juliensimon/nasa-apod huggingface dataset:
Frosty Mountains on Mars (2003-07-30)

What causes the unusual white color on some Martian mountains?  The answer can be guessed by noticing that the bright areas disappear as springtime takes hold in the south of Mars: dry ice.  Dry carbon dioxide ice sublimates directly to gas from its frozen state.  The frosty mountains, named Charitum Montes, have been covered with carbon dioxide ice over the Martian winter.  The serene scene pictured above is not a photograph, but rather a computationally constructed digital illusion resulting from the fusion of two color images from the Mars Orbital Camera and topographic data from the Mars Orbiter Laser Altimeter.  Both instruments operate from the Mars Global Surveyor robot spacecraft currently orbiting Mars.  The red planet continues to grow larger in terrestrial skies as Earth and Mars move closer to their recent-record closest approach on August 27.
Galaxy Group HCG 87 (2003-07-31)

Posing for this cosmic family photo are the galaxies of HCG (Hickson Compact Group) 87, about four hundred million light-years distant toward the amphibious constellation Capricornus. The large edge-on spiral near picture center, the fuzzy elliptical galaxy immediately to its right, and the spiral near the top of the image are identified members of the group, while the small spiral galaxy in the middle is likely a more distant background galaxy. In any event, a careful examination of the deep image reveals other galaxies which certainly lie far beyond HCG 87. While not exactly locked in a group hug, the HCG 87 galaxies are interacting gravitationally, influencing their fellow group members' structure and evolution. This new image is from an instrument undergoing commissioning on the Gemini Observatory's South Telescope at Cerro Pachon, Chile. It compares favorably with views of this photogenic galaxy group recorded by the Hubble Space Telescope.
Moons and Bright Mars (2003-08-01)

In this serene view, the moons of Earth along with the bright planet Mars shine above the city of Turku near the southwestern tip of Finland. Of course Earth's large natural satellite, the Moon, at a distance of 400,000 kilometers, is by far the brightest object in this sky. But growing brighter and closer by the hour, Mars appears as the impressively bright "star" at the right, about 64 million kilometers from Turku. Streaking across the twilight sky between the two celestial beacons, Earth's largest artificial moon, the International Space Station, orbits about 400 kilometers above the planet's surface. To capture the moment, amateur astronomer Petteri Kankaro used a digital camera and combined exposures beginning at 23:34 Universal Time on July 17th.

Image credit: Petteri Kankaro
Island Universe, Cosmic Sand (2003-08-02)

On August 13, 2002, while counting Perseid meteors under dark, early morning Arizona skies, Rick Scott set out to photograph their fleeting but fiery trails. The equipment he used included a telephoto lens and fast color film. After 21 pictures he'd caught only two meteors, but luckily this was one of them. Tracking the sky, his ten minute long exposure shows a field of many stars in our own Milky Way galaxy, most too faint to be seen by the unaided eye. Flashing from lower left to upper right, the bright meteor would have been an easy eyeful though, as friction with Earth's atmosphere vaporized the hurtling grain of cosmic sand, a piece of dust from Comet Swift-Tuttle. Just above and left of center, well beyond the stars of the Milky Way, lies the island universe known as M31 or the Andromeda galaxy. The visible meteor trail begins about 100 kilometers above Earth's surface, one of the closest celestial objects seen in the sky. In contrast, Andromeda, about 2 million light-years away, is the most distant object easily visible to the naked-eye.

Image credit: Rick Scott
Ice Fishing for Cosmic Neutrinos (2003-08-03)

Scientists are melting holes in the bottom of the world.  In fact, several holes have been melted near the South Pole, and they are now being used as astronomical observatories.  Astronomers with the Antarctic Muon and Neutrino Detector Array (AMANDA) lower into each vertical lake a string knotted with basketball-sized light detectors.  The water in each hole soon refreezes.  The detectors are sensitive to blue light emitted in the surrounding clear ice. Such light is expected from ice collisions with high-energy neutrinos emitted by objects or explosions out in the universe.  The above picture was taken looking down into the deep abyss.  Instruments were lowered down past 2000 meters.  Analyses of data from the AMANDA II detectors have recently been used to create the first map of the high-energy neutrino sky.
In the Center of the Virgo Cluster (2003-08-04)

