APOD Retrospective: November 29

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: November 29

Post by bystander » Tue Nov 29, 2011 4:43 am

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2014 Get out your red/blue glasses and float next to a comet! The Rosetta mission lander Philae's ROLIS camera snapped the two frames used to create this stereo anaglyph for 3D viewing during its November 12 descent to the nucleus of Comet 67P/Churyumov-Gerasimenko. The comet's curious double lobed nucleus is seen nearly end on from a distance of about 3 kilometers, about 1 hour before Philae arrived at the surface. Philae's initial landing site is near the center of the front facing lobe. Part of a landing gear foot cuts across the upper right corner, in the close foreground of the 3D-view. Philae bounced twice in the comet's weak gravity after its first contact with the surface. Using high resolution camera images from the Rosetta orbiter along with data from the lander's instruments, controllers have followed Philae's impromptu journey over the comet's surface and have identified a likely area for its final resting place.

2013 Sungrazing Comet ISON reached perihelion, its closest approach to the Sun, yesterday, November 28, at 18:45 UT. The comet passed just over 1 million kilometers above the solar surface, a distance less than the diameter of the Sun. These two panels follow ISON before (right) and after its close approach, imaged by the LASCO instrument onboard the Sun staring SOHO spacecraft. Overwhelming sunlight is blocked by LASCO's central occulting disk with a white circle indicating the Sun's positon and scale. The bright comet is seen along its path at the bottom of the before panel, but something much fainter exits near the top of the after panel, potentially a dust tail reforming from the debris left from ISON's perihelion passage.

2012 Did you see the big, bright, beautiful Full Moon Wednesday night? That was actually a Micro Moon! On that night, the smallest Full Moon of 2012 reached its full phase only about 4 hours before apogee, the most distant point from Earth in the Moon's elliptical orbit. Of course, earlier this year on May 6, a Full Super Moon was near perigee, the closest point in its orbit. The relative apparent size of November 28's Micro Moon (right) is compared to the famous May 6 Super Moon in these two panels, matching telescopic images from Bucharest, Romania. The difference in apparent size represents a difference in distance of just under 50,000 kilometers between apogee and perigee, given the Moon's average distance of about 385,000 kilometers. How long do you have to wait to see another Full Micro Moon? Until January 16, 2014, when the lunar full phase will occur within about 3 hours of apogee.

2011 A fantastic jumble of young blue star clusters, gigantic glowing gas clouds, and imposing dark dust lanes surrounds the central region of the active galaxy Centaurus A. This image from the Hubble Space Telescope has been processed to present a natural color picture of this cosmic maelstrom. Infrared images from the Hubble have also shown that hidden at the center of this activity are what seem to be disks of matter spiraling into a black hole with a billion times the mass of the Sun. Centaurus A itself is apparently the result of a collision of two galaxies and the left over debris is steadily being consumed by the black hole. Astronomers believe that such black hole central engines generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies. But for an active galaxy Centaurus A is close, a mere 10 million light-years away, and is a relatively convenient laboratory for exploring these powerful sources of energy.

2010 Why are planet-circling clouds disappearing and reappearing on Jupiter? Although the ultimate cause remains unknown, planetary meteorologists are beginning to better understand what is happening. Earlier this year, unexpectedly, Jupiter's dark Southern Equatorial Belt (SEB) disappeared. The changes were first noted by amateurs dedicated to watching Jupiter full time. The South Equatorial Band has been seen to change colors before, although the change has never been recorded in such detail. Detailed professional observations revealed that high-flying light-colored ammonia-based clouds formed over the planet-circling dark belt. Now those light clouds are dissipating, again unveiling the lower dark clouds. Pictured above two weeks ago, far infrared images -- depicted in false-color red -- show a powerful storm system active above the returning dark belt. Continued observations of Jupiter's current cloud opera, and our understanding of it, is sure to continue.

2009 Is this a picture of Mars or Earth? Oddly enough, it is a picture of Mars. What may appear to some as a terrestrial coastline is in fact a formation of ancient layered hills and wind-blown sand on Mars. The above-pictured region spans about three kilometers in Schiaparelli Crater. What created the layers of sediment is still a topic of research. Viable hypotheses include ancient epochs of deposit either from running water or wind-blown sand. Winds and sandstorms have smoothed and eroded the structures more recently. The "water" that appears near the bottom is actually dark colored sand. The image was taken with the Mars Global Surveyor spacecraft that operated around Mars from 1996-2006 and returned over 200,000 images.

