juliensimon/nasa-apod huggingface dataset:
Heliopause Electrostatic Rapid Transit System (2016-04-16)

Want to take a fast trip to the edge of the Solar System? Consider a ride on a Heliopause Electrostatic Rapid Transit System (HERTS). The concept is currently being tested and it might take only 10 to 15 years to make the trip of over 100 Astronomical Units (15 billion kilometers). That's fast compared to the 35 years it took Voyager 1, presently humanity's most distant spacecraft, to approach the heliopause or outer boundary of the influence of the solar wind. HERTS would use an advanced electric solar sail that works by extending multiple, 20 kilometer or so long, 1 millimeter thin, positively charged wires from a rotating spacecraft. The electrostatic force generated repels fast moving solar wind protons to create thrust. Compared to a reflective solar light sail, another propellantless deep space propulsion system, the electric solar wind sail could continue to accelerate at greater distances from the Sun, still developing thrust as it cruised toward the outer planets.
Asperatus Clouds Over New Zealand (2016-04-17)

What kind of clouds are these? Although their cause is presently unknown, such unusual atmospheric structures, as menacing as they might seem, do not appear to be harbingers of meteorological doom. Known informally as Undulatus asperatus clouds, they can be stunning in appearance, unusual in occurrence, are relatively unstudied, and have even been suggested as a new type of cloud. Whereas most low cloud decks are flat bottomed, asperatus clouds appear to have significant vertical structure underneath. Speculation therefore holds that asperatus clouds might be related to lenticular clouds that form near mountains, or mammatus clouds associated with thunderstorms, or perhaps a foehn wind -- a type of dry downward wind that flows off mountains. Such a wind called the Canterbury arch streams toward the east coast of New Zealand's South Island. The featured image, taken above Hanmer Springs in Canterbury, New Zealand, in 2005, shows great detail partly because sunlight illuminates the undulating clouds from the side.   Follow APOD on: Facebook,  Google Plus,  Instagram, or Twitter

Image credit: Witta Priester
The International Space Station over Earth (2016-04-18)

The International Space Station is the largest object ever constructed by humans in space.  The station perimeter extends over roughly the area of a football field, although only a small fraction of this is composed of modules habitable by humans. The station is so large that it could not be launched all at once -- it continues to be built piecemeal.  To function, the ISS needs huge trusses, some over 15 meters long and with masses over 10,000 kilograms, to keep it rigid and to route electricity and liquid coolants.  Pictured above, the immense space station was photographed from the now-retired space shuttle Atlantis after a week-long stay in 2010. Across the image top hangs part of a bright blue Earth, in stark contrast to the darkness of interstellar space across the bottom.
Andromeda on the Rocks (2016-04-19)

How far can you see? The Andromeda Galaxy 2.5 million light years away is the most distant object easily seen by the unaided eye. Other apparent denizens of the night sky, stars, clusters, and nebulae, typically range from a few hundred to a few thousand light-years away and lie well within our own Milky Way Galaxy. Also known as M31, the Andromeda Galaxy is the faint smudge near top center of this Earth and skyscape, taken from eastern Italy, near Monte Conero on the Adriatic sea coast. From a few centimeters to a few million light-years, the picture demonstrates a stunning range of vision. Though galaxy and seaside rocks could be seen with the eye on that clear summer night, no camera captured this view in a single exposure. Because the stars trailed above the horizon while the picture was made, separate exposures tracking the stars were combined with one of rocks and cliffs made with the camera steadied to create the tantalizing scene.

Image credit: Cristian Fattinnanzi
Galaxy Einstein Ring (2016-04-20)

Can one galaxy hide behind another?  Not in the case of SDP.81.  Here the foreground galaxy, shown in blue in an image taken by the Hubble Space Telescope, acts like a huge gravitational lens, pulling light from a background galaxy, shown in red in an image taken in radio waves by the Atacama Large Millimeter Array (ALMA), around it, keeping it visible.  The alignment is so precise that the distant galaxy is distorted into part of a ring around the foreground galaxy, a formation known as an Einstein ring.  Detailed analysis of the gravitational lens distortions indicate that a small dark satellite galaxy participates in the deflections, bolstering indication that many satellite galaxies are quite dim and dominated by dark matter.  That small galaxy is depicted by a small white dot on the left. Although spanning only a few arcseconds, the featured Einstein ring is really tens of thousands of light years across.   Comments, questions? Just click the Discuss link two lines below.
The Comet, the Owl, and the Galaxy (2016-04-21)

