juliensimon/nasa-apod huggingface dataset:
A Hall of Mountain Fogbows (2010-05-04)

If you tried to enter this hall of fog, you would find it dissipates around you. The hall is actually an optical illusion created by sunlight backscattering off of a cloud passing below the peak of the mountain from which this picture was taken. Known as a fogbow and similar in some ways to "the glory", the phenomenon is sometimes seen from airplanes.  The ring's center appears near the image bottom where the shadow of the photographer is visible. This shadow would likely change as clouds passed, creating a faux moving giant known as the Brocken Spectre.  In the picture, several concentric rings of the fogbow appear to create a hall for this mountain king.  The cause of fogbow supernumeraries arcs and glories have only been understood recently and are relatively complex.  Briefly, small droplets of water reflect, refract, and diffract sunlight backwards towards the Sun. Atmospheric backscattering phenomena have a counterpart in astronomy, where looking out from planet Earth in the direction opposite the Sun yields a bright spot called the gegenschein.    Note: The APOD text was updated for accuracy on 2010 May 9.

Image credit: A. Tudorica
(ISS Romania)
The Faces of Mars (2010-05-05)

husiastic astro-artists ranging from expert to beginner, the youngest age 10, all contributed their work to this entertaining panel featuring different faces of Mars. Their sketches are all based on telescopic views of the Red Planet from earlier this year, near its 2010 opposition. Mars offers the best telescopic views at opposition, since that's when it is closest and opposite the Sun in planet Earth's sky. Arranged in a spiral pattern, the sketches are positioned to follow the planet's rotation.  No canals are visible(!), but large surface markings such as the dramatic, dark Syrtis Major are easily identified. As often seen through an astronomical telescope eyepiece, the planet's orientation is inverted, with Mars' north polar cap at the bottom.
Northern and Southern Owls (2010-05-06)

Captured in colorful telescopic portraits, two cosmic owls glare back toward planet Earth in this intriguing comparison of planetary nebulae. On the left is M97 in the constellation Ursa Major, also known in the northern hemisphere as the Owl Nebula. On the right is its visual counterpart, the southern Owl Nebula in the constellation Hydra, cataloged as PLN 283+25.1. Both nebulae are remarkably symmetric, round, and similar in size, some 2 light-years across or about 2,000 times the diameter of Neptune's orbit. Planetary nebulae are produced during a final phase in the life of a sun-like star, an example of the fate that awaits the Sun when it runs out of nuclear fuel in another 5 billion years. Both images were made using narrowband filters and different color mappings. The image of the southern Owl also includes broadband data, bringing out the surrounding star field.

Image credit: Don Goldman
The Antennae (2010-05-07)

Some 60 million light-years away in the southerly constellation Corvus, two large galaxies collided. But the stars in the two galaxies cataloged as NGC 4038 and NGC 4039 don't collide in the course of the ponderous, billion year or so long event. Instead, their large clouds of molecular gas and dust do, triggering furious episodes of star formation near the center of the cosmic wreckage. Spanning about 500 thousand light-years, this stunning view also reveals new star clusters and matter flung far from the scene of the accident by gravitational tidal forces. Of course, the visual appearance of the far-flung arcing structures gives the galaxy pair its popular name - The Antennae.

Image credit: Star Shadows Remote
Observatory
Atlantis Lift Off (2010-05-08)

Atlantis has lifted off, but not from launch pad 39A. Instead, this sharp, wide-angle photo taken on April 13, shows the space shuttle orbiter lifted off the floor of Kennedy Space Center's Vehicle Assembly Building. Shortly afterwards, Atlantis was attached to an external fuel tank and solid rocket boosters prior to roll out. Now resting on pad 39A, Atlantis is scheduled for its actual liftoff on May 14. Embarking on the STS-132 mission to the International Space Station , that launch will represent the final scheduled launch for Atlantis. Atlantis was named for a sailing ship operated for the Woods Hole Oceanographic Institute from 1930 to 1966. The maiden voyage of the Atlantis, Orbiter Vehicle-104, began on October 3, 1985. In 1991, Atlantis deployed the Compton Gamma Ray Observatory.

