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Explanation: Sungrazing Comet ISON reached perihelion, its closest approach to the Sun, yesterday, November 28, at 18:45 UT. The comet passed just over 1 million kilometers above the solar surface, a distance less than the diameter of the Sun. These two panels follow ISON before (right) and after its close approach, imaged by the LASCO instrument onboard the Sun staring SOHO spacecraft. Overwhelming sunlight is blocked by LASCO's central occulting disk with a white circle indicating the Sun's positon and scale. The bright comet is seen along its path at the bottom of the before panel, but something much fainter...

Comet Ison was severely battered in its encounter with the Sun, and largely destroyed. Telescopes saw the giant ball of ice and dust disappear behind the star, but only a dull streamer emerge. Astronomers continued to search for the object, but it eventually became clear that the much vaunted "Comet of the Century" had gone out with a whimper. Despite its great size, Ison was probably torn apart in the immense heat and tidal forces so close to the Sun.

NASA will hold a live Google+ hangout on Thursday (Nov. 28) to webcast the solar passage of Comet ISON as it whips around the sun. The webcast will begin at 1 p.m. EST (1800 GMT) and last until 3:30 p.m. EST (2030 GMT). You will be able to watch the webcast live in the window below at the start time. LATEST STORY: Comet ISON Makes Thanksgiving Day Sun Flyby Today: Watch It Live Online

Explanation: South of the large star-forming region known as the Orion Nebula, lies bright blue reflection nebula NGC 1999. At the edge of the Orion molecular cloud complex some 1,500 light-years distant, NGC 1999's illumination is provided by the embedded variable star V380 Orionis. That nebula is marked with a dark sideways T-shape near center in this cosmic vista that spans about 10 light-years. The dark shape was once assumed to be an obscuring dust cloud seen in silhouette against the bright reflection nebula. But recent infrared images indicate the shape is likely a hole blown through the nebula itself...

You may have thought that NASA's Kepler spacecraft was finished. Well, think again. A repurposed Kepler Space telescope may soon start searching the sky again. A new mission concept, dubbed K2, would continue Kepler's search for other worlds, and introduce new opportunities to observe star clusters, young and old stars, active galaxies and supernovae. In May, the Kepler spacecraft lost the second of four gyroscope-like reaction wheels, which are used to precisely point the spacecraft, ending new data collection for the original mission. The spacecraft required three functioning wheels to maintain the precision pointing necessary to detect the signal of...

Experts gives Comet ISON only a 30 percent chance of surviving its crucial Thanksgiving Day encounter with the sun. Or maybe 40 percent. Whatever the odds, scientists say what some have called the "comet of the century" has already lived up to their expectations. But will it live up to yours? We should find out on Thursday, during a series of webcasts you can tune into while waiting for Thanksgiving dinner. You won't be able to see the comet flaring in the sky on Thursday. Instead, leave the comet-watching job to NASA's sun-watching probes, including the Solar Dynamics Observatory, the...

Explanation: Will Comet ISON survive tomorrow's close encounter with the Sun? Approaching to within a solar diameter of the Sun's surface, the fate of one of the most unusual comets of modern times will finally be determined. The comet could shed a great amount of ice and dust into a developing tail -- or break apart completely. Unfortunately, the closer Comet ISON gets to the Sun, the harder it has been for conventional telescopes to see the brightening comet in the glare of the morning Sun. Pictured in the above short time lapse video, Comet ISON was captured rising over...

Explanation: One might say this was a bell weather day for the Sierra Nevada mountains. In January, just as the Sun was setting above the district of Albayzín in Grenada, Spain, a huge cloud appeared as a bell capping the Veleta peak. Such a Cap cloud is formed by air forced upwards by a mountain peak, with the air then cooling, saturating with moisture, and finally having its molecular water condense into cloud droplets. Such a bell-shaped cloud structure is unusual as air typically moves horizontally, making most clouds nearly flat across at the bottom. Vertical waves can also give...

Explanation: How far away is spiral galaxy NGC 4921? Although presently estimated to be about 310 million light years distant, a more precise determination could be coupled with its known recession speed to help humanity better calibrate the expansion rate of the entire visible universe. Toward this goal, several images were taken by the Hubble Space Telescope in order to help identify key stellar distance markers known as Cepheid variable stars. Since NGC 4921 is a member of the Coma Cluster of Galaxies, refining its distance would also allow a better distance determination to one of the largest nearby clusters...

Explanation: Comet Hale-Bopp, the Great Comet of 1997, was quite a sight. In the above photograph taken on 1997 April 6, Comet Hale-Bopp was imaged from the Indian Cove Campground in the Joshua Tree National Park in California, USA. A flashlight was used to momentarily illuminate foreground rocks in this six minute exposure. An impressive blue ion tail was visible above a sunlight-reflecting white dust tail. Comet Hale-Bopp remained visible to the unaided eye for over a year before returning to the outer Solar System and fading. As Comet ISON approaches the Sun this week, sky enthusiasts around the Earth...

