NASA Astronomy Picture of the Day 2015-11

The Milky Way Over Monument Valley

You don't have to be at Monument Valley to see the Milky Way arch across the sky like this -- but it helps. Only at Monument Valley USA would you see a picturesque foreground that includes these iconic rock peaks called buttes. Buttes are composed of hard rock left behind after water has eroded away the surrounding soft rock. In the featured image taken in 2012, the closest butte on the left and the butte to its right are known as the Mittens, while Merrick Butte can be seen just further to the right. High overhead stretches a band of diffuse light that is the central disk of our spiral Milky Way Galaxy. The band of the Milky Way can be spotted by almost anyone on almost any clear night when far enough from a city and surrounding bright lights. APOD in Spanish: On the web and Facebook

Comet ISON Being Destroyed by the Sun

Most comets don't survive a close encounter with the Sun. Two years ago this month, though, Comet ISON was thought by some to be big enough to withstand its perilous sungrazing dive. The featured video shows the drama as it was recorded by the Solar and Heliospheric Observatory (SOHO), a joint mission of ESA and NASA. As many Earthlings watched in fascination, a bright area did emerge from closest approach, but it soon faded and dispersed. It is now assumed that no large fragments of Comet C/2012 S1 (ISON) survived. Besides the comet, the active Sun is seen to eject puffs of plasma known as coronal mass ejections. Launched in 1995, sun-orbiting SOHO has become a historic device in the discovery and tracking of comets known as sungrazers. Two months ago, a comet designated SOHO 3000 was named in honor of the record 3000th comet that was discovered on SOHO images, a total that amounts to about half of all known comets. Astrophysicists: Browse 1,100+ codes in the Astrophysics Source Code Library

Seeking Venus under the Spitzkoppe Arch

What's that in the sky? Although there was much to see in this spectacular panorama taken during the early morning hours of a day in late September, the brightest object in the sky was clearly the planet Venus. In the featured image, Venus was captured actually through a natural rock bridge, itself picturesque, in Spitzkoppe, Namibia. The planet, on the left of the opening, was complemented by a silhouette of the astrophotographer on the right. Above and beyond the rock bridge were many famous icons of a dark night sky, including, from left to right, the Pleiades star cluster, the Orion Nebula, the bright star Sirius, and the Large and Small Magellanic Clouds. This week, Venus remains visible to the east in the pre-dawn sky, being complemented by Mars, which is angularly quite close.

The Great Orion Nebula M42

The Great Nebula in Orion, also known as M42, is one of the most famous nebulae in the sky. The star forming region's glowing gas clouds and hot young stars are on the right in this sharp and colorful image that includes the bluish reflection nebulae NGC 1977 and friends on the left. Located at the edge of an otherwise invisible giant molecular cloud complex, these eye-catching nebulas represent only a small fraction of this galactic neighborhood's wealth of interstellar material. Within the well-studied stellar nursery, astronomers have also identified what appear to be numerous infant planetary systems. The gorgeous skyscape spans nearly two degrees or about 45 light-years at the Orion Nebula's estimated distance of 1,500 light-years.

NGC 1333: Stellar Nursery in Perseus

NGC 1333 is seen in visible light as a reflection nebula, dominated by bluish hues characteristic of starlight reflected by interstellar dust. A mere 1,000 light-years distant toward the heroic constellation Perseus, it lies at the edge of a large, star-forming molecular cloud. This striking close-up spans about two full moons on the sky or just over 15 light-years at the estimated distance of NGC 1333. It shows details of the dusty region along with hints of contrasting red emission from Herbig-Haro objects, jets and shocked glowing gas emanating from recently formed stars. In fact, NGC 1333 contains hundreds of stars less than a million years old, most still hidden from optical telescopes by the pervasive stardust. The chaotic environment may be similar to one in which our own Sun formed over 4.5 billion years ago.

