juliensimon/nasa-apod huggingface dataset:
Mercury Visualized from MESSENGER (2017-12-11)

What would it be like to fly over the planet Mercury? Images and data taken from NASA's robotic MESSENGER spacecraft that orbited Mercury from 2011 to 2015 have been digitally combined to envision a virtual flight that highlights much of the hot planet's surface.  In general, the Solar System's innermost world appears similar to Earth's Moon as it is covered by a heavily cratered gray terrain. MESSENGER discovered much about Mercury including that shadows near its poles likely host water ice.  The featured video opens as Mercury is viewed from the Sun-facing side and concludes with the virtual spacecraft retreating into Mercury's night.  Mercury actually rotates so slowly that it only completes three rotations for every two trips around the Sun.  In 2018, Europe and Japan plan to launch BepiColombo to better map Mercury's surface and probe its magnetic field.    Free Download: The 2018 APOD Calendar
Highlights of the Winter Sky (2017-12-12)

What's up in the sky this winter?  The featured graphic gives a few highlights for Earth's northern hemisphere.  Viewed as a clock face centered at the bottom, early winter sky events fan out toward the left, while late winter events are projected toward the right.  Objects relatively close to Earth are illustrated, in general, as nearer to the cartoon figure with the telescope at the bottom center -- although almost everything pictured can be seen without a telescope.  Highlights of this winter's sky include the Geminids meteor shower peaking this week, the constellation of Orion becoming notable in the evening sky, and many planets being visible before sunrise in February.  As true in every season, the International Space Station (ISS) can be sometimes be found drifting across your sky if you know just when and where to look.

Image credit: Universe2go.com
Meteors over Inner Mongolia (2017-12-13)

Did you ever get caught in a meteor shower? If yes, then every minute or so the sky sparked with fleeting flashes of light. This was the fate of the pictured astrophotographer during last year's Perseids meteor shower. During the featured three-hour image composite, about 90 Perseids rained down above Lake Duolun of Inner Mongolia, China. If you trace back the meteor streaks, you will find that most of them appear to radiate from a single constellation -- in this case Perseus. In fact, you can even tell which meteors are not Perseids because they track differently. Tonight promises to be another good night to get caught in a meteor shower because it is the peak for the Geminids. Gemini, the shower radiant, should rise shortly after sunset and be visible most of the night.   Free APOD Lectures: January 5 in NYC & January 9 in DC

Image credit: Haitong Yu
Jupiter Diving (2017-12-14)

Take this simulated plunge and dive into the upper atmosphere of Jupiter, the Solar System's ruling gas giant. The awesome animation is based on image data from JunoCam, and the microwave radiometer on board the Jupiter-orbiting Juno spacecraft. Your view will start about 3,000 kilometers above the southern Jovian cloud tops, but you can track your progress on the display at the left. As altitude decreases, temperature increases while you dive deeper at the location of Jupiter's famous Great Red Spot. In fact, Juno data indicates the Great Red Spot, the Solar System's largest storm system, penetrates some 300 kilometers into the giant planet's atmosphere. For comparison, the deepest point for planet Earth's oceans is just under 11 kilometers down. Don't panic though, you'll fly back out again.   Submitted to APOD: Best images (so far) of the Geminid Meteor Shower 2017.
Geminids of the North (2017-12-15)

rth's annual Geminid meteor shower did not disappoint as our fair planet plowed through dust from active asteroid 3200 Phaethon. Captured in this northern hemisphere nightscape, the meteors stream away from the shower's radiant in Gemini. To create the image, 37 individual frames recording meteor streaks were taken over period of 8.5 hours during the night of December 12/13. In the final composite they were selected and registered against the starry sky above a radio telescope dish of MUSER, a solar-dedicated radio telescope array at astronomically-named Mingantu Station in Inner Mongolia, China, about 400 kilometers from Beijing. Sirius, alpha star of Canis Major, shines brightly just above the radio dish and the Milky Way stretches toward the zenith. Yellowish Betelgeuse is a standout in Orion to the right of the northern Milky Way. The shower's radiant is at top left, high above the horizon near Castor and Pollux the twin stars of Gemini. 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.   Submitted to APOD: Best images (so far) of the Geminid Meteor Shower 2017.

