juliensimon/nasa-apod huggingface dataset:
Yukon Aurora with Star Trails (2010-03-11)

Fixed to a tripod, a camera can record graceful trails traced by stars as planet Earth rotates on its axis. But at high latitudes during March and April, it can also capture an aurora shimmering in the night. In fact, the weeks surrounding the equinox, in both spring and fall, offer a favorable season for aurora hunters. The possibilities are demonstrated in this beautiful moonlit vista from northwestern Canadian territory the Yukon. It was taken during the early morning of March 1, off the Klondike Highway about 60 kilometers south of Dawson City. To compose the picture, many short exposures were digitally combined to follow the concentric star trail arcs while including the greenish auroral curtains also known as the northern lights.

Image credit: Yuichi Takasaka
JWST: Mirrors and Masked Men (2010-03-12)

Who are these masked men? Technicians from Ball Aerospace and NASA at Marshall Space Flight Center's X-ray and Cryogenic Facility, of course, testing primary mirror segments of the James Webb Space Telescope (JWST). Scheduled for launch in 2014, JWST will be optimized for the infrared exploration of the early Universe, utilizing a primary mirror 21.3 feet across, composed of 18 hexagonal segments. Here, a group of JWST mirror segments are being prepared for tests to assure they meet the exacting mission requirements. The technicians' suits and masks help prevent contamination of the mirror surfaces. At the Marshall X-ray and Cryogenic Facility, the mirrors are tested in the large circular chamber after evacuating the air and cooling the chamber to -400 degrees Fahrenheit (only 60 degrees above absolute zero). The extremely low pressure and temperature simulate the JWST mirror operating environment in space. JWST mirror segment testing will continue for the next 18 months.
Centaurus A (2010-03-13)

Only 11 million light-years away, Centaurus A is the closest active galaxy to planet Earth. Spanning over 60,000 light-years, the peculiar elliptical galaxy, also known as NGC 5128, is featured in this sharp color image. Centaurus A is apparently the result of a collision of two otherwise normal galaxies resulting in a fantastic jumble of star clusters and imposing dark dust lanes. Near the galaxy's center, left over cosmic debris is steadily being consumed by a central black hole with a billion times the mass of the Sun. As in other active galaxies, that process likely generates the radio, X-ray, and gamma-ray energy radiated by Centaurus A.

Image credit: Tim Carruthers
Binary Black Hole in 3C 75 (2010-03-14)

What's happening in the middle of this massive galaxy? There, two bright sources at the center of this composite x-ray (blue)/radio (pink) image are thought to be co-orbiting supermassive black holes powering the giant radio source 3C 75. Surrounded by multimillion degree x-ray emitting gas, and blasting out jets of relativistic particles the supermassive black holes are separated by 25,000 light-years. At the cores of two merging galaxies in the Abell 400 galaxy cluster they are some 300 million light-years away. Astronomers conclude that these two supermassive black holes are bound together by gravity in a binary system in part because the jets' consistent swept back appearance is most likely due to their common motion as they speed through the hot cluster gas at 1200 kilometers per second. Such spectacular cosmic mergers are thought to be common in crowded galaxy cluster environments in the distant universe. In their final stages the mergers are expected to be intense sources of gravitational waves.
Illuminated Cloud Trails Above Greece (2010-03-15)

It may appear to be day, but it's night.  Those wondrous orange streaks may appear to be rays from the setting Sun, but they're actually thin clouds illuminated by the Moon as they quickly streaked toward the distant horizon. The thick clouds on the far left may appear to have many layers, but actually they are just a few simple clouds captured on numerous separate exposures.  What is surely true, though, is that the above time lapse image sequence was taken over two hours, about two weeks ago, in Sounio, Greece.  Also, those really are star trails swirling around the north star Polaris on the upper right of the image.  But what about the building in the foreground?  It may appear to be a famous ancient structure, but it's actually a small deserted church built only last century.    Your opinion requested: Is APOD a blog?