The Virgo Cluster of Galaxies is the closest cluster of galaxies to our Milky Way Galaxy.  The Virgo Cluster is so close that it spans more than 5 degrees on the sky - about 10 times the angle made by a full Moon.  It contains over 100 galaxies of many types - including spiral, elliptical, and irregular galaxies.  The Virgo Cluster is so massive that it is noticeably pulling our Galaxy toward it.  The cluster contains not only galaxies filled with stars but also gas so hot it glows in X-rays.  Motions of galaxies in and around clusters indicate that they contain more dark matter than any visible matter we can see.  Pictured above, the center of the Virgo cluster might appear to some as a human face, and includes bright Messier galaxies M86 at the top, M84 on the far right, NGC 4388 at the bottom, and NGC 4387 in the middle.

Image credit: Jean-Charles Cuillandre
Shuttle Ferry (2003-08-05)

How does a space shuttle that landed in California get back to Florida for its next launch?  The answer is by ferry.  NASA operates two commercial Boeing 747 airplanes modified to carry a space shuttle on their backs.  Designated officially as Shuttle Carrier Aircraft or SCA, the 747s were made for commercial flights but bolstered by NASA with several struts, stabilizers, and electronic monitors.  Spanning about 70 meters in length, the two aircraft's combined mass is nearly 150,000 kilograms.  Pictured above, the space shuttle Atlantis is shown being ferried back to NASA Kennedy Space Center in Florida in September 1998.
Dusty Galaxy Centaurus A (2003-08-06)

Why is peculiar galaxy Centaurus A so dusty?  Dramatic dust lanes that run across the galaxy's center mark Cen A.  These dust lanes are so thick they almost completely obscure the galaxy's center in visible light.  This is particularly unusual as Cen A's red stars and round shape are characteristic of a giant elliptical galaxy, a galaxy type usually low in dark dust.  Cen A, also known as NGC 5128, is also unusual compared to an average elliptical galaxy because it contains a higher proportion of young blue stars and is a very strong source of radio emission.  Evidence indicates that Cen A is likely the result of the collision of two normal galaxies.  During the collision, many young stars were formed, but details of the creation of Cen A's unusual dust belts are still being researched.  Cen A lies only 13 million light years away, making it the closest active galaxy.  Cen A spans 60,000 light years and can be seen with binoculars toward the constellation of Centaurus.
Palomar at Night (2003-08-07)

What's wrong with this picture? The summer night sky is clear, and moonlight illuminates the dome of the Hale 200-inch Telescope at Palomar Observatory, northeast of San Diego, California, USA. The familiar stars of the Teapot asterism in the constellation Sagittarius shine above the dome and to the right. In fact, the only thing wrong with the picture is that the observatory dome's two massive shutters are closed tight ... on a clear night. This extremely unusual situation is a precaution prompted by the presence of airborne ash and smoke from wildfires in the area on July 17 which could have damaged the historic mirror's aluminum coating. Amateur astronomer Greg Redfern notes that this year has been a particularly bad one for observatories and wildfires, with the Mt. Stromlo Australian Observatory disaster and fires also threatening telescopes on Mount Lemmon near Tucson, Arizona.

Image credit: Greg Redfern
(2003
JPL NASA Solar System Ambassador)
Blue Stragglers in NGC 6397 (2003-08-08)

In our neck of the Galaxy stars are too far apart to be in danger of colliding, but in the dense cores of globular star clusters star collisions may be relatively common. In fact, researchers have evidence that the closely spaced blue stars near the center of the above image taken by the orbiting Hubble Space Telescope were formed when stars directly collided. Pictured is the central region of NGC 6397, a globular cluster about 6,000 light-years distant, whose stars all formed at about the same time. NGC 6397's massive stars have long since evolved off the main sequence, exhausting their central supplies of nuclear fuel. This should leave the cluster with only old low mass stars; faint red main sequence stars and brighter blue and red giants. However, spectroscopic data show that the indicated stars, descriptively dubbed blue stragglers, are clearly main sequence stars which are too blue and too massive to still be there. Suggestively the stragglers appear to be two and occasionally three times as massive as the lower mass cluster stars otherwise present, supporting evidence for their formation from two and even three star collisions.
A Perseid Aurora (2003-08-09)

