APOD Retrospective: December 25

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: December 25

Post by bystander » Sun Dec 25, 2011 7:46 am

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2014 Comet Lovejoy, C/2014 Q2, is framed like a cosmic Christmas tree with starry decorations in this colorful telescopic portrait, snapped on December 16th. Its lovely coma is tinted green by diatomic C2 gas fluorescing in sunlight. Discovered in August of this year, this Comet Lovejoy is currently sweeping north through the constellation Columba, heading for Lepus south of Orion and bright enough to offer good binocular views. Not its first time through the inner Solar System, this Comet Lovejoy will pass closest to planet Earth on January 7, while its perihelion (closest point to the Sun) will be on January 30. Of course, planet Earth's own 2015 perihelion passage is scheduled for January 4. A long period comet, this Comet Lovejoy should return again ... in about 8,000 years.

Click to play embedded YouTube video.
Video Credit: Mars Express, ESA

What does the Martian moon Phobos look like? To better visualize this unusual object, images from ESA's Mars Express orbiter have been combined into a virtual rotation movie. The rotation is actually a digital illusion -- tidally-locked Phobos always keeps the same face toward its home planet, as does Earth's moon. The above video highlights Phobos' chunky shape and an unusually dark surface covered with craters and grooves. What lies beneath the surface is a topic of research since the moon is not dense enough to be filled with solid rock. Phobos is losing about of centimeter of altitude a year and is expected to break up and crash onto Mars within the next 50 million years. To better understand this unusual world, Mars Express is on course to make the closest flyby ever on Sunday.

2012 In this evocative night skyscape a starry band of the Milky Way climbs over Yosemite Valley, Sierra Nevada Range, planet Earth. Jupiter is the brightest celestial beacon on the wintry scene, though. Standing nearly opposite the Sun in the constellation Taurus, the wandering planet joins yellowish Aldebaran and the Hyades star cluster. Below, Orion always comes up sideways over a fence of mountains. And from there the twin stars of Gemini rise just across the Milky Way. As this peaceful winter night began, they followed Auriga the charioteer, its alpha star Capella near the top of the frame.

2011 This is the mess that is left when a star explodes. The Crab Nebula, the result of a supernova seen in 1054 AD, is filled with mysterious filaments. The filaments are not only tremendously complex, but appear to have less mass than expelled in the original supernova and a higher speed than expected from a free explosion. The above image, taken by the Hubble Space Telescope, is presented in three colors chosen for scientific interest. The Crab Nebula spans about 10 light-years. In the nebula's very center lies a pulsar: a neutron star as massive as the Sun but with only the size of a small town. The Crab Pulsar rotates about 30 times each second.

2010 Bright stars, clouds of dust and glowing nebulae decorate this cosmic scene, a skyscape just north of Orion's belt. Close to the plane of our Milky Way Galaxy, the wide field view spans about 5.5 degrees. Striking bluish M78, a reflection nebula, is at the left. M78's tint is due to dust preferentially reflecting the blue light of hot, young stars. In colorful contrast, the red sash of glowing hydrogen gas sweeping through the center is part of the region's faint but extensive emission nebula known as Barnard's Loop. At right, a dark dust cloud forms a prominent silhouette cataloged as LDN 1622. While M78 and the complex Barnard's Loop are some 1,500 light-years away, LDN 1622 is likely to be much closer, only about 500 light-years distant from our fair planet Earth.

2009 The graceful arc of the Milky Way begins and ends at two mountain peaks in this solemn night sky panorama. The view was created from a 24 frame mosaic, with exposures tracking Earth and sky separately. In the final composition, northern California's Mount Lassen was positioned at the left and Mount Shasta at the far right, just below the star and dust clouds of the galactic center. Lassen and Shasta are volcanoes in the Cascade Mountain Range of North America, an arc of the volcanic Pacific Ring of Fire. In the dim, snow-capped peaks, planet Earth seems to echo the subtle glow of the Milky Way's own faint, unresolved starlight.

