juliensimon/nasa-apod huggingface dataset:
Equinox at the Pyramid of the Feathered Serpent (2023-03-19)

To see the feathered serpent descend the Mayan pyramid requires exquisite timing.  You must visit El Castillo -- in Mexico's Yucatán Peninsula -- near an equinox.  Then, during the late afternoon if the sky is clear, the pyramid's own shadows create triangles that merge into the famous illusion of a slithering viper.  Also known as the Temple of Kukulkan, the impressive step-pyramid stands 30 meters tall and 55 meters wide at the base.  Built up as a series of square terraces by the pre-Columbian civilization between the 9th and 12th century, the structure can be used as a calendar and is noted for astronomical alignments. The featured composite image was captured in 2019 with Jupiter and Saturn straddling the diagonal central band of our Milky Way galaxy. Tomorrow marks another equinox -- not only at Temple of Kukulcán, but all over planet Earth.

Image credit: Robert Fedez
M1: The Expanding Crab Nebula (2023-03-20)

Are your eyes good enough to see the Crab Nebula expand?  The Crab Nebula is cataloged as M1, the first on Charles Messier's famous list of things which are not comets. In fact, the Crab is now known to be a supernova remnant, an expanding cloud of debris from the explosion of a massive star. The violent birth of the Crab was witnessed by astronomers in the year 1054. Roughly 10 light-years across today, the nebula is still expanding at a rate of over 1,000 kilometers per second. Over the past decade, its expansion has been documented in this stunning time-lapse movie. In each year from 2008 to 2022, an image was produced with the same telescope and camera from a remote observatory in Austria. The sharp, processed frames even reveal the dynamic energetic emission surrounding the rapidly spinning pulsar at the center.  The Crab Nebula lies about 6,500 light-years away toward the constellation of the Bull (Taurus).

Image credit: Detlef Hartmann
Dark Nebulae and Star Formation in Taurus (2023-03-21)

Can dust be beautiful? Yes, and it can also be useful.  The Taurus molecular cloud has several bright stars, but it is the dark dust that really draws attention.  The pervasive dust has waves and ripples and makes picturesque dust bunnies, but perhaps more importantly, it marks regions where interstellar gas is dense enough to gravitationally contract to form stars. In the image center is a light cloud lit by neighboring stars that is home not only to a famous nebula, but to a very young and massive famous star.  Both the star, T Tauri, and the nebula, Hind's Variable Nebula, are seen to vary dramatically in brightness -- but not necessarily at the same time, adding to the mystery of this intriguing region. T Tauri and similar stars are now generally recognized to be Sun-like stars that are less than a few million years old and so still in the early stages of formation. The featured image spans about four degrees not far from the Pleiades star cluster, while the featured dust field lies about 400 light-years away.

Image credit: Vikas Chander
M31: The Andromeda Galaxy (2023-03-22)

How far can you see? The most distant object easily visible to the unaided eye is M31, the great Andromeda Galaxy, over two million light-years away.  Without a telescope, even this immense spiral galaxy appears as an unremarkable, faint, nebulous cloud in the constellation Andromeda.  But a bright white nucleus, dark winding dust lanes, luminous blue spiral arms, and bright red emission nebulas are recorded in this stunning fifteen-hour telescopic digital mosaic of our closest major galactic neighbor.  But how do we know this spiral nebula is really so far away? This question was central to the famous Shapley-Curtis debate of 1920.  M31's great distance was determined in the 1920s by observations that resolved individual stars that changed their brightness in a way that gave up their true distance. The result proved that Andromeda is just like our Milky Way Galaxy -- a conclusion making the rest of the universe much more vast than had ever been previously imagined.

Image credit: Abdullah Al-Harbi
Spiral Galaxy NGC 2841 (2023-03-23)

A mere 46 million light-years distant, spiral galaxy NGC 2841 can be found in planet Earth's night sky toward the northern constellation of Ursa Major. This sharp image centered on the gorgeous island universe also captures spiky foreground Milky Way stars and more distant background galaxies within the same telescopic field of view. It shows off the bright nucleus of NGC 2841, along with its inclined galactic disk, and faint outer regions.  Dust lanes, small star-forming regions, and young star clusters are embedded in the galaxy's patchy, tightly wound spiral arms. In contrast, many other spirals exhibit broader, sweeping arms with large star-forming regions.  NGC 2841 has a diameter of over 150,000 light-years, making it even larger than our own Milky Way. X-ray images suggest that extreme outflows from giant stars and stellar explosions create plumes of hot gas extending into a halo around NGC 2841.

