juliensimon/nasa-apod huggingface dataset:
Dark Matter in a Simulated Universe (2020-10-25)

Is our universe haunted?  It might look that way on this dark matter map.  The gravity of unseen dark matter is the leading explanation for why galaxies rotate so fast, why galaxies orbit clusters so fast, why gravitational lenses so strongly deflect light, and why visible matter is distributed as it is both in the local universe and on the cosmic microwave background.  The featured image from the American Museum of Natural History's Hayden Planetarium previous Space Show Dark Universe highlights one example of how pervasive dark matter might haunt our universe.  In this frame from a detailed computer simulation, complex filaments of dark matter, shown in black, are strewn about the universe like spider webs, while the relatively rare clumps of familiar baryonic matter are colored orange. These simulations are good statistical matches to astronomical observations.  In what is perhaps a scarier turn of events, dark matter -- although quite strange and in an unknown form -- is no longer thought to be the strangest source of gravity in the universe. That honor now falls to dark energy, a more uniform source of repulsive gravity that seems to now dominate the expansion of the entire universe.

Image credit: Tom Abel &
Ralf Kaehler 
(KIPAC, 
SLAC), 
AMNH
Reflections of the Ghost Nebula (2020-10-26)

Do any shapes seem to jump out at you from this interstellar field of stars and dust?  The jeweled expanse, filled with faint, starlight-reflecting clouds, drifts through the night in the royal constellation of Cepheus. Far from your own neighborhood on planet Earth, these ghostly apparitions lurk along the plane of the Milky Way at the edge of the Cepheus Flare molecular cloud complex some 1,200 light-years away. Over two light-years across and brighter than the other spooky chimeras, VdB 141 or Sh2-136 is also known as the Ghost Nebula, seen at toward the bottom of the featured image. Within the reflection nebula are the telltale signs of dense cores collapsing in the early stages of star formation.

Image credit: Bogdan Jarzyna
Venusian Volcano Imagined (2020-10-27)

What would an erupting volcano on Venus look like? Evidence of currently active volcanoes on Venus was announced earlier this year with the unexplained warmth of regions thought to contain only ancient volcanoes.  Although large scale images of Venus have been taken with radar, thick sulfuric acid clouds would inhibit the taking of optical light vistas. Nevertheless, an artist's reconstruction of a Venusian volcano erupting is featured. Volcanoes could play an important role in a life cycle on Venus as they could push chemical foods into the cooler upper atmosphere where hungry microbes might float.  Pictured, the plume from an erupting volcano billows upwards, while a vast lava field covers part of the hot and cracked surface of Earth's overheated twin.  The possibility of airborne microbial Venusians is certainly exciting, but currently controversial.    An APOD Described on TikTok: By astrokirsten
NGC 6357: The Lobster Nebula (2020-10-28)

Why is the Lobster Nebula forming some of the most massive stars known? No one is yet sure.  Cataloged as NGC 6357, the Lobster Nebula houses the open star cluster Pismis 24 near its center -- a home to unusually bright and massive stars.  The overall blue glow near the inner star forming region results from the emission of ionized hydrogen gas.   The surrounding nebula, featured here, holds a complex tapestry of gas, dark dust, stars still forming, and newly born stars.  The intricate patterns are caused by complex interactions between interstellar winds, radiation pressures, magnetic fields, and gravity.  NGC 6357 spans about 400 light years and lies about 8,000 light years away toward the constellation of the Scorpion.

Image credit: Steven Mohr
The Ghoul of IC 2118 (2020-10-29)

Inspired by the halloween season, this telescopic portrait captures a cosmic cloud with a scary visage. The interstellar scene lies within the dusty expanse of reflection nebula IC 2118 in the constellation Orion, the Hunter. IC 2118 is about 800 light-years from your neighborhood, close to bright bluish star Rigel at Orion's foot. Often identified as the Witch Head nebula for its appearance in a wider field of view it now rises before the witching hour. With spiky stars for eyes, the ghoulish apparition identified here seems to extend an arm many light-years long toward Orion's hot supergiant star. The source of illumination for IC 2118, Rigel is just beyond this frame at the upper left.

