APOD Retrospective: October 30

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: October 30

Post by bystander » Sun Oct 30, 2011 4:03 am


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2014 Frightening forms and scary faces are a mark of the Halloween season. They also haunt this cosmic close-up of the eastern Veil Nebula. The Veil Nebula itself is a large supernova remnant, the expanding debris cloud from the death explosion of a massive star. While the Veil is roughly circular in shape and covers nearly 3 degrees on the sky in the constellation Cygnus, this portion of the eastern Veil spans only 1/2 degree, about the apparent size of the Moon. That translates to 12 light-years at the Veil's estimated distance, a reassuring 1,400 light-years from planet Earth. In the composite of image data recorded through broad and narrow band filters, emission from hydrogen atoms in the remnant is shown in red with strong emission from oxygen atoms in blue-green hues. Of course, in the western part of the Veil lies another seasonal apparition, the Witch's Broom.

2013 Frightening forms and scary faces are a mark of the Halloween season. They also haunt this cosmic close-up of the eastern Veil Nebula. The Veil Nebula itself is a large supernova remnant, the expanding debris cloud from the death explosion of a massive star. While the Veil is roughly circular in shape covering nearly 3 degrees on the sky in the constellation Cygnus, this portion of the eastern Veil spans only 1/2 degree, about the apparent size of the Moon. That translates to 12 light-years at the Veil's reassuring estimated distance of 1,400 light-years from planet Earth. In the composite of image data recorded through narrow band filters, emission from hydrogen atoms in the remnant is shown in red with strong emission from oxygen atoms in blue-green hues. In the western part of the Veil lies another seasonal apparition, the Witch's Broom.

2012 Is this what will become of our Sun? Quite possibly. The bubble of expanding gas pictured above is the planetary nebula PK 164 +31.1, the remnants of the atmosphere of a Sun-like star expelled as its supply of fusion-able core hydrogen became depleted. Visible near the center of the nebula is what remains of the core itself -- a blue-hot white dwarf star. This particularly photogenic planetary nebula shows intricate shells of gas likely expelled at different times toward the end the star's demise, and whose structure is not fully understood. This deep image of PK 164 +31.1 from the Calar Alto Observatory in Spain shows many other stars from our own Milky Way Galaxy as well as several galaxies far in the distance. PK 164 +31, also known as Jones-Emberson 1, lies about 1,600 light years away toward the constellation of the Wildcat (Lynx). Due to its faintness (magnitude 17) and low surface brightness, the object is only visible with a good-sized telescope. Although the expanding nebula will fade away over the next few thousand years, the central white dwarf may well survive for billions of years -- to when our universe may be a very different place.

2011 What caused this unusual light rock formation on Mars? Intrigued by the possibility that they could be salt deposits left over as an ancient lakebed dried-up, detailed studies of these fingers now indicate a more mundane possibility: volcanic ash. Studying the exact color of the formation indicated the possible volcanic origin. The light material appears to have eroded away from surrounding area, indicating a very low-density substance. The stark contrast between the rocks and the surrounding sand is compounded by the unusual darkness of the sand. The above picture was taken with the Thermal Emission Imaging System on the Mars Odyssey spacecraft currently orbiting Mars. The image spans about 10 kilometers inside a larger crater.

2010 Spooky shapes seem to haunt this starry expanse, drifting through the night in the royal constellation Cepheus. Of course, the shapes are cosmic dust clouds faintly visible in dimly reflected starlight. Far from your own neighborhood on planet Earth, they lurk at the edge of the Cepheus Flare molecular cloud complex some 1,200 light-years away. Over 2 light-years across the ghostly nebula known as vdB 141 or Sh2-136 is near the center of the field. The core of the dark cloud on the right is collapsing and is likely a binary star system in the early stages of formation.

2009 To the eye, this cosmic composition nicely balances the Bubble Nebula at the upper right with open star cluster M52. The pair would be lopsided on other scales, though. Embedded in a complex of interstellar dust and gas and blown by the winds from a single, massive O-type star, the Bubble Nebula (aka NGC 7635) is a mere 10 light-years wide. On the other hand, M52 is a rich open cluster of around a thousand stars. The cluster is about 25 light-years across. Seen toward the northern boundary of Cassiopeia, distance estimates for the Bubble Nebula and associated cloud complex are around 11,000 light-years, while star cluster M52 lies nearly 5,000 light-years away.

