APOD Retrospective: August 6

A nostalgic look back at Astronomy Picture of the Day
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APOD Retrospective: August 6

Postby bystander » Sat Aug 06, 2011 3:56 am

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These two detailed, true color images of Pluto were captured during the historic New Horizons flyby last month. With slightly different perspectives on the now recognizeable surface features they are presented in this first high quality stereo pair intended for viewing by denizens of planet Earth. The left hand image (left eye) is a mosaic recorded when the spacecraft was about 450,000 kilometers from Pluto. The right single image was acquired earlier, a last full look before the spacecraft's closest approach. Despite a difference in resolution, the pair combine for a stunning 3D perception of the distant, underworldly terrain.

Acquiring its first sunlit views of far northern Saturn in late 2012, the Cassini spacecraft's wide-angle camera recorded this stunning, false-color image of the ringed planet's north pole. The composite of near-infrared image data results in red hues for low clouds and green for high ones, giving the Saturnian cloudscape a vivid appearance. Enormous by terrestrial standards, Saturn's north polar hurricane-like storm is deep, red, and about 2,000 kilometers wide. Clouds at its outer edge travel at over 500 kilometers per hour. Other atmospheric vortices also swirl inside the large, yellowish green, six-sided jet stream known as the hexagon. Beyond the cloud tops at the upper right, arcs of the planet's eye-catching rings appear bright blue.

Strange shapes and textures can be found in neighborhood of the Cone Nebula. The unusual shapes originate from fine interstellar dust reacting in complex ways with the energetic light and hot gas being expelled by the young stars. The brightest star on the right of the above picture is S Mon, while the region just below it has been nicknamed the Fox Fur Nebula for its color and structure. The blue glow directly surrounding S Mon results from reflection, where neighboring dust reflects light from the bright star. The red glow that encompasses the whole region results not only from dust reflection but also emission from hydrogen gas ionized by starlight. S Mon is part of a young open cluster of stars named NGC 2264, located about 2500 light years away toward the constellation of the Unicorn (Monoceros). Even though it points right at S Mon, details of the origin of the mysterious geometric Cone Nebula, visible on the far left, remain a mystery.

Video Credit: Colin Legg; Music Credit: Nocturnal (Redux) by Unkle

Have you ever seen the night sky change? It does -- sometimes in beautiful and unexpected ways. To see it, though, usually requires patience. The above award winning video shows several of the possible changes in dramatic fashion with a time lapse video. Visible are sunset-illuminated clouds moving, stars of vivid colors rising, the long tail of a Comet Lovejoy rising, bright satellites crossing, a meteor exploding, a distant lightning storm approaching, skyscapes including the Magellanic Clouds rotating, and a fisheye sky rotating while the foreground becomes illuminated by moonlight. Frequently featuring an artistic human sculpture in the foreground and the southern sky in the background, the video closes with a time lapse clip of a total lunar eclipse. If you can identify any more of the sky events depicted -- or any of the landscapes shown -- please illuminate them with a comment.

Recorded on August 2, this telescopic composite image catches Comet Garradd (C/2009 P1) in the same field of view as globular star cluster M15. The celestial scene would have been a rewarding one for influential 18th century comet hunter Charles Messier. While Messier scanned French skies for comets, he carefully cataloged positions of things which might be fuzzy and comet-like in appearance but did not move against the background stars and so were definitely not comets. M15 (lower right), the 15th entry in his famous not-a-comet catalog, is now understood to be a cluster of over 100,000 stars some 35,000 light-years distant. The comet, discovered in August 2009 by astronomer G. J. Garradd (Siding Spring Observatory, Australia) is currently sweeping across the constellation Pegasus, some 13 light-minutes from Earth. Shining faintly around 9th magnitude, comet Garradd will brighten in the coming months, predicted to be just below naked eye visibility near its peak in February 2012.

After a long solar minimum, the Sun is no longer so quiet. On August 1, this extreme ultraviolet snapshot of the Sun from the Solar Dynamics Observatory captured a complex burst of activity playing across the Sun's northern hemisphere. The false-color image shows the hot solar plasma at temperatures ranging from 1 to 2 million kelvins. Along with the erupting filaments and prominences, a small(!) solar flare spawned in the active region at the left was accompanied by a coronal mass ejection (CME), a billion-ton cloud of energetic particles headed for planet Earth. Making the 93 million mile trip in only two days, the CME impacted Earth's magnetosphere, triggering a geomagnetic storm and both northern and southern auroral displays.

