APOD Retrospective: December 3

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: December 3

Post by owlice » Fri Dec 03, 2010 1:07 pm


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2014 Normally faint and elusive, the Jellyfish Nebula is caught in this alluring telescopic mosaic. The scene is anchored right and left by two bright stars, Mu and Eta Geminorum, at the foot of the celestial twin while the Jellyfish Nebula is the brighter arcing ridge of emission with dangling tentacles below and right of center. In fact, the cosmic jellyfish is part of bubble-shaped supernova remnant IC 443, the expanding debris cloud from a massive star that exploded. Light from the explosion first reached planet Earth over 30,000 years ago. Like its cousin in astrophysical waters the Crab Nebula supernova remnant, the Jellyfish Nebula is known to harbor a neutron star, the remnant of the collapsed stellar core. An emission nebula cataloged as Sharpless 249 fills the field at the upper left. The Jellyfish Nebula is about 5,000 light-years away. At that distance, this narrowband composite image would be about 300 light-years across.

2013 The many spectacular colors of the Rho Ophiuchi (oh'-fee-yu-kee) clouds highlight the many processes that occur there. The blue regions shine primarily by reflected light. Blue light from the star Rho Ophiuchi and nearby stars reflects more efficiently off this portion of the nebula than red light. The Earth's daytime sky appears blue for the same reason. The red and yellow regions shine primarily because of emission from the nebula's atomic and molecular gas. Light from nearby blue stars - more energetic than the bright star Antares - knocks electrons away from the gas, which then shines when the electrons recombine with the gas. The dark brown regions are caused by dust grains - born in young stellar atmospheres - which effectively block light emitted behind them. The Rho Ophiuchi star clouds, well in front of the globular cluster M4 visible above on lower left, are even more colorful than humans can see - the clouds emits light in every wavelength band from the radio to the gamma-ray.

2012 Sometimes falling ice crystals make the atmosphere into a giant lens causing arcs and halos to appear around the Sun or Moon. This past Saturday night was just such a time near Madrid, Spain, where a winter sky displayed not only a bright Moon but as many as four rare lunar halos. The brightest object, near the top of the above image, is the Moon. Light from the Moon refracts through tumbling hexagonal ice crystals into a 22 degree halo seen surrounding the Moon. Elongating the 22 degree arc horizontally is a circumscribed halo caused by column ice crystals. More rare, some moonlight refracts through more distant tumbling ice crystals to form a (third) rainbow-like arc 46 degrees from the Moon and appearing here just above a picturesque winter landscape. Furthermore, part of a whole 46 degree circular halo is also visible, so that an extremely rare -- especially for the Moon -- quadruple halo was actually imaged. The snow-capped trees in the foreground line the road Puerto de Navacerrada in the Sierra de Guadarrama mountain range near Madrid. Far in the background is a famous winter skyscape that includes Sirius, the belt of Orion, and Betelgeuse all visible between the inner and outer arcs. Halos and arcs typically last for minutes to hours, so if you do see one there should be time to invite family, friends or neighbors to share your unusual lensed vista of the sky.

2011 A single, long exposure captured these star trails above a remarkably colorful sea of clouds. As seen from Medvednica mountain, the surrounding peaks and lights illuminating the clouds from below are north of Zagreb, Croatia. Near the center of the also colorful star trail arcs, the North Celestial Pole is off the upper right edge of the frame. Even though this is the age of the digital camera, the well composed skyscape was recorded using color slide film in a medium format camera. The dreamlike scene's starry sky and ephemeral ocean could be reminiscent of an older age still, when the Pannonian Sea covered this part of central Europe some 10 million years ago.

2010 The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other's grand spiral star systems. As for the view from planet Earth, this sharp, detailed image nicely shows off M33's blue star clusters and pinkish star forming regions that trace the galaxy's loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 4 o'clock position from the galaxy center. Like M31, M33's population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.

2009 NGC 660 lies near the center of this intriguing field of galaxies swimming within the boundaries of the constellation Pisces. Over 20 million light-years away, its peculiar appearance marks it as a polar ring galaxy. A rare galaxy type, polar ring galaxies have a substantial population of stars, gas, and dust orbiting in rings nearly perpendicular to the plane of a flat galactic disk. The bizarre configuration could have been caused by the chance capture of material from a passing galaxy by the disk galaxy, with the captured debris strung out in a rotating ring. Polar Ring galaxies can be used to explore the shape of the galaxy's otherwise unseen dark matter halo by calculating the dark matter's gravitational influence on the rotation of the ring and disk. Broader than the disk, NGC 660's ring spans about 40,000 light-years.

