juliensimon/nasa-apod huggingface dataset:
East to West, Light and Shadow (2016-11-26)

On this November morning an old crescent Moon and morning star rise just before the Sun in a wide panoramic skyscape from Kenya's Amboseli National Park. Still below the limbs of an acacia tree and the eastern horizon, the Sun's position is easy to find though. It's marked at the left by the subtle convergence of light and shadow in the dawn sky. Known as crepuscular rays, the warm-colored rays of sunlight are outlined by shadows cast by unseen clouds near the horizon. Arcing above the profile of Mount Kilimanjaro, toward the right the rays of light and shadow converge at the western horizon. There known as anti-crepuscular rays, they indicate the point opposite the rising sun. The cloud shadows are very nearly parallel, but converge toward the distant horizons because of perspective.

Image credit: Babak Tafreshi
Verona Rupes: Tallest Known Cliff in the Solar System (2016-11-27)

Could you survive a jump off the tallest cliff in the Solar System? Quite possibly.  Verona Rupes on Uranus' moon Miranda is estimated to be 20 kilometers deep -- ten times the depth of the Earth's Grand Canyon.   Given Miranda's low gravity, it would take about 12 minutes for a thrill-seeking adventurer to fall from the top, reaching the bottom at the speed of a racecar -- about 200 kilometers per hour.   Even so, the fall might be survivable given proper airbag protection.  The featured image of Verona Rupes was captured by the passing Voyager 2 robotic spacecraft in 1986.  How the giant cliff was created remains unknown, but is possibly related to a large impact or tectonic surface motion.
Arp 240: A Bridge between Spiral Galaxies from Hubble (2016-11-28)

Why is there a bridge between these two spiral galaxies? Made of gas and stars, the bridge provides strong evidence that these two immense star systems have passed close to each other and experienced violent tides induced by mutual gravity. Known together as Arp 240 but individually as NGC 5257 and NGC 5258, computer modelling and the ages of star clusters indicate that the two galaxies completed a first passage near each other only about 250 million years ago. Gravitational tides not only pulled away matter, they compress gas and so caused star formation in both galaxies and the unusual bridge. Galactic mergers are thought to be common, with Arp 240 representing a snapshot of a brief stage in this inevitable process.  The Arp 240 pair are about 300 million light-years distant and can be seen with a small telescope toward the constellation of Virgo. Repeated close passages should ultimately result in a merger and with the emergence of a single combined galaxy.    Free Download: APOD 2017 Calendar: NASA Images
W5: The Soul of Star Formation (2016-11-29)

Where do stars form? Many times, stars form in energetic regions where gas and dark dust are pushed around in chaotic mayhem.  Pictured, bright massive stars near the center of W5, the Soul Nebula, are exploding and emitting ionizing light and energetic winds. The outward-moving light and gas push away and evaporate much surrounding gas and dust, but leave pillars of gas behind dense protective knots. Inside these knots, though, stars also form.  The featured image highlights the inner sanctum of W5, an arena spanning about 1,000 light years that is rich in star forming pillars. The Soul Nebula, also cataloged as IC 1848, lies about 6,500 light years away toward the constellation of the Queen of Aethopia (Cassiopeia). Likely, in few hundred million years, only a cluster of the resulting stars will remain. Then, these stars will drift apart.
Milky Way over Shipwreck (2016-11-30)

What happened to this ship? It was carried aground by a giant storm that struck the coast of Argentina in 2002.  The pictured abandoned boat, dubbed Naufragio del Chubasco, wrecked near the nearly abandoned town of Cabo Raso (population: 1). The rusting ship provides a picturesque but perhaps creepy foreground for the beautiful sky above. This sky is crowned by the grand arch of our Milky Way and features galaxies including the Large and Small Magellanic Clouds, stars including Canopus and Altair, planets including Mars and Neptune, and nebulas including the Lagoon, Carina, and the Coal Sack. The mosaic was composed from over 80 images taken in early September.  A 360-degree interactive panoramic version of this image is also available.  The adventurous astrophotographer reports that the creepiest part of taking this picture was not the abandoned ship, but the unusual prevalence of black and hairy caterpillars.