Image credit: Roberto Marinoni
Outbound Comet ZTF (2023-03-24)

Former darling of the northern sky Comet C/2022E3 (ZTF) has faded. During its closest approach to our fair planet in early February Comet ZTF was a mere 2.3 light-minutes distant. Then known as the green comet, this visitor from the remote Oort Cloud is now nearly 13.3 light-minutes away. In this deep image, composed of exposures captured on March 21, the comet still sports a broad, whitish dust tail and greenish tinted coma though. Not far on the sky from Orion's bright star Rigel, Comet ZTF shares the field of view with faint, dusty nebulae and distant background galaxies. The telephoto frame is crowded with Milky Way stars toward the constellation Eridanus. The influence of Jupiter's gravity on the comet's orbit as ZTF headed for the inner solar system, may have set the comet on an outbound journey, never to return.

Image credit: Former darling
Venus and the Da Vinci Glow (2023-03-25)

On March 23 early evening skygazers could watch Venus and a young crescent moon, both near the western horizon. On that date Earth's brilliant evening star, faint lunar night side and slender sunlit crescent were captured in this telephoto skyscape posing alongside a church tower from San Pietro di Cadore, Dolomiti, Italy. Of course the subtle lunar illumination 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. On March 24, from some locations the Moon could be seen to occult or pass in front of Venus. Around the planet tonight, a waxing lunar crescent will appear near the Pleiades star cluster.

Image credit: Giorgia Hofer
Wanderers (2023-03-26)

How far out will humanity explore? If this video's fusion of real space imagery and fictional space visualizations is on the right track, then at least the Solar System. Some of the video's wondrous sequences depict future humans drifting through the rings of Saturn, exploring Jupiter from a nearby spacecraft, and jumping off a high cliff in the low gravity of a moon of Uranus. Although no one can know the future, wandering and exploring beyond boundaries -- both physical and intellectual -- is part of the human spirit and has frequently served humanity well in the past.
Aurora Over Arctic Henge (2023-03-27)

Reports of powerful solar flares started a seven-hour quest north to capture modern monuments against an aurora-filled sky.  The peaks of iconic Arctic Henge in Raufarhöfn in northern Iceland were already aligned with the stars: some are lined up toward the exact north from one side and toward exact south from the other. The featured image, taken after sunset late last month, looks directly south, but since the composite image covers so much of the sky, the north star Polaris is actually visible at the very top of the frame. Also visible are familiar constellations including the Great Bear (Ursa Major) on the left, and the Hunter (Orion) on the lower right. The quest was successful.  The sky lit up dramatically with bright and memorable auroras that shimmered with amazing colors including red, pink, yellow, and green -- sometimes several at once.

Image credit: Cari Letelier
A Multiple Green Flash Sunset (2023-03-28)

Yes, but can your green flash do this? A green flash at sunset is a rare event that many Sun watchers pride themselves on having seen.  Once thought to be a myth, a green flash is now understood to occur when the Earth's atmosphere acts like both a prism and a lens. Different atmospheric layers create altitude-variable refraction that takes light from the top of the Sun and disperses its colors, creates two images, and magnifies it in just the right way to make a thin sliver appear green just before it disappears. Pictured, though, is an even more unusual sunset. From the high-altitude Cerro Tololo Inter-American Observatory in Chile one day last April, the Sun was captured setting beyond an atmosphere with multiple distinct thermal layers, creating several  mock images of the Sun.  This time and from this location, many of those layers produced a green flash simultaneously. Just seconds after this multiple-green-flash event was caught by two well-surprised astrophotographers, the Sun set below the clouds.

