juliensimon/nasa-apod huggingface dataset:
Our Increasingly Active Sun (2023-02-22)

Our Sun is becoming a busy place.  Only two years ago, the Sun was emerging from a solar minimum so quiet that months would go by without even a single sunspot.  In contrast, already this year and well ahead of schedule, our Sun is unusually active, already nearing solar activity levels seen a decade ago during the last solar maximum.  Our increasingly active Sun was captured two weeks ago sporting numerous interesting features. The image was recorded in a single color of light called Hydrogen Alpha, color-inverted, and false colored.  Spicules carpet much of the Sun's face.  The brightening towards the Sun's edges is caused by increased absorption of relatively cool solar gas and called limb darkening.  Just outside the Sun's disk, several scintillating prominences protrude, while prominences on the Sun's face are known as filaments and show as light streaks.  Magnetically tangled active regions are both dark and light and contain cool sunspots.  As our Sun's magnetic field winds toward solar maximum over the next few years, whether the Sun's high activity will continue to increase is unknown.

Image credit: Mehmet Ergün
Arp 78: Peculiar Galaxy in Aries (2023-02-23)

Peculiar spiral galaxy Arp 78 is found within the boundaries of the head strong constellation Aries. Some 100 million light-years beyond the stars and nebulae of our Milky Way galaxy, the island universe is an enormous 200,000 light-years across. Also known as NGC 772, it sports a prominent, outer spiral arm in this detailed cosmic portrait. Tracking along sweeping dust lanes and lined with young blue star clusters, Arp 78's overdeveloped spiral arm is pumped-up by galactic-scale gravitational tides. Interactions with its brightest companion galaxy, the more compact NGC 770 seen above and right of the larger spiral, are likely responsible. Embedded in faint star streams revealed in the deep telescopic exposure, NGC 770's fuzzy, elliptical appearance contrasts nicely with spiky foreground Milky Way stars in matching yellowish hues.

Image credit: Josep Drudis
Jones-Emberson 1 (2023-02-24)

Planetary nebula Jones-Emberson 1 is the death shroud of a dying Sun-like star. It lies some 1,600 light-years from Earth toward the sharp-eyed constellation Lynx. About 4 light-years across, the expanding remnant of the dying star's atmosphere was shrugged off into interstellar space, as the star's central supply of hydrogen and then helium for fusion was finally depleted after billions of years. Visible near the center of the planetary nebula is what remains of the stellar core, a blue-hot white dwarf star.  Also known as PK 164 +31.1, the nebula is faint and very difficult to glimpse at a telescope's eyepiece. But this deep broadband image combining 22 hours of exposure time does show it off in exceptional detail. Stars within our own Milky Way galaxy as well as background galaxies across the universe are scattered through the clear field of view. Ephemeral on the cosmic stage, Jones-Emberson 1 will fade away over the next few thousand years. Its hot, central white dwarf star will take billions of years to cool.

Image credit: Serge
Brunier, Jean-François Bax, David Vernet
Crescent Moon Occultation (2023-02-25)

On February 22, a young Moon shared the western sky at sunset with bright planets Venus and Jupiter along the ecliptic plane. The beautiful celestial conjunction was visible around planet Earth. But from some locations Jupiter hid for a while, occulted by the crescent lunar disk. The Solar System's ruling gas giant was captured here just before it disappeared behind the Moon's dark edge, seen over the Río de la Plata at Colonia del Sacramento, Uruguay.  In the serene river and skyscape Venus is not so shy, shining brightly closer to the horizon through the fading twilight. Next week Venus and Jupiter will appear even closer in your evening sky.

Image credit: Fefo Bouvier
Saturn's Iapetus: Moon with a Strange Surface (2023-02-26)

What would make a moon look like a walnut?  A strange ridge that circles Saturn's moon Iapetus's equator, visible near the bottom of the featured image, makes it appear similar to a popular edible nut.  The origin of the ridge remains unknown, though, with hypotheses including ice that welled up from below, a ring that crashed down from above, and structure left over from its formation perhaps 100 million years ago. Also strange is that about half of Iapetus is so dark that it can nearly disappear when viewed from Earth, while the rest is, reflectively, quite bright. Observations show that the degree of darkness of the terrain is strangely uniform, as if a dark coating was somehow recently applied to an ancient and highly cratered surface.  Last, several large impact basins occur around Iapetus, with a 400-kilometer wide crater visible near the image center, surrounded by deep cliffs that drop sharply to the crater floor.  The featured image was taken by the Saturn-orbiting Cassini spacecraft during a flyby of Iapetus at the end of 2004.
Zodiacal Ray with Venus and Jupiter (2023-02-27)

