juliensimon/nasa-apod huggingface dataset:
The Milky Way over St Michael's Mount (2020-09-07)

Where do land and sky converge? On every horizon -- but in this case the path on the ground leads to St Michael's Mount (Cornish: Karrek Loos yn Koos), a small historic island in Cornwall, England. The Mount is usually surrounded by shallow water, but at low tide is spanned by a human-constructed causeway.  The path on the sky, actually the central band of our Milky Way Galaxy, also appears to lead to St Michael's Mount, but really lies far in the distance.  The red nebula in the Milky Way, just above the castle, is the Lagoon Nebula, while bright Jupiter shines to the left, and a luminous meteor flashes to the right.  The foreground and background images of this featured composite were taken on the same July night and from the same location. Although meteors are fleeting and the Milky Way disk shifts in the night as the Earth turns, Jupiter will remain prominent in the sunset sky into December.    Moon Occults Mars: Notable images submitted to APOD
GW190521: Unexpected Black Holes Collide (2020-09-08)

How do black holes like this form? The two black holes that spiraled together to produce the gravitational wave event GW190521 were not only the most massive black holes ever seen by LIGO and VIRGO so far, their masses -- 66 and 85 solar masses -- were unprecedented and unexpected. Lower mass black holes, below about 65 solar masses are known to form in supernova explosions.  Conversely, higher mass black holes, above about 135 solar masses, are thought to be created by very massive stars imploding after they use up their weight-bearing nuclear-fusion-producing elements. How such intermediate mass black holes came to exist is yet unknown, although one hypothesis holds that they result from consecutive collisions of stars and black holes in dense star clusters. Featured is an illustration of the black holes just before collision, annotated with arrows indicating their spin axes. In the illustration, the spiral waves indicate the production of gravitational radiation, while the surrounding stars highlight the possibility that the merger occurred in a star cluster.  Seen last year but emanating from an epoch when the universe was only about half its present age (z ~ 0.8), black hole merger GW190521 is the farthest yet detected, to within measurement errors.   Astrophysicists: Browse 2,200+ codes in the Astrophysics Source Code Library
Pleiades: The Seven Sisters Star Cluster (2020-09-09)

Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as large and clear as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city.  With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured exposure covers a sky area several times the size of the full moon.  Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus).  A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six of the sister stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.   Teachers & Students: Ideas for utilizing APOD in the classroom.

Image credit: Raul Villaverde Fraile
Jupiter's Swimming Storm (2020-09-10)

A bright storm head with a long turbulent wake swims across Jupiter in these sharp telescopic images of the Solar System's ruling gas giant. Captured on August 26, 28, and September 1 (left to right) the storm approximately doubles in length during that period. Stretching along the jetstream of the planet's North Temperate Belt it travels eastward in successive frames, passing the Great Red Spot and whitish Oval BA, famous storms in Jupiter's southern hemisphere. Galilean moons Callisto and Io are caught in the middle frame. In fact, telescopic skygazers following Jupiter in planet Earth's night have reported dramatic fast moving storm outbreaks over the past few weeks in Jupiter's North Temperate Belt.

Image credit: Andy Casely
The Reappearance of Mars (2020-09-11)

Mars reappears just beyond the Moon's dark limb in this stack of sharp video frames captured on September 6. Of course to reappear it had to disappear in the first place. It did that over an hour earlier when the sunlit southern edge of the waning gibbous Moon passed in front of the Red Planet as seen from Maceio, Brazil. The lunar occultation came as the Moon was near apogee, about 400,000 kilometers away. Mars was almost 180 times more distant. It was the fourth lunar occultation of Mars visible from planet Earth in 2020. Visible from some southern latitudes, the fifth lunar occultation of Mars in 2020 will take place on October 3 when the Moon and Mars are both nearly opposite the Sun in planet Earth's sky.

