juliensimon/nasa-apod huggingface dataset:
Lightning Over Athens (2010-07-20)

Have you ever watched a lightning storm in awe?  Join the crowd. Oddly, nobody knows exactly how lightning is produced. What is known is that charges slowly separate in some clouds causing rapid electrical discharges (lightning), but how electrical charges get separated in clouds remains a topic of much research. 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 6,000 lightning bolts occur between clouds and the Earth every minute. Pictured above, an active lightning storm was recorded over Athens, Greece earlier this month.

Image credit: Chris Kotsiopoulos
The Crown of the Sun (2010-07-21)

During a total solar eclipse, the Sun's extensive outer atmosphere, or corona, is an inspirational sight. Subtle shades and shimmering features that engage the eye span a brightness range of over 10,000 to 1, making them notoriously difficult to capture in a single photograph. But this composite of 7 consecutive digital images over a range of exposure times comes close to revealing the crown of the Sun in all its glory. The telescopic views were recorded from the Isla de Pascua (Easter Island) during July 11's total solar eclipse and also show solar prominences extending just beyond the edge of the eclipsed sun. Remarkably, features on the dim, near side of the New Moon can also be made out, illuminated by sunlight reflected from a Full Earth.

Image credit: Alain Maury
The Meteor of 1860 (2010-07-22)

Frederic Church (1826-1900), American landscape painter of the Hudson River School, painted what he saw in nature. And on July 20th, 1860, he saw a spectacular string of fireball meteors cross the Catskill evening sky, an extremely rare Earth-grazing meteor procession. From New York City, poet Walt Whitman (1819-1892) also wrote of the "... strange huge meteor procession, dazzling and clear, shooting over our heads" in his poem Year of Meteors (1859-60). But the inspiration for Whitman's words was forgotten. His astronomical reference became a mystery, the subject of scholarly debate until Texas State University physicists Donald Olson and Russell Doescher, English professor Marilynn Olson, and Honors Program student Ava Pope, located reports documenting the date and timing of the spectacular meteor procession. The breakthrough was spotting the connection with Church's relatively little-known painting. Fittingly, the forensic astronomy team's work was just published, on the 150th anniversary of the cosmic event that inspired both poet and painter.
Messier 76 (2010-07-23)

"Nebula at the right foot of Andromeda ... " begins the description for the 76th object in Charles Messier's 18th century Catalog of Nebulae and Star Clusters. In fact, M76 is one of the fainter objects on the Messier list and is also known by the popular name of the "Little Dumbbell Nebula". Like its brighter namesake M27 (the Dumbbell Nebula), M76 is recognized as a planetary nebula - a gaseous shroud cast off by a dying sunlike star. The nebula itself is thought to be shaped more like a donut, while the box-like appearance of its brighter central region is due to our nearly edge-on view. Gas expanding more rapidly away from the donut hole produces the fainter loops of far flung material. The fainter material is emphasized in this composite image, highlighted by showing emission from hydrogen atoms in orange and oxygen atoms in complementary blue hues. The nebula's dying star can be picked out in the sharp false-color image as the blue-tinted star near the center of the box-like shape.  Distance estimates place M76 about 3 to 5 thousand light-years away, making the nebula over a light-year in diameter.

Image credit: Ken Crawford
Diamond Ring and Shadow Bands (2010-07-24)

As the total phase of July 11's solar eclipse came to an end, sunlight streaming past the edge of the Moon's silhouette created the fleeting appearance of a glistening diamond ring in the sky. Seen through a thin cloud layer from the French Polynesian atoll of Hao it also produced remarkable shadow bands, flickering across the dramatic sky. Projected onto the cloud layer, the shadow bands are parallel to the sliver of sunlight emerging from behind the Moon's edge. Caused by turbulence in Earth's atmosphere refracting the sliver of sunlight, the narrow bands were captured in this brief, 1/400th second exposure. Shining through the cloud droplets, the sunlight also produced a luminous atmospheric corona, not to be confused with the solar corona seen during eclipse totality. The atmospheric corona is centered on the bright diamond of emerging sunlight.

