APOD Retrospective: January 8

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: January 8

Post by bystander » Sun Jan 08, 2012 4:23 am

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2015 Cosmic dust clouds and young, energetic stars inhabit this telescopic vista, less than 500 light-years away toward the northern boundary of Corona Australis, the Southern Crown. The dust clouds effectively block light from more distant background stars in the Milky Way. But the striking complex of reflection nebulae cataloged as NGC 6726, 6727, and IC 4812 produce a characteristic blue color as light from the region's young hot stars is reflected by the cosmic dust. The dust also obscures from view stars still in the process of formation. At the left, smaller yellowish nebula NGC 6729 bends around young variable star R Coronae Australis. Just below it, glowing arcs and loops shocked by outflows from embedded newborn stars are identified as Herbig-Haro objects. On the sky this field of view spans about 1 degree. That corresponds to almost 9 light-years at the estimated distance of the nearby star forming region.

2014 Sunsets may be the most watched celestial event, but lately sunsets have even offered something extra. A sunspot so large it was visible to the naked eye is captured in Swiss skies in this sunset scene from January 5, crossing left to right near the center of a solar disk dimmed and distorted by Earth's dense atmosphere. Detailed views reveal a large solar active region composed of sunspots, some larger than planet Earth itself. Cataloged as active region AR 1944, on January 7 it produced a substantial solar flare and a coronal mass ejection (CME) forecast to reach Earth. The CME could trigger geomagnetic storms and aurora on January 9.

2013 The grand, winding arms are almost mesmerizing in this face-on view of NGC 7424, a spiral galaxy with a prominent central bar. About 40 million light-years distant in the headlong constellation Grus, this island universe is also about 100,000 light-years across making it remarkably similar to our own Milky Way. Following along the winding arms, many bright clusters of massive young stars can be found. The star clusters themselves are several hundred light-years in diameter. And while massive stars are born in the arms of NGC 7424, they also die there. Notably, this galaxy was home to a powerful stellar explosion, supernova SN 2001ig, which faded well before the above image was recorded.

2012 Named for a forgotten constellation, the Quadrantid Meteor Shower is an annual event for planet Earth's northern hemisphere skygazers. It usually peaks briefly in the cold, early morning hours of January 4. The shower's radiant point on the sky lies within the old, astronomically obsolete constellation Quadrans Muralis. That position is situated near the boundaries of the modern constellations Hercules, Bootes, and Draco. Many of this year's Quadrantid meteors were dim, but the one captured in this north-looking view is bright and easy to spot. In the foreground is the Maurice River's East Point Lighthouse located near the southern tip of New Jersey on the US east coast. The likely source of the dust stream that produces Quadrantid meteors was identified in 2003 as an asteroid.

2011 A mere seven hundred light years from Earth, in the constellation Aquarius, a sun-like star is dying. Its last few thousand years have produced the Helix Nebula (NGC 7293), a well studied and nearby example of a Planetary Nebula, typical of this final phase of stellar evolution. A total of 10 hours of exposure time have gone in to creating this remarkably deep view of the nebula. It shows details of the Helix's brighter inner region, about 3 light-years across, but also follows fainter outer halo features that give the nebula a span of well over six light-years. The white dot at the Helix's center is this Planetary Nebula's hot, central star. A simple looking nebula at first glance, the Helix is now understood to have a surprisingly complex geometry.

2010 Every 27 years Epsilon Aurigae fades, remaining dim for roughly two years before growing bright again. Since the 19th century, astronomers have studied the mystery star, eventually arguing that Epsilon Aur, centered in this telescopic skyview, was actually undergoing a long eclipse by a dark companion object. But the nature of the companion and even the state of bright star itself could not be pinned down by observations. Continuing to collect evidence, Citizen Sky, a team of professional and amateur astronomers, is studying the current eclipse of Epsilon Aur, reporting that it began in August 2009 and by late December had reached its deepest point. Epsilon Aur is now expected to remain dim for all of 2010, before rapidly regaining normal brightness in 2011. Meanwhile, recent infrared data from the Spitzer Space Telescope supports a model for the enigmatic system that identifies Epsilon Aur as a large but lower mass star near the end of its life, periodically eclipsed by a single star embedded in a dusty disk. The disk is estimated to have a radius of about 4 AU, or 4 times the Earth-Sun distance, and to be about 0.5 AU thick.

2009 This shock wave plows through space at over 500,000 kilometers per hour. Moving right to left in the beautifully detailed color composite, the thin, braided filaments are actually long ripples in a sheet of glowing gas seen almost edge on. Cataloged as NGC 2736, its narrow appearance suggests its popular name, the Pencil Nebula. About 5 light-years long and a mere 800 light-years away, the Pencil Nebula is only a small part of the Vela supernova remnant. The Vela remnant itself is around 100 light-years in diameter, the expanding debris cloud of a star that was seen to explode about 11,000 years ago. Initially, the shock wave was moving at millions of kilometers per hour but has slowed considerably, sweeping up surrounding interstellar gas.