Image credit: David Duarte
A Thousand Meteors (2020-09-12)

Over a thousand meteors flash through the night in this intriguing timelapse video. Starting in April 2019 the individual video frames were selected from 372 relatively clear nights of imaging from an automated wide-field observatory in rural New South Wales Australia. Arranged by local sidereal time, a timekeeping system that uses the positions of stars to measure Earth's rotation, the frames follow the full annual progression of constellations through the wide field of view seen from 33 degrees south latitude. They capture a diverse array of meteors including sporadic meteors, bright fireballs, and shower meteors (plus a lightning sprite), during the period. All frames were processed consistently and so show real variations in the local sky conditions.

Image credit: Greg Priestley
M2-9: Wings of a Butterfly Nebula (2020-09-13)

Are stars better appreciated for their art after they die?  Actually, stars usually create their most artistic displays as they die.  In the case of low-mass stars like our Sun and M2-9 pictured here, the stars transform themselves from normal stars to white dwarfs by casting off their outer gaseous envelopes.  The expended gas frequently forms an impressive display called a planetary nebula that fades gradually over thousands of years.  M2-9, a butterfly planetary nebula 2100 light-years away shown in representative colors, has wings that tell a strange but incomplete tale.  In the center, two stars orbit inside a gaseous disk 10 times the orbit of Pluto.  The expelled envelope of the dying star breaks out from the disk creating the bipolar appearance.  Much remains unknown about the physical processes that cause and shape planetary nebulae.   Almost Hyperspace: Random APOD Generator
Corn Moon Rising (2020-09-14)

A rising moon can be a dramatic sight.  A rising Full Corn Moon was captured early this month in time-lapse with a telephoto lens from nearly 30 kilometers away -- making Earth's ascending half-degree companion appear unusually impressive.  The image was captured from Portugal, although much of the foreground -- including lights from the village of Puebla de Guzmán  -- is in Spain.  A Full Corn Moon is the name attributed to a full moon at this time of year by cultures of some northern indigenous peoples of the Americas, as it coincides with the ripening of corn.  Note that the Moon does not appear larger when it is nearer the horizon -- its seemingly larger size there is only an illusion.  The next full moon -- occurring at the beginning of next month -- will be known as the Full Harvest Moon as it occurs nearest in time to the northern autumnal equinox and the northern field harvests.

Image credit: Zarcos Palma
Biomarker Phosphine Discovered in the Atmosphere of Venus (2020-09-15)

Could there be life floating in the atmosphere of Venus? Although Earth's planetary neighbor has a surface considered too extreme for any known lifeform, Venus' upper atmosphere may be sufficiently mild for tiny airborne microbes. This usually disfavored prospect took an unexpected upturn yesterday with the announcement of the discovery of Venusian phosphine. The chemical phosphine (PH3) is a considered a biomarker because it seems so hard to create from routine chemical processes thought to occur on or around a rocky world such as Venus -- but it is known to be created by microbial life on Earth.  The featured image of Venus and its thick clouds was taken in two bands of ultraviolet light by the Venus-orbing Akatsuki, a Japanese robotic satellite that has been orbiting the cloud-shrouded world since 2015.  The phosphine finding, if confirmed, may set off renewed interest in searching for other indications of life floating high in the atmosphere of our Solar System's second planet out from the Sun.   Experts Debate: How will humanity first discover extraterrestrial life?
Gravel Ejected from Asteroid Bennu (2020-09-16)

Why does asteroid Bennu eject gravel into space?  No one is sure. The discovery, occurring during several episodes by NASA's visiting OSIRIS-REx spacecraft, was unexpected. Leading ejection hypotheses include impacts by Sun-orbiting meteoroids, sudden thermal fractures of internal structures, and the sudden release of a water vapor jet.  The featured two-image composite shows an ejection event that occurred in early 2019, with sun-reflecting ejecta seen on the right. Data and simulations show that large gravel typically falls right back to the rotating 500-meter asteroid, while smaller rocks skip around the surface, and the smallest rocks completely escape the low gravity of the Earth approaching, diamond-shaped asteroid. Jets and surface ejection events were thought to be predominantly the domain of comets, responsible for their tails, comas, and later meteor showers on Earth. Robotic OSIRIS-REx arrived at 101955 Bennu in late 2018, and is planned to touchdown to collect a surface sample in October 2020. If all goes well, this sample will then be returned to Earth for a detailed analysis during 2023.  Bennu was chosen as the destination for OSIRIS-REx in part because its surface shows potential to reveal organic compounds from the early days of our Solar System, compounds that could have been the building blocks for life on Earth.    Experts Debate: How will humanity first discover extraterrestrial life?
Solar Cycle 25 Has Begun (2020-09-17)