Comet C/2014 S2 (PanSTARRS) poses for a Messier moment in this telescopic snapshot from April 18. In fact it shares the 1.5 degree wide field-of-view with two well-known entries in the 18th century comet-hunting astronomer's famous catalog. Outward bound and sweeping through northern skies just below the Big Dipper, the fading visitor to the inner Solar System was about 18 light-minutes from our fair planet. Dusty, edge-on spiral galaxy Messier 108 (upper right) is more like 45 million light-years away. A planetary nebula with an aging but intensely hot central star, the owlish Messier 97 is only about 12 thousand light-years distant though, still well within our own Milky Way galaxy. Astronomers expect the orbit of this comet PanSTARRS to return it to the inner Solar System around the year 4226.

Image credit: Bob Franke
NGC 7635: The Bubble Nebula (2016-04-22)

Blown by the wind from a massive star, this interstellar apparition has a surprisingly familiar shape. Cataloged as NGC 7635, it is also known simply as The Bubble Nebula. Although it looks delicate, the 7 light-year diameter bubble offers evidence of violent processes at work. Above and left of the Bubble's center is a hot, O-type star, several hundred thousand times more luminous and around 45 times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula and associated cloud complex lie a mere 7,100 light-years away toward the boastful constellation Cassiopeia. This sharp, tantalizing view of the cosmic bubble is a composite of Hubble Space Telescope image data from 2016, released to celebrate the 26th anniversary of Hubble's launch.  Celebrate: Planet Earth Day
Milky Way in Moonlight (2016-04-23)

A waning crescent moon, early morning twilight, and Al Hamra's city lights on the horizon can't hide the central Milky Way in this skyscape from planet Earth. Captured in a single exposure, the dreamlike scene looks southward across the region's grand canyon from Jabal Shams (Sun Mountain), near the highest peak in Oman, on the Arabian Peninsula. Mist, moonlight, and shadows still play along the steep canyon walls. Dark rifts along the luminous band of the Milky Way are the galaxy's cosmic dust clouds. Typically hundreds of light-years distant, they obscure starlight along the galactic plane, viewed edge-on from the Solar System's perspective.

Image credit: Babak Tafreshi
M16: Pillars of Star Creation (2016-04-24)

Newborn stars are forming in the Eagle Nebula.  This image, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs) emerging from pillars of molecular hydrogen gas and dust.  The giant pillars are light years in length and are so dense that interior gas contracts gravitationally to form stars.  At each pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed.  The Eagle Nebula, associated with the open star cluster M16, lies about 7000 light years away.  The pillars of creation were imaged again in 2007 by the orbiting Spitzer Space Telescope in infrared light, leading to the conjecture that the pillars may already have been destroyed by a local supernova, but light from that event has yet to reach the Earth.   Be Honest: Have you seen this image before?
Supernova Remnant Simeis 147: The Spaghetti Nebula (2016-04-25)

It's easy to get lost following the intricate strands of the Spaghetti Nebula. A supernova remnant cataloged as Simeis 147 and Sh2-240, the glowing gas filaments cover nearly 3 degrees -- 6 full moons -- on the sky.  That's about 150 light-years at the stellar debris cloud's estimated distance of 3,000 light-years. This sharp composite includes image data taken through a narrow-band filter to highlight emission from hydrogen atoms tracing the shocked, glowing gas. The supernova remnant has an estimated age of about 40,000 years, meaning light from the massive stellar explosion first reached Earth about 40,000 years ago. But the expanding remnant is not the only aftermath. The cosmic catastrophe also left behind a spinning neutron star or pulsar, all that remains of the original star's core.

