juliensimon/nasa-apod huggingface dataset:
The Structured Tails of Comet NEOWISE (2020-07-22)

What is creating the structure in Comet NEOWISE's tails? Of the two tails evident, the blue ion tail on the left points directly away from the Sun and is pushed out by the flowing and charged solar wind. Structure in the ion tail comes from different rates of expelled blue-glowing ions from the comet's nucleus, as well as the always complex and continually changing structure of our Sun's wind. Most unusual for Comet C/2020 F3 (NEOWISE), though, is the wavy structure of its dust tail. This dust tail is pushed out by sunlight, but curves as heavier dust particles are better able to resist this light pressure and continue along a solar orbit.  Comet NEOWISE's impressive dust-tail striations are not fully understood, as yet, but likely related to rotating streams of sun-reflecting grit liberated by ice melting on its 5-kilometer wide nucleus.  The featured 40-image conglomerate, digitally enhanced, was captured three days ago through the dark skies of the Gobi Desert in Inner Mongolia, China. Comet NEOWISE will make it closest pass to the Earth tomorrow as it moves out from the Sun. The comet, already fading but still visible to the unaided eye, should fade more rapidly as it recedes from the Earth.    Notable NEOWISE Images Submitted to APOD: July  21 || 20 || 19  || 18   || 17   || 16   || 15  || 14  || 13  || 12  || 11  || 10 & earlier ||

Image credit: Zixuan Lin 
(Beijing Normal U.)
Fairytale NEOWISE (2020-07-23)

Comet dust falls through a twilight sky in this dream-like scene, but it's not part of a fairytale movie. Still, Castle Neuschwanstein, nestled in the Bavarian Alps, did inspire Disneyland's Sleeping Beauty Castle. Captured on July 20, the bright streak above the castle towers is likely a Perseid meteor. Though it peaks near mid-August, the annual summer meteor shower is active now. The meteor trail over the fairytale castle can be traced back to the shower's radiant in the heroic constellation Perseus off the top right of the frame. Perseid meteors are produced by dust from periodic Comet Swift-Tuttle. With its own broad dust tail now sweeping through northern skies the celestial apparition above the distant horizon is planet Earth's current darling, Comet NEOWISE.  Comet NEOWISE Images:  July  22 || 21 || 20 || 19  || 18   || 17   || 16   || 15  || 14  || 13  || 12  || 11  || 10 & earlier ||

Image credit: Stephane Guisard
MAGIC NEOWISE (2020-07-24)

The multi-mirror, 17 meter-diameter MAGIC telescopes reflect this starry night sky from the Roque de los Muchachos European Northern Observatory on the Canary Island of La Palma. MAGIC stands for Major Atmospheric Gamma Imaging Cherenkov and the telescopes can see the brief flashes of optical light produced in particle air showers as high-energy gamma rays impact the Earth's upper atmosphere. On July 20, two of the three telescopes in view were looking for gamma rays from the center of our Milky Way galaxy. In reflection they show the bright stars of Sagittarius and Scorpius near the galactic center to the southeast. Beyond the segmented-mirror arrays, above the northwest horizon and below the Big Dipper is Comet NEOWISE. NEOWISE stands for Near Earth Object Wide-field Infrared Survey Explorer. That's the Earth-orbiting satellite used to discover the comet designated C/2020 F3, but you knew that.  Comet NEOWISE Images:  July  23 || 22 || 21 || 20 || 19  || 18   || 17   || 16   || 15  || 14  || 13  || 12  || 11  || 10 & earlier

Image credit: Urs Leutenegger
Tianwen-1 Mission to Mars (2020-07-25)

On July 23, this Long March 5 heavy-lift rocket rose into a blue morning sky from China's Hainan Island Wenchang Satellite Launch Center. The rocket carried an orbiter, lander, and rover to ask Heavenly Questions on the ambitious Tianwen-1 mission to Mars. In fact Tianwen-1 was the second of three missions scheduled for a July departure to the Red Planet. The United Arab Emirates launched its Amal (Hope) Mars probe on July 19.  NASA's launch of its Mars Perseverance Rover from Cape Canaveral Air Force Station, USA is scheduled for July 30. That is the last planned Mars launch for 2020 though. The minimum-energy launch window for an expedition to Mars is coming to a close in 2020 and will reopen in 2022.  Comet NEOWISE images from planet Earth: July 24, 23, 22