Unraveling NGC 3169

Spiral galaxy NGC 3169 appears to be unraveling in this cosmic scene, played out some 70 million light-years away just below bright star Regulus toward the faint constellation Sextans. Its beautiful spiral arms are distorted into sweeping tidal tails as NGC 3169 (top) and neighboring NGC 3166 interact gravitationally, a common fate even for bright galaxies in the local universe. In fact, drawn out stellar arcs and plumes, indications of gravitational interactions, seem rampant in the deep and colorful galaxy group photo. The picture spans 20 arc minutes, or about 400,000 light-years at the group's estimated distance, and includes smaller, dimmer NGC 3165 at bottom right. NGC 3169 is also known to shine across the spectrum from radio to X-rays, harboring an active galactic nucleus that is likely the site of a supermassive black hole.

Earth and Milky Way from Space

Since November 2000, people have been living continuously on the International Space Station. To celebrate humanity's 15th anniversary off planet Earth, consider this snapshot from space of our galaxy and our home world posing together beyond the orbital outpost. The Milky Way stretches below the curve of Earth's limb in the scene that also records a faint red, extended airglow. The galaxy's central bulge appears with starfields cut by dark rifts of obscuring interstellar dust. The picture was taken by Astronaut Scott Kelly on August 9, 2015, the 135th day of his one-year mission in space.

A Quadruple Sky Over Great Salt Lake

This was a sky to show the kids. All in all, three children, three planets, the Moon, a star, an airplane and a mom were all captured in one image near Great Salt Lake in Utah, USA in early September of 2005. Minus the airplane and the quadruple on the ground, this busy quadruple coincidence sky was visible last week all over the world. The easiest object to spot is the crescent Moon, which is easily the brightest sky orb in the featured image. Venus is the highest planet in the sky, with Jupiter to its right. The bright star Spica completes the quadruple just below Venus. The streak on the far right is an airplane. Mom is seated. Grandpa, appreciating the beauty of the moment, took the picture. This week, the pre-dawn sky shows a similar conjunction of planets.

Assembly of The International Space Station

It is the largest and most sophisticated object ever built off the Earth. It has taken numerous spaceflights and over a decade to construct. The International Space Station (ISS) is currently the premiere habitat for humans in Earth orbit, and an amalgamation of sophisticated orbiting laboratories that have examined everything from the formation of new materials and medicines created in microgravity -- to the limitations of the human body -- to the composition of the universe. This month, the ISS is celebrating 15 years of continuous human habitation. The ISS has been visited by astronauts from 15 countries, so far, and has international partners led by NASA (USA), Roscosmos (Russia), CSA (Canada), JAXA (Japan), and ESA (Europe). The featured animation shows the piece-by-piece construction of the ISS from 1998 to 2011. Spanning the length of a football field, the ISS can be seen as an unusually bright spot drifting slowly overhead by anyone who knows when and where to look.

AE Aurigae and the Flaming Star Nebula

Is star AE Aurigae on fire? No. Even though AE Aurigae is named the flaming star, the surrounding nebula IC 405 is named the Flaming Star Nebula, and the region appears to have the color of fire, there is no fire. Fire, typically defined as the rapid molecular acquisition of oxygen, happens only when sufficient oxygen is present and is not important in such high-energy, low-oxygen environments such as stars. The material that appears as smoke is mostly interstellar hydrogen, but does contain smoke-like dark filaments of carbon-rich dust grains. The bright star AE Aurigae, visible toward the right near the nebula's center, is so hot it is blue, emitting light so energetic it knocks electrons away from surrounding gas. When a proton recaptures an electron, light is emitted, as seen in the surrounding emission nebula. Pictured above, the Flaming Star nebula lies about 1,500 light years distant, spans about 5 light years, and is visible with a small telescope toward the constellation of the Charioteer (Auriga). Follow APOD on: Facebook, Google Plus, or Twitter

