juliensimon/nasa-apod huggingface dataset:
Mars: A Sheer Close-up (1997-11-13)

As the Mars Global Surveyor spacecraft maneuvers toward its final mapping orbit, its cameras have been producing some sharp views of Mars. At a resolution of better than 30 feet per pixel, this image of a portion of the immense canyon, Valles Marineris, highlights the sheer mountain cliffs over 3200 feet tall near the canyon walls. The striking and extensive layering clearly apparent in the triangular mountain face was totally unanticipated. This exciting new result challenges common theories about the surface of Mars and argues that a complex early geological history is responsible for the current Martian landscape.
Irregular Galaxy Sextans A (1997-11-14)

Grand spiral galaxies often seem to get all the glory. Their newly formed, bright, blue star clusters found along beautiful, symmetric spiral arms are guaranteed to attract attention. But small irregular galaxies form stars too, like this lovely, gumdrop-shaped galaxy, Sextans A. A member of the local group of galaxies which includes the massive spirals Andromeda and our own Milky Way, Sextans A is about 10 million light years distant. The bright Milky Way foreground stars appear yellowish in this view. Beyond them lie the stars of Sextans A with tantalizing young blue clusters clearly visible.
Uranus: The Tilted Planet (1997-11-15)

Uranus is the third largest planet after Jupiter and Saturn. This picture was snapped by the Voyager 2 spacecraft in 1986 - the only spacecraft ever to visit Uranus. Uranus has many moons and a ring system. Uranus is composed mostly of rock and ices, but with a thick hydrogen and helium atmosphere.  Uranus is peculiar in that its rotation axis is greatly tilted and sometimes points near the Sun. It remains an astronomical mystery why Uranus' axis is so tilted. Uranus and Neptune are very similar.
The Leonid Meteor Shower (1997-11-16)

The Leonid Meteor Shower will likely reach its peak in the early hours this Monday morning. Though the Moon will be bright, Leo, the shower's radiant point, will be well above the eastern horizon from Western North America and the Pacific region during this period. This year's Leonids may prove particularly exciting as observers anticipate the legendary Leonid storm of activity will occur sometime during the next few apparitions of this annual meteor shower - although most expect the meteor storm to occur in 1998 or 1999. Meteor showers result from debris left by passing comets. The Leonids specifically are small pieces of Comet Tempel-Tuttle. In the above series of time-lapse, 1-minute exposures, a 1995 Leonid is seen to leave a train of hot air that glowed persistently for several minutes.
Barringer Crater on Earth (1997-11-17)

What happens when a meteor hits the ground?  Usually nothing much, as most meteors are small, and indentations they make are soon eroded away.  49,000 years ago, however, a large meteor created Barringer Meteor Crater in Arizona, pictured above.  Barringer is over a kilometer across.  In 1920, it was the first feature on Earth to be recognized as an impact crater. Today, over 100 terrestrial impact craters have been identified. Early this morning, the Leonid Meteor Shower reaches its peak, although no impacts of this magnitude are expected.
In the Center of the Trapezium (1997-11-18)

Start with the constellation of Orion. Below Orion's belt is a fuzzy area known as the Great Nebula of Orion or M42.  In this nebula is a bright star cluster known as the Trapezium, shown above. New stellar systems are forming there in gigantic globs of gas and dust known as Proplyds.  Looking closely at the above picture also reveals that gas and dust surrounding some of the dimmer stars appears to form structures that point away from the brighter stars. The above false color image was made by combining several exposures from the Hubble Space Telescope.
Diffraction Spikes: When Stars Look Like Crosses (1997-11-19)

Unusual appendages around bright stars are commonplace, but never seem to be mentioned. What are they?  First, a telescope brings starlight falling over a large area to a small area. To get at this small area, however, one must go inside a reflecting telescope, and this can only be done with support rods,  which are right in the view of the telescope. The wave nature of light causes it to deflect when passing near these rods. Light scatters away from the original destination point ending up elsewhere and appearing as "diffraction spikes."  These annoying spikes steal precious light from the central image and hide light from fainter, more interesting stars.  Above, astronomers are more interested in the half-circled point near the image center, than the cool-looking diffraction spikes from the bright star at the bottom. Apparently, that half-circle is a new stellar system forming in the Lagoon Nebula.
Escape From The Sun (1997-11-20)