Image credit: Chris Kotsiopoulos
Detailed View of a Solar Eclipse Corona (2010-03-16)

Only in the fleeting darkness of a total solar eclipse is the light of the solar corona easily visible. Normally overwhelmed by the bright solar disk, the expansive corona, the sun's outer atmosphere, is an alluring sight. But the subtle details and extreme ranges in the corona's brightness, although discernible to the eye, are notoriously difficult to photograph. Pictured above, however, using multiple images and digital processing, is a detailed image of the Sun's corona taken during the 2008 August total solar eclipse from Mongolia.  Clearly visible are intricate layers and glowing caustics of an ever changing mixture of hot gas and magnetic fields. Bright looping prominences appear pink just above the Sun's limb. The next total solar eclipse will be in July but will only be visible in a thin swath of Earth crossing the southern Pacific Ocean and South America.

Image credit: Miloslav Druckm�ller
(Brno University of Technology),
Martin Dietzel, Peter Aniol, Vojtech Ru�in
Phobos from Mars Express (2010-03-17)

Why is this small object orbiting Mars?  The origin of Phobos, the larger of the two moons orbiting Mars, remains unknown.  Phobos and Deimos appear very similar to C-type asteroids, yet gravitationally capturing such asteroids, circularizing their orbits, and dragging them into Mars' equatorial plane seems unlikely.  Pictured above is Phobos as it appeared during last week's flyby of ESA's Mars Express, a robotic spacecraft that began orbiting Mars in 2003. Visible in great detail is Phobos' irregular shape, strangely dark terrain, numerous unusual grooves, and a spectacular chain of craters crossing the image center.   Phobos spans only about 25 kilometers in length and does not have enough gravity to compress it into a ball.  Phobos orbits so close to Mars that sometime in the next 20 million years, tidal deceleration will break up the  rubble moon into a ring whose pieces will slowly spiral down and crash onto the red planet. The Russian mission Phobos-Grunt is scheduled to launch and land on Phobos next year.
Fermi Catalogs the Gamma-ray Sky (2010-03-18)

What shines in the gamma-ray sky? The most complete answer yet to that question is offered by the Fermi Gamma-ray Space Telescope's first all-sky catalog. Fermi's sources of cosmic gamma-rays feature nature's most energetic particle accelerators, ultimately producing 100 MeV to 100 GeV photons, photons with more than 50 million to 50 billion times the energy of visible light. Distilled from 11 months of sky survey data using Fermi's Large Area Telescope (LAT), the 1,451 cataloged sources include energetic star burst galaxies and active galactic nuclei (AGN) far beyond the Milky Way. But within our own galaxy are many pulsars (PSR) and pulsar wind nebulae (PWN), supernova remnants (SNR), x-ray binary stars (HXB) and micro-quasars (MQO). Fermi's all sky map is shown centered on the Milky Way with the diffuse gamma-ray emission from the Galactic plane running horizontally through the frame. To locate the cataloged gamma-ray sources, just slide your cursor over the map. For now, 630 of the sources cataloged at gamma-ray energies remain otherwise unidentified, not associated with sources detected at lower energies.
The Seagull and the Duck (2010-03-19)

Seen as a seagull and a duck, these nebulae are not the only cosmic clouds to evoke images of flight. But both are winging their way across this broad celestial landscape, spanning almost 7 degrees across planet Earth's night sky toward the constellation Canis Major. The expansive Seagull (upper left) is itself composed of two major cataloged emission nebulae. Brighter NGC 2327 forms the head with the more diffuse IC 2177 as the wings and body. Impressively, the Seagull's wingspan would correspond to about 250 light-years at an estimated distance of 3,800 light-years. At the lower right, the Duck appears much more compact and would span only about 50 light-years given its 15,000 light-year distance estimate. Blown by energetic winds from an extremely massive, hot star near its center, the Duck nebula is cataloged as NGC 2359. Of course, the Duck's thick body and winged appendages also lend it a more dramatic popular moniker -- Thor's Helmet.

Image credit: Rogelio Bernal Andreo
Zodiacal Light Vs. Milky Way (2010-03-20)

Ghostly Zodiacal light, featured near the center of this remarkable panorama, is produced as sunlight is scattered by dust in the Solar System's ecliptic plane. In the weeks surrounding the March equinox (today at 1732 UT) Zodiacal light is more prominent after sunset in the northern hemisphere, and before sunrise in the south, when the ecliptic makes a steep angle with the horizon. In the picture, the narrow triangle of Zodiacal light extends above the western horizon and seems to end at the lovely Pleiades star cluster. Arcing above the Pleiades are stars and nebulae along the plane of our Milky Way Galaxy. Recorded on March 10 from Teide National Park on the island of Tenerife, the vista is composed of 4 separate pictures spanning over 180 degrees.

