juliensimon/nasa-apod huggingface dataset:
Capsule Returns from Asteroid Ryugu (2020-12-14)

The streak across the sky is a capsule returning from an asteroid. It returned earlier this month from the near-Earth asteroid 162173 Ryugu carrying small rocks and dust from its surface.  The canister was released by its mothership, Japan's Hayabusa2, a mission that visited Ryugu in 2018, harvested a surface sample in 2019, and zoomed back past Earth.  The jettisoned return capsule deployed a parachute and landed in rural Australia. A similar mission, NASA's OSIRIS- REx, recently captured rocks and dust from a similar asteroid, Bennu, and is scheduled to return its surface sample to Earth in 2023. Analyses of compounds from these asteroids holds promise to give humanity new insights about the early Solar System and new clues about how water and organic matter came to be on Earth.   Experts Debate: How will humanity first discover extraterrestrial life?
Great Conjunction: Saturn and Jupiter Converge (2020-12-15)

It's happening. Saturn and Jupiter are moving closer and will soon appear in almost exactly the same direction.  Coincidentally, on the night of the December solstice -- the longest night of the year in the north and the longest day in the south -- the long-awaited Great Conjunction will occur. Then, about six days from now, Saturn and Jupiter will be right next to each other -- as they are every 20 years. But this juxtaposition is not just any Great Conjunction -- it will be the closest since 1623 because the two planetary giants will pass only 1/10th of a degree from each other -- well less than the apparent diameter of a full moon.  In the next few days a crescent moon will also pass a few degrees away from the converging planets and give a preliminary opportunity for iconic photos.  The featured illustration shows the approach of Saturn and Jupiter during November and December over the French Alps.   Growing Gallery: Notable images of the Great Conjunction submitted to APOD

Image credit: Sebastian Voltmer
Sonified: The Matter of the Bullet Cluster (2020-12-16)

What's the matter with the Bullet Cluster? This massive cluster of galaxies (1E 0657-558) creates gravitational lens distortions of background galaxies in a way that has been interpreted as strong evidence for the leading theory: that dark matter exists within. Different analyses, though, indicate that a less popular alternative -- modifying gravity-- could explain cluster dynamics without dark matter, and provide a more likely progenitor scenario as well. Currently, the two scientific hypotheses are competing to explain the observations: it's invisible matter versus amended gravity. The duel is dramatic as a clear Bullet-proof example of dark matter would shatter the simplicity of modified gravity theories.  The featured sonified image is a Hubble/Chandra/Magellan composite with red depicting the X-rays emitted by hot gas, and blue depicting the suggested separated dark matter distribution.  The sonification assigns low tones to dark matter, mid-range frequencies to visible light, and high tones to X-rays.  The battle over the matter in the Bullet cluster is likely to continue as more observations, computer simulations, and analyses are completed.    Submitted to APOD: Notable images of the 2020 Geminids Meteor Shower
Gemini's Meteors (2020-12-17)

Taken over the course of an hour shortly after local midnight on December 13, 35 exposures were used to create this postcard from Earth. The composited night scene spans dark skies above the snowy Italian Dolomites during our fair planet's annual Geminid meteor shower. Sirius, alpha star of Canis Major and the brightest star in the night, is grazed by a meteor streak on the right. The Praesepe star cluster, also known as M44 or the Beehive cluster, itself contains about a thousand stars but appears as a smudge of light far above the southern alpine peaks near the top. The shower's radiant is off the top of the frame though, near Castor and Pollux the twin stars of Gemini. The radiant effect is due to perspective as the parallel meteor tracks appear to converge in the distance. As Earth sweeps through the dust trail of asteroid 3200 Phaethon, the dust that creates Gemini's meteors enters Earth's atmosphere traveling at about 22 kilometers per second.   Submitted to APOD: Notable images of the 2020 Geminids Meteor Shower

Image credit: Stefano Pellegrini
Diamond in the Sky (2020-12-18)

When the shadow of the Moon raced across planet Earth's southern hemisphere on December 14, sky watchers along the shadow's dark central path were treated to the only total solar eclipse of 2020. During the New Moon's shadow play this glistening diamond ring was seen for a moment, even in cloudy skies. Known as the diamond ring effect, the transient spectacle actually happens twice. Just before and immediately after totality, a thin sliver of solar disk visible behind the Moon's edge creates the appearance of a shiny jewel set in a dark ring. This dramatic snapshot from the path of totality in northern Patagonia, Argentina captures this eclipse's second diamond ring, along with striking solar prominences lofted beyond the edge of the Moon's silhouette.

