juliensimon/nasa-apod huggingface dataset:
Gas and Snow Jets from Comet Hartley 2 (2010-11-23)

Unusual jets have been discovered emanating from Comet Hartley 2. The EPOXI spacecraft imaged the jets in unprecedented detail during its flyby of the comet earlier this month.  Pictured above, sun-illuminated jets shoot away from the two-kilometer long decaying iceberg that orbits the Sun between Earth and Jupiter.  Comet Hartley 2 became active recently as it neared the Sun and sunlight warmed the comet. Preliminary analyses of images like that shown above indicate that the smooth regions around the middle are porous and leak frozen water vapor directly out into space.  Unexpectedly, however, the rough regions at either end appear to shoot carbon dioxide jets that expel fluffy snowballs, some as large as basketballs, from the nucleus.  Many of the dots in the above image are thought to be snowballs. The unusual jets will continue to be studied, and may yield further clues as to how comets and asteroids formed and evolved during the early years of our Solar System. Comet Hartley 2 is slowly evaporating and may completely break up over the next 1,000 years.
Flowing Auroras Over Norway (2010-11-24)

Have you ever seen an aurora?  Auroras are occurring again with increasing frequency. With the Sun being unusually dormant over the past three years, the amount of Sun-induced auroras has also been unusually low. More recently, however, our Sun has become increasingly active and exhibiting a greater abundance of sunspots, flares, and coronal mass ejections. Solar activity like this typically expels charged particles into the Solar System, some of which may trigger Earthly auroras. As this year unfolded, the above timelapse displays of picturesque auroras were captured above Troms�, Norway. Curtains of auroral light, usually green, flow, shimmer and dance as energetic particles fall toward the Earth and ionize air molecules high up in the Earth's atmosphere. With solar maximum still in the future, there may be opportunities to see spectacular aurora personally over the next three years.

Image credit: Tor Even Mathisen
Stardust in Aries (2010-11-25)

This composition in stardust covers almost 2 degrees on the sky, close to the border of the zodiacal constellation Aries and the plane of our Milky Way Galaxy. At the lower right of the gorgeous skyscape is a dusty blue reflection nebula surrounding a bright star cataloged as van den Bergh 13 (vdB 13), about 1,000 light-years away. At that estimated distance, the cosmic canvas is over 30 light-years across. Also surrounded by scattered blue starlight, vdB 16 lies toward the upper left, while dark dusty nebulae sprawl across the scene. Near the edge of a large molecular cloud, they can hide newly formed stars and young stellar objects or protostars from prying optical telescopes. Collapsing due to self-gravity, the protostars form around dense cores embedded in the molecular cloud.

Image credit: Alessandro Falesiedi
Flame Nebula Close-Up (2010-11-26)

Of course, the Flame Nebula is not on fire. Also known as NGC 2024, the nebula's suggestive reddish color is due to the glow of hydrogen atoms at the edge of the giant Orion molecular cloud complex some 1,500 light-years away. The hydrogen atoms have been ionized, or stripped of their electrons, and glow as the atoms and electrons recombine.  But what ionizes the hydrogen atoms? In this close-up view, the central dark lane of absorbing interstellar dust stands out in silhouette against the hydrogen glow and actually hides the true source of the Flame Nebula's energy from optical telescopes. Behind the dark lane lies a cluster of hot, young stars, seen at infrared wavelengths through the obscuring dust.  A young, massive star in that cluster is the likely source of energetic ultraviolet radiation that ionizes the hydrogen gas in the Flame Nebula.

Image credit: Adam Block
Star Streams of NGC 4216 (2010-11-27)

Some 40 million light-years distant, edge-on spiral galaxy NGC 4216 is nearly 100,000 light-years across, about the size of our own Milky Way. Found in the dense Virgo Galaxy Cluster, NGC 4216 is centered in this deep telescopic portrait flanked by fellow Virgo cluster members NGC 4206 (right) and NGC 4222. Like other large spirals, including the Milky Way, NGC 4216 has grown by cannibalizing smaller satellite galaxies. In fact, this view has caught it in the act, with still distinct satellite galaxies showing faint star streams extending for thousands of light-years into the halo of NGC 4216. Taken as part of a survey hunting for star streams in nearby spirals, the image was recorded with a small telescope and camera able to convincingly detect faint, extended features. Having trouble spotting the star streams? Slide your cursor over the image to see a composite negative view. The streams should more easily stand out as dark swaths against a white background.

