juliensimon/nasa-apod huggingface dataset:
When Gemini Sends Stars to Paranal (2012-12-15)

From a radiant point in the constellation of the Twins, the annual Geminid meteor shower rained down on planet Earth this week. Recorded near the shower's peak in the early hours of December 14, this skyscape captures Gemini's lovely shooting stars in a careful composite of 30 exposures, each 20 seconds long, from the dark of the Chilean Atacama Desert over ESO's Paranal Observatory. In the foreground Paranal's four Very Large Telescopes, four Auxillary Telescopes, and the VLT Survey telescope are all open and observing. The skies above are shared with bright Jupiter (left), Orion, (top left), and the faint light of the Milky Way. Dust swept up from the orbit of active asteroid 3200 Phaethon, Gemini's meteors enter the atmosphere traveling at about 22 kilometers per second.

Image credit: Stéphane Guisard
MWC 922: The Red Square Nebula (2012-12-16)

What could cause a nebula to appear square? No one is quite sure. The hot star system known as MWC 922, however, appears to be embedded in a nebula with just such a shape.  The above image combines infrared exposures from the Hale Telescope on Mt. Palomar in California, and the Keck-2 Telescope on Mauna Kea in Hawaii.  A leading progenitor hypothesis for the square nebula is that the central star or stars somehow expelled cones of gas during a late developmental stage. For MWC 922, these cones happen to incorporate nearly right angles and be visible from the sides.  Supporting evidence for the cone hypothesis includes radial spokes in the image that might run along the cone walls. Researchers speculate that the cones viewed from another angle would appear similar to the gigantic rings of supernova 1987A, possibly indicating that a star in MWC 922 might one day itself explode in a similar supernova.

Image credit: Peter Tuthill
(Sydney U.)
& James Lloyd (Cornell)
NGC 922: Collisional Ring Galaxy (2012-12-17)

Why does this galaxy have so many big black holes? No one is sure. What is sure is that NGC 922 is a ring galaxy created by the collision of a large and small galaxy about 300 million years ago. Like a rock thrown into a pond, the ancient collision sent ripples of high density gas out from the impact point near the center that partly condensed into stars. Pictured above is NGC 922 with its beautifully complex ring along the left side, as imaged recently by the Hubble Space Telescope. Observations of NGC 922 with the Chandra X-ray Observatory, however, show several glowing X-ray knots that are likely large black holes. The high number of massive black holes was somewhat surprising as the gas composition in NGC 922 -- rich in heavy elements -- should have discouraged almost anything so massive from forming.  Research is sure to continue. NGC 922 spans about 75,000 light years, lies about 150 million light years away, and can be seen with a small telescope toward the constellation of the furnace (Fornax).
A Sun Pillar Over Sweden (2012-12-18)

Have you ever seen a sun pillar?  When the air is cold and the Sun is rising or setting, falling ice crystals can reflect sunlight and create an unusual column of light.  Ice sometimes forms flat, six-sided shaped crystals as it falls from high-level clouds.  Air resistance causes these crystals to lie nearly flat much of the time as they flutter to the ground.  Sunlight reflects off crystals that are properly aligned, creating the sun-pillar effect.  In the above picture taken last week, a sun-pillar reflects light from a Sun setting over �stersund, Sweden.

Image credit: G�ran Strand
NGC 5189: An Unusually Complex Planetary Nebula (2012-12-19)

Why is this nebula so complex? When a star like our Sun is dying, it will cast off its outer layers, usually into a simple overall shape. Sometimes this shape is a sphere, sometimes a double lobe, and sometimes a ring or a helix.  In the case of planetary nebula NGC 5189, however, no such simple structure has emerged.  To help find out why, the Earth-orbiting Hubble Space Telescope recently observed NGC 5189 in great detail. Previous findings indicated the existence of multiple epochs of material outflow, including a recent one that created a bright but distorted torus running horizontally across image center.  Results appear consistent with a hypothesis that the dying star is part of a binary star system with a precessing symmetry axis. Given this new data, though, research is sure to continue. NGC 5189 spans about three light years and lies about 3,000 light years away toward the southern constellation of the Fly (Musca).   APOD Editors to Speak: RJN in Philadelphia on Jan. 3 & JTB in New York City on Jan. 4
M33: Triangulum Galaxy (2012-12-20)