Image credit: Daniel López
Equinox + 1 (2010-03-21)

Twice a year, at the Spring and Fall equinox, the Sun rises due east. In an emphatic demonstration of this celestial alignment, photographer Joe Orman recorded this inspiring image of the Sun rising exactly along the east-west oriented Western Canal, in Tempe, Arizona, USA. But he waited until one day after the northern Spring equinox, in 2001, to photograph the striking view. Why was the rising Sun due east one day after the equinox? At Tempe's latitude the Sun rises at an angle, arcing southward as it climbs above the horizon. Because the distant mountains hide the true horizon, the Sun shifts slightly southward by the time it clears the mountain tops. Waiting 24 hours allowed the Sun to rise just north of east and arc back to an exactly eastern alignment for the photo. Today is another Equinox + 1 day, with the Sun crossing the celestial equator yesterday at about 17:32 Universal Time.

Image credit: Joe Orman
The Nearby Milky Way in Cold Dust (2010-03-22)

What shapes the remarkable dust tapestry of the nearby Milky Way Galaxy? No one knows for sure.  The intricate structures, shown above, were resolved in new detail recently in a wide region of the sky imaged in far infrared light by the European Space Agency's Planck satellite. The above image is a digital fusion of three infrared colors: two taken at high resolution by Planck, while the other is an older image taken by the now defunct IRAS satellite. At these colors, the sky is dominated by the faint glow of very cold gas within only 500 light years of Earth. In the above image, red corresponds to temperatures as cold as 10 degrees Kelvin above absolute zero, while white corresponds to gas as warm at 40 Kelvins. The pink band across the lower part of the image is warm gas confined to the plane of our Galaxy. The bright regions typically hold dense molecular clouds that are slowly collapsing to form stars, whereas the dimmer regions are most usually diffuse interstellar gas and dust known as cirrus.  Why these regions have intricate filamentary shapes shared on both large and small scales remains a topic of research. Future study of the origin and evolution of dust may help in the understanding the recent history of our Galaxy as well as how planetary systems such as our Solar System came to be born.
Reinvigorated Sun and Prominence (2010-03-23)

Dramatic prominences can sometimes be seen looming just beyond the edge of the sun.  Such was the case last week as a giant prominence, visible above on the right, highlighted a Sun showing increased activity as it comes off an unusually quiet Solar Minimum.  A changing carpet of hot gas is visible in the chromosphere of the Sun in the above image taken in a very specific color of light emitted by hydrogen. A solar prominence is a cloud of solar gas held just above the surface by the Sun's magnetic field. The Earth would easily fit below the prominence on the right. Although very hot, prominences typically appear dark when viewed against the Sun, since they are slightly cooler than the surface.  A quiescent prominence typically lasts about a month, and may erupt in a Coronal Mass Ejection (CME) expelling hot gas into the Solar System.  The next day, the same prominence looked slightly different.

Image credit: Alan Friedman
(Averted Imagination)
Galaxy Wars: M81 versus M82 (2010-03-24)

On the right, surrounded by blue spiral arms, is spiral galaxy M81.  On the left, marked by red gas and dust clouds, is irregular galaxy M82.  This stunning vista shows these two mammoth galaxies locked in gravitational combat, as they have been for the past billion years.   The gravity from each galaxy dramatically affects the other during each hundred million-year pass.  Last go-round, M82's gravity likely raised density waves rippling around M81, resulting in the richness of M81's spiral arms.  But M81 left M82 with violent star forming regions and colliding gas clouds so energetic the galaxy glows in X-rays.  In a few billion years only one galaxy will remain.