Twisted magnetic fields arching from the solar surface can trap ionized gas, suspending it in huge looping structures. These majestic plasma arches are seen as prominences above the solar limb. On September 14, this dramatic and detailed image was recorded by the EIT experiment on board the space-based SOHO observatory in the light emitted by ionized Helium. It shows hot plasma escaping into space as a fiery prominence breaks free from magnetic confinement a hundred thousand miles above the Sun. These awesome events bear watching as they can affect communications and power systems ninety three million miles away on Planet Earth.
Jupiter: Moon, Ring, and Clouds (1997-11-21)

An inner moon, an edge-on, planet-girdling ring, and high altitude cloud bands are visible in this mosaic of infrared images of gas giant Jupiter. The moon Metis, 25 miles wide and about 80,000 miles from the planet, is the bright spot at the upper right. Metis lies within Jupiter's faint, tenuous ring, and may be a source of ring material. Recorded on September 17th by the NICMOS instrument on board the Hubble Space Telescope, these pictures also emphasize atmospheric features high above the main jovian cloud deck. Methane gas in Jupiter's atmosphere absorbs the near infrared light causing deeper clouds to appear dark at these wavelengths. Clouds riding above most of the atmospheric methane are bright. The circular dark spot just above the brightest cloud band is an image artifact.
Surveyor Hops (1997-11-22)

This panorama of the cratered lunar surface was constructed from images returned by the US Surveyor 6 lander. Surveyor 6 was not the first spacecraft to accomplish a soft landing on the Moon ... but it was the first to land and then lift off again! After touching down near the center of the Moon's nearside in November of 1967, NASA controllers commanded the spacecraft to hop. Briefly firing its rocket engine and lifting itself some 4 meters above the surface, the Surveyor moved about 2.5 meters to one side before setting down again. The hopping success of Surveyor 6 essentially marked the completion of the Surveyor series main mission - to determine if the lunar terrain was safe for the planned Apollo landings.
Triton: Neptune's Largest Moon (1997-11-23)

On October 10th, 1846, William Lassell was observing the newly discovered planet Neptune. He was attempting to confirm his observation, made just the previous week, that Neptune had a ring. But this time he discovered that Neptune had a satellite as well. Lassell soon proved that the ring was a product of his new telescope's distortion, but the satellite Triton remained. The above picture of Triton was taken in 1989 by the only spacecraft ever to pass Triton: Voyager 2. Voyager 2 found fascinating terrain, a thin atmosphere, and even evidence for ice volcanoes on this world of peculiar orbit and spin. Ironically, Voyager 2 also confirmed the existence of complete thin rings around Neptune - but these would have been quite invisible to Lassell!
Jet Near Light Speed (1997-11-24)

stein's Special Theory of Relativity says that nothing can travel faster than the speed of light. Jets of protons and electrons that shoot away from objects such as quasars and black holes appear to travel at speeds approaching this maximum speed, though.  Such jets carry tremendous energy and can ram straight through interstellar material. In the above frame from a computer simulation, a jet traveling only 98 percent of light speed rams and mixes with interstellar material.  Even higher energy jets might well explain the structure seen around Cygnus A.
The Comet and the Galaxy (1997-11-25)

The Moon almost ruined this photograph.  During late March and early April, Comet Hale-Bopp passed nearly in front of the Andromeda Galaxy. Here the Great Comet of 1997 and the Great Galaxy in Andromeda were photographed together on March 24th.  The problem was the brightness of the Moon. The Moon was full that night and so bright that long exposures meant to capture the tails of Hale-Bopp and the disk of M31 would capture instead only moonlight reflected off the Earth's atmosphere.  By the time the Moon would set, this opportunity would be gone.  That's why this picture was taken during the lunar eclipse.

