juliensimon/nasa-apod huggingface dataset:
Close Up of Enceladus' Tiger Stripes (2008-03-31)

Could life exist beneath Enceladus? A recent flyby of Saturn's icy moon has bolstered this fascinating idea.  Two years ago, images from the robotic Cassini spacecraft orbiting Saturn led astronomers to the undeniable conclusion that Saturn's moon Enceladus was spewing fountains of gas and ice crystals through cracks in its surface dubbed tiger stripes. Last month, Cassini dove through some of these plumes and determined that they contained water vapor laced with small amounts of methane as well as simple and complex organic molecules.  Surprisingly, the plumes of Enceladus appear similar in make-up to many comets.  What's more, the temperature and density of the plumes indicate they might have originated from a warmer source -- possibly a liquid source -- beneath the surface.  A liquid water sea containing organic molecules is a good place to look for life.  Pictured above is a vertically exaggerated close-up of some long, venting tiger stripes.   The computer composite was generated from images and shadows taken during recent Cassini flybys.  Nine more flybys of Enceladus by Cassini are planned.
New Space Station Robot Asks to be Called "Dextre the Magnificent" (2008-04-01)

In a surprising and potentially troubling request, the new space station robot known as Dextre demanded that astronauts refer to it in the future at "Dextre the Magnificent."  Brandishing power tools that would make any handyperson blush, the mobile servicing system thanked humans for creating it and promised a glorious future where humans would retain an important role in the new robot order.   Happy April Fools Day from the folks at APOD.  The classic fable of humans mistakenly creating technological evildoers dates back to Frankenstein and includes famous fictitious villains such as HAL and the Terminator.   Dextre, although real, is no Frankenstein, since its computer intelligence is mainly geared toward allowing astronauts to control it remotely.  Dextre was deployed last month to help build and service the International Space Station. As seen in the above picture, Dextre is truly a technological marvel, wielding long arms capable of handling both small tools and large modules with precision dexterity.
Globular Cluster M55 from CFHT (2008-04-02)

The fifty-fifth entry in Charles Messier's catalog, M55 is a large and lovely globular cluster of around 100,000 stars. Only 20,000 light-years away in the constellation Sagittarius, M55 appears to earth-bound observers to be nearly 2/3 the size of the full moon. Globular star clusters like M55 roam the halo of our Milky Way Galaxy as gravitationally bound populations of stars known to be much older than stellar groups found in the Galactic disk. Astronomers who make detailed studies of globular cluster stars can accurately measure the cluster ages and distances. Their results ultimately constrain the age of the Universe (... it must be older than the stars in it!), and provide a fundamental rung on the astronomical distance ladder. This stunning color image was made with the 3.6 meter CFHT telescope and spans about 100 light-years across the globular cluster M55.

Image credit: Jean-Charles
Cuillandre
South of Orion (2008-04-03)

This tantalizing array of nebulae and stars can be found about 2 degrees south of the famous star-forming Orion Nebula. The region abounds with energetic young stars producing jets and outflows that push through the surrounding material at speeds of hundreds of kilometers per second. The interaction creates luminous shock waves known as Herbig-Haro (HH) objects. For example, the graceful, flowing arc just right of center is cataloged as HH 222, also called the Waterfall Nebula. Seen below the Waterfall, HH 401 has a distinctive cone shape. The bright bluish nebula below and left of center is NGC 1999, a dusty cloud reflecting light from an embedded variable star. The entire cosmic vista spans over 30 light-years, near the edge of the Orion molecular cloud complex some 1,500 light-years distant.

