juliensimon/nasa-apod huggingface dataset:
Pluto: From Mountains to Plains (2015-12-14)

What do the sharpest views ever of Pluto show? As the robotic New Horizons spacecraft moves into the outer Solar System, it is now sending back some of the highest resolution images from its historic encounter with Pluto in July. Featured here is one recently-received, high-resolution image. On the left is al-Idrisi Montes, mountainous highlands thought composed primarily of blocks of water ice.  A sharp transitional shoreline leads to the ice plains, on the right, that compose part of the heart-shaped feature known as Sputnik Planum, which contains ices including solid nitrogen. Why the plains are textured with ice pits and segmented is currently unknown. The image was taken about 15 minutes before closest approach and shows an area about 30 kilometers across. The New Horizons spacecraft is next scheduled to fly past Kuiper Belt object 2014 MU 69 on New Year's Day 2019.   AAS Members: How does APOD help you?
Colorful Arcs over Buenos Aires (2015-12-15)

What are those colorful arcs in the sky? Like rainbows that are caused by rain, arcs of sunlight broken up into component colors can also result when ice crystals floating in Earth's atmosphere act together as a gigantic prism. The top color arc is more typical as it is part of the 22 degree halo surrounding the Sun when hexagonal ice crystals refract sunlight between two of the six sides.  More unusual, though, is the bottom color arc. Sometimes called a fire rainbow, this  circumhorizon arc is also created by ice, not fire nor even rain.   Here, a series of horizontal, thin, flat ice crystals in high cirrus clouds refract sunlight between the side and bottom faces toward the observer.  These arcs only occur when the Sun is higher than 58 degrees above the horizon. The featured sky occurred to the northwest in the early afternoon last month over a street Diagonal of La Plata City, Buenos Aires, Argentina.   Follow APOD on: Facebook,  Google Plus, or Twitter

Image credit: Sergio Mont�far  
(Planetario Ciudad de La Plata,
pna)
The Horsehead Nebula (2015-12-16)

The Horsehead Nebula is one of the most famous nebulae on the sky.  It is visible as the dark indentation to the red emission nebula in the center of the above photograph.  The horse-head feature is dark because it is really an opaque dust cloud that lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance.  After many thousands of years, the internal motions of the cloud will surely alter its appearance.  The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms.  On the image left is the Flame Nebula, an orange-tinged nebula that also contains filaments of dark dust. Just to the lower left of the Horsehead nebula featured picture is a blueish reflection nebulae that preferentially reflects the blue light from nearby stars.   Free APOD Lectures: Editor to Speak in January in Philadelphia and New York City

Image credit: Jos� Jim�nez Priego
Geminids of the South (2015-12-17)

rth's annual Geminid meteor shower did not disappoint, peaking before dawn on December 14 as our fair planet plowed through dust from active asteroid 3200 Phaethon. Captured in this southern hemisphere nightscape the meteors stream away from the shower's radiant in Gemini. To create the image, many individual frames recording meteor streaks were taken over period of 5 hours. In the final composite they were selected and registered against the starry sky above the twin 6.5 meter Magellan telescopes of Carnegie Las Campanas Observatory in Chile. Rigel in Orion, and Sirius shine brightly as the Milky Way stretches toward the zenith. Near Castor and Pollux the twin stars of Gemini, the meteor shower's radiant is low, close to the horizon. The radiant effect is due to perspective as the parallel meteor tracks appear to converge in the distance.  Gemini's meteors enter Earth's atmosphere traveling at about 22 kilometers per second.

Image credit: Yuri Beletsky
Herbig-Haro 24 (2015-12-18)

This might look like a double-bladed lightsaber, but these two cosmic jets actually beam outward from a newborn star in a galaxy near you. Constructed from Hubble Space Telescope image data, the stunning scene spans about half a light-year across Herbig-Haro 24 (HH 24), some 1,300 light-years or 400 parsecs away in the stellar nurseries of the Orion B molecular cloud complex. Hidden from direct view, HH 24's central protostar is surrounded by cold dust and gas flattened into a rotating accretion disk. As material from the disk falls toward the young stellar object it heats up. Opposing jets are blasted out along the system's rotation axis. Cutting through the region's interstellar matter, the narrow, energetic jets produce a series of glowing shock fronts along their path.
Star Streams and the Whale Galaxy (2015-12-19)