Image credit: Yin Hao
A Wintry Shower (2017-12-16)

Four Geminids flash through northern skies in this wintry night skyscape. The bright fireball and 3 fainter meteors were captured in a single 10 second exposure, near the peak of December's Geminid meteor shower. Reflecting the fireball's greenish light, a partially frozen Lake Edith in Alberta Canada's Jasper National Park lies in the foreground, with the Canadian Rocky Mountains ranging along the northern horizon. Of course, the glacial lake is cold even in summer. But photographer Jack Fusco reports that he experienced -9 degree C temperatures that night while enjoying one of the most active meteor showers he's ever seen.

Image credit: Jack Fusco
The Einstein Cross Gravitational Lens (2017-12-17)

Most galaxies have a single nucleus -- does this galaxy have four?  The strange answer leads astronomers to conclude that the nucleus of the surrounding galaxy is not even visible in this image.  The central cloverleaf is rather light emitted from a background quasar.  The gravitational field of the visible foreground galaxy breaks light from this distant quasar into four distinct images.  The quasar must be properly aligned behind the center of a massive galaxy for a mirage like this to be evident.  The general effect is known as gravitational lensing, and this specific case is known as the Einstein Cross.  Stranger still, the images of the Einstein Cross vary in relative brightness, enhanced occasionally by the additional gravitational microlensing effect of specific stars in the foreground galaxy.     Free Download: The 2018 APOD Calendar

Image credit: J. Rhoads
(Arizona State U.) et al.,
WIYN,
AURA,
NOAO,
NSF
The Kepler-90 Planetary System (2017-12-18)

Do other stars have planetary systems like our own? Yes -- one such system is Kepler-90. Cataloged by the orbiting Kepler satellite, an eighth planet has now been discovered giving Kepler-90 the same number of known planets as our Solar System. Similarities between Kepler-90 and our system include a G-type star comparable to our Sun, rocky planets comparable to our Earth, and large planets comparable in size to Jupiter and Saturn. Differences include that all of the known Kepler-90 planets orbit relatively close in -- closer than Earth's orbit around the Sun -- making them possibly too hot to harbor life. However, observations over longer time periods may discover cooler planets further out. Kepler-90 lies about 2,500 light years away, and at magnitude 14 is visible with a medium-sized telescope toward the constellation of the Dragon (Draco).  Exoplanet-finding missions planned for launch in the next decade include TESS, JWST, WFIRST, and PLATO.
The Spiral North Pole of Mars (2017-12-19)

Why is there a spiral around the North Pole of Mars?  Each winter this pole develops a new outer layer about one meter thick composed of carbon dioxide frozen out of the thin Martian atmosphere.  This fresh layer is deposited on a water-ice layer that exists year round.  Strong winds blow down from above the cap's center and swirl due to the spin of the red planet -- contributing to Planum Boreum's spiral structure.  The featured image is a perspective mosaic generated earlier this year from numerous images taken by ESA's Mars Express and elevations extracted from the laser altimeter aboard NASA's Mars Global Surveyor mission.  New missions to Mars planned in the next few years include Insight with plans to drill into Mars, and ExoMars and the Mars 2020 Rover with plans to search for signs of microscopic Martian life -- past and present.   Free APOD Lectures: January 5 in NYC & January 9 in DC
How to Wash Your Hair in Space (2017-12-20)

How can you wash your hair in space -- without gravity?  Long a bother for space-faring astronauts, Karen Nyberg, a flight engineer on the International Space Station (ISS) in 2013, gave a tutorial. Key components are a squirt package of water, no-rinse shampoo, and vigorous use of a towel and comb.  Even so, the featured video shows that the whole process should take only a few minutes.  Residual water will eventually evaporate from your hair, be captured by the space station's air conditioning system, and be purified into drinking water. After returning from a total of 180 days in space, Nyberg has worked for NASA in several capacities including as the Chief of Robotics branch.
Solstice Sun and Milky Way (2017-12-21)