2008 As the New Horizons spacecraft sweeps through the Solar System, it is taking breathtaking images of the planets. In February of last year, New Horizons passed Jupiter and the ever-active Jovian moon Io. In this montage, Jupiter was captured in three bands of infrared light making the Great Red Spot look white. Complex hurricane-like ovals, swirls, and planet-ringing bands are visible in Jupiter's complex atmosphere. Io is digitally superposed in natural color. Fortuitously, a plume was emanating from Io's volcano Tvashtar. Frost and sulfuric lava cover the volcanic moon, while red-glowing lava is visible beneath the blue sunlight-scattering plume. The robotic New Horizons spacecraft is on track to arrive at Pluto in 2015.

[imghover6=http://apod.nasa.gov/apod/image/0701/di ... _clean.jpg]http://apod.nasa.gov/apod/image/0701/di ... labels.jpg[/imghover6]Credit & Copyright: Jerry Lodriguss (Catching the Light)

Do you see it? This common question frequently precedes the rediscovery of one of the most commonly recognized configurations of stars on the northern sky: the Big Dipper. This grouping of stars is one of the few things that has likely been seen, and will be seen, by every generation. The Big Dipper is not by itself a constellation. Although part of the constellation of the Great Bear (Ursa Major), the Big Dipper is an asterism that has been known by different names to different societies. Five of the Big Dipper stars are actually near each other in space and were likely formed at nearly the same time. Connecting two stars in the far part of the Big Dipper will lead one to Polaris, the North Star, which is part of the Little Dipper. Relative stellar motions will cause the Big Dipper to slowly change its apparent configuration over the next 100,000 years.

2006 In this stunning vista recorded with the Hubble Space Telescope's Advanced Camera for Surveys, distant galaxies form a dramatic backdrop for disrupted spiral galaxy Arp 188, the Tadpole Galaxy. The cosmic tadpole is a mere 420 million light-years distant toward the northern constellation Draco. Its eye-catching tail is about 280 thousand light-years long and features massive, bright blue star clusters. One story goes that a more compact intruder galaxy crossed in front of Arp 188 - from left to right in this view - and was slung around behind the Tadpole by their gravitational attraction. During the close encounter, tidal forces drew out the spiral galaxy's stars, gas, and dust forming the spectacular tail. The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the Tadpole, can be seen through foreground spiral arms at the upper left. Following its terrestrial namesake, the Tadpole Galaxy will likely lose its tail as it grows older, the tail's star clusters forming smaller satellites of the large spiral galaxy.

2005 A mere 6,000 light-years distant and sailing through the constellation Vela, star cluster RCW 38 is full of powerful stars. It's no surprise that these stars, only a million years young with hot outer atmospheres, appear as point-like x-ray sources dotting this x-ray image from the orbiting Chandra Observatory. But the diffuse cloud of x-rays surrounding them is a bit mysterious. The image is color coded by x-ray energy, with high energies in blue, medium in green, and low energy x-rays in red. Just a few light-years across, the cloud which pervades the cluster has colors suggesting the x-rays are produced by high energy electrons moving through magnetic fields. Yet a source of energetic electrons, such as shockwaves from exploding stars (supernova remnants), or rotating neutron stars (pulsars), is not apparent in the Chandra data. Whatever their origins, the energetic particles could leave an imprint on planetary systems forming in young star cluster RCW 38, just as nearby energetic events seem to have affected the chemistry and isotopes found in our own solar system.

2004 Distant hills rise above a rocky, windswept plain in this sharp stereo scene from the Spirit rover on Mars. When viewed with red/blue glasses, the picture combines left and right images from Spirit's high resolution panoramic camera to yield a dramatic 3D perspective. The hills were estimated to lie about 2 kilometers away and be approximately 50 to 100 meters high. Along with other features of the landscape, determining their direction and distance will help pinpoint the exact location of the Spirit landing site when compared with high resolution images of the region taken from Mars orbit. Much stereo image data, allowing important estimates of three dimensional shapes, sizes, and distances, is anticipated from the rover's cameras. (Editor's note: Red/blue glasses for viewing stereo pictures can be purchased or simply constructed using red and blue plastic for filters. Try it! To view this image, the red filter is used for the left eye.)

2003 Using the orbiting Chandra X-ray Observatory, astronomers have taken this long look at the core of our Milky Way galaxy, some 26,000 light-years away. The spectacular false-color view spans about 130 light-years. It reveals an energetic region rich in x-ray sources and high-lighted by the central source, Sagittarius A*, known to be a supermassive black hole with 3 million times the mass of the Sun. Given its tremendous mass, Sagittarius A* is amazingly faint in x-rays in comparison to central black holes observed in distant galaxies, even during its frequent x-ray flares. This suggests that this supermassive black hole has been starved by a lack of infalling material. In fact, the sharp Chandra image shows clouds of multi-million degree gas dozens of light-years across flanking (upper right and lower left) the central region -- evidence that violent events have cleared much material from the vicinity of the black hole.