Image credit: Jeff Dai
A Flight through the Hubble Ultra Deep Field (2020-07-26)

What would it look like to fly through the distant universe? To find out, a team of astronomers estimated the relative distances to over 5,000 galaxies in one of the most distant fields of galaxies ever imaged: the Hubble Ultra Deep Field (HUDF). Because it takes light a long time to cross the universe, most galaxies visible in the featured video are seen when the universe was only a fraction of its current age, were still forming, and have unusual shapes when compared to modern galaxies. No mature looking spiral galaxies such as our Milky Way or the Andromeda galaxy yet exist. Toward the end of the video the virtual observer flies past the farthest galaxies in the HUDF field, recorded to have a redshift past 8. This early class of low luminosity galaxies likely contained energetic stars emitting light that transformed much of the remaining normal matter in the universe from a cold gas to a hot ionized plasma.   Astrophysicists: Browse 2,200+ codes in the Astrophysics Source Code Library
Comet and Lightning Beyond Bighorn Mountains (2020-07-27)

Normally, Steamboat Point looks cool -- but not this cool. Every day, the iconic peak of the Bighorn Mountains is an interesting sight, in particular from US Highway 14 in Wyoming. On some rare days, the rocky vertical ridges look even more incredible when seen in front of a distant lightning storm. Earlier this month, though, something even more unusual happened -- the naked-eye Comet NEOWISE rose above it in the middle of the night. Just as a distant lightning storm was occurring in the background.  Recognizing a rare opportunity, a determined astrophotographer spent a sleepless night capturing  over 1400 images of this unusual triple conjunction.  The featured image is among the best of them, with the foreground lit by the Moon off to the right.  Comet C/2020 F3 (NEOWISE) is now headed back to the outer Solar System, destined to return only in about 6700 years.   Comet NEOWISE Images: July 26 || 25 || 24  || 23 || 22 || 21 || 20 || 19  || 18   || 17   || 16   || 15  || 14  || 13  || 12  || 11  || 10 & earlier ||

Image credit: Kevin Palmer
NGC 6188: The Dragons of Ara (2020-07-28)

Dark shapes with bright edges winging their way through dusty NGC 6188 are tens of light-years long. The emission nebula is found near the edge of an otherwise dark and large molecular cloud in the southern constellation Ara, about 4,000 light-years away. Born in that region only a few million years ago, the massive young stars of the embedded Ara OB1 association sculpt the fantastic shapes and power the nebular glow with stellar winds and intense ultraviolet radiation. The recent star formation itself was likely triggered by winds and supernova explosions, from previous generations of massive stars, that swept up and compressed the molecular gas. The featured image accumulated over 10 hours through a backyard telescope in Córdoba, Argentina and was false-colored using the Hubble palette highlighting emission from sulfur, hydrogen, and oxygen atoms in red, green, and blue hues. The field of view spans about four full Moons, corresponding to about 150 light years at the estimated distance of NGC 6188.

Image credit: Ariel L. Cappelletti
The Giants of Summer (2020-07-29)

As Comet NEOWISE sweeps through northern summer skies, Jupiter and Saturn are shining brightly, near opposition. With Jupiter opposite the Sun on July 14 and Saturn on July 21, the giant planets are still near their closest to planet Earth in 2020. Sharing the constellation Sagittarius they are up all night, and offer their best and brightest views at the telescope. Both captured on July 22 from a balcony in Paris these two sharp telescopic images don't disappoint, showing off what the giant planets are famous for, Saturn's bright rings and Jupiter's Great Red Spot. These giants of the Solar System are worth following during 2020. On December 21, skygazers can watch the once-in-20-year great conjunction of Jupiter and Saturn.  Comet NEOWISE images from planet Earth: July 28, 27, 26, 25, 24

Image credit: Jean-Luc Dauvergne
The Red Planet Mars (2020-07-30)

Mars looks pretty sharp in this backyard telescope image captured on July 23 from Hoegaarden, Belgium, planet Earth. The Red Planet's bright south polar cap is bathed in sunlight at the top of the inverted view, while the dark feature known as Syrtis Major extends toward the right (eastern) edge. Rising around midnight for now, the Red Planet is months away from its own opposition in early October. Telescopic views will improve even more as Earth, in its faster orbit, catches up to Mars, the ruddy disk growing larger and brighter still. The martian Jezero Crater is within the Syrtis Major region. That's the landing site for NASA's 2020 Mars Rover Perseverance, scheduled for launch today.  Comet NEOWISE images from planet Earth: July 29, 28, 27, 26, 25, 24

