juliensimon/nasa-apod huggingface dataset:
Two Hemisphere Night Sky (2020-02-27)

The Sun is hidden by a horizon that runs across the middle in this two hemisphere view of Earth's night sky. The digitally stitched mosaics were recorded from corresponding latitudes, one 29 degrees north and one 29 degrees south of the planet's equator. On top is the northern view from the IAC observatory at La Palma taken in February 2020. Below is a well-matched southern scene from the ESO La Silla Observatory recorded in April 2016. In this projection, the Milky Way runs almost vertically above and below the horizon. Its dark clouds and and bright nebulae are prominent near the galactic center in the lower half of the frame. In the upper half, brilliant Venus is immersed in zodiacal light. Sunlight faintly scattered by interplanetary dust, the zodiacal light traces the Solar System's ecliptic plane in a complete circle through the starry sky. Large telescope domes bulge along the inverted horizon from La Silla while at La Palma, multi-mirror Magic telescopes stand above center. Explore this two hemisphere night sky and you can also find the Andromeda Galaxy and the Large and Small Magellanic Clouds.

Image credit: Petr
Horálek
South Celestial Rocket Launch (2020-02-28)

At sunset on December 6 a Rocket Lab Electron rocket was launched from a rotating planet. With multiple small satellites on board it departed on a mission to low Earth orbit dubbed Running Out of Fingers from Mahia Peninsula on New Zealand's north island. The fiery trace of the Electron's graceful launch arc is toward the south in this southern sea and skyscape. Drifting vapor trails and rocket exhaust plumes catch the sunlight even as the sky grows dark though, the setting Sun still shinning at altitude along the rocket's trajectory. Fixed to a tripod, the camera's perspective nearly aligns the peak of the rocket arc with the South Celestial Pole, but no bright star marks that location in the southern hemisphere's evening sky. Still, it's easy to find at the center of the star trail arcs in the timelapse composite.

Image credit: Brendan Gully
Julius Caesar and Leap Days (2020-02-29)

In 46 BC Julius Caesar reformed the calendar system. Based on advice by astronomer Sosigenes of Alexandria, the Julian calendar included one leap day every four years to account for the fact that an Earth year is slightly more than 365 days long. In modern terms, the time it takes for the planet to orbit the Sun once is 365.24219 mean solar days. So if calendar years contained exactly 365 days they would drift from the Earth's year by about 1 day every 4 years and eventually July (named for Julius Caesar himself) would occur during the northern hemisphere winter. By adopting a leap year with an extra day every four years, the Julian calendar year would drift much less. In 1582 Pope Gregory XIII provided the further fine-tuning that leap days should not occur in years ending in 00, unless divisible by 400. This Gregorian Calendar system is the one in wide use today. Of course, tidal friction in the Earth-Moon system slows Earth's rotation and gradually lengthens the day by about 1.4 milliseconds per century. That means that leap days like today will not be necessary ... about 4 million years from now.
A Hole in Mars (2020-03-01)

What created this unusual hole in Mars? The hole was discovered by chance in 2011 on images of the dusty slopes of Mars' Pavonis Mons volcano taken by the HiRISE instrument aboard the robotic Mars Reconnaissance Orbiter currently circling Mars. The hole, shown in representative color, appears to be an opening to an underground cavern, partly illuminated on the image right.  Analysis of this and follow-up images revealed the opening to be about 35 meters across, while the interior shadow angle indicates that the underlying cavern is roughly 20 meters deep. Why there is a circular crater surrounding this hole remains a topic of speculation, as is the full extent of the underlying cavern. Holes such as this are of particular interest because their interior caves are relatively protected from the harsh surface of Mars, making them relatively good candidates to contain Martian life. These pits are therefore prime targets for possible future spacecraft, robots, and even human interplanetary explorers.
Sharpless-308: The Dolphin Nebula (2020-03-02)

Blown by fast winds from a hot, massive star, this cosmic bubble is much larger than the dolphin it appears to be. 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 featured expansive image is dominated by the glow of ionized oxygen atoms mapped to a blue hue.