NGC 4631 is a spiral galaxy found only 25 million light-years away, toward the well-trained northern constellation Canes Venatici. Seen egde-on, the galaxy is similar in size to the Milky Way. Its distorted wedge shape suggests to some a cosmic herring and to others its popular moniker, The Whale Galaxy. The large galaxy's small, remarkably bright elliptical companion NGC 4627 lies just above its dusty yellowish core, but also identifiable are recently discovered, faint dwarf galaxies within the halo of NGC 4631. In fact, the faint extended features below (and above) NGC 4631 are now recognized as tidal star streams. The star streams are remnants of a dwarf satellite galaxy disrupted by repeated encounters with the Whale that began about 3.5 billion years ago. Even in nearby galaxies, the presence of tidal star streams is predicted by cosmological models of galaxy formation, including the formation of our own Milky Way.

Image credit: R Jay Gabany
A Dark Earth with a Red Sprite (2015-12-20)

There is something very unusual in this picture of the Earth -- can you find it? A fleeting phenomenon once thought to be only a legend has been newly caught if you know just where to look. The featured image was taken from the orbiting International Space Station (ISS) in late April and shows familiar ISS solar panels on the far left and part of a robotic arm to the far right. The rarely imaged phenomenon is known as a red sprite and it can be seen, albeit faintly, just over the bright area on the image right. This bright area and the red sprite are different types of lightning, with the white flash the more typical type. Although sprites have been reported anecdotally for as long as 300 years, they were first caught on film in 1989 -- by accident. Much remains unknown about sprites including how they occur, their effect on the atmospheric global electric circuit, and if they are somehow related to other upper atmospheric lightning phenomena such as blue jets or terrestrial gamma flashes.   Free APOD Lectures: Editor to Speak in January in Philadelphia and New York City
SN Refsdal: The First Predicted Supernova Image (2015-12-21)

It's back.  Never before has an observed supernova been predicted. The unique astronomical event occurred in the field of galaxy cluster MACS J1149.5+2223. Most bright spots in the featured image are galaxies in this cluster.  The actual supernova, dubbed Supernova Refsdal, occurred just once far across the universe and well behind this massive galaxy cluster.  Gravity caused the cluster to act as a massive gravitational lens, splitting the image of Supernova Refsdal into multiple bright images. One of these images arrived at Earth about ten years ago, likely in the upper red circle, and was missed.  Four more bright images peaked in April in the lowest red circle, spread around a massive galaxy in the cluster as the first Einstein Cross supernova. But there was more.  Analyses revealed that a sixth bright supernova image was likely still on its way to Earth and likely to arrive within the next year.  Earlier this month -- right on schedule -- this sixth bright image was recovered, in the middle red circle, as predicted.  Studying image sequences like this help humanity to understand how matter is distributed in galaxies and clusters, how fast the universe expands, and how massive stars explode.   Follow APOD on: Facebook,  Google Plus, or Twitter
Solstice Illuminated: A Year of Sky (2015-12-22)

Can you find which day is the winter solstice?  Each panel shows one day. With 360 movie panels, the sky over (almost) an entire year is shown in time lapse format as recorded by a video camera on the roof of the Exploratorium museum in San Francisco, California. The camera recorded an image every 10 seconds from before sunrise to after sunset and from mid-2009 to mid-2010.  A time stamp showing the local time of day is provided on the lower right. The videos are arranged chronologically, with July 28 shown on the upper left, and January 1 located about half way down.  In the videos, darkness indicates night, blue depicts clear day, while gray portrays pervasive daytime cloud cover. Many videos show complex patterns of clouds moving across the camera's wide field as that day progresses. The initial darkness in the middle depicts the delayed dawn and fewer daylight hours of winter. Although every day lasts 24 hours, nighttime lasts longest in the northern hemisphere in December and the surrounding winter months. Therefore, finding the panel with the longest night will locate the day of winter solstice -- which happens to be today in the northern hemisphere.  As the videos collectively end, sunset and then darkness descend first on the winter days just above the middle, and last on the mid-summer near the bottom.