Image credit: Launch Photography
Halo of the Cat's Eye (2010-05-09)

The Cat's Eye Nebula (NGC 6543) is one of the best known planetary nebulae in the sky. Its haunting symmetries are seen in the very central region of this stunning false-color picture, processed to reveal the enormous but extremely faint halo of gaseous material, over three light-years across, which surrounds the brighter, familiar planetary nebula. Made with data from the Nordic Optical Telescope in the Canary Islands, the composite picture shows extended emission from the nebula. Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star. Only much more recently however, have some planetaries been found to have halos like this one, likely formed of material shrugged off during earlier active episodes in the star's evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years.

Image credit: R. Corradi (Isaac Newton Group),
Nordic Optical Telescope
Large Eruptive Prominence Movie from SDO (2010-05-10)

Sometimes part of the Sun can just explode into space. These explosions might occur as powerful solar flares, coronal mass ejections, or comparatively tame eruptive solar prominences.  Pictured above is one of the largest solar prominence eruptions yet observed, one associated with a subsequent coronal mass ejection. The prominence erupted last month and was recorded by several Sun-sensing instruments, including the recently launched Solar Dynamics Observatory (SDO). The above time lapse sequence was captured by SDO and occurred over a few hours. In recent months, our Sun has becoming increasingly active, following a few years of an unusually dormant solar minimum.  Over the next few years our Sun is expected to reach solar maximum and exhibit a dramatic increase in sunspots and all types of solar explosions.
Herschel Crater on Mimas of Saturn (2010-05-11)

Why is this giant crater on Mimas oddly colored? Mimas, one of the smaller round moons of Saturn, sports Herschel crater, one of the larger impact craters in the entire Solar System. The robotic Cassini spacecraft now orbiting Saturn took the above image of Herschel crater in unprecedented detail while making a 10,000-kilometer record close pass by the icy world just over one month ago. Shown in contrast-enhanced false color, the above image includes color information from older Mimas images that together show more clearly that Herschel's landscape is colored slightly differently from more heavily cratered terrain nearby.  The color difference could yield surface composition clues to the violent history of Mimas.  An impact on Mimas much larger than the one that created the 130-kilometer Herschel would likely have destroyed the entire world.
M72: A Globular Cluster of Stars (2010-05-12)

Globular clusters once ruled the Milky Way.  Back in the old days, back when our Galaxy first formed, perhaps thousands of globular clusters roamed our Galaxy.  Today, there are less than 200 left.  Many globular clusters were destroyed over the eons by repeated fateful encounters with each other or the Galactic center.  Surviving relics are older than any Earth fossil, older than any other structures in our Galaxy, and limit the universe itself in raw age.  There are few, if any, young globular clusters in our Milky Way Galaxy because conditions are not ripe for more to form.  Pictured above by the Hubble Space Telescope are about 100,000 of M72's stars. M72, which spans about 50 light years and lies about 50,000 light years away, can be seen with a small telescope toward the constellation of the Water Bearer (Aquarius).
The Magnificent Horsehead Nebula (2010-05-13)

Sculpted by stellar winds and radiation, a magnificent interstellar dust cloud by chance has assumed this recognizable shape.  Fittingly named the Horsehead Nebula, it is some 1,500 light-years distant, embedded in the vast Orion cloud complex. About five light-years "tall", the dark cloud is cataloged as Barnard 33 and is visible only because its obscuring dust is silhouetted against the glowing red emission nebula IC 434.  Stars are forming within the dark cloud. Contrasting blue reflection nebula NGC 2023, surrounding a hot, young star, is at the lower left.  The gorgeous color image combines both narrowband and broadband images recorded using three different telescopes.

Image credit: Osservatorio MTM
Iguaçu Starry Night (2010-05-14)

The arc of the southern Milky Way shone brightly on this starry night. Captured on May 4, in the foreground of this gorgeous skyview is the rainforest near the spectacular Iguaçu Falls and national park at the border of Brazil and Argentina. Looking skyward along the Milky Way's arc from the left are Alpha and Beta Centauri, the Coalsack, the Southern Cross, and the Carina Nebula. Sirius, brightest star in planet Earth's night sky is at the far right.  Brilliant Canopus, second brightest star in the night, and our neighboring galaxies the Large and Small Magellanic clouds, are also included in the scene. For help finding them, just slide your cursor over the image. Much closer to home, lights near the center along the horizon are from Argentina's Iguazú Falls International Airport.

