juliensimon/nasa-apod huggingface dataset:
Deep Magellanic Clouds Image Indicates Collisions (2016-07-25)

Did the two most famous satellite galaxies of our Milky Way Galaxy once collide? No one knows for sure, but a detailed inspection of deep images like that featured here give an indication that they have. Pictured, the Large Magellanic Cloud (LMC) is on the top left and the Small Magellanic Cloud (SMC) is on the bottom right.  The surrounding field is monochrome color-inverted to highlight faint filaments, shown in gray. Perhaps surprisingly, the featured research-grade image was compiled with small telescopes to cover the large angular field -- nearly 40 degrees across.  Much of the faint nebulosity is Galactic Cirrus clouds of thin dust in our own Galaxy, but a faint stream of stars does appear to be extending from the SMC toward the LMC. Also, stars surrounding the LMC appear asymmetrically distributed, indicating in simulations that they could well have been pulled off gravitationally in one or more collisions.  Both the LMC and the SMC are visible to the unaided eye in southern skies. Future telescopic observations and computer simulations are sure to continue in a continuing effort to better understand the history of our Milky Way and its surroundings.

Image credit: Yuri Beletsky
(Carnegie
Las Campanas Observatory,
TWAN) & David Martinez-Delgado 
(U. Heidelberg)
Puzzling a Sky over Argentina (2016-07-26)

Can you find the comet? True, a careful eye can find thousands of stars, tens of constellations, four planets, three galaxies, and the central band of our Milky Way Galaxy -- all visible in the sky of this spectacular 180-degree panorama.  Also, if you know what to look for, you can identify pervasive green airglow, an earthly cloud, the south celestial pole, and even a distant cluster of stars.  But these are all easier to find than Comet 252P/LINEAR.  The featured image, taken in el Leoncito National Park, Argentina in early April, also features the dome of the Jorge Sahade telescope on the hill on the far right.  Have you found the comet yet?  If so, good for you (it was the green spot on the left), but really the harder thing to find is Small Cloud of Magellan.

Image credit: Sergio Mont�far; 
 Acknowledgement: 
Planetario Ciudad de La Plata / CASLEO observatory
M13: A Great Globular Cluster of Stars (2016-07-27)

M13 is one of the most prominent and best known globular clusters.  Visible with binoculars in the constellation of Hercules, M13 is frequently one of the first objects found by curious sky gazers seeking celestials wonders beyond normal human vision.  M13 is a colossal home to over 100,000 stars, spans over 150 light years across, lies over 20,000 light years distant, and is over 12 billion years old.  At the 1974 dedication of Arecibo Observatory, a radio message about Earth was sent in the direction of M13.  The featured image in HDR, taken through a small telescope, spans an angular size just larger than a full Moon, whereas the inset image, taken by Hubble Space Telescope, zooms in on the central 0.04 degrees.

Image credit: Dean Fournier;
Inset: ESA/Hubble & 
NASA
Herschel's Eagle Nebula (2016-07-28)

A now famous picture from the Hubble Space Telescope featured Pillars of Creation, star forming columns of cold gas and dust light-years long inside M16, the Eagle Nebula. This false-color composite image views the nearby stellar nursery using data from the Herschel Space Observatory's panoramic exploration of interstellar clouds along the plane of our Milky Way galaxy. Herschel's far infrared detectors record the emission from the region's cold dust directly. The famous pillars are included near the center of the scene. While the central group of hot young stars is not apparent at these infrared wavelengths, the stars' radiation and winds carve the shapes within the interstellar clouds. Scattered white spots are denser knots of gas and dust, clumps of material collapsing to form new stars. The Eagle Nebula is some 6,500 light-years distant, an easy target for binoculars or small telescopes in a nebula rich part of the sky toward the split constellation Serpens Cauda (the tail of the snake).

