juliensimon/nasa-apod huggingface dataset:
Rainbow Airglow over the Azores (2016-03-22)

Why would the sky glow like a giant repeating rainbow?  Airglow.  Now air glows all of the time, but it is usually hard to see. A disturbance however -- like an approaching storm -- may cause noticeable rippling in the Earth's atmosphere. These gravity waves are oscillations in air analogous to those created when a rock is thrown in calm water.  The long-duration exposure nearly along the vertical walls of airglow likely made the undulating structure particularly visible.  OK, but where do the colors originate?  The deep red glow likely originates from OH molecules about 87-kilometers high, excited by ultraviolet light from the Sun. The orange and green airglow is likely caused by sodium and oxygen atoms slightly higher up.  The featured image was captured during a climb up Mount Pico in the Azores of Portugal.  Ground lights originate from the island of Faial in the Atlantic Ocean.  A spectacular sky is visible through this banded airglow, with the central band of our Milky Way Galaxy running up the image center, and M31, the Andromeda Galaxy, visible near the top left.   Explore Your Universe: Random APOD Generator

Image credit: Miguel Claro
(TWAN);
 Rollover Annotation:  Judy Schmidt
The Great Nebula in Carina (2016-03-23)

In one of the brightest parts of Milky Way lies a nebula where some of the oddest things occur. NGC 3372, known as the Great Nebula in Carina, is home to massive stars and changing nebulas. The Keyhole Nebula (NGC 3324), the bright structure just above the image center, houses several of these massive stars and has itself  changed its appearance. The entire Carina Nebula spans over 300 light years and lies about 7,500 light-years away in the constellation of Carina.   Eta Carinae, the most energetic star in the nebula, was one of the brightest stars in the sky in the 1830s, but then faded dramatically. Eta Carinae is the brightest star near the image center, just left of the Keyhole Nebula. While Eta Carinae itself maybe on the verge of a supernova explosion, X-ray images indicate that much of the Great Carina Nebula has been a veritable supernova factory.

Image credit: Damian Peach/SEN
Hickson 91 in Piscis Austrinus (2016-03-24)

Scanning the skies for galaxies, Canadian astronomer Paul Hickson and colleagues identified some 100 compact groups of galaxies, now appropriately called Hickson Compact Groups (HCGs). This sharp telescopic image captures one such galaxy group, HCG 91, in beautiful detail. The group's three colorful spiral galaxies at the center of the field of view are locked in a gravitational tug of war, their interactions producing faint but visible tidal tails over 100,000 light-years long. Their close encounters trigger furious star formation. On a cosmic timescale the result will be a merger into a large single galaxy, a process now understood to be a normal part of the evolution of galaxies, including our own Milky Way. HCG 91 lies about 320 million light-years away in the constellation Piscis Austrinus. But the impressively deep image also catches evidence of fainter tidal tails and galaxy interactions close to 2 billion light-years distant.

Image credit: CHART32 Team
Close Comet and the Milky Way (2016-03-25)

Comet 252P/Linear's lovely greenish coma is easy to spot in this expansive southern skyscape. Visible to the naked eye from the dark site near Flinders, Victoria, Australia, the comet appears tailless. Still, its surprisingly bright coma spans about 1 degree, posed here below the nebulae, stars, and dark rifts of the Milky Way. The five panels used in the wide-field mosaic were captured after moonset and before morning twilight on March 21. That was less than 24 hours from the comet's closest approach, a mere 5.3 million kilometers from our fair planet. Sweeping quickly across the sky because it is so close to Earth, the comet should be spotted in the coming days by northern hemisphere comet watchers. In predawn but moonlit skies it will move through Sagittarius and Scorpius seen toward the southern horizon. That's near the triangle formed by bright, yellowish, Mars, Saturn, and Antares at the upper left of this frame.

Image credit: Terrastro
Solstice to Equinox Cubed (2016-03-26)

This 3 month long exposure packed the days from December 22, 2015 through March 20 into a box. Dubbed a solargraph, the unconventional, unfolded picture was recorded with a pinhole camera made from a cube-shaped container, its sides lined with photographic paper. Fixed to a single spot for the entire exposure, the simple camera recorded the Sun's path through Hungarian skies. Each day a glowing trail was burned into the photosensitive paper. From short and low, to long and high, the trails follow the progression from winter solstice to spring equinox. Of course, dark gaps in the daily sun trails are caused by cloud cover. Sunny days produce the more continuous bright tracks.