Image credit: Mariano Ribas
Conjunction after Sunset (2020-12-19)

How close will Jupiter and Saturn be at their Great Conjunction? Consider this beautiful triple conjunction of Moon, Jupiter and Saturn captured through clouds in the wintry twilight. The telephoto view looks toward the western horizon and the Alborz Mountains in Iran after sunset on December 17. The celestial gathering makes it easy to see Jupiter and fainter Saturn are separated on that date by roughly the diameter of the waxing crescent Moon. On the day of their Great Conjunction, solstice day December 21, Jupiter and Saturn may seem to nearly merge though. In their closest conjunction in 400 years they will be separated on the sky by only about 1/5 the apparent diameter of the Moon. By then the two largest worlds in the Solar System and their moons will be sharing the same field of view in telescopes around planet Earth.

Image credit: Alireza Vafa
A Volcanic Great Conjunction (2020-12-20)

Where can I see the Great Conjunction?  Near where the Sun just set. Directionally, this close passing of Jupiter and Saturn will be toward the southwest. Since the planetary pair, the Sun, and the Earth are nearly in a geometric straight line, the planets will be seen to set just where the Sun had set -- from every location on Earth.  When can I see the Great Conjunction?  Just after sunset.  Since the two planets are so near the Sun directionally, they always appear in the sky near the Sun, but can best be seen when the Earth blocks the Sun but not the planets: sunset.  Soon thereafter, Jupiter and Saturn will also set, so don't be late!   Is tomorrow night the only night that I can see the Great Conjunction?  Tomorrow night the jovian giants will appear the closest, but on any night over the next few days they will appear unusually close. Technically, the closest pass happens on 21 December at 18:20 UTC.    Will there be an erupting volcano on the horizon near the Great Conjunction? Yes, for example if you live in Guatemala where the featured image was taken. Otherwise, generally, no.  In the featured image captured last week, Jupiter and Saturn are visible toward the right, just above a tree, and bathed in the diffuse glow of zodiacal light.   Growing Gallery: Notable images of the Great Conjunction submitted to APOD

Image credit: Francisco Sojuel
Solstice: Sunrises Around the Year (2020-12-21)

Does the Sun always rise in the same direction?  No.  As the months change, the direction toward the rising Sun changes, too.  The featured image shows the direction of sunrise every month during 2019 as seen from near the city of Amman, Jordan.  The camera in the image is always facing due east, with north toward the left and south toward the right.  Although the Sun always rises in the east in general, it rises furthest to the south of east on the December solstice, and furthest north of east on the June solstice. Today is the December solstice, the day of least sunlight in the Northern Hemisphere and of most sunlight in the Southern Hemisphere.  In many countries, the December Solstice is considered an official change in season: for example the first day of winter in the North.  Solar heating and stored energy in the Earth's surface and atmosphere are near their lowest during winter, making the winter months usually the coldest of the year.  On the brighter side, in the north, daylight hours will now increase every day from until June.   Sunset: The Great Conjunction of Jupiter & Saturn

Image credit: Zaid M. Al-Abbadi
Trifid Pillars and Jets (2020-12-22)

Dust pillars are like interstellar mountains.  They survive because they are more dense than their surroundings, but they are being slowly eroded away by a hostile environment.  Visible in the featured picture is the end of a huge gas and dust pillar in the Trifid Nebula (M20), punctuated by a smaller pillar pointing up and an unusual jet pointing to the left.  Many of the dots are newly formed low-mass stars. A star near the small pillar's end is slowly being stripped of its accreting gas by radiation from a tremendously brighter star situated off the top of the image.  The jet extends nearly a light-year and would not be visible without external illumination.  As gas and dust evaporate from the pillars, the hidden stellar source of this jet will likely be uncovered, possibly over the next 20,000 years.   Growing Gallery: Notable images of the Great Conjunction submitted to APOD
Jupiter Meets Saturn: A Red Spotted Great Conjunction (2020-12-23)