This wide, sharp telescopic view reveals galaxies scattered beyond the stars at the northern boundary of the high-flying constellation Pegasus. Prominent at the upper right is NGC 7331. A mere 50 million light-years away, the large spiral is one of the brighter galaxies not included in Charles Messier's famous 18th century catalog. The disturbed looking group of galaxies at the lower left is well-known as Stephan's Quintet. About 300 million light-years distant, the quintet dramatically illustrates a multiple galaxy collision, its powerful, ongoing interactions posed for a brief cosmic snapshot. On the sky, the quintet and NGC 7331 are separated by about half a degree.

Globular clusters once ruled the Milky Way. Back in the old days, back when our Galaxy first formed, perhaps thousands of globular clusters roamed our Galaxy. Today, there are perhaps 200 left. Many globular clusters were destroyed over the eons by repeated fateful encounters with each other or the Galactic center. Surviving relics are older than any Earth fossil, older than any other structures in our Galaxy, and limit the universe itself in raw age. There are few, if any, young globular clusters in our Milky Way Galaxy because conditions are not ripe for more to form. Things are different next door, however, in the neighboring LMC galaxy. Pictured above is a "young" globular cluster residing there: NGC 1818. Observations show it formed only about 40 million years ago - just yesterday compared to the 12 billion year ages of globular clusters in our own Milky Way.

Can a gas cloud eat a galaxy? It's not even close. The odd looking "creature" or "hand" extending down from the top of the above photo is a gas cloud known as a cometary globule. This globule, however, has ruptured. Cometary globules are typically characterized by dusty heads and elongated tails. These features cause cometary globules to have visual similarities to comets, but in reality they are very much different. Globules are frequently the birthplaces of stars, and many show very young stars in their heads. The reason for the rupture in the head of this object is not completely known. The galaxy to the near the bottom of the image is huge, very far in the distance, and only placed near CG4 by chance superposition.

High atop a Chilean mountain lies one of the premier observatories of the southern sky: the Cerro Tololo Inter-American Observatory (CTIO). Pictured above is the dome surrounding one of the site's best known instruments, the 4-meter Blanco Telescope. Far behind the dome are thousands of individual stars and diffuse light from three galaxies: the Small Magellanic Cloud (upper left), the Large Magellanic Cloud (lower left), and our Milky Way Galaxy (right). Also visible just to Blanco's right is the famous superposition of four bright stars known as the Southern Cross. A single 20 second exposure, this digital image was recorded with a sensitive detector intended for astronomical imaging.

Comet dust rained down on planet Earth last August, streaking through dark skies in the annual Perseid meteor shower. So, while enjoying the anticipated space weather, astronomer Fred Bruenjes recorded a series of many 30 second long exposures spanning about six hours on the night of August 11/12 using a wide angle lens. Combining those frames which captured meteor flashes, he produced this dramatic view of the Perseids of summer. Although the comet dust particles are traveling parallel to each other, the resulting shower meteors clearly seem to radiate from a single point on the sky in the eponymous constellation Perseus. The radiant effect is due to perspective, as the parallel tracks appear to converge at a distance. Bruenjes notes that there are 51 Perseid meteors in the composite image, including one seen nearly head-on. This year, the Perseids Meteor Shower will peak in the early morning hours on Friday, August 12.

On a flight from Vienna to Brussels, astronomer Franz Kerschbaum looked out the window and photographed this beautiful atmospheric phenomenon, the glory, shining in the direction directly opposite the Sun. Before airplanes, the glory, known to some as the heiligenschein or the Specter of the Brocken, was occasionally seen from mountaintops. There, when conditions were right, one could look away from the Sun and see what appeared to be the shadow of a giant surrounded by a bright halo. Of course, the giant turns out to be the observer, and in the modern version a silhouette of a plane frequently occupies the glory's center. The cause of the glory is relatively complex. Briefly, small droplets of water reflect, refract, and diffract sunlight backwards towards the Sun. The phenomenon has a counterpart in astronomy, where looking out from planet Earth in the direction opposite the Sun yields a bright spot called the gegenschein.

Why is peculiar galaxy Centaurus A so dusty? Dramatic dust lanes that run across the galaxy's center mark Cen A. These dust lanes are so thick they almost completely obscure the galaxy's center in visible light. This is particularly unusual as Cen A's red stars and round shape are characteristic of a giant elliptical galaxy, a galaxy type usually low in dark dust. Cen A, also known as NGC 5128, is also unusual compared to an average elliptical galaxy because it contains a higher proportion of young blue stars and is a very strong source of radio emission. Evidence indicates that Cen A is likely the result of the collision of two normal galaxies. During the collision, many young stars were formed, but details of the creation of Cen A's unusual dust belts are still being researched. Cen A lies only 13 million light years away, making it the closest active galaxy. Cen A spans 60,000 light years and can be seen with binoculars toward the constellation of Centaurus.

