding back the truth or having to go along with the party line. This time around, she says, there is a profound sense of being inarticulate,and struggling to speak.
In her article, Spiller writes “In this lifetime, they are not allowed to speak superficially. To feel ‘straight’ with themselves, they must communicate fully, from the authenticity of their entire being. Naturally, it takes time for them to get in touch with this level of authenticity.”
Jan Spiller sees a past life echo for people born under Mercury retrograde with a challenge to speak from the depths of one’s being. This is to overcome lives of having to hide their true thoughts, leading to a painful disconnection.
There are gifts that come from the struggle to speak in such a whole-hearted way. Spiller writes, “They are learning to reconnect with the authenticity of their own unique ideas and preferences and decision-making tendencies. Because of the necessity of including their emotional component when making decisions, many times these people have exceptional artistic talents.”
When you have Mercury Rx in your natal chart, how it behaves will depend on the element, quality and what house it is in.
In people born under water signs, for example, Mercury makes your mind search for the emotional essence, and from that, you can form a picture of perception. As with the retrograde cycle, the processes of the mind are different and may take longer. You may swim in different channels of the mind. Sometimes it feels like you’re speaking another language. And it can make you feel misunderstood until you learn to translate what you perceive into language others can understand.
The collage effect of Mercury retrograde makes it hard to see how things will play out. You may see the end before the middle, or a vision of what’s to come. But if this resonates with you, try working with, rather than against your own Mercury Rx. Instead of swimming against the tide, look for mediums where this kind of perception is valued and even rewarded.
Trust your perceptions, and find ways of expressing yourself through art, music, dance. The arts allow a different kind of language, that of symbol and collage, to stand on its own. No translation necessary! Trust that you have a unique way of seeing the world, one that is worth sharing.
- Ashman, Bernie. How to Survive Mercury Retrograde: And Venus and Mars, Too. Llewellyn Publications, 2016. Print.
- McGuirk, Leslie. The Power of Mercury: Understanding Mercury Retrograde and Unlocking the Astrological Secrets of Communication. HarperElixir, 2016. Print.
- Miller, Susan. “Mercury Retrograde and What It Means for You.” AstrologyZone. 2016. Web. April 22 2018.
- Yott, Donald H. Astrology and Reincarnation. Samuel Weiser, 1989. Print
from www.ThoughCo.com, by Molly Hall | 0.872862 | 3.092015 |
Astronomers have pinpointed what appears to be the first moon detected outside this solar system, a large gaseous world the size of Neptune that is unlike any other known moon and orbits a gas planet much more massive than Jupiter.
The discovery, detailed by researchers on Wednesday, was a surprise, and not because it showed that moons exist elsewhere - they felt it was only a matter of time for one to be found in another star system. They were amazed instead by how different this moon was from the roughly 180 known in our solar system.
"It's big and weird by solar system standards," Columbia University astronomy professor David Kipping said of the moon, known as an exomoon because it is outside our solar system.
Our solar system's moons all are rocky or icy objects. The newly discovered exomoon and the planet it orbits, estimated to be several times the mass of our solar system's largest planet Jupiter, are both gaseous, an unexpected pairing. They are located 8,000 light years from Earth.
Kipping and study co-author Alex Teachey, a Columbia graduate student, said their observations using NASA's Hubble Space Telescope and Kepler Space Telescope provided the first clear evidence of an exomoon, but further Hubble observations next May must be used to confirm the finding.
The exomoon is exponentially larger than our solar system's biggest moon. Jupiter's moon Ganymede has a diameter of about 5260 km. The exomoon is estimated to be roughly the size of Neptune, the smallest of our solar system's four gas planets, with a diameter of about 49,000 km.
The exomoon and its planet orbit Kepler-1625, a star similar in temperature to our sun but about 70 per cent larger. The exomoon orbits roughly 1.9 million miles (3 million km) from its planet. The exomoon's mass is about 1.5 per cent that of its planet.
Kipping and Teachey relied on the "transit" method already used by researchers to discover nearly 4,000 planets outside our solar system, called exoplanets. They observed a dip in Kepler-1625's brightness when the planet and then the exomoon passed in front of it.
The size and gaseous composition of the exomoon challenge current moon formation theories.
"You could argue that because larger objects are easier to detect than smaller ones, this is really the lowest-hanging fruit, so it might not be wholly unexpected that the first exomoon detection would be among the largest possible," Teachey said.
