APOD Retrospective: January 19

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: January 19

Post by bystander » Thu Jan 19, 2012 5:01 am


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2015 The Great Nebula in Orion is an intriguing place. Visible to the unaided eye, it appears as a small fuzzy patch in the constellation of Orion. But this image, an illusory-color four-panel mosaic taken in different bands of infrared light with the Earth orbiting WISE observatory, shows the Orion Nebula to be a bustling neighborhood of recently formed stars, hot gas, and dark dust. The power behind much of the Orion Nebula (M42) is the stars of the Trapezium star cluster, seen near the center of the above wide field image. The orange glow surrounding the bright stars pictured here is their own starlight reflected by intricate dust filaments that cover much of the region. The current Orion Nebula cloud complex, which includes the Horsehead Nebula, will slowly disperse over the next 100,000 years.

2014 Billions of years from now, only one of these two galaxies will remain. Until then, spiral galaxies NGC 2207 and IC 2163 will slowly pull each other apart, creating tides of matter, sheets of shocked gas, lanes of dark dust, bursts of star formation, and streams of cast-away stars. Astronomers predict that NGC 2207, the larger galaxy on the left, will eventually incorporate IC 2163, the smaller galaxy on the right. In the most recent encounter that about peaked 40 million years ago, the smaller galaxy is swinging around counter-clockwise, and is now slightly behind the larger galaxy. The space between stars is so vast that when galaxies collide, the stars in them usually do not collide.

2013 A gaze across a cosmic skyscape, this telescopic mosaic reveals the continuous beauty of things that are. The evocative scene spans some 6 degrees or 12 Full Moons in planet Earth's sky. At the left, folds of red, glowing gas are a small part of an immense, 300 light-year wide arc. Known as Barnard's loop, the structure is too faint to be seen with the eye, shaped by long gone supernova explosions and the winds from massive stars, and still traced by the light of hydrogen atoms. Barnard's loop lies about 1,500 light-years away roughly centered on the Great Orion Nebula, a stellar nursery along the edge of Orion's molecular clouds. But beyond lie other fertile star fields in the plane of our Milky Way Galaxy. At the right, the long-exposure composite finds NGC 2170, a dusty complex of nebulae near a neighboring molecular cloud some 2,400 light-years distant.

2012 Begirt with many a blazing star, Orion, the Hunter, is one of the most easily recognizable constellations. In this night skyscape from January 15, the hunter's stars rise in the northern hemisphere's winter sky, framed by bare trees and bounded below by terrestrial lights around Lough Eske (Lake of Fish) in County Donegal, Ireland. Red giant star Betelgeuse is striking in yellowish hues at Orion's shoulder above and left of center. Rivaling the bright red giant, Rigel, a blue supergiant star holds the opposing position near Orion's foot. Of course, the sword of Orion hangs from the hunter's three belt stars near picture center, but the middle star in the sword is not a star at all. A slightly fuzzy pinkish glow hints at its true nature, a nearby stellar nursery visible to the unaided eye known as the Orion Nebula.

2011 Late last year, a new, remarkably bright storm erupted in Saturn's northern hemisphere. Amateur astronomers first spotted it in early December, with the ringed gas giant rising in planet Earth's predawn sky. Orbiting Saturn, the Cassini spacecraft was able to record this close-up of the complex disturbance from a distance of 1.8 million kilometers on December 24th. Over time, the storm has evolved, spreading substantially in longitude, and now stretches far around the planet. Saturn's thin rings are also seen slicing across this space-based view, casting broad shadows on the planet's southern hemisphere.

2010 They might look like trees on Mars, but they're not. Groups of dark brown streaks have been photographed by the Mars Reconnaissance Orbiter on melting pinkish sand dunes covered with light frost. The above image was taken in 2008 April near the North Pole of Mars. At that time, dark sand on the interior of Martian sand dunes became more and more visible as the spring Sun melted the lighter carbon dioxide ice. When occurring near the top of a dune, dark sand may cascade down the dune leaving dark surface streaks -- streaks that might appear at first to be trees standing in front of the lighter regions, but cast no shadows. Objects about 25 centimeters across are resolved on this image spanning about one kilometer. Close ups of some parts of this image show billowing plumes indicating that the sand slides were occurring even when the image was being taken.

2009 Why is there methane on Mars? No one is sure. An important confirmation that methane exists in the atmosphere of Mars occurred last week, bolstering previous controversial claims made as early as 2003. The confirmation was made spectroscopically using large ground-based telescopes by finding precise colors absorbed on Mars that match those absorbed by methane on Earth. Given that methane is destroyed in the open martian air in a matter of years, the present existence of the fragile gas indicates that it is currently being released, somehow, from the surface of Mars. One prospect is that microbes living underground are creating it, or created it in the past. If true, this opens the exciting possibility that life might be present under the surface of Mars even today. Given the present data, however, it is also possible that a purely geologic process, potentially involving volcanism or rust and not involving any life forms, is the methane creator. Pictured above is an image of Mars superposed with a map of the recent methane detection.