Just after the Moon set but before the Sun rose in the early morning hours of 2000 August 12, meteors pelted the Earth from the direction of the constellation  Perseus, while ions pelted the Earth from the Sun.  The meteors were expected as sub-sand grains long left behind by Comet Swift-Tuttle annually create the Perseids Meteor Shower.  The aurorae were unexpected, however, as electrons, protons, and heavier ions raced out from a large Coronal Mass Ejection that had occurred just days before on the Sun.  In the foreground is Hahn's Peak, an extinct volcano in Colorado, USA. The Perseid meteor shower peaks this year over the next few days, with as much as one bright meteor per minute visible from some locations.

Image credit: Jimmy Westlake
(Colorado Mountain College)
Lunation (2003-08-10)

Our Moon's appearance changes nightly.  This time-lapse sequence shows what our Moon looks like during a lunation, a complete lunar cycle.  As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible.  The Moon always keeps the same face toward the Earth.  The Moon's apparent size changes slightly, though, and a slight wobble called a libration is discernable as it progresses along its elliptical orbit. During the cycle, sunlight reflects from the Moon at different angles, and so illuminates different features differently.  A full lunation takes about 29.5 days, just under a month (moon-th).

Image credit: Ant�nio Cidad�o
Elements of the Swan Nebula (2003-08-11)

In the depths of the dark clouds of dust and molecular gas known as M17, stars continue to form.  Also known as the Omega Nebula and Horseshoe Nebula, the darkness of M17's  molecular clouds results from background starlight being absorbed by thick filaments of carbon-based smoke-sized dust.  As bright massive stars form, they produce intense and energetic light that slowly boils away the dark shroud.  Colors in the above image were picked to highlight specific elements that emit nebular light: red indicates emission from sulfur, green from hydrogen, and blue from oxygen.  The Swan Nebula is visible with binoculars towards the constellation of Sagittarius, lies 5000 light-years away, and spans 20 light-years across.

Image credit: Russell Croman
X-Rays from Stephan's Quintet (2003-08-12)

Stephan's Quintet is a picturesque but clearly troubled grouping of galaxies about 300 million light-years away toward the high-flying constellation Pegasus. Spanning over 200,000 light-years at that distance, this composite false-color image illustrates the powerful nature of this multiple galaxy collision, showing x-ray data from the Chandra Observatory in blue superposed on optical data in yellow. The x-rays from the central blue cloud running vertically through the image are produced by gas heated to millions of degrees by an energetic shock on a cosmic scale. The shock was likely the result of the interstellar gas in the large spiral galaxy, seen immediately to the right of the cloud, colliding with the quintet's tenuous intergalactic gas as this galaxy plunged through group's central regions. In fact, over billions of years, repeated passages of the group galaxies through the hot intergalactic gas should progressively strip them of their own star forming material. In this view, the large spiral galaxy just seen peeking above the bottom edge is an unrelated foreground galaxy a mere 35 million light-years distant.
Mars Rising Behind Poodle Rock (2003-08-13)

Have you seen Mars lately?  As Earth and Mars near their closest approach in nearly 60,000 years on August 27, the red planet has begun to appear dramatically bright and show interesting details through telescopes and binoculars.  Although not yet visible at sunset, Mars can be seen rising increasingly earlier in the evening.  Once above the horizon, Mars is easy to spot, as it sports a distinct orange-red hue and it is the brightest object in the sky after the Sun, the nearby Moon, and Venus. After Earth overtakes Mars in their respective solar orbits, Mars will be visible right from sunset, although its historic brightness will then begin to fade.  Pictured above, Mars was captured rising in the south east next to Poodle Rock in Valley of Fire State Park, Nevada, USA.

