juliensimon/nasa-apod huggingface dataset:
Field of Rosette (2010-02-14)

What surrounds the florid Rosette nebula?  To better picture this area of the sky, the famous flowery emission nebula on the far right has been captured recently in a deep and dramatic wide field image that features several other sky highlights. Designated NGC 2237, the center of the Rosette nebula is populated by the bright blue stars of open cluster NGC 2244, whose winds and energetic light are evacuating the nebula's center. Below the famous flower, a symbol of Valentine's Day, is a column of dust and gas that appears like a rose's stem but extends hundreds of light years. Across the above image, the bright blue star just left and below the center is called S Monocerotis.  The star is part of the open cluster of stars labelled NGC 2264 and known as the Snowflake cluster. To the right of S Mon is a dark pointy featured called the Cone nebula, a nebula likely shaped by winds flowing out a massive star obscured by dust. To the left of S Mon is the Fox Fur nebula, a tumultuous region created by the rapidly evolving Snowflake cluster. The Rosette region, at about 5,000 light years distant, is about twice as far away as the region surrounding S Mon. The entire field can be seen with a small telescope toward the constellation of the Unicorn (Monoceros).     Note: Take an Astronomy Class Online for Free

Image credit: Rogelio Bernal Andreo
(Deep Sky Colors)
Cassini Spacecraft Crosses Saturn's Ring Plane (2010-02-15)

If this is Saturn, where are the rings?  When Saturn's "appendages" disappeared in 1612, Galileo did not understand why.   Later that century, it became understood that Saturn's unusual protrusions were rings and that when the Earth crosses the ring plane, the edge-on rings will appear to disappear.  This is because Saturn's rings are confined to a plane many times thinner, in proportion, than a  razor blade.  In modern times, the robot Cassini spacecraft orbiting Saturn now also crosses Saturn's ring plane.  A series of plane crossing images from 2005 February was dug out of the vast online Cassini raw image archive by interested Spanish amateur Fernando Garcia Navarro.  Pictured above, digitally cropped and set in representative colors, is the striking result.  Saturn's thin ring plane appears in blue, bands and clouds in Saturn's upper atmosphere appear in gold. Since Saturn just passed its equinox, today the ring plane is pointed close to the Sun and the rings could not cast the high dark shadows seen across the top of this image, taken back in 2005. Moons appear as bumps in the rings.
Dark Shuttle Approaching (2010-02-16)

What's that approaching? Astronauts on board the International Space Station first saw it far in the distance.  Soon it enlarged to become a dark silhouette. As it came even closer, the silhouette appeared to be a spaceship. Finally, at just past 11 pm (CST) last Tuesday, the object, revealed to be the Space Shuttle Endeavour, docked as expected with the Earth-orbiting space station.  Pictured above, Endeavour was imaged near Earth's horizon as it approached, where several layers of the Earth's atmosphere were visible. Directly behind the shuttle is the mesosphere, which appears blue.  The atmospheric layer that appears white is the stratosphere, while the orange layer is Earth's Troposphere. This shuttle mission, which began with a dramatic night launch and will continue into next week, has many tasks planned. These tasks include the delivery of the Tranquility Module which includes a cupola bay window complex that may allow even better views of spaceships approaching and leaving the space station.
An Unusually Smooth Surface on Saturn's Calypso (2010-02-17)

Why is this moon of Saturn so smooth? This past weekend, humanity's Saturn-orbiting Cassini spacecraft passed as close to Saturn's small moon Calypso as it ever has, and imaged the small moon in unprecedented detail. Pictured above is an early return, raw, unprocessed image of the 20-km long irregularly shaped moon. Like its sister moon Telesto and the shepherd moon Pandora, Calypso has shown itself to be unusually smooth, much smoother than most of Saturn's larger moons. A leading hypothesis for Calypso's smoothness is that much of the moon's surface is actually a relatively loose jumble of rubble -- making Calypso a rubble-pile moon.  The loose nature of the small ice pieces allows them to fill in many small craters and other surface features. Calypso orbits Saturn always behind Saturn's much larger moon Tethys, whereas Telesto's orbit always precedes Tethys. Calypso's extremely white surface -- not unlike fresh snow -- may result from the continuous accumulation of fresh ice particles falling in from Saturn's E ring.
Vesta Near Opposition (2010-02-18)