Welcome to December's solstice, first day of winter in the north and summer for the southern hemisphere. Astronomical markers of the seasons, solstice and equinox dates are based on the Sun's place in its annual journey along the ecliptic, through planet Earth's sky. At this solstice, the Sun reaches its maximum southern declination of -23.5 degrees today at 16:28 UTC, while its right ascension coordinate on the celestial sphere is 18 hours. That puts the Sun in the constellation Sagittarius in a direction near the center of our Milky Way galaxy. In fact, if you could see today's Solstice Sun against faint background stars and nebulae (that's really hard to do, especially in the daytime ...) your view might look something like this composited panorama. To make it, images of our fair galaxy were taken under dark Namibian night skies, then stitched together in a panoramic view. From a snapshot made on December 21, 2015, the Sun was digitally overlayed as a brilliant star at today's northern winter solstice position, close to the center of the Milky Way.

Image credit: Stefan Seip
Gemini's Meteors (2017-12-22)

From dark skies above Heilongjiang province in northeastern China, meteors rain down on a wintry landscape in this beautiful composited night scene. The 48 meteors are part of last week's annual Geminid meteor shower. Despite temperatures of -28 degrees C, all were recorded in camera exposures made during the peak hour of the celestial spectacle. They stream away from the shower's radiant high above the horizon near the two bright stars of the zodiacal constellation of the Twins. A very active shower, this year the December 13-14 peak of the Geminids arrived just before the December 16 closest approach of asteroid 3200 Phaethon to planet Earth. Mysterious 3200 Phaethon is the Geminid shower's likely parent body.

Image credit: Jeff Dai
Phaethon's Brood (2017-12-23)

Based on its well-measured orbit, 3200 Phaethon (sounds like FAY-eh-thon) is recognized as the source of the meteroid stream responsible for the annual Geminid meteor shower. Even though most meteor showers' parents are comets, 3200 Phaethon is a known and closely tracked near-Earth asteroid with a 1.4 year orbital period. Rocky and sun-baked, its perihelion or closest approach to the Sun is well within the orbit of innermost planet Mercury. In this telescopic field of view, the asteroid's rapid motion against faint background stars of the heroic constellation Perseus left a short trail during the two minute total exposure time. The parallel streaks of its meteoric children flashed much more quickly across the scene. The family portrait was recorded near the Geminid meteor shower's very active peak on December 13. That was just before 3200 Phaethon's historic December 16 closest approach to planet Earth.   Gallery: Images from yesterday's photogenic SpaceX launch in California

Image credit: Mikiya Sato
SpaceX Rocket Launch Plume over California (2017-12-24)

What's happened to the sky? On Friday, the photogenic launch plume from a SpaceX rocket launch created quite a spectacle over parts of southern California and Arizona.  Looking at times like a giant space fish, the impressive rocket launch from Vandenberg Air Force Base near Lompoc, California, was so bright because it was backlit by the setting Sun. Lifting off during a minuscule one-second launch window, the Falcon 9 rocket successfully delivered to low Earth orbit ten Iridium NEXT satellites that are part of a developing global communications network. The plume from the first stage is seen on the right, while the soaring upper stage rocket is seen at the apex of the plume toward the left. Several good videos of the launch were taken.  The featured image was captured from Orange County, California, in a 2.5 second duration exposure.   Gallery: More images of the SpaceX launch

Image credit: Craig Bobchin
Fireball in the Arctic (2017-12-25)

Something very bright suddenly lit up the arctic -- what was it? The original idea was to take a series of aurora images that could be made into a time-lapse video.  But when night suddenly turned into day, the astrophotographer quickly realized that he was seeing something even more spectacular. Moving through the sky -- in front of the Big Dipper no less -- was a Geminid meteor so bright it could be called a fireball. The meteor brightened and flashed for several seconds as it went.  By a stroke of good fortune, the aurora camera was able to capture the whole track. Taken the night after the Geminids Meteor Shower peaked, the astrophotographer's location was near Lovozero Lake in Murmansk, Russia, just north of the Arctic Circle.   Free APOD Lectures: January 5 in NYC & January 9 in DC

Image credit: Yang Sutie
Grand Spiral Galaxy NGC 1232 (2017-12-26)