Image credit: Babak Tafreshi
The Elusive Jellyfish Nebula (2010-05-15)

Normally faint and elusive, the Jellyfish Nebula is caught in this alluring, false-color, telescopic view. Flanked by two bright stars, Mu and Eta Geminorum, at the foot of a celestial twin, the Jellyfish Nebula is the brighter arcing ridge of emission with dangling tentacles below and right of center. In fact, the cosmic jellyfish is seen to be part of bubble-shaped supernova remnant IC 443, the expanding debris cloud from a massive star that exploded. Light from the explosion first reached planet Earth over 30,000 years ago. Like its cousin in astrophysical waters the Crab Nebula supernova remnant, IC 443 is known to harbor a neutron star, the remnant of the collapsed stellar core. Emission nebula Sharpless 249 fills the field at the upper left. The Jellyfish Nebula is about 5,000 light-years away. At that distance, this image would be about 300 light-years across. The color scheme used in the narrowband composite was made popular in Hubble Space Telescope images, mapping emission from oxygen, hydrogen, and sulfur atoms to blue, green and red colors.

Image credit: Bob Franke
Crescent Venus and Moon (2010-05-16)

There's something behind these clouds.  Those faint graceful arcs, upon inspection, are actually far, far in the distance.  They are the Earth's Moon and the planet Venus.  Both the Moon and Venus are bright enough to be seen during the day, and both are quite capable of showing a crescent phase.   To see Venus, which appears quite small, in a crescent phase requires binoculars or a telescope. In the above dramatic daytime image taken from Budapest, Hungary in 2004, the Moon and Venus shared a similar crescent phase a few minutes before the Moon eclipsed the larger but more distant world.   Similarly, visible today in parts of Africa and Asia, a crescent Moon will again eclipse Venus during the day. About an hour after the above image was taken, Venus reappeared.

Image credit: Iv�n �der
Panorama of the Whale Galaxy (2010-05-17)

The see the full length of this blue whale, scroll right. NGC 4631 is a big beautiful spiral galaxy seen edge-on at only about 30 million light-years away.  This galaxy's slightly distorted wedge shape led to its popular moniker of the Whale galaxy.  The Whale's dark interstellar dust clouds and young bright blue star clusters highlight this panoramic color image. The band of NGC 4631 not only appears similar to band of our own Milky Way Galaxy, but its size is truly similar to our Milky Way as well.  The galaxy is also known to have spouted a halo of hot gas glowing in x-rays. The Whale galaxy spans about 140,000 light years and can be seen with a small telescope toward the constellation of the Hunting Dogs (Canes Venatici).
Tentacles of the Tarantula Nebula (2010-05-18)

The largest, most violent star forming region known in the whole Local Group of galaxies lies in our neighboring galaxy the Large Magellanic Cloud (LMC).  Were the Tarantula Nebula at the distance of the Orion Nebula -- a local star forming region -- it would take up fully half the sky.  Also called 30 Doradus, the red and pink gas indicates a massive emission nebula, although supernova remnants and dark nebula also exist there.  The bright knot of stars left of center is called R136 and contains many of the most massive, hottest, and brightest stars known.  The above image taken with the European Southern Observatory's (ESO's) Wide Field Imager is one of the most detailed ever of this vast star forming region. A recent Hubble image of part of the nebula has uncovered a very massive star escaping from the region.
Milky Way Over Ancient Ghost Panel (2010-05-19)

Long before Stonehenge was built, well before the Dead Sea Scrolls were written, ancient artists painted life-sized figures on canyon walls in Utah, USA -- but why? Nobody is sure. The entire panel of figures, which dates back about 7,000 years, is called the Great Gallery and was found on the walls of Horseshoe Canyon in Canyonlands National Park. The humans who painted them likely hunted Mammoths. The unusual fuzziness of largest figure led to this mural section's informal designation as the Holy Ghost Panel, although the intended attribution and societal importance of the figure are really unknown.  The above image was taken during a clear night in March. The oldest objects in the above image are not the pictographs, however, but the stars of our Milky Way Galaxy far in the background, some of which are billions of years old.