Image credit: Stephen Schneider
Happy People Dancing on Planet Earth (2010-07-25)

What are these humans doing?  Dancing.  Many humans on Earth exhibit periods of happiness, and one method of displaying happiness is dancing. Happiness and dancing transcend political boundaries and occur in practically every human society. Above, Matt Harding traveled through many nations on Earth, started dancing, and filmed the result.  The video is perhaps a dramatic example that humans from all over planet Earth feel a common bond as part of a single species. Happiness is frequently contagious -- few people are able to watch the above video without smiling.
Lutetia: The Largest Asteroid Yet Visited (2010-07-26)

As humans explore the universe, the record for largest asteroid visited by a spacecraft has increased yet again.  Earlier this month, ESA's robotic Rosetta spacecraft zipped past the asteroid 21 Lutetia taking data and snapping images in an effort to better determine the history of the asteroid and the origin of its unusual colors.  Although of unknown composition, Lutetia is not massive enough for gravity to pull it into a sphere. Pictured above on the upper right, the 100-kilometer across Lutetia is shown in comparison with the other nine asteroids and four comets that have been visited, so far, by human-launched spacecraft. Orbiting in the main asteroid belt, Lutetia shows itself to be a heavily cratered remnant of the early Solar System. The Rosetta spacecraft is now continuing onto comet Churyumov-Gerasimenko where a landing is planned for 2014.
The Milky Way Over Bryce Canyon (2010-07-27)

What are those strange rock structures? They are towers and walls of sedimentary rock that are particularly plentiful in Bryce Canyon in Utah, USA. The rock columns may rise higher than 50 meters and are called hoodoos. On the far left is Thor's Hammer, perhaps the most famous hoodoo. The tall rock columns were carved, most typically, when a unusually dense cap of rock provided a layer of protection to rock underneath from rain-based erosion.  In the above panoramic picture taken earlier this month and compressed horizontally, the foreground rocks were momentarily illuminated by a roving spotlight. Visible in the background are a few water clouds a few kilometers away hovering over the nearby Earth. Visible well beyond that are thousands of individually discernible stars averaging a few hundred light years away in the nearby Milky Way Galaxy. Far in the distance lie billions of stars that are thousands of light years away and compose the faintly glowing arch that is the visible central band of the flat disk of our Milky Way.  Over many years, wind and rain will eventually cause the tops of the hoodoos to topple, whereafter the underlying column will likely completely erode away.

Image credit: Ben Cooper
The Trifid Nebula is Stars and Dust (2010-07-28)

Unspeakable beauty and unimaginable bedlam can be found together in the Trifid Nebula. Also known as M20, this photogenic nebula is visible with good binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos. The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas. The dark dust filaments that lace M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. Which bright young stars light up the blue reflection nebula is still being investigated. The light from M20 we see today left perhaps 3,000 years ago, although the exact distance remains unknown. Light takes about 50 years to cross M20.

Image credit: Robert Gendler
Sunset, Shadowrise (2010-07-29)

From central Australia, this serene 360 degree panorama follows a clear horizon as twilight began on May 28. At left, a bright western sky is still illuminated by the setting Sun. But sweeping right, toward a view centered on the countryside's dominating sandstone formation called Uluru or Ayers Rock, the sky takes on progressively darker hues and subtle colors. Behind Uluru is the shadow of planet Earth itself, a dark blue arch rising in the east. Cast through the dense atmosphere and still close to the horizon, Earth's long shadow is bounded above by a pinkish glow or antitwilight arch. Known as the Belt of Venus, the lovely color of the antitwilight arch is due to backscattering of reddened light from the setting Sun. On that night, a nearly full Moon also rose above Earth's shadow in the eastern sky.

Image credit: Barden Ridge Observatory
Eclipse on the Beach (2010-07-30)

As the New Moon's shadow slid across the southern Pacific on July 11, people gathered along the white, sandy Anakena Beach on the north side of Easter Island to watch a total solar eclipse. The experience was captured in this tantalizing composite image, constructed from a sequence of 50 consecutive exposures. At their center is the totally eclipsed Sun surrounded by a shimmering solar corona. From the well chosen viewpoint, palm trees appear in silhouette against a darkened sky and the faint light reflected in the water. Of course, towering above the onlookers, at the boundaries of land, ocean, and sky are Moai, the island's mysterious monolithic statues.