2008 The tantalizing Pleiades star cluster seems to lie just beyond the trees above a dark castle tower in this dramatic view of The World at Night. Recorded earlier this month, the starry sky also features bright star Aldebaran below the Pleiades and a small, faint, fuzzy cloud otherwise known as Comet Holmes near picture center at the top of the field. Starry Night Castle might be an appropriate name for the medieval castle ruin in the foreground. But its traditional name is Mörby Castle, found north of Stockholm, near lake Skedviken in Norrtälje, Sweden.

2007 Comets grow bright when they're close to the Sun, basking in the intense solar radiation. Of course, they're also usually impossible to see against the overwhelming scattered sunlight. But surprising Comet McNaught - whose January 12 closest approach to the Sun (perihelion passage) was well inside the orbit of Mercury - gave an enjoyable performance in bright blue daytime skies. In fact, comet expert David Levy captured this remarkable inset (upper left) telescopic view of McNaught within an hour of perihelion, with the comet in broad daylight only about 7 degrees away from the Sun's position. Stefan Seip's wider daytime view of the comet and fluffy clouds was recorded approximately a day later. Seip used a polarizing filter and a telescope/camera set up near Stuttgart, Germany. No longer visible in broad daylight, Comet McNaught is now touring twilight southern skies.

2006 Few cosmic vistas excite the imagination like the Orion Nebula. Also known as M42, the nebula's glowing gas surrounds hot young stars at the edge of an immense interstellar molecular cloud only 1,500 light-years away. The Orion Nebula offers one of the best opportunities to study how stars are born partly because it is the nearest large star-forming region, but also because the nebula's energetic stars have blown away obscuring gas and dust clouds that would otherwise block our view - providing an intimate look at a range of ongoing stages of starbirth and evolution. This detailed image of the Orion Nebula is the sharpest ever, constructed using data from the Hubble Space Telescope's Advanced Camera for Surveys and the European Southern Observatory's La Silla 2.2 meter telescope. The mosaic contains a billion pixels at full resolution and reveals about 3,000 stars. In apparent size, the picture is as large as the Full Moon. At the distance of M42 it spans thirteen light-years.

2005 What are these surface features on Titan? Scroll right to see the panoramic view captured last week by the Huygens probe as it descended toward Saturn's mysterious moon. Scientists are not yet sure what the above image is showing. On the far left, a boundary seems to exist between some sort of smooth dark terrain and a type of choppier terrain in the distance. In the image center and on the left, white areas cover the image that might be a type of ground fog. The Huygens probe landed in the dark area of the far right, finding a portion of Titan's surface that had the consistency of wet sand and a surface temperature of -179 degrees Celsius. Huygen's battery lasted an unexpectedly long three hours as it beamed back images and data to the Saturn-orbiting Cassini mothership and an armada of Earth's most sensitive radio telescopes. Analysis of the Huygens' images will likely continue for years in attempts to better understand this cloud-engulfed moon.

2004 Flying past a comet nucleus is dangerous. On January 2, the robot spacecraft STARDUST became one of the first to plow through the surrounding cloud of dust and grit to photograph the very heart of a comet. Pictured above is a short movie of the encounter showing unprecedented surface details of the icy center of Comet Wild 2. The STARDUST camera pivoted to remain pointed at the nucleus as the spacecraft passed. Heavily shielded from the onslaught of cometary debris, STARDUST survived the beating in excellent condition. Surprisingly, although the nucleus appeared to be solid, the the surrounding coma appeared to be highly fragmented into several distinct streams of particles. Souvenirs captured by the spacecraft will be ejected as the spacecraft passes the Earth in January 2006.

2003 Scientists have found, unexpectedly, tiny time capsules from billions of years in the past. The discovery involves small molecules that can apparently become trapped during the formation of large enclosed molecules known as fullerenes, or buckyballs. Luann Becker (UCSB) and collaborators recently found fullerenes in an ancient meteorite that fell to Earth about 30 years ago. Extra-terrestrial fullerenes inside the meteorite survived, and upon inspection, were not empty inside. The small molecules trapped inside are giving a glimpse of what the Solar System was like during its formation. Pictured above is a computer simulation showing a relatively small fullerene (60-atoms of carbon) situated above a hydrogenated silicon surface. How these fullerenes formed, how they survived, where else they can be found, and what else might be found inside these tiny time capsules is developing into an exciting area of research.