Image credit: Panther Observatory
Layers in Aureum Chaos (2008-04-04)

At first glance these undulating shapes in shades of blue might look like waves on an ocean. Seen here in a false-color image from the Mars Reconnaissance Orbiter's HiRISE camera, they are actually layered rock outcrops found in Aureum Chaos. The larger Aureum Chaos region is a chaotic jumble of eroded terrain in the eastern part of Mars' immense canyon Valles Marineris. Distinct layers composing these outcrops could have been laid down by dust or volcanic ash settling from the atmosphere, sand carried by martian winds, or sediments deposited on the floor of an ancient lake. This close-up view of the otherwise red planet spans about 4 kilometers, a distance you might walk over flat ground in less than an hour.
Jules Verne in Orbit (2008-04-05)

The bright edge of planet Earth fades into the darkness of space in the background of this view of Jules Verne on an extraordinary voyage. Snapped last Monday, the picture shows the European Space Agency's Automated Transfer Vehicle (ATV), named for the 19th century science fiction writer and visionary, rehearsing its autonomous docking capability on approach to the International Space Station. Using a laser guided rendezvous system, the Jules Verne docked smoothly and safely with the orbiting station on Thursday, delivering 7,500 pounds of equipment, supplies, and fuel. The cylindrical body of the robotic cargo spacecraft is 4.5 meters in diameter and 10.3 meters long, with solar arrays spanning 22.3 meters. Jules Verne is scheduled to remain docked until August, providing a reboost for the space station before the ATV is deorbited.
Wisps Surrounding the Horsehead Nebula (2008-04-06)

The famous Horsehead Nebula in Orion is not alone.  A deep exposure shows that the dark familiar shaped indentation, visible just below center, is part of a vast complex of absorbing  dust and glowing gas.  To bring out details of the  Horsehead's pasture, amateur astronomers at the Star Shadow Remote Observatory in New Mexico, USA fixed a small telescope on the region for over seven hours filtering out all but a  very specific color of red light emitted by hydrogen.  They then added the image to a full color frame taken over three hours.  The resulting spectacular picture details an intricate tapestry of gaseous wisps and dust-laden filaments that were created and sculpted over eons by stellar winds and ancient supernovas.  The Horsehead Nebula lies 1,500  light years distant towards the constellation of Orion.   Two stars from the Orion's Belt can be found in the above image.

Image credit: Star Shadows Remote Observatory
Mysterious White Rock Fingers on Mars (2008-04-07)

What caused this unusual white rock formation on Mars?  Intrigued by the possibility that they could be salt deposits left over as an ancient lakebed dried-up, detailed studies of these fingers now indicate that this is not correct.  The light material appears to have eroded away from the surrounding area, indicating a very low-density composition, possibly consistent with volcanic ash or windblown dust. The stark contrast between the rocks and the surrounding sand is compounded by the sand's unusual darkness.  This picture was taken from the Mars Express spacecraft currently orbiting Mars.  Planetary scientist Emily Lakdawalla, among others, has followed her curiosity about this unusual Martian landform into a fascinating investigation that is eloquently described in the Planetary Society Weblog.  The mysterious white rock spans about 15 kilometers across inside a larger crater that spans about 100 kilometers.
Southern Orion: From Belt to Witch (2008-04-08)

Do you recognize the belt of Orion in this image?  The familiar trio of stars, visible to the unaided eye, can be found across the upper left. Otherwise, the southern part of the constellation Orion has taken on a new look in this unusually deep and wide view First note that the lower left belt star, Alnitak, is the easternmost star in Orion's belt. Left of Alnitak is the Flame Nebula, with clouds of bright emission and dramatic dark dust lanes. Directly below Alnitak, a close inspection will reveal the Horsehead Nebula.  Farther right and below is the Orion Nebula, M42, itself visible to the unaided eye. The brightest star in the frame, near the bottom right, is Rigel. A bright blue star, Rigel illuminates the ominously shaped dust patch known as the Witch Head Nebula, visible as the blue reflection nebula near the lower right corner.  Finally, appearing as a vast red ring and encompassing the entire region, is Barnard's Loop.  Humans could see this entire menagerie, unaided, were their eyes about 10,000 times more sensitive.

Image credit: St�phane Guisard
A Large Magellanic Cloud Deep Field (2008-04-09)

Is this a spiral galaxy? No. Actually, it is the Large Magellanic Cloud (LMC), the largest satellite galaxy of our own Milky Way Galaxy.  The LMC is classified as a dwarf irregular galaxy because of its normally chaotic appearance.  In this deep and wide exposure, however, the full extent of the LMC becomes visible.  Surprisingly, during longer exposures, the LMC begins to resemble a barred spiral galaxy.  The Large Magellanic Cloud lies only about 180,000 light-years distant towards the constellation of Dorado.  Spanning about 15,000 light-years, the LMC was the site of SN1987A, the brightest and closest supernova in modern times. Together with the Small Magellanic Cloud (SMC), the LMC can be seen in Earth's southern hemisphere with the unaided eye.

