APOD Retrospective: June 2

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: June 2

Post by bystander » Fri May 25, 2012 7:28 pm

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2015 One of these two bright sky objects is moving. On the right is the famous star Polaris. Although only the 45th brightest star in the sky, Polaris is famous for appearing stationary. Once you find it, it will always appear in the same direction -- all night and all day -- for the rest of your life. This is because the northern spin pole of the Earth -- called the North Celestial Pole -- points near Polaris. On the left, about ten million times closer, is Comet Lovejoy, which noticeably changes its sky position by the hour. The featured image was taken last week. Officially designated C/2014 Q2 (Lovejoy), this disintegrating snowball is on a visit from the outer Solar System and will only appear near the North Star for a few more weeks. That should be long enough, however, for northerners with binoculars or a small telescope to see the greenish coma of this fleeting newcomer, perhaps with the help of a good star map.

2014 The space station has caught a dragon. Specifically, in mid-April, the International Space Station captured the unmanned SpaceX Dragon capsule sent to resupply the orbiting outpost. Pictured above, the station's Canadarm2 had just grabbed the commercial spaceship. The Dragon capsule was filled with over 5000 lbs (2260 kilos) of supplies and experiments to be used by the current band of six ISS astronauts who compose Expedition 39, as well as the six astronauts who compose Expedition 40. After docking with the ISS, the Dragon capsule was unloaded and eventually released, splashing down in the Pacific Ocean on May 18. The current Expedition 40 crew, now complete, will apply themselves to many tasks including the deployment of the Napor-mini RSA experiment which will use phased array radar and a small optical telescope to monitor possible emergency situations on the Earth below.

2013 What kind of cloud is this? A roll cloud. These rare long clouds may form near advancing cold fronts. In particular, a downdraft from an advancing storm front can cause moist warm air to rise, cool below its dew point, and so form a cloud. When this happens uniformly along an extended front, a roll cloud may form. Roll clouds may actually have air circulating along the long horizontal axis of the cloud. A roll cloud is not thought to be able to morph into a tornado. Unlike a similar shelf cloud, a roll cloud, a type of Arcus cloud, is completely detached from their parent cumulonimbus cloud. Pictured above, a roll cloud extends far into the distance in 2009 January above Las Olas Beach in Maldonado, Uruguay.

2012 Follow the handle of the Big Dipper away from the dipper's bowl until you get to the handle's last bright star. Then, just slide your telescope a little south and west and you might find this stunning pair of interacting galaxies, the 51st entry in Charles Messier famous catalog. Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also cataloged as NGC 5194. Its spiral arms and dust lanes clearly sweep in front of its companion galaxy (top), NGC 5195. The pair are about 31 million light-years distant and officially lie within the angular boundaries of the small constellation Canes Venatici. Though M51 looks faint and fuzzy to the human eye, deep images like this one can reveal the faint tidal debris around the smaller galaxy.

2011 This luminous night view of the space shuttle orbiter Endeavour, docked with the International Space Station for a final time, was captured on May 28. Orbiting 350 kilometers above planet Earth, Endeavour's payload bay is lit up as it hurtles through Earth's shadow at 17,000 miles per hour. At the top of the frame, the jointed appendages of the station's robotic manipulator arm Dextre appear in silhouette. Motion during the long exposure produced streaks in the starry background and the city lights on the darkened planet below. Completing a 16 day mission, Endeavour made a final landing at Kennedy Space Center in the dark, early morning hours of June 1.

2010 Did this meteor take a twisting path? No one is sure. Considered opinions are solicited. Meteors, usually sand sized grains that originate in comets, will typically disintegrate as they enter the Earth's atmosphere. A fast moving meteor ionizes molecules in the Earth's atmosphere that subsequently glow when they reacquire electrons. Meteor paths that twist noticeably have been noted before, and even photographed, but attributing such behavior to the motion of the meteor itself and neither the wind-blown meteor train nor the observer remains somewhat controversial. The above meteor, imaged two weeks ago streaking over the Teide Observatory in Tenerife, Canary Islands, appears to swagger as much as several minutes of arc, which the experienced astrophotographer did not think could be attributed to drifting of the resulting train or motion of the camera mount. If truly an indication of a twisted meteor path, an underlying reason could be the pictured meteor was markedly non-spherical in shape, non-uniform in composition, or electrically charged. Non-uniform meteors, for example, may evaporate more on one side than another, causing a rotating meteor to wobble. Understanding meteors is important partly because meteors are candidates to have seeded Earth with prebiotic molecules that allowed for the development of life.