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 composite image, a 25 panel mosaic, 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 1 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: Robert Gendler
Orion over El Castillo (2012-12-21)

Welcome to the December solstice, a day the world does not end ... even according to the Mayan Calendar. To celebrate, consider this dramatic picture of Orion rising over El Castillo, the central pyramid at Chichén Itzá, one of the great Mayan centers on the Yucatán peninsula. Also known as the Temple of Kukulkan it stands 30 meters tall and 55 meters wide at the base. Built up as a series of square terraces by the pre-Columbian civilization between the 9th and 12th century, the structure can be used as a calendar and is noted for astronomical alignments. In fact, the Mayans were accomplished astronomers and mathematicians, accurately using the cyclic motions of the stars, Sun, Moon, and planets to measure time and construct calendars. Peering through clouds in this night skyscape, stars in the modern constellation Orion the Hunter represented a turtle in the Mayan sky. Tak sáamal.

Image credit: Stéphane Guisard
Saturn at Night (2012-12-22)

Splendors seldom seen are revealed in this glorious picture from Saturn's shadow. Imaged by Cassini on October 17, 2012 during its 174th orbit, the ringed planet's night side is viewed from a perspective 19 degrees below the ring plane at a distance of about 800,000 kilometers with the Sun almost directly behind the planet. A 60 frame mosaic, images made with infrared, red, and violet filters were combined to create an enhanced, false-color view. Strongly backlit, the rings look bright away from the planet but dark in silhouette against the gas giant. Above center, they reflect a faint, eerie light on the cloud tops while Saturn casts its own dark shadow on the rings. A similar Cassini image from 2006 also featured planet Earth as a pale blue dot in the distance. Instead, this scene includes icy moons Enceladus (closer to the rings) and Tethys below the rings on the left.
Comet Hale-Bopp Over Val Parola Pass (2012-12-23)

Comet Hale-Bopp, the Great Comet of 1997, became much brighter than any surrounding stars. It was seen even over bright city lights. Away from city lights, however, it put on quite a spectacular show. Here Comet Hale-Bopp was photographed above Val Parola Pass in the Dolomite mountains surrounding Cortina d'Ampezzo, Italy. Comet Hale-Bopp's blue ion tail, consisting of ions from the comet's nucleus, is pushed out by the solar wind. The white dust tail is composed of larger particles of dust from the nucleus driven by the pressure of sunlight, that orbit behind the comet. Observations showed that Comet Hale-Bopp's nucleus spins about once every 12 hours. A comet that may well exceed Hale-Bopp's peak brightness is expected to fall into the inner Solar System next year.

Image credit: A. Dimai, (Col Druscie Obs.),
AAC
Hyades for the Holidays (2012-12-24)

Recognized since antiquity and depicted on the shield of Achilles according to Homer, stars of the Hyades cluster form the head of the constellation Taurus the Bull. Their general V-shape is anchored by Aldebaran, the eye of the Bull and by far the constellation's brightest star. Yellowish in appearance, red giant Aldebaran is not a Hyades cluster member, though. Modern astronomy puts the Hyades cluster 151 light-years away making it the nearest established open star cluster, while Aldebaran lies at less than half that distance, along the same line-of-sight. Along with colorful Hyades stars, this stellar holiday portrait locates Aldebaran just below center, as well as another open star cluster in Taurus, NGC 1647 at the left, some 2,000 light-years or more in the background. Just slide your cursor over the image to identify the stars. The central Hyades stars are spread out over about 15 light-years. Formed some 800 million years ago, the Hyades star cluster may share a common origin with M44 (Praesepe), a naked-eye open star cluster in Cancer, based on M44's motion through space and remarkably similar age.