2008 Clouds of glowing hydrogen gas fill this colorful skyscape in the faint but fanciful constellation Monoceros, the Unicorn. A star forming region cataloged as NGC 2264, the complex jumble of cosmic gas and dust is about 2,700 light-years distant and mixes reddish emission nebulae excited by energetic light from newborn stars with dark interstellar dust clouds. Where the otherwise obscuring dust clouds lie close to the hot, young stars they also reflect starlight, forming blue reflection nebulae. The wide mosaic spans about 3/4 degree or nearly 1.5 full moons, covering 40 light-years at the distance of NGC 2264. Its cast of cosmic characters includes the the Fox Fur Nebula, whose convoluted pelt lies at the upper left, bright variable star S Mon immersed in the blue-tinted haze just below the Fox Fur, and the Cone Nebula at the far right. Of course, the stars of NGC 2264 are also known as the Christmas Tree star cluster. The triangular tree shape traced by the stars appears sideways here, with its apex at the Cone Nebula and its broader base centered near S Mon.

2007 Welcome to The World At Night. Sharing the night sky seen around the world, this view from Monument Valley, USA includes a picturesque foreground of famous buttes. Buttes are composed of hard rock left behind after water eroded away the surrounding soft rock. The two buttes on the image left are known as the Mittens, while Merrick Butte is on the right. Recorded just last week, planet Mars is at the left of the skyscape, a glowing beacon of orange that is the brightest object in the frame. To the right of Mars lies the constellation of Orion. Betelgeuse is the reddish star near the center and the Belt of Orion and the Orion Nebula are farther right. Finally, the bright blue star Rigel appears above Merrick Butte in this stunning view of The World At Night.

2006 The International Space Station (ISS) will be the largest human-made object ever to orbit the Earth. The station is so large that it could not be launched all at once -- it is being built piecemeal with large sections added continually by flights of the Space Shuttle. To function, the ISS needs trusses to keep it rigid and to route electricity and liquid coolants. These trusses are huge, extending over 15 meters long, and with masses over 10,000 kilograms. Pictured above earlier this month, astronauts Robert L. Curbeam (USA) and Christer Fuglesang (Sweden) work to attach a new truss segment to the ISS and begin to upgrade the power grid.

2005 Sometimes the simplest shapes are the hardest to explain. For example, the origin of the mysterious cone-shaped region seen on the far left remains a mystery. The interstellar formation, dubbed the Cone Nebula, is located about 2700 light years away. Other features in the image include red emission from diffuse interstellar hydrogen, wispy filaments of dark dust, and bright star S Monocerotis, visible on the far right. Blue reflection nebulae surround the brighter stars. The dark Cone Nebula region clearly contains much dust which blocks light from the emission nebula and open cluster NGC 2264 behind it. One hypothesis holds that the Cone Nebula is formed by wind particles from an energetic source blowing past the Bok Globule at the head of the cone.

2004 As a present to APOD readers, digital imager Mattias Malmer offers a very high resolution view of big beautiful Saturn. A labor of love, his full mosaic, composite image is contained in a large 5 megabyte jpeg file (preview here, download here) and spans the gorgeous gas giant from ring tip to ring tip. It was pieced together from 102 frames (N00020905 to N00021033) recorded by the Cassini spacecraft ISS on October 6, 2004. The red, green, and blue frames are all uncalibrated, unvalidated images available to the public through the Cassini web site. Malmer's full panorama has a pixel size of 8400 by 3300, so only a substantially cropped version appears above. Enjoy the view and have a safe and Happy Holiday Season!

2003 At Table Mountain Observatory, near Wrightwood California, USA on October 26, wild fires were approaching from the east. But looking toward the west just after sunset, astronomer James Young could still enjoy this comforting view of a young crescent Moon and brilliant Venus through the the fading twilight. Setting over the horizon of Mt. Baden-Powell, the thin crescent was only about 37 hours "old", or 37 hours after its exact New Moon phase. After disappearing from morning twilight in August, Venus was becoming prominent in its role in western skies as the evening star. A similar lovely pairing of thin crescent Moon and stunning evening star can be seen toward the west in today's evening twilight. Happy Holidays and Best Wishes from APOD!