Main belt asteroid 4 Vesta is at its brightest now. The small world is near opposition (opposite the Sun in the sky) and closest to Earth. But even at its brightest, Vesta is just too faint to spot with the naked-eye. Still, over the next few days it will be relatively easy to find in the constellation Leo, sharing a typical binocular field of view with bright star Gamma Leonis (aka Algieba). In fact on February 16 Vesta passed between Gamma Leonis and close neighbor on the sky 40 Leonis. Gamma Leonis is the brightest star in these two panels, while the second brightest star, 40 Leonis, is directy to its right. As marked, Vesta is the third brightest "star" in the field. Vesta shifts position between the two panels from well below 40 Leonis on Feb. 14 to near the top of the frame from Feb. 16, shooting the gap between the close Gamma/40 Leonis pair. Of course, premier close-up views of the asteroid will be possible after the ion-powered Dawn spacecraft arrives at Vesta in August of 2011.

Image credit: Jimmy Westlake
WISE Infrared Andromeda (2010-02-19)

This sharp, wide-field view features infrared light from the spiral Andromeda Galaxy (M31). Dust heated by Andromeda's young stars is shown in yellow and red, while its older population of stars appears as a bluish haze. The false-color skyscape is a mosaic of images from NASA's new Wide-field Infrared Survey Explorer (WISE) satellite. With over twice the diameter of our Milky Way, Andromeda is the largest galaxy in the local group. Andromeda's own satellite galaxies M110 (below) and M32 (above) are also included in the combined fields. Launched in December 2009, WISE began a six month long infrared survey of the entire sky on January 14. Expected to discover near-Earth asteroids as well as explore the distant universe, its sensitive infrared detectors are cooled by frozen hydrogen.
Geostationary Highway (2010-02-20)

Put a satellite in a circular orbit about 42,000 kilometers from the center of the Earth (36,000 kilometers or so above the surface) and it will orbit once in 24 hours. Because that matches Earth's rotation period, it is known as a geosynchronous orbit. If that orbit is also in the plane of the equator, the satellite will hang in the sky over a fixed location in a geostationary orbit. As predicted in the 1940s by futurist Arthur C. Clarke, geostationary orbits are in common use for communication and weather satellites, a scenario now well-known to astroimagers. Deep images of the night sky made with telescopes that follow the stars can also pick up geostationary satellites glinting in sunlight still shining far above the Earth's surface. Because they all move with the Earth's rotation against the background of stars, the satellites leave trails that seem to follow a highway across the celestial landscape.  For example, in this wide view of the nearly equatorial Orion region, individual frames were added to create a 10 minute long exposure. It shows Orion's belt stars and well-known nebulae along with many 2.5 degree long geostationary satellite trails. The frames are from an ingenious movie, featuring the geostationary satellite highway.

Image credit: Babak Tafreshi
NGC 2440: Cocoon of a New White Dwarf (2010-02-21)

Like a butterfly, a white dwarf star begins its life by casting off a cocoon that enclosed its former self.  In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! In the above cocoon, the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf can be seen as the bright dot near the photo's center.  Our Sun will eventually become a white dwarf butterfly but not for another 5 billion years.  The above false color image was post-processed by Forrest Hamilton.
Galaxy Group Hickson 31 (2010-02-22)

Will the result of these galactic collisions be one big elliptical galaxy? Quite possibly, but not for another billion years. Pictured above, several of the dwarf galaxies of in the Hickson Compact Group 31 are seen slowly merging.  Two of the brighter galaxies are colliding on the far left, while an elongated galaxy above is connected to them by an unusual bridge of stars. Inspection of the above image further indicates that the bright duo trail a rope of stars pointing to the spiral galaxy on the far right. Most assuredly, the pictured galaxies of Hickson Compact Group 31 will pass through and destroy each other, millions of stars will form and explode, and thousands of nebula will form and dissipate before the dust settles and the final galaxy emerges about one billion years from now. The above image is a composite of images taken in infrared light by the Spitzer Space Telescope, ultraviolet light by the GALEX space telescope, and visible light by the Hubble Space Telescope.  Hickson Compact Group 31 spans about 150 thousand light years and lies about 150 million light years away toward the constellation of Eridanus.
Exceptional Rocket Waves Destroy Sun Dog (2010-02-23)

