juliensimon/nasa-apod huggingface dataset:
Moon Shadow (1998-03-12)

When the Moon's shadow reached out and touched the Earth last month, the result was a Solar Eclipse. Such an eclipse is total only for observers located along a narrow path corresponding to the ground track of the shadow's dark central portion or "umbra". For this eclipse, racing along at nearly 1,200 miles per hour, the Moon's umbra obligingly crossed over land along pleasant tropical locales in South America and the Caribbean islands. Totality lasted for about 3 minutes or less at a given location.  Sizable fractions of North and South America fell within the lighter but much wider outer shadow region, the "penumbra", and witnessed a partial eclipse. This movie gif follows the Moon's shadow from Central and South America eastward across the Atlantic - as seen from the vantage point of an orbiting Geostationary Operational Environmental Satellite (GOES), 22,000 miles above Earth. The three frame animation spans about 2 hours. GOES satellite images are a corner stone of U.S. weather monitoring and forecast operations.
Asteroids (1998-03-13)

No asteroid or comet is known to be on a collision course with Earth. The asteroid designated 1997 XF11 had been predicted to come uncomfortably close, but new estimates place its passing beyond the orbit of the Moon. This earth-approaching asteroid was discovered by SpaceWatch astronomer Jim Scotti in December of last year. Orbital computations using new observations suggested that it would pass within 30,000 miles of the Earth's center on October 26, 2028 - a very near miss considering that the radius of the Earth itself is about 4,000 miles. However, more recent and further refined calculations based on both new and archival data indicate that the closest approach will be 600,000 miles in 2028. Imaged by NASA spacecraft, the three potato-shaped objects above are large main-belt asteroids orbiting between Mars and Jupiter. Shown to the same scale from left to right are Mathilde, Gaspra, and Ida. Mathilde has dimensions of about 37 by 29 miles. The asteroid 1997 XF11 is much smaller, probably a mile wide, yet the impact of an asteroid of this size could have catastrophic effects. Over the last two decades, teams of astronomers have just begun to catalog and track near-earth objects.
A Spiral Galaxy Gallery (1998-03-14)

A progression of beautiful spiral galaxies is illustrated above with three photographs from NASA's Ultraviolet Imaging Telescope (UIT). Flying above the Earth's obscuring layer of atmosphere on the Space Shuttle Columbia during the Astro-1 mission in 1990, UIT's cameras were able to image these distant spirals in the ultraviolet light produced by hot, young stars. These bright stars, newly condensed from gas and dust clouds, give away the location of the spiral arms they are born in. Because they are massive (many times the mass of the Sun), they are shortlived. Dying and fading before they move too far from their birth place they make excellent tracers of spiral structure. From left to right the galaxies are known as M33, M74, and M81 and have progressively more tightly wound spiral arms. Astronomers would classify these as Scd, Sc, and Sb type spirals using a galaxy classification scheme first worked out by Edwin Hubble.
Unusual M82: The Cigar Galaxy (1998-03-15)

Something strange happened to this galaxy, but what?  M82 is a nearby galaxy in the group of galaxies dominated by itself, M81, and NGC 3077.  M82 is thought by some to be limping away from a close encounter with M81. This galactic collision might have stirred up the inner stars and gas in M82, causing the unusual dark lanes of dust visible in the above photograph.  M82 is a starburst galaxy with a very active center containing star clusters far brighter than any in our own Milky Way Galaxy.

Image credit: P. Challis 
(CfA),
1.2-m Telescope,
Whipple Observatory
Asteroids in the Distance (1998-03-16)

Rocks from space hit Earth every day.  The larger the rock, though, the less often Earth is struck.  Many kilograms of space dust pitter to Earth daily. Larger bits appear initially as a bright meteor. Baseball-sized rocks and ice-balls streak through our atmosphere daily, most evaporating quickly to nothing.  Significant threats do exist for rocks near 100 meters in diameter, which strike Earth roughly every 1000 years.  An object this size could cause significant tidal waves were it to strike an ocean, potentially devastating even distant shores.  A collision with a massive asteroid, over 1 km across, is more rare, occurring typically millions of years apart, but could have truly global consequences.  Many asteroids remain undiscovered.  In fact, the discovery of several was announced last week; one is shown as the long blue streak in the above photograph. Such an interplanetary collision would not affect Earth's orbit so much as raise dust that would affect Earth's climate.  One likely result is a global extinction of many species of life, possibly dwarfing the ongoing extinction occurring now.
Clouds Over Tharsis on Mars (1998-03-17)