2002 Galaxies are made up of stars, but are all stars found within galaxies? Using the Hubble Space Telescope, researchers exploring the Virgo Cluster of galaxies have found about 600 red giant stars adrift in intergalactic space. Above is an artist's vision of the sky from a hypothetical planet of such a lonely sun. The night sky on a world orbiting an intergalactic star would be a stark contrast to Earth's - which features a spectacle of stars, all members of our own Milky Way Galaxy. As suggested by the illustration, a setting red sun would leave behind a dark sky flecked only with faint, fuzzy, apparitions of Virgo Cluster galaxies. Possibly ejected from their home galaxies during galaxy-galaxy collisions, these isolated suns may well represent part of a large, previously unseen stellar population, filling the space between Virgo Cluster galaxies.

2001 Q: Why are black holes black? A: Because they have an event horizon. The event horizon is that one-way boundary predicted by general relativity beyond which nothing, not even light, can return. X-ray astronomers using the space-based Chandra Observatory now believe they have direct evidence for event horizons - therefore black holes - in binary star systems which can be detected in x-ray light. These binaries, sometimes called x-ray novae, are known to consist of relatively normal stars dumping material on to massive, compact companions. As illustrated, the material swirls toward the companion in an accretion disk which itself glows in x-rays. If the compact companion is a neutron star (right), the material ultimately smashes into the solid surface and glows even more brightly in high energy x-rays. But if it is indeed a black hole with a defining event horizon, then the x-ray hot material approaches the speed of light as it swirls past the surface of no return and is lost from view. Recent work describes observations of two classes of x-ray binaries, one class 100 times fainter than the other. The results imply the presence of an event horizon in the fainter class which causes the extreme difference in x-ray brightness.

2000 A black hole glides silently through space. Is there any way to know it's there? Until last week, all objects that might be black holes in our Galaxy were part of binary star systems. There, gas from the companion star was hypothesized to swirl around the black hole, heat up, and emit X-rays before falling in. Last week, however, analysis was released of a mysteriously dark object that floated in front of a distant background star, dramatically increasing this star's light by the lens effect of its gravity, as pictured above. The high mass and low light of this strange lens have astronomers guessing they might just have detected a lone black hole, weighing in at six times the mass of our Sun. The existence of isolated black holes is not in itself surprising, as they should be the end result of the cores of massive stars.

1999 Telescopes are not very useful during lightning storms. Nevertheless, with lightning illuminating a dark landscape, the picturesque dome of the famous Kitt Peak 2.1-meter Telescope makes for a dramatic photograph. A passing car created the red and yellow streaks visible in the foreground. The 2.1-meter Telescope has participated in many important astronomical discoveries including the discovery of the Lyman-alpha forest, the first gravitational lens, and the first pulsating white dwarf.

1998 The Hubble Double Bubble Planetary Nebula is bubbling over with excitement. More mundanely known as Hubble 5, this bipolar planetary nebula is being created by a hot wind of particles streaming away from the central star system. The hot gas expands into the surrounding interstellar medium in a fashion similar to the inflation of hot air balloons. A supersonic shock-wave can form at the boundary, causing newly excited gas there to shine as electrons recombine with resident elements. In the above picture, colors are assigned according to the energy of the recombinant radiation. This star system lies about 2200 light-years from Earth, and likely includes a Sun-like star slowly transforming itself into a white dwarf.

1997 Perhaps the most famous astronomical image in recent years reveals newborn stars upon pillars of gas and dust - uncovered as researchers used the Hubble Space Telescope to explore the Eagle Nebula in 1995. This stunning picture provides a first hand glimpse of star birth as evaporating gaseous globules (EGGs) are captured emerging from pillars of molecular hydrogen gas and dust. These pillars, dubbed "elephant trunks," are light years in length and are so dense that interior gas gravitationally contracts to form stars. At each pillars' end, the intense radiation of bright young stars causes low density gas to boil away, leaving stellar nurseries of dense EGGs exposed.

1996 This dusty disk, viewed edge on surrounding Beta Pictoris, a star only 50 lightyears distant, may signal the presence of an infant solar system. Beta Pictoris is a young Sun-like star just completing its formative stages. About 10 years ago it made the news when astronomers detected a disk around the star because planets are expected to form in such circumstellar disks. Did planets form around Beta Pic? The above recent Hubble Space Telescope image offers supporting evidence that they did. In this false color image, the overwhelming light from the star itself is masked out and features of the inner disk are revealed. The inner part (white area) appears to be slightly warped with respect to the line centered on the axis of the outer parts of the disk. This warp could be caused by a large planet orbiting within the inner clear zone, too faint to be seen directly against the stellar glare. If so, this is an indication that planetary systems are common in our galaxy. Is anybody out there?

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