juliensimon/nasa-apod huggingface dataset:
A Mercury Transit Music Video from SDO (2016-05-11)

What's that small black dot moving across the Sun? Mercury. Possibly the clearest view of Mercury crossing in front of the Sun earlier this week was from Earth orbit. The Solar Dynamics Observatory obtained an uninterrupted vista recording it not only in optical light but also in bands of ultraviolet light. Featured here is a composite movie of the crossing set to music. Although the event might prove successful scientifically for better determining components of Mercury' ultra-thin atmosphere, the event surely proved successful culturally by involving people throughout the world in observing a rare astronomical phenomenon. Many spectacular images of this Mercury transit from around (and above) the globe are being  proudly displayed.   Astrophysicists: Browse 1,250+ codes in the Astrophysics Source Code Library
A Transit of Mercury (2016-05-12)

On May 9, the diminutive disk of Mercury spent about seven and a half hours crossing in front of the Sun as viewed from the general vicinity of Earth. It was the third of 14 transits of the Solar System's innermost planet in the 21st century. Captured from Fulham, London, England, planet Earth the tiny silhouette shares the enormous solar disk with prominences, filaments, and active regions in this sharp image. But Mercury's round disk (left of center) appears to be the only dark spot, despite the planet-sized sunspots scattered across the Sun. Made with an H-alpha filter that narrowly transmits the red light from hydrogen atoms, the image emphasizes the chromosphere, stretching above the photosphere or normally visible solar surface. In H-alpha pictures of the chromosphere, normally dark sunspot regions are dominated by bright splotches called plages.

Image credit: Howard
Brown-Greaves
ISS and Mercury Too (2016-05-13)

Transits of Mercury are relatively rare. Monday's leisurely 7.5 hour long event was only the 3rd of 14 Mercury transits in the 21st century. If you're willing to travel, transits of the International Space Station can be more frequent though, and much quicker. This sharp video frame composite was taken from a well-chosen location in Philadelphia, USA. It follows the space station, moving from upper right to lower left, as it crossed the Sun's disk in 0.6 seconds. Mercury too is included as the small, round, almost stationary silhouette just below center. In apparent size, the International Space Station looms larger from low Earth orbit, about 450 kilometers from Philadelphia. Mercury was about 84 million kilometers away. (Editor's note: The stunning video includes another double transit, Mercury and a Pilatus PC12 aircraft. Even quicker than the ISS to cross the Sun, the aircraft was about 1 kilometer away.)

Image credit: Thierry Legault
Falcon 9 and Milky Way (2016-05-14)

On May 6, the after midnight launch of a SpaceX Falcon 9 rocket lit up dark skies over Merritt Island, planet Earth. Its second stage bound for Earth orbit, the rocket's arc seems to be on course for the center of the Milky Way in this pleasing composite image looking toward the southeast. Two consecutive exposures made with camera fixed to a tripod were combined to follow rocket and home galaxy. A 3 minute long exposure at low sensitivity allowed the rocket's first stage burn to trace the bright orange arc and a 30 second exposure at high sensitivity captured the stars and the faint Milky Way. Bright orange Mars dominates the starry sky at the upper right. A few minutes later, booster engines were restarted and the Falcon 9's first stage headed for a landing on the autonomous spaceport drone ship Of Course I Still Love You, patiently waiting in the Atlantic 400 miles east of the Cape Canaveral launch site.

Image credit: Derek Demeter
Milky Way Over Quiver Tree Forest (2016-05-15)

In front of a famous background of stars and galaxies lies some of Earth's more unusual trees. Known as quiver trees, they are actually succulent aloe plants that can grow to tree-like proportions. The quiver tree name is derived from the historical usefulness of their hollowed branches as dart holders. Occurring primarily in southern Africa, the trees pictured in the above 16-exposure composite are in Quiver Tree Forest located in southern Namibia. Some of the tallest quiver trees in the park are estimated to be about 300 years old. Behind the trees is light from the small town of Keetmanshoop, Namibia. Far in the distance, arching across the background, is the majestic central band of our Milky Way Galaxy. Even further in the distance, visible on the image left, are the Large and Small Magellanic Clouds, smaller satellite galaxies of the Milky Way that are prominent in the skies of Earth's southern hemisphere.