Image credit: Guillaume Blanchard
Four Planet Sunset (2010-07-31)

This mesmerizing sunset photo was taken from the summit of volcanic Mount Lawu, 3,265 meters above sea level, on July 21. The view looks west, toward the city lights of Surakarta (aka Solo), Central Java, Indonesia. Two other volcanic peaks, sharp Merapi (left) and Merbabu lie along the colorful horizon. Four planets shine in the twilight sky above them. Spread out near the plane of the ecliptic are Mercury, Venus, Mars, and Saturn, along with bright Regulus, alpha star of the constellation Leo. For help finding them, just put your cursor over the picture. In fact, these four planets still shine in western skies at sunset, with Venus, Mars, and Saturn grouped much more tightly this weekend and in early August. By August 12, a young crescent Moon will join the four planet sunset.

Image credit: Jia Hao
Venus' Once Molten Surface (2010-08-01)

If you could look across Venus with radar eyes, what might you see? This computer reconstruction of the surface of Venus was created from data from the Magellan spacecraft.  Magellan orbited Venus and used radar to map our neighboring planet's surface between 1990 and 1994. Magellan found many interesting surface features, including the large circular domes, typically 25-kilometers across, that are depicted above.  Volcanism is thought to have created the domes, although the precise mechanism remains unknown. Venus' surface is so hot and hostile that no surface probe has lasted more than a few minutes.
Prometheus Creating Saturn Ring Streamers (2010-08-02)

What's causing those strange dark streaks in the rings of Saturn? Prometheus.  Specifically, an orbital dance involving Saturn's moon Prometheus keeps creating unusual light and dark streamers in the F-Ring of Saturn. Now Prometheus orbits Saturn just inside the thin F-ring, but ventures into its inner edge about every 15 hours. Prometheus' gravity then pulls the closest ring particles toward the 80-km moon.  The result is not only a stream of bright ring particles but also a dark ribbon where ring particles used to be.  Since Prometheus orbits faster than the ring particles, the icy moon pulls out a new streamer every pass.  Above, several streamers or kinks are visible at once. The above photograph was taken in June by the robotic Cassini Spacecraft orbiting Saturn. The oblong moon Prometheus is visible on the far left.
The Planet and the Radio Dish (2010-08-03)

What planet is this?  Although seemingly something out of The Little Prince, the planet is actually Earth. More specifically, it is a small part of the Earth incorporated into a four image stereographic "Little Planet " projection. The central fisheye image points down, while the surrounding wide-angle images were taken at a 30 degree tilt and added digitally later. Earth-anchored items surrounding the image center include green grass, dark shadows, and trees near and far.  At the image top ("noon" if the planet were a clock) is the well-lit Parkes Radio Telescope dish in New South Wales, Australia. The surrounding sky contains many jewels of the night including the Moon at 9 pm, the plane of our Milky Way Galaxy at 1:30 pm and 7 pm, and the Small Magellanic Cloud galaxy at 5 pm. A full field interactive version of this scene can be found here.

Image credit: Alex Cherney
(Terrastro)
Eclipse Shadow Cone Over Patagonia (2010-08-04)

Sometimes, during a total eclipse of the Sun, a strange shadow of darkness can be seen stretching off into the distance.  Called shadow cones, they are visible because the Earth's atmosphere is not completely transparent, scattering sunlight and hence appearing blue during the day.  Shadow cones are particularly dramatic for eclipses near the horizon, as geometry creates a long corridor of sun-blocked air.  Visible above is a shadow cone caught during a sunset total solar eclipse visible last month from Patagonia, Argentina. The eclipsed Sun itself still appears bright around the edges of the Moon because of light from the surrounding corona.  A few minutes later, the Moon began to move away from the Sun as both set behind distant Andes mountains.

Image credit: Daniel Fischer 
(Cosmic Mirror)
M8: The Lagoon Nebula (2010-08-05)

This beautiful cosmic cloud is a popular stop on telescopic tours of the constellation Sagittarius. Eighteenth century cosmic tourist Charles Messier cataloged the bright nebula as M8. Modern day astronomers recognize the Lagoon Nebula as an active stellar nursery about 5,000 light-years distant, in the direction of the center of our Milky Way Galaxy. Remarkable features can be traced through this sharp picture, showing off the Lagoon's filaments of glowing gas and dark dust clouds. Twisting near the center of the Lagoon, the bright hourglass shape is the turbulent result of extreme stellar winds and intense starlight. The alluring view is a color composite of both broad and narrow band images captured while M8 was high in dark, Chilean skies. It records the Lagoon with a bluer hue than typically represented in images dominated by the red light of the region's hydrogen emission. At the nebula's estimated distance, the picture spans about 30 light-years.

