juliensimon/nasa-apod huggingface dataset:
A Farewell to Tails (1997-12-15)

As 1997 fades, so does the Great Comet of 1997: Comet Hale-Bopp. Discovered even before the Great Comet of 1996, Comet Hale-Bopp became the brightest comet since 1976.  Many will remember Comet Hale-Bopp as a comet with a coma so bright it could be seen by eye even when near the Moon. Others will remember spectacular photographs that appeared in magazines and on the web.  Amateurs, inspired by the beauty of the comet, took most of these photographs.  In particular, today APOD salutes Wally Pacholka, who took the above famous photograph.  Mr. Pacholka reports that he repeatedly drove 150 miles to a national park, stayed up half the night, and took hundreds of photos while carefully waving a flashlight to momentarily illuminate the foreground.  His equipment consisted only of a standard 35-mm camera which, for pointing accuracy, he piggybacked on a telescope bought at age 12 with money earned from a paper route.

Image credit: W. Pacholka
Night Lightning on Jupiter (1997-12-16)

Why is there lightning on Jupiter?  Lightning is a sudden rush of electrically charged particles from one location to another.  To create lightning, charges must first separate inside a cloud. On Earth, drafts of colliding ice and water droplets usually create this charge separation, but what happens on Jupiter?  Many astronomers theorize that Jovian lightning is also created in clouds containing water ice.  To help investigate this, the above photograph was taken in October by the Galileo spacecraft now orbiting Jupiter.  Clouds are dimly lit by sunlight reflected off Jupiter's moon Io. The bright flashes appear to originate in active regions at the level where water clouds would exist, and illuminate an even lower cloud level containing ammonia. One thing is for sure: lightning on Jupiter is a lot brighter than lighting on Earth.
Stonehenge: Ancient Monument to the Sun (1997-12-17)

Stonehenge consists of large carved stones assembled about 4000 years ago.  Long before modern England was established, ancient inhabitants somehow moved 25 ton rocks nearly 20 miles to complete it.  From similar constructs of the era, people could learn the time of year by watching how the Sun and Moon rose and set relative to accurately placed stones and pits. The placement of the boulders at Stonehenge, however, is not impressively accurate by today's standards, nor even by the standards of that time.  Therefore, modern scholars interpret Stonehenge as a colossal monument to the Sun in celebration of the predictability of the seasons.

Image credit: Clive Ruggles
Gamma-Ray Burster (1997-12-18)

Gamma-ray bursts seem to be the most powerful explosions in the Universe. Yet their sources continue to elude researchers who stand in awe and frustration at the bursts' transient, enigmatic behavior. The blinking gif above illustrates the latest hard-won result in the quest to identify and understand the nature of the bursters. These Apache Point Observatory optical images from Monday and Tuesday this week have helped identify a faint, fading object (red arrow) near the position of a gamma-ray burst. The gamma-ray burst triggered satellite observatories on Sunday, December 14th. Faint stars near the constellation Ursa Major (the Big Dipper) also appear in these "negative" images of the sky. Though thousands of bursts have been detected by satellites sensitive to gamma rays, it is likely that this object represents only the third known optical counterpart to a gamma-ray burst.
NGC 6826: The Blinking Eye (1997-12-19)

The colorful planetary nebula phase of a sun-like star's life is brief. Almost in the "blink of an eye" - cosmically speaking - the star's outer layers are cast off, forming an expanding emission nebula. This nebula lasts perhaps 10 thousand years compared to a 10 billion year stellar life span. Spectacular planetary nebulae are familiar objects to both professional and amateur astronomers, but they still contain a few surprises. For instance, the lovely nebula NGC 6826, also known as the Blinking Eye Nebula, has mysterious red FLIERS seen on either side of the Hubble Space Telescope image above. Are they also expanding outward from the central star? If so, their "bow shocks" point in the wrong direction!
Apollo 16: Exploring Plum Crater (1997-12-20)

Apollo 16 spent three days on Earth's Moon in April 1972. The fifth lunar landing mission out of six, Apollo 16 was famous for deploying and using an ultraviolet telescope as the first lunar observatory, and for collecting rocks and data on the mysterious lunar highlands.  In the above picture, astronaut John W. Young photographs Charles M. Duke, Jr. collecting rock samples at the Descartes landing site. Duke stands by Plum Crater while the Lunar Roving Vehicle waits parked in the background. The Lunar Roving Vehicle allowed the astronauts to travel great distances to investigate surface features and collect rocks. High above, Thomas K. Mattingly orbits in the Command Module.
A Winter Solstice (1997-12-21)

Today is the Winter Solstice, the shortest day of the year in the Northern Hemisphere. The yearly cycle of Seasons on planet Earth once again finds the Sun at its lowest point in the Northern Sky. The Sun's own 11 year cycle of activity is progressing toward a maximum which will occur in 2000-2001. This image of the Sun in the light of ionized Helium was recorded by the space-based SOHO observatory only three days ago and shows many prominences and active regions.
David N. Schramm 1945-1997 (1997-12-22)