Image credit: Casey Good/Steve Timmons
Fear and Dread: The Moons of Mars (2020-10-30)

On Halloween fear and dread will stalk your night skies, also known as Phobos and Deimos the moons of Mars. The 2020 opposition of Mars was on October 13, so the Red Planet will still rise shortly before sunset. Near Halloween's Full Moon on the sky, its strange yellowish glow will outshine other stars throughout the night. But the two tiny Martian moons are very faint and in close orbits, making them hard to spot, even with a small telescope. You can find them in this carefully annotated composite view though. The overexposed planet's glare is reduced and orbital paths for inner moon Phobos and outer moon Deimos are overlayed on digitally combined images captured on October 6. The diminutive moons of Mars were discovered in August of 1877 by astronomer Asaph Hall at the US Naval Observatory using the Great Equatorial 26-inch Alvan Clark refractor.

Image credit: Dennis Simmons
In the Center of the Trifid Nebula (2020-11-01)

What's happening at the center of the Trifid Nebula? Three prominent dust lanes that give the Trifid its name all come together. Mountains of opaque dust appear near the bottom, while other dark filaments of dust are visible threaded throughout the nebula.  A single massive star visible near the center causes much of the Trifid's glow.  The Trifid, cataloged as M20, is only about 300,000 years old, making it among the youngest emission nebulas known.  The star forming nebula lies about 9,000 light years away toward the constellation of the Archer (Sagittarius). The region pictured here spans about 10 light years.  The featured image is a composite with luminance taken from an image by the 8.2-m ground-based Subaru Telescope, detail provided by the 2.4-m orbiting Hubble Space Telescope, color data provided by Martin Pugh and image assembly and processing provided by Robert Gendler.   Portal Universe: Random APOD Generator
Half Sun with Prominence (2020-11-02)

What's happening to the Sun? Clearly, the Sun's lower half is hidden behind a thick cloud.  Averaging over the entire Earth, clouds block the Sun about 2/3rds of the time, although much less over many land locations. On the Sun's upper right is a prominence of magnetically levitating hot gas. The prominence might seem small but it could easily envelop our  Earth and persist for over a month.  The featured image is a combination of two exposures, one optimizing the cloud and prominence, and the other optimizing the Sun's texture.  Both were taken about an hour apart with the same camera and from the same location in Lynnwood, Washington, USA.  The shaggy texture derives from the Sun's chromosphere, an atmospheric layer that stands out in the specifically exposed color.  The uniformity of the texture shows the surface to be relatively calm, indicative of a Sun just past the solar minimum in its 11-year cycle. In the years ahead, the Sun will progress toward a more active epoch where sunspots, prominences, and ultimately auroras on Earth will be more common: solar maximum.    Gallery: Notable images of the Halloween Blue Moon of 2020 submitted to APOD

Image credit: Rainee Colacurcio
Tagging Bennu: The Movie (2020-11-03)

This is what it looks like to punch an asteroid. Last month, NASA's robotic spacecraft OSIRIS-REx descended toward, thumped into, and then quickly moved away from the small near-Earth asteroid 101955 Bennu.  The featured video depicts the Touch-And-Go (TAG) sampling event over a three-hour period.  As the movie begins, the automated probe approaches the 500-meter, diamond-shaped, space rock as it rotates noticeably below. About 20 seconds into the video, Nightingale comes into view -- a touchdown area chosen to be relatively flat and devoid of large boulders that could damage the spaceship.  At 34 seconds, the shadow of OSIRIS-REx's sampling arm suddenly comes into view, while very soon thereafter rocks and gravel fly from the arm's abrupt hard impact.  The wily spacecraft was able to capture and successfully stow some of Bennu's ejecta for return to Earth for a detailed analysis.  This long return is scheduled to start in 2021 March with arrival back on Earth in 2023 September. If the return sample does successfully reach Earth, it will be scrutinized for organic compounds that might have seeded a young Earth, rare or unusual elements and minerals, and clues about the early history of our Solar System.
Fifty Gravitational Wave Events Illustrated (2020-11-04)