Image credit: Wally Pacholka (Astropics)
Dark Matter Map (2003-08-14)

The total mass within giant galaxy cluster CL0025+1654, about 4.5 billion light-years away, produces a cosmic gravitational lens -- bending light as predicted by Einstein's theory of gravity and forming detectable images of even more distant background galaxies. Of course, the total cluster mass is the sum of the galaxies themselves, seen as ordinary luminous matter, plus the cluster's invisible dark matter whose nature remains unknown. But by analyzing the distribution of luminous matter and the properties of the gravitational lensing due to total cluster mass, researchers have solved the problem of tracing the dark matter layout. Their resulting map shows the otherwise invisible dark matter in blue, and the positions of the cluster galaxies in yellow. The work, based on extensive Hubble Space Telescope observations, reveals that the cluster's dark matter is not evenly distributed, but follows the clumps of luminous matter closely.
Sedimentary Mars (2003-08-15)

High-resolution imaging of an area in the Schiaparelli Basin of Mars on June 3 by the MGS Mars Orbiter camera produced this stunning example of layered formations within an old impact crater. On planet Earth, such structures would be seen in sedimentary rock -- material deposited at the bottom of ancient lakes or oceans and then subsequently weathered away to reveal the layers. With the Sun shining from the left, the central layer appears to stand above the others within the 2.3 kilometer wide crater. The crater could well have been filled with water in Mars' distant past, perhaps resting at the bottom of a lake filling the Schiaparelli impact basin. Still, such layers might also have been formed by material settling out of the windy martian atmosphere. As satellites continue to examine the martian surface from orbit, NASA's Spirit and Opportunity spacecraft will attempt to land on on Mars early next year to further explore the tantalizing history of water on the Red Planet.
Thackeray's Globules (2003-08-16)

Rich star fields and glowing hydrogen gas silhouette dense, opaque clouds of interstellar gas and dust in this Hubble Space Telescope close-up of IC 2944, a bright star forming region in Centaurus, 5,900 light-years away. The largest of these dark globules, first spotted by South African astronomer A. D. Thackeray in 1950, is likely two separate but overlapping clouds, each more than one light-year wide. Combined the clouds contain material equivalent to about 15 times the mass of the Sun, but will they actually collapse to form massive stars? Along with other data, the sharp Hubble images indicate that Thackeray's globules are fractured and churning as a result of intense ultraviolet radiation from young, hot stars already energizing and heating the bright emission nebula. These and similar dark globules known to be associated with other star forming regions may ultimately be dissipated by their hostile environment -- like cosmic lumps of butter in a hot frying pan.
Natural Saturn On The Cassini Cruise (2003-08-17)

What could you see approaching Saturn aboard an interplanetary cruise ship? Your view would likely resemble this subtly shaded image of the gorgeous ringed gas giant. Processed by the Hubble Heritage project, the picture intentionally avoids overemphasizing color contrasts and presents a natural looking Saturn with cloud bands, storms, nearly edge-on rings, and the small round shadow of the moon Enceladus near the center of the planet's disk. Of course, seats were not available on the only ship currently en route, the Cassini spacecraft. Cassini flew by Jupiter at the turn of the millennium and is scheduled to arrive at Saturn in the year 2004. After an extended cruise to a world 1,400 million kilometers from the Sun, Cassini will tour the Saturnian system, conducting a remote, robotic exploration with software and instruments designed by denizens of planet Earth.
Bright Lights, Dark City (2003-08-18)

Last Thursday, millions of people had an unexpectedly good view of a dark night sky.  Usually, the reflection of city lights off of local air impurities makes it hard for casual observers to see more than a handful of stars from a bright urban area.  A large power outage in northeast North America, however, dimmed most city lights and brought unfamiliar celestial wonders to many who looked up.  The unexpected starscape was perhaps a small perk in the face of hardships endured by many during the black out.  Prominent in the above four-image digital montage are two of the few celestial wonders that can be seen even above the usual glare of city light pollution: the Moon and Mars.  Both appear on the far left, with Mars to the upper right of the Moon.  Scrolling right will show how eerily dark New York City appeared from across the Hudson River in New Jersey at about 10 pm on 2003 August 14.  Visible lights are mostly attributable to cars, local power generators, flashlights, and candles.