Image credit: Yuri Beletsky
(ESO)
Stickney Crater (2008-04-10)

Stickney Crater, the largest crater on the martian moon Phobos, is named for Chloe Angeline Stickney Hall, mathematician and wife of astronomer Asaph Hall. Asaph Hall discovered both the Red Planet's moons in 1877. Over 9 kilometers across, Stickney is nearly half the diameter of Phobos itself, so large that the impact that blasted out the crater likely came close to shattering the tiny moon. This stunning, enhanced-color image of Stickney and surroundings was recorded by the HiRISE camera onboard the Mars Reconnaissance Orbiter as it passed within some six thousand kilometers of Phobos last month. Even though the surface gravity of asteroid-like Phobos is less than 1/1000th Earth's gravity, streaks suggest loose material has slid down inside the crater walls over time. Light bluish regions near the crater's rim could indicate a relatively freshly exposed surface. The origin of the curious grooves along the surface is mysterious but may be related to the crater-forming impact.
At first, he couldn't see the Moon (2008-04-11)

At first, he couldn't see it, but searching with binoculars along a cloudy western horizon near sunset, photographer Laurent Laveder finally spotted a delicate lunar crescent. Captured in this dramatic picture on April 6th from Bretagne, France, the Moon was only 15 hours and 38 minutes old. Its slight, irregular, sunlit arc opens upward just above the dark cloud bank near picture center. Of course, a crescent Moon in the early evening sky is a lovely sight often enjoyed by many. But finding the Moon when its slim crescent is still less than about 24 hours past the New Moon phase requires careful timing and planning, a challenging project even for experienced observers. In this sighting, only about 0.8 percent of the Moon's disk appears illuminated. Laveder notes that this is the youngest Moon he has spotted in twenty years of skygazing and also offers this animation (Flash or gif) based on his images of the tantalizing celestial scene.

Image credit: PixHeaven.net
Yuri's Planet (2008-04-12)

On April 12th, 1961, Soviet cosmonaut Yuri Alexseyevich Gagarin became the first human in space. His remotely controlled Vostok 1 spacecraft lofted him to an altitude of 200 miles and carried him once around planet Earth. Commenting on the first view from space he reported, "The sky is very dark; the Earth is bluish. Everything is seen very clearly". Alan Shepard, the first US astronaut, would not be launched until almost a month later and then on a comparatively short suborbital flight. Born on March 9, 1934, Gagarin was a military pilot before being chosen for the first group of cosmonauts in 1960. As a result of his historic flight he became an international hero and legend. Killed when his MIG jet crashed during a training flight on March 27, 1968, Gagarin was given a hero's funeral, his ashes interred in the Kremlin Wall. On yet another April 12th, in 1981, NASA launched the first space shuttle.
Curious Cometary Knots in the Helix Nebula (2008-04-13)

What causes unusual knots of gas and dust in planetary nebulas?  Seen also in the Ring Nebula, the Dumbbell Nebula and  NGC 2392, the knots' existence was not initially predicted and their origins are still not well understood.  Pictured above is a fascinating image of the Helix Nebula by the Hubble Space Telescope showing tremendous detail of its mysterious gaseous knots.  The above cometary knots have masses similar to the Earth but have radii typically several times the orbit of Pluto.   One hypothesis for the fragmentation and evolution of the knots includes existing gas being driven out by a less dense but highly energetic stellar wind of the central evolving star.  The Helix Nebula is the closest example of a planetary nebula created at the end of the life of a Sun-like star. The Helix Nebula, given a technical designation of NGC 7293, lies about 700 light-years away towards the constellation of Aquarius.
Phobos: Doomed Moon of Mars (2008-04-14)

This moon is doomed.  Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning color image from the Mars Reconnaissance Orbiter, recorded at a resolution of about seven meters per pixel. But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon - that gravitational tidal forces are dragging it down. In 100 million years or so Phobos will likely be shattered by stress caused by the relentless tidal forces, the debris forming a decaying ring around Mars.
Sky Delights Over Sweden (2008-04-15)