2002 Rich star fields and glowing hydrogen gas silhouette dense, opaque clouds of interstellar gas and dust in this Hubble Space Telescope close-up of IC 2944, a bright star forming region in Centaurus, 5,900 light-years away. The largest of these dark globules, first spotted by South African astronomer A. D. Thackeray in 1950, is likely two separate but overlapping clouds, each more than one light-year wide. Combined the clouds contain material equivalent to about 15 times the mass of the Sun, but will they actually collapse to form massive stars? Along with other data, the sharp Hubble images indicate that Thackeray's globules are fractured and churning as a result of intense ultraviolet radiation from young, hot stars already energizing and heating the bright emission nebula. These and similar dark globules known to be associated with other star forming regions may ultimately be dissipated by their hostile environment -- like cosmic lumps of butter in a hot frying pan. The chevron shape of the picture outlines the detectors of the Hubble's WFPC2 camera.

2001 The large Martian crater above just left of center: is this a fresh crater, a degraded crater, or a ghost crater? Complex image recognition tasks like these are currently done more reliably by a human than a computer. Additionally, there are so many craters on Mars that NASA just doesn't have enough people to classify them all! Therefore, you can help humanity's understanding of the surface of Mars by volunteering to classify craters. All you need for this pilot study is a proper web browser and a mouse. If asked to classify the above crater, you might best respond that it appears relatively fresh, as it exhibits a sharp rim and a well-preserved interior. Degraded craters are typically older and have their rims more rounded, while "ghost craters" are the oldest of all and only faintly discernable.


Albert Einstein (1879-1955) is considered by many the greatest astrophysicist and single most significant Person of the 20th Century. He is pictured here in the Swiss Patent Office where he did much of his defining work. Einstein's many visionary scientific contributions include the equivalence of mass and energy (E=mc^2), how the maximum speed limit of light affects measurements of time and space (special relativity), and a more accurate theory of gravity based on simple geometric concepts (general relativity). One reason Einstein was awarded the 1921 Nobel Prize in Physics was to make the prize more prestigious.

1999 These technicians are working on the solar-paneled Mars Polar Lander - yet another robotic spacecraft scheduled to invade the red planet. Mars Polar Lander is part of a series of missions focusing on a search for evidence of past or present life. Successfully launched atop a Delta II rocket on January 3rd, it should be the first to make a soft landing near Mars' South Pole. Its arrival is planned for December, springtime for the Martian Southern Hemisphere. Riding along are two separate microprobes intended to penetrate up to 2 meters beneath the soil in an attempt to directly determine if subsurface water ice is present. Mars Polar Lander will also carry another first to Mars ... a microphone.

1998 Tuesday, January 6, at 9:28 p.m. EST, NASA's Lunar Prospector spacecraft climbed into the sky above Cape Canaveral Air Station riding an Athena II rocket. Representing NASA's first Moon mission since the 1972 flight of Apollo 17, this launch also occurred on the 30th anniversary of the launch of the Surveyor 7 lunar lander. The three stage launch vehicle's fiery trail is in the foreground of this time exposure while the Moon, near first quarter phase, is shown in the background some 250,000 miles from the Cape. Prospector will cover that distance in about 5 days, entering lunar orbit on Sunday. Prospector carries no cameras to image the well-photographed lunar surface. Instead, its array of instruments will map the lunar gravity, magnetic field, internal structure, and surface composition. The result, a detailed global view of current lunar properties, is expected to dramatically impact humanity's understanding of the origins of the Moon and the Solar System. From its vantage point in polar orbit, only 63 miles above the lunar surface, Prospector will also conduct a sensitive search for water ice which may be preserved in permanent shadow at the Moon's South Pole.

1997 The Sun's surface is not smooth. It has thousands of bumps called granules and usually a few dark depressions called sunspots. Each of the numerous granules is the size of an Earth continent, but much shorter lived. A granule can only be expected to last a few minutes before dissipating and being replaced by a newly rising granule. In this way a granule acts much like a rising bubble in boiling water. The above black and white, visible-light picture is quite unusual because the usual relative darkening visible near the edges of the Solar disk have been digitally removed. Visible near the center are two large sunspots while the computer enhancement brings out two bright plages close to the right solar limb.

1996 The Milky Way Galaxy is not alone. It is part of a gathering of about 25 galaxies known as the Local Group. Members include the Great Andromeda Galaxy (M31), M32, M33, the Large Magellanic Clouds, the Small Magellanic Clouds, Dwingeloo 1, several small irregular galaxies, and many dwarf elliptical galaxies. Pictured is one of the many dwarf ellipticals: NGC 205. Like M32, NGC 205 is a companion to the large M31, and can sometimes be seen to the south of M31's center in photographs. The above image shows this galaxy to be unusual for an elliptical galaxy in that it contains at least two dust clouds (at 7 and 11 o'clock - they are visible but hard to spot) and signs of recent star formation. This galaxy is sometimes known as M110, although it was actually not part of Messier's original catalog.

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