The findings were published in the journal Science Advances. | 0.8617 | 3.888392 |
Astronomers Discover New Type of Pulsating White Dwarf Star
News story originally written on May 1, 2008
University of Texas at Austin astronomers Michael H. Montgomery and Kurtis A. Williams, along with graduate student Steven DeGennaro, have predicted and confirmed the existence of a new type of variable star, with the help of the 2.1-meter Otto Struve Telescope at McDonald Observatory. The discovery is announced in today's issue of Astrophysical Journal Letters .
This research was funded by the National Science Foundation and the Delaware Asteroseismic Research Center.
Called a "pulsating carbon white dwarf," this is the first new class of variable white dwarf star discovered in more than 25 years. Because the overwhelming majority of stars in the universe--including the sun--will end their lives as white dwarfs, studying the pulsations (i.e., variations in light output) of these newly discovered examples gives astronomers a window on an important end point in the lives of most stars.
A white dwarf star is the leftover remnant of a sun-like star that has burned all of the nuclear fuel in its core. It is extremely dense, packing half to 1.5 times the sun's mass into a volume about the size of Earth. Until recently, there were thought to be two main types of white dwarfs: those with an outer layer of hydrogen (about 80 percent of white dwarfs), and those with an outer layer of helium, whose hydrogen shells have somehow been stripped away (the other 20 percent).
Last year, University of Arizona astronomers Patrick Dufour and James Liebert discovered a third type of white dwarf star. For reasons that are not understood, these "hot carbon white dwarfs" have had both their hydrogen and helium shells stripped off, leaving their carbon layer exposed. Astronomers suspect that these could be among the most massive white dwarfs of all, the remnants of stars slightly too small to end their lives in a supernova explosion.
After these new carbon white dwarfs were announced, Montgomery calculated that pulsations in these stars were possible. Pulsating stars are of interest to astronomers because the changes in their light output can reveal what goes on in their interiors--similar to the way geologists study seismic waves from earthquakes to understand what goes on in Earth's interior. In fact, this type of star-study is called "asteroseismology."
So, Montgomery and Williams' team began a systematic study of carbon white dwarfs with the Struve Telescope at McDonald Observatory, looking for pulsators. DeGennaro discovered that a star about 800 light-years away in the constellation Ursa Major, called SDSS J142625.71+575218.3, fits the bill. Its light intensity varies regularly by nearly two percent about every eight minutes.
"The discovery that one of these stars is pulsating is remarkably important," said NSF astronomer Michael Briley. "This will allow us to probe the white dwarf's interior, which in turn should help us solve the riddle of where the carbon white dwarfs come from and what happens to their hydrogen and helium."
The star lies about ten degrees east northeast of Mizar, the middle star in the handle of the Big Dipper. This white dwarf has about the same mass as our Sun, but its diameter is smaller than Earth's. The star has a temperature of 35,000 degrees Fahrenheit (19,500 C), and is only 1/600th as bright as the Sun.
None of the other stars in their sample were found to pulsate. Given the masses and temperatures of the stars in their sample, SDSS J142625.71+575218.3 is the only one expected to pulsate, based on Montgomery's calculations.
The astronomers speculate that the pulsations are caused by changes in the star's carbon outer envelope as the star cools down from its formation as a hot white dwarf. The ionized carbon atoms in the star's outer layers return to a neutral state, triggering the pulsations.
There is a chance that the star's variations might have another cause. Further study is needed, the astronomers say. Either way, studying these stars will shed light on the unknown process that strips away their surface layers of hydrogen and helium to lay bare their carbon interiors.
Text above is courtesy of the National Science Foundation | 0.841768 | 3.841851 |
In my first post about the Triangulum Galaxy (M33), I mentioned that there were many star formation regions visible in the galaxy. I also pointed out the largest known such region, NGC 604, which is in that galaxy neighbor.
These star formation regions are called HII regions because they are made up primarily of ionized hydrogen gas. (HII is a reference to that ionized hydrogen. Astronomers refer to neutral hydrogen as HI and molecular hydrogen as H2.) You’ll find some images that highlight these regions below, and I’ll also say more about these regions and their nature. See my previous post for more information as well. If you just want pretty pictures (and who doesn’t want pretty pictures?), please visit this page for larger versions than included below.