The general trend of monthly sunspot data now confirms that the minimum of the approximately 11 year cycle of solar activity occurred in December 2019, marking the start of Solar Cycle 25. That quiet Sun, at minimum activity, appears on the right of this split hemispherical view. In contrast, the left side shows the active Sun at the recognized maximum of Solar Cycle 24, captured in April 2014. The extreme ultraviolet images from the orbiting Solar Dynamics Observatory highlight coronal loops and active regions in the light of highly ionized iron atoms. Driving the space weather around our fair planet, Solar Cycle 24 was a relatively calm one and predictions are that cycle 25 will be calm too. The cycle 25 activity maximum is expected in July 2025. Solar Cycle 1, the first solar cycle determined from early records of sunspot data, is considered to begin with a minimum in February 1755.
Arp 78: Peculiar Galaxy in Aries (2020-09-18)

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. Also known as NGC 772, the island universe is over 100,000 light-years across and sports a single prominent outer spiral arm in this detailed cosmic portrait. Its brightest companion galaxy, compact NGC 770, is toward the upper right of the larger spiral. NGC 770's fuzzy, elliptical appearance contrasts nicely with a spiky foreground Milky Way star in matching yellowish hues. Tracking along sweeping dust lanes and lined with young blue star clusters, Arp 78's large spiral arm is likely due to gravitational tidal interactions. Faint streams of material seem to connect Arp 78 with its nearby companion galaxies.

Image credit: Bernard Miller
Orion in Depth (2020-09-19)

Orion is a familiar constellation. The apparent positions of its stars in two dimensions create a well-known pattern on the bowl of planet Earth's night sky. Orion may not look quite so familiar in this 3D view though. The illustration reconstructs the relative positions of Orion's bright stars, including data from the Hipparcus catalog of parallax distances. The most distant star shown is Alnilam. The middle one in the projected line of three that make up Orion's belt when viewed from planet Earth, Alnilam is nearly 2,000 light-years away, almost 3 times as far as fellow belt stars Alnitak and Mintaka. Though Rigel and Betelgeuse apparently shine brighter in planet Earth's sky, that makes more distant Alnilam intrinsically (in absolute magnitude) the brightest of the familiar stars in Orion. In the Hipparcus catalog, errors in measured parallaxes for Orion's stars can translate in to distance errors of a 100 light-years or so.

Image credit: Ronald Davison
Breaking Distant Light (2020-09-20)

In the distant universe, time appears to run slowly.  Since time-dilated light appears shifted toward the red end of the spectrum (redshifted), astronomers are able to use cosmological time-slowing to help measure vast distances in the universe.  Featured, the light from distant galaxies has been broken up into its constituent colors (spectra), allowing astronomers to measure the cosmological redshift of known spectral lines.  The novelty of the featured image is that the distance to hundreds of galaxies can be measured from a single frame, in this case one taken by the Visible MultiObject Spectrograph (VIMOS) operating at the Very Large Telescope (VLT) array in Chile.  Analyzing the space distribution of distant objects will allow insight into when and how stars and galaxies formed, clustered, and evolved in the early universe.
Omega Sunrise (2020-09-21)

Capturing this sunrise required both luck and timing.  First and foremost, precise timing was needed to capture a sailboat crossing right in front of a rising Sun.  Additionally, by a lucky coincidence, the background Sun itself appears unusual -- it looks like the Greek letter Omega (Ω).  In reality, the Sun remained its circular self -- the Omega illusion was created by sunlight refracting through warm air just above the water.  Optically, the feet of the capital Omega are actually an inverted image of the Sun region just above it.  Although somewhat rare, optical effects caused by the Earth's atmosphere can make distant objects near the horizon -- including the Sun and Moon -- look quite unusual.  This single exposure image was taken over the Mediterranean Sea just over two weeks ago near Valencia, Spain.