What's causing that unusual ray of light extending from the horizon? Dust orbiting the Sun. At certain times of the year, a band of sun-reflecting dust from the inner Solar System appears prominently after sunset or before sunrise and is called zodiacal light.  The dust was emitted mostly from faint Jupiter-family comets and slowly spirals into the Sun. The featured HDR image, acquired in mid-February from the Sierra Nevada National Park in Spain, captures the glowing band of zodiacal light going right in front of the bright evening planets Jupiter (upper) and Venus (lower). Emitted from well behind the zodiacal light is a dark night sky that prominently includes the Pleiades star cluster. Jupiter and Venus are slowly switching places in the evening sky, and just in the next few days nearing their closest angular approach.

Image credit: Ruslan Merzlyakov 
(astrorms)
Crescent Moon Beyond Greek Temple (2023-02-28)

Why is a thin crescent moon never seen far from a horizon? Because the only geometry that gives a thin crescent lunar phase occurs when the Moon appears close to the Sun in the sky.  The crescent is not caused by the shadow of the Earth, but by seeing only a small part of the Moon directly illuminated by the Sun.  Moreover, the thickest part of the crescent always occurs in the direction of the Sun.  In the evening, a thin crescent Moon will set shortly after the Sun and not be seen for the rest of the night. Alternatively, in the morning, a crescent Moon will rise shortly before the Sun after not being seen for most of the night. Pictured two weeks ago, a crescent moon was captured near the horizon, just before sunrise, far behind remnants of the ancient Temple of Poseidon in Greece.

Image credit: Elias Chasiotis
The Flaming Star Nebula (2023-03-01)

Is star AE Aurigae on fire? No.  Even though AE Aurigae is named the Flaming Star and the surrounding nebula IC 405 is named the Flaming Star Nebula, and even though the nebula appears to some like a swirling flame, there is no fire.  Fire, typically defined as the rapid molecular acquisition of oxygen, happens only when sufficient oxygen is present and is not important in such high-energy, low-oxygen environments such as stars.  The bright star AE Aurigae occurs near the center of the Flaming Star Nebula and is so hot it glows blue, emitting light so energetic it knocks electrons away from surrounding gas. When a proton recaptures an electron, light is emitted, as seen in the surrounding emission nebula.  Captured here three weeks ago, the Flaming Star Nebula is visible near the composite image's center, between the red Tadpole Nebula on the left and blue-tailed Comet ZTF on the right.  The Flaming Star Nebula lies about 1,500 light years distant, spans about 5 light years, and is visible with a small telescope toward the constellation of the Charioteer (Auriga).

Image credit: Thomas Röell
Unraveling NGC 3169 (2023-03-02)

Spiral galaxy NGC 3169 looks to be unraveling like a ball of cosmic yarn. It lies some 70 million light-years away, south of bright star Regulus toward the faint constellation Sextans. Wound up spiral arms are pulled out into sweeping tidal tails as NGC 3169 (left) and neighboring NGC 3166 interact gravitationally. Eventually the galaxies will merge into one, a common fate even for bright galaxies in the local universe. Drawn out stellar arcs and plumes are clear indications of the ongoing gravitational interactions across the deep and colorful galaxy group photo. The telescopic frame spans about 20 arc minutes or about 400,000 light-years at the group's estimated distance, and includes smaller, bluish NGC 3165 at the right. NGC 3169 is also known to shine across the spectrum from radio to X-rays, harboring an active galactic nucleus that is the site of a supermassive black hole.