Image credit: T. Slovinský & 
P. Horálek 
(IoP Opava);
CTIO, 
NOIRLab,
NSF,
AURA
Sh2-308: A Dolphin Shaped Star Bubble (2023-03-29)

Which star created this bubble? It wasn't the bright star on the bubble's right. And it also wasn't a giant space dolphin. It was the star in the blue nebula's center, a famously energetic Wolf-Rayet star. Wolf-Rayet stars in general have over 20 times the mass of our Sun and expel fast particle winds that can create iconic looking nebulas. In this case, the resulting star bubble spans over 60 light years, is about 70,000 years old, and happens to look like the head of a dolphin.  Named Sh2-308 and dubbed the Dolphin-Head Nebula, the gas ball lies about 5,000 light years away and covers as much sky as the full moon -- although it is much dimmer. The nearby red-tinged clouds on the left of the featured image may owe their glow and shape to energetic light emitted from the same Wolf-Rayet star.

Image credit: Aleix Roig 
(AstroCatInfo)
NGC 4372 and the Dark Doodad (2023-03-30)

The delightful Dark Doodad Nebula drifts through southern skies, a tantalizing target for binoculars toward the small constellation Musca, The Fly. The dusty cosmic cloud is seen against rich starfields just south of the Coalsack Nebula and the Southern Cross. Stretching for about 3 degrees across the center of this telephoto field of view, the Dark Doodad is punctuated near its southern tip (upper right) by yellowish globular star cluster NGC 4372. Of course NGC 4372 roams the halo of our Milky Way Galaxy, a background object some 20,000 light-years away and only by chance along our line-of-sight to the Dark Doodad. The Dark Doodad's well defined silhouette belongs to the Musca molecular cloud, but its better known alliterative moniker was first coined by astro-imager and writer Dennis di Cicco in 1986 while observing Comet Halley from the Australian outback. The Dark Doodad is around 700 light-years distant and over 30 light-years long.

Image credit: Matias Tomasello
Seeing Titan (2023-03-31)

Shrouded in a thick atmosphere, Saturn's largest moon Titan really is hard to see. Small particles suspended in the upper atmosphere cause an almost impenetrable haze, strongly scattering light at visible wavelengths and hiding Titan's surface features from prying eyes. But Titan's surface is better imaged at infrared wavelengths where scattering is weaker and atmospheric absorption is reduced. Arrayed around this visible light image (center) of Titan are some of the clearest global infrared views of the tantalizing moon so far. In false color, the six panels present a consistent processing of 13 years of infrared image data from the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini spacecraft orbiting Saturn from 2004 to 2017. They offer a stunning comparison with Cassini's visible light view. NASA's revolutionary rotorcraft mission to Titan is due to launch in 2027.
NGC 2442: Galaxy in Volans (2023-04-01)

Distorted galaxy NGC 2442 can be found in the southern constellation of the flying fish, (Piscis) Volans. Located about 50 million light-years away, the galaxy's two spiral arms extending from a pronounced central bar give it a hook-shaped appearance in this deep colorful image, with spiky foreground stars scattered across the telescopic field of view. The image also reveals the distant galaxy's obscuring dust lanes, young blue star clusters and reddish star forming regions surrounding a core of yellowish light from an older population of stars. But the star forming regions seem more concentrated along the drawn-out (upper right) spiral arm. The distorted structure is likely the result of an ancient close encounter with the smaller galaxy seen near the top left of the frame. The two interacting galaxies are separated by about 150,000 light-years at the estimated distance of NGC 2442.

Image credit: Nicolas Rolland
M57: The Ring Nebula from Hubble (2023-04-02)

It was noticed hundreds of years ago by stargazers who could not understand its unusual shape.  It looked like a ring on the sky. Except for the rings of Saturn, the Ring Nebula (M57) may be the most famous celestial circle. We now know what it is, and that its iconic shape is due to our lucky perspective. The recent mapping of the expanding nebula's 3-D structure, based in part on this clear Hubble image,indicates that the nebula is a relatively dense, donut-like ring wrapped around the middle of an (American) football-shaped cloud of glowing gas. Our view from planet Earth looks down the long axis of the football, face-on to the ring. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from the dying, once sun-like star, now a tiny pinprick of light seen at the nebula's center. Intense ultraviolet light from the hot central star ionizes atoms in the gas. The Ring Nebula is about one light-year across and 2,500 light-years away.
The Galactic Center Radio Arc (2023-04-03)