2008 Sunday, the sky seemed to smile over much of planet Earth. Visible the world over was an unusual superposition of our Moon and the planets Venus and Jupiter. Pictures taken at the right time show a crescent Moon that appears to be a smile when paired with the planetary conjunction of seemingly nearby Jupiter and Venus. Pictured above is the scene as it appeared from Mt. Wilson Observatory overlooking Los Angeles, California, USA after sunset on 2008 November 30. Highest in the sky and farthest in the distance is the planet Jupiter. Significantly closer and visible to Jupiter's lower left is Venus, appearing through Earth's atmospheric clouds as unusually blue. On the far right, above the horizon, is our Moon, in a waxing crescent phase. Thin clouds illuminated by the Moon appear unusually orange. Sprawling across the bottom of the image are the hills of Los Angeles, many covered by a thin haze, while LA skyscrapers are visible on the far left. The conjunction of Venus and Jupiter will continue to be visible toward the west after sunset during much of this month. Hours after the taking of this image, however, the Moon approached the distant duo, briefly eclipsed Venus, and then moved on.

2007 Every eleven years, our Sun goes through a solar cycle. A complete solar cycle has now been imaged by the sun-orbiting SOHO spacecraft, celebrating the 12th anniversary of its launch yesterday. A solar cycle is caused by the changing magnetic field of the Sun, and varies from solar maximum, when sunspot, coronal mass ejection, and flare phenomena are most frequent, to solar minimum, when such activity is relatively infrequent. Solar minimums occurred in 1996 and 2007, while the last solar maximum occurred in 2001. This picture is composed of a SOHO image of the Sun in extreme ultraviolet light for each year of the last solar cycle, with images picked to illustrate the relative activity of the Sun.

2006 This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning color image from the Mars Express spacecraft, recorded at a resolution of about seven meters per pixel. But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon - that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

2005 Fifteen years ago, in December of 1990, the Space Shuttle Orbiter Columbia carried an array of astronomical telescopes high above the Earth's obscuring atmosphere to explore the Universe at ultraviolet and x-ray wavelengths. The telescopes, known by the acronyms UIT, HUT, WUPPE, and BBXRT, are seen here in Columbia's payload bay against a spectacular view of the constellation Orion. The ultraviolet telescopes were mounted on a common structure - HUT is visible in this view along with a star tracker (the silver cone at the left). Taken during the nighttime portion of the shuttle's 90 minute orbit, the picture shows the telescopes and structures illuminated by moonlight.

2004 The Milky Way is an ordinary 12 billion year old spiral galaxy, and even our middle-aged Sun is pushing 4.5 billion years. But all the stars in dwarf galaxy I Zwicky 18 are much younger. In fact, based on Hubble Space Telescope image data, that galaxy's first stars formed only about 500 million years ago, making it the youngest known galaxy. In this view, the bright knots are the two major star forming regions of I Zwicky 18, embedded in expanding filaments of glowing interstellar gas. Scattered, much older background galaxies are seen as small red blobs, and a companion galaxy lies just beyond the upper right corner of the cropped picture. Astronomers believe that diminutive I Zwicky 18 resembles the earliest galaxies formed, but also want to understand how such a young galaxy can be only 45 million light-years away - surrounded by mature galaxies in an aging Universe. The tiny galaxy itself is a mere 3,000 light-years across.

2003 How can the Moon rise through a mountain? It cannot -- what was photographed here is a moonrise through the shadow of a large volcano. The volcano is Mauna Kea, Hawai'i, USA, a frequent spot for spectacular photographs since it is arguably the premier observing location on planet Earth. The Sun has just set in the opposite direction, behind the camera. Additionally, the Moon has just passed full phase -- were it precisely at full phase it would rise, possibly eclipsed, at the very peak of the shadow. Refraction of moonlight through the Earth's atmosphere makes the Moon appear slightly oval. Cinder cones from old volcanic eruptions are visible in the foreground. Cloud tops below Mauna Kea's summit have unusually flat tops, indicating a decrease in air moisture that frequently keeps the air unusually dry, another attribute of this stellar observing site.

2002 On December 4th, for the second time in as many years, the Moon's shadow will track across southern Africa bringing a total solar eclipse to African skies. Reaching Africa just before 6:00 Universal Time, the narrow path of totality - corresponding to the path of the Moon's umbra or dark central shadow - will run eastward through Angola, Namibia (Caprivi Strip), Botswana, Zimbabwe, South Africa's Kruger National Park, and Mozambique. Moving out across the Indian Ocean it will ultimately cross onto the Australian continent at sunset (around 9:10 UT). Observers directly in this path could catch at most a minute or so of the eclipse at its total phase, but at least a partial eclipse will be visible over much of Africa, Australia, some parts of Indonesia, and eastern Antarctica. While watching last year's June 21 eclipse, astronomer Fred Espenak recorded a series of exposures used to construct this dramatic composite image. The sequence follows the 2001 geocentric celestial event from start to finish above a thorny acacia tree near Chisamba, Zambia.