2008 Spooky shapes seem to haunt this starry expanse, drifting through the night in the royal constellation Cepheus. Of course, the shapes are cosmic dust clouds faintly visible in dimly reflected starlight. Far from your own neighborhood on planet Earth, they lurk at the edge of the Cepheus Flare molecular cloud complex some 1,200 light-years away. Over 2 light-years across and brighter than the other ghostly apparitions, the nebula known as vdB 141 or Sh2-136 near the center of the field is even seen in infrared light. Also cataloged as Bok globule CB230, the core of that cloud is collapsing and is likely a binary star system in the early stages of formation.

2007 Go outside tonight and see Comet Holmes. No binoculars or telescopes are needed -- just curiosity and a sky map. Last week, Comet 17P/Holmes underwent an unusual outburst that vaulted it unexpectedly from obscurity into one of the brightest comets in recent years. Sky enthusiasts from the northern hemisphere have been following the comet's progress closely. In this animation recorded from Quebec, Canada, the coma of Comet Holmes is seen noticeably expanding over the past few days. Jupiter has been placed artificially nearby to allow for a comparison of angular sizes and scaled to the size it would appear at the current location of Comet Holmes. How Comet Holmes will further evolve is unknown, with one possibility being that the expanding gas cloud that started from its recent outburst will slowly disperse and fade.

2006 There's something behind these clouds. Those faint graceful arcs, upon inspection, are actually far, far in the distance. They are the Earth's Moon and the planet Venus. Both the Moon and Venus are bright enough to be seen during the day, and both are quite capable of showing a crescent phase. To see Venus, which appears quite small, in a crescent phase requires binoculars or a telescope. In the above dramatic daytime image taken from Budapest, Hungary, the Moon and Venus shared a similar crescent phase a few minutes before the Moon eclipsed the larger but more distant world. About an hour later, Venus reappeared.

2005 It was a dark and stormy night. But on 2003 August 29th the red planet Mars, near its closest approach to Earth in almost 60,000 years, shone brightly in the sky against a background of stars in the constellation Aquarius. In the foreground of this scary view, huge thunder clouds are lit by lightning strokes from within. Mars, of course, has nothing to do with storms on Earth, though both have the power to excite the imagination and wonder of Earthdwellers. Tonight, the night before Halloween, Mars will also pass close to the Earth, closer than it will come during the next thirteen years. And once again, the red planet Mars will look particularly bright, although much smaller and dimmer than the Moon and even Venus.

2004 Does this look familiar? Red and orange hues haunting the face of the Moon should remind you of the October 27th total lunar eclipse. Created from exposures taken at intervals of 8.5 minutes during the total eclipse phase, the midpoint of the eclipse corresponds to the central exposure. The play of light across the lunar surface nicely demonstrates that the Earth's shadow is not uniformly dark as it extends into space. In fact, lunar maria and montes are still visible in the dimmed, reddened sunlight scattered into the cone-shaped shadow region, or umbra, by the atmosphere. Still, while processing the pictures into this composite image, astronomer Sebastien Gauthier was reminded of another haunting orange face. Have a safe and happy Halloween!

2003 Vivid auroral displays were triggered by a cloud of high energy particles and magnetic fields from the Sun that collided with planet Earth's magnetosphere yesterday, October 29, at about 06:30 Universal Time. The collision was anticipated, following an intense solar flare and coronal mass ejection detected on October 28, and many anxious skywatchers were rewarded with an enjoyable light show. While aurorae don't normally haunt skies in the southern United States, they were reported from locations in Missouri, Texas, New Mexico, and California in the early morning hours. Near Yampa, Colorado astronomer Jimmy Westlake also spent early yesterday morning enjoying the stormy space weather. He was impressed by this colorful apparition of the northern lights -- produced by oxygen and nitrogen atoms excited by collisions with energetic particles from the magnetosphere and returning to lower energy states, at altitudes of 100 kilometers or more. Brighter stars shine through the extreme high-altitude glow which shows much lower clouds and the distant horizon in silhouette.

2002 Will this year's Leonid meteor shower be as good as last year's? No one knows for sure. Possibly, however, in the waning nighttime hours of November 18 and lasting throughout much of November 19, sky gazers across the globe may get their last chance ever to see a meteor storm. Although the glare of a nearly full Moon will likely hide the presence of many faint meteors, plenty of bright meteors may well streak across the other side of the sky. The above image was taken during 2001 as Leonids stormed over Uluru (Ayers Rock), Australia. The image is actually a digital composite of 22 separate frames, including one at sunset. The Gum Nebula is visible on the upper left.