Image credit: Olivér Nagy
NGC 6357: Cathedral to Massive Stars (2016-03-27)

How massive can a normal star be?  Estimates made from distance, brightness and standard solar models had given one star in the open cluster Pismis 24 over 200 times the mass of our Sun, making it one of the most massive stars known.  This star is the brightest object located just above the gas front in the featured image.  Close inspection of images taken with the Hubble Space Telescope, however, have shown that Pismis 24-1 derives its brilliant luminosity not from a single star but from three at least.  Component stars would still remain near 100 solar masses, making them among the more massive stars currently on record.  Toward the bottom of the image, stars are still forming in the associated emission nebula NGC 6357. Appearing perhaps like a Gothic cathedral, energetic stars near the center appear to be breaking out and illuminating a spectacular cocoon.
Orion's Belt and Sword over Teide's Peak (2016-03-28)

The southern part of Orion, the famous constellation and mythical hunter, appears quite picturesque posing here over a famous volcano. Located in the Canary Islands off the northwest coast of Africa, the snow-peaked Teide is one of the largest volcanoes on Earth. Lights from a group planning to summit Teide before dawn are visible below the volcano's peak.  In this composite of exposures taken from the same location one night last month, the three iconic belt stars of Orion are seen just above the peak, while the famous Orion Nebula and the rest of Orion's sword are visible beyond the volcano's left slope.  Also visible in the long duration sky image are the Horsehead Nebula, seen as a dark indentation on the red emission nebula to the belt's left, and the Flame Nebula, evident just above and to the right of the Horsehead.

Image credit: Cesar & Carlos Tejedor
NASA's Curiosity Rover at Namib Dune (360 View) (2016-03-29)

Point or tilt to see a spectacular view of Mars visible to the Curiosity rover last December.  In the foreground, part of Curiosity itself is visible, including its dusty sundial.  Starting about seven meters back, the robotic rover is seen posing in front of a 5-meter tall dark sand dune named Namib, one of many dunes that span Bagnold field. Further in the distance is the summit of Mt. Sharp, the 5.5-kilometer peak at the center of 150-km wide Gale crater, the crater where Curiosity landed a few years ago. The featured composite spans a full 360-degrees around by combining several images taken on the same day, while the result has been color adjusted to mimic Earth lighting.  Most recently, Curiosity is crossing the rocky and uneven Naukluft Plateau as it continues to make its way around and up Mt. Sharp.   Note: If your browser does not support YouTube 360 panoramas, see a cool static version of the image here.
NGC 6188 and NGC 6164 (2016-03-30)

Fantastic shapes lurk in clouds of glowing gas in the giant star forming region NGC 6188. The emission nebula is found about 4,000 light years away near the edge of a large molecular cloud unseen at visible wavelengths, in the southern constellation Ara. Massive, young stars of the embedded Ara OB1 association were formed in that region only a few million years ago, sculpting the dark shapes and powering 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. Joining NGC 6188 on this cosmic canvas, visible toward the lower right, is rare emission nebula NGC 6164, also created by one of the region's massive O-type stars. Similar in appearance to many planetary nebulae, NGC 6164's striking, symmetric gaseous shroud and faint halo surround its bright central star near the bottom edge. The impressively wide field of view spans over 3 degrees (six full Moons), corresponding to over 200 light years at the estimated distance of NGC 6188. Three image sets have been included in the featured composite.

Image credit: Martin Pugh
Big Dipper to Southern Cross (2016-03-31)

Welcome to an equatorial night. This remarkable 24 frame night skyscape was captured from Maba Beach on the Indonesian island of Halmahera during the evening of March 4. Seen from a mere 0.7 degrees northern latitude, both famous northern and southern asterisms and navigational aids lie within the panoramic view. The Big Dipper is on the far left and Southern Cross at the far right. Beyond the fading campfire on that night a yellow-orange celestial triangle is set by Mars, Antares, and Saturn. It stands above the rising central Milky Way, or "Miett" in the local Maba language. Of course, you can follow the pole pointing stars in the cup of the Big Dipper or body of the Southern Cross to the north and south celestial poles. Both lie just at the horizon in the view from the island's equatorial beach.