Image credit: Bret Webster
M87: Elliptical Galaxy with Jet (2010-05-20)

In spiral galaxies, majestic winding arms of young stars, gas, and dust rotate in a flat disk around a bulging galactic nucleus. But elliptical galaxies seem to be simpler. Lacking gas and dust to form new stars, their randomly swarming older stars, give them an ellipsoidal (egg-like) shape. Still, elliptical galaxies can be very large. Centered in this telescopic view and over 120,000 light-years in diameter, larger than our own Milky Way, elliptical galaxy M87 (NGC 4486) is the dominant galaxy of the Virgo Galaxy Cluster. Some 50 million light-years away, M87 is likely home to a supermassive black hole responsible for a high-energy jet of particles emerging from the giant galaxy's central region. In this well-processed image, M87's jet is near the one o'clock position. Other galaxies are also in the field of view, including large Virgo Cluster ellipticals NGC 4478 right of center and NGC 4476 near the right edge.

Image credit: Adam Block
Calm, Crescent Moon, and Venus (2010-05-21)

Last weekend, the Moon and Venus formed a beautiful close pair in the west after sunset, a scene enjoyed by skygazers all over the world. In this lovely view of the conjunction from Sweden, a calm lake Vallentuna lies in the foreground with sunset colors still fading behind the treeline on the far shore. The young Moon's sunlit crescent is bright, but its entire outline can be seen by Earthshine, light reflected from planet Earth itself. For well-placed skygazers, on Sunday, May 16 the Moon actually occulted (passed in front of) brilliant Venus.  For many, the occultation was visible during daylight hours.

Image credit: Clear Skies
Dark Filament of the Sun (2010-05-22)

Suspended by magnetic fields above a solar active region this dark filament stretches over 40 earth-diameters. The ominous structure appears to be frozen in time near the Sun's edge, but solar filaments are unstable and often erupt. The detailed scene was captured on May 18 in extreme ultraviolet light by cameras on board the Solar Dynamics Observatory. While the cooler plasma of the filament looks dark, hotter, brighter plasma below traces magnetic field lines emerging from the active region. When seen arcing above the edge of the Sun, filaments actually look bright against the dark background of space and are called prominences.
Station and Shuttle Transit the Sun (2010-05-23)

That's no sunspot.  On the upper right of the above image of the Sun, the dark patches are actually the International Space Station (ISS) and the Space Shuttle Atlantis on mission STS-132.  In the past, many skygazers have spotted the space station and space shuttles as bright stars gliding through twilight skies, still glinting in the sunlight while orbiting about 350 kilometers above the Earth's surface. But here, astrophotographer Thierry Lagault accurately computed the occurrence of a rarer opportunity to record the spacefaring combination moving quickly in silhouette across the solar disk. He snapped the above picture on last Sunday on May 16, about 50 minutes before the shuttle docked with the space station.  Atlantis was recently launched to the ISS for its last mission before being retired.

Image credit: Thierry Legault
Rho Ophiuchi Wide Field (2010-05-24)

The clouds surrounding the star system Rho Ophiuchi compose one of the closest star forming regions.  Rho Ophiuchi itself is a binary star system visible in the light-colored region on the image right. The star system, located only 400 light years away, is distinguished by its colorful surroundings, which include a red emission nebula and numerous light and dark brown dust lanes. Near the upper right of the Rho Ophiuchi molecular cloud system is the yellow star Antares, while a distant but coincidently-superposed globular cluster of stars, M4, is visible between Antares and the red emission nebula. Near the image bottom lies IC 4592, the Blue Horsehead nebula.  The blue glow that surrounds the Blue Horsehead's eye -- and other stars around the image -- is a reflection nebula composed of fine dust. On the above image left is a geometrically angled reflection nebula cataloged as Sharpless 1.  Here, the bright star near the dust vortex creates the light of surrounding reflection nebula. Although most of these features are visible through a small telescope pointed toward the constellations of Ophiuchus, Scorpius, and Sagittarius, the only way to see the intricate details of the dust swirls, as featured above, is to use a long exposure camera.