2009 What causes the mysterious spokes in Saturn's rings? Visible in the above image as light ghostlike impressions, spokes were first discovered in the mid-1970s and first photographed by the Voyager spacecraft that buzzed by Saturn in the early 1980s. Their existence was unexpected. Oddly, the spokes are more commonly observed when Saturn's rings are more nearly edge on to the Sun, and so were conspicuously absent from initial images sent back by the robot Cassini spacecraft now orbiting Saturn. Analyses of archived Voyager images have led to the conclusions that the transient spokes, which may form and dissipate over a few hours, are composed of electrically charged sheets of small dust-sized particles. Hypotheses for spoke creation include small meteors impacting the rings and electron beams from Saturnian atmospheric lightning spraying the rings. As Saturn approaches equinox, spoke sightings like that pictured above are becoming increasingly common, giving planetary scientists fresh images and data with which to test origin hypotheses.

2008 Is that ice under the Phoenix spacecraft on Mars? Quite possibly. Phoenix, which landed a week ago, was expected to dig under the Martian soil to search for ice, but the lander's braking rockets may already have uncovered some during descent. Pictured above is an image taken last week by the Robotic Arm Camera showing the unusual light-colored substance just in front of Phoenix's landing pad. Over the next few weeks, Phoenix will continue to photograph its surroundings, analyze the composition of this hard light substrate, and dig into the surrounding soil. Were the unusual light substrate indeed Martian ice, it would give Phoenix a convenient pedestal to investigate the history of water on Mars, and to better determine whether the boundary between ice and soil was ever capable of supporting life.

2007 Get out your red/blue glasses and check out this satisfying stereo anaglyph of the Full Moon. A corresponding stereo image pair, intended for cross-eyed viewing, is also available through this link. Regardless of your preferred technique for stereo viewing, the 3D effect comes from combining pictures of the same scene taken at different angles -- mimicking the slightly different perspective of each eye. Perhaps surprisingly for Earthdwellers, getting two pictures of the Full Moon from different angles only requires a little patience. In this case, photographer Laurent Laveder used pictures taken months apart, one in November 2006 and one in January 2007. He relied on the Moon's continuous libration or wobble as it orbits to produce two shifted images of a Full Moon.

2006 IC 443 is typical of the aftermath of a stellar explosion, the ultimate fate of massive stars. Seen in this false-color composite image, the supernova remnant is still glowing across the spectrum, from radio (blue) to optical (red) to x-ray (green) energies -- even though light from the stellar explosion that created the expanding cosmic cloud first reached planet Earth thousands of years ago. The odd thing about IC 443 is the apparent motion of its dense neutron star, the collapsed remnant of the stellar core. The close-up inset shows the swept-back wake created as the neutron star hurtles through the hot gas, but that direction is not aligned with the direction toward the apparent center of the remnant. The misalignment suggests that the explosion site was offset from the center or that fast-moving gas in the nebula has influenced the wake. The wide view of IC 443, also known as the Jellyfish nebula, spans about 65 light-years at the supernova remnant's estimated distance of 5,000 light-years.

2005 Eta Carinae, one of the most massive and unstable stars in the Milky Way Galaxy, has a profound effect on its environment. Found in the the South Pillar region of the Carina Nebula, these fantastic pillars of glowing dust and gas with embedded newborn stars were sculpted by the intense wind and radiation from Eta Carinae and other massive stars. Glowing brightly in planet Earth's southern sky, the expansive Eta Carinae Nebula is a mere 10,000 light-years distant. Still, this remarkable cosmic vista is largely obscured by nebular dust and only revealed here in penetrating infrared light by the Spitzer Space Telescope. Eta Carinae itself is off the top left of the false-color image, with the bright-tipped dust pillars pointing suggestively toward the massive star's position. The Spitzer image spans almost 200 light-years at the distance of Eta Carinae.

2004 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 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 far 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.

2003 Fogs of clouds and dust covered parts of southern Mars during last Martian winter. Giant volcanoes, such as Ascraeus Mons, the central circular feature near the top of the image, were surrounded by large water clouds. Slightly southwest, Pavonis Mons and Arisa Mons also peeked above their water clouds. The rough terrain below center is Labyrinthus Noctis, a maze of deep troughs running over 200 kilometers long. Directly south, a large white dust storm fogs Syria Planum, a large plateau. This image mosaic was taken by the Mars Global Surveyor spacecraft currently orbiting Mars. Soon, five more Earth-launched spacecraft should arrive at the Red Planet, named for the Roman god of war.