Image credit: Petr Horálek
Europa: Discover Life Under the Ice (2016-04-01)

Looking for an interplanetary vacation destination? Consider a visit to Europa, one of the Solar System's most tantalizing moons. Ice-covered Europa follows an elliptical path in its 85 hour orbit around our ruling gas giant Jupiter. Heat generated from strong tidal flexing by Jupiter's gravity keeps Europa's salty subsurface ocean liquid all year round. That also means even in the absence of sunlight Europa has energy that could support simple life forms. Unfortunately, it is currently not possible to make reservations at restaurants on Europa, where you might enjoy a dish of the local extreme shrimp. But you can always choose another destination from Visions of the Future.
Pluto's Bladed Terrain in 3D (2016-04-02)

Get out your red/blue glasses and gaze across a mountainous region informally known as Tartarus Dorsa. This scene sprawls some 300 kilometers (about 180 miles) across the Plutonian landscape. The color anaglyph creates a stereo view by combining parts of two images taken about 14 minutes apart during the New Horizons historic flyby of Pluto last July. Along with shadows near the terminator, or line between Pluto's dim day and night, the 3D perspective emphasizes the alignment of narrow, steep ridges. The region's remarkable bladed landforms typically extend 500 meters high and are 3 to 5 kilometers apart. Referring to a part of Hades in ancient Greek mythology, Tartarus Dorsa borders Tombaugh Regio to the east.
Close-up of the Bubble Nebula (2016-04-03)

It's the bubble versus the cloud. NGC 7635, the Bubble Nebula, is being pushed out by the stellar wind of massive central star BD+602522. Next door, though, lives a giant molecular cloud, visible to the right. At this place in space, an irresistible force meets an immovable object in an interesting way. The cloud is able to contain the expansion of the bubble gas, but gets blasted by the hot radiation from the bubble's central star. The radiation heats up dense regions of the molecular cloud causing it to glow. The Bubble Nebula, featured here in scientifically mapped colors to bring up contrast, is about 10 light-years across and part of a much larger complex of stars and shells. The Bubble Nebula can be seen with a small telescope towards the constellation of the Queen of Aethiopia (Cassiopeia).   Astrophysicists: Browse 1,200+ codes in the Astrophysics Source Code Library
Lucid Dreaming (2016-04-04)

Is this the real world?  Or is it just fantasy?  The truth started with a dream -- a dream that the spectacular Seljarlandsfoss waterfall in southern Iceland could be photographed with a backdrop of an aurora-filled sky.  Soon after a promising space weather report, the visionary astrophotographer and his partner sprang into action.  After arriving, capturing an image of the background sky, complete with a cool green aurora, turned out to be the easy part.  The hard part was capturing the waterfall itself, for one reason because mist kept fogging the lens!  Easy come, easy go -- it took about 100 times where someone had to go back to the camera -- on a cold night and over slippery rocks -- to see how the last exposure turned out, wipe the lens, and reset the camera for the next try. Later, the best images of land and sky were digitally combined.  Visible in the sky, even well behind the aurora, are numerous stars of the northern sky. The resulting title -- given by the astrophotographer -- was influenced by a dream-like quality of the resulting image, possibly combined with the knowledge that some things really mattered in this effort to make a dream come true.

Image credit: Arnar Kristjansson; 
 Rollover Annotation:  Judy Schmidt
Cancri 55 e: Climate Patterns on a Lava World (2016-04-05)

Why might you want to visit super-earth Cancri 55 e? Its extremely hot climate would be a deterrent, and fresh lava flows might be common.  Discovered in 2004, the planet Cancri 55 e has twice the diameter of our Earth and about 10 times Earth's mass. The planet orbits its 40 light-year distant Sun-like star well inside the orbit of Mercury, so close that it is tidally locked, meaning that it always keeps the same face toward the object it orbits -- like our Moon does as it orbits the Earth. Astronomers have recently measured temperature changes on this exoplanet using infrared observations with the Spitzer Space Telescope. Given these observations, an artist created the featured video with educated guesses about what one revolution of Cancri 55 e might look like. Depicted are full phase, when the planet is fully illuminated, and new (dark) phase when it passes near the line of sight to Earth.  The illustrated red bands on the Cancri 55 e indicate bands of lava that might flow on the planet.  A recent density determination for 55 Cancri e show that this exoplanet is not made primarily of oxygen, as are the inner planets in our Solar System, but rather of carbon.  Therefore, one reason to visit Cancri 55 e might be to study its core, because this planet's great internal pressure might be sufficient to make the carbon found there into one huge diamond.   New for Programmers: NASA Open API for APOD
Auroras and the Magnetosphere of Jupiter (2016-04-06)