Image credit: Chilesope 2, 
Pleaides Astrophotography Team (Peking U.)
Apollo 13 Views of the Moon (2020-03-03)

What if the only way to get back to Earth was to go around the far side of the Moon? Such was the dilemma of the Apollo 13 Crew in 1970 as they tried to return home in their unexpectedly damaged spacecraft. With the Moon in the middle, their perilous journey substituted spectacular views of the lunar farside for radio contact with NASA's Mission Control. These views have now been digitally recreated from detailed images of the Moon taken by the robotic Lunar Reconnaissance Orbiter. The featured video starts by showing Earth disappear behind a dark lunar limb, while eight minutes later the Sun rises around the opposite side of the Moon and begins to illuminate the Moon's unusual and spectacularly cratered surface.  Radio contact was only re-established several minutes after that, as a crescent Earth rose into view.  With the gravity of the Moon and the advice of many industrious NASA engineers and scientists, a few days later Apollo 13 opened its parachutes over the Pacific Ocean and landed safely back on Earth.
The Slow Dance of Galaxies NGC 5394 and 5395 (2020-03-04)

If you like slow dances, then this may be one for you.  A single turn in this dance takes several hundred million years.  Two galaxies, NGC 5394 and NGC 5395, slowly whirl about each other in a gravitational interaction that sets off a flourish of sparks in the form of new stars.  The featured image, taken with the Gemini North 8-meter telescope on Maunakea, Hawaii, USA, combines four different colors.  Emission from hydrogen gas, colored red, marks stellar nurseries where new stars drive the evolution of the galaxies.  Also visible are dark dust lanes that mark gas that will eventually become stellar nurseries. If you look carefully you will see many more galaxies in the background, some involved in their own slow cosmic dances.   APOD across world languages: Arabic, Catalan, Chinese (Beijing), Chinese (Taiwan), Croatian, Czech, Dutch, Farsi, French, French, German, Hebrew, Indonesian, Japanese, Korean, Montenegrin, Polish, Russian, Serbian, Slovenian,  Spanish and Ukrainian
The Light, the Dark, and the Dusty (2020-03-05)

This colorful skyscape spans about four full moons across nebula rich starfields along the plane of our Milky Way Galaxy in the royal northern constellation Cepheus. Near the edge of the region's massive molecular cloud some 2,400 light-years away, bright reddish emission region Sharpless (Sh) 155 is left of center, also known as the Cave Nebula. About 10 light-years across the cosmic cave's bright walls of gas are ionized by ultraviolet light from the hot young stars around it. Dusty blue reflection nebulae, like vdB 155 at lower right, and dense obscuring clouds of dust also abound on the interstellar canvas. Astronomical explorations have revealed other dramatic signs of star formation, including the bright red fleck of Herbig-Haro (HH) 168. Below center in the frame, the Herbig-Haro object emission is generated by energetic jets from a newborn star.

Image credit: Casey Good
Mars Panorama from Curiosity (2020-03-06)

The Mars Rover named Curiosity recorded high-resolution, 360 degree views of its location on Mars late last year. The panoramic scene was stitched from over 1,000 images from Curiosity's Mast camera or Mastcam. In this version, captured with Mastcam's medium angle lens, the rover's deck and robotic arm are in the foreground, stretched and distorted by the extreme wide perspective. Just beyond the rover are regions of clay rich rock, evidence for an ancient watery environment, with a clear view toward more distant martian ridges and buttes. Gale crater wall runs across the center (toward the north) in the background over 30 kilometers in the distance. The upper reaches of Mt. Sharp are at the far right. Images to construct the panorama were recorded over 4 consecutive sols between local noon and 2pm to provide consistent lighting. Zoom in to the panoramic scene and you can easily spot the shadow casting sundial mounted on rover's deck (right). In July NASA plans to launch a new rover to Mars named Perseverance.
Pic du Midi Panorama (2020-03-07)