Image credit: ESA/Herschel/PACS
Blue Danube Analemma (2016-07-29)

The Sun's annual waltz through planet Earth's sky forms a graceful curve known as an analemma. The analemma's figure 8 shape is tipped vertically at far right in this well-composed fisheye view from Budapest, Hungary. Captured at a chosen spot on the western bank of the Danube river, the Sun's position was recorded at 11:44 Central European Time on individual exposures over days spanning 2015 July 23 to 2016 July 4. Of course, on the northern summer solstice the Sun is at the top of the curve, but at the midpoints for the autumn and spring equinoxes. With snow on the ground, the photographer's shadow and equipment bag also appear in the base picture used for the composite panorama, taken on 2016 January 7. On that date, just after the winter solstice, the Sun was leaving the bottom of the beautiful curve over the blue Danube.

Image credit: György Soponyai
Ripples Through a Dark Sky (2016-07-30)

Sunlight ripples through a dark sky on this Swedish summer midnight as noctilucent or night shining clouds seem to imitate the river below. In fact, the seasonal clouds often appear at high latitudes in corresponding summer months. Also known as polar mesospheric clouds, they form as water vapor is driven into the cold upper atmosphere. Fine dust supplied by disintegrating meteors or volcanic ash provides sites where water vapor can condense, turning to ice at the cold temperatures in the mesosphere. Poised at the edge of space some 80 kilometers above, these icy clouds really do reflect sunlight toward the ground. They are visible here even though the Sun itself was below the horizon, as seen on July 16 from Sweden's Färnebofjärdens National Park.

Image credit: Clear Skies
A Huge Solar Filament Erupts (2016-07-31)

Filaments sometimes explode off the Sun.  Featured, a huge filament had been seen hovering over the Sun's surface for over a week before it erupted late in 2010.  The image sequence was taken by the Earth-orbiting Solar Dynamics Observatory (SDO) in one color of ultraviolet light.  The explosion created a Coronal Mass Ejection that dispersed high energy plasma into the Solar System.  This plasma cloud, though, missed the Earth and so did not cause auroras.  The featured eruption depicted how widely separated areas of the Sun can sometimes act in unison.  Explosions like this will likely become less common over the next few years as our Sun goes through a Solar Minimum in its surface magnetic activity.
Behind Saturn (2016-08-01)

What's behind Saturn? The first answer is the camera itself, perched on the Cassini spacecraft currently orbiting behind the planet with the  most grand ring system in our Solar System. The unusual perspective places Cassini on the far side of Saturn from the Sun so that more than half of Saturn appears dark -- a perspective that no Earth-based observer could achieve.  Behind Saturn, in the context of the featured infrared image, is Saturn's moon Tethys, visible as the small speck above the unusual hexagonal cloud pattern that encompasses Saturn's North Pole.  Tethys actually orbits Saturn right in the ring plane, which places the 1000-km moon much farther from Cassini than the planet itself. Cassini has been studying Saturn and its moons for 12 years, but, unfortunately, its amazing mission will soon come to an end. In order to protect life that may exist on or inside Saturn's moons, the robotic spacecraft will be directed to crash into Saturn's thick atmosphere next September.   Follow APOD on: Facebook,  Google Plus,  Instagram, or Twitter
A Rocket Booster Falls Back to Earth (2016-08-02)

What's that crossing the sky? Although it looked a bit like a large meteor, it was actually the booster of a Chinese rocket returning to Earth after its launch two days earlier.  On the night of July 27, the rocket component heated up and broke up into glowing pieces as it re-entered Earth's atmosphere.  The path of the falling booster took it over several US states, moving west to east, from California to Utah. Space debris can usually be distinguished from meteors by its slow speed and expansive break up.  The featured video was taken in front of the Provo City Library in Utah, which was coincidently occupied by over 100 people -- many with smartphones already out of their pockets playing Pok�mon GO.

Image credit: Matthew Holt
Behold the Universe (2016-08-03)

What if you climbed up on a rock and discovered the Universe?  You can.  Although others have noted much of it before, you can locate for yourself stars, planets, and even the plane of our Milky Way Galaxy. All you need is a dark clear sky -- the rock is optional.  If you have a camera, you can further image faint nebulas, galaxies, and long filaments of interstellar dust.  If you can process digital images, you can bring out faint features, highlight specific colors, and merge foreground and background images. In fact, an industrious astrophotographer has done all of these to create the presented picture. All of the component images were taken early last month on the same night within a few meters of each other.  The picturesque setting was Sand Beach in Stonington, Maine, USA with the camera pointed south over Penobscot Bay.   News: APOD is now available through Facebook translated into Catalan.