Image credit: Florian Breuer
Clouds of the Carina Nebula (2016-05-16)

What forms lurk in the mists of the Carina Nebula? The dark ominous figures are actually molecular clouds, knots of molecular gas and dust so thick they have become opaque.  In comparison, however,  these clouds are typically much less dense than Earth's atmosphere.  Featured here is a detailed image of the core of the Carina Nebula, a part where both dark and colorful clouds of gas and dust are particularly prominent.  The image was captured last month from Siding Spring Observatory in Australia.  Although the nebula is predominantly composed of hydrogen gas -- here colored green, the image was assigned colors so that light emitted by trace amounts of sulfur and oxygen appear red and blue, respectively.  The entire Carina Nebula, cataloged as NGC 3372, 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.

Image credit: John Ebersole
The Orion Nebula in Visible and Infrared (2016-05-17)

The Great Nebula in Orion is a colorful place.  Visible to the unaided eye, it appears as a small fuzzy patch in the constellation of Orion.  Long exposure, multi-wavelength images like this, however, show the Orion Nebula to be a busy neighborhood of young stars, hot gas, and dark dust.  This digital composite features not only three colors of visible light but four colors of infrared light taken by NASA's orbiting Spitzer Space Telescope as well.  The power behind much of the Orion Nebula (M42) is the Trapezium - four of the brightest stars in the nebula.  Many of the filamentary structures visible are actually shock waves - fronts where fast moving material encounters slow moving gas.  The Orion Nebula spans about 40 light years and is located about 1500 light years away in the same spiral arm of our Galaxy as the Sun.   Follow APOD on: Facebook,  Google Plus,  Instagram, or Twitter

Image credit: Infrared: NASA, 
Spitzer Space Telescope;
Visible: 
Oliver Czernetz, 
Siding Spring Obs.
Halo from Atacama (2016-05-18)

Influenced by the strong Pacific El Nino, cloudy skies have more often come to Chile's high Atacama Desert this season, despite its reputation as an astronomer's paradise. Located in one of the driest, darkest places on planet Earth, domes of the region's twin 6.5 meter Magellan telescopes of Carnegie Las Campanas Observatory were closed on May 13. Still, a first quarter Moon and bright stars shine through in this panoramic night skyscape, the lunar disk surrounded by a beautiful, bright halo. The angular radius of the halo is 22 degrees. Not determined by the brightness or phase of the Moon itself, the angle is set by the hexagonal geometry of atmospheric ice crystals that reflect and refract the moonlight. On that night, the brilliant star just inside the halo's radius was really planet Jupiter. The brightest star flanking the halo to the far left is Canopus, with Arcturus on the halo's right.  Participate: Take an Aesthetics & Astronomy Survey

Image credit: Yuri Beletsky
The Surface of Europa (2016-05-19)

An enhanced-color view, this image covers a 350 by 750 kilometer swath across the surface of Jupiter's tantalizing moon Europa. The close-up combines high-resolution image data with lower resolution color data from observations made in 1998 by the Galileo spacecraft. Smooth ice plains, long fractures, and jumbled blocks of chaos terrain are thought to hide a deep ocean of salty liquid water beneath. Though the ice-covered alien ocean world is outside the Solar System's habitable zone, new studies show the potential chemistry driving its oxygen and hydrogen production, a key indicator of the energy available for life, could produce amounts comparable in scale to planet Earth. Hydrogen would be generated by chemical reactions of the salty water in contact with the rocky ocean floor. Oxygen and other compounds that react with hydrogen would come from Europa's surface. There water ice molecules would be split apart by the intense flux of high-energy radiation from Jupiter and cycled into the Europan ocean from above.  Participate: Take an Aesthetics & Astronomy Survey
3D Mercury Transit (2016-05-20)