When and where do clouds form on Mars? The Mars Global Surveyor spacecraft currently orbiting Mars is finding out.  Photographs released last week showed clouds forming above Tharsis, a huge bulge on Mars about 4000 kilometers across and 7 kilometers high containing several large volcanoes. These clouds temporarily disappeared as a large dust storm emerged from the South, the first developing dust storm to be tracked by an orbiting spacecraft.  Mars Global Surveyor continues to aerobrake during on its ongoing mission to survey the planet Mars.
Interstellar Dust-Bunnies of NGC 891 (1998-03-18)

What is going on in NGC 891?  This galaxy appeared previously to be very similar to our own Milky Way Galaxy: a spiral galaxy seen nearly edge-on.  However, recent high-resolution images of NGC 891's dust show unusual filamentary patterns extending well away from its Galactic disk. This interstellar dust was probably thrown out of the galactic disk toward the halo by stellar supernovae explosions.  Because dust is so fragile, its appearance after surviving disk expulsion can be very telling. Newly discovered phenomena, however, sometimes appear so complex that more questions are raised than are answered.

Image credit: WIYN, 
Inc., 3.5-m WIYN Telescope
Mars: A Canyon's Edge (1998-03-19)

High resolution Mars Global Surveyor images were combined with Viking Orbiter color data to produce this stunning, detailed view of a Martian canyon's edge. The area pictured is about 6 miles wide and represents a tiny part of the northern edge of the canyon Valles Marineris, whose total length is about 2,500 miles. Details 20 to 30 feet across can be seen in the high resolution data. The composition of the thin, well-defined layers in the steep canyon walls is unknown, but their presence points to a complex and active Martian geologic history. In the later half of the 1970s, NASA's Viking Orbiters photographed Mars extensively, yet Surveyor's sharp new images have produced some striking and unanticipated results.
Mars: Ridges Near The South Pole (1998-03-20)

No, it's not breakfast ... but looking down from an orbiting spacecraft, the odd intersecting ridges covering this area of Mars do present a waffle-like appearance. The cause of the ridge pattern is unknown but it suggests that more complex layered deposits lie below. The south polar region in this Mars Global Surveyor image measures about 8.5 by 12 miles and is spread with a layer of bright, seasonal carbon dioxide frost. Mysterious dark spots which pepper some of the interridge areas are 60 to 300 feet across. Their exact nature is also unknown, but these spots have apparently defrosted early and lack the bright layer of frozen carbon dioxide.
The Gamma Ray Sky (1998-03-21)

What if you could "see" gamma rays? If you could, the sky would seem to be filled with a shimmering high-energy glow from the most exotic and mysterious objects in the Universe. In the early 1990s NASA's orbiting Compton Observatory, produced this premier vista of the entire sky in gamma rays - photons with more than 40 million times the energy of visible light. The diffuse gamma-ray glow from the plane of our Milky Way Galaxy runs horizontally through the false color image. The brightest spots in the galactic plane (right of center) are pulsars - spinning magnetized neutron stars formed in the violent crucibles of stellar explosions. Above and below the plane, quasars, believed to be powered by supermassive black holes, produce gamma-ray beacons at the edges of the universe. The nature of many of the fainter sources remains unknown.
Sunspots: Magnetic Depressions (1998-03-22)

Our Sun has spots! These spots appear dark in photographs like the one above, but in fact sunspots are quite bright - they are just dark compared to the rest of the Sun. Sunspots are about the size of the Earth and frequently occur in groups, as shown above. Sunspots occur when a concentrated portion of the Solar magnetic field pokes through the surface.  This field slows energy from entering the sunspot region, causing sunspots to appear cooler, darker, and lower than the surrounding surface.  Sunspots typically last a few days before dissipating. The number of sunspots is always changing, generally going from a maximum to a minimum about every 5 ½ years. In fact, the Sun just passed a minimum two years ago.  The Sun and sunspots should never be looked at directly.
Starbirth in NGC 1808 (1998-03-23)

