NASA Astronomy Picture of the Day 2014-9

Airglow Ripples over Tibet

Why would the sky look like a giant target? Airglow. Following a giant thunderstorm over Bangladesh in late April, giant circular ripples of glowing air appeared over Tibet, China, as pictured above. The unusual pattern is created by atmospheric gravity waves, waves of alternating air pressure that can grow with height as the air thins, in this case about 90 kilometers up. Unlike auroras powered by collisions with energetic charged particles and seen at high latitudes, airglow is due to chemiluminescence, the production of light in a chemical reaction. More typically seen near the horizon, airglow keeps the night sky from ever being completely dark. Now Available: APOD 2015 Wall Calendars

Holometer: A Microscope into Space and Time

How different are space and time at very small scales? To explore the unfamiliar domain of the miniscule Planck scale -- where normally unnoticeable quantum effects might become dominant -- a newly developed instrument called the Fermilab Holometer has begun operating at the Fermi National Accelerator Laboratory (Fermilab) near Chicago, Illinois, USA. The instrument seeks to determine if slight but simultaneous jiggles of a mirror in two directions expose a fundamental type of holographic noise that always exceeds a minimum amount. Pictured above is one of the end mirrors of a Holometer prototype. Although the discovery of holographic noise would surely be groundbreaking, the dependence of such noise on a specific laboratory length scale would surprise some spacetime enthusiasts. One reason for this is the Lorentz Invariance postulate of Einstein's special relativity, which states that all length scales should appear contracted to a relatively moving observer -- even the diminutive Planck length. Still, the experiment is unique and many are curious what the results will show. Astrophysicists: Browse 900+ codes in the Astrophysics Source Code Library

M6: The Butterfly Cluster

To some, the outline of the open cluster of stars M6 resembles a butterfly. M6, also known as NGC 6405, spans about 20 light-years and lies about 2,000 light years distant. M6, pictured above, can best be seen in a dark sky with binoculars towards the constellation of the Scorpion (Scorpius), coving about as much of the sky as the full moon. Like other open clusters, M6 is composed predominantly of young blue stars, although the brightest star is nearly orange. M6 is estimated to be about 100 million years old. Determining the distance to clusters like M6 helps astronomers calibrate the distance scale of the universe. Now Available: APOD 2015 Wall Calendars

Cloud, Clusters and Comet Siding Spring

On October 19th, a good place to watch Comet Siding Spring will be from Mars. Then, this inbound visitor (C/2013 A1) to the inner solar system, discovered in January 2013 by Robert McNaught at Australia's Siding Spring Observatory, will pass within 132,000 kilometers of the Red Planet. That's a near miss, equivalent to just over 1/3 the Earth-Moon distance. Great views of the comet for denizens of planet Earth's southern hemisphere are possible now, though. This telescopic snapshot from August 29 captured the comet's whitish coma and arcing dust tail sweeping through southern skies. The fabulous field of view includes, the Small Magellanic Cloud and globular star clusters 47 Tucanae (right) and NGC 362 (upper left). Worried about all those spacecraft in Martian orbit? Streaking dust particles from the comet could pose a danger and controllers plan to position Mars orbiters on the opposite side of the planet during the comet's close flyby.

A Sagittarius Starscape

This rich starscape spans nearly 7 degrees on the sky, toward the Sagittarius spiral arm and the center of our Milky Way galaxy. A telescopic mosaic, it features well-known bright nebulae and star clusters cataloged by 18th century cosmic tourist Charles Messier. Still popular stops for skygazers M16, the Eagle (far right), and M17, the Swan (near center) nebulae are the brightest star-forming emission regions. With wingspans of 100 light-years or so, they shine with the telltale reddish glow of hydrogen atoms from over 5,000 light-years away. Colorful open star cluster M25 near the upper left edge of the scene is closer, a mere 2,000 light-years distant and about 20 light-years across. M24, also known as the Sagittarius Star Cloud, crowds in just left of center along the bottom of the frame, fainter and more distant Milky Way stars seen through a narrow window in obscuring fields of interstellar dust.

Moonbow Beach

Like a rainbow at night, a beautiful moonbow shines above the western horizon in this deserted beach scene from Molokai Island, Hawaii, USA, planet Earth. Captured last June 17 in early morning hours, the lights along the horizon are from Honolulu and cities on the island of Oahu some 30 miles away. So where was the Moon? A rainbow is produced by sunlight internally reflected in rain drops from the direction opposite the Sun back toward the observer. As the light passes from air to water and back to air again, longer wavelengths are refracted (bent) less than shorter ones resulting in the separation of colors. And so the moonbow is produced as raindrops reflect moonlight from the direction opposite the Moon. That puts the Moon directly behind the photographer, still low and rising over the eastern horizon, a few days past its full phase.