It was time for their close-up. Two days ago  Jupiter and Saturn passed a tenth of a degree from each other in what is known a Great Conjunction. Although the two planets pass each other on the sky every 20 years, this was the closest pass in nearly four centuries.  Taken early in day of the Great Conjunction, the featured multiple-exposure combination captures not only both giant planets in a single frame, but also Jupiter's four largest moons (left to right) Callisto, Ganymede, Io, and Europa --  and Saturn's largest moon Titan. If you look very closely, the clear Chilescope image even captures Jupiter's Great Red Spot. The now-separating planets can still be seen remarkably close -- within about a degree -- as they set just after the Sun, toward the west, each night for the remainder of the year.    Gallery: Notable images of the Great Conjunction submitted to APOD

Image credit: Damian Peach
Portrait of NGC 1055 (2020-12-24)

Big, beautiful spiral galaxy NGC 1055 is a dominant member of a small galaxy group a mere 60 million light-years away toward the aquatically intimidating constellation Cetus. Seen edge-on, the island universe spans over 100,000 light-years, a little larger than our own Milky Way galaxy. The colorful, spiky stars decorating this cosmic portrait of NGC 1055 are in the foreground, well within the Milky Way. But the telltale pinkish star forming regions are scattered through winding dust lanes along the distant galaxy's thin disk. With a smattering of even more distant background galaxies, the deep image also reveals a boxy halo that extends far above and below the central bluge and disk of NGC 1055. The halo itself is laced with faint, narrow structures, and could represent the mixed and spread out debris from a satellite galaxy disrupted by the larger spiral some 10 billion years ago.

Image credit: Martin Pugh
Northern Winter Night (2020-12-25)

Orion always seems to come up sideways on northern winter evenings. Those familiar stars of the constellation of the Hunter are caught above the trees in this colorful night skyscape. Not a star at all but still visible to eye, the Great Nebula of Orion shines below the Hunter's belt stars. The camera's exposure reveals the stellar nursery's faint pinkish glow. Betelgeuse, giant star at Orion's shoulder, has the color of warm and cozy terrestrial lighting, but so does another familiar stellar giant, Aldebaran. Alpha star of the constellation Taurus the Bull, Aldebaran anchors the recognizable V-shape traced by the Hyades Cluster toward the top of the starry frame.

Image credit: Adam Block
Fox Fur, Unicorn, and Christmas Tree (2020-12-26)

Clouds of glowing hydrogen gas fill this colorful skyscape in the faint but fanciful constellation Monoceros, the Unicorn. A star forming region 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 telescopic image spans about 1.5 degrees or 3 full moons, covering nearly 80 light-years at the distance of NGC 2264. Its cast of cosmic characters includes the the Fox Fur Nebula, whose dusty, convoluted pelt lies left of center, bright variable star S Monocerotis immersed in the blue-tinted haze near center, and the Cone Nebula pointing in from the right side of the frame. Of course, the stars of NGC 2264 are also known as the Christmas Tree star cluster. The triangular tree shape is seen on its side here. Traced by brighter stars it has its apex at the Cone Nebula. The tree's broader base is centered near S Monocerotis.

Image credit: Miguel Claro
Cosmic Latte: The Average Color of the Universe (2020-12-27)

What color is the universe?  More precisely, if the entire sky were smeared out, what color would the final mix be?  This whimsical question came up when trying to determine what stars are commonplace in nearby galaxies. The answer, depicted above, is a conditionally perceived shade of beige. In computer parlance: #FFF8E7.  To determine this, astronomers computationally averaged the light emitted by one of the larger samples of galaxies analyzed: the 200,000 galaxies of the 2dF survey.  The resulting cosmic spectrum has some emission in all parts of the electromagnetic spectrum, but a single perceived composite color.  This color has become much less blue over the past 10 billion years, indicating that redder stars are becoming more prevalent.  In a contest to better name the color, notable entries included skyvory, univeige, and the winner: cosmic latte.   Gallery: Notable images of the Great Conjunction submitted to APOD
M16: Inside the Eagle Nebula (2020-12-28)

