juliensimon/nasa-apod huggingface dataset:
Seasonal Streaks Point to Recent Flowing Water on Mars (2015-09-30)

What creates these changing streaks on Mars? Called Recurring Slope Linea (RSL), these dark features start on the slopes of hills and craters but don't usually extend to the bottom. What's even more unusual is that these streaks appear to change with the season, appearing fresh and growing during warm weather and disappearing during the winter. After much study, including a recent chemical analyses, a leading hypothesis has emerged that these streaks are likely created by new occurrences of liquid salty water that evaporates as it flows. The source for the briny water is still unclear, with two possibilities being condensation from the Martian atmosphere and underground reservoirs. An exciting inference is that if these briny flows are not too salty, they may be able to support microbial life on Mars even today. The featured image of a hill inside Horowitz Crater was investigated by instruments aboard the robotic Mars Reconnaissance Orbiter that has been returning data from Mars since 2006.   Retrospective: Today in APOD History
Eclipsed in Southern Skies (2015-10-01)

This stunning panorama in southern skies was recorded on the colorful night of September 27/28 from Carnegie Las Campanas Observatory. A diffuse glow and dark rifts of the central Milky Way hang over domes of the twin 6.5 meter Magellan telescopes. But most eye-catching is the deep red glow of the Moon. Immersed in Earth's shadow during the much anticipated perigee-total-lunar eclipse, the Moon's surface reflects the light of sunsets and sunrises scattered and refracted into the planet's cone-shaped umbra. Along with the dramatic hue of the eclipsed Moon, other colors of that night captured by the sensitive digital camera include the red and green shades of atmospheric airglow. Viewers can also spot the Andromeda Galaxy below the Moon, seen as a tiny smudge through the reddish airglow and lights along the horizon. The Magellanic Clouds, satellite galaxies of the Milky Way, join in at the far left of the full panorama frame.

Image credit: Yuri Beletsky
Charon: Moon of Pluto (2015-10-02)

A darkened and mysterious north polar region informally known as Mordor Macula caps this premier high-resolution portrait of Charon, Pluto's largest moon. Captured by New Horizons near its closest approach on July 14, the image data was transmitted to Earth on September 21. The combined blue, red, and infrared data is processed to enhance colors, following variations in surface properties with a resolution of about 2.9 kilometers (1.8 miles). In fact, Charon is 1,214 kilometers (754 miles) across, about 1/10th the size of planet Earth but a whopping 1/2 the diameter of Pluto itself. That makes it the largest satellite relative to its planet in the solar system. This remarkable image of Charon's Pluto-facing hemisphere shows a clearer view of an apparently moon-girdling belt of fractures and canyons that seems to separate smooth southern plains from varied northern terrain.
A Blue Blood Moon (2015-10-03)

This sharp telescopic snapshot caught late September's Harvest Moon completely immersed in Earth's dark umbral shadow, at the beginning of a total lunar eclipse. It was the final eclipse in a tetrad, a string of four consecutive total lunar eclipses. A dark apparition of the Full Moon near perigee, this total eclipse's color was a deep blood red, the lunar surface reflecting light within Earth's shadow filtered through the lower atmosphere. Seen from a lunar perspective, the reddened light comes from all the sunsets and sunrises around the edges of a silhouetted Earth. But close to the shadow's edge, the limb of the eclipsed Moon shows a distinct blue hue. The blue eclipsed moonlight is still filtered through Earth's atmosphere though, originating as rays of sunlight pass through layers high in the upper stratosphere, colored by ozone that scatters red light and transmits blue.

Image credit: Dominique Dierick
The Sombrero Galaxy in Infrared (2015-10-04)

This floating ring is the size of a galaxy.  In fact, it is a galaxy -- or at least part of one: the photogenic Sombrero Galaxy, one of the largest galaxies in the nearby Virgo Cluster of Galaxies.  The dark band of dust that obscures the mid-section of the Sombrero Galaxy in optical light actually glows brightly in infrared light.  The above image, digitally sharpened, shows the infrared glow, recently recorded by the orbiting Spitzer Space Telescope, superposed in false-color on an existing image taken by NASA's Hubble Space Telescope in optical light. The Sombrero Galaxy, also known as M104, spans about 50,000 light years across and lies 28 million light years away.  M104 can be seen with a small telescope in the direction of the constellation Virgo.
Orion Over and Under Tibet (2015-10-05)

