APOD Retrospective: September 18

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: September 18

Post by bystander » Sun Sep 18, 2011 5:21 am

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2015 This shadowy landscape of majestic mountains and icy plains stretches toward the horizon of a small, distant world. It was captured from a range of about 18,000 kilometers when New Horizons looked back toward Pluto, 15 minutes after the spacecraft's closest approach on July 14. The dramatic, low-angle, near-twilight scene follows rugged mountains still popularly known as Norgay Montes from foreground left, and Hillary Montes along the horizon, giving way to smooth Sputnik Planum at right. Layers of Pluto's tenuous atmosphere are also revealed in the backlit view. With a strangely familiar appearance, the frigid terrain likely includes ices of nitrogen and carbon monoxide with water-ice mountains rising up to 3,500 meters (11,000 feet). That's comparable in height to the majestic mountains of planet Earth. This Plutonian landscape is 380 kilometers (230 miles) across.
2014 In this crowded starfield covering over 2 degrees within the high flying constellation Cygnus, the eye is drawn to the Cocoon Nebula. A compact star forming region, the cosmic Cocoon punctuates a long trail of obscuring interstellar dust clouds. Cataloged as IC 5146, the nebula is nearly 15 light-years wide, located some 4,000 light years away. Like other star forming regions, it stands out in red, glowing, hydrogen gas excited by the young, hot stars and blue, dust-reflected starlight at the edge of an otherwise invisible molecular cloud. In fact, the bright star near the center of this nebula is likely only a few hundred thousand years old, powering the nebular glow as it clears out a cavity in the molecular cloud's star forming dust and gas. But the long dusty filaments that appear dark in this visible light image are themselves hiding stars in the process of formation that can be seen seen at infrared wavelengths.

2013 Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as dusty as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city. With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The above exposure took about 20 minutes and covers a sky area several times the size of the full moon. Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus). A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.

2012 Is it art? Earlier this month, space station astronaut Aki Hoshide (Japan) recorded this striking image while helping to augment the capabilities of the Earth-orbiting International Space Station (ISS). Visible in this outworldly assemblage is the Sun, the Earth, two portions of a robotic arm, an astronaut's spacesuit, the deep darkness of space, and the unusual camera taking the picture. This image joins other historic -- and possibly artistic -- self-portraits taken previously in space. The Expedition 32 mission ended yesterday when an attached capsule undocked with the ISS and returned some of the crew to Earth.

2011 Here is one of the sharper views of the Sun ever taken. This stunning image shows remarkable details of a dark sunspot across the image bottom and numerous boiling granules which appear like kernels of corn across the top. Taken in 2002, the picture was made using the Swedish Solar Telescope operating on the Canary Island of La Palma. The high resolution image was achieved using sophisticated adaptive optics, digital image stacking, and other processing techniques to counter the blurring effect of Earth's atmosphere. Currently a sunspot group is crossing the Sun that is so large it can be easily seen by the cautious observer even without magnification.

2010 Chances are the brightest star you've seen lately is actually planet Jupiter. Jupiter rules the sky in this labeled view of a starry September night from the Alborz mountains in Iran, complete with the trail of a red flashlight illuminating the mountain road. On September 21st (Universal Time) Jupiter will be at opposition, the point opposite the Sun along its orbit, rising just as the Sun sets. For this opposition, Jupiter will be slightly brighter and closer to planet Earth than in any year since 1963. Much fainter and also approaching its own opposition on September 21st, is the distant planet Uranus. Very near Jupiter on the sky, the fainter planet is easy to spot in binoculars (similar to the inset view), well above and right of brilliant Jupiter and about as bright as one of Jupiter's own Galilean moons. Remarkably close to the opposition of both planets, the point on the sky exactly opposite the Sun on September 23rd is marked the Vernal Equinox. On that date, a Full Moon will join the celestial scene. Of course, any Full Moon is also at opposition.

2009 Get out your red/blue glasses and check out this close-up of spacesuited NASA astronaut John Olivas outside the International Space Station. Carefully constructed from two photographs (ISS020-E-038481, ISS02-0E-038482) taken during space shuttle orbiter Discovery's latest visit to the orbiting outpost, the 3D anaglyph creates the compelling illusion that you can actually reach out and take his gloved hand. The photographer, fellow spacewalker ESA astronaut Christer Fuglesang, along with ISS structures and planet Earth's horizon, are reflected in Olivas' helmet visor. Last Friday, the two returned to Earth along with the rest of Discovery's crew, landing at Edwards Air Force base in California.

2008 A familiar sight for northern hemisphere astronomers, the Ring Nebula (M57) is some 2,000 light-years away in the musical constellation Lyra. The central ring is about one light-year across, but this remarkably deep exposure - a collaborative effort combining data from two different telescopes - explores the looping filaments of glowing gas extending much farther from the nebula's central star. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from a dying, sun-like star. This composite image includes over 16 hours of narrow-band data intended to record the red emission from hydrogen atoms, but the pronounced blue/green color is due to emission from oxygen atoms at higher temperatures within the ring. The much more distant spiral galaxy IC 1296 is also visible at the upper right.