From afar, the whole thing looks like an Eagle.  A closer look at the Eagle Nebula, however, shows the bright region is actually a window into the center of a larger dark shell of dust.  Through this window, a brightly-lit workshop appears where a whole open cluster of stars is being formed.  In this cavity tall pillars and round globules of dark dust and cold molecular gas remain where stars are still forming.  Already visible are several young bright blue stars whose light and winds are burning away and pushing back the remaining filaments and walls of gas and dust.  The Eagle emission nebula, tagged M16, lies about 6500 light years away, spans about 20 light-years, and is visible with binoculars toward the constellation of the Serpent (Serpens).  This picture involved over 12 hours of imaging and combines three specific emitted colors emitted by sulfur (colored as red), hydrogen (yellow), and oxygen (blue).   Gallery: Notable images of the recent Total Solar Eclipse submitted to APOD

Image credit: Nicolas Paladini
Earth During a Total Solar Eclipse (2020-12-29)

What does the Earth look like during a total solar eclipse? It appears dark in the region where people see the eclipse, because that's where the shadow of the Moon falls. The shadow spot rapidly shoots across the Earth at nearly 2,000 kilometers per hour, darkening locations in its path -- typically for only a few minutes -- before moving on. The featured video shows the Earth during the total solar eclipse earlier this month.  The time-lapse sequence, taken from a geostationary satellite, starts with the Earth below showing night but the sun soon rises at the lower right.  Clouds shift as day breaks over the blue planet. Suddenly the circular shadow of the Moon appears on the left and moves rapidly across South America, disappearing on the lower right.  The video ends as nightfall begins again.  The next total solar eclipse will occur next December -- but be visible only from parts of Antarctica.   Gallery: Notable images of the recent Total Solar Eclipse submitted to APOD
Jupiter and Saturn Great Conjunction: The Movie (2020-12-30)

Yes, but have you seen a movie of Jupiter and Saturn's Great Conjunction? The featured time-lapse video was composed from a series of images taken from Thailand and shows the two giant planets as they angularly passed about a tenth of a degree from each other.  The first Great Conjunction sequence shows a relative close up over five days with moons and cloud bands easily visible, followed by a second video sequence, zoomed out, over 9 days.  Even though Jupiter and Saturn appeared to pass unusually close together on the sky on December 21, 2020, in actuality they were still nearly a billion kilometers apart.  The two gas giants are destined for similar meet ups every 19.86 years.  However, they had not come this close, angularly, for the past 397 years, and will not again for another 60 years.  If you're willing to wait until the year 7541, though, you can see Jupiter  pass directly in front of Saturn.    Gallery: Notable images of the Great Conjunction submitted to APOD
Trail of the Returner (2020-12-31)

Familiar stars of a northern winter's night shine in this night skyview, taken near Zhangye, Gansu, China and the border with Inner Mongolia. During the early hours of December 17 Orion is near center in the single exposure that captures a fireball streaking across the sky, almost as bright as yellowish Mars shining on the right. Splitting Gemini's twin bright stars Castor and Pollux near the top of the frame, the fireball's trail and timing are consistent with the second skipping atmospheric entry of the Chang'e 5 mission's returner capsule. The returner capsule was successfully recovered after landing in Inner Mongolia, planet Earth with about 2 kilograms of lunar material on board. The lunar sample is thought to contain relatively young material collected near the Mons Rumker region of the Moon's Oceanus Procellarum. Launched on November 23 UT, China's Chang'e 5 mission is the first lunar sample return mission since the Soviet Union’s Luna 24 mission in 1976.