2001 Will it be curtains for one of these auroras? A quick inspection indicates that it is curtains for both, as the designation "curtains" well categorizes the type of aurora pattern pictured. Another (informal) type is the corona. The above auroras resulted from outbursts of ionic particles from the Sun during the last week of September. A polarity change in the solar magnetic field at the Earth then triggered auroras over the next few days. The above picture was taken on October 3 as fleeting space radiation pelted the Earth's atmosphere high above the Yukon in Canada.

2000 A magnetic compass does not point toward the true North Pole of the Earth. Rather, it more closely points toward the North Magnetic Pole of the Earth. The North Magnetic Pole is currently located in northern Canada. It wanders in an elliptical path each day, and moves, on the average, more than forty meters northward each day. Evidence indicates that the North Magnetic Pole has wandered over much of the Earth's surface in the 4.5 billion years since the Earth formed. The Earth's magnetic field is created by Earth's partially ionized outer core, which rotates more rapidly than the Earth's surface. Indicated in the above picture is Ellef Ringnes Island, the current location of Earth's North Magnetic Pole.

1999 This topographical map of the southern hemisphere of Mars was generated using data from the Mars Orbiter Laser Altimeter (MOLA). Flying on the Mars Global Surveyor spacecraft, MOLA has bounced a laser beam off the Martian surface over 200,000,000 times producing a wealth of detailed elevation measurements. The MOLA measurements have been color-coded so, for example, the white areas at left are the highest elevations in the southern Tharsis region and not snow-covered peaks. These areas are more than 6 kilometers above the hypothetical Martian "sea-level". Likewise, deep blues and purples are not water oceans but correspond to the lowest elevations (more than 4 kilometers below "sea-level"), like those found within the giant Hellas impact basin at right. In fact, liquid water is not present on Mars' surface today, but may have been in the past. NASA's Mars Polar Lander spacecraft is scheduled to embark on an investigation of the role of water in the climate history of the Red Planet. The lander is targeted to touch down within the long, thin ellipse indicated here just below the Martian South Pole today at 20:00 UTC.

1998 Going gently into the night, Deep Space 1's ion drive has been running smoothly since it was restarted on November 24. How powerful is this high-tech spacecraft's ion propulsion system? At full throttle the engine will consume about 2,100 watts of electrical power generated by solar panels and produce about 1/50th of a pound of thrust. This is roughly equivalent to the force you exert when holding up a single sheet of paper! While clearly not suitable for vehicles which need rapid acceleration, ion propulsion is advantageous to use for missions involving asteroid and comet rendezvous. For these long space voyages which ultimately require a lot of energy, the continuous, gentle nudge of an ion engine easily wins out over brief, powerful, but less efficient blasts from chemical rockets. Pictured here during ground tests, the Deep Space 1 craft is now about three million miles from planet Earth.

1997 Runaway stars are massive stars traveling rapidly through interstellar space. Like a ship plowing through the interstellar medium, runaway star HD 77581 has produced this graceful arcing bow wave or "bow shock" - compressing the gaseous material in its path. Located near the centre of this European Southern Observatory photograph, HD 77581 itself is so bright that it saturates the sensitive camera and produces the spiky cross shape. This star is over 6,000 light-years away in the constellation Vela, and appears to move at over 50 miles per second. What force could set this star in motion? A clue to the answer may lie in its optically invisible companion star, an X-ray bright pulsar known as Vela X-1. This pulsar is clearly the remnant of a supernova explosion ... which seems to have given this massive star and its companion a mighty kick!

1996 Like a butterfly, a white dwarf star begins its life by casting off a cocoon that enclosed its former self. In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! The above cocoon, the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf can be seen as the bright dot near the photo's center. Our Sun will eventually become a "white dwarf butterfly", but not for another 5 billion years. The above false color image recently entered the public domain and was post-processed by F. Hamilton.

1995 In 1993, a star in the galaxy M81 exploded. Above is a picture of the hot material ejected by this supernova explosion. The picture was taken in X-rays with the Advanced Satellite for Cosmology and Astrophysics (ASCA). Since M81 is a relatively nearby galaxy, it can be examined in close detail by observatories on or near the Earth. Since the Earth's atmosphere protects the surface from interstellar X-radiation, the above photo was taken from space. Studying the nature and distribution of the X-rays has allowed astronomers to determine the composition and temperature of the expanding supernova gas.

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Re: APOD: December 3: A Retrospective

Post by Beyond » Mon Dec 06, 2010 1:00 am

Owlice, the sky is "Happy" over los Angles because it is ABOVE the Smog :!:
The Smog does have a kind of Golden Glow to it though.
To find the Truth, you must go Beyond.