Image credit: Juan Antonio Sendra
Equinox in the Sky (2020-09-22)

Does the Sun set in the same direction every day? No, the direction of sunset depends on the time of the year. Although the Sun always sets approximately toward the west, on an equinox like today the Sun sets directly toward the west. After today's September equinox, the Sun will set increasingly toward the southwest, reaching its maximum displacement at the December solstice.  Before today's September equinox, the Sun had set toward the northwest, reaching its maximum displacement at the June solstice. The featured time-lapse image shows seven bands of the Sun setting one day each month from 2019 December through 2020 June.  These image sequences were taken from Alberta, Canada -- well north of the Earth's equator -- and feature the city of Edmonton in the foreground.  The middle band shows the Sun setting during the last equinox -- in March.  From this location, the Sun will set along this same equinox band again today.

Image credit: Luca Vanzella
ISS Transits Mars (2020-09-23)

Yes, but have you ever seen the space station do this? If you know when and where to look, watching the bright International Space Station (ISS) drift across your night sky is a fascinating sight -- but not very unusual.  Images of the ISS crossing in front of the half-degree Moon or Sun do exist, but are somewhat rare as they take planning, timing, and patience to acquire.  Catching the ISS crossing in front of minuscule Mars, though, is on another level. Using online software, the featured photographer learned that the unusual transit would be visible only momentarily along a very narrow stretch of nearby land spanning just 90 meters.  Within this stretch, the equivalent ground velocity of the passing ISS image would be a quick 7.4 kilometers per second. However, with a standard camera, a small telescope, an exact location to set up his equipment, an exact direction to point the telescope, and sub-millisecond timing -- he created a video from which the featured 0.00035 second exposure was extracted.  In the resulting image capture, details on both Mars and the ISS are visible simultaneously.  The featured image was acquired last Monday at 05:15:47 local time from just northeast of San Diego, California, USA.  Although typically much smaller, angularly, than the ISS, Mars is approaching its maximum angular size in the next few weeks, because the blue planet (Earth) is set to pass its closest to the red planet (Mars) in their respective orbits around the Sun.    Portal Universe: Random APOD Generator

Image credit: Tom Glenn
Enceladus in Infrared (2020-09-24)

One of our Solar System's most tantalizing worlds, icy Saturnian moon Enceladus appears in these detailed hemisphere views from the Cassini spacecraft. In false color, the five panels present 13 years of infrared image data from Cassini's Visual and Infrared Mapping Spectrometer and Imaging Science Subsystem. Fresh ice is colored red, and the most dramatic features look like long gashes in the 500 kilometer diameter moon's south polar region. They correspond to the location of tiger stripes, surface fractures that likely connect to an ocean beneath the Enceladus ice shell. The fractures are the source of the moon's icy plumes that continuously spew into space. The plumes were discovered by by Cassini in 2005. Now, reddish hues in the northern half of the leading hemisphere view also indicate a recent resurfacing of other regions of the geologically active moon, a world that may hold conditions suitable for life.   Experts Debate: How will humanity first discover extraterrestrial life?
Moon over Andromeda (2020-09-25)

The Great Spiral Galaxy in Andromeda (also known as M31), a mere 2.5 million light-years distant, is the closest large spiral to our own Milky Way. Andromeda is visible to the unaided eye as a small, faint, fuzzy patch, but because its surface brightness is so low, casual skygazers can't appreciate the galaxy's impressive extent in planet Earth's sky. This entertaining composite image compares the angular size of the nearby galaxy to a brighter, more familiar celestial sight. In it, a deep exposure of Andromeda, tracing beautiful blue star clusters in spiral arms far beyond the bright yellow core, is combined with a typical view of a nearly full Moon. Shown at the same angular scale, the Moon covers about 1/2 degree on the sky, while the galaxy is clearly several times that size. The deep Andromeda exposure also includes two bright satellite galaxies, M32 and M110 (below and right).