Image credit: Sergio Mont�far  
(Planetario Ciudad de La Plata)
Flaming Star Nebula (2016-12-01)

A runaway star lights the Flaming Star Nebula in this cosmic scene. Otherwise known as IC 405, the Flaming Star Nebula's billowing interstellar clouds of gas and dust lie about 1,500 light-years away toward the constellation of Auriga. AE Aurigae, the bright star at upper left in the frame, is a massive and intensely hot O-type star moving rapidly through space, likely ejected from a collision of multiple star-systems in the vicinity of the Orion Nebula millions of years ago. Now close to IC 405, the high-speed star's ionizing ultraviolet radiation powers the visible reddish glow as the nebula's hydrogen atoms are stripped of their electrons and recombine. Its intense blue starlight is reflected by the nebula's dusty filaments. Like all massive stars AE Aurigae will be short-lived though, furiously burning through its supply of fuel for nuclear fusion and exploding as a supernova. The colorful telescopic snapshot spans about 5 light-years at the estimated distance of the Flaming Star Nebula.

Image credit: Adam Block
A Triple Star is Born (2016-12-02)

A triple star system is forming, enshrouded within this dusty natal disk some 750 light-years away in the Perseus molecular cloud. Imaged at millimeter wavelengths by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the extreme close-up shows two protostars separated by a mere 61 AU (1 AU is the Earth-Sun distance) with a third 183 AU from the central protostar. The ALMA image also reveals a clear spiral structure indicating instability and fragmentation led to the multiple protostellar objects within the disk. Astronomers estimate that the system, cataloged as L1448 IRS3B, is less than 150,000 years old. Captured at an early phase, the starforming scenario is likely not at all uncommon, since almost half of all sun-like stars have at least one companion.
Galaxies in Pegasus (2016-12-03)

This wide, sharp telescopic view reveals galaxies scattered beyond the stars of the Milky Way at the northern boundary of the high-flying constellation Pegasus. Prominent at the upper right is NGC 7331. A mere 50 million light-years away, the large spiral is one of the brighter galaxies not included in Charles Messier's famous 18th century catalog. The disturbed looking group of galaxies at the lower left is well-known as Stephan's Quintet. About 300 million light-years distant, the quintet dramatically illustrates a multiple galaxy collision, its powerful, ongoing interactions posed for a brief cosmic snapshot. On the sky, the quintet and NGC 7331 are separated by about half a degree.

Image credit: Péter
Feltóti
Orion and Official Star Names (2016-12-04)

Familiar stars in Orion and constellations across the sky now have official names. Over the past year, the International Astronomical Union, the only body officially tasked with naming stars, approved names already in common use for 227 of the brightest stars, including the most famous stars on the sky Sirius, Polaris, and Betelgeuse.  Pictured, the constellation of Orion is shown with several of these now-official star names superposed.  Spanning about 30 degrees, this breath-taking vista stretches across the well-known constellation from head to toe (left to right) and beyond. The common names for all three stars in Orion's belt are also now official.  At 1,500 light years away, the Great Orion Nebula is the closest large star forming region, here visible just right and below center. Also visible are famous nebulae including the Horsehead Nebula and the Witch Head Nebula. Of course, the Orion Nebula and bright stars are easy to see with the unaided eye, but dust clouds and emission from the extensive interstellar gas in this nebula-rich complex, are too faint and much harder to record. In the featured mosaic of broadband telescopic images, additional image data acquired with a narrow hydrogen alpha filter was used to bring out the pervasive tendrils of energized atomic hydrogen gas like in the arc of the giant Barnard's Loop.    Open Science: Browse 1,350+ codes in the Astrophysics Source Code Library

Image credit: Rogelio
Bernal Andreo
Lightning over Colorado (2016-12-05)

Have you ever watched a lightning storm in awe?  Join the crowd. Oddly, nobody knows exactly how lightning is produced. What is known is that charges slowly separate in some clouds causing rapid electrical discharges (lightning), but how electrical charges get separated in clouds remains a topic of much research. Lightning usually takes a jagged course, rapidly heating a thin column of air to about three times the surface temperature of the Sun.  The resulting shock wave starts supersonically and decays into the loud sound known as thunder.  Lightning bolts are common in clouds during rainstorms, and on average 44 lightning bolts occur on the  Earth every second. Pictured, over 60 images were stacked to capture the flow of lightning-producing storm clouds in July over Colorado Springs, Colorado, USA.    Follow APOD on: Facebook,  Google Plus,  Instagram, or Twitter

