APOD Retrospective: March 8

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

Post by bystander » Thu Mar 08, 2012 4:32 am

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2015 The center of our Milky Way Galaxy is hidden from the prying eyes of optical telescopes by clouds of obscuring dust and gas. But in this stunning vista, the Spitzer Space Telescope's infrared cameras, penetrate much of the dust revealing the stars of the crowded galactic center region. A mosaic of many smaller snapshots, the detailed, false-color image shows older, cool stars in bluish hues. Reddish glowing dust clouds are associated with young, hot stars in stellar nurseries. The very center of the Milky Way was only recently found capable of forming newborn stars. The galactic center lies some 26,000 light-years away, toward the constellation Sagittarius. At that distance, this picture spans about 900 light-years.

2014 Get out your red/blue glasses (red for the left eye) and look out over this expansive martian landscape. The panoramic stereo view is composed of images from the roving Curiosity's Navcam taken at a rest stop during a 100 meter drive on Sol 548 (February 19). The 5.5 kilometer high peak of Mount Sharp, also known as Aeolis Mons, is on the horizon, its base a destination for Curiosity. In the foreground are rows of striated rocks along the Junda outcrop. Centered toward the south-southeast the scene spans 160 degrees. (Another Navcam image here looks back along Curiosity's route at the end of the Sol's drive on Mars.)

[imghover6=http://apod.nasa.gov/apod/image/1303/ab ... ble900.jpg]http://apod.nasa.gov/apod/image/1303/ab ... 0label.jpg[/imghover6]Credit: NASA, ESA, Hubble Heritage/ESA-Hubble Collaboration - Acknowledgment: Nick Rose

Want to use a cluster of galaxies as a telescope? It's easier than you might think as distant galaxy clusters naturally act as strong gravitional lenses. In accordance with Einstein's theory of general relativity, the cluster gravitational mass, dominated by dark matter, bends light and creates magnified, distorted images of even more distant background galaxies. This sharp infrared Hubble image illustrates the case for galaxy cluster Abell 68 as a gravitational telescope, explored by amateur astronomer Nick Rose during the ESA-Hubble Hidden Treasures image processing competition. Putting your cursor over the picture will label highlights in the scene. Labels 1 and 2 show two lensed images of the same background galaxy. The distorted galaxy image labeled 2 resembles a vintage space invader! Label 3 marks a cluster member galaxy, not gravitationally lensed, stripped of its own gas as it plows through the denser intergalactic medium. Label 4 includes many background galaxies imaged as elongated streaks and arcs. Abell 68 itself is some 2.1 billion light-years distant toward the constellation Vulpecula. The central region of the cluster covered in the Hubble view spans over 1.2 million light-years.

2012 A broad expanse of glowing gas and dust presents a bird-like visage to astronomers from planet Earth, suggesting its popular moniker - The Seagull Nebula. This portrait of the cosmic bird covers a 1.6 degree wide swath across the plane of the Milky Way, near the direction of Sirius, alpha star of the constellation Canis Major. Of course, the region includes objects with other catalog designations: notably NGC 2327, a compact, dusty emission region with an embedded massive star that forms the bird's head (aka the Parrot Nebula, above center). IC 2177 forms the sweeping arc of the seagull's wings. Dominated by the reddish glow of atomic hydrogen, the complex of gas and dust clouds with bright young stars spans over 100 light-years at an estimated 3,800 light-year distance.

2011 How thin are the rings of Saturn? Brightness measurements from different angles have shown Saturn's rings to be about one kilometer thick, making them many times thinner, in relative proportion, than a razor blade. This thinness sometimes appears in dramatic fashion during an image taken nearly along the ring plane. The robot Cassini spacecraft now orbiting Saturn has now captured another shot that dramatically highlights the ring's thinness. The above image was taken in mid January in infrared and polarized light. Titan looms just over the thin rings, while dark ring shadows on Saturn show the Sun to be above the ring plane. Close inspection of the image will show the smaller moon Enceladus on the far right. Cassini, humanity's first mission to orbit Saturn, currently has operations planned until 2017.

2010 What's that bright object in the sky? A common question with answers that vary by time and season, the quick answer just after sunset in middle of last month, from the northern hemisphere, was Mars. The above picturesque panorama, taken during a ski trip from the Alps in Switzerland, shows not only Mars, but much more. Pine trees line the foreground, while numerous slopes leading up to the snow covered Allalinhorn mountain are visible in the distance. Stars dot the background, with the Beehive star cluster (M44) visible just below and to the left of Mars, while stars Castor and Pollux peek through the tree tops to the Mars' upper right. Mars will remain bright and in the constellation of the Crab (Cancer) until mid-May.