Image credit: Ken Murphy  
(MurphLab);
 Music:  Ariel (Moby)
Geminid Meteors over Xinglong Observatory (2015-12-23)

Where do Geminid meteors come from?  In terms of location on the sky, as the featured image composite beautifully demonstrates, the sand-sized bits of rock that create the streaks of the Geminid Meteor Shower appear to flow out from the constellation of Gemini. In terms of parent body, Solar System trajectories point to the asteroid 3200 Phaethon -- but this results in a bit of a mystery since that unusual object appears mostly dormant.  Perhaps, 3200 Phaethon undergoes greater dust-liberating events than we know, but even if so, exactly what happens and why remains a riddle.  Peaking last week, over 50 meteors including a bright fireball were captured streaking above Xinglong Observatory in China.  Since the Geminids of December are one of the most predictable and active meteor showers, investigations into details of its origin are likely to continue.    AAS Conventioneers: APOD Town Meeting Wednesday at 2:15 pm

Image credit: Steed Yu and 
NightChina.net
Star Colors and Pinyon Pine (2015-12-24)

Beautiful, luminous decorations on this pinyon pine tree are actually bright stars in the constellation Scorpius and the faint glow of the central Milky Way. Captured in June from the north rim of the Grand Canyon of planet Earth, the shallow, close focus image has rendered pine needles on the tree branch sharp, but blurred the distant stars, their light smeared into remarkably colorful disks. Of course, temperature determines the color of a star. Most of the out-of-focus bright stars of Scorpius show a predominately blue hue, their surface temperatures much hotter than the Sun's. Cooler and larger than the Sun, and noticably redder on the scene, is giant star Antares at the heart of the scorpion. In focused, telescopic views the whitish disk at the upper right would be immediately recognizable though, reflecting the Sun's light as ringed gas giant Saturn.

Image credit: Stan Honda
To Scale: The Solar System (2015-12-25)

Want to build a scale model Solar System? A blue marble 1.4 centimeters (about half an inch) across would be a good choice for a scale model Earth. Since the Sun is 109 times the diameter of Earth, a 1.5 meter diameter balloon could represent the Sun. But the distance between the Earth and Sun, 150 million kilometers, would translate to just under 180 meters (590 feet) at the same scale. That would mean the completed project, including the orbits of the outer planets, is probably not going to fit in your backyard. Still, you might find enough room on a dry lakebed. Check out this video for an inspirational road trip through the Solar System to scale.

Image credit: Wylie Overstreet
Southern Craters and Galaxies (2015-12-26)

The Henbury craters in the Northern Territory, Australia, planet Earth, are the scars of an impact over 4,000 years old. When an ancient meteorite fragmented into dozens of pieces, the largest made the 180 meter diameter crater whose weathered walls and floor are lit in the foreground of this southern hemisphere nightscape. The vertical panoramic view follows our magnificent Milky Way galaxy stretching above horizon, its rich central starfields cut by obscuring dust clouds. A glance along the galactic plane also reveals Alpha and Beta Centauri and the stars of the Southern Cross. Captured in the region's spectacular, dark skies, the Small Magellanic Cloud, satellite of the Milky Way, is the bright galaxy to the left. Not the lights of a nearby town, the visible glow on the horizon below it is the Large Magellanic Cloud rising.

Image credit: Babak Tafreshi
Doomed Star Eta Carinae (2015-12-27)

Carinae may be about to explode.  But no one knows when - it may be next year, it may be one million years from now. Eta Carinae's mass - about 100 times greater than our Sun - makes it an excellent candidate for a full blown supernova. Historical records do show that about 150 years ago Eta Carinae underwent an unusual outburst that made it one of the brightest stars in the southern sky.  Eta Carinae, in the Keyhole Nebula, is the only star currently thought to emit natural LASER light. This featured image, taken in 1996, brought out new details in the unusual nebula that surrounds this rogue star.  Now clearly visible are two distinct lobes, a hot central region, and strange radial streaks.  The lobes are filled with lanes of gas and dust which absorb the blue and ultraviolet light emitted near the center.  The streaks remain unexplained.   Free APOD Lectures: Editor to Speak in January in Philadelphia and New York City
Falcon 9 First Stage Landing (2015-12-28)

