juliensimon/nasa-apod huggingface dataset:
STARFORGE: A Star Formation Simulation (2021-06-23)

How do stars form?  Most form in giant molecular clouds located in the central disk of a galaxy.  The process is started, influenced, and limited by the stellar winds, jets, high energy starlight, and supernova explosions of previously existing stars. The featured video shows these complex interactions as computed by the STARFORGE simulation of a gas cloud 20,000 times the mass of our Sun. In the time-lapse visualization, lighter regions indicate denser gas, color encodes the gas speed (purple is slow, orange is fast), while dots indicate the positions of newly formed stars. As the video begins, a gas cloud spanning about 50 light years begins to condense under its own gravity.  Within 2 million years, the first stars form, while newly formed massive stars are seen to expel impressive jets. The simulation is frozen after 4.3 million years, and the volume then rotated to gain a three-dimensional perspective. Much remains unknown about star formation, including the effect of the jets in limiting the masses of subsequently formed stars.    Portal Universe: Random APOD Generator
Messier 99 (2021-06-24)

Grand design spiral galaxy Messier 99 looks majestic on a truly cosmic scale. This recently processed full galaxy portrait stretches over 70,000 light-years across M99. The sharp view is a combination of ultraviolet, visible, and infrared image data from the Hubble Space Telescope. About 50 million light-years distant toward the well-groomed constellation Coma Bernices, the face-on spiral is a member of the nearby Virgo Galaxy Cluster. Also cataloged as NGC 4254, a close encounter with another Virgo cluster member has likely influenced the shape of its well-defined, blue spiral arms.
Andromeda in a Single Shot (2021-06-25)

How far can you see? The Andromeda Galaxy, 2.5 million light years away, is the most distant object easily seen by the unaided eye. Other denizens of the night sky, like stars, clusters, and nebulae, are typically hundreds to thousands of light-years distant. That's far beyond the Solar System but well within our own Milky Way Galaxy. Also known as M31, the external galaxy poses directly above a chimney in this well-planned deep night skyscape from an old mine in southern Portugal. The image was captured in a single exposure tracking the sky, so the foreground is slightly blurred by the camera's motion while Andromeda itself looms large. The galaxy's brighter central region, normally all that's visible to the naked-eye, can be seen extending to spiral arms with fainter outer reaches spanning over 4 full moons across the sky. Of course in only 5 billion years or so, the stars of Andromeda could span the entire night sky as the Andromeda Galaxy merges with the Milky Way.

Image credit: Miguel Claro
Pixels in the Sun (2021-06-26)

These two panels, composed of video frames made with a safe solar telescope and hydrogen alpha filter, show remarkably sharp details on the solar disk and giant prominences along the Sun's edge on June 6 (top) and June 18. Taken from Beijing, China, they also show a transit of the International Space Station and China's new Tiangong Space Station in silhouette against the bright Sun. The International Space Station is near center in the bottom panel, crossing the solar disk left of bright active region AR2833 and below a large looping solar filament. China's space station is below solar active region AR2827 and right of center in the top panel, seen as a smaller, combined "+" and "-" shape. The pictures of the transiting orbital outposts were taken with the same equipment and at the same pixel scale, with the International Space Station some 492 kilometers away. China's space station was over 400 kilometers from the camera.

Image credit: Wang Letian
The Dancing Auroras of Saturn (2021-06-27)

What drives auroras on Saturn? To help find out, scientists have sorted through hundreds of infrared images of Saturn taken by the Cassini spacecraft for other purposes, trying to find enough aurora images to correlate changes and make movies. Once made, some movies clearly show that Saturnian auroras can change not only with the angle of the Sun, but also as the planet rotates. Furthermore, some auroral changes appear related to waves in Saturn's magnetosphere likely caused by Saturn's moons. Pictured here, a false-colored image taken in 2007 shows Saturn in three bands of infrared light.  The rings reflect relatively blue sunlight, while the planet itself glows in comparatively low energy red.  A band of southern aurora in visible in green. In has recently been found that auroras heat Saturn's upper atmosphere. Understanding Saturn's auroras is a path toward a better understanding of Earth's auroras.
A Paper Moon Solar Eclipse (2021-06-28)