Image credit: Catching the Light
Yosemite Winter Night (2012-12-25)

In this evocative night skyscape a starry band of the Milky Way climbs over Yosemite Valley, Sierra Nevada Range, planet Earth. Jupiter is the brightest celestial beacon on the wintry scene, though. Standing nearly opposite the Sun in the constellation Taurus, the wandering planet joins yellowish Aldebaran and the Hyades star cluster. Below, Orion always comes up sideways over a fence of mountains. And from there the twin stars of Gemini rise just across the Milky Way. As this peaceful winter night began, they followed Auriga the charioteer, its alpha star Capella near the top of the frame.

Image credit: Wally Pacholka
Makemake of the Outer Solar System (2012-12-26)

Makemake is one of the largest objects known in the outer Solar System. Pronounced MAH-kay MAH-kay, this Kuiper belt object is about two-thirds the size of Pluto, orbits the Sun only slightly further out than Pluto, and appears only slightly dimmer than Pluto. Makemake, however, has an orbit much more tilted to the ecliptic plane of the planets than Pluto.  Discovered by a team led by Mike Brown (Caltech) in 2005, the outer Solar System orb was officially named Makemake for the creator of humanity in the Rapa Nui mythology of Easter Island. In 2008, Makemake was classified as a dwarf planet under the subcategory plutoid, making Makemake the third cataloged plutoid after Pluto and Eris.  Makemake is known to be a world somewhat red in appearance, with colors indicating it is likely covered with patchy areas of frozen methane. No images of Makemake's surface yet exist, but an artist's illustration of the distant world is shown above. Careful monitoring of the brightness drop of a distant star recently eclipsed by Makemake indicates that the dwarf planet has little atmosphere.
Curiosity Rover at Rocknest on Mars (2012-12-27)

What's in this smooth soil on Mars? In late October, NASA's robotic Curiosity rover stopped near a place dubbed Rocknest as it continues to explore Gale Crater on Mars. Rocknest is the group of stones seen near the top left of the above image -- just to the left of Curiosity's mast. Of particular interest was the unusually smooth patch of soil named Wind Drift seen to the left of Curiosity, which was likely created by the Martian wind blowing fine particles into Rocknest's wake. The above image shows part of Mt. Sharp in the background to upper right, and, oddly, almost the entire rover itself, digitally reconstructed from 55 frames while digitally removing an extended arm. Curiosity scooped several sand samples from Wind Drift into its Chemistry and Mineralogy Experiment (CheMin) and the Sample Analysis at Mars (SAM) laboratory for a detailed analysis. Preliminary data from the soil indicates a small amount of one-carbon organic material the origin of which it presently unknown. Although the organic signal might be just contaminants from Earth, the exciting possibility that it could be from Mars itself will remain a focus of future exploration and research.   Best of APOD 2012: Download a free 2013 APOD Calendar  Follow APOD on: Facebook (Daily) (Sky) (Spanish) or Google Plus (Daily) (River)
NGC 6188 and NGC 6164 (2012-12-28)

Fantastic shapes lurk in clouds of glowing hydrogen gas in NGC 6188, about 4,000 light-years away. The emission nebula is found near the edge of a large molecular cloud unseen at visible wavelengths, in the southern constellation Ara. Massive, young stars of the embedded Ara OB1 association were formed in that region only a few million years ago, sculpting the dark shapes and powering the nebular glow with stellar winds and intense ultraviolet radiation. The recent star formation itself was likely triggered by winds and supernova explosions, from previous generations of massive stars, that swept up and compressed the molecular gas. Joining NGC 6188 on this cosmic canvas is rare emission nebula NGC 6164, also created by one of the region's massive O-type stars. Similar in appearance to many planetary nebulae, NGC 6164's striking, symmetric gaseous shroud and faint halo surround its bright central star at the lower right. The field of view spans about two full Moons, corresponding to 70 light years at the estimated distance of NGC 6188.   Best of APOD 2012: Download a free 2013 APOD Calendar  Follow APOD on: Facebook (Daily) (Sky) (Spanish) or Google Plus (Daily) (River)

Image credit: Kfir Simon
Zeta Oph: Runaway Star (2012-12-29)