Image credit: Giuseppe Donatiello (Italy) and Tim Stone (USA)
NGC 6872: A Stretched Spiral Galaxy (2016-04-26)

What makes this spiral galaxy so long?  Measuring over 700,000 light years across from top to bottom, NGC 6872, also known as the Condor galaxy, is one of the most elongated  barred spiral galaxies known.  The galaxy's protracted shape likely results from its continuing collision with the smaller galaxy IC 4970, visible just above center.  Of particular interest is NGC 6872's spiral arm on the upper left, as pictured here, which exhibits an unusually high amount of blue star forming regions.  The light we see today left these colliding giants before the days of the dinosaurs, about 300 million years ago.  NGC 6872 is visible with a small telescope toward the constellation of the Peacock (Pavo).
Omega Centauri: The Brightest Globular Star Cluster (2016-04-27)

This huge ball of stars predates our Sun. Long before humankind evolved, before dinosaurs roamed, and even before our Earth existed, ancient globs of stars condensed and orbited a young Milky Way Galaxy. Of the 200 or so globular clusters that survive today, Omega Centauri is the largest, containing over ten million stars. Omega Centauri is also the brightest globular cluster, at apparent visual magnitude 3.9 it is visible to southern observers with the unaided eye. Cataloged as NGC 5139, Omega Centauri is about 18,000 light-years away and 150 light-years in diameter.  Unlike many other globular clusters, the stars in Omega Centauri show several different ages and trace chemical abundances, indicating that the globular star cluster has a complex history over its 12 billion year age.

Image credit: Roberto Colombari
A Dust Angel Nebula (2016-04-28)

The combined light of stars along the Milky Way are reflected by these cosmic dust clouds that soar some 300 light-years or so above the plane of our galaxy. Dubbed the Angel Nebula, the faint apparition is part of an expansive complex of dim and relatively unexplored, diffuse molecular clouds. Commonly found at high galactic latitudes, the dusty galactic cirrus can be traced over large regions toward the North and South Galactic poles. Along with the refection of starlight, studies indicate the dust clouds produce a faint reddish luminescence, as interstellar dust grains convert invisible ultraviolet radiation to visible red light. Also capturing nearby Milky Way stars and an array of distant background galaxies, the deep, wide-field 3x5 degree image spans about 10 Full Moons across planet Earth's sky toward the constellation Ursa Major.

Image credit: Rogelio Bernal
Andreo
Fermi's Gamma-ray Moon (2016-04-29)

If you could only see gamma-rays, photons with up to a billion or more times the energy of visible light, the Moon would be brighter than the Sun! That startling notion underlies this novel image of the Moon, based on data collected by the Fermi Gamma-ray Space Telescope's Large Area Telescope (LAT) instrument during its first seven years of operation (2008-2015). Fermi's gamma-ray vision doesn't distinguish details on the lunar surface, but a gamma-ray glow consistent with the Moon's size and position is clearly found at the center of the false color map. The brightest pixels correspond to the most significant detections of lunar gamma-rays. Why is the gamma-ray Moon so bright? High-energy charged particles streaming through the Solar System known as cosmic rays constantly bombard the lunar surface, unprotected by a magnetic field, generating the gamma-ray glow. Because the cosmic rays come from all sides, the gamma-ray Moon is always full and does not go through phases. The first gamma-ray image of the Moon was captured by the EGRET instrument onboard the Compton Gamma-ray Observatory, launched 25 years ago.
Moon over Makemake (2016-04-30)

Makemake, second brightest dwarf planet of the Kuiper belt, has a moon. Nicknamed MK2, Makemake's moon reflects sunlight with a charcoal-dark surface, about 1,300 times fainter than its parent body. Still, it was spotted in Hubble Space Telescope observations intended to search for faint companions with the same technique used to find the small satellites of Pluto. Just as for Pluto and its satellites, further observations of Makemake and orbiting moon will measure the system's mass and density and allow a broader understanding of the distant worlds. About 160 kilometers (100 miles) across compared to Makemake's 1,400 kilometer diameter, MK2's relative size and contrast are shown in this artist's vision. An imagined scene of an unexplored frontier of the Solar System, it looks back from a spacecraft's vantage as the dim Sun shines along the Milky Way. Of course, the Sun is over 50 times farther from Makemake than it is from planet Earth.
Contemplating the Sun (2016-05-01)

Have you contemplated your home star recently? Featured here, a Sun partially eclipsed on the top left by the Moon is also seen eclipsed by earthlings contemplating the eclipse below. The spectacular menagerie of silhouettes was taken in 2012 from the Glen Canyon National Recreation Area near Page, Arizona, USA, where park rangers and astronomers expounded on the unusual event to interested gatherers. Also faintly visible on the Sun's disk, just to the lower right of the dark Moon's disk, is a group of sunspots.  Although a partial solar eclipse by the Moon is indeed a good chance to contemplate the Sun, a great chance -- and one that is significantly more rare -- will occur next week when the Sun undergoes a partial eclipse by the planet Mercury.