On May 9, innermost planet Mercury crossed IN FRONT of the Sun. Though pictures project the event in only two dimensions, a remarkable three dimensional perspective on the transit is possible by free viewing this stereo pair. The images were made 23 minutes apart and rotated so that Mercury's position shifts horizontally between the two. As a result, Mercury's orbital motion produced an exaggerated parallax simulating binocular vision. Between the two exposures, the appropriately named planet's speedy 47.4 kilometer per second orbital velocity actually carried it over 65,000 kilometers. Taken first, the left image is intended for the right eye, so a cross-eyed view is needed to see Mercury's tiny silhouette suspended in the foreground. Try it. Merging the text below the images helps.  Participate: Take an Aesthetics & Astronomy Survey

Image credit: Stefan Seip
Milky Way and Planets Near Opposition (2016-05-21)

In this early May night skyscape, a mountain road near Bursa, Turkey seems to lead toward bright planets Mars and Saturn and the center of our Milky Way Galaxy, a direction nearly opposite the Sun in planet Earth's sky. The brightest celestial beacon on the scene, Mars, reaches its opposition tonight and Saturn in early June. Both will remain nearly opposite the Sun, up all night and close to Earth for the coming weeks, so the time is right for good telescopic viewing. Mars and Saturn form the tight celestial triangle with red giant star Antares just right of the Milky Way's central bulge. But tonight the Moon is also at opposition. Easy to see near bright Mars and Saturn, the Full Moon's light will wash out the central Milky Way's fainter starlight though, even in dark mountain skies.  Participate: Take an Aesthetics & Astronomy Survey

Image credit: Tunç Tezel
LL Orionis: When Cosmic Winds Collide (2016-05-22)

What created this great arc in space?  This arcing, graceful structure is actually a bow shock about half a light-year across, created as the wind from young star LL Orionis collides with the Orion Nebula flow. Adrift in Orion's stellar nursery and still in its formative years, variable star LL Orionis produces a wind more energetic than the wind from our own middle-aged sun. As the fast stellar wind runs into slow moving gas a shock front is formed, analogous to the bow wave of a boat moving through water or a plane traveling at supersonic speed. The slower gas is flowing away from the Orion Nebula's hot central star cluster, the Trapezium, located off the lower right hand edge of the picture. In three dimensions, LL Ori's wrap-around shock front is shaped like a bowl that appears brightest when viewed along the "bottom" edge. The complex stellar nursery in Orion shows a myriad of similar fluid shapes associated with star formation, including the bow shock surrounding a faint star at the upper right. Part of a mosaic covering the Great Nebula in Orion, this composite color image was recorded in 1995 by the Hubble Space Telescope.   Follow APOD on: Facebook,  Google Plus,  Instagram, or Twitter
Inside a Daya Bay Antineutrino Detector (2016-05-23)

Why is there more matter than antimatter in the Universe?  To better understand this facet of basic physics, energy departments in China and the USA led in the creation of the Daya Bay Reactor Neutrino Experiment. Located under thick rock about 50 kilometers northeast of Hong Kong, China, eight Daya Bay detectors monitor antineutrinos emitted by six nearby nuclear reactors. Featured here, a camera looks along one of the Daya Bay detectors, imaging photon sensors that pick up faint light emitted by antineutrinos interacting with fluids in the detector.  Early results indicate an unexpectedly high rate of one type of antineutrino changing into another, a rate which, if confirmed, could imply the existence of a previously undetected type of neutrino as well as impact humanity's comprehension of fundamental particle reactions that occurred within the first few seconds of the Big Bang.   Astrophysicists: Browse 1,250+ codes in the Astrophysics Source Code Library

Image credit: DOE, 
Berkeley Lab - 
Roy Kaltschmidt, photographer
Milky Way Over the Spanish Peaks (2016-05-24)

That's not lightning, and it did not strike between those mountains. The diagonal band is actually the central band of our Milky Way Galaxy, while the twin peaks are actually called the Spanish Peaks -- but located in Colorado, USA. Although each Spanish peak is composed of a slightly different type of rock, both are approximately 25 million years old.  This serene yet spirited image composite was meticulously created by merging a series of images all taken from the same location on one night and early last month. In the first series of exposures, the background sky was built up, with great detail being revealed in the Milky Way dust lanes as well as the large colorful region surrounding the star Rho Ophiuchus just right of center.  One sky image, though, was taken using a fogging filter so that brighter stars would appear more spread out and so more prominent. As a bonus, the planets Mars and Saturn are placed right above peaks and make an orange triangle with the bright star Antares. Later that night, after the moonrise, the Moon itself naturally illuminated the snow covered mountain tops.