The booster has landed. Spaceflight took a step toward the less expensive last week when the first stage of a Falcon 9 rocket set down on a landing pad not far from its Florida launch.  Previously, most rocket stages remained unrecovered -- with the significant exception of the Space Shuttles landing on a runway and their solid rocket boosters being fished back from the sea.  The landing occurred while the Falcon 9 second stage continued up to launch several communications satellites into low Earth orbit. The controlled landing, produced by SpaceX, was the first of its kind, but followed a booster landing last month by Blue Origin that did not involve launching satellites. Boeing and SpaceX were selected last year by NASA to launch future astronauts to the International Space Station. The pictured rocket booster will be analyzed for wear and reusability, but then is scheduled to be retired.   Follow APOD on: Facebook,  Google Plus, or Twitter
Dust of the Orion Nebula (2015-12-29)

What surrounds a hotbed of star formation?  In the case of the Orion Nebula -- dust.  The entire Orion field, located about 1600 light years away, is inundated with intricate and picturesque filaments of dust. Opaque to visible light, dust is created in the outer atmosphere of massive cool stars and expelled by a strong outer wind of particles. The Trapezium and other forming star clusters are embedded in the nebula. The intricate filaments of dust surrounding M42 and M43 appear brown in the featured image, while central glowing gas is highlighted in red. Over the next few million years much of Orion's dust will be slowly destroyed by the very stars now being formed, or dispersed into the Galaxy.   Explore the Universe: Random APOD Generator

Image credit: Raul Villaverde Fraile
The Fox Fur Nebula (2015-12-30)

This interstellar canine is formed of cosmic dust and gas interacting with the energetic light and winds from hot young stars.  The shape, visual texture, and color, combine to give the region the popular name Fox Fur Nebula. The characteristic blue glow on the left is dust reflecting light from the bright star S Mon, the bright star just below the top edge of the featured image. Textured red and black areas are a combination of the cosmic dust and reddish emission from ionized hydrogen gas.  S Mon is part of a young open cluster of stars, NGC 2264, located about 2,500 light years away toward the constellation of the Unicorn (Monoceros).   AAS Conventioneers: APOD Town Meeting Wednesday at 2:15 pm

Image credit: John Vermette
Solstice Sun at Lulworth Cove (2015-12-31)

A southern exposure and striking symmetry made Lulworth Cove, along the Jurassic Coast of England, planet Earth a beautiful setting during December's Solstice. Five frames in this dramatic composite view follow the lowest arc of the Sun, from sunrise to sunset, during the shortest day of the year. The solstice arc spans about 103 degrees at this northern latitude. Of course, erosion by wave action has produced the cove's remarkable shape in the coastal limestone layers. The cove's narrow entrance is responsible, creating a circular wave diffraction pattern. The wave pattern is made clearer by the low solstice Sun.

Image credit: Chris
Kotsiopoulos
Comet Catalina Tails (2016-01-01)

A new year's treat for binoculars, as 2016 begins Comet Catalina (C/2013 US10) now sweeps through planet Earth's predawn skies near bright Arcturus, alpha star of Bootes. But this telescopic mosaic from December 21 follows the pretty tails of the comet across a field of view as wide as 10 full moons. The smattering of distant galaxies and faint stars in the background are in the constellation Virgo. Trailing behind the comet's orbit, Catalina's dust tail fans out below and left in the frame. Its ion tail is angled toward the top right, away from the Sun and buffeted by the solar wind. On January 17, the outward bound visitor from the Oort Cloud will make its closest approach to Earth, a mere 110 million kilometers away, seen near bright stars along the handle of the Big Dipper.

Image credit: José J. Chambó
Sky Lights in the New Year (2016-01-02)

Triggered by the impact of a coronal mass ejection on New Year's eve, a moderate geomagnetic storm brought a celebration of sky lights to planet Earth's high latitudes yesterday. In this New Year's nightscape, the shimmering reddish curtains of aurora australis along a southern horizon are captured over Morgiana, SW Victoria, Australia. Of course, more permanent jewels of the southern skies are on the scene. The southern Milky Way, Alpha and Beta Centauri, and bright stars of the Southern Cross are on the left. In silhouette, branches of the large foreground tree stretch across the Milky Way's satellite galaxies, the Large and Small Magellanic clouds. The bright star framed near the tips of tree branches at right is Achernar. Alpha star of the constellation Eridanus, Achernar is sometimes known as the southern end of the river.