Image credit: Mike Selby
RCW 86: Historical Supernova Remnant (2023-03-03)

In 185 AD, Chinese astronomers recorded the appearance of a new star in the Nanmen asterism. That part of the sky is identified with Alpha and Beta Centauri on modern star charts. The new star was visible to the naked-eye for months, and is now thought to be the earliest recorded supernova. This deep telescopic view reveals the wispy outlines of emission nebula RCW 86, just visible against the starry background, understood to be the remnant of that stellar explosion. Captured by the wide-field Dark Energy Camera operating at Cerro Tololo Inter-American Observatory in Chile, the image traces the full extent of a ragged shell of gas ionized by the still expanding shock wave. Space-based images indicate an abundance of the element iron in RCW 86 and the absence of a neutron star or pulsar within the remnant, suggesting that the original supernova was Type Ia. Unlike the core collapse supernova explosion of a massive star, a Type Ia supernova is a thermonuclear detonation on a white dwarf star that accretes material from a companion in a binary star system. Near the plane of our Milky Way galaxy and larger than the full moon on the sky this supernova remnant is too faint to be seen by eye though. RCW 86 is some 8,000 light-years distant and around 100 light-years across.
10 Days of Venus and Jupiter (2023-03-04)

Venus and Jupiter may have caught your attention lately.  The impending close conjunction of the two brightest planets visible in clear evening skies has been hard to miss. With Jupiter at the top, starting on February 21 and ending on March 2, their close approach is chronicled daily, left to right, in these panels from Dhanbad, India. Near the western horizon, the evening sky colors and exposures used for each panel depend on the local conditions near sunset. On February 22, Jupiter and Venus were joined by the young crescent Moon. The celestial pair appeared to be only the width of a full moon apart by March 2. Of course on that date the two planets were physically separated by over 600 million kilometers in their orbits around the Sun. In the coming days Jupiter will slowly settle into the glare at sunset, but Venus will continue to move farther from the Sun in the western sky to excel in its current role as the brilliant evening star.   Jupiter & Venus Conjunction Gallery: Notable Submissions to APOD

Image credit: Soumyadeep Mukherjee
Jupiter and Venus over Italy (2023-03-05)

What are those two bright spots? Planets.  A few days ago, the two brightest planets in the night sky passed within a single degree of each other in what is termed a conjunction. Visible just after sunset in much of the world, the two bright spots were Jupiter (left) and Venus (right).  The featured image was taken near closest approach from Cirica, Sicily, Italy. The week before, Venus was rising higher in the sunset sky to meet the dropping Jupiter. Now they have switched places. Of course, Venus remains much closer to both the Sun and the Earth than Jupiter -- the apparent closeness between the planets in the sky of Earth was only angular.  You can still see the popular pair for an hour or so after sunset this month although they continue to separate, and Jupiter continues to set earlier each night.   Jupiter & Venus Conjunction Gallery: Notable Submissions to APOD

Image credit: Giovanni Tumino
Jupiter and Venus from Earth (2023-03-06)

It was visible around the world. The sunset conjunction of Jupiter and Venus in 2012 was visible almost no matter where you lived on Earth.  Anyone on the planet with a clear western horizon at sunset could see them. Pictured here in 2012, a creative photographer traveled away from the town lights of Szubin, Poland to image a near closest approach of the two planets. The bright planets were then separated only by three degrees and his daughter struck a humorous pose. A faint red sunset still glowed in the background. Jupiter and Venus are together again this month after sunset, passing within a degree of each other about a week ago.    Jupiter & Venus Conjunction Gallery: Notable Submissions to APOD

Image credit: Marek Nikodem 
(PPSAE)
Deep Field: The Large Magellanic Cloud (2023-03-07)

Is this a spiral galaxy? No. Actually, it is the Large Magellanic Cloud (LMC), the largest satellite galaxy of our own Milky Way Galaxy.  The LMC is classified as a dwarf irregular galaxy because of its normally chaotic appearance.  In this deep and wide exposure, however, the full extent of the LMC becomes visible.  Surprisingly, during longer exposures, the LMC begins to resemble a barred spiral galaxy.  The Large Magellanic Cloud lies only about 180,000 light-years distant towards the constellation of the Dolphinfish (Dorado).  Spanning about 15,000 light-years, the LMC was the site of SN1987A, the brightest and closest supernova in modern times. Together with the Small Magellanic Cloud (SMC), the LMC can be seen in Earth's southern hemisphere with the unaided eye.   Your Sky Surprise: What picture did APOD feature on your birthday? (post 1995)