This night was so serene you could see Orion rise downwards. The unusual spectacle was captured in this single-exposure image, featuring a deep sky around the famous constellation of Orion that appeared both above -- and reflected in -- a peaceful lake in the Gyirong Valley of Tibet, China.  Taken last year at this time, the three belt stars of Orion can be seen lined up almost vertically above and below the Himalayan Mountains. The complex Orion Nebula can be seen to the belt stars' right, while the red-glowing circular structure surrounding Orion is Barnard's Loop.  Also, the bright red star Betelgeuse is doubly visible on the image left, while bright blue Rigel appears twice on the image right. Familiar Orion is becoming increasingly visible as Winter (Summer) descends on the Northern (Southern) hemisphere.   Follow APOD on: Facebook,  Google Plus, or Twitter

Image credit: Jeff Dai
Flying Past Pluto (2015-10-06)

What would it look like to fly past Pluto? The robotic New Horizons spacecraft did just this in late July and continues to return stunning pictures of the dwarf planet.  Some well-chosen flyby images have now been digitally sequenced to create the featured video.  The animation begins by showing New Horizon's approach to the Pluto system, with Pluto and its largest moon Charon orbiting a common center of mass.  As the spacecraft bears down on Pluto uniquely, surprising surface features are nearly resolved that, unfortunately, quickly rotate out of view. New Horizons then passes just above and near a large, fascinating, light-colored, heart-shaped, and unusually smooth region now known as Tombaugh Regio.  The spacecraft then pivots to look back at Pluto's night side, seeing an encompassing atmospheric haze.  Finally, Pluto fades away in a final sequence illustrated with the orbits of many of Pluto's smaller moons. Although humanity has no current plans to return to Pluto, the New Horizons spacecraft may well be directed next to fly past an asteroid currently known only as 2014 MU69.
La Palma Eclipse Sequence (2015-10-07)

At left, a dramatic image sequence follows late September's total lunar eclipse above a rugged landscape and sea of clouds from the Canary island of La Palma. Composited in a circular fisheye projection, the brightness of the Full Perigee Moon changes drastically in transition from outside the total eclipse phase compared to its dim glow during the 72 minute long totality. At right, a single frame captures the dark red lunar disk in a moment during the total eclipse phase, the Moon deep within Earth's shadow. In fact, the size of the eclipsed Moon image at right approximately illustrates the relative size of Earth and Moon, when compared to the circular projection of the eclipse sequence.

Image credit: Miguel Claro
M83: The Thousand-Ruby Galaxy (2015-10-08)

Big, bright, and beautiful, spiral galaxy M83 lies a mere twelve million light-years away, near the southeastern tip of the very long constellation Hydra. Prominent spiral arms traced by dark dust lanes and blue star clusters lend this galaxy its popular name, The Southern Pinwheel.  But reddish star forming regions that dot the sweeping arms highlighted in this sparkling color composite also suggest another nickname, The Thousand-Ruby Galaxy. About 40,000 light-years across, M83 is a member of a group of galaxies that includes active galaxy Centaurus A. In fact, the core of M83 itself is bright at x-ray energies, showing a high concentration of neutron stars and black holes left from an intense burst of star formation. This sharp composite color image also features spiky foreground Milky Way stars and distant background galaxies. The image data was taken from the Subaru Telescope, the European Southern Observatory's Wide Field Imager camera, and the Hubble Legacy Archive.

Image credit: Robert Gendler
The Moon Entering Earth's Shadow (2015-10-09)

On September 27/28, from all over the planet's nightside moon watchers enjoyed a total lunar eclipse. The dramatic celestial spectacle was widely imaged, but this lunar eclipse picture may look a little strange and unfamiliar, made with a point and shoot camera of a bygone era. Loaded with a 4x5 inch sheet of film, the Speed Graphic camera was fixed to a tripod on the Island of Cyprus. Its shutter locked open for 90 minutes, it recorded the trail of the Full Moon at perigee from the beginning of the partial eclipse phase (top) until mid-totality found the Moon near the western horizon. Entering Earth's shadow, the Moon grew dimmer and its moontrail narrower as the eclipse progressed.