An Unexpected Rocket Plume over San Francisco

What is that unusual light in the sky? A common question, this particular light was not only bright but moving and expanding. It appeared just as the astrophotographer and his friend were photographing the Golden Gate Bridge in San Francisco, California against a more predictable night sky. They were not alone in seeing this unusual display -- at least hundreds of people in California reported a similar sight. The consensus of experienced sky observers was that the plume resulted from a rocket launch -- an explanation that was soon confirmed as an unpublicized test of a submarine-launched, unarmed, Trident II D5 nuclear missile. Such tests are not uncommon but do not usually occur just after sunset near a major metropolitan area -- when they are particularly noticeable to many people. Were plume images not posted to the Internet and quickly identified, such a sky spectacle might have been understood by some to be associated with more grandiose -- but incorrect -- explanations.

Kenya Morning Moon, Planets, and Taurid

On November 8, a waning crescent Moon joined the continuing parade of planets in Earth's early morning skies. Captured here from Amboseli National Park, Kenya, even the overexposed moonlight can't washout brilliant Venus though, lined up near the ecliptic plane with faint Mars and bright Jupiter above. As if Moon and planets aren't enough, a comparably bright Taurid meteor also streaks through the scene. In fact November's Taurid meteor showers have had a high proportion of bright fireballs. Apparently streaming from radiants in Taurus, the meteors are caused by our fair planet's annual passage through debris from Comet 2P/Encke. The comet's dust grains are catching up with Earth's atmosphere at a relatively low speed of about 27 kilometers per second.

The Tadpoles of IC 410

This telescopic close-up shows off the otherwise faint emission nebula IC 410. It also features two remarkable inhabitants of the cosmic pond of gas and dust below and right of center, the tadpoles of IC 410. Partly obscured by foreground dust, the nebula itself surrounds NGC 1893, a young galactic cluster of stars. Formed in the interstellar cloud a mere 4 million years ago, the intensely hot, bright cluster stars energize the glowing gas. Composed of denser cooler gas and dust, the tadpoles are around 10 light-years long and are likely sites of ongoing star formation. Sculpted by winds and radiation from the cluster stars, their heads are outlined by bright ridges of ionized gas while their tails trail away from the cluster's central region. IC 410 lies some 10,000 light-years away, toward the nebula-rich constellation Auriga.

Wright Mons on Pluto

Long shadows are cast by a low Sun across this rugged looking terrain. Captured by New Horizons, the scene is found just south of the southern tip Sputnik Planum, the informally named smooth, bright heart region of Pluto. Centered is a feature provisionally known as Wright Mons, a broad, tall mountain, about 150 kilometers across and 4 kilometers high, with a 56 kilometer wide, deep summit depression. Of course, broad mountains with central craters are found elsewhere in the Solar System, like Mauna Loa on planet Earth and Olympus Mons on Mars. In fact, New Horizons scientists announced the striking similarity of Pluto's Wright Mons, and nearby Piccard Mons, to large shield volcanoes strongly suggests the two could be giant cryovolcanoes that once erupted molten ice from the interior of the cold, distant world.

Leonids Over Monument Valley

There was a shower over Monument Valley -- but not water. Meteors. The featured image -- actually a composite of six exposures of about 30 seconds each -- was taken in 2001, a year when there was a very active Leonids shower. At that time, Earth was moving through a particularly dense swarm of sand-sized debris from Comet Tempel-Tuttle, so that meteor rates approached one visible streak per second. The meteors appear parallel because they all fall to Earth from the meteor shower radiant -- a point on the sky towards the constellation of the Lion (Leo). The yearly Leonids meteor shower peaks again this week. Although the Moon's glow should not obstruct the visibility of many meteors, this year's shower will peak with perhaps 15 meteors visible in an hour, a rate which is good but not expected to rival the 2001 Leonids. By the way -- how many meteors can you identify in the featured image?