Explanation: Still intact, on November 21 Comet ISON (C/2012 S1) swept into this animated field of view (left) from the HI-1 camera on the STEREO-A spacecraft. The camera has also captured periodic Comet Encke, Mercury, and Earth, with the Sun cropped out of the frame at the right, the source of the billowing solar wind. From STEREO's perspective in interplanetary space, planet Earth is actually the most distant of the group, seen in its orbit beyond the Sun. Mercury is closest, but both planets are still so bright they create sharp vertical lines in the camera's detector. Both comets clearly...

Explanation: An astronomical trip from the California Nebula to the Pleiades star cluster would cover just over 12 degrees across planet Earth's night sky. That's equivalent to the angular extent of 25 Full Moons, as your telescope sweeps past the borders of the constellations Perseus and Taurus. This wide and deep mosaic image of the region explores the cosmic landscape's dusty nebulae and colors otherwise too faint for your eye to see. On the left, cataloged as NGC 1499, the California Nebula does have a familiar shape, though its coastline is actually over 60 light-years long and lies about 1,500...

Explanation: Star trails arc above a moonlit beach and jetty in this serene sea and night skyscape. Captured on November 19, the single time exposure looks south down the Atlantic coast from Cape Cod, Massachusetts, USA. But the longest and brightest trail is a Minotaur 1 rocket, a stage separation and exhaust plume visible along the rocket's fiery path toward low Earth orbit. The multi-stage Minotaur was launched from the Mid-Atlantic Regional Spaceport at NASA's Wallops Flight Facility at 8:15 pm Eastern Time in Virginia, about 400 miles away. On board were a remarkable 29 satellites destined for low Earth...

An exploded star some 3.8 billion light-years away is forcing scientists to overhaul much of what they thought they knew about gamma-ray bursts – intense blasts of radiation triggered, in this case, by a star tens of times more massive than the sun that exhausted its nuclear fuel, exploded, then collapsed to form a black hole. Last April, gamma rays from the blast struck detectors in gamma-ray observatories orbiting Earth, triggering a frenzy of space- and ground-based observations. Many of them fly in the face of explanations researchers have developed during the past 30 years for the processes driving the...

Explanation: What are black hole jets made of? Many black holes in stellar systems are surely surrounded by disks of gas and plasma gravitationally pulled from a close binary star companion. Some of this material, after approaching the black hole, ends up being expelled from the star system in powerful jets emanating from the poles of the spinning black hole. Recent evidence indicates that these jets are composed not only electrons and protons, but also the nuclei of heavy elements such as iron and nickel. The discovery was made in system 4U1630-47 using CSIRO’s Compact Array of radio telescopes in...

Explanation: Stars, like bees, swarm around the center of bright globular cluster M15. This ball of over 100,000 stars is a relic from the early years of our Galaxy, and continues to orbit the Milky Way's center. M15, one of about 170 globular clusters remaining, is noted for being easily visible with only binoculars, having at its center one of the densest concentrations of stars known, and containing a high abundance of variable stars and pulsars. Released only recently, this sharp image taken by the Earth-orbiting Hubble Space Telescope spans about 120 light years. It shows the dramatic increase in...

Explanation: What's happening in the sky? On this cold winter night in Iceland, quite a lot. First, in the foreground, lies the largest glacier in Iceland: Vatnajokull. On the far left, bright green auroras appear to emanate from the glacier as if it was a volcano. Aurora light is reflected by the foreground lake Jökulsárlón. On the far right is a long and unusual lenticular cloud tinged with green light emitted from another aurora well behind it. Just above this lenticular cloud are unusual iridescent lenticular clouds displaying a broad spectral range of colors. Far beyond the lenticular is the...

Comet ISON could break up into itty-bitty pieces long before it gets closer to the Sun, selfishly denying us all the opportunity to see it shine brightly in the night sky. The comet is currently visible in the predawn sky, but it may not be there for long if astroboffins from the Max Planck Institute for Solar System Research and the Astronomical Institute at Ludwig Maximilian University are right. In a post on the International Astronomical Union's Comets and Asteroids Facebook page, the scientists reported spotting "wings" coming from the comet, which may suggest that the nucleus has broken up....

Explanation: Comet McNaught, the Great Comet of 2007, grew a spectacularly long and filamentary tail. The magnificent tail spread across the sky and was visible for several days to Southern Hemisphere observers just after sunset. The amazing tail showed its greatest extent on long-duration, wide-angle camera exposures. During some times, just the tail itself estimated to attain a peak brightness of magnitude -5 (minus five), was caught by the comet's discoverer in the above image just after sunset in January 2007 from Siding Spring Observatory in Australia. Comet McNaught, the brightest comet in decades, then faded as it moved further...

Explanation: Falling through planet Earth's predawn skies toward its close encounter with the Sun on November 28, Comet ISON is coming to life. The much anticipated comet has now been reported to have substantially increased in activity, surging to naked-eye visibility for dark sites and sprouting a more complex tail. ISON's tail stretches over two degrees in this telephoto skyview from southern Kenya, captured on the morning of November 14. Shown in two panels, the enlarged negative version on the right makes details of the long tail easier to trace, including the tail's separated filaments toward the top of the...