Image credit: Thodoris
Tzalavras
Stardust in Perseus (2015-10-10)

This cosmic expanse of dust, gas, and stars covers some 6 degrees on the sky in the heroic constellation Perseus. At upper left in the gorgeous skyscape is the intriguing young star cluster IC 348 and neighboring Flying Ghost Nebula. At right, another active star forming region NGC 1333 is connected by dark and dusty tendrils on the outskirts of the giant Perseus Molecular Cloud, about 850 light-years away. Other dusty nebulae are scattered around the field of view, along with the faint reddish glow of hydrogen gas. In fact, the cosmic dust tends to hide the newly formed stars and young stellar objects or protostars from prying optical telescopes. Collapsing due to self-gravity, the protostars form from the dense cores embedded in the dusty molecular cloud. At the molecular cloud's estimated distance, this field of view would span almost 90 light-years.

Image credit: Lynn Hilborn
In the Center of the Trifid Nebula (2015-10-11)

Clouds of glowing gas mingle with dust lanes in the Trifid Nebula, a star forming region toward the constellation of the Archer (Sagittarius).  In the center, the three prominent dust lanes that give the Trifid its name all come together. Mountains of opaque dust appear on the right, while other dark filaments of dust are visible threaded throughout the nebula.  A single massive star visible near the center causes much of the Trifid's glow.  The Trifid, also known as M20, is only about 300,000 years old, making it among the youngest emission nebulae known.  The nebula lies about 9,000 light years away and the part pictured here spans about 10 light years.  The above image is a composite with luminance taken from an image by the 8.2-m ground-based Subaru Telescope, detail provided by the 2.4-m orbiting Hubble Space Telescope, color data provided by Martin Pugh and image assembly and processing provided by Robert Gendler.   Follow APOD on: Facebook,  Google Plus, or Twitter
Galaxy, Stars, and Dust (2015-10-12)

Spiky stars and spooky shapes abound in this deep cosmic skyscape. Its well-composed field of view covers about a Full Moon on the sky toward the constellation Pegasus. Of course the brighter stars show diffraction spikes, the commonly seen effect of internal supports in reflecting telescopes, and lie well within our own Milky Way galaxy. The faint but pervasive clouds of interstellar dust ride above the galactic plane and dimly reflect the Milky Way's combined starlight. Known as high latitude cirrus or integrated flux nebulae they are associated with molecular clouds. In this case, the diffuse cloud cataloged as MBM 54, less than a thousand light-years distant, fills the scene. The galaxy seemingly tangled in the dust is the striking spiral galaxy NGC 7497 some 60 million light-years away. Seen almost edge-on near the center of the field, NGC 7497's own spiral arms and dust lanes echo the colors of the Milky Way's stars and dust.   Astrophysicists: Browse 1,100+ codes in the Astrophysics Source Code Library

Image credit: Eric Coles and Mel Helm
The Elephant's Trunk in IC 1396 (2015-10-13)

Like an illustration in a galactic Just So Story, the Elephant's Trunk Nebula winds through the emission nebula and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Of course, the cosmic elephant's trunk is over 20 light-years long. This composite was recorded through narrow band filters that transmit the light from ionized hydrogen, sulfur, and oxygen atoms in the region. The resulting image highlights the bright swept-back ridges that outline pockets of cool interstellar dust and gas. Such embedded, dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within the obscuring cosmic dust. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning over 5 degrees.

Image credit: J.C. Canonne, P. Bernhard, 
D. Chaplain & L. Bourgon
A Gegenschein Lunar Eclipse (2015-10-14)

Is there anything interesting to see in the direction opposite the Sun? One night last month, there were quite a few things. First, the red-glowing orb on the lower right of the featured image is the full moon, darkened and reddened because it has entered Earth's shadow. Beyond Earth's cone of darkness are backscattering dust particles orbiting the Sun that standout with a diffuse glow called the gegenschein, visible as a faint band rising from the central horizon and passing behind the Moon. A nearly horizontal stripe of green airglow is also discernable just above the horizon, partly blocked by blowing orange sand.  Visible in the distant sky as the blue dot near the top of the image is the star Sirius, while the central band of our Milky Way Galaxy arches up on the image left and down again on the right. The fuzzy light patches just left of center are the Large and Small Magellanic Clouds. Red emission nebulas too numerous to mention are scattered about the sky, but are labelled in a companion annotated image.  In the image foreground is the desolate Deadvlei region of the Namib-Naukluft National Park in Namibia, featuring the astrophotographer himself surveying a land and sky so amazing that he described it as one of the top experiences of his life.    Quiz: Astronomy Picture of the Day Caption or Harlequin Novel?