Image credit: Star Shadows Remote
Observatory
The Not So Quiet Sun (2010-08-06)

After a long solar minimum, the Sun is no longer so quiet. On August 1, this extreme ultraviolet snapshot of the Sun from the Solar Dynamics Observatory captured a complex burst of activity playing across the Sun's northern hemisphere. The false-color image shows the hot solar plasma at temperatures ranging from 1 to 2 million kelvins. Along with the erupting filaments and prominences, a small(!) solar flare spawned in the active region at the left was accompanied by a coronal mass ejection (CME), a billion-ton cloud of energetic particles headed for planet Earth. Making the 93 million mile trip in only two days, the CME impacted Earth's magnetosphere, triggering a geomagnetic storm and both northern and southern auroral displays.
Rainbow at Sunset (2010-08-07)

Where is the Sun when you see a rainbow? Behind you, of course. But you can see both a rainbow and the Sun (far right) side by side in this graceful panorama recorded on July 28. The cloudy sunset view covers a full 360 degrees around the horizon, composed using 20 individual images taken from an observatory on the outskirts of Potsdam, Germany. The rainbow itself is produced by sunlight internally reflected in rain drops from the direction opposite the Sun back toward the observer. As the sunlight passes through the drops, from air to water and back to air again, longer wavelengths (redder colors) are refracted or bent less than shorter wavelengths (bluer colors), separating the sunlight into the colors of the rainbow. This sharp picture captures the full, bright, primary rainbow arc as well as more subtle effects. You can see a partial, dimmer, secondary rainbow arc above and left of the primary, and faint arcs just inside the primary rainbow called supernumerary rainbows.

Image credit: Inastars Observatory Potsdam
Two Hours Before Neptune (2010-08-08)

Two hours before closest approach to Neptune in 1989, the Voyager 2 robot spacecraft snapped this picture. Clearly visible for the first time were long light-colored cirrus-type clouds floating high in Neptune's atmosphere. Shadows of these clouds can even be seen on lower cloud decks.  Most of Neptune's atmosphere is made of hydrogen and helium, which is invisible.  Neptune's blue color therefore comes from smaller amounts of atmospheric methane, which preferentially absorbs red light.  Neptune has the fastest winds in the Solar System, with gusts reaching 2000 kilometers per hour.  Speculation holds that diamonds may be created in the dense hot conditions that exist under the cloud tops of Uranus and Neptune.
IRAS 05437+2502: An Enigmatic Star Cloud from Hubble (2010-08-09)

What's lighting up nebula IRAS 05437+2502? No one is sure. Particularly enigmatic is the bright upside-down V that defines the upper edge of this floating mountain of interstellar dust, visible near the image center. In general, this ghost-like nebula involves a small star forming region filled with dark dust that was first noted in images taken by the IRAS satellite in infrared light in 1983. Shown above is a spectacular, recently released image from the Hubble Space Telescope that, although showing many new details, has not uncovered a clear cause of the bright sharp arc. One hypothesis holds that the glowing arc was created by a massive star that somehow attained a high velocity and has now left the nebula. Small, faint IRAS 05437+2502 spans only 1/18th of a full moon toward the constellation of the Bull (Taurus).
The Sand Dunes of Titan (2010-08-10)

Why do some sand dunes on Titan appear backwards? Central Titan, it turns out, is covered by sand, some of which appears strange. Images from the Cassini spacecraft currently orbiting Saturn have uncovered long rows of huge sand dunes near Titan's equator that rise as high as 300 meters. Shadows indicate that most dune shapes are created by wind blowing from the west. The problem is, the typical wind at Titan's equator blows from the east. One recent hypothesis that might solve this grainy conundrum posits that the only winds strong enough to move sand and create dunes occur during rare equinoxes and blow strongly from the west. The above images show a radar swath of Titan's equatorial sand dunes at the top, while similar sand dunes that formed in Namibia on Earth at the bottom. Why central Titan is even covered by so much sand is still being investigated.
Crepuscular Rays Over Lake Michigan (2010-08-11)