What created those rocket waves, and why did they destroy that sun dog? Close inspection of the above image shows not only a rocket rising near the center, but unusual air ripples around it and a colorful sundog to the far right. The rocket, carrying the Solar Dynamics Observatory (SDO), lifted off two weeks ago from Cape Canaveral, Florida, USA into a cold blue sky.  The SDO is designed to observe the Sun continuously over the next several years, exploring the Sun's atmosphere at high resolution and fast time scales. The air ripples -- seen about one minute after launch -- were unexpected, as was the sudden disappearance of the sundog after the ripples passed. Noticed and recorded by several onlookers, there has been much speculation about the origin of the ripples.  An ongoing discussion about them can be joined here in APOD's discussion board the Asterisk. A leading hypothesis holds that the ripples resulted from a sonic boom created as the rocket broke the sound barrier, which then jumbled a thin layer of ice crystals that were aligned to create the sundog. Lingering questions include why other rocket launches don't produce air ripples as noticeable, and why the ripples appeared more prominent above the rocket. If you know of images of any other aircraft or spacecraft that have produced similar air ripples, please post them to the discussion thread -- they may be help create a better understanding of the effect.

Image credit: George C. Privon
(U. Virginia)
Astronaut Installs Panoramic Space Window (2010-02-24)

This space job was almost complete. Floating just below the International Space Station, astronaut Nicholas Patrick put some finishing touches on the newly installed cupola space windows last week. Patrick was a mission specialist onboard the recently completed space shuttle Endeavor's STS-130 mission to the ISS. Pictured, Patrick floats near the outermost of seven windows on the new cupola of the just-installed Tranquility module.   Patrick hovers about 340 kilometers over the Earth's surface, well in front of the blue sky, blue water, and white clouds pictured far in the background. In the above image, covers on windows three and four were in place and clearly labelled.  Images from inside the ISS's new panoramic cupola are now available.
Edge-on Spiral Galaxy NGC 891 (2010-02-25)

This beautiful cosmic portrait features NGC 891. The spiral galaxy spans about 100 thousand light-years and is seen almost exactly edge-on from our perspective. In fact, about 30 million light-years distant in the constellation Andromeda, NGC 891 looks a lot like our Milky Way. At first glance, it has a flat, thin, galactic disk and a central bulge cut along the middle by regions of dark obscuring dust. Also apparent in NGC 891's edge-on presentation are filaments of dust that extend hundreds of light-years above and below the center line. The dust has likely been blown out of the disk by supernova explosions or intense star formation activity. Faint neighboring galaxies can also been seen near this galaxy's disk.

Image credit: Bob Franke
Chasing Carina (2010-02-26)

A jewel of the southern sky, the Great Carina Nebula, aka NGC 3372, spans over 300 light-years. Near the upper right of this expansive skyscape, it is much larger than the more northerly Orion Nebula. In fact, the Carina Nebula is one of our galaxy's largest star-forming regions and home to young, extremely massive stars, including the still enigmatic variable Eta Carinae, a star with well over 100 times the mass of the Sun. Nebulae near the center of the 10 degree wide field include NGC 3576 and NGC 3603. Near center at the top of the frame is open star cluster NGC 3532, the Wishing Well Cluster. More compact, NGC 3766, the Pearl Cluster, can be spotted at the left. Anchoring the lower left of the cosmic canvas is another large star-forming region, IC 2948/2944 with embedded star cluster Collinder 249. That region is popularly known as the Running Chicken Nebula.

Image credit: Dieter Willasch
Dawn's Endeavour (2010-02-27)

On February 21st, the Space Shuttle Endeavour and the International Space Station (ISS) flew through the sky near dawn over Whitby, Ontario, Canada. Along with star trails, both were captured in this single time exposure. Glinting in sunlight 350 kilometers above the Earth, Endeavour slightly preceeded the ISS arcing over the horizon. But the brighter trail and the brighter flare belongs to the space station just visited by Endeavour. Near the completion of the STS-130 mission, hours later Endeavour made a night landing at Kennedy Space Center.