Galaxies are fascinating not only for what is visible, but for what is invisible. Grand spiral galaxy NGC 1232, captured in detail by one of the Very Large Telescopes, is a good example.  The visible is dominated by millions of bright stars and dark dust, caught up in a gravitational swirl of spiral arms revolving about the center. Open clusters containing bright blue stars can be seen sprinkled along these spiral arms, while dark lanes of dense interstellar dust can be seen sprinkled between them. Less visible, but detectable, are billions of dim normal stars and vast tracts of interstellar gas, together wielding such high mass that they dominate the dynamics of the inner galaxy.  Leading theories indicate that even greater amounts of matter are invisible, in a form we don't yet know. This pervasive dark matter is postulated, in part, to explain the motions of the visible matter in the outer regions of galaxies.    Free APOD Lectures: January 5 in NYC & January 9 in DC
The Horsehead Nebula (2017-12-27)

One of the most identifiable nebulae in the sky, the Horsehead Nebula in Orion, is part of a large, dark, molecular cloud.  Also known as Barnard 33, the unusual shape was first discovered on a photographic plate in the late 1800s.  The red glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis.  The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead's neck casts a shadow to the left.  Streams of gas leaving the nebula are funneled by a strong magnetic field.  Bright spots in the Horsehead Nebula's base are young stars just in the process of forming.  Light takes about 1,500 years to reach us from the Horsehead Nebula.  The featured image was taken with the large 3.6-m Canada-France-Hawaii Telescope in Hawaii, USA.   Free APOD Lectures: January 5 in NYC & January 9 in DC
Recycling Cassiopeia A (2017-12-28)

Massive stars in our Milky Way Galaxy live spectacular lives.  Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation can begin anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant would have been first seen in planet Earth's sky about 350 years ago, although it took that light about 11,000 years to reach us. This false-color Chandra X-ray Observatory image shows the still hot filaments and knots in the Cassiopeia A remnant. High-energy emission from specific elements has been color coded, silicon in red, sulfur in yellow, calcium in green and iron in purple, to help astronomers explore the recycling of our galaxy's star stuff - Still expanding, the blast wave is seen as the blue outer ring. The sharp X-ray image, spans about 30 light-years at the estimated distance of Cassiopeia A. The bright speck near the center is a neutron star, the incredibly dense, collapsed remains of the massive stellar core.
M78 Wide Field (2017-12-29)

Interstellar dust clouds and glowing nebulae abound in the fertile constellation of Orion. One of the brightest, M78, is centered in this colorful, wide field view, covering an area north of Orion's belt. At a distance of about 1,500 light-years, the bluish reflection nebula is around 5 light-years across. Its tint is due to dust preferentially reflecting the blue light of hot, young stars. Reflection nebula NGC 2071 is just to the left of M78. To the right, and much more compact in appearance, the intriguing McNeil's Nebula is a recently recognized variable nebula associated with a young sun-like star. Deeper red flecks of emission from Herbig-Haro objects, energetic jets from stars in the process of formation, stand out against the dark dust lanes. The exposure also brings out the region's fainter pervasive glow of atomic hydrogen gas.

Image credit: Fabian Neyer
Apollo 17 VIP Site Anaglyph (2017-12-30)

Get out your red/blue glasses and check out this stereo scene from Taurus-Littrow valley on the Moon! The color anaglyph features a detailed 3D view of Apollo 17's Lunar Rover in the foreground -- behind it lies the Lunar Module and distant lunar hills. Because the world was going to be able to watch the Lunar Module's ascent stage liftoff via the rover's TV camera, this parking place was also known as the VIP Site. In December of 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt spent about 75 hours on the Moon, while colleague Ronald Evans orbited overhead. The crew returned with 110 kilograms of rock and soil samples, more than from any of the other lunar landing sites. Cernan and Schmitt are still the last to walk (or drive) on the Moon.
To Fly Free in Space (2017-12-31)

What would it be like to fly free in space?  At about 100 meters from the cargo bay of the space shuttle Challenger, Bruce McCandless II was living the dream -- floating farther out than anyone had ever been before.  Guided by a Manned Maneuvering Unit (MMU), astronaut McCandless, pictured, was floating free in space. McCandless and fellow NASA astronaut Robert Stewart were the first to experience such an "untethered space walk" during Space Shuttle mission 41-B in 1984.  The MMU worked by shooting jets of nitrogen and was used to help deploy and retrieve satellites.  With a mass over 140 kilograms, an MMU is heavy on Earth, but, like everything, is weightless when drifting in orbit. The MMU was replaced with the SAFER backpack propulsion unit.   Memorial: Astronaut Bruce McCandless II Dies at 80
Sun Halo over Sweden (2018-01-01)

