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The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Recently, several geologic processes have been identified in the canyon. The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s. News: Mars closest in over 50,000 years on Wednesday
2003-08-24
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Does gravity have a magnetic counterpart? Spin any electric charge and you get a magnetic field. Spin any mass and, according to Einstein, you should get a very slight effect that acts something like magnetism. This effect is expected to be so small that it is beyond practical experience and ground laboratory measurement. In a bold attempt to directly measure gravitomagnetism, NASA launched in 2004 the smoothest spheres ever manufactured into space to see how they spin. These four spheres, each roughly the size of a ping-pong ball, are the key to the ultra-precise gyroscopes at the core of Gravity Probe B. Last week, after accounting for persistent background signals, the results were announced -- the gyroscopes precessed at a rate consistent with the gravitational predictions of Einstein's General Theory of Relativity. The results, which bolster existing findings, may have untold long term benefits as well as shorter term benefits such as better clocks and global positioning trackers.
2011-05-10
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South of Antares, in the tail of the nebula-rich constellation Scorpius, lies emission nebula IC 4628. Nearby hot, massive stars, millions of years young, irradiate the nebula with invisible ultraviolet light, stripping electrons from atoms. The electrons eventually recombine with the atoms to produce the visible nebular glow, dominated by the red emission of hydrogen. At an estimated distance of 6,000 light-years, the region shown is about 250 light-years across, spanning over three full moons on the sky. The nebula is also cataloged as Gum 56 for Australian astronomer Colin Stanley Gum, but seafood-loving deep sky-enthusiasts might know this cosmic cloud as the Prawn Nebula. The graceful color image is a new astronomical composition taken over several nights in April from Rio Hurtado, Chile.
2023-07-26Daniel Stern
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This is the mess that is left when a star explodes. The Crab Nebula, the result of a supernova seen in 1054 AD, is filled with mysterious filaments. The filaments are not only tremendously complex, but appear to have less mass than expelled in the original supernova and a higher speed than expected from a free explosion. The featured image, taken by the Hubble Space Telescope, is presented in three colors chosen for scientific interest. The Crab Nebula spans about 10 light-years. In the nebula's very center lies a pulsar: a neutron star as massive as the Sun but with only the size of a small town. The Crab Pulsar rotates about 30 times each second. Discovery + Outreach: Graduate student research position open for APOD
2023-01-15
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Comet-like plumes are blowing over the volcanic peaks of Mount Etna in this wintry mountain-and-skyscape from planet Earth. The stacked and blended combination of individual exposures recorded during the cold night of January 23, also capture naked-eye Comet ZTF just above Etna's snowy slopes. Of course the effect of increasing sunlight on the comet's nucleus and the solar wind are responsible for the comet's greenish coma and broad dusty tail. This weekend Comet ZTF is dashing across northern skies between north star Polaris and the Big Dipper. From a dark site you can only just spot it as a fuzzy patch though. That's still an impressive achievement if you consider you are gazing at a visitor from the distant Oort cloud with your own eyes. But binoculars or a small telescope will make for an even more enjoyable view of this Comet ZTF in the coming days. Comet ZTF Gallery: Notable Submissions to APOD
2023-01-28Dario Giannobile
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Most of us watch the Moon at night. But the Moon spends nearly as many daylight hours above our horizon, though in bright daytime skies the lunar disk looks pale and can be a little harder to see. Of course in daytime skies the Moon also appears to cycle through its phases, shining by reflected sunlight as it orbits our fair planet. For daytime moonwatchers, the Moon is probably easier to spot when the visible sunlit portion of the lunar disk is large and waxing following first quarter or waning approaching its third quarter phase. And though it might look unusual, a daytime moon is often seen even in urban skies. Captured here in a telephoto snapshot taken on March 12, a waxing daytime Moon is aligned near the edge of a popular observation deck that overlooks New York City's borough of Manahattan.
2025-04-12Jordi Coy
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After a star like the Sun completes fusion in its core, it throws off its outer layers in a brief, beautiful cosmic display called a planetary nebula. NGC 3242 is such a planetary nebula, with the stellar remnant white dwarf star visible at the center. This nebula is sometimes called The Ghost of Jupiter for its faint, but similar appearance to our solar system's ruling gas giant planet. NGC 3242 is light-years across however, and much farther away than the measly 40 light-minutes distance to Jupiter. In fact, while watching this ghostly nebula expand over time, astronomers have estimated the distance to NGC 3242 to be about 1,400 light-years. The red FLIERs visible near the edges of the nebula are still a bit mysterious, though.