Image credit: Luc Debeck
Mars 2020 from 5,000 Feet (2020-07-31)

On Thursday this snapshot from a small plane 5,000 feet above Florida's Space Coast caught a rocket's trail rising into the blue morning sky. It was July's third launch of a mission from planet Earth bound for Mars. The Atlas V rocket left Cape Canaveral Air Force Station from Space Launch Complex 41 at 7:50am EDT carrying NASA's Mars 2020 Perseverance Rover. The car-sized Perseverance is headed for a landing at Jezero Crater on the Red Planet in February 2021.  On board the sophisticated rover is the Ingenuity Mars Helicopter.  Mars 2020 Launch: photos from planet Earth

Image credit: John Kraus
The Elephant's Trunk Nebula in Cepheus (2020-08-01)

Like an illustration in a galactic Just So Story, the Elephant's Trunk Nebula winds through the emission nebula and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Also known as vdB 142, the cosmic elephant's trunk is over 20 light-years long. This detailed close-up view was recorded through narrow band filters that transmit the light from ionized hydrogen and oxygen atoms in the region.  The resulting composite highlights the bright swept-back ridges that outline pockets of cool interstellar dust and gas. Such embedded, dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning over 5 degrees. This dramatic scene spans a 1 degree wide field of view though, about the size of 2 Full Moons.  Mars 2020 Launch: photos from planet Earth

Image credit: Chad Leader
Two Worlds, One Sun (2020-08-02)

How different does sunset appear from Mars than from Earth? For comparison, two images of our common star were taken at sunset, one from Earth and one from Mars. These images were scaled to have same angular width and featured here side-by-side. A quick inspection will reveal that the Sun appears slightly smaller from Mars than from Earth. This makes sense since Mars is 50% further from the Sun than Earth. More striking, perhaps, is that the Martian sunset is noticeably bluer near the Sun than the typically orange colors near the setting Sun from Earth. The reason for the blue hues from Mars is not fully understood, but thought to be related to forward scattering properties of Martian dust. The terrestrial sunset was taken in 2012 March from Marseille, France, while the Martian sunset was captured in 2015 by NASA's robotic Curiosity rover from Gale crater on Mars. Last week a new rover and a helicopter -- onboard Mars 2020 -- launched for Mars.

Image credit: Damia Bouic; 
 Right Image Credit:  NASA,
JPL-Caltech,
MSSS;
 Digital processing: 
Damia Bouic
Comet NEOWISE over Vikos Gorge (2020-08-03)

Did the Earth part to show us this comet?  Of course not, even if this image makes it seem that way. Pictured far in the background is Comet NEOWISE as it appeared about two weeks ago over northern Greece. Above the comet are many stars including the bright stars of the Big Dipper (also the Sorcerer, in Aztec mythology), an asterism that many people around the world used to find the naked-eye comet as it hovered in the northern sky over the past month.  In the foreground is Vikos Gorge, the deepest gorge on Earth, relative to its width. The gorge was slowly created by erosion from the Voidomatis River over the past few million years.  Capturing this image took a lot of planning, waiting, luck, braving high winds, and avoiding local wolves.  Comet C/2020 F3 (NEOWISE) continues to fade and is now best visible through binoculars as it coasts back to the outer Solar System.    Notable Comet NEOWISE Images: July 31 30, 29, 28, 27, 26, 25, 24

Image credit: Constantine Emmanouilidi
NGC 2442: Galaxy in Volans (2020-08-04)

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 have a hook-like appearance in wide-field images. But this mosaicked close-up, constructed from Hubble Space Telescope and European Southern Observatory data, follows the galaxy's structure in amazing detail. Obscuring dust lanes, young blue star clusters and reddish star forming regions surround a core of yellowish light from an older population of stars. The sharp image data also reveal more distant background galaxies seen right through NGC 2442's star clusters and nebulae. The image spans about 75,000 light-years at the estimated distance of NGC 2442.