The center of galaxy NGC 1808 is bursting with new stars, but why? Being a barred spiral galaxy makes NGC 1808 somewhat similar to our own Milky Way Galaxy.  But the disk of NGC 1808 (inset) is quite warped, and its center is unusually bright and blue. The above picture of NGC 1808's center, in representative color, was recently taken by the Hubble Space Telescope and released yesterday. Perhaps gravitational pull from a recent pass of neighboring galaxy NGC 1792 has caused matter to move inward along NGC 1808's bar, triggering the burst of star formation.  Also prominent are blue clusters of stars and filaments of dark dust obscuring even more activity.
A Baby Galaxy (1998-03-24)

What's the farthest galaxy known? The answer keeps changing as astronomers compete to find new galaxies which top the list.  The new record holder is now the faint red smudge indicated in the above image by the arrow.  Detected light left this galaxy billions of years ago, well before the Earth formed, when the universe was younger than 1/10th of its present age.  Astronomers have measured a redshift of 5.34 for this galaxy, breaking the "5 barrier" for the first time.  Young galaxies are of much interest to astronomers because many unanswered questions exist on when and how galaxies formed in the early universe.  Although this galaxy's distance exceeds that of even the farthest known quasar, it is still in front of the pervasive glowing gas that is now seen as the cosmic microwave background radiation.
Planetary Nebula NGC 7027 in Infrared (1998-03-25)

NGC 7027 is one of the smallest known planetary nebulae. Even so, NGC 7027 is 14,000 times larger than the Earth-Sun distance. Planetary nebula are so named because the first few discovered appeared similar to planets.  Planetary nebula are actually dying stars, though, that have recently run out of nuclear fuel.  The outer gaseous shells are expelled by an unknown process, frequently creating spectacular displays.  In the above picture in infrared light, the hot central star is visible. Our Sun will become a planetary nebula in about 5 billion years.
Galaxies Away (1998-03-26)

This striking pair of galaxies is far, far away ... about 350 million light-years from Earth. Cataloged as AM0500-620, the pair is located in the southern constellation Dorado. The background elliptical and foreground spiral galaxy are representative of two of the three major classes of galaxies which inhabit our Universe. Within the disks of spiral galaxies, like our own Milky Way, gas, dust, and young blue star clusters trace out grand spiral "arms". The dust lanes along the arms of this particular spiral stand out dramatically in this Hubble Space Telescope image as they obligingly sweep in front of the background elliptical. Like the central bulges of spiral galaxies, elliptical galaxies tend toward spherical shapes resulting from more random motions of their stars. But while spirals produce new stars, star formation in ellipticals which lack gas and dust seems to have stopped. How do galaxies evolve with cosmic time? Evidence is growing that graceful galaxy shapes can hide a violent history.
Lunar Dust and Duct Tape (1998-03-27)

Why is the Moon dusty? On Earth, rocks are weathered by wind and water, creating soil and sand. On the Moon, the long history of micrometeorite bombardment has blasted away at the rocky surface creating a layer of powdery lunar soil or regolith. This lunar regolith could be a scientific and industrial bonanza. But for the Apollo astronauts and their equipment, the pervasive, fine, gritty dust was definitely a problem. On the lunar surface in December 1972, Apollo 17 astronauts Harrison Schmitt and Eugene Cernan needed to repair one of their lunar rover's fenders in an effort to keep the "rooster tails" of dust away from themselves and their gear. This picture reveals the wheel and fender of their dust covered rover along with the ingenious application of spare maps, clamps, and a grey strip of "duct tape".
Von Braun's Wheel (1998-03-28)

Orbiting 1,075 miles above the Earth, a 250 foot wide, inflated, reinforced nylon "wheel" was conceived in the early 1950s to function as a navigational aid, meteorological station, military platform, and way station for space exploration by rocket pioneer Wernher von Braun. The wheel-shaped station could be easily rotated creating artificial gravity so that the astronauts would not suffer the effects of prolonged weightlessness. Von Braun and his team favored building a permanently occupied Earth orbiting space station from which to stage a lunar exploration program. But in the 1960s NASA adopted the Apollo Program, which called for astronauts to transfer to a landing vehicle after achieving lunar orbit, bypassing the construction of von Braun's wheel.
NGC 3293: A Bright Young Open Cluster (1998-03-29)