Image credit: Gill Fry
A Starry Night of Iceland (2016-01-03)

On some nights, the sky is the best show in town. On this night, the sky was not only the best show in town, but a composite image of the sky won an international competition for landscape astrophotography. The featured winning image was taken in 2011 over J�kuls�rl�n, the largest glacial lake in Iceland.  The photographer combined six exposures to capture not only two green auroral rings, but their reflections off the serene lake. Visible in the distant background sky is the band of our Milky Way Galaxy and the Andromeda galaxy. A powerful coronal mass ejection from the Sun caused auroras to be seen as far south as Wisconsin, USA.  Solar activity over the past week has resulted in auroras just over the past few days.   Follow APOD on: Facebook,  Google Plus, or Twitter
Earthset from the Lunar Reconnaissance Orbiter (2016-01-04)

On the Moon, the Earth never rises -- or sets.  If you were to sit on the surface of the Moon, you would see the Earth just hang in the sky. This is because the Moon always keeps the same side toward the Earth. Curiously, the featured image does picture the Earth setting over a lunar edge.  This was possible because the image was taken from a spacecraft orbiting the Moon - specifically the Lunar Reconnaissance Orbiter (LRO). In fact, LRO orbits the Moon so fast that, from the spacecraft, the Earth appears to set anew about every two hours. The featured image captured one such Earthset about three months ago.  By contrast, from the surface of the Earth, the Moon sets about once a day -- with the primary cause being the rotation of the Earth. LRO was launched in 2009 and, while creating a detailed three dimensional map of the Moon's surface, is also surveying the Moon for water and possible good landing spots for future astronauts.   Free APOD Lectures: Editor to speak this coming weekend in Philadelphia and New York City
The Lagoon Nebula in Hydrogen, Sulfur, and Oxygen (2016-01-05)

The majestic Lagoon Nebula is filled with hot gas and the home for many young stars. Spanning 100 light years across while lying only about 5000 light years distant, the Lagoon Nebula is so big and bright that it can be seen without a telescope toward the constellation of the Archer (Sagittarius).  Many bright stars are visible from NGC 6530, an open cluster that formed in the nebula only several million years ago. The greater nebula, also known as M8 and NGC 6523, is named "Lagoon" for the band of dust seen to the right of the open cluster's center. The featured image was taken in the light emitted by Hydrogen (shown in brown), Sulfur (red), and Oxygen (blue) and displayed in enhanced color. The featured picture is a newly processed panorama of M8, capturing twice the diameter of the Full Moon. Star formation continues in the Lagoon Nebula as witnessed by the many globules that exist there.   AAS Conventioneers: APOD Town Meeting Wednesday at 2:15 pm

Image credit: John Nemcik
Comets and Bright Star (2016-01-06)

This timely, telescopic, two panel mosaic spans about 10 full moons across planet Earth's predawn skies. Recorded as the year began from Tenerife, Canary Islands, near the top of the frame are the faint coma and tail of Comet Borrelly (P/19). A comet with a seven year orbital period, Borrelly's nucleus was visited by the ion propelled spacecraft Deep Space 1 near the beginning of the 21st century. Anchoring the scene at the bottom is brilliant star Arcturus (Alpha Bootes) and Comet Catalina (C/2013 US10) a first time visitor from the Oort Cloud. Catalina's yellowish dust tail extends below and right. Buffeted by winds and storms from the Sun, the comet's complex ion tail sweeps up and toward the right, across most of the field of view. Remarkably, one of the composition's 30 second exposure subframes also caught the trail of a bright meteor, slashing toward the left between comets and bright star.

Image credit: Fritz
Helmut Hemmerich
High Energy Andromeda (2016-01-07)

A mere 2.5 million light-years away, the Andromeda Galaxy, also known as M31, really is just next door as large galaxies go. In this (inset) scan, image data from NASA's Nuclear Spectrosopic Telescope Array has yielded the best high-energy X-ray view yet of our large neighboring spiral, revealing some 40 extreme sources of X-rays, X-ray binary star systems that contain a black hole or neutron star orbiting a more normal stellar companion. In fact, larger Andromeda and our own Milky Way are the most massive members of the local galaxy group. Andromeda is close enough that NuSTAR can examine its population of X-ray binaries in detail, comparing them to our own. The background image of Andromeda was taken by NASA's Galaxy Evolution Explorer in energetic ultraviolet light.