Image credit: Yuri Beletsky
(Carnegie
Las Campanas Observatory,
TWAN)
Artificial Night Sky Brightness (2023-03-08)

Where have all the dim stars gone?  From many places on the Earth including major cities, the night sky has been reduced from a fascinating display of thousands of stars to a diffuse glow through which only a few stars are visible.  The featured map indicates the relative amount of light pollution that occurs across the Earth.  The cause of the pollution is artificial light reflecting off molecules and aerosols in the atmosphere.  Parts of the Eastern United States and Western Europe  colored red, for example, have an artificial night sky glow over ten times that of the natural sky.  In any area marked orange or red, the central band of our Milky Way Galaxy is no longer visible. The International Dark Sky Association suggests common types of fixtures that provide relatively little amounts of light pollution.   Light Up Your Internal Night Sky: Random APOD Generator
DART vs Dimorphos (2023-03-09)

On the first planetary defense test mission from planet Earth, the DART spacecraft captured this close-up on 26 September 2022, three seconds before slamming into the surface of asteroid moonlet Dimorphos. The spacecraft's outline with two long solar panels is traced at its projected point of impact between two boulders. The larger boulder is about 6.5 meters across. While the DART (Double Asteroid Redirection Test) spacecraft had a mass of some 570 kilograms, the estimated mass of Dimorphos, the smaller member of a near-Earth binary asteroid system, was about 5 billion kilograms. The direct kinetic impact of the spacecraft measurably altered the speed of Dimorphos by a fraction of a percent, reducing its 12 hour orbital period around its larger companion asteroid 65803 Didymos by about 33 minutes. Beyond successfully demonstrating a technique to change an asteroid's orbit that can prevent future asteroid strikes on planet Earth, the planetary-scale impact experiment has given the 150-meter-sized Dimorphos a comet-like tail of material.
Orion and the Running Man (2023-03-10)

Few cosmic vistas excite the imagination like The Great Nebula in Orion. Visible as a faint celestial smudge to the naked-eye, the nearest large star-forming region sprawls across this sharp telescopic image, recorded on a cold January night in dark skies from West Virginia, planet Earth. Also known as M42, the Orion Nebula's glowing gas surrounds hot, young stars. About 40 light-years across, it lies at the edge of an immense interstellar molecular cloud only 1,500 light-years away within the same spiral arm of our Milky Way galaxy as the Sun. Along with dusty bluish reflection nebula NGC 1977 and friends near the top of the frame, the eye-catching nebulae represent only a small fraction of our galactic neighborhood's wealth of star-forming material. Within the well-studied stellar nursery, astronomers have also identified what appear to be numerous infant solar systems.

Image credit: Abraham Jones
3D Bennu (2023-03-11)

Put on your red/blue glasses and float next to asteroid 101955 Bennu. Shaped like a spinning toy top with boulders littering its rough surface, the tiny Solar System world is about one Empire State Building (less than 500 meters) across. Frames used to construct this 3D anaglyph were taken by PolyCam on the OSIRIS_REx spacecraft on December 3, 2018 from a distance of about 80 kilometers. With a sample from the asteroid's rocky surface on board, OSIRIS_REx departed Bennu's vicinity in May of 2021 and is now enroute to planet Earth. The robotic spacecraft is scheduled to return the sample to Earth this September.
Saturn's Hyperion: A Moon with Odd Craters (2023-03-12)

What lies at the bottom of Hyperion's strange craters?  To help find out, the robot Cassini spacecraft that once orbited Saturn swooped past the sponge-textured moon and took images of unprecedented detail.  A six-image mosaic from the 2005 pass, featured here in scientifically assigned colors, shows a remarkable world strewn with strange craters and an odd, sponge-like surface.   At the bottom of most craters lies some type of unknown dark reddish material.  This material appears similar to that covering part of another of Saturn's moons, Iapetus, and might sink into the ice moon as it better absorbs warming sunlight. Hyperion is about 250 kilometers across,  rotates chaotically, and has a density so low that it likely houses a vast system of caverns inside.
Rainbow Tree (2023-03-13)

What lies at the end of a rainbow? Something different for everyone.  For the photographer taking this picture, for example, one end of the rainbow ended at a tree. Others nearby, though, would likely see the rainbow end somewhere else.  The reason is because a rainbow's position depends on the observer.  The center of a rainbow always appears in the direction opposite the Sun, but that direction lines up differently on the horizon from different locations. This rainbow's arc indicates that its center is about 40 degrees to the left and slightly below the horizon, while the Sun is well behind the camera and just above the horizon. Reflections and refractions of sunlight from raindrops in a distant storm in the direction of the rainbow are what causes the colorful bands of light. This single exposure image was captured in early January near Knight's Ferry, California, USA.