What causes this unusual curving structure near the center of our Galaxy? The long parallel rays slanting across the top of the featured radio image are known collectively as the Galactic Center Radio Arc and point out from the Galactic plane.  The Radio Arc is connected to the Galactic Center by strange curving filaments known as the Arches.  The bright radio structure at the bottom right surrounds a black hole at the Galactic Center and is known as Sagittarius A*.  One origin hypothesis holds that the Radio Arc and the Arches have their geometry because they contain hot plasma flowing along lines of a constant magnetic field.  Images from NASA's Chandra X-ray Observatory appear to show this plasma colliding with a nearby cloud of cold gas.
Olympus Mons: Largest Volcano in the Solar System (2023-04-04)

The largest volcano in our Solar System is on Mars.  Although three times higher than Earth's Mount Everest, Olympus Mons will not be difficult for humans to climb because of the volcano's shallow slopes and Mars' low gravity.  Covering an area greater than the entire Hawaiian volcano chain, the slopes of Olympus Mons typically rise only a few degrees at a time.  Olympus Mons is an immense shield volcano, built long ago by fluid lava.  A relatively static surface crust allowed it to build up over time. Its last eruption is thought to have been about 25 million years ago.  The featured image was taken by the European Space Agency's robotic Mars Express spacecraft currently orbiting the  Red Planet.    Your Sky Surprise: What picture did APOD feature on your birthday? (post 1995)
Rubin's Galaxy (2023-04-05)

In this Hubble Space Telescope image the bright, spiky stars lie in the foreground toward the heroic northern constellation Perseus and well within our own Milky Way galaxy. In sharp focus beyond is UGC 2885, a giant spiral galaxy about 232 million light-years distant. Some 800,000 light-years across compared to the Milky Way's diameter of 100,000 light-years or so, it has around 1 trillion stars. That's about 10 times as many stars as the Milky Way. Part of an investigation to understand how galaxies can grow to such enormous sizes, UGC 2885 was also part of An Interesting Voyage and astronomer Vera Rubin's pioneering study of the rotation of spiral galaxies. Her work was the first to convincingly demonstrate the dominating presence of dark matter in our universe.
Terran 1 Burns Methalox (2023-04-06)

Relativity's Terran 1 Rocket is mostly 3D-printed. It burns a cryogenic rocket fuel composed of liquid methane and liquid oxygen (methalox). In this close-up of a Terran 1 launch on the night of March 22 from Cape Canaveral, icy chunks fall through the stunning frame as intense blue exhaust streams from its nine Aeon 1 engines. In a largely successful flight the inovative rocket achieved main engine cutoff and stage separation but fell short of orbit after an anomaly at the beginning of its second stage flight. Of course this Terran 1 rocket was never intended to travel to Mars. Still, the methane and liquid oxygen components of its methalox fuel can be made solely from materials found on the Red Planet. Methalox manufactured on Mars could be used as fuel for rockets returning to planet Earth.
Rigel Wide (2023-04-07)

Brilliant, blue, supergiant star Rigel marks the foot of Orion the Hunter in planet Earth's night. Designated Beta Orionis, it's at the center of this remarkably deep and wide field of view.  Rigel's blue color indicates that it is much hotter than its rival supergiant in Orion the yellowish Betelgeuse (Alpha Orionis), though both stars are massive enough to eventually end their days as core collapse supernovae. Some 860 light-years away, Rigel is hotter than the Sun too and extends to about 74 times the solar radius. That's about the size of the orbit of Mercury. In the 10 degree wide frame toward the nebula rich constellation, the Orion Nebula is at the upper left. To the right of Rigel and illuminated by its brilliant blue starlight lies the dusty Witch Head Nebula. Rigel is part of a multiple star system, though its companion stars are much fainter.

Image credit: Rheinhold Wittich
M100: A Grand Design Spiral Galaxy (2023-04-08)

Majestic on a truly cosmic scale, M100 is appropriately known as a grand design spiral galaxy.  It is a large galaxy of over 100 billion stars with well-defined spiral arms that is similar to our own Milky Way Galaxy.  One of the brightest members of the Virgo Cluster of galaxies, M100 (alias NGC 4321) is 56 million light-years distant toward the constellation of Berenice's Hair (Coma Berenices).  This Hubble Space Telescope image of M100 was taken with the Wide Field Camera 3 and accentuates bright blue star clusters and intricate winding dust lanes which are hallmarks of this class of galaxies.  Studies of variable stars in M100 have played an important role in determining the size and age of the Universe.
The Egg Nebula in Polarized Light (2023-04-09)