2005-10-29
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Most photographs don't adequately portray the magnificence of the Sun's corona. Seeing the corona first-hand during a total solar eclipse is best. The human eye can adapt to see features and extent that photographic film usually cannot. Welcome, however, to the digital age. The above picture is a combination of thirty-three photographs that were digitally processed to highlight faint features of a total eclipse that occurred in March of 2006. The images of the Sun's corona were digitally altered to enhance dim, outlying waves and filaments. Shadow seekers need not fret, though, since as yet there is no way that digital image processing can mimic the fun involved in experiencing a total solar eclipse. Last week, a spectacular total solar eclipse occurred over southern Asia, while the The next total solar eclipse will be visible from the South Pacific on 2010 July 11. Note: An APOD editor will review great space images this Saturday night at Ft. Wilkins, Michigan.
2009-07-26Koen van Gorp
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Towering pillars of cold gas and dark dust adorn the center star forming region of Sharpless 171. An open cluster of stars is forming there from the gas in cold molecular clouds. As energetic light emitted by young massive stars boils away the opaque dust, the region fragments and picturesque pillars of the remnant gas and dust form and slowly evaporate. The energetic light also illuminates the surrounding hydrogen gas, energize it to glow as a red emission nebula. Pictured above is the active central region of the Sharpless 171 greater emission nebula. Sharpless 171 incorporates NGC 7822 and the active region Cederblad 214, much of which is imaged above. The area above spans about 20 light years, lies about 3,000 light years away, and can be seen with a telescope toward the northern constellation of the King of Ethiopia (Cepheus).
2005-09-27
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September's equinox arrives today at 0905 UT. As the Sun crosses the celestial equator heading south, spring begins in the southern hemisphere and autumn in the north. And though the seasonal connection is still puzzling, both spring and autumn bring an increase in geomagnetic storms. So as northern nights grow longer, the equinox also heralds the arrival of a good season for viewing aurora. Recorded earlier this month, these curtains of September's shimmering green light sprawl across a gorgeous night skyscape. In the foreground lies Hidden Lake Territorial Park near Yellowknife, Northwest Territories, Canada. Calm water reflects the aurora, with bright star trails peering through the mesmerizing sky glow. Of course, shining at altitudes of 100 kilometers or so, planet Earth's auroras are visible from space.
2011-09-23Yuichi Takasaka
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Just possibly, a new comet may become bright enough to see without binoculars later this month. Comet C/1999 S4 LINEAR is rapidly approaching both the Earth and the Sun from the outer Solar System, and should be at its brightest around 2000 July 25 in the early evening sky of northern observers. The comet was discovered by chance by project LINEAR last September. The above time-lapse sequence of Comet LINEAR was taken on 2000 July 2 from Arizona and shows the comet's movement over only 19 minutes. Although Comet LINEAR's positions will be known quite accurately, the comet's future brightness and tail length can only be guessed, and it is quite possible that neither will become very impressive.
2000-07-04Wil Milan
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What causes gamma-ray bursts? The most energetic type of explosions known in the cosmos has been an enigma since discovered over 30 years ago. It now appears that there may not be one unique type of progenitor. Long duration gamma-ray bursts (GRBs) have been localized, over the past few years, to blue regions in the universe rich in star formation. Massive young stars nearing the end of their short lives commonly explode in these regions. Astronomers associate these long duration GRBs, that can last from seconds to minutes, with a type of stellar explosion common in young massive stars. Over the past few months, short duration GRBs have finally been localized and found to occur in different types of regions -- not only blue regions rich in star formation. Many astronomers therefore now theorize that short GRBs, which typically last less than one second, are the result of a different progenitor process than long GRBs. A leading model is that a short GRB will occur when a neutron star either impacts another neutron star or a black hole. Such collisions may occur well after star-forming regions have otherwise burned out. Pictured in the above illustration, two energized neutrons stars finally approach each other in their orbits, a death spiral that might end with a short GRB.
2005-10-17
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The bright edge of planet Earth fades into the darkness of space in the background of this view of Jules Verne on an extraordinary voyage. Snapped last Monday, the picture shows the European Space Agency's Automated Transfer Vehicle (ATV), named for the 19th century science fiction writer and visionary, rehearsing its autonomous docking capability on approach to the International Space Station. Using a laser guided rendezvous system, the Jules Verne docked smoothly and safely with the orbiting station on Thursday, delivering 7,500 pounds of equipment, supplies, and fuel. The cylindrical body of the robotic cargo spacecraft is 4.5 meters in diameter and 10.3 meters long, with solar arrays spanning 22.3 meters. Jules Verne is scheduled to remain docked until August, providing a reboost for the space station before the ATV is deorbited.
2008-04-05
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The Great Nebula in Orion, an immense, nearby starbirth region, is arguably the most famous of all astronomical nebulae. The Orion Nebula, also known as M42, is shown above through ultraviolet and blue filters augmented with three exact colors specifically emitted by hydrogen, oxygen, and sulfur. In addition to housing a bright open cluster of stars known as the Trapezium, the Orion Nebula contains many stellar nurseries. These nurseries contain glowing gas, hot young stars, proplyds, and stellar jets spewing material at high speeds. Many of the filamentary structures visible in this image are actually shock waves - fronts where fast moving material encounters slow moving gas. The Orion Nebula spans about 40 light years and is located about 1500 light years away in the same spiral arm of our Galaxy as the Sun.