2008 Night skies over Chilean mountain top observatories can be dark and clear, with glorious cosmic vistas. In this recent example, the plane of our Milky Way galaxy stretches parallel to the horizon, the galactic center's star clusters, dark dust clouds, and glowing nebulae hovering in the west. Recorded after sunset, the wedge of light extending upward through the scene is Zodiacal light, sunlight scattered by dust along the solar system's ecliptic plane. A faint meteor was also caught in the view, but approaching a conjunction, brilliant Venus and bright Jupiter dominate the skyscape. A close pairing through this weekend, by Monday, December 1, they will be joined by the young crescent Moon. Look west after sunset and the tight celestial triangle formed by Moon, Venus, and Jupiter, the three brightest beacons in the night, will be a spectacular sight, even from bright-sky urban locations all over the world.

2007 This cosmic expanse of dust, gas, and stars covers some 4 degrees on the sky in the heroic constellation Perseus. Centered in the gorgeous skyscape is the dusty blue reflection nebula NGC 1333, about 1,000 light-years away. At that estimated distance, the field of view is nearly 70 light-years across. Other reflection nebulae are scattered around, along with remarkable dark dust nebulae and the faint reddish glow of hydrogen gas. These dust and gas clouds lie near the edge of a large molecular cloud. Themselves telltale signs of star-forming regions, they tend to hide the newly formed stars and young stellar objects or protostars from prying optical telescopes. Collapsing due to self-gravity, the protostars form around dense cores embedded in the molecular cloud.

2006 They are so large, they are almost unreal. The radio dishes of the Very Large Array (VLA) of radio telescopes might appear to some as a strange combination of a dinosaur skeleton and common satellite-TV receiving dish. Together, the 27 dishes of the VLA combine high sensitivity with high resolution, enabling a series of important astronomical discoveries, including water ice on planet Mercury, micro-quasars in our Galaxy, gravitationally-induced Einstein rings around distant galaxies, and radio counterparts to cosmologically distant gamma-ray bursts. Pictured above, a dish from the VLA was photographed last week near Socorro, New Mexico, USA.

2005 It's easy to get lost following the intricate filaments in this detailed image of faint supernova remnant Simeis 147. Seen towards the constellation Taurus it covers nearly 3 degrees (6 full moons) on the sky corresponding to a width of 150 light-years at the stellar debris cloud's estimated distance of 3,000 light-years. The above image is a color composite of 66 blue and red color band images from the National Geographic Palomar Observatory Sky Survey taken with the wide field Samuel Oschin 48-inch Telescope. The area of the sky shown covers over 70 times the area of the full Moon. This supernova remnant has an apparent age of about 100,000 years - meaning light from the massive stellar explosion first reached Earth 100,000 years ago - but this expanding remnant is not the only aftermath. The cosmic catastrophe also left behind a spinning neutron star or pulsar, all that remains of the original star's core.

2004 Tethys is one of the larger and closer moons of Saturn. The Cassini spacecraft now orbiting Saturn passed near the frozen moon at the end of October, capturing the most detailed images since the Voyager spacecrafts in the early 1980s. Tethys is composed almost completely of water ice and shows a large impact crater that nearly circles the moon. Because this crater did not disrupt the moon, Tethys is hypothesized to be at least partly liquid in its past. Two smaller moons, Telesto and Calypso, orbit Saturn just ahead of and behind Tethys. Giovanni Cassini discovered Tethys in 1684. The Cassini spacecraft is scheduled for a close fly-by of Tethys in September 2005.

2003 Hurtling through space a mere 3,000 miles above the Martian surface, the diminutive moon Phobos (below and left of center) was imaged against the backdrop of a large shield volcano by the Viking 2 Orbiter in 1977. This dramatic picture looks down from the Orbiter's viewpoint about 8,000 miles above the volcano, Ascraeus Mons. Phobos itself is 5,000 miles below the Orbiter. North is toward the top with the Sun illuminating the scene from the South (black dots are reference marks). For scale, Ascraeus Mons is about 200 miles across at its base while asteroid sized Phobos is about 15 miles in diameter. In this spectacular moon-planet image, volcanic calderas (craters) are visible at the summit of Ascraeus Mons -- while impact craters on the sunlit side of Phobos' surface can also be seen!

2002 Open clusters of stars can be near or far, young or old, and diffuse or compact. Open clusters may contain from 100 to 10,000 stars, all of which formed at nearly the same time. Bright blue stars frequently distinguish younger open clusters. M35, pictured above on the upper left, is a relatively nearby at 2800 light years distant, relatively young at 150 million years old, and relatively diffuse, with about 2500 stars spread out over a volume 30 light years across. An older and more compact open cluster, NGC 2158, is visible above on the lower right. NGC 2158 is four times more distant that M35, over 10 times older, and much more compact as it contains many more stars in roughly the same volume of space. NGC 2158's bright blue stars have self-destructed, leaving cluster light to be dominated by older and yellower stars. Both clusters are visible toward the constellation of Gemini -- M35 with binoculars and NGC 2158 with a small telescope.