Where is the center of the Egg Nebula? Emerging from a cosmic egg, the star in the center of the Egg Nebula is casting away shells of gas and dust as it slowly transforms itself into a white dwarf star.  The Egg Nebula is a rapidly evolving pre- planetary nebula spanning about one light year. It lies some 3,000 light-years away toward the northern constellation Cygnus. Thick dust blocks the center star from view, while the dust shells farther out reflect light from this star.  Light vibrating in the plane defined by each dust grain, the central star, and the observer is preferentially reflected, causing an effect known as polarization.  Measuring the orientation of the polarized light for the Egg Nebula gives clues to location of the hidden source.  Taken by Hubble's Advanced Camera for Surveys in 2002, this image is rendered in artificial "Easter-Egg" colors coded to highlight the orientation of polarization.
IC 2944: The Running Chicken Nebula (2023-04-10)

To some, it looks like a giant chicken running across the sky. To others, it looks like a gaseous nebula where star formation takes place. Cataloged as IC 2944, the Running Chicken Nebula spans about 100 light years and lies about 6,000 light years away toward the constellation of the Centaur (Centaurus).  The featured image, shown in scientifically assigned colors, was captured recently in a 16-hour exposure over three nights. The star cluster Collinder 249 is visible embedded in the nebula's glowing gas.  Although difficult to discern here, several dark molecular clouds with distinct shapes can be found inside the nebula.

Image credit: Daniel Stern
North Star: Polaris and Surrounding Dust (2023-04-11)

Why is Polaris called the North Star? First, Polaris is the nearest bright star toward the north spin axis of the Earth.  Therefore, as the Earth turns, stars appear to revolve around Polaris, but Polaris itself always stays in the same northerly direction -- making it the North Star.  Since no bright star is near the south spin axis of the Earth, there is currently no bright South Star.  Thousands of years ago, Earth's spin axis pointed in a slightly different direction so that Vega was the North Star.  Although Polaris is not the brightest star on the sky, it is easily located because it is nearly aligned with two stars in the cup of the Big Dipper. Polaris is near the center of the eight-degree wide featured image, a digital composite of hundreds of exposures that brings out faint gas and dust of the Integrated Flux Nebula (IFN) all over the frame as well as the globular star cluster NGC 188 on the far left.  The surface of Cepheid Polaris slowly pulsates, causing the famous star to change its brightness by a few percent over the course of a few days.    Explore Your Universe: Random APOD Generator

Image credit: Javier Zayaz
NGC 206 and the Star Clouds of Andromeda (2023-04-12)

The large stellar association cataloged as NGC 206 is nestled within the dusty arms of the neighboring Andromeda galaxy along with the galaxy's pinkish star-forming regions. Also known as M31, the spiral galaxy is a mere 2.5 million light-years away. NGC 206 is found right of center in this sharp and detailed close-up of the southwestern extent of Andromeda's disk. The bright, blue stars of NGC 206 indicate its youth. In fact, its youngest massive stars are less than 10 million years old. Much larger than the open or galactic clusters of young stars in the disk of our Milky Way galaxy, NGC 206 spans about 4,000 light-years. That's comparable in size to the giant stellar nurseries NGC 604 in nearby spiral M33 and the Tarantula Nebula in the Large Magellanic Cloud.

Image credit: Howard Trottier
NGC 2419: Intergalactic Wanderer (2023-04-13)

Stars of the globular cluster NGC 2419 are packed into this Hubble Space Telescope field of view toward the mostly stealthy constellation Lynx. The two brighter spiky stars near the edge of the frame are within our own galaxy. NGC 2419 itself is remote though, some 300,000 light-years away. In comparison, the Milky Way's satellite galaxy, the Large Magellanic Cloud, is only about 160,000 light-years distant. Roughly similar to other large globular star clusters like Omega Centauri, NGC 2419 is intrinsically bright, but appears faint because it is so far away. Its extreme distance makes it difficult to study and compare its properties with other globular clusters that roam the halo of our Milky Way galaxy. Sometimes called "the Intergalactic Wanderer", NGC 2419 really does seem to have come from beyond the Milky Way. Measurements of the cluster's motion through space suggest it once belonged to the Sagittarius dwarf spheroidal galaxy, another small satellite galaxy being disrupted by repeated encounters with the much larger Milky Way.