Jupiter has auroras.  Like near the Earth, the magnetic field of our Solar System's largest planet compresses when impacted by a gust of charged particles from the Sun. This magnetic compression funnels charged particles towards Jupiter's poles and down into the atmosphere. There, electrons are temporarily excited or knocked away from atmospheric gases, after which, when de-exciting or recombining with atmospheric ions, auroral light is emitted. The featured illustration portrays the magnificent magnetosphere around Jupiter in action. In the inset image released last month, the Earth-orbiting Chandra X-ray Observatory shows unexpectedly powerful X-ray light emitted by Jovian auroras, depicted in false-colored purple.  That Chandra inset is superposed over an optical image taken at a different time by the Hubble Space Telescope.  This aurora on Jupiter was seen in October 2011, several days after the Sun emitted a powerful Coronal Mass Ejection (CME).
Wolf-Lundmark-Melotte (2016-04-07)

Named for the three astronomers instrumental in its discovery and identification, Wolf - Lundmark - Melotte (WLM) is a lonely dwarf galaxy. Seen toward the mostly southern constellation Cetus, about 3 million light-years from the Milky Way, it is one of the most remote members of our local galaxy group. In fact, it may never have interacted with any other local group galaxy. Still, telltale pinkish star forming regions and hot, young, bluish stars speckle the isolated island universe. Older, cool yellowish stars fade into the small galaxy's halo, extending about 8,000 light-years across. This sharp portrait of WLM was captured by the 268-megapixel OmegaCAM widefield imager and survey telescope at ESO's Paranal Observatory.
Lapland Northern Lights (2016-04-08)

rly spring in the northern hemisphere is good season for aurora hunters. Near an equinox Earth's magnetic field is oriented to favor interactions with the solar wind that trigger the alluring glow of the northern lights. On March 28/29 the skies over Kaunispää Hill, Lapland, Finland did not disappoint. That night's expansive auroral curtains are captured in this striking panoramic view that covers a full 360 degrees. Local skywatchers were mesmerized by bright displays lasted throughout the dark hours, shimmering with colors easily visible to the naked eye.

Image credit: Juan Carlos Casado
A Green Flash of Spring (2016-04-09)

Taken on March 20 from the top of Haleakala on the isle of Maui, planet Earth, the first sunrise of northern spring is pictured in this vacation snapshot. The telephoto view from the volcanic caldera above a sea of clouds also captures an elusive green flash near the Sun's upper limb. Atmospheric layers with sharp temperature changes cause the colorful flash as the Sun rises behind a distant cloud bank. Refraction along sight lines through the layers creates multiple distorted images of the Sun, and for a moment, can visibly deflect shorter wavelength green light.

Image credit: Murray Schukar
Cassini Approaches Saturn (2016-04-10)

Cassini, a robot spacecraft launched in 1997 by NASA, became close enough in 2002 to resolve many rings and moons of its destination planet: Saturn.  At that time, Cassini snapped several images during an engineering test.  Several of those images were combined into the contrast-enhanced color composite featured here.  Saturn's rings and cloud-tops are visible toward the image bottom, while Titan, its largest moon, is visible as the speck toward the top.  When arriving at Saturn in July 2004, the Cassini orbiter began to circle and study the Saturnian system.  A highlight was when Cassini launched the Huygens probe that made an unprecedented landing on Titan in 2005, sending back detailed pictures. Now nearing the end of its mission, Cassini is scheduled to embark on a Grand Finale phase in late 2016 where it will repeatedly dive between the giant planet and its innermost rings.
The Comet and the Star Cluster (2016-04-11)

Comet Linear has become unexpectedly bright. The comet, discovered in 2000, underwent a 100-fold outburst just a week before it passed a mere 14 lunar distances from Earth late last month. The comet was captured here last week at about magnitude 6 -- just bright enough to be seen by the unaided eye -- passing in front of the distant globular star cluster M14. Comet 252/P LINEAR is one of a rare group of comets that vacillate between the Earth and Jupiter every 5 years.  How the comet will evolve from here is unknown, but hopes run high that it will remain a good object for binoculars in northern skies for the next week or two.