Image credit: Ken Crawford
Anticrepuscular Rays Over Colorado (2010-11-28)

What's happening over the horizon?  Although the scene may appear somehow supernatural, nothing more unusual is occurring than a setting Sun and some well placed clouds.  Pictured above are anticrepuscular rays.  To understand them, start by picturing common crepuscular rays that are seen any time that sunlight pours though scattered clouds. Now although sunlight indeed travels along straight lines, the projections of these lines onto the spherical sky are great circles.  Therefore, the crepuscular rays from a setting (or rising) sun will appear to re-converge on the other side of the sky.  At the anti-solar point 180 degrees around from the Sun, they are referred to as anticrepuscular rays.  Pictured above is a particularly striking set of anticrepuscular rays photographed in 2001 from a moving car just outside of Boulder, Colorado, USA.

Image credit: John Britton
Dark Belt Reappearing on Jupiter (2010-11-29)

Why are planet-circling clouds disappearing and reappearing on Jupiter? Although the ultimate cause remains unknown, planetary meteorologists are beginning to better understand what is happening. Earlier this year, unexpectedly, Jupiter's dark Southern Equatorial Belt (SEB) disappeared. The changes were first noted by amateurs dedicated to watching Jupiter full time. The South Equatorial Band has been seen to change colors before, although the change has never been recorded in such detail.  Detailed professional observations revealed that high-flying light-colored ammonia-based clouds formed over the planet-circling dark belt. Now those light clouds are dissipating, again unveiling the lower dark clouds. Pictured above two weeks ago, far infrared images -- depicted in false-color red -- show a powerful storm system active above the returning dark belt.  Continued observations of Jupiter's current cloud opera, and our understanding of it, is sure to continue.
A Supercell Thunderstorm Cloud Over Montana (2010-11-30)

Is that a spaceship or a cloud? Although it may seem like an alien mothership, it's actually a impressive thunderstorm cloud called a supercell. Such colossal storm systems center on mesocyclones -- rotating updrafts that can span several kilometers and deliver torrential rain and high winds including tornadoes.  Jagged sculptured clouds adorn the supercell's edge, while wind swept dust and rain dominate the center.  A tree waits patiently in the foreground.    The above supercell cloud was photographed in July west of Glasgow, Montana, USA, caused minor damage, and lasted several hours before moving on.

Image credit: Sean R. Heavey
Martian Moon Phobos from Mars Express (2010-12-01)

Why is Phobos so dark?  Phobos, the largest and innermost of two Martian moons, is the darkest moon in the entire Solar System.  Its unusual orbit and color indicate that it may be a captured asteroid composed of a mixture of ice and dark rock.  The above picture of Phobos near the limb of Mars was captured last month by the robot spacecraft Mars Express currently orbiting Mars.  Phobos is a heavily cratered and barren moon, with its largest crater located on the far side.  From images like this, Phobos has been determined to be covered by perhaps a meter of loose dust.  Phobos orbits so close to Mars that from some places it would appear to rise and set twice a day, but from other places it would not be visible at all.  Phobos' orbit around Mars is continually decaying -- it will likely break up with pieces crashing to the Martian surface in about 50 million years.
Hartley 2 Star Cluster Tour (2010-12-02)

rly in November, small but active Comet Hartley 2 (103/P Hartley) became the fifth comet imaged close-up by a spacecraft from planet Earth. Continuing its own tour of the solar system with a 6 year orbital period, Hartley 2 is now appearing in the nautical constellation Puppis. Still a target for binoculars or small telescopes from dark sky locations, the comet is captured in this composite image from November 27, sharing the rich 2.5 degree wide field of view with some star clusters well known to earthbound skygazers. Below and right of the comet's alluring green coma lies bright M47, a young open star cluster some 80 milion years old, about 1,600 light-years away. Below and left open cluster M46 is older, around 300 million years of age, and 5,400 light-years distant. Hartley 2's short, faint tail even extends up and right toward another fainter star cluster in the scene, NGC 2423. On November 27, Comet Hartley 2 was about 2.25 light-minutes from Earth. Sweeping toward the bottom of this field, by November 28 the comet's path had carried it between M46 and M47.