Image credit: J. C. Casado
Uranian Moons, Rings, And Clouds (1997-11-26)

The giant planet Uranus is faint and featureless when viewed in visible light. But this pair of near-infrared mosaics from the Hubble Space Telescope's NICMOS camera reveals moons, rings, and clouds of this distant gas planet. The color coded images highlight different atmospheric layers - blue represents the deepest layers while the highest cloud features have a reddish tinge. Racing around the planet, high, bright clouds are seen to move substantially between the two pictures taken only ninety minutes apart. Ring systems are a common to the solar system's giant planets. Here the main Uranian ring seems to vary in width and is clearly brightest near the top. The eight specks beyond the ring system are small Uranian moons which also show counter-clockwise motion over ninety minutes as traced by the arrows on the right hand image.
Jupiter's Inner Moons (1997-11-27)

The potato-shaped inner moons of Jupiter are lined-up in this mosaic "family portrait" of these tiny Jovian satellites. The individual images were recorded over the last year by NASA's Galileo spacecraft and are scaled to the moons' relative sizes. Left to right in increasing order of distance from Jupiter are Metis (longest dimension 37 miles), Adrastea (12 miles), Amalthea (154 miles), and Thebe (72 miles). All these moons orbit in the zone between Io and Jupiter's rings, are bombarded by high-energy ions within the Jovian magnetosphere, and are probably locked in synchronous rotation by Jupiter's strong gravity. Why are they shaped like potatoes? Like the asteroids and the diminutive moons of Mars, their own gravity is not strong enough to mold them into spheres.
Beta Pictoris Revisited (1997-11-28)

In the early 1980s, Beta Pictoris became one of the most important stars in the sky. Satellite and ground-based telescopic observations revealed the presence of a surrounding outer disk of material and an inner "clear" zone about the size of our solar system - strong evidence for the formation of planets. Beta Pictoris is 50 light years away and any orbiting planets are too small and faint to image at that distance. But evidence continues to mount that this star indeed has comet-like bodies in the disk and a Jupiter-sized planet orbiting within the central zone. Shown here in false color, this recent, highly detailed picture was obtained at the European Southern Observatory by blocking the overwhelming direct starlight and imaging the near-infrared light from the disk. The disk's warped bright inner region is indirect evidence for an orbiting planet.
Lasers in Eta Carinae (1997-11-29)

Have you heard about the great LASER light show in the sky? A team led by K. Davidson (U. Michigan) and S. Johansson (U. Lund) discovered that the chaotically variable star Eta Carinae emits ultraviolet light in such a narrow band that it is most probably LASER light! This artist's vision depicts a model that could account for their Hubble Space Telescope observations. In this model, Eta Carinae emits many LASER beams from its surrounding cloud of energized gas.  Infrared LASERS and microwave MASERS are extremely rare astrophysical phenomena, but this natural ultraviolet LASER is the first of its kind to be discovered.
Mercury: A Cratered Inferno (1997-11-30)

Mercury's surface looks similar to our Moon's. Each is heavily cratered and made of rock.  Mercury's diameter is about 4800 km, while the Moon's is slightly less at about 3500 km (compared with about 12,700 km for the Earth). But Mercury is unique in many ways.  Mercury is the closest planet to the Sun, orbiting at about 1/3 the radius of the Earth's orbit. As Mercury slowly rotates, its surface temperature varies from an unbearably cold -180 degrees Celsius to an unbearably hot 400 degrees Celsius. The place nearest the Sun in Mercury's orbit changes slightly each orbit - a fact used by Albert Einstein to help verify the correctness of his then newly discovered theory of gravity: General Relativity.  The above picture was taken by the only spacecraft ever to pass Mercury: Mariner 10 in 1974.
Orion: The Big Picture (1997-12-01)

Orion is big. Some of the stars that form the constellation of Orion are part of a giant gas cloud complex that stretches over 100 light years and appears more than 50 times the diameter of the Moon.  Components of this cloud include the Horsehead Nebula, the Orion Nebula, the Trapezium open cluster, and small disks containing stellar systems which are just forming.  At 1500 light years, Orion is the closest star forming region to Earth.  Close inspection of the photo's center should reveal the three stars which form the belt of Orion.