Full Moon Silhouettes

Have you ever watched the Moon rise? The slow rise of a nearly full moon over a clear horizon can be an impressive sight. One impressive moonrise was imaged in early 2013 over Mount Victoria Lookout in Wellington, New Zealand. With detailed planning, an industrious astrophotographer placed a camera about two kilometers away and pointed it across the lookout to where the Moon would surely soon be making its nightly debut. The above single shot sequence is unedited and shown in real time -- it is not a time lapse. People on Mount Victoria Lookout can be seen in silhouette themselves admiring the dawn of Earth's largest satellite. Seeing a moonrise yourself is not difficult: it happens every day, although only half the time at night. Each day the Moon rises about fifty minutes later than the previous day, with a full moon always rising at sunset. A good time to see a moonrise will occur at sunset on Tuesday as the Moon's relative closeness to Earth during a full phase -- called a supermoon -- will cause it to appear slightly larger and brighter than usual.

Super Moon vs. Micro Moon

What is so super about tomorrow's supermoon? Tomorrow, a full moon will occur that appears slightly larger and brighter than usual. The reason is that the Moon's fully illuminated phase occurs within a short time from perigee - when the Moon is its closest to the Earth in its elliptical orbit. Although the precise conditions that define a supermoon vary, given one definition, tomorrow's will be the third supermoon of the year -- and the third consecutive month that a supermoon occurs. One reason supermoons are popular is because they are so easy to see -- just go outside and sunset and watch an impressive full moon rise! Since perigee actually occurs today, tonight's sunset moonrise should also be impressive. Pictured above, a supermoon from 2012 is compared to a micromoon -- when a full Moon occurs near the furthest part of the Moon's orbit -- so that it appears smaller and dimmer than usual. Given many definitions, at least one supermoon occurs each year, with the next being 2015 August 30.

An Aurora Cupcake with a Milky Way Topping

This sky looked delicious. Double auroral ovals were captured above the town lights of Östersund, Sweden, last week. Pictured above, the green ovals occurred lower to the ground than violet aurora rays above, making the whole display look a bit like a cupcake. To top it off, far in the distance, the central band or our Milky Way Galaxy slants down from the upper left. The auroras were caused by our Sun ejecting plasma clouds into the Solar System just a few days before, ionized particles that subsequently impacted the magnetosphere of the Earth. Aurora displays may continue this week as an active sunspot group rotated into view just a few days ago.

Laniakea: Our Home Supercluster of Galaxies

It is not only one of the largest structures known -- it is our home. The just-identified Laniakea Supercluster of galaxies contains thousands of galaxies that includes our Milky Way Galaxy, the Local Group of galaxies, and the entire nearby Virgo Cluster of Galaxies. The colossal supercluster is shown in the above computer-generated visualization, where green areas are rich with white-dot galaxies and white lines indicate motion towards the supercluster center. An outline of Laniakea is given in orange, while the blue dot shows our location. Outside the orange line, galaxies flow into other galactic concentrations. The Laniakea Supercluster spans about 500 million light years and contains about 100,000 times the mass of our Milky Way Galaxy. The discoverers of Laniakea gave it a name that means "immense heaven" in Hawaiian.

Zodiacal Light before Dawn

You might not guess it, but sunrise was still hours away when this nightscape was taken, a view along the eastern horizon from a remote location in Chile's Atacama desert. Stretching high into the otherwise dark, starry sky the unusually bright conical glow is sunlight though, scattered by dust along the solar system's ecliptic plane . Known as Zodiacal light, the apparition is also nicknamed the "false dawn". Near center, bright star Aldebaran and the Pleiades star cluster seem immersed in the Zodiacal light, with Orion toward the right edge of the frame. Reddish emission from NGC 1499, the California Nebula, can also be seen through the tinge of airglow along the horizon. Sliding your cursor over the picture (or following this link) will label the sky over this future site of the Giant Magellan Telescope at Las Campanas Observatory.

Supernova Remnant Puppis A

Driven by the explosion of a massive star, supernova remnant Puppis A is blasting into the surrounding interstellar medium about 7,000 light-years away. At that distance, this remarkable false-color exploration of its complex expansion is about 180 light-years wide. It is based on the most complete X-ray data set so far from the Chandra and XMM/Newton observations, and infrared data from the Spitzer Space Telescope. In blue hues, the filamentary X-ray glow is from gas heated by the supernova's shock wave, while the infrared emission shown in red and green is from warm dust. The bright pastel tones trace the regions where shocked gas and warmed dust mingle. Light from the initial supernova itself, triggered by the collapse of the massive star's core, would have reached Earth about 3,700 years ago, though the Puppis A supernova remnant remains a strong source in the X-ray sky.