Image credit: Bill Rosen
Mars Through a Small Telescope (2003-08-19)

How does Mars appear through a small telescope?  Viewed with the unaided eye or through a small telescope, possibly the most striking part of Mars' appearance is its red color.  The color derives from rust, iron oxide, which composes perhaps 10% of the Martian soil.  The oxygen that rusts the surface iron on Mars originates predominantly from carbon dioxide gas, which composes 95% of the Martian atmosphere.  Mars nears its closest approach with Earth in nearly 60 millennia on August 27, the red planet continues to appear larger, brighter, and a good target for sky enthusiasts.  Pictured above, Mars was captured from the Canary Islands of Spain during three days in three different orientations earlier this month.  Visible through the small telescope are white polar caps of water and carbon-dioxide ice, light red areas rich in lightly colored craters, and dark red areas dominated by relatively smooth lowlands.

Image credit: Francisco A. Rodriguez Ramirez
(AstroEduca)
The E Nebula in Aquila (2003-08-20)

Several unusual strands of darkness are prominent toward the constellation of Aquila.  This particular dark nebula is known as the E Nebula, for its evocative shape, or B142 and B143, for its position(s) on a list of such nebula compiled by Barnard.  The E Nebula spans roughly the angle of a full Moon and lies about 2000 light years distant.  The nebula can be seen with binoculars and is particularly visible during the summer months in Earth's northern hemisphere.  Other names for dark nebula include absorption nebula, as they efficiently absorb visible light emitted behind them, and molecular clouds, as they frequently attain temperatures low enough so that several different types of stable molecules can exist.  The low temperatures of these interstellar clouds facilitate the formation of dense knots of gas that may then collapse into bright stars.

Image credit: Chris Cook
X-Rays from M17 (2003-08-21)

About 5,000 light-years away, toward the constellation Sagittarius and the center of our galaxy, lies the bright star forming region cataloged as M17. In visible light, M17's bowed and hollowed-out appearance has resulted in many popular names like the Horseshoe, Swan, Omega, and Lobster nebula. But what has sculpted this glowing gas cloud? This Chandra Observatory image of x-rays from M17 provides a clue. Many massive young stars are responsible for the pink central region of the false-color x-ray picture, their colliding stellar winds producing the multimillion degree gas cloud which extends ten or so light-years to the left. When compared with visible light images, this x-ray hot cloud is partly surrounded by the nebula's cooler gas. In fact, having carved out a central cavity the hot gas seems to be flowing out of the horseshoe shape like champagne from an uncorked bottle ... suggesting yet another name for star forming region M17.
Shadow Rise (2003-08-22)

As the Sun sets, the Earth's shadow rises up from the east. The subtle beauty of this daily apparition is often overlooked in favor of the brighter, more colorful western horizon. But while gazing toward a nearly full rising Moon on August 9, astronomer Steve Mandel admired the shadow rise from his driveway near Soquel, California, USA. His view looks east from the northern tip of Monterey Bay toward Fremont Peak, the highest point in the small mountain range on the horizon. The Earth's rising shadow is cast through the dense atmosphere and is seen in his picture as the dark blue band along the horizon, bounded above by a pinkish purple glow or antitwilight arch. Also known as the Belt of Venus, the arch's lovely color is due to backscattering of reddened light from the setting Sun.

Image credit: Steve Mandel
The Tarantula Zone (2003-08-23)

The Tarantula Nebula is more than 1,000 light-years across - a giant emission nebula within our neighboring galaxy the Large Magellanic Cloud. Inside this cosmic arachnid lies a central young cluster of massive stars, cataloged as R136, whose intense radiation and strong winds have helped energize the nebular glow and shape the spidery filaments. In this impressive color mosaic of images from the Wide-Field Imager camera on ESO's 2.2 meter telescope at La Silla Observatory, other young star clusters can be seen still within the nebula's grasp. Also notable among the denizens of the Tarantula zone are several dark clouds invading the nebula's outer limits as well as the dense cluster of stars NGC 2100 at the extreme left edge of the picture. The small but expanding remnant of supernova 1987a, the closest supernova in modern history, lies just off the lower right corner of the field. The rich mosaic's field of view covers an area on the sky about the size of the full moon in the southern constellation Dorado.