Image credit: J. C. Casado
Micro-Quasar GRS1915 Puffs (1997-12-02)

On the far side of our Galaxy, gas clouds explode away from a small black hole.  This might seem peculiar, as black holes are supposed to attract matter. But material falling toward a black hole collides and heats up, creating an environment similar to a quasar that is far from stable.  In the above time-lapse sequence, micro-quasar GRS1915 expels bubbles of hot gas in spectacular jets.  These computer enhanced radio images show one plasma bubble coming almost directly toward us at 90 percent the speed of light, and another moving away. Each of the four frames marks the passage of one day. Originally detected on October 29th, these bubbles have now faded from view.
Runaway Star (1997-12-03)

Runaway stars are massive stars traveling rapidly through interstellar space. Like a ship plowing through the interstellar medium, runaway star HD 77581 has produced this graceful arcing bow wave or "bow shock" - compressing the gaseous material in its path. Located near the centre of this European Southern Observatory photograph, HD 77581 itself is so bright that it saturates the sensitive camera and produces the spiky cross shape. This star is over 6,000 light-years away in the constellation Vela, and appears to move at over 50 miles per second. What force could set this star in motion? A clue to the answer may lie in its optically invisible companion star, an X-ray bright pulsar known as Vela X-1. This pulsar is clearly the remnant of a supernova explosion ... which seems to have given this massive star and its companion a mighty kick!
A Sky Full Of Planets (1997-12-04)

Look up tonight. Just after sunset, the crescent moon and all five "naked-eye" planets (Mercury, Venus, Mars, Jupiter, and Saturn) will be visible (depending on your latitude), lying near our solar system's ecliptic plane. Venus and Jupiter will shine brilliantly as the brightest "stars" in the sky, but Mercury will be near the horizon and hard to see. A pair of binoculars will also reveal Uranus and Neptune and observers with a telescope and a good site may even be able to glimpse faint Pluto just above the Western horizon in the fading twilight (not shown on the chart above). Enjoy this lovely spectacle any clear night through about December 8. A similar gathering is expected in May 2000 but the planets will be hidden from view by the solar glare. A night sky as full of planets as this one will occur again though ... in about 100 years.
Seeing Through Galaxies (1997-12-05)

In this dramatic picture, spiral galaxy NGC 5091 appears in the foreground. Tilted nearly edge-on, the dust lanes between its spiral arms are clearly visible.  The large elliptical galaxy NGC 5090 lies just beyond it - both are about 100 million light years distant in the southern constellation Centaurus.  Can you see through the spiral galaxy? The detailed answer to this question has important implications for determining the nature of dark matter and the measurement of star formation rates. Comparing the overlapping and non-overlapping parts of this and other pairs of galaxies offers a neat way to find the answer.
A Quasar Portrait Gallery (1997-12-06)

QUASARs (QUASi-stellAR objects) lie near the edge of the observable Universe. Discovered in 1963, astronomers were astounded that such objects could be visible across billions of light-years, as this implies they must emit prodigious amounts of energy. Where does the energy come from? Many believe the quasar's central engine is a giant black hole fueled by tremendous amounts of infalling gas, dust, and stars. This gallery of quasar portraits from the Hubble Space Telescope offers a look at their local neighborhoods: the quasars themselves appear as the bright star-like objects with diffraction spikes. The images in the center and right hand columns reveal quasars associated with disrupted colliding and merging galaxies which should provide plenty of debris to feed a hungry black hole.
A Distant Cluster of Galaxies (1997-12-07)

In this 1994 Hubble Space Telescope photograph, every bright object is a galaxy. Oddly - most of them are spiral galaxies. This rich cluster of galaxies, named CL 0939+4713, is almost half way across the visible universe. Photos like this indicate that clusters in the past contained a higher fraction of spirals than do nearby clusters which are usually dominated by elliptical galaxies.
The Trifid Nebula in Red, White and Blue (1997-12-08)

Three dark dust lanes give the picturesque Trifid Nebula its name.  The red and blue colors of the Trifid Nebula are present in different regions and are created by different processes.  A big bright star near the center of the red region appears white hot and emits light so energetic it knocks electrons away from gas surrounding it.  When an electron is recaptured by a proton, red light is frequently emitted.  The blue region is centered on another bright star but this region's dust reflects light to us.  The two regions are thus called an emission nebula and reflection nebula, respectively.  The Trifid Nebula can be seen in Sagittarius toward the Galactic Center with a small telescope.