Image credit: Adam Block
Moon Pairs and the Synodic Month (2020-09-26)

Observe the Moon each night and its visible sunlit portion will gradually change. In phases progressing from New Moon to Full Moon to New Moon again, a lunar cycle or synodic month is completed in about 29.5 days. They look full, but top left to bottom right these panels do show the range of lunar phases for a complete synodic month during August 2019 from Ragusa, Sicily, Italy, planet Earth. For this lunar cycle project the panels organize images of the lunar phases in pairs. Each individual image is paired with another image separated by about 15 days, or approximately half a synodic month. As a result the opposite sunlit portions complete the lunar disk and the shadow line at the boundary of lunar night and day, the terminator, steadily marches across the Moon's familiar nearside. For extra credit, what lunar phase would you pair with the Moon tonight?

Image credit: Marcella Giulia Pace
Lightning over Colorado (2020-09-27)

Have you ever watched a lightning storm in awe?  Join the crowd. Oddly, details about how lightning is produced remains a topic of research. What is known is that updrafts carry light ice crystals into collisions with larger and softer ice balls, causing the smaller crystals to become positively charged.  After enough charge becomes separated, the rapid electrical discharge that is lightning occurs. Lightning usually takes a jagged course, rapidly heating a thin column of air to about three times the surface temperature of the Sun.  The resulting shock wave starts supersonically and decays into the loud sound known as thunder.  Lightning bolts are common in clouds during rainstorms, and on average 44 lightning bolts occur on the  Earth every second. Pictured, over 60 images were stacked to capture the flow of lightning-producing storm clouds in July over Colorado Springs, Colorado, USA.    Follow APOD in English on: Facebook,  Instagram, or Twitter

Image credit: Joe Randall
Filaments of the Cygnus Loop (2020-09-28)

What lies at the edge of an expanding supernova?  Subtle and delicate in appearance, these ribbons of shocked interstellar gas are part of a blast wave at the expanding edge of a violent stellar explosion that would have been easily visible to humans during the late stone age, about 20,000 years ago.  The featured image was recorded by the Hubble Space Telescope and is a closeup of the outer edge of a supernova remnant known as the Cygnus Loop or Veil Nebula.  The filamentary shock front is moving toward the top of the frame at about 170 kilometers per second, while glowing in light emitted by atoms of excited hydrogen gas.  The distances to stars thought to be interacting with the Cygnus Loop have recently been found by the Gaia mission to be about 2400 light years distant.  The whole Cygnus Loop spans six full Moons across the sky, corresponding to about 130 light years, and parts can be seen with a small telescope toward the constellation of the Swan (Cygnus).
GW Orionis: A Star System with Tilted Rings (2020-09-29)

Triple star system GW Orionis appears to demonstrate that planets can form and orbit in multiple planes. In contrast, all the planets and moons in our Solar System orbit in nearly the same plane.  The picturesque system has three prominent stars, a warped disk, and inner tilted rings of gas and grit.  The featured animation characterizes the GW Ori system from observations with the European Southern Observatory's VLT and ALMA telescopes in Chile. The first part of the illustrative video shows a grand vista of the entire system from a distant orbit, while the second sequence takes you inside the tilted rings to resolve the three central co-orbiting stars.  Computer simulations indicate that multiple stars in systems like GW Ori could warp and break-up disks into unaligned, exoplanet-forming rings.
Sonified: Eagle Nebula Pillars (2020-09-30)

Yes, but have you ever experienced the Eagle Nebula with your ears ? The famous nebula, M16, is best known for the feast it gives your eyes, highlighting bright young stars forming deep inside dark towering structures.  These light-years long columns of cold gas and dust are some 6,500 light-years distant toward the constellation of the Serpent (Serpens).  Sculpted and eroded by the energetic ultraviolet light and powerful winds from M16's cluster of massive stars, the cosmic pillars themselves are destined for destruction.  But the turbulent environment of star formation within M16, whose spectacular details are captured in this combined Hubble (visible) and Chandra (X-ray) image, is likely similar to the environment that formed our own Sun. In the featured video, listen for stars and dust sounding off as the line of sonification moves left to right, with vertical position determining pitch.