Like a ship plowing through cosmic seas, runaway star Zeta Ophiuchi produces the arcing interstellar bow wave or bow shock seen in this stunning infrared portrait. In the false-color view, bluish Zeta Oph, a star about 20 times more massive than the Sun, lies near the center of the frame, moving toward the left at 24 kilometers per second. Its strong stellar wind precedes it, compressing and heating the dusty interstellar material and shaping the curved shock front. Around it are clouds of relatively undisturbed material. What set this star in motion? Zeta Oph was likely once a member of a binary star system, its companion star was more massive and hence shorter lived. When the companion exploded as a supernova catastrophically losing mass, Zeta Oph was flung out of the system. About 460 light-years away, Zeta Oph is 65,000 times more luminous than the Sun and would be one of the brighter stars in the sky if it weren't surrounded by obscuring dust. The image spans about 1.5 degrees or 12 light-years at the estimated distance of Zeta Ophiuchi.   Best of APOD 2012: Download a free 2013 APOD Calendar  Follow APOD on: Facebook (Daily) (Sky) (Spanish) or Google Plus (Daily) (River)
Doomed Star Eta Carinae (2012-12-30)

Carinae may be about to explode.  But no one knows when - it may be next year, it may be one million years from now. Eta Carinae's mass - about 100 times greater than our Sun - makes it an excellent candidate for a full blown supernova. Historical records do show that about 150 years ago Eta Carinae underwent an unusual outburst that made it one of the brightest stars in the southern sky.  Eta Carinae, in the Keyhole Nebula, is the only star currently thought to emit natural LASER light. This image, taken in 1996, brought out new details in the unusual nebula that surrounds this rogue star.  Now clearly visible are two distinct lobes, a hot central region, and strange radial streaks.  The lobes are filled with lanes of gas and dust which absorb the blue and ultraviolet light emitted near the center.  The streaks remain unexplained.   APOD Editors to Speak: RJN in Philadelphia on Jan. 3 & JTB in New York City on Jan. 4
Saturn's Rings from the Dark Side (2012-12-31)

What do Saturn's rings look like from the dark side?  From Earth, we usually see Saturn's rings from the same side of the ring plane that the Sun illuminates them -- one might call this the bright side. Geometrically, in the above picture taken in August by the robot Cassini spacecraft now orbiting Saturn, the Sun is behind the camera but on the other side of the ring plane. Such a vantage point gives a breathtaking views of the most splendid ring system in the Solar System. Strangely, the rings have similarities to a photographic negative of a front view. For example, the dark band in the middle is actually the normally bright B-ring. The ring brightness as recorded from different angles indicates ring thickness and particle density of ring particles.  At the top left of the frame is Saturn's moon Tethys, which although harder to find, contains much more mass than the  entire ring system.   Best of APOD 2012: Download a free 2013 APOD Calendar  Follow APOD on: Facebook (Daily) (Sky) (Spanish) or Google Plus (Daily) (River)
A Double Star Cluster (2013-01-01)

Few star clusters are seen to be so close to each other. Some 7,000 light-years away, though, this pair of open or galactic star clusters is an easy binocular target, a lovely starfield in the northern constellation Perseus. Also visible to the unaided eye from dark sky areas, it was cataloged in 130 BC by Greek astronomer Hipparchus. Now known as h and chi Persei, or NGC 869 (above right) and NGC 884, the clusters themselves are separated by only a few hundred light-years and contain stars much younger and hotter than the Sun. In addition to being physically close together, the clusters' ages based on their individual stars are similar - evidence that both clusters were likely a product of the same star-forming region.   APOD Editors to Speak: RJN in Philadelphia on Jan. 3 & JTB in New York City on Jan. 4

Image credit: F. Antonucci, M. Angelini, & F. Tagliani,
ADARA Astrobrallo
The Einstein Cross Gravitational Lens (2013-01-02)

Most galaxies have a single nucleus -- does this galaxy have four?  The strange answer leads astronomers to conclude that the nucleus of the surrounding galaxy is not even visible in this image.  The central cloverleaf is rather light emitted from a background quasar.  The gravitational field of the visible foreground galaxy breaks light from this distant quasar into four distinct images.  The quasar must be properly aligned behind the center of a massive galaxy for a mirage like this to be evident.  The general effect is known as gravitational lensing, and this specific case is known as the Einstein Cross.  Stranger still, the images of the Einstein Cross vary in relative brightness, enhanced occasionally by the additional gravitational microlensing effect of specific stars in the foreground galaxy.    Follow APOD on: Facebook (Daily) (Sky) (Spanish) or Google Plus (Daily) (River)