Image credit: Robert Gendler
Picture Rocks Sun Dagger (2020-08-05)

Ancient sun daggers will not hurt you, but they may tell you the time.  A sun dagger is a dagger-shaped gap in a shadow created by sunlight streaming through a crevice in a nearby rock. Starting over a thousand year ago, native people of the American southwest carved spiral petroglyphs into rocks that became illuminated by sun daggers in different ways as the Sun shifts in the sky. A type of sundial, where the end of the sundagger points in the spiral at high noon (for example) indicates a time of year, possibly illuminating a solstice or equinox.  Sun daggers are thought to have been used by Sun Priests during lone vigils with prayers and offerings.  Of the few known, the featured video discusses the historic Picture Rocks Sun Dagger near Tucson, Arizona, USA, likely created by a Hohokam Sun Priest around 1000 AD.

Image credit: Martha Schaefer, 
Brad Schaefer, 
Jim Stamm;
 Music & License: 
Awakening  
(Wojciech Usarewicz), 
Lone Tree Music
Messier 20 and 21 (2020-08-06)

The beautiful Trifid Nebula, also known as Messier 20, is easy to find with a small telescope in the nebula rich constellation Sagittarius. About 5,000 light-years away, the colorful study in cosmic contrasts shares this well-composed, nearly 1 degree wide field with open star cluster Messier 21 (right). Trisected by dust lanes the Trifid itself is about 40 light-years across and a mere 300,000 years old. That makes it one of the youngest star forming regions in our sky, with newborn and embryonic stars embedded in its natal dust and gas clouds. Estimates of the distance to open star cluster M21 are similar to M20's, but though they share this gorgeous telescopic skyscape there is no apparent connection between the two. In fact, M21's stars are much older, about 8 million years old.

Image credit: Emanuele Petrilli
The Pipe Nebula (2020-08-07)

st of Antares, dark markings sprawl through crowded star fields toward the center of our Milky Way Galaxy. Cataloged in the early 20th century by astronomer E. E. Barnard, the obscuring interstellar dust clouds include B59, B72, B77 and B78, seen in against the starry background. Here, their combined shape suggests a pipe stem and bowl, and so the dark nebula's popular name is the Pipe Nebula. The deep and expansive view covers a full 10 by 10 degree field in the pronounceable constellation Ophiuchus. The Pipe Nebula is part of the Ophiuchus dark cloud complex located at a distance of about 450 light-years. Dense cores of gas and dust within the Pipe Nebula are collapsing to form stars.

Image credit: Jose Mtanous
Crescent Saturn (2020-08-08)

From Earth, Saturn never shows a crescent phase. But when viewed from a spacecraft the majestic giant planet can show just a sunlit slice. This image of crescent Saturn in natural color was taken by the robotic Cassini spacecraft in 2007. It captures Saturn's rings from the side of the ring plane opposite the Sun -- the unilluminated side -- another vista not visible from Earth. Visible are subtle colors of cloud bands, the complex shadows of the rings on the planet, and the shadow of the planet on the rings. The moons Mimas, at 2 o'clock, and Janus 4 o'clock, can be seen as specks of light, but the real challenge is to find Pandora (8 o'clock).  From Earth, Saturn's disk is nearly full now and opposite the Sun. Along with bright fellow giant planet Jupiter it rises in the early evening.
The Origin of Elements (2020-08-09)

The hydrogen in your body, present in every molecule of water, came from the Big Bang.  There are no other appreciable sources of hydrogen in the universe.  The carbon in your body was made by nuclear fusion in the interior of stars, as was the oxygen.  Much of the iron in your body was made during supernovas of stars that occurred long ago and far away.  The gold in your jewelry was likely made from neutron stars during collisions that may have been visible as short-duration gamma-ray bursts or gravitational wave events. Elements like phosphorus and copper are present in our bodies in only small amounts but are essential to the functioning of all known life.  The featured periodic table is color coded to indicate humanity's best guess as to the nuclear origin of all known elements.  The sites of nuclear creation of some elements, such as copper, are not really well known and are continuing topics of observational and computational research.   Almost Hyperspace: Random APOD Generator
Perseids from Perseus (2020-08-10)

Where are all these meteors coming from?  In terms of direction on the sky, the pointed answer is the constellation of Perseus.  That is why the meteor shower that peaks tomorrow night is known as the Perseids -- the meteors all appear to came from a radiant toward Perseus. In terms of parent body, though, the sand-sized debris that makes up the Perseids meteors come from Comet Swift-Tuttle. The comet follows a well-defined orbit around our Sun, and the part of the orbit that approaches Earth is superposed in front of the Perseus. Therefore, when Earth crosses this orbit, the radiant point of falling debris appears in Perseus. Featured here, a composite image taken over eight nights and containing over 400 meteors from 2018 August's Perseids meteor shower shows many bright meteors that streaked over Kolonica Observatory in Slovakia.  This year's Perseids holds promise to be one of the best meteor showers of the year.