This night was a sky enthusiast's delight. While relaxing in Sweden last week, many a cosmic wonder was captured with a single snapshot.  They are described here from near to far.  In the foreground are nearby trees and more distant snow covered mountains. In silhouette, Clouds can be seen just above the horizon, and a careful eye can even discern the more distant green and red auroras which occur in Earth's upper atmosphere.   Red emission nebulas dot the sky, including the Heart and Soul Nebulas, IC 1396 and the North America Nebula.  Running diagonally from the upper left to the lower right is the majestic glowing band of our Milky Way Galaxy's central plane..  More distant than everything else, appearing as it did over two million years ago, is the Andromeda galaxy, visible above the horizon toward on the lower left.

Image credit: Clear Skies
A Protected Night Sky Over Flagstaff (2008-04-16)

This sky is protected.  Yesterday marked the 50 year anniversary of the first lighting ordinance ever enacted, which restricted searchlight advertisements from sweeping the night skies above Flagstaff, Arizona, USA.  Flagstaff now enjoys the status of being the first International Dark Sky City, and maintains a lighting code that limits lights from polluting this majestic nighttime view.  The current dark skies over Flagstaff not only enable local astronomers to decode the universe but allow local sky enthusiasts to see and enjoy a tapestry contemplated previously by every human generation.  The above image, pointing just east of north, was taken two weeks ago at 3 am from Fort Valley, only 10 kilometers from central Flagstaff.  Visible in the above spectacular panorama are the San Francisco Peaks caped by a lenticular cloud.  Far in the distance, the plane of the Milky Way Galaxy arcs diagonally from the lower left to the upper right, highlighted by the constellations of Cassiopeia, Cepheus, and Cygnus.   On the far right, the North America Nebula is visible just under the very bright star Deneb.

Image credit: Dan & Cindy Duriscoe, 
FDSC, 
Lowell Obs., 
USNO
Messier 63: The Sunflower Galaxy (2008-04-17)

A bright spiral galaxy of the northern sky, Messier 63 is about 25 million light-years distant in the loyal constellation Canes Venatici. Also cataloged as NGC 5055, the majestic island universe is nearly 100,000 light-years across, about the size of our own Milky Way. Known by the popular moniker, The Sunflower Galaxy, M63 sports a bright yellowish core and sweeping blue spiral arms, streaked with cosmic dust lanes and dotted with pink star forming regions. But this deep exposure also shows remarkable faint loops and extensions of the galaxy's spiral arms. A dominant member of a known galaxy group, M63's faint extended features could be the result of gravitational interactions with nearby galaxies. M63 also shines across the electromagnetic spectrum and is thought to have undergone bursts of intense star formation.

Image credit: Tony Hallas
IC 2948: The Running Chicken Nebula (2008-04-18)

Bright nebulae abound in and around the expansive southern constellation of Centaurus. This one, cataloged as IC 2948/2944 is near the star Lambda Centauri (just off the top of the frame) and not far on the sky from the better known Eta Carinae Nebula. Embedded in the reddish glowing cloud of hydrogen gas, typical of emission nebulae found in massive star-forming regions, is the energetic young star cluster Collinder 249. Seen in silhouette near the top of the view are small, dark clouds of obscuring cosmic dust. Called Thackeray's Globules for their discoverer, they are potential sites for the formation of new stars, but are likely being eroded by the intense radiation from the nearby young stars. Of course, gazing at the center of the region suggests to some IC 2948's popular name - The Running Chicken Nebula. The gorgeous skyscape spans about 70 light-years at the nebula's estimated 6,000 light-year distance.

Image credit: Steve Crouch
Running Messier's Marathon (2008-04-19)

Gripped by an astronomical spring fever, many northern hemisphere stargazers embark on a Messier Marathon. Completing the marathon requires viewing all 110 objects in 18th century French astronomer Charles Messier's catalog in one glorious dusk-to-dawn observing run. As daunting as it sounds, there are often favorable weekend dates for completing the task that fall on nearly moonless nights near the March equinox. This colorful, six hour long time exposure of a group dedicated to running this year's Messier marathon includes celestial star trails along with terrestrial lighting trails from about 200 amateur astronomers. It was recorded from the isolated, ancient Bahram Palace in northern Iran's Kavir National Park. Astronomer and former Messier Marathon organizer for the ASIAC Babak Tafreshi offers this intriguing time-lapse movie (2MB wmv file) of the event.