What's happened to the Sun?  Sometimes it looks like the Sun is being viewed through a giant  lens.  In the featured video, however, there are actually millions of tiny lenses: ice crystals.  Water may freeze in the  atmosphere into small, flat, six-sided, ice crystals.  As these crystals flutter to the ground, much time is spent with their faces flat and parallel to the ground.  An observer may find themselves in the same plane as many of the falling ice crystals near sunrise or sunset.  During this alignment, each crystal can act like a miniature lens, refracting sunlight into our view and creating phenomena like parhelia, the technical term for sundogs.  The featured video was taken a month ago on the side of a ski hill at the Vemdalen Ski Resort in central  Sweden. Visible in the center is the most direct image of the Sun, while two bright sundogs glow prominently from both the left and the right.  Also visible is the bright 22 degree halo -- as well as the rarer and much fainter 46 degree halo -- also created by sunlight refracting through atmospheric ice crystals.

Image credit: H�kan Hammar 
(Vemdalen Ski Resort, 
SkiStar)
Unexpected X-Rays from Perseus Galaxy Cluster (2018-01-02)

Why does the Perseus galaxy cluster shine so strangely in one specific color of X-rays? No one is sure, but a much-debated hypothesis holds that these X-rays are a clue to the long-sought identity of dark matter. At the center of this mystery is a 3.5 Kilo-electronvolt (KeV) X-ray color that appears to glow excessively only when regions well outside the cluster center are observed, whereas the area directly surrounding a likely central supermassive black hole is actually deficient in 3.5 keV X-rays. One proposed resolution -- quite controversial -- is that something never seen before might be present: fluorescent dark matter (FDM). This form of particle dark matter might be able to absorb 3.5 keV X-radiation.  If operating, FDM, after absorption, might later emit these X-rays from all over the cluster, creating an emission line. However, when seen superposed in front of the central region surrounding the black hole, FDM's absorption would be more prominent, creating an absorption line.  Pictured, a composite image of the Perseus galaxy cluster shows visible and radio light in red, and X-ray light from the Earth-orbiting Chandra Observatory in blue.    Free APOD Lectures: January 5 in NYC & January 9 in DC
The Helix Nebula from CFHT (2018-01-03)

Will our Sun look like this one day?  The Helix Nebula is one of brightest and closest examples of a planetary nebula, a gas cloud created at the end of the life of a Sun-like star. The outer gasses of the star expelled into space appear from our vantage point as if we are looking down a helix. The remnant central stellar core, destined to become a white dwarf star, glows in light so energetic it causes the previously expelled gas to fluoresce. The Helix Nebula, given a technical designation of NGC 7293, lies about 700 light-years away towards the constellation of the Water Bearer (Aquarius) and spans about 2.5 light-years. The featured picture was taken with the Canada-France-Hawaii Telescope (CFHT) located atop a dormant volcano in Hawaii, USA. A close-up of the inner edge of the Helix Nebula shows complex gas knots of unknown origin.   Free APOD Lectures: January 5 in NYC & January 9 in DC
M1: The Incredible Expanding Crab (2018-01-04)

The Crab Nebula is cataloged as M1, the first on Charles Messier's famous list of things which are not comets. In fact, the Crab is now known to be a supernova remnant, an expanding cloud of debris from the explosion of a massive star. The violent birth of the Crab was witnessed by astronomers in the year 1054. Roughly 10 light-years across today, the nebula is still expanding at a rate of over 1,000 kilometers per second. Over the past decade, its expansion has been documented in this stunning time-lapse movie. In each year from 2008 to 2017, an image was produced with the same telescope and camera from a remote observatory in Austria. Combined in the time-lapse movie, the 10 images represent 32 hours of total integration time. The sharp, processed frames even reveal the dynamic energetic emission within the incredible expanding Crab. The Crab Nebula lies about 6,500 light-years away in the constellation Taurus.

Image credit: Detlef Hartmann