2001 The active Sun has thrown a lot our way lately, including storms of particles streaming outward in the solar wind and clouds of plasma which triggered awesome auroral displays. Still, a growing body of intriguing observations from the LASCO instrument on board the space-based SOlar and Heliospheric Observatory (SOHO) indicates material also flows back toward the Sun, starting from over 2 million kilometers above its visible surface. Relatively hard to detect against the outflowing solar corona, a dark inflowing cloud's relative motion is tracked above in two highly processed images recorded an hour apart. The solar surface, graphically shown by the yellow quarter circle at the lower right, is blocked from view by a smooth occulting disk. Fighting against a solar wind outflow of about 120 kilometers per second the cloud seems to be moving inward at 50-100 kilometers per second. Occasionally appearing as often as once per hour, the clouds, seem to be dragged in by collapsing magnetic field loops rather than gravity alone. Researchers are now working to relate this surprising inflow to the solar wind and magnetic environment of the Sun.

2000 Here is what a meteor shower looks like from orbit. During the peak of the 1997 Leonid Meteor Shower, the MSX satellite imaged from above 29 meteors over a 48 minute period entering the Earth's atmosphere. From above, meteors create short bright streaks. Visible beneath the meteors are clouds lit by reflected moonlight, while visible above is the constellation of Aries. The directions of the meteor streaks are nearly parallel, confirming that the meteors all originate from the same meteor stream. Recent analysis of the 2000 Leonids meteor shower indicates to many astronomers that the 2001 Leonids may develop into a real meteor storm, with meteor rates perhaps exceeding one per second visible from parts of Asia.

1999 Some features of HH-34 are understood -- some are not. At the core of Herbig-Haro 34 lies a seemingly typical young star. This star, though, somehow ejects energetic "bullets" of high-energy particles, appearing as red streaks toward the lower right of the this image. Astronomers speculate that a burst of these particles might rebound when gas from a disk surrounding the star momentarily collapses onto the star. Visible near the end of each light-year long jet is a glowing cap. HH-34 lies about 1500 light-years away in the Orion Nebula star-forming region. The cause of the large arc of gas on the upper left known as the waterfall remains unexplained.

1998 The Arecibo radio telescope is currently the largest single-dish telescope in the world. First opening in 1963, this 305 meter (1000 foot) radio telescope resides in a natural valley of Puerto Rico. The Arecibo telescope has been used for many astronomical research projects, including searches and studies of pulsars, and mapping atomic and molecular gas in the Galaxy and the universe. As the Arecibo dish can also be used to send radio waves, it has bounced and recorded radiation off of planets in our Solar System, and has even broadcast messages to areas of the Galaxy that might contain intelligent extra-terrestrial life. Any person in the world may use the telescope, providing their proposal is selected by a review committee.

1997 Have you heard about the great LASER light show in the sky? A team led by K. Davidson (U. Michigan) and S. Johansson (U. Lund) discovered that the chaotically variable star Eta Carinae emits ultraviolet light in such a narrow band that it is most probably LASER light! This artist's vision depicts a model that could account for their Hubble Space Telescope observations. In this model, Eta Carinae emits many LASER beams from its surrounding cloud of energized gas. Infrared LASERS and microwave MASERS are extremely rare astrophysical phenomena, but this natural ultraviolet LASER is the first of its kind to be discovered.

1996 Is Io the solar system's Fissure King? Well, probably not ... but it is the most active volcanic moon. Active volcanoes on Jupiter's moon Io were a surprise discovery of the Voyager missions of the late 1970s. The extent of Io's volcanic activity today is being investigated close-up by the Galileo spacecraft currently exploring the Jovian system. The two frames above show a roughly 300 mile square area around the Io volcano called Marduk. The left-hand view of Marduk was made by Voyager in 1979, the right-hand view by Galileo earlier this year. A comparison reveals that dramatic changes have occured, including the creation of a dark, linear feature running diagonally through the Galileo image that is probably a huge volcanic fissure.

1995 Named for Nobel laureate physicist Arthur Holly Compton, the Compton Gamma Ray Observatory (CGRO) Satellite was launched in April of 1991 aboard the Space Shuttle Atlantis. CGRO's mission is to explore the Universe at gamma-ray energies. The massive space based observatory is seen here held upright in the shuttle payload bay behind smiling astronaut Jerry Ross. Ross and his colleague Jay Apt have just finished a successful, unplanned spacewalk to free a jammed antenna prior to releasing CGRO into orbit. CGRO has been operating successfully since, providing the first all-sky survey at gamma-ray energies along with exciting new observations of the sun, quasars, pulsars, supernova, black holes, and gamma-ray bursts.

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