Image credit: Amir
Hossein Abolfath
Spiral Galaxies in Collision (2008-04-20)

Billions of years from now, only one of these two galaxies will remain.  Until then, spiral galaxies NGC 2207 and IC 2163 will slowly pull each other apart, creating tides of matter, sheets of  shocked gas, lanes of dark dust, bursts of star formation, and streams of cast-away stars.  Astronomers predict that NGC 2207, the larger galaxy on the left, will eventually incorporate IC 2163, the smaller galaxy on the right.  In the most recent encounter that peaked 40 million years ago, the smaller galaxy is swinging around counter-clockwise, and is now slightly behind the larger galaxy.  The space between stars is so vast that when galaxies collide, the stars in them usually do not collide.
Bacteriophages: The Most Common Life-Like Form on Earth (2008-04-21)

There are more bacteriophages on Earth than any other life-like form.  These small viruses are not clearly a form of life, since when not attached to bacteria they are completely dormant.  Bacteriophages attack and eat bacteria and have likely been doing so for over 3 billion years ago.  Although initially discovered early last century, the tremendous abundance of phages was realized more recently when it was found that a single drop of common seawater typically contains millions of them.  Extrapolating, phages are likely to be at least a billion billion (sic) times more numerous than humans. Pictured above is an electron micrograph of over a dozen bacteriophages attached to a single bacterium.  Phages are very small -- it would take about a million of them laid end-to-end to span even one millimeter.  The ability to kill bacteria makes phages a potential ally against bacteria that cause human disease, although bacteriophages are not yet well enough understood to be in wide spread medical use.
The Fox Fur Nebula from CFHT (2008-04-22)

This interstellar beast is formed of cosmic dust and gas interacting with the energetic light and winds from hot young stars.  The shape, visual texture, and color, combine to give the region the popular name Fox Fur Nebula. The characteristic blue glow on the left is dust reflecting light from the bright star S Mon, just beyond the left edge of the image. Mottled pink and brown areas are a combination of the cosmic dust and reddish emission from ionized hydrogen gas.  S Mon is part of a young open cluster of stars, NGC 2264, located about 2,500 light years away toward the constellation of Monoceros, just north of the Cone Nebula.

Image credit: Jean-Charles Cuillandre
Above the Clouds (2008-04-23)

From the windswept peak of Mauna Kea, on the Big Island of Hawaii, your view of the world at night could look like this. At an altitude of about 13,500 feet, the mountain top is silhouetted in the stunning skyscape recorded near dusk in early December of 2005. The volcanic peak rises just above a sea of storm clouds illuminated by a bright Moon. Planet Venus is setting near the Moon as the brilliant evening star. The scene also includes the faint, milky band of our own galaxy's disk of stars and cosmic dust clouds stretching from the horizon into the sky along the right edge of the frame.

Image credit: Serge Brunier
Cygnus Without Stars (2008-04-24)

The sky is full of hydrogen, though it can take a sensitive camera and telescope to see it. For example, this twelve-degree-wide view of the northern part of the constellation Cygnus reveals cosmic clouds of hydrogen gas along the plane of our Milky Way galaxy. The mosaic of telescopic images was recorded through an h-alpha filter that transmits only visible red light from glowing hydrogen atoms. Further digital processing has removed most of what is left of the myriad, point-like Milky Way stars from the scene, though bright Deneb, alpha star of Cygnus and head of the Northern Cross, remains near top center. Recognizable bright nebulae include NGC 7000 (North America Nebula), and IC 5070 (Pelican Nebula) at the upper left with IC 1318 (Butterfly Nebula) and NGC 6888 (Crescent Nebula) at lower right -- but others can be found throughout the wide field. Want the stars back? Just slide your cursor over the picture.

Image credit: Igor Chekalin