A surreal night skyscape, this panorama stitched from 12 photos looks to the west at an evening winter sky over Pic du Midi Observatory, Pyrenees Mountains, Planet Earth. Telescope domes and a tall communications tower inhabit the rugged foreground. On the right, lights from Tarbes, France about 35 kilometers away impinge on the designated dark sky site though, but more distant terrestrial lights seen toward the left are from cities in Spain. Stars and nebulae of the northern winter's Milky Way arc through the sky above. Known to the planet's night skygazers, the Pleiades and Hyades star clusters still hang over the western horizon near center. Captured in mid February the familiar stars of the constellation Orion are to the left and include the no longer fainting star Betelgeuse.

Image credit: Patrick Lécureuil
Wolf-Rayet Star 124: Stellar Wind Machine (2020-03-08)

Some stars explode in slow motion.  Rare, massive Wolf-Rayet stars are so tumultuous and hot that they are slowly disintegrating right before our telescopes.  Glowing gas globs each typically over 30 times more massive than the Earth are being expelled by violent stellar winds.  Wolf-Rayet star WR 124, visible near the featured image center spanning six light years across, is thus creating the surrounding nebula known as M1-67.  Details of why this star has been slowly blowing itself apart over the past 20,000 years remains a topic of research.  WR 124 lies 15,000 light-years away towards the constellation of the Arrow (Sagitta).  The fate of any given Wolf-Rayet star likely depends on how massive it is, but many are thought to end their lives with spectacular explosions such as supernovas or gamma-ray bursts.
Milky Way and Zodiacal Light over Chile (2020-03-09)

What is the band of light connecting the ground to the Milky Way?  Zodiacal light -- a stream of dust that orbits the Sun in the inner Solar System. It is most easily seen just before sunrise, where it has been called a false dawn, or just after sunset. The origin of zodiacal dust remains a topic of research, but is hypothesized to result from asteroid collisions and comet tails.  The featured wide-angle image shows the central band of our Milky Way Galaxy arching across the top, while the Large Magellanic Cloud (LMC), a satellite galaxy to our Milky Way, is visible on the far left. The image is a combination of over 30 exposures taken last July near La Serena among the mountains of Chile.  During the next two months, zodiacal light can appear quite prominent in northern skies just after sunset.   Almost Hyperspace: Random APOD Generator

Image credit: Roman Ponča
(ht: Masaryk U.)
Wide Field: Fox Fur, Unicorn, and Christmas Tree (2020-03-10)

What do the following things have in common: a cone, the fur of a fox, and a Christmas tree?  Answer: they all occur in the constellation of the unicorn (Monoceros).  Pictured as a star forming region and cataloged as NGC 2264, the complex jumble of cosmic gas and dust is about 2,700 light-years distant and mixes reddish emission nebulae excited by energetic light from newborn stars with dark interstellar dust clouds. Where the otherwise obscuring dust clouds lie close to the hot, young stars they also reflect starlight, forming blue reflection nebulae. The featured wide-field image spans over three times the diameter of a full moon, covering over 100 light-years at the distance of NGC 2264. Its cast of cosmic characters includes the Fox Fur Nebula, whose convoluted pelt lies just to the lower right of the image center, bright variable star S Mon visible just above the Fox Fur, and the Cone Nebula just to the left.  Given their distribution, the stars of NGC 2264 are also known as the Christmas Tree star cluster.