Image credit: Joe Randall
Aurora over Jupiter's South Pole from Juno (2016-12-06)

Why is there a glowing oval over Jupiter's South Pole? Aurora.  Near the closest part of its first pass near Jupiter in August, NASA's robotic spacecraft Juno captured this dramatic infrared image of a bright auroral ring. Auroras are caused by high energy particles from the Sun interacting with a planet's magnetic field, and ovals around magnetic poles are common.  Data from Juno are giving preliminary indications that Jupiter's magnetic field and aurorae are unexpectedly powerful and complex.  Unfortunately, a computer glitch caused Juno to go into safe mode during its October pass near the Jovian giant in October. That glitch has now been resolved, making Juno ready for its next pass over Jupiter's cloud tops this coming Sunday.
NGC 4696: Filaments around a Black Hole (2016-12-07)

What's happening at the center of elliptical galaxy NGC 4696? There, long tendrils of gas and dust have been imaged in great detail as shown by this recently released image from the Hubble Space Telescope.  These filaments appear to connect to the central region of the galaxy, a region thought occupied by a supermassive black hole.  Speculation holds that this black hole pumps out energy that heats surrounding gas, pushes out cooler filaments of gas and dust, and shuts down star formation. Balanced by magnetic fields, these filaments then appear to spiral back in toward and eventually circle the central black hole. NGC 4696 is the largest galaxy in the Centaurus Cluster of Galaxies, located about 150 million light years from Earth. The featured image shows a region about 45,000 light years across.
Whirlpool with Comets (2016-12-08)

Not a comet, bright spiral galaxy Messier 51 is popularly known as the Whirlpool Galaxy. Just off the handle of the Big Dipper in northern skies, you can spot it at the upper left in this image from December 1st. The pretty 4 by 2.5 degree wide field of view does contain two comets though. Different in appearance, both comets are new visitors to the inner Solar System and are currently faint telescopic objects, highest above northern horizons in morning twilight. At lower left newly discovered comet NEOWISE (C/2016 U1) shows off a round fuzzy coma in the greenish light of diatomic carbon gas fluorescing in sunlight. Sunlight reflects from dust in the coma and stubby tail of comet Johnson (C/2015 V2) at upper right.

Image credit: José
J. Chambó
IC 4628: The Prawn Nebula (2016-12-09)

South of Antares, in the tail of the nebula-rich constellation Scorpius, lies emission nebula IC 4628. Nearby hot, massive stars, millions of years young, irradiate the nebula with invisible ultraviolet light, stripping electrons from atoms. The electrons eventually recombine with the atoms to produce the visible nebular glow, dominated by the red emission of hydrogen. At an estimated distance of 6,000 light-years, the region shown is about 250 light-years across, spanning over three full moons on the sky. The nebula is also cataloged as Gum 56 for Australian astronomer Colin Stanley Gum, but seafood-loving astronomers might know this cosmic cloud as the Prawn Nebula. The tantalizing color image is a new astronomical composition using data from the European Southern Observatory's wide field OmegaCAM and amateur images made under dark skies on the Canary Island of Tenerife.

Image credit: R. Colombari
The Lunar X (2016-12-10)

The striking X appearing in this lunarscape is easily visible in binoculars or a small telescope. Yet, not too many have seen it. The catch is this lunar X is fleeting, only apparent in the hours before the Moon's first quarter phase. At the terminator, or shadow line between lunar day and night, the X illusion is produced by a configuration of the craters Blanchinus, La Caille and Purbach. Near the Moon's first quarter phase, an astronaut standing close to the craters' position would see the slowly rising Sun very near the horizon. Temporarily, the crater walls would be in sunlight while the crater floors were still in darkness. Seen from planet Earth, contrasting sections of bright walls against the dark floors by chance look remarkably like an X. This sharp image of the Lunar X was captured at approximately 16:45 UT on December 6, 2016. For extra credit, sweep your gaze along the lunar terminator and you can also spot the Lunar V.