Image credit: CARA Project
M33: Triangulum Galaxy (2010-12-03)

The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other's grand spiral star systems. As for the view from planet Earth, this sharp, detailed image nicely shows off M33's blue star clusters and pinkish star forming regions that trace the galaxy's loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 4 o'clock position from the galaxy center. Like M31, M33's population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.

Image credit: Manfred Konrad
Sunset at the Spiral Jetty (2010-12-04)

In dwindling twilight at an August day's end, these broad dark bands appeared in the sky for a moment, seen from Robert Smithson's Spiral Jetty on the eastern shore of Utah's Great Salt Lake. Outlined by rays of sunlight known as crepuscular rays, they are actually shadows cast by clouds near the distant western horizon, the setting Sun having disappeared from direct view behind them. The cloud shadows are parallel, but seem to converge in the distance because of perspective. Coiled in the salt-encrusted lake surface, Smithson's most famous earthwork provides a dramatic contrast to the converging lines. The Spiral Jetty was constructed in 1970, when the water level was unusually low and was completely submerged in a few years as the level rose. Now just above water again, it has spent much of its existence submerged in the briny lake.

Image credit: Arne Erisoty
Moonrise Through Mauna Kea's Shadow (2010-12-05)

How can the Moon rise through a mountain?  It cannot -- what was photographed here is a moonrise through the shadow of a large volcano.  The volcano is Mauna Kea, Hawai'i, USA, a frequent spot for spectacular photographs since it is arguably the premier observing location on planet Earth. The Sun has just set in the opposite direction, behind the camera. Additionally, the Moon has just passed full phase -- were it precisely at full phase it would rise, possibly eclipsed, at the very peak of the shadow. Refraction of moonlight through the Earth's atmosphere makes the Moon appear slightly oval.  Cinder cones from old volcanic eruptions are visible in the foreground. Cloud tops below Mauna Kea's summit have unusually flat tops, indicating a decrease in air moisture that frequently keeps the air unusually dry, another attribute of this stellar observing site.

Image credit: Michael Connelley
(U. Hawaii)
Mono Lake: Home to the Strange Microbe GFAJ-1 (2010-12-06)

How strange could alien life be? An indication that the fundamental elements that compose most terrestrial life forms might differ out in the universe was found in unusual Mono Lake in California, USA. Bacteria in Mono's lakebed gives indications that it not only can tolerate a large abundance of normally toxic arsenic, but possibly use arsenic as a replacement for phosphorus, an element needed by every other known Earth-based life form. The result is surprising -- and perhaps controversial -- partly because arsenic-incorporating organic molecules were thought to be much more fragile than phosphorus-incorporating organic molecules.   Pictured above is 7.5-km wide Mono Lake as seen from nearby Mount Dana.  The inset picture shows GFAJ-1, the unusual bacteria that might be able to survive on another world.    Best Astronomy Images: APOD Editor to speak in Philadelphia on Jan 5 and New York City on Jan 7
Too Close to a Black Hole (2010-12-07)

What would you see if you went right up to a black hole? Above is a computer generated image highlighting how strange things would look. The black hole has such strong gravity that light is noticeably bent towards it - causing some very unusual visual distortions. Every star in the normal frame has at least two bright images - one on each side of the black hole. Near the black hole, you can see the whole sky - light from every direction is bent around and comes back to you. The original background map was taken from the 2MASS infrared sky survey, with stars from the Henry Draper catalog superposed.  Black holes are thought to be the densest state of matter, and there is indirect evidence for their presence in stellar binary systems and the centers of globular clusters, galaxies, and quasars.