Over fifty gravitational wave events have now been detected. These events mark the distant, violent collisions of two black holes, a black hole and a neutron star, or two neutron stars.  Most of the 50 events were detected in 2019 by the LIGO gravitational wave detectors in the USA and the VIRGO detector in Europe.  In the featured illustration summarizing the masses of the first 50 events, blue dots indicate higher-mass black holes while orange dots denote lower-mass neutron stars. Astrophysicists are currently uncertain, though, about the nature of events marked in white involving masses that appear to be in the middle -- between two and five solar masses.  The night sky in optical light is dominated by nearby and bright planets and stars that have been known since the dawn of humanity. In contrast, the sky in gravitational waves is dominated by distant and dark black holes  that have only been known about for less than five years.  This contrast is enlightening -- understanding the gravitational wave sky is already reshaping humanity's knowledge not only of star birth and death across the universe, but properties of the universe itself.
North of Orion's Belt (2020-11-05)

Bright stars, interstellar clouds of dust and glowing nebulae fill this cosmic scene, a skyscape just north of Orion's belt. Close to the plane of our Milky Way Galaxy, the wide field view spans just under 5 degrees or about 10 full moons on the sky. Striking bluish M78, a reflection nebula, is at the lower right. M78's tint is due to dust preferentially reflecting the blue light of hot, young stars. In colorful contrast, the red swath of glowing hydrogen gas streaming through the center is part of the region's faint but extensive emission nebula known as Barnard's Loop. At upper left, a dark dust cloud forms a prominent silhouette cataloged as LDN 1622. While M78 and the complex Barnard's Loop are some 1,500 light-years away, LDN 1622 is likely to be much closer, only about 500 light-years distant from our fair planet Earth.

Image credit: Terry Hancock
Moon over ISS (2020-11-06)

Completing one orbit of our fair planet in 90 minutes the International Space Station can easily be spotted by eye as a very bright star moving through the night sky. Have you seen it? The next time you do, you will have recognized the location of over 20 years of continuous human presence in space. In fact, the Expedition 1 crew to the ISS docked with the orbital outpost some 400 kilometers above the Earth on November 2, 2000. No telescope is required to spot the ISS flashing through the night. But this telescopic field of view does reveal remarkable details of the space station captured as it transited the waning gibbous moon on November 3, just one day after the space age milestone. The well-timed telescopic snapshot also contains the location of another inspirational human achievement. About 400,000 kilometers away, the Apollo 11 landing site on the dark, smooth lunar Sea of Tranquility is to the right of the ISS silhouette.

Image credit: Derek Demeter
The Hercules Cluster of Galaxies (2020-11-07)

These are galaxies of the Hercules Cluster, an archipelago of island universes a mere 500 million light-years away. Also known as Abell 2151, this cluster is loaded with gas and dust rich, star-forming spiral galaxies but has relatively few elliptical galaxies, which lack gas and dust and the associated newborn stars. The colors in this deep composite image clearly show the star forming galaxies with a blue tint and galaxies with older stellar populations with a yellowish cast. The sharp picture spans about 1/2 degree across the cluster center, corresponding to over 4 million light-years at the cluster's estimated distance. Diffraction spikes around brighter foreground stars in our own Milky Way galaxy are produced by the imaging telescope's mirror support vanes. In the cosmic vista many galaxies seem to be colliding or merging while others seem distorted - clear evidence that cluster galaxies commonly interact. In fact, the Hercules Cluster itself may be seen as the result of ongoing mergers of smaller galaxy clusters and is thought to be similar to young galaxy clusters in the much more distant, early Universe.

Image credit: Howard Trottier
Martian Moon Phobos from Mars Express (2020-11-08)

Why is Phobos so dark?  Phobos, the largest and innermost of two Martian moons, is the darkest moon in the entire Solar System.  Its unusual orbit and color indicate that it may be a captured asteroid composed of a mixture of ice and dark rock.  The featured picture of Phobos near the limb of Mars was captured in 2010 by the robot spacecraft Mars Express currently orbiting Mars.  Phobos is a heavily cratered and barren moon, with its largest crater located on the far side.  From images like this, Phobos has been determined to be covered by perhaps a meter of loose dust.  Phobos orbits so close to Mars that from some places it would appear to rise and set twice a day, but from other places it would not be visible at all.  Phobos' orbit around Mars is continually decaying -- it will likely break up with pieces crashing to the Martian surface in about 50 million years.
In Green Company: Aurora over Norway (2020-11-09)

Raise your arms if you see an aurora. With those instructions, two nights went by with, well, clouds -- mostly. On the third night of returning to same peaks, though, the sky not only cleared up but lit up with a spectacular auroral display. Arms went high in the air, patience and experience paid off, and the creative featured image was captured as a composite from three separate exposures. The setting is a summit of the Austnesfjorden fjord close to the town of Svolvear on the Lofoten islands in northern Norway. The time was early 2014. Although our Sun has just passed the solar minimum of its 11-year cycle, surface activity should pick up over the next few years with the promise of triggering more spectacular auroras on Earth.