2007 Volcano Tungurahua erupted spectacularly last year. Pictured above, molten rock so hot it glows visibly pours down the sides of the 5,000-meter high Tungurahua, while a cloud of dark ash is seen being ejected toward the left. Wispy white clouds flow around the lava-lit peak, while a star-lit sky shines in the distance. The above image was captured last year as ash fell around the adventurous photographer. Located in Ecuador, Tungurahua has become active roughly every 90 years since for the last 1,300 years. Volcano Tungurahua has started erupting again this year and continues erupting at a lower level even today.

2006 Is Pluto the largest dwarf planet? No! Currently, the largest known dwarf planet is (136199) Eris, renamed last week from 2003 UB313. Eris is just slightly larger than Pluto, but orbits as far as twice Pluto's distance from the Sun. Eris is shown above in an image taken by a 10-meter Keck Telescope from Hawaii, USA. Like Pluto, Eris has a moon, which has been officially named by the International Astronomical Union as (136199) Eris I (Dysnomia). Dysnomia is visible above just to the right of Eris. Dwarf planets Pluto and Eris are trans-Neptunian objects that orbit in the Kuiper belt of objects past Neptune. Eris was discovered in 2003, and is likely composed of frozen water-ice and methane. Since Pluto's recent demotion by the IAU from planet to dwarf planet status, Pluto has recently also been given a new numeric designation: (134340) Pluto. Currently, the only other officially designated "dwarf planet" is (1) Ceres.

2005 The Great Nebula in Orion, an immense, nearby starbirth region, is probably the most famous of all astronomical nebulas. Here, glowing gas surrounds hot young stars at the edge of an immense interstellar molecular cloud only 1500 light-years away. In the above deep image, faint wisps and sheets of dust and gas are particularly evident. The Great Nebula in Orion can be found with the unaided eye just below and to the left of the easily identifiable belt of three stars in the popular constellation Orion. In addition to housing a bright open cluster of stars known as the Trapezium, the Orion Nebula contains many stellar nurseries. These nurseries contain hydrogen gas, hot young stars, proplyds, and stellar jets spewing material at high speeds. Also known as M42, the Orion Nebula spans about 40 light years and is located in the same spiral arm of our Galaxy as the Sun.

2004 The fifty-fifth entry in Charles Messier's catalog, M55 is a large and lovely globular cluster of around 100,000 stars. Only 20,000 light-years away in the constellation Sagittarius, M55 appears to earth-bound observers to be nearly 2/3 the size of the full moon. Globular star clusters like M55 roam the halo of our Milky Way Galaxy as gravitationally bound populations of stars known to be much older than stellar groups found in the galactic disk. Astronomers who make detailed studies of globular cluster stars can accurately measure the cluster ages and distances. Their results ultimately constrain the age of the Universe (... it must be older than the stars in it! ), and provide a fundamental rung on the astronomical distance ladder. This stunning three-color image made with astronomical (BVI) filters spans about 100 light-years across the globular cluster M55.

2003 These three views of Saturn were recorded by the Hubble Space Telescope on March 7th of this year, as the southern hemisphere of the solar system's most gorgeous planet reached its maximum 27 degree tilt toward Earth. The images used to construct the false-color pictures were made through a combination of filters covering the electromagnetic spectrum from ultraviolet (top), to visible (middle) and infrared (bottom) wavelengths highlighting different features in the Saturnian atmospheric bands and rings. Well known for its bright ring system and large, mysterious moon Titan, gas giant Saturn is also a planet with a dynamic atmosphere and high-speed winds. In fact, in the 1980s, Voyager spacecraft measured equatorial winds of over 1,000 miles per hour. Giant storm systems, comparable in size to planet Earth itself, have been seen erupting in Saturn's cloud tops.

2002 Many vast star fields in the plane of our Milky Way Galaxy are rich in clouds of stars, dust, and gas. First and foremost, visible in the above picture are millions of stars, many of which are similar to our Sun. Next huge filaments of dark interstellar dust run across the image and block the light from millions of more stars yet further across our Galaxy. The bright red region on the left is the Omega Nebula, an emission nebula of mostly hot hydrogen gas also known as M17. A small bright grouping of stars near the image center is the open cluster M18, while the long bright streak of stars just right of center is M24. On the far right of the image is the picturesque red emission nebula IC 1283 flanked by two blue reflection nebulas NGC 6589 and NGC 6590. These objects are visible with a small telescope toward the constellation of Sagittarius.

2001 Just after landing on Mars in 1997, the robotic Mars Pathfinder main station took a quick first look around. This insurance panorama was taken even before the Sagan Memorial Station camera was raised to its two-meter-high perch. The full view is best seen by slowly scrolling to the right. The unique perspective captures many Mars Pathfinder instruments in the close foreground including a screen for judging sky illumination, communications antennae, solar panels, and two ramps leading down to the surface for the robot probe Sojourner. After taking the ramp on the right, Sojourner can be seen on the Martian surface. Visible on the surface are numerous rocks and hills that came to be better studied. The Mars Pathfinder mission went on to return 16,000 images and data that resulted in many discoveries, including evidence for warmer and wetter conditions on Mars in the past. After nearly three spectacular months exploring the surface, Mars Pathfinder dropped out of communication, likely the result of depleted battery power.