Image credit: Malcolm Park
Pauli Exclusion Principle: Why You Don't Implode (2010-02-28)

Why doesn't matter just bunch up?  The same principle that keeps neutron stars and white dwarf stars from imploding also keeps people from imploding and makes normal matter mostly empty space. The observed reason is known as the Pauli Exclusion Principle.  The principle states that identical fermions -- one type of fundamental matter -- cannot be in the same place at the same time and with the same orientation.  The other type of matter, bosons, do not have this property, as demonstrated clearly by recently created Bose-Einstein condensates.  Earlier this decade, the Pauli Exclusion Principle was demonstrated graphically in the above picture of clouds of two isotopes of lithium -- the left cloud composed of bosons while the right cloud is composed of fermions.  As temperature drops, the bosons bunch together, while the fermions better keep their distance.  The reason why the Pauli Exclusion Principle is true and the physical limits of the principle are still unknown.

Image credit: Andrew Truscott &
Randall Hulet
(Rice U.)
Slope Streaks in Acheron Fossae on Mars (2010-03-01)

What creates these picturesque dark streaks on Mars? No one knows for sure.  A leading hypothesis is that streaks like these are caused by fine grained sand sliding down the banks of troughs and craters. Pictured above, dark sand appears to have flowed hundreds of meters down the slopes of Acheron Fossae.  The sand appears to flow like a liquid around boulders, and, for some reason, lightens significantly over time. This sand flow process is one of several which can rapidly change the surface of Mars, with other processes including dust devils, dust storms, and the freezing and melting of areas of ice. The above image was taken by the HiRise camera on board the Mars Reconnaissance Orbiter which has been orbiting Mars since 2006.  Acheron Fossae is a 700 kilometer long trough in the Diacria quadrangle of Mars.
M78 and Reflecting Dust Clouds in Orion (2010-03-02)

An eerie blue glow and ominous columns of dark dust highlight M78 and other bright reflection nebula in the constellation of Orion.  The dark filamentary dust not only absorbs light, but also reflects the light of several bright blue stars that formed recently in the nebula.  Of the two reflection nebulas pictured above, the more famous nebula is M78, in the image center, while NGC 2071 can be seen to its lower left. The same type of scattering that colors the daytime sky further enhances the blue color.  M78 is about five light-years across and visible through a small telescope.  M78 appears above only as it was 1600 years ago, however, because that is how long it takes light to go from there to here.  M78 belongs to the larger Orion Molecular Cloud Complex that contains the Great Nebula in Orion and the Horsehead Nebula.

Image credit: Ignacio de la Cueva Torregrosa
The International Space Station from Above (2010-03-03)

The International Space Station (ISS) is the largest human-made object ever to orbit the Earth.  The ISS is so large that it can be seen drifting overhead with the unaided eye, and is frequently imaged from the ground in picturesque fashion.  Last month, the station was visited again by space shuttle, which resupplied the station and added a new module.   The ISS is currently operated by the Expedition 22 crew, now consisting five astronauts including two supplied by USA's NASA, two by Russia's RKA, and one by Japan's JAXA.   After departing the ISS, the crew of the space shuttle Endeavour captured the above spectacular vista of the orbiting space city high above the clouds, waters, and lands of Earth.  Visible components include modules, trusses, and expansive solar arrays that gather sunlight that is turned into needed electricity.   Share Quiz: Can anyone identify the landscape behind the space station?
NGC 4565: Galaxy on Edge (2010-03-04)

Magnificent spiral galaxy NGC 4565 is viewed edge-on from planet Earth. Also known as the Needle Galaxy for its narrow profile, bright NGC 4565 is a stop on many telescopic tours of the northern sky, in the faint but well-groomed constellation Coma Berenices. This sharp, colorful image reveals the galaxy's bulging central core cut by obscuring dust lanes that lace NGC 4565's thin galactic plane. An assortment of other galaxies is included in the pretty field of view. Neighboring galaxy NGC 4562 is at the upper right. NGC 4565 itself lies about 40 million light-years distant, spanning some 100,000 light-years.  Easily spotted with small telescopes, sky enthusiasts consider NGC 4565 to be a prominent celestial masterpiece Messier missed.

