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What is that large dark spot on Jupiter? It's the shadow of Ganymede, Jupiter's largest moon. When Jupiter's moons cross between the Jovian giant and the Sun, they created shadows just like when the Earth's moon crosses between the Earth and the Sun. Also like on Earth, if you were in a dark shadow on Jupiter, you would see a moon completely eclipse the Sun. Unlike on Earth, moon shadows occur most days on Jupiter -- what's more unusual is that a spacecraft was close enough to record one with a high-resolution image. That spacecraft, Juno, was passing so close to Jupiter in late February that nearby clouds and the dark eclipse shadow appear relatively large. Juno has made many discoveries about our Solar System's largest planet, including, recently, rapidly expanding circular auroras. Explore Your Universe: Random APOD Generator
2022-04-27
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This popular group is famous as the Leo Triplet - a gathering of three magnificent galaxies in one field of view. Crowd pleasers when imaged with even modest telescopes, these galaxies can be introduced individually as NGC 3628 (left), M66 (bottom right), and M65 (top right). All three are large spiral galaxies. They tend to look dissimilar because their galactic disks are tilted at different angles to our line of sight. NGC 3628 is seen edge-on, with obscuring dust lanes cutting across the plane of the galaxy, while the disks of M66 and M65 are both inclined enough to show off their spiral structure. Gravitational interactions between galaxies in the group have also left telltale signs, including the warped and inflated disk of NGC 3628 and the drawn out spiral arms of M66. This gorgeous deep view of the region was taken by the new VLT Survey Telescope (VST) and spans about one degree (two full moons) on the sky. The field covers over 500 thousand light-years at the trio's estimated distance of 30 million light-years.
2011-08-03
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Mercury, the closest planet to the Sun, remains the most mysterious of the Solar System's inner planets. Hiding in the Sun's glare it is a difficult target for Earth bound observers. The only spacecraft to explore Mercury close-up was Mariner 10 which executed three flybys of Mercury in 1974 and 1975, surveying approximately 45 percent of its surface. Mariner 10 deftly manuevered to photograph part of the sunlit hemisphere during each approach, passed behind the planet, and continued to image the sun-facing side as the spacecraft receded. Its highest resolution photographs recorded features approximately a mile across. A reprocessing of the Mariner 10 data has resulted in this dramatic mosaic. Like the Earth's Moon, Mercury's surface shows the scars of impact cratering - the smooth vertical band and patches visible above represent regions where no image information is available.
2001-11-24
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Why is this aurora strikingly pink? When photographing picturesque Crater Lake in Oregon, USA last month, the background sky lit up with auroras of unusual colors. Although much is known about the physical mechanisms that create auroras, accurately predicting the occurrence and colors of auroras remains a topic of investigation. Typically, it is known, the lowest auroras appear green. These occur at about 100 kilometers high and involve atmospheric oxygen atoms excited by fast moving plasma from space. The next highest auroras -- at about 200 kilometers up -- appear red, and are also emitted by resettling atmospheric oxygen. Some of the highest auroras visible -- as high as 500 kilometers up -- appear blue, and are caused by sunlight-scattering nitrogen ions. When looking from the ground through different layers of distant auroras, their colors can combine to produce unique and spectacular hues, in this case rare pink hues seen above. As Solar Maximum nears over the next two years, particle explosions from the Sun are sure to continue and likely to create even more memorable nighttime displays. Students: Browse a free online astronomy course.
2012-07-25 Brad Goldpaint (Goldpaint Photography)
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This timely, telescopic, two panel mosaic spans about 10 full moons across planet Earth's predawn skies. Recorded as the year began from Tenerife, Canary Islands, near the top of the frame are the faint coma and tail of Comet Borrelly (P/19). A comet with a seven year orbital period, Borrelly's nucleus was visited by the ion propelled spacecraft Deep Space 1 near the beginning of the 21st century. Anchoring the scene at the bottom is brilliant star Arcturus (Alpha Bootes) and Comet Catalina (C/2013 US10) a first time visitor from the Oort Cloud. Catalina's yellowish dust tail extends below and right. Buffeted by winds and storms from the Sun, the comet's complex ion tail sweeps up and toward the right, across most of the field of view. Remarkably, one of the composition's 30 second exposure subframes also caught the trail of a bright meteor, slashing toward the left between comets and bright star.
2016-01-06 Fritz Helmut Hemmerich
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joying the bright Moon's absence from early morning skies, observers around the world reported lovely displays during this year's Perseid meteor shower. As anticipated, peak rates were about one meteor per minute. Though most Perseids were faint, this bright and colorful fireball meteor flashed through skies over Japan on August 12 at 0317 JST. Ending at the upper right, the meteor's trail points down and to the left, back to the shower's radiant point between the constellations of Perseus and Cassiopeia, seen here just above the tower structure in the foreground. The Pleiades star cluster is also visible well below the meteor's trail. Perseid shower meteors can be traced to particles of dust from the tail of comet Swift-Tuttle. The comet dust impacts the atmosphere at speeds of around 60 kilometers per second. While this annual shower's peak has come and gone, Perseid meteors should still be visible over the next few nights, but at a greatly reduced rate.
2004-08-13 Katsuhiro Mouri & Shuji Kobayashi (Nagoya City Science Museum / Planetarium)
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There's nothing like it in our own Galaxy. Globular clusters as young as NGC 1850 don't exist here. Globular clusters only 40 millions of years old can still be found in the neighboring LMC galaxy, though, but perhaps none so unusual as NGC 1850. Close inspection of the above photograph will reveal two clusters. Below and right of the main group of stars known as NGC 1850A is a smaller, still younger group dubbed NGC 1850B. This cluster is made of stars only about four million years old. The large red cloud of gas surrounding the clusters may have been predominantly created by supernovae explosions of stars in the younger cluster. The red supernova remnant N57D is visible on the upper left.
2000-12-24
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Like a butterfly, a white dwarf star begins its life by casting off a cocoon that enclosed its former self. In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! The above cocoon, the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf can be seen as the bright dot near the photo's center. Our Sun will eventually become a "white dwarf butterfly", but not for another 5 billion years. The above false color image and was post-processed by Forrest Hamilton.
2001-08-05
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Lapping at rocks along the shore of the Island of Nangan, Taiwan, planet Earth, waves are infused with a subtle blue light in this sea and night skyscape. Composed of a series of long exposures made on April 16 the image captures the faint glow from Noctiluca scintillans. Also known as sea sparkles or blue tears, the marine plankton's bioluminescence is stimulated by wave motion. City lights along the coast of mainland China shine beneath low clouds in the west but stars and the faint Milky Way still fill the night above. Over the horizon the galaxy's central bulge and dark rifts seem to echo the rocks and luminous waves.
2015-04-24 Rogelio Bernal Andreo
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Ranging throughout the solar system, these pictures all have something in common. They were taken with an 8 inch diameter telescope, a size popular with amateur astronomy buffs, and slightly modified "web cam" of the type widely used to send images out over the internet. The results are clearly remarkable for such inexpensive and readily available equipment. Each sharp image was produced from 20 to 30 frames which were digitally stacked and processed using free software. Until recently, digital imaging for amateur astronomers required a specialized camera, but the advent of low-light video surveillance cameras and web cams now presents other options for relatively bright solar system objects. Want to try some unconventional web cam astronomy? Geoff Chester, Public Affairs Officer at the U.S. Naval Observatory, offers these images and an account of his own adventures from a suburban front lawn near Washington D.C.
2001-07-14 Geoff Chester