2002 Orion always comes up sideways ... and was caught in the act earlier this month by astronomer Jimmy Westlake, stargazing eastward over the Rocky Mountains north of Leadville, Colorado, USA. To make this gorgeous image, Westlake placed his camera on a tripod for two exposures. The first lasted for 18 minutes allowing the stars to trail as they rose above the mountain range. After a minute long pause, the second exposure began and lasted only 25 seconds decorating the end of each trail with a celestial point of light. The three bright stars in Orion's belt stand in a nearly vertical line above the mountain peak right of center. Hanging from his belt, the stars and nebulae of the Hunter's sword follow the slope down and to the right. A festive yellow-orange Betelgeuse is the brightest star above the peak just left of center, but brighter still, planet Saturn shines near the upper left corner. In the foreground on planet Earth, a frozen lake and snowy mountains are lit by a four day old crescent Moon. Happy Holidays and Best Wishes from APOD!

2001 How did stars form in the early universe? Astronomers are gaining insight by studying NGC 6822, a nearby galaxy classified as irregular by modern standards but appearing more typical of galaxies billions of years ago. Inspection of NGC 6822 shows several bright star groups, including two dubbed Hubble-X and Hubble-V. Pictured above, the Hubble Space Telescope has resolved Hubble V into the energetic stars that are lighting up the surrounding gas. Each star in the central dense knot of Hubble V shines brighter than 100,000 Suns. The Hubble V gas cloud spans about 200 light years and lies about 1.5 million light-years away toward the constellation Sagittarius.

2000 If you look closely at the shadow of this tree, you will see something quite unusual: it is composed of hundreds of images of a partially eclipsed Sun. Early today, trees across North America will be casting similar shadows as a partial eclipse of the Sun takes place. In a partial eclipse, the Moon does not cover the entire Sun. The above effect is created by small spaces between leaves and branches acting as pinhole lenses. Looking at shadows involving eclipse light is relatively safe - looking directly at the Sun, even during an eclipse, is dangerous and proper precautions should be taken. The above picture was taken in 1994 on the campus of Northwestern University.

1999 The Apollo 8 astronauts spent the 1968 Christmas Season orbiting the Moon, returning with striking images of both Moon and Earth from space - pictures which inspired the world. While in lunar orbit in 1994, the prospecting Clementine spacecraft also turned its cameras toward the home world and the result was this mosaic of 70 high resolution images of our planet from a cosmic perspective. The swirling clouds and dramatic colors give the Earth the appearance of a delicate, painted ornament hanging in space. Best Wishes and Seasons Greetings from Astronomy Picture Of The Day!

Credit: Howard Bond (STScI), NASA

If our Galaxy were a Christmas tree, planetary nebulae would adorn it like colorful lighted ornaments twinkling on a cosmic scale. Glowing shrouds of gas ejected by red giant stars, planetary nebulae like NGC 6578 (left) and IC 3568 last for a mere 10,000 years or so as swollen stellar giants are transformed into fading, cooling white dwarf stars. Meanwhile ... have a safe, happy holiday season and Best Wishes to all from APOD!

1997 Seen from the Pik Terskol Observatory in the northern Caucasus mountains, comet Hale-Bopp and the bright stars of the constellation Perseus hang above the snowy, moon-lit landscape. Although it reminds Northern Hemisphere dwellers of an idyllic Winter scene, this picture was actually recorded in the spring - on April 13th of this year. Seasons Greetings and Best Wishes from APOD!

1996 The Apollo 8 astronauts spent the 1968 Christmas Season in lunar orbit, returning with striking images of the Moon and Earth from space which inspired the world. While in lunar orbit in 1994, the prospecting Clementine spacecraft also turned its cameras toward the home world - the result was this mosaic of 70 high resolution images of our planet from a cosmic perspective. The swirling clouds and dramatic colors give the Earth the appearance of a delicate, painted ornament hanging in space. Best Wishes and Seasons Greetings!

1995 During the 1968 Christmas season Frank Borman, James Lovell, and William Anders flew the Apollo 8 command module From the Earth to the Moon and back (launched Dec. 21, achieved 10 lunar orbits, landed Dec. 27). The Apollo 8 mission's impressive list of firsts includes; the first manned flight using the Saturn V rocket, the first humans to journey to the Earth's Moon, and the first to photograph the Earth from deep space. The famous picture above, showing the Earth rising above the Moon's limb as seen from lunar orbit, was a marvelous gift to the world. This was astronaut James Lovell's third mission. His last flight would be as commander of Apollo 13.

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