2009 Although the phase of this moon might appear familiar, the moon itself might not. In fact, this gibbous phase shows part of Jupiter's moon Europa. The robot spacecraft Galileo captured this image mosaic during its mission orbiting Jupiter from 1995 - 2003. Visible are plains of bright ice, cracks that run to the horizon, and dark patches that likely contain both ice and dirt. Raised terrain is particularly apparent near the terminator, where it casts shadows. Europa is nearly the same size as Earth's Moon, but much smoother, showing few highlands or large impact craters. Evidence and images from the Galileo spacecraft, indicated that liquid oceans might exist below the icy surface. To test speculation that these seas hold life, ESA and NASA have together started preliminary development of the Europa Jupiter System Mission , a spacecraft proposed to better study Europa. If the surface ice is thin enough, a future mission might drop hydrobots to burrow into the oceans and search for life.

2008 The striking spiral galaxy M104 is famous for its nearly edge-on profile featuring a broad ring of obscuring dust. Seen in silhouette against a bright bulge of stars, the swath of cosmic dust lanes lends a hat-like appearance to the galaxy in optical images suggesting the more popular moniker, The Sombrero Galaxy. Here, Hubble Space Telescope archival image data has been reprocessed to create this alternative look at the well-known galaxy. The newly developed processing improves the visibility of details otherwise lost in overwhelming glare, in this case allowing features of the galaxy's dust lanes to be followed well into the bright central region. About 50,000 light-years across and 28 million light-years away, M104 is one of the largest galaxies at the southern edge of the Virgo Galaxy Cluster.

2007 This dramatic image features a dark red Moon during a total lunar eclipse -- celestial shadow play enjoyed by many denizens of planet Earth last Saturday. Recorded near Wildon, Austria, the picture is a composite of two exposures; a relatively short exposure to feature the lunar surface and a longer exposure to capture background stars in the constellation Leo. Completely immersed in Earth's cone-shaped shadow during the total eclipse phase, the lunar surface is still illuminated by sunlight, reddened and refracted into the dark shadow region by a dusty atmosphere. As a result, familiar details of the Moon's nearside are easy to pick out, including the smooth lunar mare and the large ray crater Tycho. In this telescopic view, the background stars are faint and most would be invisible to the naked eye.

2006 Is the continent at the end of the Earth slowly melting? For millions of years, Antarctica, the frozen continent at the southern end of planet Earth, has been encased in a gigantic sheet of ice. Recently, the orbiting robotic GRACE satellite has been taking sensitive measurements of the gravity for the entire Earth, including Antarctica. Recent analysis of Gravity Recovery and Climate Experiment (GRACE) data indicate that the Antarctic ice sheet might have lost enough mass to cause the worlds' oceans to rise about 1.2 millimeters, on the average, from between 2002 and 2005. Although this may not seem like much, the equivalent amount of water is about 150 trillion liters, equivalent to the amount of water used by US residents in three months. Uncertainties in the measurement make the mass loss uncertain by about 80 trillion liters. Pictured above is an iceberg that is a small part of the Antarctic ice sheet. The picture was taken on the Riiser-Larsen ice shelf in December 1995. Future research will likely focus on trying to better understand the data, take more data, predict future trends, and understand possible effects of these trends on the future climate of our entire home planet.

2005 Whatever hit Mimas nearly destroyed it. What remains is one of the largest impact craters on one of Saturn's smallest moons. The crater, named Herschel after the 1789 discoverer of Mimas, Sir William Herschel, spans about 130 kilometers and is pictured above in the dramatic light of its terminator. Mimas' low mass produces a surface gravity just strong enough to create a spherical body but weak enough to allow such relatively large surface features. Mimas is made of mostly water ice with a smattering of rock - so it is accurately described as a big dirty snowball. The above image was taken during the 2005 January flyby of the robot spacecraft Cassini now in orbit around Saturn.

2004 The crescent Moon passed nearly in front of Venus two weeks ago. The close conjunction of the night sky's two brightest objects created a striking pose for many viewing the evening sky just after sunset. Such a pose, shown above, was captured between clouds over Corona Del Mar Beach in California, USA. To be precise, the Moon appeared to pass only about three degrees from Venus on February 23. A similar conjunction will occur later this month, on March 24, when Venus appears near its furthest from the Sun while the Moon passes only about 2 degrees away.

2003 Nearly 400 years ago astronomer Johannes Kepler observed comet tails blown by a solar breeze and suggested that vessels might likewise navigate through space using appropriately fashioned sails. It is now widely recognized that sunlight does indeed produce a force which moves comet tails and a large, reflective sail could be a practical means of propelling a spacecraft. In fact, the illustration above represents one concept explored by NASA centers to develop an interstellar probe pushed along by sunlight reflected from an ultrathin sail. Nearly half a kilometer wide, the delicate solar sail would be unfurled in space. Continuous pressure from sunlight would ultimately accelerate the craft to speeds about five times higher than possible with conventional rockets -- without requiring any fuel! If launched in 2010 such a probe could overtake Voyager 1, the most distant spacecraft bound for interstellar space, in 2018 going as far in eight years as the Voyager will have journeyed in 41 years.