Ionized Hydrogen and H-alpha Emissions
Because they are made up of ionized gas, these clouds glow. Stelar radiation strips the hydrogen atoms of their single electron, but the free electrons also seek to recombine with the bare protons. When they do so, they first form atoms with a fair amount of excess energy. As the atoms settle down into lower energy states, they emit radiation. When an electron settles down the last jump to its lowest energy state, it emits a photon of a specific energy, and thus with a specific wavelength of light. This light is a narrow line in the spectrum which is called H-alpha by astronomers, and is a deep red color. Filters can be used to isolate this particular light in a telescope, enabling one to see only the light generated by this particular atomic energy dance. Thus, one can very easily see these HII regions against the general background of stelar and other radiation. H-alpha is an important wavelength that astronomers use to study objects in space and can help us better understand the dynamics of a astronomical system.
M33 in H-alpha
This image is the galaxy M33 in H-alpha. As you can see, much of the galaxy fades away. Instead, we most prominently see the patches of light from the HII regions. The very large HII region called NGC 604 really stands out in the upper right quadrant. (An illustration of it’s location, with a Hubble Telescope image of the area, can be found here.) But you can also fairly easily trace the major spiral arms in this image. These stallar formation regions concentrate in the galactic disk, and then very often along the arms of a spiral galaxy. Thus the arms of a spiral galaxy are revealed to be largely defined by regions of fairly recent, and ongoing, stelar formation. Spiral galaxies are also among the younger galaxies we see. The older galaxies tend to be elliptical galaxies without arms and with a relatively featureless profile. They typically have very few HII regions and little stelar formation going on. The molecular clouds from which stars may form have generally been dissipated or used up by the time galaxies reach that stage in their evolution. This makes some sense if the galactic arms are intimately connected with stelar formation processes.
In order to see these regions better in the context of the galaxy seen in the broader visible light spectrum, I have created the image below. The H-alpha image has been combined as bright red areas which stand out against the spiral arms and dust lanes of M33.
The Life Cycle of an HII Region
HII regions begin life as large and very cold molecular clouds, consisting mostly of hydrogen in molecular form. Something trigers areas of the cloud to collapse and form a star. (There are a variety of mechanisms that are believed to be possible causes.) Not every star will produce the glowing emission nebulas we see in H-alpha above. It takes a fair amount of energy to ionize the hydrogen. Many stars just don’t have what it takes. At the heart of an HII region, there will be a young and very massive star. Only these massive stars, many of them at least 15 times as massive as our sun, produce enough ultraviolet radiation to ionize the nearby gas. These stars burn very hot and very quickly, but are often obscured by the cloud they are embedded in. The ionized region falls within a sphere around the star, the size of which depends on the density of the cloud and the amount of ultraviolet radiation it produces. The hotter, brighter, and more massive the star, the more UV radiation. The denser the cloud, the smaller the region, because the quota of atoms that can be ionized is more quickly reached.
These emission nebulas are also fairly short lived. As the young star burns, radiation and solar winds will blow away the leftover gasses of the cloud in which it formed. The nebula will glow only when there is sufficient gas within the sphere of ionizing radiation from the star. When the gas cloud is dissipated by stellar radiation (or the star has drifted out of the cloud), the HII region will no longer continue to be ionized, revert to HI, and go dark. These nebula will only last a few million years. The longest lasting of the stars that fuel their ionization will only burn normally for perhaps 10-20 million years. The most massive of these stars may even go supernova after just a couple of million years.
Very often, the large, bright stars that give birth to an HII region’s ionization will also form in groups. Large HII regions form when the spheres created by each individual star overlap in space. There must be some large groups of these bright stars in some regions of M33, given the size of some of the HII regions seen there.
Larger version of the images here, as well as my recent standard color version, and instrument and exposure information can be seen at this page. Also see my astrophotography gallery for other astrophotographs. | 0.854306 | 3.898214 |
Ever since enthusiasm started growing over the possibility that there could be a ninth major planet orbiting the sun beyond Neptune, astronomers have been busy hunting it.
One group is investigating four new moving objects found by members of the public to see if they are potential new solar system discoveries. As exciting as this is, researchers are also making discoveries that question the entire prospect of a ninth planet.