2002 Which way to the interstate? What appears to be a caricature of a complex highway system on Earth is actually a system of ridges and cracks on the icy surface of Jupiter's moon Europa. The distance between parallel ridges in the above photograph is typically about 1 kilometer. The complexity of the cracks and ridges tell a story of Europa's past that is mostly undecipherable -- planetary geologists try to understand just the general origin of the overall features. One noteworthy feature is the overall white sheen, possibly indicating the presence of frost. Another is the dark centers between parallel ridges, which might indicate that dirty water from an underground ocean recently welled up in the cracks and froze. Recent research indicates that enough carbon exists to support an underwater biosphere, but that Europa's ice crust may be over three kilometers thick in some places.

2001 In the Summer of 1054 A.D. Chinese astronomers reported that a star in the constellation of Taurus suddenly became as bright as the full Moon. Fading slowly, it remained visible for over a year. It is now understood that a spectacular supernova explosion - the detonation of a massive star whose remains are now visible as the Crab Nebula- was responsible for the apparition. The core of the star collapsed to form a rotating neutron star or pulsar, one of the most exotic objects known to modern astronomers. Like a cosmic lighthouse, the rotating Crab pulsar generates beams of radio, visible, x-ray and gamma-ray energy which, as the name suggests, produce pulses as they sweep across our view. Using a stunning series of visible light images taken with the Hubble Space Telescope (HST) in 1995, astronomers have discovered spectacular pulsar powered motions within the Crab nebula. Highlights of this HST Crab "movie" show wisps of material moving away from the pulsar at half the speed of light, a scintillating halo, and an intense knot of emission dancing, sprite-like, above the pulsar's pole. Only 10 kilometers wide but more massive than the sun, the pulsar's energy drives the dynamics and emission of the nebula itself which is more than 10 light-years across.

2000 IC3328 is an otherwise unremarkable dwarf elliptical galaxy about 50 million light-years away in the Virgo cluster. But hidden within IC3328 is a subtle, beautifully symmetric spiral structure! A team of astronomers recently made this totally surprising discovery using detailed digital images from the European Southern Observatory's 8.2 meter Antu telescope. They numerically modeled the smooth distribution of light for this galaxy (left) to enable more accurate measurements of its distance. When the smooth distribution was subtracted from the digital image, the startling spiral structure became apparent (right). Typical of large, rotating, disk galaxies with density waves, spiral structure is unprecedented in the blob-shaped aggregates of stars normally classified as elliptical galaxies. What created the "secret" spiral in IC3328? Some possibilities under consideration include tidal interactions with nearby galaxies and amplified internal stellar motions.

1999 It's 2 AM on Mars and surface temperatures range from -65C to -120C, as measured by the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor spacecraft. TES data used to make this detailed temperature map were acquired while passing over the night side of the Red Planet during 500 mapping orbits of Mars. With the warmest temperatures shown in white, progressing through red, yellow, and green colors to the coldest temperatures in blue, the map reveals the northern hemisphere during summer while the south experiences the cold martian winter. Near Mars' equator, the variations in nighttime temperatures are related to surface materials. Cold blue areas are covered with fine dust particles and the warmer regions are covered with coarser sand and rocks.

1998 The Butterfly Nebula is only thousands of years old. As a central star of a binary system aged, it threw off its outer envelopes of gas in a strong stellar wind. The remaining stellar core is so hot it ionizes the previously ejected gas, causing it to glow. The different colors of this planetary nebula are determined by small differences in its composition. This bipolar nebula will continue to shine brightly for only a few thousand more years, after which its central star will fade and become a white dwarf star. The above picture is one of the first ever taken by the Very Large Telescope (VLT), a new 8.2-meter telescope located in Chile.

1997 This galaxy is having a bad millennium. In fact, the past 100 million years haven't been so good, and probably the next billion or so should be quite tumultuous. NGC 4039 was a normal spiral galaxy, minding its own business, when NGC 4038 crashed into it. The evolving wreckage, known as the "Antennae", is pictured above. As gravity pulls each galaxy apart, clouds of gas slam into each other and bright blue knots are formed. These knots are large clusters of stars imbedded in vast regions of ionized hydrogen gas. The high abundance of relatively dim star clusters is quite unlike our Milky Way's globular cluster system, though. Perhaps some of these young star clusters will go on to form globular clusters, while others will disperse through close gravitational encounters. The above picture is centered around the larger of the two interacting galaxies: NGC 4038. The diagonal streak across the upper left is unrelated to the colliding galaxies. The color contrast in the above three-color mosaic was chosen to highlight extended features.

1996 This fish-eye view of a dramatic night launch of the Shuttle Atlantis on mission STS-76 was recorded on March 22, 1996. The mission carried 6 astronauts aloft, and returned with 5 -- delivering one crew member, Shannon Lucid, to the Mir Space Station. Lucid is currently onboard the Mir as a cosmonaut guest researcher. NASA Shuttle flights to Mir are part of the Phase 1 program for construction of the International Space Station.

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