It may look like a paper Moon.  Sailing past a  canvas Sun.  But those are not cardboard clouds.  And it's not make believe.  The featured picture of an orange colored sky is real -- a digital composite of two exposures of the solar eclipse that occurred earlier this month.  The first exposure was taken with a regular telescope that captured an overexposed Sun and an underexposed Moon, while the second image was taken with a solar telescope that captured details of the chromosphere of the background Sun. The Sun's canvas-like texture was brought up by imaging in a very specific shade of red emitted by hydrogen.  Several prominences can be seen around the Sun's edge.  The image was captured just before sunset from Xilingol, Inner Mongolia, China. It's also not make-believe to imagine that the Moon is made of dense rock, the Sun is made of hot gas, and clouds are made of floating droplets of water and ice.

Image credit: Wang Letian  
(Eyes at Night)
Orion Nebula: The Hubble View (2021-06-29)

Few cosmic vistas excite the imagination like the Orion Nebula. Also known as M42, the nebula's glowing gas surrounds hot young stars at the edge of an immense interstellar molecular cloud only 1,500 light-years away. The Orion Nebula offers one of the best opportunities to study how stars are born partly because it is the nearest large star-forming region, but also because the nebula's energetic stars have blown away obscuring gas and dust clouds that would otherwise block our view - providing an intimate look at a range of ongoing stages of starbirth and evolution. The featured image of the Orion Nebula is among the sharpest ever, constructed using data from the Hubble Space Telescope.  The entire Orion Nebula spans about 40 light years and is located in the same spiral arm of our Galaxy as the Sun.
Simulation: Formation of the First Stars (2021-06-30)

How did the first stars form? To help find out, the SPHINX computer simulation of star formation in the very early universe was created, some results of which are shown in the featured video. Time since the Big Bang is shown in millions of years on the upper left.  Even 100 million years after the Big Bang, matter was spread too uniformly across the cosmos for stars to be born.  Besides background radiation, the universe was dark. Soon, slight matter clumps rich in hydrogen gas begin to coalesce into the first stars. In the time-lapse video, purple denotes gas, white denotes light, and gold shows radiation so energetic that it ionizes hydrogen, breaking it up into charged electrons and protons.  The gold-colored regions also track the most massive stars that die with powerful supernovas. The inset circle highlights a central region that is becoming a galaxy.  The simulation continues until the universe was about 550 million years old.  To assess the accuracy of the SPHINX simulations and the assumptions that went into them, the results are not only being compared to current deep observations, but will also be compared with more direct observations of the early universe planned with NASA's pending James Webb Space Telescope.
Perseverance Selfie with Ingenuity (2021-07-01)

On sol 46 (April 6, 2021) the Perseverance rover held out a robotic arm to take its first selfie on Mars. The WATSON camera at the end of the arm was designed to take close-ups of martian rocks and surface details though, and not a quick snap shot of friends and smiling faces. In the end, teamwork and weeks of planning on Mars time was required to program a complex series of exposures and camera motions to include Perseverance and its surroundings. The resulting 62 frames were composed into a detailed mosiac, one of the most complicated Mars rover selfies ever taken. In this version of the selfie, the rover's Mastcam-Z and SuperCam instruments are looking toward WATSON and the end of the rover's outstretched arm. About 4 meters (13 feet) from Perseverance is a robotic companion, the Mars Ingenuity helicopter.
AR2835: Islands in the Photosphere (2021-07-02)

Awash in a sea of incandescent plasma and anchored in strong magnetic fields, sunspots are planet-sized dark islands in the solar photosphere, the bright surface of the Sun. Found in solar active regions, sunspots look dark only because they are slightly cooler though, with temperatures of about 4,000 kelvins compared to 6,000 kelvins for the surrounding solar surface. These sunspots lie in active region AR2835. The largest active region now crossing the Sun, AR2835 is captured in this sharp telescopic close-up from July 1 in a field of view that spans about 150,000 kilometers or over ten Earth diameters. With powerful magnetic fields, solar active regions are often responsible for solar flares and coronal mass ejections, storms which affect space weather near planet Earth.