One such finding is our discovery of a minor planet in the outer solar system: 2013 SY99. This small, icy world has an orbit so distant that it takes 20,000 years for one long, looping passage. We found SY99 with the Canada-France-Hawaii Telescope as part of the Outer Solar System Origins Survey. SY99’s great distance means it travels very slowly across the sky. Our measurements of its motion show that its orbit is a very stretched ellipse, with the closest approach to the sun at 50 times that between the Earth and the sun (a distance of 50 “astronomical units”).
The new minor planet loops even further out than previously discovered dwarf planets such as Sedna and 2013 VP113. The long axis of its orbital ellipse is 730 astronomical units. Our observations with other telescopes show that SY99 is a small, reddish world, some 250 kilometres in diameter, or about the size of Wales in the UK.
SY99 is one of only seven known small icy worlds that orbit beyond Neptune at remarkable distances. How these “extreme trans-Neptunian objects” were placed on their orbits is uncertain: their distant paths are isolated in space. Their closest approach to the sun is so far beyond Neptune that they are thought to be “detached” from the strong gravitational influence of the giant planets in our solar system. But at their furthest points, they are still too close to be nudged around by the slow tides of the galaxy itself.
It’s been suggested that the extreme trans-Neptunian objects could be clustered in space by the gravitational influence of a “Planet Nine” that orbits much further out than Neptune. This planet’s gravity could lift out and detach their orbits – constantly changing their tilt. But this planet is far from proven.
In fact, its existence is based on the orbits of only six objects, which are very faint and hard to discover even with large telescopes. They are therefore prone to odd biases. It’s a bit like looking down into the deep ocean at a school of fish. The fish swimming near the surface are clearly visible. But the ones even only a meter down are fainter and murky, and take quite a lot of peering to be certain. The great bulk of the school, in the depths, is completely invisible. But the fish at the surface and their behaviour betray the existence of a whole school.
The biases mean SY99’s discovery can’t prove or disprove the existence of a Planet Nine. However, computer models do show that a Planet Nine would be an unfriendly neighbour to tiny worlds like SY99: its gravitational influence would starkly change its orbit – throwing it from the solar system entirely, or poking it into an orbit so highly inclined and distant that we wouldn’t be able to see it. SY99 would have to be one of an utterly vast throng of small worlds, continuously being sucked in and cast out by the planet.
The alternative explanation
But it turns out that there are other explanations. Our study based on computer modelling, accepted for publication in the Astronomical Journal, hint at the influence of an idea from everyday physics called diffusion. This is a very common type of behaviour in the natural world. Diffusion typically explains the random movement of a substance from a region of higher concentration to one of lower concentration – such as the way perfume drifts across a room.
We showed that a related form of diffusion can cause the orbits of minor planets to change from an ellipse that is initially only 730 astronomical units on its long axis to one that is as big as 2,000 astronomical units or bigger – and change it back again. In this process, the size of each orbit would vary by a random amount. When SY99 comes to its closest approach every 20,000 years, Neptune will often be in a different part of its orbit on the opposite side of the solar system. But at encounters where both SY99 and Neptune are close, Neptune’s gravity will subtly nudge SY99, minutely changing its velocity. As SY99 travels out away from the sun, the shape of its next orbit will be different.
The long axis of SY99’s ellipse will alter, becoming either larger or smaller, in what physicists call a “random walk”. The orbit change takes place on truly astronomical time scales. It diffuses over the space of tens of millions of years. The long axis of SY99’s ellipse would change by hundreds of astronomical units over the 4.5 billion-year history of the solar system.
Several other extreme trans-Neptunian objects with smaller orbits also show diffusion, on a smaller scale. Where one goes, more can follow. It’s entirely plausible that the gradual effects of diffusion act on the tens of millions of tiny worlds orbiting in the near fringe of the Oort cloud (a shell of icy objects at the edge of the solar system). This gentle influence would slowly lead some of them to randomly shift their orbits closer to us, where we see them as extreme trans-Neptunian objects.
However, diffusion won’t explain the distant orbit of Sedna, which has its closest point too far out from Neptune for it to change its orbit’s shape. Perhaps Sedna gained its orbit from a passing star, aeons ago. But diffusion could certainly be bringing in extreme trans-Neptunian objects from the inner Oort cloud – without the need for a Planet Nine. To find out for sure, we’ll need to make more discoveries in this most distant region using our largest telescopes.
Source: The Conversation | 0.8699 | 3.889457 |
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