Image credit: Leonardo Orazi
NGC 2442: Galaxy in Volans (2010-03-25)

Distorted galaxy NGC 2442 can be found in the southern constellation of the flying fish, (Piscis) Volans. Located about 50 million light-years away, the galaxy's two spiral arms extending from a pronounced central bar have a hook-like appearance in wide-field images. But this mosaicked close-up, constructed from Hubble Space Telescope data, follows the galaxy's structure in amazing detail. Obscuring dust lanes, young blue star clusters and reddish star forming regions surround a core of yellowish light from an older population of stars. The sharp Hubble data also reveal more distant background galaxies seen right through NGC 2442's star clusters and nebulae. The image spans about 75,000 light-years at the estimated distance of NGC 2442.
Young Moon and Sister Stars (2010-03-26)

A young crescent Moon shares the western sky with sister stars of the Pleiades cluster in this pretty, evening skyscape recorded on the March equinox from San Antonio, Texas.  In the processed digital image, multiple exposures of the celestial scene were combined to show details of the bright lunar surface along with the Pleiades stars. Astronomical images of the well-known Pleiades often show the cluster's alluring blue reflection nebulae, but they are washed-out here in the bright moonlight. Still, during this particular night, skygazers in South and Central America could even watch the 5 day old Moon occult or pass in front of some of the brighter Pleiades stars.

Image credit: Anna Morris
Hesiodus Sunrise Ray (2010-03-27)

Stark shadows of mountains and crater walls stand out along the lunar terminator, or shadow line between night and day, in this telescopic image. Of course, if viewed from the lunar surface near the terminator line, the Sun would be rising and still close to the lunar horizon. But the picture's inset at the left highlights a more elusive lunar sunrise phenomenon. Streaming through a gap in the eastern wall of 45 kilometer wide Hesiodus crater, the low-angle sunlight produces a long sunrise ray playing along the otherwise shadowed crater floor. Sunrise rays are short-lived and can be rewarding to spot for Moon enthusiasts with telescopes. Seen in Hesiodus and other craters, the ray timing can be calculated based on the observer's location. This picture of a first quarter Moon was recorded at 23:45 UT on February 22nd from Stuttgart, Germany. In the inset, the larger crater Pitatus is at the right. For location, Hesiodus and Pitatus are circled at the bottom of the picture.

Image credit: Stefan Seip
M16: Pillars of Creation (2010-03-28)

It has become one of the most famous images of modern times. 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 again imaged by the orbiting Chandra X-ray Observatory, and it was found that most EGGS are not strong emitters of X-rays.
Moonset Over Pleasant Bay (2010-03-29)

It was a sky for the imagination. In the early evening last week, the sky illuminating the unaided eye was perhaps even more illuminating to the mind's eye.  The unaided eye saw clouds framing the Moon setting over a calm and reflective bay, spruce trees lining the nearby shores, the Pleiades open star cluster (M45) glowing prominently in the center of the sky, the Andromeda galaxy hovering just over the horizon on the right, and the belt stars of Orion lined up on the left, just below the bright orange star Betelgeuse.  The bright star Sirius peeked out of the trees on the far left.  The mind's eye might further imagine, however, some of the constellations coming to life, with Orion the Hunter taking up his sword and shield, followed into battle by his Big Dog  (Canis Major, whose right eye is Sirius), and watched from across the sky by Cassiopeia, the Queen of Ethiopia, sitting on her Throne.  The above image was taken over Pleasant Bay, Maine, USA, and digitally merged with constellations from Uranographicarum, drawn in the 17th century by J. Hevelius.

Image credit: A. Dunlap-Smith;
Drawing Acknowledgement:
J. Hevelius
Unusual Starburst Galaxy NGC 1313 (2010-03-30)

Why is this galaxy so discombobulated?  Usually, galaxies this topsy-turvy result from a recent collision with a neighboring galaxy. Spiral galaxy NGC 1313, however, appears to be alone.  Brightly lit with new and blue massive stars, star formation appears so rampant in NGC 1313 that it has been labeled a starburst galaxy.  Strange features of NGC 1313 include that its spiral arms are lopsided and its rotational axis is not at the center of the nuclear bar.  Pictured above, NGC 1313 spans about 50,000 light years and lies only about 15 million light years away toward the constellation of the Reticle (Reticulum). Continued numerical modeling of galaxies like NGC 1313 might shed some light on its unusual nature.