Image credit: Jos� J. Chamb� 
(Cometografia)
Combined Solar Eclipse Corona from Earth and Space (2016-04-12)

Sometimes, a total eclipse is a good time to eye the Sun. Taking advantage of an unusual juxtaposition of Earth, Moon and Sun, the featured image depicts the total solar eclipse that occurred last month as it appeared -- nearly simultaneously -- from both Earth and space.  The innermost image shows the total eclipse from the ground, with the central pupil created by the bright Sun covered by a comparatively dark Moon.  Surrounding the blocked solar disk is the tenuous corona of Sun imaged in white light, easily visible from the ground only during an eclipse.  Normally, this corona is hard to track far from the Sun, but the featured montage matches it to false-colored observations of the Sun from NASA and ESA's space-based, Sun-orbiting, Solar and Heliospheric Observatory (SOHO). Observations like this allow the study of the constantly changing magnetic activity both near and far from the Sun, the same activity that ultimately drives Earth's auroras.   APOD is also available in: Arabic, Bahasa Indonesian, Catalan, Chinese, Chinese, Croatian, Czech, Dutch, Farsi, Farsi, Galego, German, French, Hebrew, Japanese, Korean, Montenegrin, Polish, Romanian, Russian, Serbian, Slovenian, Spanish, and Turkish
Orion in Red and Blue (2016-04-13)

When did Orion become so flashy? This colorful rendition of part of the constellation of Orion comes from red light emitted by hydrogen and sulfur (SII), and blue-green light emitted by oxygen (OIII).  Hues on the featured image were then digitally reassigned to be indicative of their elemental origins -- but also striking to the human eye.  The breathtaking composite was painstakingly composed from hundreds of images which took nearly 200 hours to collect.  Pictured, Barnard's Loop, across the image bottom, appears to cradle interstellar constructs including the intricate Orion Nebula seen just right of center.  The Flame Nebula can also be quickly located, but it takes a careful eye to identify the slight indentation of the dark Horsehead Nebula. As to Orion's flashiness -- a leading explanation for the origin of Barnard's Loop is a supernova blast that occurred about two million years ago.   Share the Sky: NASA Open API for APOD

Image credit: David Lindemann
Full Venus and Crescent Moon Rise (2016-04-14)

Inner planet Venus and a thin crescent Moon are never found far from the Sun in planet Earth's skies. Taken near dawn on April 6, this timelapse composite shows them both rising just before the Sun. The mountaintop Teide Observatory domes on the fortunate island of Tenerife appear in silhouette against the twilight. In fact, the series of telephoto exposures follows the occultation of Venus by the Moon in three frames. Far from Earth in its orbit and in a nearly full phase, Venus was 96 percent illuminated. Near perigee or closest approach to Earth, the Moon's slender crescent represents about 2 percent of the lunar disk in sunlight. Seen in the first two exposures, the brilliant morning star only vanishes in the third as it winks out behind the bright lunar limb. Five minutes of the dramatic occultation at dawn is compressed into 15 seconds in this timelapse video (vimeo).

Image credit: El Cielo de Canarias
Mercury and Crescent Moon Set (2016-04-15)

Innermost planet Mercury and a thin crescent Moon are never found far from the Sun in planet Earth's skies. Taken near dusk on April 8, this colorful evening skyscape shows them both setting toward the western horizon just after the Sun. The broad Tagus River and city lights of Lisbon, Portugal run through the foreground under the serene twilight sky. Near perigee or closest approach to Earth, the Moon's bright, slender crescent represents about 3 percent of the lunar disk in sunlight. Of course as seen from the Moon, a nearly full Earth would light up the lunar night, and that strong perigee earthshine makes the rest of the lunar disk visible in this scene. Bright Mercury stays well above the western horizon at sunset for northern skywatchers in the coming days. The fleeting planet reaches maximum elongation, or angular distance from the Sun, on April 18. But Mercury will swing back toward the Sun and actually cross the solar disk on May 9, the first transit of Mercury since November 8, 2006.

Image credit: Miguel Claro