Image credit: Petr Hor�lek;
 Rollover Annotation:  Judy Schmidt
M16 and the Eagle Nebula (2015-10-15)

A star cluster around 2 million years young surrounded by natal clouds of dust and glowing gas, M16 is also known as The Eagle Nebula. This beautifully detailed image of the region includes cosmic sculptures made famous in Hubble Space Telescope close-ups of the starforming complex. Described as elephant trunks or Pillars of Creation, dense, dusty columns rising near the center are light-years in length but are gravitationally contracting to form stars. Energetic radiation from the cluster stars erodes material near the tips, eventually exposing the embedded new stars. Extending from the ridge of bright emission left of center is another dusty starforming column known as the Fairy of Eagle Nebula. M16 and the Eagle Nebula lie about 7,000 light-years away, 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: Jimmy Walker
Night Hides the World (2015-10-16)

Stars come out as evening twilight fades in this serene skyscape following the Persian proverb "Night hides the world, but reveals a universe." The scene finds the Sun setting over northern Kenya and the night will soon hide the shores of Lake Turkana, home to many Nile crocodiles. The region is also known for its abundance of hominid fossils. On that past November night, a brilliant Venus, then the world's evening star, dominates the starry skies above. But also revealed are faint stars, cosmic dust clouds, and glowing nebulae along the graceful arc of our own Milky Way galaxy.

Image credit: Babak Tafreshi
Bright Spiral Galaxy M81 (2015-10-17)

One of the brightest galaxies in planet Earth's sky is similar in size to our Milky Way Galaxy: big, beautiful M81. The grand spiral galaxy can be found toward the northern constellation of the Great Bear (Ursa Major). This superbly detailed image reveals M81's bright yellow nucleus, blue spiral arms, tell tale pinkish star forming regions, and sweeping cosmic dust lanes with a scale comparable to the Milky Way. Hinting at a disorderly past, a remarkable dust lane actually runs straight through the disk, to the left of the galactic center, contrary to M81's other prominent spiral features. The errant dust lane may be the lingering result of a close encounter between between M81 and its smaller companion galaxy, M82. Scrutiny of variable stars in M81 has yielded one of the best determined distances for an external galaxy -- 11.8 million light-years. M81's dwarf companion galaxy Holmberg IX can be seen just above the large spiral.

Image credit: Ken Crawford
Mammatus Clouds Over Saskatchewan (2015-10-18)

Why is this cloud so bubbly?  Normally, cloud bottoms are flat. The flatness is caused by moist warm air that rises and cools and so condenses into water droplets at a specific temperature, which usually corresponds to a very specific height.  As water droplets grow, an opaque cloud forms.  Under some conditions, however, cloud pockets can develop that contain large droplets of water or ice that fall into clear air as they evaporate.  Such pockets may occur in turbulent air near a thunderstorm.  Resulting mammatus clouds can appear especially dramatic if sunlit from the side.  These mammatus clouds were photographed over Regina, Saskatchewan, Canada during the summer of 2012.
The Southern Cross in a Southern Sky (2015-10-19)

Have you ever seen the Southern Cross? This famous constellation is best seen from Earth's Southern Hemisphere. Captured from Rio de Janeiro, Brazil, the four bright stars that mark the Southern Cross are visible just above the horizon in the featured image. On the left of this constellation, also known as The Crux, is the orange star Gamma Crucis.  The band of stars, dust, and gas rising through the middle of the image mosaic is part our Milky Way Galaxy.  Just to the right of the Southern Cross is the dark Coal Sack Nebula, and the bright nebula at the top of the image is the Carina Nebula.  The Southern Cross is such a famous constellation that it is depicted on the national flags of Australia and New Zealand.   Follow APOD on: Facebook,  Google Plus, or Twitter

Image credit: Carlos Fairbairn
When Black Holes Collide (2015-10-20)