Image credit: Michael
Teoh
Along the Milky Way (2021-07-03)

You can't walk along the Milky Way. Still, under a dark sky you can explore it. To the eye the pale luminous trail of light arcing through the sky on a dark, moonless night does appear to be a path through the heavens. The glowing celestial band is the faint, collective light of distant stars cut by swaths of obscuring interstellar dust clouds. It lies along the plane of our home galaxy, so named because it looks like a milky way. Since Galileo's time, the Milky Way has been revealed to telescopic skygazers to be filled with congeries of innumerable stars and cosmic wonders.

Image credit: Rolf Weisenfeld
The Face on Mars (2021-07-04)

Wouldn't it be fun if clouds were castles?  Wouldn't it be fun if the laundry on the bedroom chair was a superhero?  Wouldn't it be fun if rock mesas on Mars were interplanetary monuments to the human face?  Clouds, though, are floating droplets of water and ice.  Laundry is cotton, wool, or plastic, woven into garments.  Famous Martian rock mesas known by names like the Face on Mars appear quite natural when seen more clearly on better images.  Is reality boring? Nobody knows why some clouds make rain.  Nobody knows if life ever developed on Mars.  Nobody knows why the laundry on the bedroom chair smells like root beer.  Scientific exploration can not only resolve mysteries, but uncover new knowledge, greater mysteries, and yet deeper questions.  As humanity explores our universe, perhaps fun -- through discovery --  is just beginning.
IC 4592: The Blue Horsehead Reflection Nebula (2021-07-05)

Do you see the horse's head?   What you are seeing is not the famous Horsehead nebula toward Orion but rather a fainter nebula that only takes on a familiar form with deeper imaging.  The main part of the here imaged molecular cloud complex is a reflection nebula cataloged as IC 4592.  Reflection nebulas are actually made up of very fine dust that normally appears dark but can look quite blue when reflecting the visible light of energetic nearby stars.  In this case, the source of much of the reflected light is a star at the eye of the horse.  That star is part of Nu Scorpii, one of the brighter star systems toward the constellation of the Scorpion (Scorpius).   A second reflection nebula dubbed IC 4601 is visible surrounding two stars to the right of the image center.   Almost Hyperspace: Random APOD Generator

Image credit: Adam Block,
Steward Observatory,
University of Arizona
Saturn and Six Moons (2021-07-06)

How many moons does Saturn have? So far 82 have been confirmed, the smallest being only a fraction of a kilometer across. Six of its largest satellites can be seen here in a composite image with 13 short exposure of the bright planet, and 13 long exposures of the brightest of its faint moons, taken over two weeks last month.  Larger than Earth's Moon and even slightly larger than Mercury,Saturn's largest moon Titan has a diameter of 5,150 kilometers and was captured making nearly a complete orbit around its ringed parent planet.  Saturn's first known natural satellite, Titan was discovered in 1655 by Dutch astronomer Christiaan Huygens, in contrast with several newly discovered moons announced in 2019.  The trail on the far right belongs to Iapetus, Saturn's third largest moon. The radius of painted Iapetus' orbit is so large that only a portion of it was captured here. Saturn leads Jupiter across the night sky this month, rising soon after sunset toward the southeast, and remaining visible until dawn.

Image credit: Mohammad Ranjbaran;
 MR Thanks: 
Amir Ehteshami
Flight Through the Orion Nebula in Infrared Light (2021-07-07)

What would it look like to fly into the Orion Nebula?  The exciting dynamic visualization of the Orion Nebula is based on real astronomical data and adept movie rendering techniques. Up close and personal with a famous stellar nursery normally seen from 1,500 light-years away, the digitally modeled representation based is based on infrared data from the Spitzer Space Telescope. The perspective moves along a valley over a light-year wide, in the wall of the region's giant molecular cloud. Orion's valley ends in a cavity carved by the energetic winds and radiation of the massive central stars of the Trapezium star cluster. The entire Orion Nebula spans about 40 light years and is located in the same spiral arm of our Galaxy as the Sun.
Perihelion to Aphelion (2021-07-08)

Aphelion for 2021 occurred on July 5th. That's the point in Earth's elliptical orbit when it is farthest from the Sun. Of course, the distance from the Sun doesn't determine the seasons. Those are governed by the tilt of Earth's axis of rotation, so July is still summer in the north and winter in the southern hemisphere. But it does mean that on July 5 the Sun was at its smallest apparent size when viewed from planet Earth. This composite neatly compares two pictures of the Sun, both taken with the same telescope and camera. The left half was captured close to the date of the 2021 perihelion (January 2), the closest point in Earth's orbit. The right was recorded just before the aphelion in 2021. Otherwise difficult to notice, the change in the Sun's apparent diameter between perihelion and aphelion amounts to a little over 3 percent.