Image credit: Greg Gurdak
An Extreme Black Hole Outburst (2020-03-11)

Astronomers believe they have now found the most powerful example of a black hole outburst yet seen in our Universe.  The composite, false-color featured image is of a cluster of galaxies in the constellation of Ophiuchus, the serpent-bearer.  The composite includes X-ray images (from the Chandra X-ray Observatory and XMM-Newton) in purple, and a radio image (from India's Giant Metrewave Radio Telescope) in blue (along with an infrared image of the galaxies and stars in the field in white for good measure).  The dashed line marks the border of a cavity blown out by the supermassive black hole which lurks at the center of the galaxy marked by the cross.  Radio emission fills this cavity.  This big blowout is believed to be due to the black hole eating too much and experiencing a transient bout of "black hole nausea", which resulted in the ejection of a powerful radio jet blasting into intergalactic space.  The amount of energy needed to blow this cavity is equivalent to about 10 billion supernova explosions.
Falcon 9 Boostback (2020-03-12)

Short star trails appear in this single 84 second long exposure, taken on March 6 from a rotating planet. The remarkable scene also captures the flight of a Falcon 9 rocket and Dragon cargo spacecraft over Cape Canaveral Air Force Station shortly after launch, on a resupply mission bound for the International Space Station. Beginning its return to a landing zone about 9 kilometers from the launch site, the Falcon 9 first stage boostback burn arcs toward the top of the frame. The second stage continues toward low Earth orbit though, its own fiery arc traced below the first stage boostback burn from the camera's perspective, along with expanding exhaust plumes from the two stages. This Dragon spacecraft was a veteran of two previous resupply missions. Successfully returning to the landing zone, this Falcon 9 first stage had flown before too. Its second landing marked the 50th landing of a SpaceX orbital class rocket booster.

Image credit: John Kraus
Starry Night by Jean-Francois Millet (2020-03-13)

A dramatic nocturnal landscape from around 1850, this oil painting is the work of French artist Jean-Francois Millet. In the dark and atmospheric night sky are shooting stars, known too as meteors, above a landscape showing a path through the faintly lit countryside that leads toward trees and a cart in silhouette on the horizon. Millet was raised in a farming family in Normandy and is known for his paintings of rural scenes and peasant life. This Starry Night was painted after the artist moved to Barbizon, about 30 kilometers southeast of any 19th century light pollution from Paris. Millet wrote to his brother at this time, "If only you knew how beautiful the night is ... the calm and grandeur of it are so awesome that I find that I actually feel overwhelmed." Dutch artist Vincent van Gogh was an admirer of Millet's work, and later also painted two dramatic starry nights.
Moonrise and Mountain Shadow (2020-03-14)

What phase of the Moon is 3.14 radians from the Sun? The Full Moon, of course. Even though the Moon might look full for several days, the Moon is truly at its full phase when it is 3.14 radians (aka 180 degrees) from the Sun in ecliptic longitude. That's opposite the Sun in planet Earth's sky. Rising as the Sun set on March 9, only an hour or so after the moment of its full phase, this orange tinted and slightly flattened Moon still looked full. It was photographed opposite the setting Sun from Teide National Park on the Canary Island of Tenerife. Also opposite the setting Sun, seen from near the Teide volcano peak about 3,500 meters above sea level, is the mountain's rising triangular shadow extending into Earth's dense atmosphere. Below the distant ridge line on the left are the white telescope domes of Teide Observatory

Image credit: El Cielo de Canarias
The Snows of Churyumov-Gerasimenko (2020-03-15)

You couldn't really be caught in this blizzard while standing by a cliff on Churyumov-Gerasimenko. Orbiting the comet -- frequently abbreviated as 67P or CG -- in June of 2016, the Rosetta spacecraft's narrow angle camera did record streaks of dust and ice particles -- similar to snow -- as they drifted across the field of view near the camera and above the comet's surface. Some of the bright specks in the scene, however, are likely due to a rain of energetic charged particles or cosmic rays hitting the camera, and the dense background of stars in the direction of the constellation of the Big Dog (Canis Major). In the featured video, these background stars are easy to spot trailing from top to bottom. The stunning movie was constructed from 33 consecutive images taken over 25 minutes while Rosetta cruised some 13 kilometers from the comet's nucleus.
A Moon Dressed Like Saturn (2020-03-16)