Median Mashup: Hubble's Top 100

Now, as you sip your cosmic latte you can view 100 Hubble Space Telescope images at the same time. The popular scenes of the cosmos as captured from low Earth orbit are all combined into this single digital presentation. To make it, Hubble's top 100 images were downloaded and resized to identical pixel dimensions. At each point the 100 pixel values were arranged from lowest to highest, and the middle or median value was chosen for the final image. The combined image results in a visual abstraction - light from across the Universe surrounded by darkness.

M27: The Dumbbell Nebula

The first hint of what will become of our Sun was discovered inadvertently in 1764. At that time, Charles Messier was compiling a list of diffuse objects not to be confused with comets. The 27th object on Messier's list, now known as M27 or the Dumbbell Nebula, is a planetary nebula, the type of nebula our Sun will produce when nuclear fusion stops in its core. M27 is one of the brightest planetary nebulae on the sky, and can be seen toward the constellation of the Fox (Vulpecula) with binoculars. It takes light about 1000 years to reach us from M27, shown above in colors emitted by hydrogen and oxygen. Understanding the physics and significance of M27 was well beyond 18th century science. Even today, many things remain mysterious about bipolar planetary nebula like M27, including the physical mechanism that expels a low-mass star's gaseous outer-envelope, leaving an X-ray hot white dwarf.

62 Kilometers above Comet Churyumov-Gerasimenko

Spacecraft Rosetta continues to approach, circle, and map Comet Churyumov-Gerasimenko. Crossing the inner Solar System for ten years to reach the vicinity of the comet last month, the robotic spacecraft continues to image the unusual double-lobed comet nucleus. The reconstructed-color image featured, taken about 10 days ago, indicates how dark this comet nucleus is. On the average, the comet's surface reflects only about four percent of impinging visible light, making it as dark as coal. Comet 67P/Churyumov–Gerasimenko spans about four kilometers in length and has a surface gravity so low that an astronaut could jump off of it. In about two months, Rosetta is scheduled to release the first probe ever to attempt a controlled landing on a comet's nucleus. Astronomers: Has an APOD image ever helped your research?

Milky Way above Atacama Salt Lagoon

Galaxies, stars, and a serene reflecting pool combine to create this memorable land and skyscape. The featured panorama is a 12-image mosaic taken last month from the Salar de Atacama salt flat in northern Chile. The calm water is Laguna Cejar, a salty lagoon featuring a large central sinkhole. On the image left, the astrophotographer's fiancee is seen capturing the same photogenic scene. The night sky is lit up with countless stars, the Large and Small Magellanic Cloud galaxies on the left, and the band of our Milky Way galaxy running diagonally up the right. The Milky Way may appear to be causing havoc at the horizon, but those are just the normal lights of a nearby town. Follow APOD on: Facebook, Google Plus, or Twitter

Aurora over Maine

It has been a good week for auroras. Earlier this month active sunspot region 2158 rotated into view and unleashed a series of flares and plasma ejections into the Solar System during its journey across the Sun's disk. In particular, a pair of Coronal Mass Ejections (CMEs) impacted the Earth's magnetosphere toward the end of last week, creating the most intense geomagnetic storm so far this year. Although power outages were feared by some, the most dramatic effects of these impacting plasma clouds were auroras seen as far south as Wisconsin, USA. In the featured image taken last Friday night, rays and sheets of multicolored auroras were captured over Acadia National Park, in Maine, USA. Since another CME plasma cloud is currently approaching the Earth, tonight offers another good chance to see an impressive auroral display. Almost Hyperspace: Random APOD Generator

Cocoon Nebula Wide Field

In this crowded starfield covering over 2 degrees within the high flying constellation Cygnus, the eye is drawn to the Cocoon Nebula. A compact star forming region, the cosmic Cocoon punctuates a long trail of obscuring interstellar dust clouds. Cataloged as IC 5146, the nebula is nearly 15 light-years wide, located some 4,000 light years away. Like other star forming regions, it stands out in red, glowing, hydrogen gas excited by the young, hot stars and blue, dust-reflected starlight at the edge of an otherwise invisible molecular cloud. In fact, the bright star near the center of this nebula is likely only a few hundred thousand years old, powering the nebular glow as it clears out a cavity in the molecular cloud's star forming dust and gas. But the long dusty filaments that appear dark in this visible light image are themselves hiding stars in the process of formation that can be seen seen at infrared wavelengths.