Image credit: Martin Pugh;
 Rollover Annotation:  Judy Schmidt
NGC 5078 and Friends (2016-05-25)

This sharp telescopic field of view holds two bright galaxies.  Barred spiral NGC 5101 (top right) and nearly edge-on system NGC 5078 are separated on the sky by about 0.5 degrees or about the apparent width of a full moon. Found within the boundaries of the serpentine constellation Hydra, both are estimated to be around 90 million light-years away and similar in size to our own large Milky Way galaxy. In fact, if they both lie at the same distance their projected separation would be only 800,000 light-years or so. That's easily less than half the distance between the Milky Way and the Andromeda Galaxy. NGC 5078 is interacting with a smaller companion galaxy, cataloged as IC 879, seen just left of the larger galaxy's bright core. Even more distant background galaxies are scattered around the colorful field. Some are even visible right through the face-on disk of NGC 5101. But the prominent spiky stars are in the foreground, well within our own Milky Way.

Image credit: Dietmar Hager
IC 5067 in the Pelican Nebula (2016-05-26)

The prominent ridge of emission featured in this sharp, colorful skyscape is cataloged as IC 5067. Part of a larger emission nebula with a distinctive shape, popularly called The Pelican Nebula, the ridge spans about 10 light-years following the curve of the cosmic pelican's head and neck. This false-color view also translates the pervasive glow of narrow emission lines from atoms in the nebula to a color palette made popular in Hubble Space Telescope images of star forming regions. Fantastic, dark shapes inhabiting the 1/2 degree wide field are clouds of cool gas and dust sculpted by the winds and radiation from hot, massive stars. Close-ups of some of the sculpted clouds show clear signs of newly forming stars. The Pelican Nebula, itself cataloged as IC 5070, is about 2,000 light-years away. To find it, look northeast of bright star Deneb in the high flying constellation Cygnus.

Image credit: Subaru
Telescope (NAOJ)
The Great Carina Nebula (2016-05-27)

A jewel of the southern sky, the Great Carina Nebula, also known as NGC 3372, spans over 300 light-years, one of our galaxy's largest star forming regions. Like the smaller, more northerly Great Orion Nebula, the Carina Nebula is easily visible to the unaided eye, though at a distance of 7,500 light-years it is some 5 times farther away. This gorgeous telescopic close-up reveals remarkable details of the region's central glowing filaments of interstellar gas and obscuring cosmic dust clouds. The field of view is over 50 light-years across. The Carina Nebula is home to young, extremely massive stars, including the stars of open cluster Trumpler 14 (below and right of center) and the still enigmatic variable Eta Carinae, a star with well over 100 times the mass of the Sun.  Eta Carinae is the brightest star, seen here just above the dusty Keyhole Nebula (NGC 3324). While Eta Carinae itself maybe on the verge of a supernova explosion, X-ray images indicate that the Great Carina Nebula has been a veritable supernova factory.

Image credit: Barden Ridge Observatory
Cat's Eye Wide and Deep (2016-05-28)

The Cat's Eye Nebula (NGC 6543) is one of the best known planetary nebulae in the sky. Its more familiar outlines are seen in the brighter central region of the nebula in this impressive wide-angle view. But the composite image combines many short and long exposures to also reveal an extremely faint outer halo. At an estimated distance of 3,000 light-years, the faint outer halo is over 5 light-years across. Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star. More recently, some planetary nebulae are found to have halos like this one, likely formed of material shrugged off during earlier episodes in the star's evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years. Visible on the left, some 50 million light-years beyond the watchful planetary nebula, lies spiral galaxy NGC 6552.