Image credit: Dietmar Hager
Deep Auriga (2010-03-05)

The plane of our Milky Way Galaxy runs right through Auriga, the Charioteer. A good part of the ancient northern constellation's rich collection of nebulae and star clusters is featured in this expansive, 10 degree wide skyscape. Bright star Elnath lies near the bottom right, linking Auriga to another constellation, Taurus, the Bull. Three open star clusters, Charles Messier's M36, M37, and M38 line up in the dense star field above and left of Elnath, familiar to many binocular-equipped skygazers. But the deep exposure also brings out the reddish emission nebulae of star-forming regions IC 405, IC 410, and IC 417. E. E. Barnard's dark nebulae B34 and B226 just stand out against a brighter background. For help identifying even more of Auriga's deep sky highlights, put your cursor over the image.

Image credit: Tunç Tezel
Pillar at Sunset (2010-03-06)

Reddened light from the setting Sun illuminates the cloud banks hugging this snowy, rugged terrain. Inspiring a moment of quiet contemplation, the sunset scene included a remarkable pillar of light that seemed to connect the clouds in the sky with the mountains below. Known as a Sun pillar, the luminous column was produced by sunlight reflecting from flat, six-sided ice crystals formed high in the cold atmosphere and fluttering toward the ground. Last Monday, astronomers watched this Sun pillar slowly fade, as the twilight deepened and clearing, dark skies came to Mt. Jelm and the Wyoming Infrared Observatory.

Image credit: Reddened
light
Spirit Rover at Engineering Flats on Mars (2010-03-07)

Is it art?  If so, the paintbrush was the Spirit robotic rover, the canvas was the soil on Mars, and the artists were the scientists and engineers of the Mars Exploration Rover Mission.  This panoramic picture, created in 2004 and shown above compressed horizontally, was mostly unintentional -- the MERS team was primarily instructing Spirit to investigate rocks in and around Hank's Hollow in a location called Engineering Flats on Mars. After creating the ground display with its treads, the Spirit rover was instructed to photograph the area along with itself in shadow.  In 2010 as winter approaches in northern Mars, Spirit, still mired in sand, has been placed in an energy saving "hibernating" mode until spring arrives and more direct sunlight might be used to power the robotic explorer.
Mars Over the Allalinhorn (2010-03-08)

What's that bright object in the sky? A common question with answers that vary by time and season, the quick answer just after sunset in middle of last month, from the northern hemisphere, was Mars. The above picturesque panorama, taken during a ski trip from the Alps in Switzerland, shows not only Mars, but much more.  Pine trees line the foreground, while numerous slopes leading up to the snow covered Allalinhorn mountain are visible in the distance.  Stars dot the background, with the Beehive star cluster (M44) visible just below and to the left of Mars, while stars Castor and Pollux peek through the tree tops to the Mars' upper right.  Mars will remain bright and in the constellation of the Crab (Cancer) until mid-May.

Image credit: Till Credner
(AlltheSky.com)
Galaxies Beyond the Heart: Maffei 1 and 2 (2010-03-09)

The two galaxies on the far left were unknown until 1968.  Although they would have appeared as two of the brighter galaxies on the night sky, the opaque dust of the central band of our Milky Way Galaxy had obscured them from being seen in visible light. The above image in infrared light taken by the recently launched Wide-Field Infrared Survey Explorer (WISE), however, finds these galaxies in great detail far behind -- but seemingly next to -- the photogenic Heart nebula (IC 1805).  The spiral galaxy near the top is the easiest to spot and is known as Maffei 2.  Just below and to its right is fuzzy-looking  Maffei 1, the closest giant elliptical galaxy to Earth. The above false-colored image spans three full moons from top to bottom.  The Maffei galaxies each span about 15,000 light years across and lie about 10 million light years away toward the constellation of the Queen of Ethiopia (Cassiopeia).  On the image right, stars, gaseous filaments, and warm dust highlight a detailed infrared view of the Heart nebula.
Saturn's Moon Helene from Cassini (2010-03-10)

What's happening on the surface of Saturn's moon Helene? The moon was imaged in unprecedented detail last week as the robotic Cassini spacecraft orbiting Saturn swooped to within two Earth diameters of the diminutive moon. Although conventional craters and hills appear, the above raw and unprocessed image also shows terrain that appears unusually smooth and streaked. Planetary astronomers will be inspecting these detailed images of Helene to glean clues about the origin and evolution of the 30-km across floating iceberg. Helene is also unusual because it circles Saturn just ahead of the large moon Dione, making it one of only four known Saturnian moons to occupy a gravitational well known as a stable Lagrange point.