Image credit: A. Garrett Evans;
 Rollover Annotation:  Judy Schmidt
M63: Sunflower Galaxy Wide Field (2016-08-04)

The Sunflower Galaxy blooms near the center of this wide field telescopic view. The scene spans about 2 degrees or 4 full moons on the sky toward the loyal constellation Canes Venatici. More formally known as Messier 63, the majestic island universe is nearly 100,000 light-years across, about the size of our own Milky Way Galaxy. Surrounding its bright yellowish core, sweeping spiral arms are streaked with cosmic dust lanes and dotted with star forming regions. A dominant member of a known galaxy group, M63 has faint, extended features that could be the the remains of dwarf satellite galaxies, evidence that large galaxies grow by accreting small ones. M63 shines across the electromagnetic spectrum and is thought to have undergone bursts of intense star formation.

Image credit: Deep Sky West
Apollo 15 Panorama (2016-08-05)

On July 31, 1971, Apollo 15 astronauts Jim Irwin and Dave Scott deployed the first Lunar Roving Vehicle on the Moon. Using it to explore their Hadley-Apennine landing site they spent nearly three days on the Moon while Al Worden orbited above. This digitally stitched panorama shows Scott examining a boulder on the slope of 3.5 kilometer high Mons Hadley Delta to the left of their electric-powered, four-wheel drive vehicle. The sun at his back, Irwin casts the strong shadow to the rover's right. The panoramic view extends farther right to the sunward direction, over Hadley Rille and lunar terrain, revealed in harsh, unfiltered sunlight. In total, the rover traversed 28 kilometers (17 miles) on the lunar surface. The Apollo 15 mission returned about 76 kilograms of moon rocks to planet Earth.

Image credit: Apollo 15
Las Campanas Moon and Mercury (2016-08-06)

Last Thursday the view toward sunset from the 2.5 kilometer summit of Cerro Las Campanas in the remote Chilean Andes was amazing.  Bright but fading Mercury stood very close to a two day old Moon. Both a sunlit lunar crescent and earthlit lunar nightside are captured with the fleeting innermost planet in this breathtaking mountainscape. Even below the conjunction of Moon and Mercury, a close pairing of brilliant Venus and bright star Regulus hangs in the sky, still above the colorful western horizon. Of course amazing skies above Las Campanas are not unexpected. The region is currently home to the twin Magellan telescopes of the Las Campanas Observatory and the summit location is the site of the future Giant Magellan Telescope.

Image credit: Yuri Beletsky
Io: Moon over Jupiter (2016-08-07)

How big is Jupiter's moon Io? The most volcanic body in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite. Gliding past Jupiter at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view of active Io with the largest gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size. Although in the featured picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts Io nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon. In July, NASA's Juno satellite began orbiting Jupiter and will sometimes swoop to within 5,000 kilometers of Jupiter's cloud tops.
Perseid Meteors over Mount Shasta (2016-08-08)

Where are all of these meteors coming from?  In terms of direction on the sky, the pointed answer is the constellation of Perseus.  That is why the meteor shower that peaks later this week is known as the Perseids -- the meteors all appear to came from a radiant toward Perseus. In terms of parent body, though, the sand-sized debris that makes up the Perseids meteors come from Comet Swift-Tuttle. The comet follows a well-defined orbit around our Sun, and the part of the orbit that approaches Earth is superposed in front of the Perseus. Therefore, when Earth crosses this orbit, the radiant point of falling debris appears in Perseus. Featured here, a composite image containing over 60 meteors from last August's Perseids meteor shower shows many bright meteors that streaked over Mount Shasta, California, USA.  This year's Perseids holds promise to be the best meteor shower of the year.   Transparent Science:  Browse 1,300+ codes in the Astrophysics Source Code Library

Image credit: Brad Goldpaint  
(Goldpaint Photography)
Mars at Closest Approach (2016-08-09)