Image credit: Robert Gendler
Millions of Stars in Omega Centauri (2010-03-31)

Featured in the sharp telescopic image, globular star cluster Omega Centauri (NGC 5139) is some 15,000 light-years away and 150 light-years in diameter. Packed with about 10 million stars much older than the Sun, Omega Cen is the largest of 200 or so known globular clusters that roam the halo of our Milky Way galaxy. Though most star clusters consist of stars with the same age and composition, the enigmatic Omega Cen exhibits the presence of different stellar populations with a spread of ages and chemical abundances. In fact, Omega Cen may be the remnant core of a small galaxy merging with the Milky Way.

Image credit: South Florida Dark Sky Observers
Evidence Mounts for Water on the Moon (2010-04-01)

In 2009, space missions revealed tantalizing signs of water on or near the lunar surface, once thought of as a dry and desolate environment. But researchers are now offering this archival picture as further evidence that humans might one day be able to use the Moon's newly discovered resource to directly quench their thirst. Found in a pile of old Apollo lunar surface photographs, the picture reveals an object at the far left of the frame that appears to be a drinking fountain, surprisingly close to one of the Lunar Module landing struts. When asked why no mention of the object was in their reports, the astronauts replied that they discovered their spacesuit gloves were too bulky to allow them to activate the fountain, so they had simply ignored it during their stay on the lunar surface. Perhaps not coincidentally, this picture was taken exactly 40 years ago, on April Fools Day ...
Serene Paraselene (2010-04-02)

Nestled in the Austrian Alps, frozen Lake Ossiach stretches across the foreground of this serene view. Recorded on March 1, the night sky includes a nearly full Moon and bright planet Saturn seen through thin clouds near picture center. It also includes a remarkably bright and colorful moondog or paraselene at the left. Analogous to a sundog or parhelion, the paraselene is produced by moonlight shining through thin, hexagonal-shaped ice crystals in high cirrus clouds. As determined by the ice crystal geometry, the Moon is 22 degrees from the lovely paraselene.

Image credit: Tamas Ladanyi
NGC 602 and Beyond (2010-04-03)

Near the outskirts of the Small Magellanic Cloud, a satellite galaxy some 200 thousand light-years distant, lies 5 million year young star cluster NGC 602. Surrounded by natal gas and dust, NGC 602 is featured in this stunning Hubble image of the region. Fantastic ridges and swept back shapes strongly suggest that energetic radiation and shock waves from NGC 602's massive young stars have eroded the dusty material and triggered a progression of star formation moving away from the cluster's center. At the estimated distance of the Small Magellanic Cloud, the picture spans about 200 light-years, but a tantalizing assortment of background galaxies are also visible in the sharp Hubble view. The background galaxies are hundreds of millions of light-years or more beyond NGC 602.
The Belt of Venus over the Valley of the Moon (2010-04-04)

Although you've surely seen it, you might not have noticed it. During a cloudless twilight, just before sunrise or after sunset, part of the atmosphere above the horizon appears slightly off-color, slightly pink. Called the Belt of Venus, this off-color band between the dark eclipsed sky and the blue sky can be seen in nearly every direction including that opposite the Sun.  Straight above, blue sky is normal sunlight reflecting off the atmosphere. In the Belt of Venus, however, the atmosphere reflects light from the setting (or rising) Sun which appears more red.  The Belt of Venus can be seen from any location with a clear horizon. Pictured above, the Belt of Venus was photographed above morning fog in the Valley of the Moon, a famous wine-producing region in northern California, USA. The belt is frequently caught by accident in other photographs.

Image credit: Christine Churchill
Prometheus Remastered (2010-04-05)

What does Saturn's shepherd moon Prometheus really look like? The raw images from the robotic Cassini spacecraft's January flyby of the small moon showed tantalizing clues on grainy images, but now that the Cassini team has digitally remastered these images, many more details have come out. Pictured above, Prometheus more clearly shows its oblong shape as well as numerous craters over its 100-kilometer length. In the above image, the bright part of Prometheus is lit directly by the Sun, while much of the dark part is still discernible through sunlight first reflected off of Saturn. These new surface details, together with the moon's high reflectivity, can now help humanity better understand the history of Prometheus and Saturn's rings. Today, Cassini has a planned targeted flyby of Saturn's largest moon Titan, while on Wednesday, Cassini is scheduled to swoop to within 600 kilometers of Dione.