Image credit: Max Rive
The Central Soul Nebula Without Stars (2020-11-10)

This cosmic close-up looks deep inside the Soul Nebula. The dark and brooding dust clouds near the top, outlined by bright ridges of glowing gas, are cataloged as IC 1871. About 25 light-years across, the telescopic field of view spans only a small part of the much larger Heart and Soul nebulae. At an estimated distance of 6,500 light-years the star-forming complex lies within the Perseus spiral arm of our  Milky Way Galaxy, seen in planet Earth's skies toward the constellation Cassiopeia. An example of triggered star formation, the dense star-forming clouds in the Soul Nebula are themselves sculpted by the intense winds and radiation of the region's massive young stars. In the featured image, stars have been digitally removed to highlight the commotion in the gas and dust.

Image credit: Jason Guenzel
Colors of the Moon (2020-11-11)

What color is the Moon? It depends on the night.  Outside of the Earth's atmosphere, the dark Moon, which shines by reflected sunlight, appears a magnificently brown-tinged gray.  Viewed from inside the Earth's atmosphere, though, the moon can appear quite different.  The featured image highlights a collection of apparent colors of the full moon documented by one astrophotographer over 10 years from different locations across Italy. A red or yellow colored moon usually indicates a moon seen near the horizon.  There, some of the blue light has been scattered away by a long path through the Earth's atmosphere, sometimes laden with fine dust. A blue-colored moon is more rare and can indicate a moon seen through an atmosphere carrying larger dust particles.  What created the purple moon is unclear -- it may be a combination of several effects.  The last image captures the total lunar eclipse of 2018 July -- where the moon, in Earth's shadow, appeared a faint red -- due to light refracted through air around the Earth. The next full moon will occur at the end of this month (moon-th) and is known in some cultures as the Beaver Moon.

Image credit: Marcella Giulia Pace
Comet ATLAS and Orion's Belt (2020-11-12)

With its closest approach to planet Earth scheduled for November 14, this Comet ATLAS (C/2020 M3) was discovered just this summer, another comet found by the NASA funded Asteroid Terrestrial-impact Last Alert System. It won't get as bright as Comet NEOWISE but it can still be spotted using binoculars, as it currently sweeps through the familiar constellation of Orion. This telephoto field from November 8, blends exposures registered on the comet with exposures registered on Orion's stars. It creates an effectively deep skyview that shows colors and details you can't quite see though, even in binoculars. The comet's telltale greenish coma is toward the upper left, above Orion's three belt stars lined-up across the frame below center. You'll also probably spot the Orion Nebula, and famous Horsehead Nebula in the stunning field of view. Of course one of Orion's belt stars is nearly 2,000 light-years away. On November 14, this comet ATLAS will fly a mere 2.9 light-minutes from Earth.

Image credit: Charles Bracken
The Tarantula Zone (2020-11-13)

The Tarantula Nebula, also known as 30 Doradus, is more than a thousand light-years in diameter, a giant star forming region within nearby satellite galaxy the Large Magellanic Cloud. About 180 thousand light-years away, it's the largest, most violent star forming region known in the whole Local Group of galaxies. The cosmic arachnid sprawls across the top of this spectacular view, composed with narrowband filter data centered on emission from ionized hydrogen and oxygen atoms. Within the Tarantula (NGC 2070), intense radiation, stellar winds and supernova shocks from the central young cluster of massive stars, cataloged as R136, energize the nebular glow and shape the spidery filaments. Around the Tarantula are other star forming regions with young star clusters, filaments, and blown-out bubble-shaped clouds. In fact, the frame includes the site of the closest supernova in modern times, SN 1987A, right of center. The rich field of view spans about 2 degrees or 4 full moons, in the southern constellation Dorado. But were the Tarantula Nebula closer, say 1,500 light-years distant like the local star forming Orion Nebula, it would take up half the sky.