When does Mars appear the largest? This occurs when Earth sweeps past Mars in their respective orbits around the Sun, creating a momentary Sun-Earth-Mars alignment called opposition. The featured image shows the Mars opposition that occurred earlier this year, as well as how Mars will look later this year.  Mars actually changes its size continuously -- the monthly jumps in size are illustrative.  During the first months of the year,  Earth's view toward Mars is from relatively far away and from a relatively sideways angle -- making Mars appear small and at less than full phase (gibbous).  As months progress, Mars appears increasingly larger and fuller.  The day Earth and Mars were closest together was on May 30.  By June, Earth had passed Mars, and part of the other side of Mars appeared shadowed.  Mars will now appear increasingly smaller during 2016.  Even if you watch Mars from Earth all along its orbit, though, Mars will never show a crescent phase.   Note: The video originally featured in this APOD has been replaced.
Colliding Galaxies in Stephan's Quintet (2016-08-10)

Will either of these galaxies survive?  In what might be dubbed as a semi-final round in a galactic elimination tournament, the two spirals of NGC 7318 are colliding. The featured picture was created from images taken by the Hubble Space Telescope.  When galaxies crash into each other, many things may happen including gravitational distortion, gas condensing to produce new episodes of star formation, and ultimately the two galaxies combining into one. Since these two galaxies are part of Stephan's Quintet, a final round of battling galaxies will likely occur over the next few billion years with the eventual result of many scattered stars and one large galaxy. Quite possibly, the remaining galaxy will not be easily identified with any of its initial galactic components.  Stephan's Quintet was the first identified galaxy group, lies about 300 million light years away, and is visible through a moderately-sized telescope toward the constellation of the Winged Horse (Pegasus).   Free Download: APOD 2017 Calendar: NASA Images

Image credit: Jose Jimenez Priego
Perseid, Aurora, and Noctilucent Clouds (2016-08-11)

Night skies over northern Sweden can hold some tantalizing sights in August. Gazing toward the Big Dipper, this beautiful skyscape captures three of them in a single frame taken last August 12/13. Though receding from northern skies for the season, night shining or noctilucent clouds are hanging just above the horizon. Extreme altitude icy condensations on meteoric dust, they were caught here just below an early apparition of a lovely green auroral band, also shining near the edge of space. The flash of a Perseid meteor near the peak of the annual shower punctuates the scene. In fact, this year's Perseid shower will peak in the coming days, offering a continuing chance for a night sky photographer's hat trick.

Image credit: Göran Strand
The Easterbunny Comes to NGC 4725 (2016-08-12)

At first called "Easterbunny" by its discovery team, officially named Makemake is the second brightest dwarf planet of the Kuiper belt. The icy world appears twice in this astronomical image, based on data taken on June 29 and 30 of the bright spiral galaxy NGC 4725. Makemake is marked by short red lines, its position shifting across a homemade telescope's field-of-view over two nights along a distant orbit. On those dates nearly coincident with the line-of-sight to the spiral galaxy in the constellation Coma Berenices, Makemake was about 52.5 astronomical units or 7.3 light-hours away. NGC 4725 is over 100,000 light-years across and 41 million light-years distant. Makemake is now known to have at least one moon. NGC 4725 is a famous one-armed spiral galaxy.  Look Up! Perseid Meteor Shower

Image credit: Bob English
Perseid from Torralba del Burgo (2016-08-13)

Perseid meteors rained on planet Earth last night. This year the stream of dust from periodic comet Swift-Tuttle has produced a stunningly active shower of bright cosmic streaks. In this 25 second long exposure, one luminous Perseid trail, fast and colorful with a small explosion at the end, is witnessed by night skygazers from Torralba del Burgo, Soria, Spain. A second fainter meteor trail appears well below the first. The two can be extended to intersect at the meteor shower's radiant just above the brighter stars of the heroic constellation Perseus. Though the meteor shower's activity is waning, in the coming days Perseids will still flash through the night. But you won't see any if you don't go outside and look up.