Image credit: Alessandro Marchini
The Extraordinary Spiral in LL Pegasi (2016-12-11)

What created the strange spiral structure on the left?  No one is sure, although it is likely related to a star in a binary star system entering the planetary nebula phase, when its outer atmosphere is ejected.  The huge spiral spans about a third of a light year across and, winding four or five complete turns, has a regularity that is without precedent.  Given the expansion rate of the spiral gas, a new layer must appear about every 800 years, a close match to the time it takes for the two stars to orbit each other. The star system that created it is most commonly known as LL Pegasi, but also AFGL 3068. The unusual structure itself has been cataloged as IRAS 23166+1655. The featured image was taken in near-infrared light by the Hubble Space Telescope. Why the spiral glows is itself a mystery, with a leading hypothesis being illumination by light reflected from nearby stars.
Over Saturn's Turbulent North Pole (2016-12-12)

The Cassini spacecraft's Grand Finale at Saturn has begun. The Grand Finale will allow Cassini to explore Saturn and some of Saturn's moons and rings in unprecedented detail.  The first phase started two weeks ago when a close flyby of Titan changed Cassini's orbit into one that passes near Saturn's poles and just outside of Saturn's outermost F-ring. Featured here is an image taken during the first of Cassini's 20 week-long F-ring orbits around Saturn.  Visible are the central polar vortex on the upper left, a hexagonal cloud boundary through the image center, and numerous light-colored turbulent storm systems. In 2017 April, Cassini will again use the gravity of Titan to begin a new series of 22 Proximal orbits -- trajectories that will take Cassini inside of Saturn's rings for the first time.  Cassini's new science adventure is scheduled to end on 2017 September 17, though, when the robotic spacecraft will be directed into a dramatic mission-ending dive into Saturn's atmosphere.    Free Download: APOD 2017 Calendar: NASA Images
Meteors over Four Girls Mountain (2016-12-13)

On some nights it rains meteors.  Peaking over the next two nights, asteroid dust is expected to rain down on Earth during the annual Geminids meteor shower. This year, unfortunately, fainter Geminids will be harder to see because of the brightness of the Long Nights Full Moon, which occurs Wednesday. Pictured, an image from this year's Perseids meteor shower in August captured multiple streaks over Four Girls Mountain in central China. The bright Pleaides open star cluster appears toward the upper right, while numerous emission nebulas are visible in red, many superposed on the diagonal band of the Milky Way.   Free Download: APOD 2017 Calendar: NASA Images

Image credit: Alvin Wu
The Lagoon Nebula in High Definition (2016-12-14)

Stars are battling gas and dust in the Lagoon Nebula but the photographers are winning. Also known as M8, this photogenic nebula is visible even without binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos. The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dark dust filaments that lace M8 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. The light from M8 we see today left about 5,000 years ago. Light takes about 50 years to cross this section of M8. Data used to compose this image was taken with the wide-field camera OmegaCam of the ESO's VLT Survey Telescope (VST).   Free Download: APOD 2017 Calendar: NASA Images

Image credit: R. Colombari
Seagull to Sirius (2016-12-15)

This broad, beautiful mosaic spans almost 20 degrees across planet Earth's sky. The nebula-rich region lies near the edge of the Orion-Eridanus superbubble, filled with looping, expanding shells of gas and dust embedded in molecular clouds near the plane of the Milky Way Galaxy. Recognizable at the left is the expansive Seagull Nebula, composed of emission nebula NGC 2327, seen as the seagull's head, with the more diffuse IC 2177 as the wings and body. Some 3,800 light-years away, the wings of the Seagull Nebula spread about 240 light-years, still within our local spiral arm. The bluish light of Sirius, alpha star of Canis Major and brightest star in the night, easily dominates the scene at right but shines from a distance of only 8.6 light-years. Study the big picture and you should also be rewarded with star cluster Messier 41, also known as NGC 2287, not to mention the mighty Thor's Helmet.