Image credit: Jason Ware
Mysterious Features on Ganymede (1997-12-09)

Where is the rest of the circle? Jupiter's largest moon Ganymede has some truly unusual terrain, including the pictured half circle above cut by nearly parallel curves.  Full circles can be easily explained by impact craters, but partial circles imply that some resurfacing has occurred since the original impact.  The diameter of the half circle is about 32 kilometers.  Also of interest is a dense linear crater chain that cuts across the top of the half-circle.  Mysteries like these are typically solved by the hard work of reconstructing a sequence of natural occurrences, which in this case may yield a better understanding of Ganymede's interesting past.
Sprint the Flying Space Camera (1997-12-10)

Yes, but can your soccer ball do this?  The ball near the middle of the above photograph is actually a robotic camera designed to float about a Space Shuttle and the International Space Station and take pictures. Named "Sprint", it is NASA's first Autonomous Extravehicular Activity Robotic Camera (AERCam) and was tested earlier this month by the crew of Space Shuttle Columbia. Sprint's diameter is actually about 50 percent larger than a soccer ball, and astronauts make a goal of not kicking it.
A Martian Lake Bed? (1997-12-11)

Look closely. In this Mars Global Surveyor image of the Martian surface just south of Schiaparelli crater, dark lines appear to criss-cross light colored depressions. One tantalizing possibility is simply that the feature near the center is similar to a dried-up lake bed on planet Earth, where light colored mineral deposits are left as water evaporates and cracks are produced as the ground dries. This potential Martian lake bed is roughly 3/4 miles across and may provide further evidence that Mars once possessed surface water. Recently announced results from the Mars Pathfinder mission also point to a Martian past which included a denser atmosphere and surface water - conditions which could have supported life.
Phi Persei: Double Star (1997-12-12)

It's clear who is the biggest star in this binary system. Based on recent results, this artist's vision of the double star Phi Persei, 720 light years away, shows a bright, rapidly rotating massive star surrounded by a disk of gas. A small companion star orbits 100 million miles away. The bigger star is presently about 9 times more massive than the small one ... but it wasn't always this way. Ten million years ago the small companion was actually the most massive star in the system and because of its greater mass evolved into a giant star more quickly. After losing its swollen outer layers to the now massive star, all that remains is a stripped down, intensely hot core of about 1 solar mass. In another ten million years, the roles may reverse as the now massive star swells into its own giant phase "returning" mass to its companion. Will these stars end their lives as white dwarfs or supernovae? Astronomers consider the ultimate fate of such mass-exchanging, interacting binary systems an open question and a challenge for present theories of stellar evolution.
The Coma Cluster of Galaxies (1997-12-13)

Almost every object in the above photograph is a galaxy. The Coma Cluster of Galaxies pictured is one of the densest clusters known - it contains thousands of galaxies. Each of these galaxies house billions of stars - just as our own Milky Way Galaxy does. Although nearby when compared to most other clusters, light from the Coma Cluster still takes hundreds of millions of years to reach us. In fact, the Coma Cluster is so big it takes light millions of years just to go from one side to the other!  Most galaxies in Coma and other clusters are ellipticals, while most galaxies outside of clusters are spirals. The nature of Coma's X-ray emission is still being investigated.
The Radio Sky: Tuned to 408MHz (1997-12-14)

Tune your radio telescope to 408MHz (408 million cycles per second) and check out the Radio Sky! You should find that frequency on your dial somewhere between US broadcast television channels 13 and 14. In the 1970s large dish antennas at three radio observatories, Jodrell Bank, MPIfR, and Parkes Observatory, were used to do just that - the data were combined to map the entire sky. Near this frequency, cosmic radio waves are generated by high energy electrons spiraling along magnetic fields. In the resulting false color image, the galactic plane runs horizontally through the center, but no stars are visible. Instead, many of the bright sources near the plane are distant pulsars, star forming regions, and supernova remnants, while the grand looping structures are pieces of bubbles blown by local stellar activity. External galaxies like Centaurus A, located above the plane to the right of center, and the LMC (below and right) also shine in the radio sky.