How fast do fundamental particles wobble? A surprising answer to this seemingly inconsequential question is coming out of Brookhaven National Laboratory in New York, USA and may not only indicate that the Standard Model of Particle Physics is incomplete but also that our universe is filled with a previously undetected type of fundamental particle. Specifically, the muon, a particle with similarities to a heavy electron, has had its relatively large wobble under scrutiny since 1999 in an experiment known as g-2 (gee-minus-two), pictured above. The result galvanizes other experimental groups around the world to confirm it, and pressures theorists to better understand it. The rate of wobble is sensitive to a strange sea of virtual particles that pop into and out of existence everywhere. The unexpected wobble rate may indicate that this sea houses virtual particles that include nearly invisible supersymmetric counterparts to known particles. If so, a nearly invisible universe of real supersymmetric particles might exist all around us.

The Hubble Space Telescope (HST) is the largest orbiting public optical telescope in history. Its 2.4 meter diameter reflecting mirror and its perch above Earth's atmosphere allow it to create exceptionally sharp images. Originally launched in 1990, HST optics were repaired to their intended accuracy in 1993 by the first of several regular servicing missions. Astronomers using HST continue to make numerous monumental scientific discoveries, including new estimates of the age and composition of our universe, previously unknown galaxies, evidence of massive black holes in the centers of galaxies, protoplanetary star systems and star forming regions, and a better understanding of physical processes in our universe. A larger Next Generation Space Telescope (NGST) may be launched as early as 2007.

Almost every object in the above photograph is a galaxy. The Coma Cluster of Galaxies pictured above is one of the densest clusters known - it contains thousands of galaxies. Each of these galaxies houses billions of stars - just as our own Milky Way Galaxy does. Although nearby when compared to most other clusters, light from the Coma Cluster still takes hundreds of millions of years to reach us. In fact, the Coma Cluster is so big it takes light millions of years just to go from one side to the other! Most galaxies in Coma and other clusters are ellipticals, while most galaxies outside of clusters are spirals. The nature of Coma's X-ray emission is still being investigated.

It is a hurricane twice the size of the Earth. It has been raging at least as long as telescopes could see it, and shows no signs of slowing. It is Jupiter's Great Red Spot, the largest swirling storm system in the Solar System. Like most astronomical phenomena, the Great Red Spot was neither predicted nor immediately understood after its discovery. Still today, details of how and why the Great Red Spot changes its shape, size, and color remain mysterious. A better understanding of the weather on Jupiter may help contribute to the better understanding of weather here on Earth. In the pictures on the left, the Hubble Space Telescope has captured Jupiter's Great Red Spot in various states over the past several years.

This famous cosmic dust cloud was imaged in infrared light by the European Space Agency's Infrared Space Observatory (ISO) satellite. The false-color picture shows the bright infrared emission from dust and molecular gas in part of the Orion star forming region surrounding the Horsehead Nebula. In visible light, the horsehead-shaped dust cloud looks dark against a background of bright glowing gas. But in this image, the interstellar infrared glow engulfs much of the horse's head. Just above and to the right of center, only the top remains crowned by a bright, newborn star. The very bright object at the lower left is the reflection nebula NGC 2023, a dense concentration of interstellar gas and dust which is also associated with newly formed stars.

Good cameras were able to obtain impressive photographs of Comet Hale-Bopp when at its brightest earlier this year. In the above photograph taken April 5th, Comet Hale-Bopp was imaged from the Indian Cove Campground in the Joshua Tree National Forest in California, USA. A flashlight was used to momentarily illuminate foreground rocks in this 30 second exposure. Comet Hale-Bopp is still visible to the unaided eye in Earth's Southern Hemisphere, with observers there reporting it to be about 4th magnitude. The comet is now passing nearly in front of the star Sirius, and shows only a slight dust tail.

Is there life beneath Europa's frozen surface? Some believe the oceans found there of carbon-enriched water are the best chance for life, outside the Earth, in our Solar System. Europa, the fourth largest moon of Jupiter, was recently discovered to have a thin oxygen atmosphere by scientists using the Hubble Space Telescope. Although Earth's atmospheric abundance of oxygen is indicative of life, astronomers speculate that Europa's oxygen arises purely from physical processes. But what an interesting coincidence! The above picture was taken by a Voyager spacecraft in 1979, but the spacecraft Galileo is currently circling Jupiter and has been photographing Europa. The first of these pictures will be released two days from today. Will they show the unexpected?

On April 12, 1981, space flight entered a new era with the first launch of Space Shuttle Columbia, shown above. NASA's Space Shuttles land like a normal plane, carry a heavy cargo, carry a large crew, make use of cheap solid fuel, and are reusable. Previous to this flight, no manned orbiting space ship had ever landed on a runway. Space Shuttles now are the flagships and the workhorses of NASA's space going rockets. For more information about NASA's Space Shuttle missions, see the NASA Space Shuttle Launches page.

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