Image credit: Rogelio Bernal
Andreo
Meteors vs Supermoon (2016-12-16)

Geminid meteors battled supermoonlight in planet Earth's night skies on December 13/14. Traveling at 35 kilometers (22 miles) per second, the bits of dust from the mysterious asteroid 3200 Phaethon that produce the meteor streaks are faster than a speeding bullet. Still, only the brightest were visible during the long night of 2016's final Perigee Full Moon. Captured in exposures made over several hours, a few meteors from the shower's radiant in Gemini can be traced through this composite nightscape. With stars of Orion near the horizon, the overexposed lunar disk illuminates still waters of the Miyun reservoir northeast of Beijing, China.

Image credit: Wang, Letian
Southern Jupiter from Perijove 3 (2016-12-17)

Southern Jupiter looms some 37,000 kilometers away in this JunoCam image from December 11. The image data was captured near Juno's third perijove or closest approach to Jupiter, the spacecraft still in its 53 day long looping orbit. With the south polar region on the left, the large whitish oval toward the right is massive, counterclockwise rotating storm system. Smaller than the more famous Great Red Spot, the oval storm is only about half the diameter of planet Earth, one of a string of white ovals currently in the southern hemisphere of the Solar System's, ruling gas giant.
The Cartwheel Galaxy from Hubble (2016-12-18)

To some, it looks like the wheel of a cart. In fact, because of its outward oval appearance, the presence of a central galaxy, and their connection with what looks like the spokes of a wheel, the galaxy on the right is known as the Cartwheel Galaxy. To others, however, it looks like a complicated interaction between galaxies awaiting explanation. Along with the two galaxies on the left, the Cartwheel is part of a group of galaxies about 400 million light years away in the constellation Sculptor.  The large galaxy's rim spans over 100,000 light years and is composed of star forming regions filled with extremely bright and massive stars.  Pictured, the Cartwheel's ring-like shape is the result of gravitational disruption caused by a smaller galaxy passing through a large one, compressing the interstellar gas and dust and causing a star formation wave to move out like a ripple across the surface of a pond.   Free Download: APOD 2017 Calendar: NASA Images
Supermoon over Spanish Castle (2016-12-19)

No, this castle was not built with the Moon attached.  To create the spectacular juxtaposition, careful planning and a bit of good weather was needed.  Pictured, the last supermoon of 2016 was captured last week rising directly beyond one of the towers of Bellver Castle in Palma de Mallorca on the Balearic Islands of Spain.  The supermoon was the last full moon of 2016 and known to some as the Oak Moon. Bellver Castle was built in the early 1300s and has served as a home -- but occasional as a prison -- to numerous kings and queens.  The Moon was built about 4.5 billion years ago, possibly resulting from a great collision with a Mars-sized celestial body and Earth.  The next supermoon, defined as when the moon appears slightly larger and brighter than usual, will occur on 2017 December 3 and be visible not only behind castles but all over the Earth.

Image credit: Tomeu Mas
Sharpless 308: Star Bubble (2016-12-20)

Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged as Sharpless 2-308 it lies some 5,200 light-years away toward the constellation of the Big Dog (Canis Major) and covers slightly more of the sky than a full moon. That corresponds to a diameter of 60 light-years at its estimated distance. The massive star that created the bubble, a Wolf-Rayet star, is the bright one near the center of the nebula. Wolf-Rayet stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution. The windblown nebula has an age of about 70,000 years. Relatively faint emission captured in the expansive image is dominated by the glow of ionized oxygen atoms mapped to a blue hue.

Image credit: Anis Abdul
Traces of the Sun (2016-12-21)

This year the December Solstice is today, December 21, at 10:44 UT, the first day of winter in the north and summer in the south. To celebrate, watch this amazing timelapse video tracing the Sun's apparent movement over an entire year from Hungary. During the year, a fixed video camera captured an image every minute. In total, 116,000 exposures follow the Sun's position across the field of view, starting from the 2015 June 21 solstice through the 2016 June 20 solstice. The intervening 2015 December 22 solstice is at the bottom of the frame. The timelapse sequences constructed show the Sun's movement over one day to begin with, followed by traces of the Sun's position during the days of one year, solstice to solstice. Gaps in the daily curves are due to cloud cover. The video ends with stunning animation sequences of analemmas, those figure-8 curves you get by photographing the Sun at the same time each day throughout a year, stepping across planet Earth's sky.

Image credit: György
Bajmóczy