Image credit: Steven Gilbert
Crossing Mars (2016-05-02)

Where is NASA's rover Curiosity going on Mars? Its geographical goals are on the slopes of Mount Sharp, whose peak is seen in the background on the right.  A key scientific goal, however, remains to better assess when and where conditions on Mars were once suitable for life, in particular microbial life.  To further this goal, Curiosity was directed to cross the rugged terrain of Nautkluft Plateau, visible in the featured image on the foreground left.  Curiosity is crossing toward smoother uphill sites with rocks containing hematite and sulfates, sites that could give the rolling rover new clues on how long this part of Mars was wet -- and hence more favorable for life -- before drying out.  Of recent concern, however, is Curiosity's aluminum wheels, which are showing increasing signs of wear.  Although already fulfilling the goals of its two year study, Curiosity's mission has been extended as it continues to uncover valuable information about the extraordinary past of Mars, the next planet out from the Sun from Earth.
Aurora over Sweden (2016-05-03)

It was bright and green and stretched across the sky. This striking aurora display was captured last month just outside of �stersund, Sweden. Six photographic fields were merged to create the featured panorama spanning almost 180 degrees.  Particularly striking aspects of this aurora include its sweeping arc-like shape and its stark definition.  Lake Storsj�n is seen in the foreground, while several familiar constellations and the star Polaris are visible through the aurora, far in the background.  Coincidently, the aurora appears to avoid the Moon visible on the lower left.  The aurora appeared a day after a large hole opened in the Sun's corona allowing particularly energetic particles to flow out into the Solar System.  The green color of the aurora is caused by oxygen atoms recombining with ambient electrons high in the Earth's atmosphere.

Image credit: Göran Strand
A Mercury Transit Sequence (2016-05-04)

This coming Monday, Mercury will cross the face of the Sun, as seen from Earth. Called a transit, the last time this happened was in 2006.  Because the plane of Mercury's orbit is not exactly coincident with the plane of Earth's orbit, Mercury usually appears to pass over or under the Sun.  The above time-lapse sequence, superimposed on a single frame, was taken from a balcony in Belgium shows the entire  transit of 2003 May 7.  The solar crossing lasted over five hours, so that the above 23 images were taken roughly 15 minutes apart.  The north pole of the Sun, the Earth's orbit, and Mercury's orbit, although all different, all occur in directions slightly above the left of the image. Near the center and on the far right, sunspots are visible. After Monday, the next transit of Mercury will occur in 2019.   NASA Coverage: 2016 May 9 Mercury Transit of the Sun

Image credit: Dominique Dierick
The SONG and the Hunter (2016-05-05)

Near first quarter, the Moon in March lights this snowy, rugged landscape, a view across the top of Tenerife toward La Palma in the Canary Islands Spanish archipelago. The large Teide volcano, the highest point in Spain, looms over the horizon. Shining above are familiar bright stars of Orion, the Hunter. Adding to the dreamlike scene is the 1 meter diameter prototype telescope of the global network project called the Stellar Observations Network Group or SONG. The SONG's fully robotic observatory was captured during the 30 second exposure while the observatory dome, with slit open, was rotated across the field of view.

Image credit: Mads
Fredslund Andersen
NGC 7023: The Iris Nebula (2016-05-06)

These cosmic clouds have blossomed 1,300 light-years away, in the fertile starfields of the constellation Cepheus. Called the Iris Nebula, NGC 7023 is not the only nebula to evoke the imagery of flowers, though. Still, this deep telescopic image shows off the Iris Nebula's range of colors and symmetries, embedded in surrounding fields of interstellar dust. Within the Iris itself, dusty nebular material surrounds a hot, young star. The dominant color of the brighter reflection nebula is blue, characteristic of dust grains reflecting starlight. Central filaments of the reflection nebula glow with a faint reddish photoluminesence as some dust grains effectively convert the star's invisible ultraviolet radiation to visible red light. Infrared observations indicate that this nebula contains complex carbon molecules known as PAHs. The pretty blue petals of the Iris Nebula span about six light-years. The colorful field-of-view stretches almost five Full Moons across the sky.