Image credit: Richard Jaworski
M82: Starburst Galaxy with a Superwind (2021-07-09)

M82 is a starburst galaxy with a superwind. In fact, through ensuing supernova explosions and powerful winds from massive stars, the burst of star formation in M82 is driving a prodigious outflow. Evidence for the superwind from the galaxy's central regions is clear in sharp telescopic snapshot. The composite image highlights emission from long outflow filaments of atomic hydrogen gas in reddish hues. Some of the gas in the superwind, enriched in heavy elements forged in the massive stars, will eventually escape into intergalactic space. Triggered by a close encounter with nearby large galaxy M81, the furious burst of star formation in M82 should last about 100 million years or so. Also known as the Cigar Galaxy for its elongated visual appearance, M82 is about 30,000 light-years across. It lies 12 million light-years away near the northern boundary of Ursa Major.

Image credit: Team ARO
Mercury and the Da Vinci Glow (2021-07-10)

On July 8th early morning risers saw Mercury near an old Moon low on the eastern horizon. On that date bright planet, faint glow of lunar night side, and sunlit crescent were captured in this predawn skyscape from Tenerife's Teide National Park in the Canary Islands.  Never far from the Sun in planet Earth's sky, the fleeting inner planet shines near its brightest in the morning twilight scene. Mercury lies just below the zeta star of the constellation Taurus, Zeta Tauri, near the tip of the celestial bull's horn. Of course the Moon's ashen glow is earthshine, earthlight reflected from the Moon's night side. A description of earthshine, in terms of sunlight reflected by Earth's oceans illuminating the Moon's dark surface, was written over 500 years ago by Leonardo da Vinci. Waiting for the coming dawn in the foreground are the Teide Observatory's sentinels of the Sun, also known as (large domes left to right) the THEMIS, VTT, and GREGOR solar telescopes.

Image credit: Gabriel Funes
Find the Moon (2021-07-11)

Where's the Moon? Somewhere in this image, the Earth's Moon is hiding.  The entire Moon is visible, in its completely full phase, in plain sight. Even the photographer's keen eye couldn't find it even though he knew exactly where to look -- only the long exposure of his camera picked it up -- barely.  Although by now you might be congratulating yourself on finding it, why was it so difficult to see? For one reason, this photograph was taken during a total lunar eclipse, when the Earth's shadow made the Moon much dimmer than a normal full Moon. For another, the image, taken in Colorado, USA, was captured just before sunrise. With the Moon on the exact opposite side of the sky from the Sun, this meant that the Sun was just below the horizon, but still slightly illuminating the sky. Last, as the Moon was only about two degrees above the horizon, the large volume of air between the camera and the horizon scattered a lot of light away from the background Moon. Twelve minutes after this image was acquired in 2012, the Sun peeked over the horizon and the Moon set.

Image credit: Jimmy Westlake
(Colorado Mountain College)
M27: The Dumbbell Nebula (2021-07-12)

What will become of our Sun? The first hint of our Sun's future was discovered inadvertently in 1764. At that time, Charles Messier was compiling a list of diffuse objects not to be confused with comets. The 27th object on Messier's list, now known as M27 or the Dumbbell Nebula, is a planetary nebula, one of the brightest planetary nebulae on the sky -- and visible toward the constellation of the Fox (Vulpecula) with binoculars. It takes light about 1000 years to reach us from M27, featured here in colors emitted by hydrogen and oxygen. We now know that in about 6 billion years, our Sun will shed its outer gases into a planetary nebula like M27, while its remaining center will become an X-ray hot white dwarf star.  Understanding the physics and significance of M27 was well beyond 18th century science, though. Even today, many things remain mysterious about planetary nebulas, including how their intricate shapes are created.