Image credit: Rogelio Bernal Andreo
Looking Back Across Mars (2010-05-25)

It's been a long trip for the Martian rover Opportunity. Last week Opportunity surpassed Viking 1 as the longest running mission on Mars, now extending well over six years. Pictured above, Opportunity's tire tracks cross a nearly featureless Martian desert, emanating from a distant horizon.  Landing in 2004 in Meridiani Planum, the robotic Opportunity has embarked on its longest and most  dangerous trek yet, now aiming to reach large Endeavor Crater sometime next year. Endeavor, it is hoped, holds new clues to the ancient geology of Mars and whether Mars could once have harbored life.
Clouds and Stars over Cotopaxi Volcano in Ecuador (2010-05-26)

What's happening above the Cotopaxi volcano in Ecuador? Quite a bit, from the looks of the above one-night, time-lapse movie, taken earlier this month. The majestic volcano is first seen through breaks in fast moving clouds as the movie begins. Soon the clouds have dissipated and a sky filled with stars seems to rotate about the snow-peaked volcano's peak.  The band of our Milky Way Galaxy, the dark Coal Sack nebula, and the Southern Cross can all be seen overhead. Satellites streak by from several directions. Soon thin clouds roll by and seem to make the brightest stars sparkle. On the volcano (starting at about 1:13 of the movie), the lights of climbers flash. Near the end of the movie, a bright airplane passes over the peak with a residual trail seen drifting away.

Image credit: Stéphane Guisard
M13: The Great Globular Cluster in Hercules (2010-05-27)

In 1716, English astronomer Edmond Halley noted, "This is but a little Patch, but it shews itself to the naked Eye, when the Sky is serene and the Moon absent." Of course, M13 is now modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Telescopic views reveal the spectacular cluster's hundreds of thousands of stars. At a distance of 25,000 light-years, the cluster stars crowd into a region 150 light-years in diameter, but approaching the cluster core upwards of 100 stars could be contained in a cube just 3 light-years on a side. For comparison, the closest star to the Sun is over 4 light-years away. Along with the cluster's dense core, the outer reaches of M13 are highlighted in this sharp color image. The cluster's evolved red and blue giant stars show up in yellowish and blue tints.

Image credit: Osservatorio MTM
Atlantis over Rhodes (2010-05-28)

A moonlit chapel stands in the foreground of this night-scape from the historic Greek island of Rhodes. The tantalizing sky above features a colorful lunar corona, where bright moonlight is diffracted by water droplets in the thin clouds drifting in front of the lunar disk. Captured in the early evening on May 17, the image is a composite of 9 exposures in sequence, each 20 seconds long. It shows star trails too, including the very bright trail of planet Venus setting, below the Moon, near the right edge of the frame. Arcing from the horizon on the right to the picture's left edge is a surprisingly colorful trail produced by space shuttle orbiter Atlantis docked with the International Space Station. Some 350 kilometers above Earth's surface, the orbiter and station pair are still bathed in sunlight. Though it might seem more appropriate when seen in skies over Rhodes, the shuttle orbiter Atlantis wasn't directly named for the legendary island of Atlantis. Instead, it was named for 1930s vintage sailing ship RV Atlantis, the first research vessel operated by the Woods Hole Oceanographic Institute.

Image credit: Tamas Ladanyi
Black Holes in Merging Galaxies (2010-05-29)

Violent galaxy mergers can feed supermassive black holes. Theoretically, the result is intense emission from regions near the supermassive black holes, creating the some of the most luminous objects in the universe. Astronomers dub these Active Galactic Nuclei, or just AGN. But for decades only about 1 percent of AGN seemed to be associated with galaxy mergers. New results from a premier sky survey by NASA's Swift satellite at hard (energetic) X-ray energies now solidly show a strong association of AGN with merging galaxies, though. The hard X-rays more readily penetrate dust and gas clouds in merging galaxies and reveal the presence of emission from the active black holes. In fact, these panels show the location (circled) of Swift X-ray detected supermassive black holes in a variety of merging galaxy systems. The optical images are from the Kitt Peak National Observatory in Arizona. At top center is NGC 7319 and the compact galaxy group known as Stephan's Quintet.