Image credit: Alain Riazuelo
Intrepid Crater on Mars (2010-12-08)

The robotic rover Opportunity has chanced across another small crater on Mars. Pictured above is Intrepid Crater, a 20-meter across impact basin  slightly larger than Nereus Crater that Opportunity chanced across last year. The above image is in approximately true color but horizontally compressed to accommodate a wide angle panorama.  Intrepid Crater was named after the lunar module Intrepid that carried Apollo 12 astronauts to Earth's Moon 41 years ago last month. Beyond Intrepid Crater and past long patches of rusty Martian desert lie peaks from the rim of large Endeavour Crater, visible on the horizon.  If Opportunity can avoid ridged rocks and soft sand, it may reach Endeavour sometime next year.   Call for Reports: Recent Fireball over the United Kingdom
M81 and Arp's Loop (2010-12-09)

One of the brightest galaxies in planet Earth's sky and similar in size to the Milky Way, big, beautiful spiral M81 lies 11.8 million light-years away in the northern constellation Ursa Major. This deep image of the region reveals details in the bright yellow core, but at the same time follows fainter features along the galaxy's gorgeous blue spiral arms and sweeping dust lanes. It also follows the expansive, arcing feature, known as Arp's loop, that seems to rise from the galaxy's disk at the right. Studied in the 1960s, Arp's loop has been thought to be a tidal tail, material pulled out of M81 by gravitational interaction with its large neighboring galaxy M82. But a recent investigation demonstrates that much of Arp's loop likely lies within our own galaxy. The loop's colors in visible and infrared light match the colors of pervasive clouds of dust, relatively unexplored galactic cirrus only a few hundred light-years above the plane of the Milky Way. Along with the Milky Way's stars, the dust clouds lie in the foreground of this remarkable view.  M81's dwarf companion galaxy, Holmberg IX, can be seen just above and left of the large spiral. On the sky, this image spans about 0.5 degrees, about the size of the Full Moon.   Call for Reports: Recent Fireball over the United Kingdom

Image credit: R Jay GaBany
A Twilight Occultation (2010-12-10)

A thin, one day old crescent Moon hugged the western horizon after sunset on Monday, December 6. The Moon also occulted or passed in front of Mars. But only some well-placed skygazers along a band through North America were able to catch this lunar occultation's final act in fading twilight. For example, this telephoto image nicely captures Mars as a pinprick of light, shortly after it emerged from behind the crescent Moon's sunlit edge. With a tangle of tree limbs in silhouette, the luminous skyview is from De Soto, Kansas in the central US. Of course, this month's upcoming total lunar eclipse will entertain a much wider audience of Moon enthusiasts during the night of December 20/21.   Call for Security Camera Videos: Recent Fireball over the United Kingdom

Image credit: Doug Zubenel
Meteor in the Desert Sky (2010-12-11)

Created as planet Earth sweeps through dusty debris from mysterious, asteroid-like, 3200 Phaethon, the annual Geminid Meteor Shower should be the best meteor shower of the year. The Geminids are predicted to peak on the night of December 13/14, but you can start watching for Geminid meteors this weekend. The best viewing is after midnight in a dark, moonless sky, with the shower's radiant constellation Gemini well above the horizon - a situation that favors skygazers in the northern hemisphere. In this picture from the 2009 Geminid shower, a bright meteor with a greenish tinge flashes through the sky over the Mojave Desert near Barstow, California, USA. Recognizable in the background are bright stars in the northern asterism known as the Big Dipper, framing the meteor streak.

Image credit: Wally Pacholka
Leonids Above Torre de la Guaita (2010-12-12)

In 1999, Leonids Meteor Shower came to an impressive crescendo. Observers in Europe saw a sharp peak in the number of meteors visible around 0210 UTC during the early morning hours of November 18. Meteor counts then exceeded 1000 per hour - the minimum needed to define a true meteor storm. At other times and from other locations around the world, observers typically reported respectable rates of between 30 and 100 meteors per hour. This photograph is a 20-minute exposure ending just before the main Leonids peak began. Visible are at least five Leonid meteors streaking high above the Torre de la Guaita, an observation tower used during the 12th century in Girona, Spain.  Over the next few nights, the Geminids are expected to put on the best meteor show of this year.