A Blazing Fireball between the Orion Nebula and Rigel

What's happening to that meteor? A few days ago, a bright fireball was photographed from the Alps mountain range in Switzerland as it blazed across the sky. The fireball, likely from the Taurids meteor shower, was notable not only for how bright it was, but for the rare orange light it created that lingered for several minutes. Initially, the orange glow made it seem like the meteor trail was on fire. However, the orange glow, known as a persistent train, originated neither from fire nor sunlight-reflecting smoke. Rather, the persistent train's glow emanated from atoms in the Earth's atmosphere in the path of the meteor -- atoms that had an electron knocked away and emit light during reacquisition. Persistent trains often drift, so that the long 3-minute exposure actually captured the initial wind-blown displacement of these bright former ions. The featured image was acquired when trying to image the famous Orion Nebula, visible on the upper left. The bright blue star Rigel, part of the constellation of Orion, is visible to the right. This week the fireball-rich Taurids meteor shower continues to be active even though it has passed its peak, while the more active Leonids meteor shower is just peaking. Follow APOD on: Facebook, Google Plus, or Twitter

The Pelican Nebula in Gas, Dust, and Stars

The Pelican Nebula is slowly being transformed. IC 5070, the official designation, is divided from the larger North America Nebula by a molecular cloud filled with dark dust. The Pelican, however, receives much study because it is a particularly active mix of star formation and evolving gas clouds. The featured picture was produced in three specific colors -- light emitted by sulfur, hydrogen, and oxygen -- that can help us to better understand these interactions. The light from young energetic stars is slowly transforming the cold gas to hot gas, with the advancing boundary between the two, known as an ionization front, visible in bright orange on the right. Particularly dense tentacles of cold gas remain. Millions of years from now this nebula might no longer be known as the Pelican, as the balance and placement of stars and gas will surely leave something that appears completely different. Yearly Astronomy Review: APOD editor to speak in January in Philadelphia and New York City

A Sudden Jet on Comet 67P

There she blows! A dramatic demonstration of how short-lived some comet jets can be was documented in late July by the robotic Rosetta spacecraft orbiting the nucleus of Comet 67P/Churyumov-Gerasimenko. The featured animation depicts changes in the rotating comet with three illuminating stills. Although the first frame shows nothing unusual, the second frame shows a sudden strong jet shooting off the 67P's surface only 20 minutes later, while the third frame -- taken 20 minutes after that -- shows but a slight remnant of the once-active jet. As comets near the Sun, they can produce long and beautiful tails that stream across the inner Solar System. How comet jets produce these tails is a topic of research -- helped by images like this. Another recent Rosetta measurement indicates that the water on Earth could not have come from comets like 67P because of significant differences in impurities. Comet 67P spans about four kilometers, orbits the Sun between Earth and Jupiter, and has been the home for ESA's Rosetta spaceship since 2014 August. Rosetta is currently scheduled to make a slow crash onto Comet 67P's surface in late 2016.

Centaurus A

What's the closest active galaxy to planet Earth? That would be Centaurus A, only 11 million light-years distant. Spanning over 60,000 light-years, the peculiar elliptical galaxy is also known as NGC 5128. Forged in a collision of two otherwise normal galaxies, Centaurus A's fantastic jumble of young blue star clusters, pinkish star forming regions, and imposing dark dust lanes are seen here in remarkable detail. The colorful galaxy portrait is a composite of image data from space- and ground-based telescopes large and small. Near the galaxy's center, left over cosmic debris is steadily being consumed by a central black hole with a billion times the mass of the Sun. As in other active galaxies, that process generates the radio, X-ray, and gamma-ray energy radiated by Centaurus A.

Leonids and Friends

Leonid meteors rained down on planet Earth this week, the annual shower of dusty debris from the orbit of Comet 55P/Tempel-Tuttle. Leonids streak through this composite night skyview from a backyard observatory in southern Ontario. Recorded with camera fixed to a tripod, the individual frames capture the bright meteor activity throughout the night of November 16/17, about a day before the shower's very modest peak. The frames are registered to the fixed field of view, so the meteor trails are not all aligned to the background star field recorded that same evening when nebula-rich Orion stood above the southern horizon. As a result, the trails don't appear to point back to the shower's radiant in Leo, situated off the left edge of the star field frame. In fact, some trails could be of Taurid meteors, a shower also active in November, or even sporadic meteors, including a bright fireball with its reflection near the horizon.