Why does Saturn appear so big? It doesn't -- what is pictured are foreground clouds on Earth crossing in front of the Moon. The Moon shows a slight crescent phase with most of its surface visible by reflected Earthlight known as ashen glow. The Sun directly illuminates the brightly lit lunar crescent from the bottom, which means that the Sun must be below the horizon and so the image was taken before sunrise.  This double take-inducing picture was captured on 2019 December 24, two days before the Moon slid in front of the Sun to create a solar eclipse. In the foreground, lights from small Guatemalan towns are visible behind the huge volcano Pacaya.   Follow APOD in English on: Instagram, Facebook,  Reddit, or Twitter

Image credit: Francisco Sojuel
M77: Spiral Galaxy with an Active Center (2020-03-17)

What's happening in the center of nearby spiral galaxy M77? The face-on galaxy lies a mere 47 million light-years away toward the constellation of the Sea Monster (Cetus).  At that estimated distance, this gorgeous island universe is about 100 thousand light-years across.  Also known as NGC 1068, its compact and very bright core is well studied by astronomers exploring the mysteries of supermassive black holes in active Seyfert galaxies.  M77 and its active core glows bright at x-ray, ultraviolet, visible, infrared, and radio wavelengths.  The featured sharp image of M77 was taken by the Hubble Space Telescope and is dominated by the (visible) red light emitted by hydrogen.  The image shows details of the spiral's winding spiral arms as traced by obscuring dust clouds, and red-tinted star forming regions close in to the galaxy's luminous core.    Astrophysicists: Browse 2,100+ codes in the Astrophysics Source Code Library
Anticrepuscular Rays over Florida (2020-03-18)

What's happening behind those clouds?  Although the scene may appear somehow supernatural, nothing more unusual is occurring than a Sun setting on the other side of the sky.  Pictured here 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.  Featured here is a particularly striking display of anticrepuscular rays photographed in 2016 over Dry Tortugas National Park in Florida, USA.

Image credit: Bryan Goff
M13: The Great Globular Cluster in Hercules (2020-03-19)

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 less modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Sharp telescopic views like this one 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. 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. The remarkable range of brightness recorded in this image follows stars into the dense cluster core and reveals three subtle dark lanes forming the apparent shape of a propeller just below and slightly left of center. Distant background galaxies in the medium-wide field of view include NGC 6207 at the upper left.

Image credit: Eric Coles
Morning, Planets, Moon and Montreal (2020-03-20)

Dawn's early light came to Montreal, northern planet Earth, on March 18, the day before the vernal equinox. At the end of that nearly equal night the Moon stands above a dense constellation of urban lights in this serene city and skyscape. Of course the Moon's waning crescent faces toward the rising Sun. Skygazers could easily spot bright Jupiter just above the Moon, close on the sky to a fainter Mars. Saturn, a telescopic favorite, is just a pinprick of light below and farther left of the closer conjunction of Moon, Jupiter and Mars. Near the ecliptic, even Mercury is rising along a line extended to the horizon from Jupiter and Saturn. The elusive inner planet is very close to the horizon though, and not quite visible in this morning's sky.

Image credit: Arnaud Mariat
Comet ATLAS and the Mighty Galaxies (2020-03-21)

Comet ATLAS C/2019 Y4 was discovered by the NASA funded Asteroid Terrestrial-impact Last Alert System, the last comet discovery reported in 2019. Now growing brighter in northern night skies, the comet's pretty greenish coma is at the upper left of this telescopic skyview captured from a remotely operated observatory in New Mexico on March 18. At lower right are M81 and M82, well-known as large, gravitationally interacting galaxies. Seen through faint dust clouds above the Milky Way, the galaxy pair lies about 12 million light-years distant, toward the constellation Ursa Major. In bound Comet ATLAS is about 9 light-minutes from Earth, still beyond the orbit of Mars. The comet's elongated orbit is similar to orbit of the Great Comet of 1844 though, a trajectory that will return this comet to the inner Solar System in about 6,000 years.  Comet ATLAS will reach a perihelion or closest approach to the Sun on May 31 inside the orbit of Mercury and may become a naked-eye comet in the coming days.

Image credit: CARA Project