What could cause such rays of dark? Dark sky rays were caught in spectacular fashion earlier last month from Pentwater, Michigan, USA, looking west over Lake Michigan. The cause is something surprisingly familiar: shadows.  Clouds near the horizon can block sunlight from reflecting off air, making columns outward from the Sun appear unusually dark. Cloud shadows can be thought of as the complement of the more commonly highlighted crepuscular rays, also visible above, where sunlight pours though cloud holes. Sometimes, on the opposite side of the sky, anticrepuscular rays can also be seen.

Image credit: Kurt Voigts
Perseid Prelude (2010-08-12)

ch August, as planet Earth swings through dust trailing along the orbit of periodic comet Swift-Tuttle, skygazers can enjoy the Perseid Meteor Shower. The shower should build to its peak now, best seen from later tonight after moonset, until dawn tomorrow morning when Earth moves through the denser part of the wide dust trail. But shower meteors have been spotted for many days, like this bright Perseid streaking through skies near Lake Balaton, Hungary on August 8. In the foreground is the region's Church of St. Andrew ruin, with bright Jupiter dominating the sky to its right. Two galaxies lie in the background of the wide-angle, 3 frame panorama; our own Milky Way's luminous arc, and the faint smudge of the more distant Andromeda Galaxy just above the ruin's leftmost wall. If you watch for Perseid meteors tonight, be sure and check out the early evening sky show too, featuring bright planets and a young crescent Moon near the western horizon after sunset.

Image credit: Tamas Ladanyi
Arp 286: Trio in Virgo (2010-08-13)

A remarkable telescopic composition in yellow and blue, this scene features a trio of interacting galaxies almost 90 million light-years away, toward the constellation Virgo. On the left, two, spiky, foreground Milky Way stars echo the trio galaxy hues, a reminder that stars in our own galaxy are like those in the distant island universes. Predominately yellow, with sweeping spiral arms and dust lanes, NGC 5566 is enormous, about 150,000 light-years across. Just below it lies small, blue NGC 5569. Near center, the third galaxy, NGC 5560, is multicolored and apparently stretched and distorted by its interaction with NGC 5566. The galaxy trio is also included in Halton Arp's 1966 Atlas of Peculiar Galaxies as Arp 286. Of course, such cosmic interactions are now appreciated as a common part of the evolution of galaxies.

Image credit: Stephen Leshin
Night of the Perseids (2010-08-14)

On the night of August 12, from moonset until dawn was a good time to see meteors. Enthusiasts watched as comet dust rained on planet Earth, streaking through dark skies during the annual Perseid Meteor Shower. Anticipating the shower approaching its peak, astronomer Marco Verstraaten recorded a series of exposures capturing meteors over a period of 6 hours using a wide angle lens from a not-so-dark site in the Netherlands. Combining them still produced this dramatic night sky view with many colorful meteor streaks. The starry backdrop includes the Milky Way and even the faint Andromeda Galaxy, right of center. Although the comet dust particles are traveling parallel to each other, the shower meteors clearly seem to radiate from a spot on the sky in the eponymous constellation Perseus. The radiant effect is due to perspective, as the parallel tracks appear to converge at a distance. Bright stars in Perseus extend into the gap between the foreground trees.

Image credit: Marco Verstraaten
Layered Hills in Arabia Terra on Mars (2010-08-15)

Why are some hills on Mars so layered?  The answer is still under investigation.  Clearly, dark windblown sand surrounds outcropping of light sedimentary rock across the floor of crater Arabia Terra.  The light rock clearly appears structured into many layers, the lowest of which is likely very old.  Although the dark sand forms dunes, rippled dunes of lighter colored sand are easier to see surrounding the stepped mesas.  Blown sand possibly itself eroded once-larger mesas into the layered hills.  Most of the layered shelves are wide enough to drive a truck around.  The above image, showing an area about 3 kilometers across, was taken in 2003 October by the now defunct Mars Global Surveyor spacecraft orbiting Mars.