Image credit: Bray Falls & 
Keith Quattrocchi
Saturn's Iapetus: Painted Moon in 3D (2021-07-13)

What has happened to Saturn's moon Iapetus?  Vast sections of this strange world are dark brown,  while others are as bright white.  The composition of the dark material is unknown, but infrared spectra indicate that it possibly contains some dark form of carbon. Iapetus also has an unusual equatorial ridge that makes it appear like a walnut.  To help better understand this seemingly painted moon, NASA directed the robotic Cassini spacecraft orbiting Saturn to swoop within 2,000 kilometers in 2007. Iapetus is pictured here in 3D.  A huge impact crater seen in the south spans a tremendous 450 kilometers and appears superposed on an older crater of similar size. The dark material is seen increasingly coating the easternmost part of Iapetus, darkening craters and highlands alike.  Close inspection indicates that the dark coating typically faces the moon's equator and is less than a meter thick. A leading hypothesis is that the dark material is mostly dirt leftover when relatively warm but dirty ice sublimates. An initial coating of dark material may have been effectively painted on by the accretion of meteor-liberated debris from other moons.
GW200115: Simulation of a Black Hole Merging with a Neutron Star (2021-07-14)

What happens when a black hole destroys a neutron star? Analyses indicate that just such an event created gravitational wave event GW200115, detected in 2020 January by LIGO and Virgo observatories. To better understand the unusual event, the featured visualization was created from a computer simulation. The visualization video starts with the black hole (about 6 times the Sun's mass) and neutron star (about 1.5 times the Sun's mass) circling each other, together emitting an increasing amount of gravitational radiation. The picturesque pattern of gravitational wave emission is shown in blue. The duo spiral together increasingly fast until the neutron star becomes completely absorbed by the black hole.  Since the neutron star did not break apart during the collision, little light escaped -- which matches the lack of an observed optical counterpart. The remaining black hole rings briefly, and as that dies down so do the emitted gravitational waves.  The 30-second time-lapse video may seem short, but it actually lasts about 1000 times longer than the real merger event.    Astrophysicists: Browse 2,500+ codes in the Astrophysics Source Code Library
The Dark Tower in Scorpius (2021-07-15)

In silhouette against a crowded star field along the tail of the arachnalogical 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, 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: Martin Pugh
Love and War by Moonlight (2021-07-16)

Venus, named for the Roman goddess of love, and Mars, the war god's namesake, come together by moonlight in this serene skyview, recorded on July 11 from Lualaba province, Democratic Republic of Congo, planet Earth. Taken in the western twilight sky shortly after sunset the exposure also records earthshine illuminating the otherwise dark surface of the young crescent Moon. Of course the Moon has moved on. Venus still shines in the west though as the evening star, third brightest object in Earth's sky, after the Sun and the Moon itself. Seen here above a brilliant Venus, Mars moved even closer to the brighter planet and by July 13 could be seen only about a Moon's width away. Mars has since slowly wandered away from much brighter Venus in the twilight, but both are sliding toward bright star Regulus. Alpha star of the constellation Leo, Regulus lies off the top of this frame and anticipates a visit from Venus and then Mars in twilight skies of the coming days.

Image credit: Shi Huan
Alphonsus and Arzachel (2021-07-17)

Point your telescope at tonight's first quarter Moon. Along the terminator, the shadow line between night and day, you might find these two large craters staring back at you with an owlish gaze. Alphonsus (left) and Arzachel are ancient impact craters on the north eastern shores of Mare Nubium, the lunar Sea of Clouds. The larger Alphonsus is over 100 kilometers in diameter. A low sun angle highlights the crater's sharp 1.5 kilometer high central peak in bright sunlight and dark shadow. Scouting for potential Apollo moon landing sites, the Ranger 9 spacecraft returned closeup pictures of Alphonsus before crashing in the crater just northeast (toward the upper left) of its central mountain in 1965. Alpetragius, between Alphonsus and Arzachel, is the small crater with the deeply shadowed floor and overly large central beak.

Image credit: Noel Donnard