What happens when two black holes collide? This extreme scenario likely occurs in the centers of some merging galaxies and multiple star systems. The featured video shows a computer animation of the final stages of such a merger, while highlighting the gravitational lensing effects that would appear on a background starfield. The black regions indicate the event horizons of the dynamic duo, while a surrounding ring of shifting background stars indicates the position of their combined Einstein ring. All background stars not only have images visible outside of this Einstein ring, but also have one or more companion images visible on the inside. Eventually the two black holes coalesce.  The end stages of such a merger may provide a strong and predictable blast of gravitational radiation, a much sought after form of radiation different than light that has never yet been directly observed.   Space Music Video: APOD images from September 2015

Image credit: Simulating Extreme Spacetimes
Collaboration
The Fractured North Pole of Saturn's Enceladus (2015-10-21)

The north pole of Saturn's moon Enceladus is unexpectedly fascinating and complex. Previous to the latest flyby of the robotic Cassini spacecraft, the northern region was known mostly for its unusually high abundance of craters. Last week's flyby, however, returned images of unprecedented detail, including the featured image showing the expected craters coupled with an unexpected and circuitous pattern of picturesque cracks and fractures.  Broken terrain has been recorded at lower latitudes, with deep canyons dubbed Tiger Stripes near Enceladus' South Pole. The fractures may further indicate global interplay between the surface and potential seas underneath, seas that future missions might target for signs of life.   Retrospective: Today in APOD History
Star Factory Messier 17 (2015-10-22)

Sculpted by stellar winds and radiation, the star factory known as Messier 17 lies some 5,500 light-years away in the nebula-rich constellation Sagittarius. At that distance, this 1/3 degree wide field of view spans over 30 light-years. The sharp composite, color image, highlights faint details of the region's gas and dust clouds against a backdrop of central Milky Way stars. Stellar winds and energetic light from hot, massive stars formed from M17's stock of cosmic gas and dust have slowly carved away at the remaining interstellar material producing the cavernous appearance and undulating shapes. M17 is also known as the Omega Nebula or the Swan Nebula.

Image credit: ESO
Starburst Galaxy Messier 94 (2015-10-23)

Beautiful island universe Messier 94 lies a mere 15 million light-years distant in the northern constellation of the hunting dogs, Canes Venatici. A popular target for earth-based astronomers, the face-on spiral galaxy is about 30,000 light-years across, with spiral arms sweeping through the outskirts of its broad disk. But this Hubble Space Telescope field of view spans about 7,000 light-years or so across M94's central region. The sharp close-up examines the galaxy's compact, bright nucleus and prominent inner dust lanes, surrounded by a remarkable bluish ring of young, massive stars. The massive stars in the ring are all likely less than 10 million years old, indicating the galaxy experienced a well-defined era of rapid star formation. As a result, while the small, bright nucleus is typical of the Seyfert class of active galaxies, M94 is also known as a starburst galaxy. Because M94 is relatively nearby, astronomers can explore in detail reasons for the galaxy's burst of star formation.
Jupiter in 2015 (2015-10-24)

Two remarkable global maps of Jupiter's banded cloud tops can be compared by just sliding your cursor over this sharp projection (or follow this link) of image data from the Hubble Space Telescope. Both captured on January 19, during back-to-back 10 hour rotations of the ruling gas giant, the all-planet projections represent the first in a series of planned annual portraits by the Outer Planet Atmospheres Legacy program.  Comparing the two highlights cloud movements and measures wind speeds in the planet's dynamic atmosphere. In fact, the Great Red Spot, the famous long-lived swirling storm boasting 300 mile per hour winds, is seen sporting a rotating, twisting filament. The images confirm that Great Red Spot is still shrinking, though still larger than planet Earth. Posing next to it (lower right) is Oval BA, also known as Red Spot Junior.
Jupiter and Venus from Earth (2015-10-25)

It was visible around the world. The sunset conjunction of Jupiter and Venus in 2012 was visible almost no matter where you lived on Earth.  Anyone on the planet with a clear western horizon at sunset could see them. Pictured above in 2012, a creative photographer traveled away from the town lights of Szubin, Poland to image a near closest approach of the two planets. The bright planets were separated only by three degrees and his daughter striking a humorous pose. A faint red sunset still glowed in the background. Jupiter and Venus will be at it again this week before sunrise, passing under two degree from each other -- and even with bonus planet Mars nearby.    Follow APOD on: Facebook,  Google Plus, or Twitter

Image credit: Marek Nikodem (PPSAE)