Potentially Habitable Moons

For astrobiologists, these may be the four most tantalizing moons in our Solar System. Shown at the same scale, their exploration by interplanetary spacecraft has launched the idea that moons, not just planets, could have environments supporting life. The Galileo mission to Jupiter discovered Europa's global subsurface ocean of liquid water and indications of Ganymede's interior seas. At Saturn, the Cassini probe detected erupting fountains of water ice from Enceladus indicating warmer subsurface water on even that small moon, while finding surface lakes of frigid but still liquid hydrocarbons beneath the dense atmosphere of large moon Titan. Now looking beyond the Solar System, new research suggests that sizable exomoons, could actually outnumber exoplanets in stellar habitable zones. That would make moons the most common type of habitable world in the Universe.

Shoreline of the Universe

Against dark rifts of interstellar dust, the ebb and flow of starlight along the Milky Way looks like waves breaking on a cosmic shore in this night skyscape. Taken with a digital camera from the dunes of Hatteras Island, North Carolina, planet Earth, the monochrome image is reminiscent of the time when sensitive black and white film was a popular choice for dimly lit night- and astro-photography. Looking south, the bright stars of Sagittarius and Scorpius are near the center of the frame. Wandering Mars, Saturn, and Zubenelgenubi (Alpha Librae) form the compact triangle of bright celestial beacons farther right of the galaxy's central bulge. Of course, the evocative black and white beach scene could also be from that vintage 1950s scifi movie you never saw, "It Came From Beyond the Dunes."

Saturn at Equinox

How would Saturn look if its ring plane pointed right at the Sun? Before August 2009, nobody knew. Every 15 years, as seen from Earth, Saturn's rings point toward the Earth and appear to disappear. The disappearing rings are no longer a mystery -- Saturn's rings are known to be so thin and the Earth is so near the Sun that when the rings point toward the Sun, they also point nearly edge-on at the Earth. Fortunately, in this third millennium, humanity is advanced enough to have a spacecraft that can see the rings during equinox from the side. In August 2009, that Saturn-orbiting spacecraft, Cassini, was able to snap a series of unprecedented pictures of Saturn's rings during equinox. A digital composite of 75 such images is shown above. The rings appear unusually dark, and a very thin ring shadow line can be made out on Saturn's cloud-tops. Objects sticking out of the ring plane are brightly illuminated and cast long shadows. Inspection of these images is helping humanity to understand the specific sizes of Saturn's ring particles and the general dynamics of orbital motion. This week, Earth undergoes an equinox. APOD Wall Calendar: Moons and Planets

Earth at Equinox

rth is at equinox. Over the next 24 hours, day and night have nearly equal duration all over planet Earth. Technically, equinox transpires at 2:29 am Universal Time tomorrow, but this occurs today in North and South America. This September equinox signal that winter is approaching in the northern hemisphere, and summer is approaching in the south. At equinox, the dividing line between the sunlit half of Earth and the nighttime half of Earth temporarily passes through Earth's north and south spin poles. This dividing line is shown in clear detail in the featured video, taken by the Russian meteorological satellite Elektro-L during last year's September equinox. The Elektro-L satellite is in geostationary orbit over one spot on Earth's equator and always points directly toward the Earth. The featured video shows a time lapse for an entire day surrounding the equinox, with a new image taken every 30 minutes. Cloud motions are visible as well as the reflection of the Sun are visible as the equinox day progressed. The next Earth equinox is scheduled for March. Almost Hyperspace: Random APOD Generator

Aurora and Volcanic Light Pillar

That's no sunset. And that thin red line just above it -- that's not a sun pillar. The red glow on the horizon originates from a volcanic eruption, and the red line is the eruption's reflection from fluttering atmospheric ice crystals. This unusual volcanic light pillar was captured over Iceland earlier this month. The featured scene looks north from Jökulsárlón toward the erupting volcano Bárðarbunga in the Holuhraun lava field. Even the foreground sky is picturesque, with textured grey clouds in the lower atmosphere, shimmering green aurora in the upper atmosphere, and bright stars far in the distance. Although the last eruption from Holuhraun was in 1797, the present volcanic activity continues. APOD Wall Calendar: Land and Skyscapes

The Lagoon Nebula in Stars Dust and Gas

The large majestic Lagoon Nebula is home for many young stars and hot gas. Spanning 100 light years across while lying only about 5000 light years distant, the Lagoon Nebula is so big and bright that it can be seen without a telescope toward the constellation of Sagittarius. Many bright stars are visible from NGC 6530, an open cluster that formed in the nebula only several million years ago. The greater nebula, also known as M8 and NGC 6523, is named "Lagoon" for the band of dust seen to the left of the open cluster's center. A bright knot of gas and dust in the nebula's center is known as the Hourglass Nebula. The featured picture is a newly processed panorama of M8, capturing five times the diameter of the Moon. Star formation continues in the Lagoon Nebula as witnessed by the many globules that exist there. APOD Wall Calendar: Nebulas and Star Clusters