Image credit: Ignacio Diaz Bobillo
Venus, Mercury, and the Waning Moon (2020-11-14)

Yesterday, early morning risers around planet Earth were treated to a waning Moon low in the east as the sky grew bright before dawn. From the Island of Ortigia, Syracuse, Sicily, Italy this simple snapshot found the slender sunlit crescent just before sunrise. Never wandering far from the Sun in Earth's sky, inner planets Venus and Mercury shared the calm seaside view. Also in the frame, right of the line-up of Luna and planets, is bright star Spica, alpha star of the constellation Virgo and one of the 20 brightest stars in Earth's night. Tomorrow the Moon will be New. The dark lunar disk means mostly dark nights for planet Earth in the coming week and a good chance to watch the annual Leonid Meteor Shower.

Image credit: Kevin Saragozza
Edge-On Galaxy NGC 5866 (2020-11-15)

Why is this galaxy so thin?  Many disk galaxies are just as thin as NGC 5866, pictured here, but are not seen edge-on from our vantage point.  One galaxy that is situated edge-on is our own Milky Way Galaxy.  Classified as a lenticular galaxy, NGC 5866 has numerous and complex dust lanes appearing dark and red, while many of the bright stars in the disk give it a more blue underlying hue.  The blue disk of young stars can be seen extending past the dust in the extremely thin galactic plane, while the bulge in the disk center appears tinged more orange from the older and redder stars that likely exist there. Although similar in mass to our Milky Way Galaxy, light takes about 60,000 years to cross NGC 5866, about 30 percent less than light takes to cross our own Galaxy. In general, many disk galaxies are very thin because the gas that formed them collided with itself as it rotated about the gravitational center. Galaxy NGC 5866 lies about 44 million light years distant toward the constellation of the Dragon (Draco).    Almost Hyperspace: Random APOD Generator
Light and Glory over Crete (2020-11-16)

The month was July, the place was the Greek island of Crete, and the sky was spectacular. Of course there were the usual stars like Polaris, Vega, and Antares -- and that common asterism everyone knows: the Big Dipper. But this sky was just getting started.  The band of the Milky Way Galaxy stunned as it arched across the night like a bridge made of stars and dust but dotted with red nebula like candy. The planets Saturn and Jupiter were so bright you wanted to stop people on the beach and point them out. The air glowed like a rainbow -- but what really grabbed the glory was a comet. Just above the northern horizon, Comet NEOWISE spread its tails like nothing you had ever seen before or might ever see again.  Staring in amazement, there was only one thing to do: take a picture.   Coverage: NASA's SpaceX Crew-1 Mission

Image credit: Tomáš Slovinský
A Glowing STEVE and the Milky Way (2020-11-17)

What's creating these long glowing streaks in the sky? No one is sure.  Known as Strong Thermal Emission Velocity Enhancements (STEVEs), these luminous light-purple sky ribbons may resemble regular auroras, but recent research reveals significant differences. A STEVE's great length and unusual colors, when measured precisely, indicate that it may be related to a subauroral ion drift (SAID), a supersonic river of hot atmospheric ions thought previously to be invisible.  Some STEVEs are now also thought to be accompanied by green picket fence structures, a series of sky slats that can appear outside of the main auroral oval that does not involve much glowing nitrogen. The featured wide-angle composite image shows a STEVE in a dark sky above Childs Lake, Manitoba, Canada in 2017, crossing in front of the central band of our Milky Way Galaxy.
A Double Star Cluster in Perseus (2020-11-18)

Most star clusters are singularly impressive.  Open clusters NGC 869 and NGC 884, however, could be considered doubly impressive.  Also known as "h and chi Persei", this unusual double cluster, shown above, is bright enough to be seen from a dark location without even binoculars.  Although their discovery surely predates recorded history, the Greek astronomer Hipparchus notably cataloged the double cluster.  The clusters are over 7,000 light years distant toward the constellation of Perseus, but are separated by only hundreds of light years. In addition to being physically close together, the clusters' ages based on their individual stars are similar - evidence that both clusters were likely a product of the same star-forming region.

Image credit: Greg Polanski