Image credit: Juan Carlos Casado
Contemplating the Sky (2010-12-13)

Have you contemplated your sky recently?  Tonight will be a good one for midnight meditators at many northerly locations as meteors from the Geminids meteor shower will frequently streak through.  The Geminds meteor shower has slowly been building to a crescendo and should peak tonight. Pictured above ten days ago, a group of celestial sightseers in the Maranjab Desert in Iran, were treated to a dark and wondrous pre-dawn sky that contained the planet Venus and a crescent Moon. Tonight Mars and Mercury should be visible just above the southwestern horizon at sunset, while the first quarter Moon will set around midnight.

Image credit: Amir Taheri
Launch of a Delta IV Heavy (2010-12-14)

It is the tallest rocket in active use. The Delta IV Heavy is the largest of the Delta series, packing the punch of three rocket boosters instead of the usual one. The resulting rocket, the most powerful in use by the US Air Force, is capable of lifting over 23,000 kilograms into low Earth orbit, comparable to NASA's Space Shuttle. Pictured above is the second launch of the Delta IV Heavy from Cape Canaveral, Florida, USA in 2007, and the first night launch.  Complex service towers are visible to each side of the soaring rocket. The rocket successfully lifted a reconnaissance satellite to low Earth orbit. The Delta IV Heavy has since completed several more successful lift-offs, while its next launch is currently planned from Vandenberg Air Force Base, California, USA, next month.

Image credit: Ben Cooper
A Huge Solar Filament Erupts (2010-12-15)

Click the arrow and watch an unusually long filament explode out from the Sun.  The filament had been seen hovering over the Sun's surface for over a week before it erupted earlier this month.  The image sequence was taken by the Earth-orbiting Solar Dynamics Observatory (SDO) in one color of ultraviolet light specifically emitted by helium, and another color of X-ray light specifically emitted by iron.  The explosion created Coronal Mass Ejections which dispersed high energy plasma into the Solar System.  This plasma cloud, though, missed the Earth and so did not cause auroras.  The above eruption and an unusually expansive eruption that occurred in August are showing how widely separated areas of the Sun can sometimes act in unison.  Explosions like this will likely become more common over the next few years as our Sun moves toward Solar Maximum activity.   Best Astronomy Images: APOD Editor to speak in Philadelphia on Jan 5 and New York City on Jan 7
Geminids over Kitt Peak (2010-12-16)

Two large telescope domes stand in the foreground of this night sky view from Kitt Peak National Observatory, near Tucson, Arizona, USA. The dramatic scene was recorded early Tuesday morning, near the peak of December's Geminid Meteor Shower. With dome slit open, the building closest to the camera houses the 2.3 Meter (90 inch) Bok Telescope operated by Steward Observatory, University of Arizona. Behind the Bok is the Mayall 4 Meter telescope dome. Of course, no telescopes were needed to enjoy the meteors streaking through the sky! The composite image consists of 13 exposures each 15 seconds long, taken with a wide angle lens over a period of about 2 hours during Kitt Peak's warm, clear, night. An annual celestial event, this meteor shower is the result of planet Earth plowing through dust from mysterious, asteroid-like object 3200 Phaethon.

Image credit: David A. Harvey
A Meteor Moment (2010-12-17)

Intensely bright, this fireball meteor flashed through Tuesday's cold, clear, early morning skies over the Karkas Mountains in central Iran, near the peak of the annual Geminid Meteor Shower. To capture the meteor moment and wintery night skyscape, the photographer's camera was fixed to a tripod, its shutter open for about 1.5 minutes. During that time, the multitude of stars slowly traced short, arcing trails through the sky, a reflection of planet Earth's daily rotation on its axis. The meteor's brilliant dash through the scene was brief, though. Changing color as it went, it also left a reddish swirl of hot, glowing gas near the center of its path. The mountains appear in silhouette against the steady glow of distant city lights.

Image credit: Amir Hossein Abolfath