Hot blue stars shine brightly in this beautiful, recently formed galactic or "open" star cluster. Open cluster NGC 3293 is located in the constellation Carina, lies at a distance of about 8000 light years, and has a particularly high abundance of these young bright stars. A study of NGC 3293 implies that the blue stars are only about 6 million years old, whereas the cluster's dimmer, redder stars appear to be about 20 million years old. If true, star formation in this open cluster took at least 15 million years. Even this amount of time is short, however, when compared with the billions of years stars like our Sun live, and the over-ten billion year lifetimes of many galaxies and our universe. NGC 3293 appears just in front dense dust lane emanating from the Carina Nebula.

Image credit: Anglo-Australian Telescope
Board
A Bulls-Eye Einstein Ring (1998-03-30)

Can one galaxy hide behind another? Not in the case of B1938+666.  Here the foreground galaxy acts like a huge gravitational lens, pulling the light from the background object around it, keeping it visible. Here the alignment is so precise that the distant galaxy is distorted into a nearly perfect giant ring around the foreground galaxy, a formation known as an Einstein ring.  The bright peak at the center of the bulls-eye is the nearer galaxy.  The cosmic mirage was found initially with the MERLIN radio telescope array. The follow-up image shown above from the Hubble Space Telescope was released earlier today.  Although appearing extremely small at 1 arcsecond diameter, the above Einstein ring is really tens of thousands of light years across.
M20: The Trifid Nebula (1998-03-31)

Unspeakable beauty and unimaginable bedlam can be found together in the Trifid Nebula. Also known as M20, this photogenic nebula is visible with good binoculars in the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos.  The red-glowing gas results from high-energy light striking interstellar hydrogen gas. The dark dust filaments that lace M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. Which bright young star lights up the blue reflection nebula is still being investigated. The light from M20 we see today left perhaps 3000 years ago.  Light takes about 50 years to cross M20.

Image credit: Anglo-Australian Telescope
Board
Astronaut Kicks Lunar Field Goal (1998-04-01)

Score three points for NASA.  With time running out late in Apollo 15's mission to the Moon in 1971, Astronaut David Scott prepared to "split the uprights" and bring about yet another dramatic end-of-the-mission win for NASA.  Scott used a special "lunar football" designed for the rugged games held on the Moon. R1D1, a predecessor to R2D2, cheers from the sideline. Happy April Fools Day from the folks at APOD.  In reality, Astronaut Scott adjusts one of Apollo 15's lunar experiments. The foreground device actually measured high-energy particles that escape from the Sun.
Iridium Flare (1998-04-02)

Have you seen an Iridium flare? Satellites in low Earth orbit reflect sunlight and are often visible gliding across early evening and predawn skies. But sun glints from Iridium commercial digital communications satellites are providing the most spectacular sightings. This Iridium flare photographed on September 20, 1997 by Belgian amateur astronomer Chris Dorreman reached an impressive -8 magnitude (about as bright as the half illuminated Moon). The one minute long exposure shows star trails nearly perpendicular to the bright, flaring track of the satellite and a "ghost" image of the flare at the far right. Iridium is the 77th element and so was a good name for the originally intended constellation of 77 satellites. Subsequently, plans were scaled down to 66 satellites with about 51 now in orbit and glinting away. Typical flares last 10 to 20 seconds. When can you catch a flare? The brightness, timing, and direction of a flare depend critically on your longitude and latitude, but satellite observers can make accurate predictions days in advance.

Image credit: Chris Dorreman
Hen-1357: New Born Nebula (1998-04-03)

This Hubble Space Telescope picture shows Hen-1357, the youngest known planetary nebula. Graceful, gentle curves and symmetry suggest its popular name - The Stingray Nebula. Observations in the 1970s detected no nebular material, but this image from March 1996 clearly shows the Stingray's emerging bubbles and rings of shocked and ionized gas. The gas is energized by the hot central star as it nears the end of its life, evolving toward a final white dwarf phase. The image also shows a companion star (at about 10 o'clock) within the nebula. Astronomers suspect that such companions account for the complex shapes and rings of this and many other planetary nebulae. This cosmic infant is about 130 times the size of our own solar system and growing. It is 18,000 light-years distant, in the southern constellation Ara.
Mercury Astronauts and a Redstone (1998-04-04)