Image credit: Zhuoxiao Wang
Galaxies and the South Celestial Pole (2021-01-01)

The South Celestial Pole is easy to spot in star trail images of the southern sky. The extension of Earth's axis of rotation to the south, it's at the center of all the southern star trail arcs. In this starry panorama streching about 60 degrees across deep southern skies the South Celestial Pole is somewhere near the middle though, flanked by bright galaxies and southern celestial gems. Across the top of the frame are the stars and nebulae along the plane of our own Milky Way Galaxy. Gamma Crucis, a yellowish giant star heads the Southern Cross near top center, with the dark expanse of the Coalsack nebula tucked under the cross arm on the left. Eta Carinae and the reddish glow of the Great Carina Nebula shine along the galactic plane near the right edge. At the bottom are the Large and Small Magellanic clouds, external galaxies in their own right and satellites of the mighty Milky Way. A line from Gamma Crucis through the blue star at the bottom of the southern cross, Alpha Crucis, points toward the South Celestial Pole, but where exactly is it? Just look for south pole star Sigma Octantis. Analog to Polaris the north pole star, Sigma Octantis is little over one degree fom the the South Celestial pole.

Image credit: Petr Horalek
21st Century Wet Collodion Moon (2021-01-02)

In the mid 19th century, one of the first photographic technologies used to record the lunar surface was the wet-plate collodion process, notably employed by British astronomer Warren De la Rue. To capture an image, a thick, transparent mixture was used to coat a glass plate, sensitized with silver nitrate, exposed at the telescope, and then developed to create a negative image on the plate. To maintain photographic sensitivity, the entire process, from coating to exposure to developing, had to be completed before the plate dried, in a span of about 10 to 15 minutes. This modern version of a wet-plate collodion image celebrates lunar photography's early days, reproducing the process using modern chemicals to coat a glass plate from a 21st century hardware store. Captured last November 28 with an 8x10 view camera and backyard telescope, it faithfully records large craters, bright rays, and dark, smooth mare of the waxing gibbous Moon. Subsequently digitized, the image on the plate was 8.5 centimeters in diameter and exposed while tracking for 2 minutes. The wet plate's effective photographic sensitivity was about ISO 1.  In your smart phone, the camera sensor probably has a photographic sensitivity range of ISO 100 to 6400 (and needs to be kept dry ...).

Image credit: Mike Smolinsky
A Phoenix Aurora over Iceland (2021-01-03)

All of the other aurora watchers had gone home. By 3:30 am in Iceland, on a quiet September night, much of that night's auroras had died down. Suddenly, unexpectedly, a new burst of particles streamed down from space, lighting up the Earth's atmosphere once again. This time, surprisingly, pareidoliacally, the night lit up with an  amazing shape reminiscent of a giant phoenix. With camera equipment at the ready, two quick sky images were taken, followed immediately by a third of the land.  The mountain in the background is Helgafell, while the small foreground river is called Kaldá, both located about 30 kilometers north of Iceland's capital Reykjavík. Seasoned skywatchers will note that just above the mountain, toward the left, is the constellation of Orion, while the Pleiades star cluster is also visible just above the frame center.  The 2016 aurora, which lasted only a minute and was soon gone forever --  would possibly be dismissed as an fanciful fable -- were it not captured in the featured, digitally-composed, image mosaic.    Almost Hyperspace: Random APOD Generator

Image credit: Hallgrimur P. Helgason;
 Rollover Annotation:  Judy Schmidt
Sprite Lightning at 100,000 Frames Per Second (2021-01-04)

What causes sprite lightning? Mysterious bursts of light in the sky that momentarily resemble gigantic jellyfish have been recorded for over 30 years, but apart from a general association with positive cloud-to-ground lightning, their root cause remains unknown. Some thunderstorms have them -- most don't.  Recently, however, high speed videos are better detailing how sprites actually develop.  The featured video, captured in mid-2019, is fast enough -- at about 100,000 frames per second -- to time-resolve several sprite "bombs" dropping and developing into the multi-pronged streamers that appear on still images. Unfortunately, the visual clues provided by videos like these do not fully resolve the sprite origins mystery. High speed vidoes do indicate to some researchers, though, that sprites are more likely to occur when plasma irregularities exist in the upper atmosphere.    Astrophysicists: Browse 2,300+ codes in the Astrophysics Source Code Library

Image credit: Matthew G McHarg, Jacob L Harley, 
Thomas Ashcraft, Hans Nielsen