Image credit: J. Rhoads
(Arizona State U.) et al.,
WIYN,
AURA,
NOAO,
NSF
Open Star Clusters M35 and NGC 2158 (2013-01-03)

Open clusters of stars can be near or far, young or old, and diffuse or compact.  Found near the plane of our Milky Way galaxy, they contain from 100 to 10,000 stars, all of which formed at nearly the same time.  Bright blue stars frequently distinguish younger open clusters.  M35, on the upper left, is relatively nearby at 2800 light years distant, relatively young at 150 million years old, and relatively diffuse, with about 2500 stars spread out over a volume 30 light years across.  An older and more compact open cluster, NGC 2158, is at the lower right.  NGC 2158 is four times more distant than M35, over 10 times older, and much more compact with many more stars in roughly the same volume of space.  NGC 2158's bright blue stars have self-destructed, leaving cluster light to be dominated by older and yellower stars.  Both clusters are seen toward the constellation of Gemini.   APOD Editors to Speak: RJN in Philadelphia on Jan. 3 & JTB in New York City on Jan. 4

Image credit: Dieter Willasch
Sunrise at Tycho (2013-01-04)

Tycho crater's central peak complex casts a long, dark shadow near local sunrise in this spectacular lunarscape. The dramatic oblique view was recorded on June 10, 2011 by the Lunar Reconnaissance Orbiter. Shown in amazing detail, boulder strewn slopes and jagged shadows appear in the highest resolution version at 1.5 meters per pixel. The rugged complex is about 15 kilometers wide, formed in uplift by the giant impact that created the well-known ray crater 100 million years ago. The summit of its central peak reaches 2 kilometers above the Tycho crater floor.
Stereo Helene (2013-01-05)

Get out your red/blue glasses and float next to Helene, small, icy moon of Saturn. Appropriately named, Helene is one of four known Trojan moons, so called because it orbits at a Lagrange point. A Lagrange point is a gravitationally stable position near two massive bodies, in this case Saturn and larger moon Dione. In fact, irregularly shaped ( about 36 by 32 by 30 kilometers) Helene orbits at Dione's leading Lagrange point while brotherly ice moon Polydeuces follows at Dione's trailing Lagrange point. The sharp stereo anaglyph was constructed from two Cassini images (N00172886, N00172892) captured during a close flyby in 2011. It shows part of the Saturn-facing hemisphere of Helene mottled with craters and gully-like features.
The Dark Tower in Scorpius (2013-01-06)

In silhouette against a crowded star field toward the constellation Scorpius, this dusty cosmic cloud evokes for some the image of an ominous dark tower. In fact, clumps of dust and molecular gas collapsing to form stars may well lurk within the dark nebula, a structure that spans almost 40 light-years across this gorgeous telescopic portrait. Known as a cometary globule, the swept-back cloud, extending from the lower right to the head (top of the tower) left and above center, is shaped by intense ultraviolet radiation from the OB association of very hot stars in NGC 6231, off the upper edge of the scene. That energetic ultraviolet light also powers the globule's bordering reddish glow of hydrogen gas. Hot stars embedded in the dust can be seen as bluish reflection nebulae. This dark tower, NGC 6231, and associated nebulae are about 5,000 light-years away.

Image credit: Don Goldman
AE Aurigae and the Flaming Star Nebula (2013-01-07)

AE Aurigae is called the flaming star. The surrounding nebula IC 405 is named the Flaming Star Nebula and the region seems to harbor smoke, but 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. 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 near the nebula center, is so hot it is blue, emitting light so energetic it knocks electrons away from atoms in the surrounding gas. When an atom recaptures an electron, light is emitted creating the surrounding emission nebula. In this cosmic portrait, 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).   Best of APOD 2012: Download a free 2013 APOD Calendar

Image credit: Martin Pugh