Space suited project Mercury astronauts John H. Glenn, Virgil I. Grissom, and Alan B. Shepard Jr. (left to right) are posing in front of a Redstone rocket in this vintage 1961 NASA publicity photo. Project Mercury was the first U.S. program designed to put humans in space. It resulted in 6 flights using one-man capsules and Redstone and Atlas rockets. Shortly after the first U.S. manned flight on May 5, 1961, a suborbital flight piloted by Alan Shepard, President Kennedy announced the goal of a manned lunar landing by 1970. This goal was achieved by NASA's Apollo program and Shepard himself walked on the moon as commander of the Apollo 14 mission. Virgil Grissom died in a tragic fire during an Apollo launch pad test in 1967. Senator John Glenn will fly again on the 25th voyage of the Space Shuttle Discovery.
X-Ray Pleiades (1998-04-05)

The Pleiades star cluster is one of the jewels of the northern sky. To the unaided eye it appears as a lovely and tantalizing grouping of stars in the constellation of Taurus, while telescopic views reveal cluster stars surrounded by delicate blue wisps of dust-reflected starlight. To the X-ray telescopes on board the orbiting ROSAT observatory, the cluster also presents an impressive, but slightly altered, appearance. This false color image was produced from ROSAT observations by translating different X-ray energy bands to visual colors - the lowest energies are shown in red, medium in green, and highest energies in blue. (The green boxes mark the position of the seven brightest visual stars.) The Pleiades stars seen in X-rays have extremely hot, tenuous outer atmospheres called coronas and the range of colors corresponds to different coronal temperatures.
A Face On Mars (1998-04-06)

This image, showing what looks to be a human face (above center) and other features of the Cydonia region on the Martian surface, was produced using data from NASA's Viking 1 orbiter in 1976. Described in a NASA press release as a "rock formation which resembles a human head", some have since offered the extraordinary explanation that the face is an artificial construct built by a civilization on Mars! However, most scientists have a more conventional view - that this feature is indeed a natural Martian hill whose illusory face-like appearance depends on illumination and viewing angle. This month, the Mars Global Surveyor satellite will be in position to take new pictures of this region of controversial Martian features along with areas around the Mars Pathfinder and Viking landing sites.
Return To Cydonia (1998-04-07)

Yesterday the Mars Global Surveyor project released a new close-up image of a portion of the Cydonia region on Mars. This cropped and processed version shows an area about 2 miles wide (the full version covers a strip nearly 2.6 miles wide by 25 miles long) and at full resolution has a pixel size of about 14 feet. The rock formation visible is the famous feature seen as the "Face on Mars" in 1976 Viking orbiter images. Such complex looking landforms in the Cydonia region are thought to be the result of erosion and weathering of ancient crust by Martian winds, frost, and possibly surface water. Mars Global Surveyor is scheduled to take other images of the Cydonia region and the Mars Pathfinder and Viking landing sites this month.
Nabta: Older than Stonehenge (1998-04-08)

In the Sahara Desert in Egypt lie the oldest known astronomically aligned stones in the world: Nabta. Over one thousand years before the creation of Stonehenge, local herders built a stone circle and other structures on the shoreline of a lake that has long since dried up.  Over 6000 years ago, stone slabs three meters high were dragged over a kilometer to create the site.  Shown above is one of the stones that remains.  Little is known about the ultimate purpose of  Nabta and the nature of the people who built it.
Quasar in an Elliptical Galaxy (1998-04-09)

Where do quasars live?  Quasars are the brightest objects in the universe, so bright they can be seen from across the universe.  Observations continue to show that most quasars are surrounded by a relatively faint nebulous patch.  Astronomers are trying to identify the nature of these patches. The above false-color picture shows a central quasar embedded in an unusual elliptical galaxy.  The galaxy is being gravitationally distorted by a neighboring galaxy. Recent evidence indicates that most quasars live near the centers of large, elliptical galaxies - even those quasars where no host galaxy could be found before.  Quasars themselves are thought to result from matter falling toward  supermassive black-holes.