2001 What's happening over the horizon? Although the scene may appear somehow supernatural, nothing more unusual is occurring than a setting Sun and some well placed clouds. Pictured above are anticrepuscular rays. To understand them, start by picturing common crepuscular rays that are seen any time that sunlight pours though scattered clouds. Now although sunlight indeed travels along straight lines, the projections of these lines onto the spherical sky are great circles. Therefore, the crepuscular rays from a setting (or rising) sun will appear to re-converge on the other side of the sky. At the anti-solar point 180 degrees around from the Sun, they are referred to as anticrepuscular rays. Pictured above is a particularly striking set of anticrepuscular rays photographed earlier this month from a moving car just outside of Boulder, Colorado, USA.

2000 Accelerate a charge and you'll get electromagnetic radiation: light. But accelerate any mass and you'll get gravitational radiation. Light is seen all the time, but, so far, a confirmed direct detection of gravitational radiation has yet to be made. When absorbed, gravitational waves (GWs) create a tiny symmetric jiggle similar to squashing a rubber ball and letting go quickly. Separated detectors can be used to discern GWs from everyday bumps. Powerful astronomical GW sources would coincidentally jiggle even detectors on opposite ends of the Earth. Pictured above are the two-kilometer-long arms of one such detector: the LIGO Hanford Observatory in Washington, which recently achieved a phase-lock milestone to future GW detection. When it and its sister interferometer in Louisiana come online in 2002, they may see a GW sky so strange it won't be immediately understood. APOD mourns the recent passing of Joseph Weber, a visionary thinker and pioneer in gravitational wave detection.

1999 This sharp color image featuring Mars rock Yogi and the rolling Sojourner robot shows off Yogi's two-toned surface. Yogi appears to be leaning into the prevailing winds causing some to suggest that its color contrast may be caused by the accumulation of rust colored dust on its windward face. The Pathfinder spacecraft, now the Sagan Memorial Station, has ended the primary mission phase after returning a scientific bonanza from the surface of Mars. The Sojourner robot rolled hundreds of feet on the martian surface, circumnavigated the lander, and produced a wealth of data and images. Mars Pathfinder and Soujourner landed on July 4, 1997 and lasted about 3 months, well beyond their designed lifetime.

1998 At left, the Space Shuttle Discovery waits in darkness on Kennedy Space Center's launch pad 39B. At right, on Thursday October 29, Discovery blasts through a bright afternoon sky returning Senator John Glenn to space over 36 years after he became the first American in orbit. Paving the way in 1962 Glenn flew solo, but today he is part of a crew of seven astronauts shepherding scientific payloads on shuttle mission STS-95. On tape, fellow Mercury Program astronaut Scott Carpenter again wished, "... Godspeed John Glenn." while Kennedy Space Center launch control offered, "Let the wings of Discovery lift us into the future." At age 77, John Glenn, a legend and hero of NASA's first human spaceflight program, has become the oldest space traveler. From orbit, Glenn commented, "... zero-g and I feel fine!"

1997 Every day is a cloudy day on Jupiter, the Solar System's reigning gas giant. This 3-dimensional visualization presents a simplified model view from between Jovian cloud decks based on imaging and spectral data recorded by the Galileo spacecraft. The separation between the cloud layers and the height variations have been exaggerated. The upper cloud layer is haze a few tens of miles thick. Heights in the lower cloud layers have been color coded; light bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. Streaks in the lower layer suggestively lead to a dark blue area, a relatively clear, dry region similar to the site where Galileo's atmospheric probe made the first entry into a gas giant planet's atmosphere on December 7th, 1995.

1996 NGC 2997 is a grand design spiral galaxy. Its small nucleus and sprawling spiral arms give it a type "Sc" designation. NGC 2997 is speeding away from us at about 1100 kilometers per second, which would place it at about 55 million light years distant, given current estimates of the expansion rate of our universe. NGC 2997 is thought to have a mass of about 100 billion times that of our Sun, but is probably less massive than our own Milky Way Galaxy. NGC 2997 is not seen face-on - it is thought tilted by about 45 degrees. NGC 2997 is particularly notable for a nucleus surrounded by a chain of hot giant clouds of ionized hydrogen.

1995 Will comet Hale-Bopp become the brightest comet of the Century in early 1997? Since its discovery in July this year, Hale-Bopp has caused much speculation. Even though it is still beyond the orbit of Jupiter it is astonishingly bright and expected to get much brighter as it plunges inward, toward the Sun. In this latest Hubble Space Telescope image a bright clump of material (above center) has apparently been ejected by evaporation and the rotation of the icy nucleus (below center). Astronomers are using this and other observations to try to figure out if Hale-Bopp is really a giant comet or a smaller object which will fizzle out sooner than expected as it approaches the Sun.

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