Image credit: Eric Houck
W5: The Soul Nebula (2023-03-14)

Stars are forming in the Soul of the Queen of Aethopia. More specifically, a large star forming region called the Soul Nebula can be found in the direction of the constellation Cassiopeia, whom Greek mythology credits as the vain wife of a King who long ago ruled lands surrounding the upper Nile river. Also known as Westerhout 5 (W5), the Soul Nebula houses several open clusters of stars, ridges and pillars darkened by cosmic dust, and huge evacuated bubbles formed by the winds of young massive stars. Located about 6,500 light years away, the Soul Nebula spans about 100 light years and is usually imaged next to its celestial neighbor the Heart Nebula (IC 1805). The featured image is a composite of exposures made in different colors: red as emitted by hydrogen gas, yellow as emitted by sulfur, and blue as emitted by oxygen.

Image credit: José Jiménez (Astromet)
Jupiter and Venus Converge over Germany (2023-03-15)

This was a sky to show the kids. Early this month the two brightest planets in the night sky, Jupiter and Venus, appeared to converge. At their closest, the two planets were separated by only about the angular width of the full moon. The spectacle occurred just after sunset and was seen and photographed all across planet Earth. The displayed image was taken near to the time of closest approach from Wiltingen, Germany, and features the astrophotographer, spouse, and their two children.  Of course, Venus remains much closer to both the Sun and the Earth than Jupiter -- the apparent closeness between the planets in the sky of Earth was only angular.  Jupiter and Venus have passed and now appear increasingly far apart. Similar planetary convergence opportunities will eventually arise.  In a few months, for example, Mars and Venus will appear to congregate just as the Sun sets.   Jupiter & Venus Conjunction Gallery: Notable Submissions to APOD

Image credit: Michael Luy 
(Trier Observatory)
Millions of Stars in Omega Centauri (2023-03-16)

Globular star cluster Omega Centauri, also known as NGC 5139, is 15,000 light-years away. The cluster is packed with about 10 million stars much older than the Sun within a volume about 150 light-years in diameter. It's the largest and brightest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy. Though most star clusters consist of stars with the same age and composition, the enigmatic Omega Cen exhibits the presence of different stellar populations with a spread of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way. Omega Centauri's red giant stars (with a yellowish hue) are easy to pick out in this sharp, color telescopic view.

Image credit: Neil Corke
The Medusa Nebula (2023-03-17)

Braided and serpentine filaments of glowing gas suggest this nebula's popular name, The Medusa Nebula. Also known as Abell 21, this Medusa is an old planetary nebula some 1,500 light-years away in the constellation Gemini. Like its mythological namesake, the nebula is associated with a dramatic transformation. The planetary nebula phase represents a final stage in the evolution of low mass stars like the sun as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation from the hot star powers the nebular glow. The Medusa's transforming star is the faint one near the center of the overall bright crescent shape. In this deep telescopic view, fainter filaments clearly extend below and right of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across.

Image credit: Chesterfield Astronomical Society
Wolf-Rayet 124 (2023-03-18)

Driven by powerful stellar winds, expanding shrouds of gas and dust frame hot, luminous star Wolf-Rayet 124 in this sharp infrared view. The eye-catching 6-spike star pattern is characteristic of stellar images made with the 18 hexagonal mirrors of the James Webb Space Telescope. About 15,000 light-years distant toward the pointed northern constellation Sagitta, WR 124 has over 30 times the mass of the Sun. Produced in a brief and rarely spotted phase of massive star evolution in the Milky Way, this star's turbulent nebula is nearly 6 light-years across. It heralds WR 124's impending stellar death in a supernova explosion.  Formed in the expanding nebula, dusty interstellar debris that survives the supernova will influence the formation of future generations of stars.