Recycling NGC 5291

Following an ancient galaxy-galaxy collision 200 million light-years from Earth, debris from a gas-rich galaxy, NGC 5291, was flung far into intergalactic space. NGC 5291 and the likely interloper, also known as the "Seashell" galaxy, are captured near the center of this spectacular scene. The sharp, ground-based telescopic image looks toward the galaxy cluster Abell 3574 in the southern constellation Centaurus. Stretched along the 100,000 light-year long tidal tails, are clumps resembling dwarf galaxies, but lacking old stars, apparently dominated by young stars and active star forming regions. Found to be unusually rich in elements heavier than hydrogen and helium, the dwarf galaxies were likely born in intergalactic space, recycling the enriched debris from NGC 5291 itself.

Phobos: Doomed Moon of Mars

This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning color image from the robotic Mars Reconnaissance Orbiter, recorded at a resolution of about seven meters per pixel. But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon - that gravitational tidal forces are dragging it down. A recent analysis of the long grooves indicates that they may result from global stretching caused by tides -- the differing force of Mars' gravity on different sides of Phobos. These grooves may then be an early phase in the disintegration of Phobos into a ring of debris around Mars. Follow APOD on: Facebook, Google Plus, or Twitter

A 212-Hour Exposure of Orion

The constellation of Orion is much more than three stars in a row. It is a direction in space that is rich with impressive nebulas. To better appreciate this well-known swath of sky, an extremely long exposure was taken over many clear nights in 2013 and 2014. After 212 hours of camera time and an additional year of processing, the featured 1400-exposure collage spanning over 40 times the angular diameter of the Moon emerged. Of the many interesting details that have become visible, one that particularly draws the eye is Barnard's Loop, the bright red circular filament arcing down from the middle. The Rosette Nebula is not the giant red nebula near the top of the image -- that is a larger but lesser known nebula known as Lambda Orionis. The Rosette Nebula is visible, though: it is the red and white nebula on the upper left. The bright orange star just above the frame center is Betelgeuse, while the bright blue star on the lower right is Rigel. Other famous nebulas visible include the Witch Head Nebula, the Flame Nebula, the Fox Fur Nebula, and, if you know just where to look, the comparatively small Horsehead Nebula. About those famous three stars that cross the belt of Orion the Hunter -- in this busy frame they can be hard to locate, but a discerning eye will find them just below and to the right of the image center.

Aurora over Clouds

Auroras usually occur high above the clouds. The auroral glow is created when fast-moving particles ejected from the Sun impact the Earth's magnetosphere, from which charged particles spiral along the Earth's magnetic field to strike atoms and molecules high in the Earth's atmosphere. An oxygen atom, for example, will glow in the green light commonly emitted by an aurora after being energized by such a collision. The lowest part of an aurora will typically occur at 100 kilometers up, while most clouds usually exist only below about 10 kilometers. The relative heights of clouds and auroras are shown clearly in the featured picture from Dyrholaey, Iceland. There, a determined astrophotographer withstood high winds and initially overcast skies in an attempt to capture aurora over a picturesque lighthouse, only to take, by chance, the featured picture along the way.

Unusual Pits Discovered on Pluto

Why are there unusual pits on Pluto? The indentations were discovered during the New Horizons spacecraft's flyby of the dwarf planet in July. The largest pits span a kilometer across and dip tens of meters into a lake of frozen nitrogen, a lake that sprawls across Sputnik Planum, part of the famous light-colored heart-shaped region named Tombaugh Regio. Although most pits in the Solar System are created by impact craters, these depressions look different -- many are similarly sized, densely packed, and aligned. Rather, it is thought that something has caused these specific areas of ice to sublimate and evaporate away. In fact, the lack of overlying impact craters indicates these pits formed relatively recently. Even though the robotic New Horizons is now off to a new destination, it continues to beam back to Earth new images and data from its dramatic encounter with Pluto.