Image credit: Federico Pelliccia
Three Worlds for TRAPPIST-1 (2016-05-07)

Three new found worlds orbit the ultracool dwarf star TRAPPIST-1, a mere 40 light-years away. Their transits were first detected by the Belgian robotic TRAnsiting Planets and Planetesimals Small Telescope, TRAPPIST, at ESO's La Silla Observatory in Chile. The newly discovered exoplanets are all similar in size to Earth. Because they orbit very close to their faint, tiny star they could also have regions where surface temperatures allow for the presence of liquid water, a key ingredient for life. Their tantalizing proximity to Earth makes them prime candidates for future telescopic explorations of the atmospheres of these potentially habitable planets.  All three worlds appear in this artist's vision, an imagined scene near the horizon of the system's outermost planet. Of course, the inner planet is transiting the dim, red, nearly Jupiter-sized parent star.
Mercury's Transit: An Unusual Spot on the Sun (2016-05-08)

What's that dot on the Sun? If you look closely, it is almost perfectly round.  The dot is the result of an unusual type of solar eclipse that occurred in 2006.  Usually it is the Earth's Moon that eclipses the Sun.  This time, the planet Mercury took a turn.  Like the approach to New Moon before a solar eclipse, the phase of Mercury became a continually thinner crescent as the planet progressed toward an alignment with the Sun.  Eventually the phase of Mercury dropped to zero and the dark spot of Mercury crossed our parent star.  The situation could technically be labeled a Mercurian annular eclipse with an extraordinarily large ring of fire.  From above the cratered planes of the night side of Mercury, the Earth appeared in its fullest phase.  Hours later, as Mercury continued in its orbit, a slight crescent phase appeared again.  This was ten years ago -- the next Mercurian solar eclipse will occur tomorrow.   NASA Coverage: Tomorrow's Transit of Mercury across the Sun

Image credit: David Cortner
Webb Telescope Mirror Rises after Assembly (2016-05-09)

Move over Hubble -- here comes the James Webb Space Telescope (JWST). JWST promises to be the new most powerful telescope in space.  In the last month, the 18-segment gold-plated primary mirror for JWST was unveiled. In the featured time-lapse video taken last week, the 6.5-meter diameter mirror was raised to a vertical position.  The dramatic 30-second sequence shows NASA engineers monitoring the test as room lights glint brightly off the mirror's highly reflective surface.  The beryllium mirrors have been coated with a thin film of gold to make them more reflective to infrared light.  The science goals of JWST include studying the workings of the early universe and the properties of planets orbiting nearby stars.  Because of the mirror's great size, it will be folded for launch and then, assuming all goes as planned, dramatically unfolded again in space.  The JWST, a joint mission of the space agencies of the USA, Europe, and Canada, is currently scheduled to be launched in late 2018.    NASA Coverage: Today's Transit of Mercury across the Sun
Saturn and Mars visit Milky Way Star Clouds (2016-05-10)

Planets, stars, nebulas and a galaxy -- this impressive image has them all. Closest to home are the two planets Mars (right) and Saturn (center), visible as the two bright orange spots in the upper half of the featured image. On the central right are the colorful Rho Ophiuchus star clouds featuring the bright orange star Antares lined up below Mars.  These interstellar clouds contain both red emission nebulas and blue reflection nebulas.  At the top right of the image is the Blue Horsehead reflection nebula. On the lower left are many dark absorption nebulas that extend from the central band of our Milky Way Galaxy. The featured deep composite was composed of multiple deep exposures taken last month from Brazil.  Although you need a telescope to see the nebulosities, Saturn and Mars will remain visible to the unaided eye this month toward the east, just after sunset.    Follow APOD on: Facebook,  Google Plus,  Instagram, or Twitter

Image credit: Carlos Eduardo Fairbairn ;
 Rollover Annotation:  Judy Schmidt