NGC 206 and the Star Clouds of Andromeda

The large stellar association cataloged as NGC 206 is nestled within the dusty arms of the neighboring Andromeda galaxy. Also known as M31, the spiral galaxy is a mere 2.5 million light-years away. NGC 206 is near top center in this gorgeous close-up of the southwestern extent of Andromeda's disk, a remarkable composite of data from space and ground-based observatories. The bright, blue stars of NGC 206 indicate its youth. In fact, its youngest massive stars are less than 10 million years old. Much larger than the open or galactic clusters of young stars in the disk of our Milky Way galaxy, NGC 206 spans about 4,000 light-years. That's comparable in size to the giant stellar nurseries NGC 604 in nearby spiral M33 and the Tarantula Nebula, in the Large Magellanic Cloud. Star forming sites within Andromeda are revealed by the telltale reddish emission from clouds of ionized hydrogen gas.

MAVEN at Mars

Launched on November 18, 2013, the MAVEN (Mars Atmosphere and Volatile EvolutioN) spacecraft completed its interplanetary voyage September 21, captured into a wide, elliptical orbit around Mars. MAVEN's imaging ultraviolet spectrograph has already begun its planned exploration of the Red Planet's upper atmosphere, acquiring this image data from an altitude of 36,500 kilometers. In false color, the three ultraviolet wavelength bands show light reflected from atomic hydrogen (in blue), atomic oxygen (in green) and the planet's surface (in red). Low mass atomic hydrogen is seen to extend thousands of kilometers into space, with the cloud of more massive oxygen atoms held closer by Mars' gravity. Both are by products of the breakdown of water and carbon dioxide in Mars' atmosphere and the MAVEN data can be used to determine the rate of water loss over time. In fact, MAVEN is the first mission dedicated to exploring Mars' tenuous upper atmosphere, ionosphere and interactions with the Sun and solar wind. But the most recent addition to the fleet of spacecraft from planet Earth now in martian orbit is MOM.

A Launch and a Landing

Taken from an Atlantic beach, Cape Canaveral, planet Earth, four identically framed digital images are combined in this night skyscape. Slightly shifted short star trails dot the sky, but the exposure times were adjusted to follow the flight of a Falcon 9 rocket. The September 21 launch delivered a Dragon X capsule filled with supplies to the International Space Station. Above the bright flare seen just after launch, the rocket's first stage firing trails upward from the left. After separation, the second stage burn begins near center with the vehicle climbing toward low Earth orbit. At the horizon, the flare near center records the re-ignition and controlled descent of the Falcon 9's first stage to a soft splashdown off the coast.

Two Black Holes Dancing in 3C 75

What's happening at the center of active galaxy 3C 75? The two bright sources at the center of this composite x-ray (blue)/ radio (pink) image are co-orbiting supermassive black holes powering the giant radio source 3C 75. Surrounded by multimillion degree x-ray emitting gas, and blasting out jets of relativistic particles the supermassive black holes are separated by 25,000 light-years. At the cores of two merging galaxies in the Abell 400 galaxy cluster they are some 300 million light-years away. Astronomers conclude that these two supermassive black holes are bound together by gravity in a binary system in part because the jets' consistent swept back appearance is most likely due to their common motion as they speed through the hot cluster gas at 1200 kilometers per second. Such spectacular cosmic mergers are thought to be common in crowded galaxy cluster environments in the distant universe. In their final stages the mergers are expected to be intense sources of gravitational waves. APOD Wall Calendar: Galaxies

Unusual Rocks near Pahrump Hills on Mars

How did these Martian rocks form? As the robotic Curiosity rover has approached Pahrump Hills on Mars, it has seen an interesting and textured landscape dotted by some unusual rocks. The featured image shows a curiously round rock spanning about two centimeters across. Seemingly a larger version of numerous spherules dubbed blueberries found by the Opportunity rover on Mars in 2004, what caused this roundness remains unknown. Possibilities include frequent tumbling in flowing water, sprayed molten rock in a volcanic eruption, or a concretion mechanism. The inset image, taken a few days later, shows another small but unusually shaped rock structure. As Curiosity rolls around and up Mount Sharp, different layers of the landscape will be imaged and studied to better understand the ancient history of the region and to investigate whether Mars could once have harbored life. APOD Wall Calendar: Moons and Planets

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