Image credit: Fernando Cabrerizo
The Keyhole in the Carina Nebula (2016-08-14)

The dark dusty Keyhole Nebula gets its name from its unusual shape.  The looping Keyhole, in this featured classic image by the Hubble Space Telescope, is a smaller region inside the larger Carina Nebula.  Dramatic dark dust knots and complex features are sculpted by the winds and radiation of the Carina Nebula's many massive and energetic stars. In particular, the shape of the dust cloud on the upper left of the Keyhole Nebula may stimulate the human imagination to appear similar to, for example, a superhero flying through a cloud, arm up, with a saved person in tow below. The region lies about 7,500 light-years away in planet Earth's southern sky. The Keyhole Nebula was created by the dying star Eta Carina , out of the frame, which is prone to violent outbursts during its final centuries.   Free Download: APOD 2017 Calendar: NASA Images
Human as Spaceship (2016-08-15)

You are a spaceship soaring through the universe. So is your dog. We all carry with us trillions of microorganisms as we go through life. These multitudes of bacteria, fungi, and archaea have different DNA than you. Collectively called your microbiome, your shipmates outnumber your own cells. Your crew members form communities, help digest food, engage in battles against intruders, and sometimes commute on a liquid superhighway from one end of your body to the other.  Much of what your microbiome does, however, remains unknown. You are the captain, but being nice to your crew may allow you to explore more of your local cosmos.    Perseid Meteors 2016: Album 1 & Album 2

Image credit: Charis Tsevis; 
 Composition:  R. J. Nemiroff
Five Planets and the Moon over Australia (2016-08-16)

It is not a coincidence that planets line up. That's because all of the planets orbit the Sun in (nearly) a single sheet called the plane of the ecliptic. When viewed from inside that plane -- as Earth dwellers are likely to do -- the planets all appear confined to a single band. It is a coincidence, though, when several of the brightest planets all appear in nearly the same direction.  Such a coincidence was captured last week. Featured above, six planets and Earth's Moon were all imaged together last week, just after sunset, from Mornington Peninsula in Victoria, Australia. A second band is visible across the top of this tall image -- the central band of our Milky Way Galaxy.   Perseid Meteors 2016: Album 1 & Album 2

Image credit: Terrastro
Meteor before Galaxy (2016-08-17)

What's that green streak in front of the Andromeda galaxy? A meteor. While photographing the Andromeda galaxy last Friday, near the peak of the Perseid Meteor Shower, a sand-sized rock from deep space crossed right in front of our Milky Way Galaxy's far-distant companion. The small meteor took only a fraction of a second to pass through this 10-degree field.  The meteor flared several times while braking violently upon entering Earth's atmosphere.  The green color was created, at least in part, by the meteor's gas glowing as it vaporized. Although the exposure was timed to catch a Perseids meteor, the orientation of the imaged streak seems a better match to a meteor from the Southern Delta Aquariids, a meteor shower that peaked a few weeks earlier.    Free Download: APOD 2017 Calendar: NASA Images

Image credit: Fritz
Helmut Hemmerich
Perseid Night at Yosemite (2016-08-18)

The 2016 Perseid meteor shower performed well on the night of August 11/12. The sky on that memorable evening was recorded from a perch overlooking Yosemite Valley, planet Earth, in this scene composed of 25 separate images selected from an all-night set of sequential exposures. Each image contains a single meteor and was placed in alignment using the background stars. The digital manipulation accounts for the Earth's rotation throughout the night and allows the explosion of colorful trails to be viewed in perspective toward the shower's radiant in the constellation Perseus. The fading alpenglow gently lights the west face of El Capitan just after sunset. Just before sunrise, a faint band zodiacal light, or the false dawn, shines upward from the east, left of Half Dome at the valley's far horizon. Car lights illuminate the valley road. Of course, the image is filled with other celestial sights from that Perseid night, including the Milky Way and the Pleiades star cluster.

Image credit: Mike Shaw
Perseid Fireball at Sunset Crater (2016-08-19)

On the night of August 12, this bright Perseid meteor flashed above volcanic Sunset Crater National Monument, Arizona, USA, planet Earth. Streaking along the summer Milky Way, its initial color is likely due to the shower meteor's characteristically high speed. Entering at 60 kilometers per second, Perseid meteors are capable of exciting green emission from oxygen atoms while passing through the tenuous atmosphere at high altitudes. Also characteristic of bright meteors, this Perseid left a visibly glowing persistent train. Its evolution is seen over a three minute sequence (left to right) spanning the bottom of the frame.  The camera ultimately captured a dramatic timelapse video of the twisting, drifting train.

Image credit: Jeremy
Perez