2002 Trailing a thick column of exhaust, the Space Shuttle Columbia blasted into the twilight morning sky on March 1, its thundering rockets briefly flooding a cloud bank with the light of a false dawn. The event marked the start of the ongoing eleven day mission to upgrade the Hubble Space Telescope. Hubble's upgrades include the installation of new solar arrays and a new camera. Columbia's crew is scheduled to complete the work today in the last of five space walks. Columbia's launch also marks the first flight of the oldest operating space shuttle after receiving extensive upgrades itself, designed to increase its capabilities for missions to low Earth orbit. The shuttle landing is expected at Kennedy Space Center on March 12.

2001 Have you seen a bright evening star in the western sky lately? That's no star, that's planet Venus the second "rock" from the Sun. Blazing at -4.6 magnitude, Venus, after the Sun and Moon, is the third brightest celestial body in planet Earth's sky. Venus is closer to the Sun than Earth and as Venus orbits the Sun it is seen to go through phases similar to the Moon. But unlike the Moon, as Venus waxes and wanes its distance from Earth and hence its apparent size changes drastically. This causes Venus to look brighter as it looms large in its crescent phases than when it is smaller and nearly full. Taken on January 28th, this dramatic picture finds a crescent Venus near its brightest to the right of a crescent Moon. The brilliant rivals seem poised above a satellite dish of the Scripps Satellite Oceanography Facility. Closer to the horizon, just below and to the right of the satellite dish, Mercury pierces the twilight glow.

2000 As the robot spacecraft NEAR lowers itself toward asteroid 433 Eros, more surface details are becoming visible. Last week's maneuvers brought NEAR to within 204 kilometers of the floating mountain's surface. With increased resolution, NEAR's camera then documented Eros' unusual shape, craters large and small, boulders, and mysterious grooves similar to asteroid Gaspra and Martian moon Phobos. If you could stand on Eros, you would still be too small to be visible on this recent image, which shows features as small as 20 meters across. However, you would feel gravity only 1/1000 that on Earth, so that you could easily jump over even this large 5 kilometer wide crater.

1999 Venus and Jupiter appeared unusually close together in the sky last month. The conjunction was easily visible to the unaided eye because Venus appears brighter than any background star. The two planets were not significantly closer in space - Venus just passed nearly in front of Jupiter as seen from the Earth. Visible in the above photograph are actually five planets. The faint dot near the top is Saturn. Venus is the brightest spot near the center, and Jupiter is just above it. Perhaps the hardest to see is Mercury, visible below Venus but above the foreground Earth. A single line nearly connects all the planets, a result of all planets orbiting the Sun in a single plane called the ecliptic.

1998 The Space Shuttle Discovery's orbital maneuvering system (OMS) engine firing produced this dramatic flare as it cruised "upside down" in low Earth orbit. Discovery was named for a ship commanded by Captain James Cook RN, the 18th Century English astronomer and navigator. Cook's voyages of discovery established new standards in scientific exploration and brought extensive knowledge of the unknown Pacific regions, including Australia, New Zealand, and the Hawaiian Island archipelago to Europeans. The Space Shuttle Endeavor, also named after one of Cook's ships, is the most recent addition to NASA's four-orbiter shuttle fleet.

1997 Our Earth is not at rest. The Earth moves around the Sun. The Sun orbits the center of the Milky Way Galaxy. The Milky Way Galaxy orbits in the Local Group. The Local Group falls toward the Virgo Cluster of Galaxies. But these speeds are less than the speed that all of these objects together move relative to the microwave background. In the above all-sky map, radiation in the Earth's direction of motion appears blueshifted and hence hotter, while radiation on the opposite side of the sky is redshifted and colder. The map indicates that the Local Group moves at about 600 kilometers per second relative to this primordial radiation. This high speed was initially unexpected and its magnitude is still unexplained. Why are we moving so fast? What is out there?

1996 Jodrell Bank in England is the home of the Lovell Telescope one of the largest radio telescopes in the world. Completed in 1957 under the direction of Bernard Lovell, the 250 ft. diameter dish was the largest steerable radio telescope. The telescope has been used to monitor extremely faint radio emissions from space, including the transmissions of the Pioneer spacecraft in the distant Solar System. The telescope has been used in many astronomical investigations, including the determination of structure in local interstellar gas, searches for pulsars, determining molecular abundances towards the Galactic center, and mapping hydrogen emission in galaxies. Currently, the telescope is not really for sale.

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