Image credit: Josh Smith
Valles Marineris: The Grand Canyon of Mars (2016-05-29)

Mars will look good in Earth's skies over the next few days -- but not this good. To get a view this amazing, a spacecraft had to actually visit the red planet. Running across the image center, though, is one the largest canyons in the Solar System. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep.  By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep.  The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled.  Several geologic processes have been identified in the canyon.  The featured mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.  Tomorrow, Mars and Earth will pass the closest in 11 years, resulting in the red planet being quite noticeable toward the southeast after sunset.
Galaxy Evolution Tracking Animation (2016-05-30)

How did the universe evolve from such a smooth beginning? To help understand, computational cosmologists and NASA produced the featured time-lapse animated video depicting a computer simulation of part of the universe. The 100-million light-year simulation starts about 20 million years after the Big Bang and runs until the present.  After a smooth beginning, gravity causes clumps of matter to form into galaxies which immediately begin falling toward each other. Soon, many of them condense into long filaments while others violently merge into a huge and hot cluster of galaxies.  Investigating of potential universe attributes in simulations like this have helped shape the engineering design the James Webb Space Telescope, currently scheduled for launch in late 2018.
Stars and Gas of the Running Chicken Nebula (2016-05-31)

To some, it looks like a giant chicken running across the sky. To others, it looks like a gaseous nebula where star formation takes place. Cataloged as IC 2944, the Running Chicken Nebula spans about 100 light years and lies about 6,000 light years away toward the constellation of the Centaur (Centaurus).  The featured image, shown in scientifically assigned colors, was captured recently in an 11-hour exposure from a backyard near Melbourne, Australia.  Two star clusters are visible: the Pearl Cluster seen on the far left, and Collinder 249 embedded in the nebula's glowing gas.  Although difficult to discern here, several dark molecular clouds with distinct shapes can be found inside the nebula.   Follow APOD on: Facebook,  Google Plus,  Instagram, or Twitter

Image credit: Andrew Campbell
Tycho's Supernova Remnant Expands (2016-06-01)

What star created this huge expanding puffball?  Featured here is the first expansion movie ever created for Tycho's supernova remnant, the result of a stellar explosion first recorded over 400 years ago by the famous astronomer Tycho Brahe.  The 2-second video is a time-lapse composite of  X-ray images taken by the orbiting Chandra X-ray Observatory between the years 2000 and 2015, added to a stock optical frame. The expanding gas cloud is extremely hot, while slightly different expansion speeds have given the cloud a puffy appearance.  Although the star that created SN 1572, is likely completely gone, a star dubbed Tycho G, too dim to be discerned here, is thought to be a companion. Finding progenitor remnants of Tycho's supernova is particularly important because the supernova is of Type Ia, an important rung in the distance ladder that calibrates the scale of the visible universe.   The peak brightness of Type Ia supernovas is thought to be well understood, making them quite valuable in exploring the relationship between faintness and farness in the distant universe.
Three Planets from Pic du Midi (2016-06-02)

Seen any planets lately? All three planets now shining brightly in the night sky are imaged in these panels, captured last week with the 1 meter telescope at Pic du Midi Observatory in the French Pyrenees. Near opposition and closest to Earth on May 30, Mars is presently offering the best ground-based photo-ops in the last decade. The sharp image finds clouds above the Red Planet's north pole (top) and towering volcanos near its right limb. Saturn reaches its own opposition tonight, its bright rings and gaps clearly revealed in the telescopic portrait. Jupiter is currently highest during the evening twilight and shows off its planet-girdling cloud bands and Great Red Spot in this scene. Of course close-up images of the ruling gas giant will follow the July arrival of the solar-powered Juno spacecraft and JunoCam.

Image credit: JL. Dauvergne
NGC 4631: The Whale Galaxy (2016-06-03)

NGC 4631 is a big beautiful spiral galaxy. Seen edge-on, it lies only 25 million light-years away in the well-trained northern constellation Canes Venatici. The galaxy's slightly distorted wedge shape suggests to some a cosmic herring and to others its popular moniker, The Whale Galaxy. Either way, it is similar in size to our own Milky Way. In this sharp color image, the galaxy's yellowish core, dark dust clouds, bright blue star clusters, and red star forming regions are easy to spot. A companion galaxy, the small elliptical NGC 4627 is just above the Whale Galaxy. Faint star streams seen in deep images are the remnants of small companion galaxies disrupted by repeated encounters with the Whale in the distant past. The Whale Galaxy is also known to have spouted a halo of hot gas glowing in X-rays.

Image credit: Martin Pugh