Image credit: Petr Horálek
Churning Clouds on Jupiter (2020-08-11)

Where is Jupiter's ammonia? Gaseous ammonia was expected to be seen in Jupiter's upper atmosphere by the orbiting Juno spacecraft -- but in many clouds is almost absent. Recent Juno data, however, gives some clues: some high-level clouds appear to be home to an unexpected type of electrical discharge dubbed shallow lightning. Great charge separations are needed for lightning, which might be created by colliding mushballs lifted by rising updrafts of gas.  Ammonia and water stick to these mushballs which rise until they get too heavy -- after which they fall deep into Jupiter's atmosphere and melt.  By this process, ammonia found missing from Jupiter's upper atmosphere reappears below.  Pictured by Juno, churning clouds on Jupiter show not only mesmerizing complexity but some high-level, light-colored pop-up clouds. Understanding atmospheric dynamics on Jupiter gives valuable perspective to similar atmospheric and lightning phenomena that occur on our home Earth.    Peaking Tonight: The Perseid Meteor Shower
The Shifting Tails of Comet NEOWISE (2020-08-12)

Keep your eye on the ion tail of Comet NEOWISE.  A tale of this tail is the trail of the Earth. As with all comets, the blue ion tail always points away from the Sun. But as Comet C/2020 F3 (NEOWISE) rounded our Sun, its ion tail pointed in slightly different directions. This is because between 2020 July 17 and July 25 when the featured images were taken, the Earth moved noticeably in its orbit around the Sun. But the Earth's motion made the Sun appear to shift in the sky. So even though you can't see the Sun directly in the featured image(s), the directions of the ion tails reveal this apparent solar shift. The Sun's apparent motion is in the ecliptic, the common plane where all planets orbit.  The featured five image composite was meticulously composed to accurately place each comet image -- and the five extrapolated solar positions -- on a single foreground image of Turó de l'Home Mountain, north of Barcelona, Spain Comet NEOWISE is no longer the impressive naked-eye object it was last month, but it can still be found with a small telescope as it heads back to the outer Solar System.

Image credit: Ignacio Llorens
Jupiter and Saturn Rising Beyond Alien Throne Rock (2020-08-13)

What planets are those behind that unusual rock spire? Saturn (lower left) and Jupiter.  This month, after sunset, the bright planetary duo are quite prominent toward the southeast.  Now your view of our Solar System's largest planets might not include a picturesque hoodoo in the foreground, nor the spectacular central band of our Milky Way Galaxy across the background, but should be quite eye-catching anyway.  The featured image is a composite of consecutive foreground and background exposures all taken in late May with the same camera and from the same location -- the badlands of the  Ah-Shi-Sle-Pah Wilderness in the San Juan Basin in New Mexico, USA.  The rock spire, informally dubbed 'Alien Throne', stands about 3 meters tall. Saturn and Jupiter will remain visible together after sunset for several months.

Image credit: Marcin Zając
NGC 5189: An Unusually Complex Planetary Nebula (2020-08-14)

Why is this nebula so complex? When a star like our Sun is dying, it will cast off its outer layers, usually into a simple overall shape. Sometimes this shape is a sphere, sometimes a double lobe, and sometimes a ring or a helix.  In the case of planetary nebula NGC 5189, however, besides an overall "Z" shape (the featured image is flipped horizontally and so appears as an "S"), no such simple structure has emerged.  To help find out why, the Earth-orbiting Hubble Space Telescope has observed NGC 5189 in great detail. Previous findings indicated the existence of multiple epochs of material outflow, including a recent one that created a bright but distorted torus running horizontally across image center.  Hubble results appear consistent with a hypothesis that the dying star is part of a binary star system with a precessing symmetry axis. NGC 5189 spans about three light years and lies about 3,000 light years away toward the southern constellation of the Fly (Musca).