2000 Last Monday the crew of Space Shuttle Atlantis took in this view as they approached the developing International Space Station (ISS). From top to bottom, the astronauts saw a station currently consisting of the Progress supply module, the Zvezda service module, the Zarya cargo module, and the Unity connecting module. Never before had astronauts seen the station since the remote-controlled additions of Progress and Zvezda. Energy collecting flat solar panels can be seen extending from some of the modules. Soon after this picture was taken, Atlantis docked with the ISS at the Unity end. The astronauts have worked hard unloading supplies, installing and testing equipment, and even planning to reboost the floating space station to a higher orbit. The Shuttle and its entire crew are scheduled to return to Earth Wednesday. The Space Shuttle Discovery is then scheduled to visit the ISS in two weeks.

1999 Space suited project Mercury astronauts John H. Glenn, Virgil I. Grissom, and Alan B. Shepard Jr. (left to right) are posing in front of a Redstone rocket in this vintage 1961 NASA publicity photo. Project Mercury was the first U.S. program designed to put humans in space. It resulted in 6 flights using one-man capsules and Redstone and Atlas rockets. Shortly after the first U.S. manned flight on May 5, 1961, a suborbital flight piloted by Alan Shepard, President Kennedy announced the goal of a manned lunar landing by 1970. This goal was achieved by NASA's Apollo program and Shepard himself walked on the moon as commander of the Apollo 14 mission. Alan Shepard passed away in 1998. Virgil Grissom died in a tragic fire during an Apollo launch pad test in 1967. Senator John Glenn flew again on the 25th voyage of the Space Shuttle Discovery.

1998 Launched on January 6th, NASA's Lunar Prospector spacecraft has been exploring the Moon with instruments designed to sense global properties while orbiting pole-to-pole, 63 miles above the lunar surface. Now over half way through its primary mission, impressive science results include a much-needed precision gravity map of the lunar surface, global maps of elemental composition, the detection of mini-magnetospheres related to large impact sites, and evidence pointing toward a small iron-rich lunar core. But perhaps the most spectacular recent announcement has underscored Prospector's earlier block-buster - the detection of substantial water-ice at both the North and South lunar poles. An analysis of data collected so far is consistent with near-pure water ice deposits - the residue of cometary impacts - buried beneath as much as 18 inches of dry dusty regolith. And the estimates now suggest 10 times more water in each polar region than previously thought! The small Prospector spacecraft carries no cameras for lunar imaging, but the Moon is relatively well photographed. This detailed, color-enhanced nearside mosaic was produced from images taken by the Galileo spacecraft as it passed the Moon in December of 1992.

1997 On August 27th twisting magnetic fields propelled this huge eruptive prominence a hundred thousand miles above the Sun's surface. The seething plasma of ionized gases is at a temperature of about 150,000 degrees Farenheit and spans over 200,000 miles (about 27 Earths). The Extreme ultraviolet Imaging Telescope (EIT) onboard the space-based SOHO observatory recorded this exquisitely detailed image in the light of ionized Helium atoms from its vantage point in a Halo orbit. This is the largest solar prominence observed by SOHO instruments since they began exploring solar phenomena in early 1996.

1996 What if you could see infrared light? Because this light is less absorbed by dust than visible light, you could peer into the center of our Milky Way Galaxy. The stars there are normally hidden from direct view by the interstellar dust clouds which line the Galactic plane. Above is a false color image of the entire sky made by the DIRBE instrument onboard NASA's COBE Satellite using infrared light with a wavelength of 3.5 microns - about 7 times longer than the wavelength of visible light. The galactic plane runs horizontally along the middle of the image. At this wavelength, the cool stars in our galaxy shine brightly and can be seen to define the plane of the Milky Way and the central bulge. Interplanetary dust, which tends to lie along the plane of our own solar system, scatters sunlight and emits radiation at these wavelengths too. The faint glow it produces results in the "S" shape apparent in this infrared all-sky view.

1995 Magellan and his crew had plenty of time to study the southern sky during their famous voyage around the world. As a result, two fuzzy cloud like objects, nestled among the southern constellations of Doradus and Tucana are now known as the Clouds of Magellan. The Magellanic Clouds are small irregular galaxies, satellites of our larger Milky Way spiral galaxy. The Large Magellanic Cloud (LMC) pictured above is the closest galaxy to our own Milky Way, at a distance of about 180,000 light years. The Magellanic Clouds are joined to the Milky Way by a stream of cold hydrogen gas whose origin is still controversial. An unusual effect called gravitational lensing has recently been detected in a few LMC stars, and there is hope this could tell us important information about the true composition of our universe.

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