Planets of the Morning

Planet Earth's horizon stretches across this recent Solar System group portrait, seen from the southern hemisphere's Las Campanas Observatory. Taken before dawn it traces the ecliptic with a line-up familiar to November's early morning risers. Toward the east are bright planets Venus, Mars, and Jupiter as well as Regulus, alpha star of the constellation Leo. Of course the planets are immersed in the faint glow of zodiacal light, visible from the dark site rising at an angle from the horizon. Sometimes known as the false dawn, it's no accident the zodiacal light and planets both lie along the ecliptic. Formed in the flattened protoplanetary disk, the Solar System's planets all orbit near the ecliptic plane, while dust near the plane scatters sunlight, the source of the faint zodiacal glow.

Gravity's Grin

Albert Einstein's general theory of relativity, published 100 years ago this month, predicted the phenomenon of gravitational lensing. And that's what gives these distant galaxies such a whimsical appearance, seen through the looking glass of X-ray and optical image data from the Chandra and Hubble space telescopes. Nicknamed the Cheshire Cat galaxy group, the group's two large elliptical galaxies are suggestively framed by arcs. The arcs are optical images of distant background galaxies lensed by the foreground group's total distribution of gravitational mass dominated by dark matter. In fact the two large elliptical "eye" galaxies represent the brightest members of their own galaxy groups which are merging. Their relative collisional speed of nearly 1,350 kilometers/second heats gas to millions of degrees producing the X-ray glow shown in purple hues. Curiouser about galaxy group mergers? The Cheshire Cat group grins in the constellation Ursa Major, some 4.6 billion light-years away.

Rosetta and Comet Outbound

Not a bright comet, 67P/Churyumov-Gerasimenko now sweeps slowly through planet Earth's predawn skies near the line-up of planets along the ecliptic. Still, this composite of telescopic images follows the comet's progress as it moves away from the Sun beyond the orbit of Mars, from late September (left) through late November (far right). Its faint but extensive coma and tails are viewed against the colorful background of stars near the eastern edge of the constellation Leo. A year ago, before its perihelion passage, the comet was less active, though. Then the Rosetta mission's lander Philae made its historic landing, touching down on the surface of the comet's nucleus.

Dark Sand Cascades on Mars

They might look like trees on Mars, but they're not. Groups of dark brown streaks have been photographed by the Mars Reconnaissance Orbiter on melting pinkish sand dunes covered with light frost. The above image was taken in 2008 April near the North Pole of Mars. At that time, dark sand on the interior of Martian sand dunes became more and more visible as the spring Sun melted the lighter carbon dioxide ice. When occurring near the top of a dune, dark sand may cascade down the dune leaving dark surface streaks -- streaks that might appear at first to be trees standing in front of the lighter regions, but cast no shadows. Objects about 25 centimeters across are resolved on this image spanning about one kilometer. Close ups of some parts of this image show billowing plumes indicating that the sand slides were occurring even while the image was being taken.

In the Center of Spiral Galaxy NGC 3521

This huge swirling mass of stars, gas, and dust occurs near the center of a nearby spiral galaxy. Gorgeous spiral NGC 3521 is a mere 35 million light-years distant, toward the constellation Leo. Spanning some 50,000 light-years, its central region is shown in this dramatic image, constructed from data from the Hubble Space Telescope. The close-up view highlights this galaxy's characteristic multiple, patchy, irregular spiral arms laced with dust and clusters of young, blue stars. In contrast, many other spirals exhibit grand, sweeping arms. A relatively bright galaxy in planet Earth's sky, NGC 3521 is easily visible in small telescopes, but often overlooked by amateur imagers in favor of other Leo spiral galaxies, like M65 and M66.

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