2004-07-13WFI, MPG/ESO 2.2-m Telescope, La Silla, ESO
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How much of planet Earth is made of water? Very little, actually. Although oceans of water cover about 70 percent of Earth's surface, these oceans are shallow compared to the Earth's radius. The featured illustration shows what would happen if all of the water on or near the surface of the Earth were bunched up into a ball. The radius of this ball would be only about 700 kilometers, less than half the radius of the Earth's Moon, and slightly smaller than Saturn's moon Rhea which, like many moons in our outer Solar System, is mostly water ice. The next smallest ball depicts all of Earth's liquid fresh water, while the tiniest ball shows the volume of all of Earth's fresh-water lakes and rivers. How any of this water came to be on the Earth and whether any significant amount is trapped far beneath Earth's surface remain topics of research.
2025-09-07
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Also known as the Moon's ashen glow, Earthshine is Earthlight illuminating the Moon's night side. Taken on Nowruz, the March 20 equinox, from Esfahan, Iran, planet Earth, this telescopic image captures strong Earthshine from an old Moon. The darker earthlit disk is in the arms of a bright sunlit crescent. But the view from the Moon would have been enchanting too. When the Moon appears in Earth's sky as a slender crescent, a dazzlingly bright, nearly full Earth would be seen from the lunar surface. The Earth's brightness due to reflected sunlight is known to be strongly influenced by cloud cover. Still, a description of Earthshine, in terms of sunlight reflected by Earth's oceans in turn illuminating the Moon's dark surface, was written 500 years ago by Leonardo da Vinci.
2012-03-24M. Taha Ghouchkanlu
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What are those colorful rings around the Moon? A corona. Rings like this will sometimes appear when the Moon is seen through thin clouds. The effect is created by the quantum mechanical diffraction of light around individual, similarly-sized water droplets in an intervening but mostly-transparent cloud. Since light of different colors has different wavelengths, each color diffracts differently. Lunar Coronae are one of the few quantum mechanical color effects that can be easily seen with the unaided eye. The featured lunar corona was captured around full Moon above Turin, Italy in 2014. Similar coronae that form around the Sun are usually harder to see because of the Sun's great brightness.
2019-09-16Giorgia Hofer (Cortina Astronomical Association)
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How prevalent was water on Mars? Results from the Spirit rover now indicate that Gusev crater likely had a wet past, a result that comes shortly after Spirit's twin rover Opportunity uncovered clear evidence of past water at Meridiani Planum on the other side of Mars. Evidence uncovered by Spirit and released last week focussed on a large rock of unusual shape nicknamed Humphrey, shown above near the image bottom. Detailed inspection of the rock revealed a bright material filling internal cracks. Such material may have crystallized from water trickling through the volcanic rock. The amount of Mars once covered by ancient water remains unknown, as both rovers landed in regions thought likely to once be underwater. Spirit continues to roll across Mars, recently passing the 300-meter mark on its way to Bonneville crater.
2004-03-10
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What are these Earthlings trying to tell us? The above message was broadcast from Earth towards the globular star cluster M13 in 1974. During the dedication of the Arecibo Observatory - still the largest radio telescope in the world - a string of 1's and 0's representing the above diagram was sent. This attempt at extraterrestrial communication was mostly ceremonial - humanity regularly broadcasts radio and television signals out into space accidentally. Even were this message received, M13 is so far away we would have to wait almost 50,000 years to hear an answer. The above message gives a few simple facts about humanity and its knowledge: from left to right are numbers from one to ten, atoms including hydrogen and carbon, some interesting molecules, DNA, a human with description, basics of our Solar System, and basics of the sending telescope. Several searches for extraterrestrial intelligence are currently underway, including one where you can use your own home computer.
2005-03-13
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June's Full Moon (full phase on June 13, 0411 UT) is traditionally known as the Strawberry Moon or Rose Moon. Of course those names might also describe the appearance of this Full Moon, rising last month over the small Swedish village of Marieby. The Moon looks large in the image because the scene was captured with a long focal length lens from a place about 8 kilometers from the foreground houses. But just by eye a Full Moon rising, even on Friday the 13th, will appear to loom impossibly large near the horizon. That effect has long been recognized as the Moon Illusion. Unlike the magnification provided by a telescope or telephoto lens, the cause of the Moon illusion is still poorly understood and not explained by atmospheric optical effects, such as scattering and refraction. Those effects do produce the Moon's blushing color and ragged edge also seen in the photograph.
2014-06-13Göran Strand