David N. Schramm effectively combined the very big with the very small.  Among his many scientific achievements, Schramm and collaborators successfully used Big Bang cosmology to predict that only three families of elementary particles exist in the universe, which was subsequently confirmed by high energy particle accelerators.  Schramm and collaborators realized that  current relative elemental abundance measurements, when combined with nuclear reaction rates, constrain the amount of normal matter to be much less than that implied by the movements of stars and galaxies. Therefore, most of the universe might be made of some sort of dark matter. Schramm was a champion wrestler, a mountain climber, an inspiration to scientists and students, and was alone piloting a plane when it crashed last Friday.
M2-9: Wings of a Butterfly Nebula (1997-12-23)

Are stars better appreciated for their art after they die?  Actually, stars usually create their most artistic displays as they die.  In the case of low-mass stars like our Sun and M2-9 pictured above, the stars transform themselves from normal stars to white dwarfs by casting off their outer gaseous envelopes.  The expended gas frequently forms an impressive display called a planetary nebula that fades gradually over thousand of years. M2-9, a butterfly planetary nebula 2100 light-years away shown in representative colors, has wings that tell a strange but incomplete tale. In the center, two stars orbit inside a gaseous disk 10 times the orbit of Pluto.  The expelled envelope of the dying star breaks out from the disk creating the bipolar appearance.  Much remains unknown about the physical processes that cause planetary nebulae.
30 Doradus Across the Spectrum (1997-12-24)

30 Doradus is lit up like a Christmas tree.  Shining in light across the electromagnetic spectrum, 30 Doradus glows because of all the energetic processes that go on there.  A distinctive region visible in a Milky Way satellite galaxy called the Large Magellanic Cloud (LMC), 30 Doradus is a hotbed of star formation, supernova explosions, and ionized plasma. The above image is a composite of three pictures taken in three different wavelength bands of light.  Red represents X-ray emission created by gas as hot as 1 million degrees Kelvin. Green represents emission from ionized hydrogen gas, and blue represents ultraviolet radiation primarily emitted by hot stars.  At the conclusion of this symphony of star formation and light in a few million years, astronomers expect that a new globular cluster will have formed.
A Hale-Bopp Holiday (1997-12-25)

Seen from the Pik Terskol Observatory in the northern Caucasus mountains, comet Hale-Bopp and the bright stars of the constellation Perseus hang above the snowy, moon-lit landscape. Although it reminds Northern Hemisphere dwellers of an idyllic Winter scene, this picture was actually recorded in the spring - on April 13th of this year. Seasons Greetings and Best Wishes from APOD!

Image credit: T. Credner
West Of The Great Red Spot (1997-12-26)

The turbulent region West of Jupiter's Great Red Spot is highlighted in this recent picture constructed from data recorded by the Galileo spacecraft. The image is color coded to show cloud height and thickness; white clouds are high and thick, light blue clouds are high and thin, and reddish clouds are low. The edge of the Red Spot itself appears blue here (lower right) and spans about 6,600 miles along the curving limb of the planet (north is up). Westward winds, deflected north by the circulation within the Great Red Spot, collide with Eastward winds at higher latitudes and generate the roiling, turbulent structures. The largest eddies near the Northwestern edge of the Red Spot are bright, suggesting upward convection and high altitude cloud formation are taking place there.
Keck: The Largest Optical Telescopes (1997-12-27)

In buildings eight stories tall rest mirrors ten meters across that are slowly allowing humanity to map the universe. Alone, each is the world's largest optical telescope: Keck. Together, the twin Keck telescopes have the resolving power of a single telescope 90-meter in diameter, able to discern sources just milliarcseconds apart. Since opening in 1992, the real power of Keck I (left) has been in its enormous light-gathering ability - allowing astronomers to study faint and distant objects in our Galaxy and the universe. Keck II, completed last year, and its twin are located on the dormant volcano Mauna Kea, Hawaii, USA. In the distance is Maui's volcano Haleakala. One reason Keck was built was because of the difficulty for astronomers to get funding for a smaller telescope.
Pluto: The Frozen Planet (1997-12-28)

The Hubble Space Telescope imaged Pluto and its moon Charon in 1994. Pluto is usually the most distant planet from the Sun but because of its elliptic orbit Pluto crossed inside of Neptune's orbit in 1979 and will cross back out again in 1999.  Compared to the other planets, very little is known about Pluto. Pluto is smaller than any other planet and even smaller than several other planet's moons. From Pluto, the Sun is just a tiny point of light. Pluto is probably composed of frozen rock and ice, much like Neptune's moon Triton. Pluto has not yet been visited by a spacecraft, but a mission is being planned for the next decade.
The Milky Way in Infrared (1997-12-29)

At night, from a dark location, part of the clear sky looks milky.  This unusual swath of dim light is generally visible during any month and from any location.  Until the invention of the telescope, nobody really knew what the "Milky Way" was.  About 300 years ago telescopes caused a startling revelation: the Milky Way was made of stars.  Only 70 years ago, more powerful telescopes brought the further revelation that the Milky Way is only one galaxy among many.  Now telescopes in space allow yet deeper understanding.  The above picture was taken by the COBE satellite and shows the plane of our Galaxy in infrared light. The thin disk of our home spiral galaxy is clearly apparent, with stars appearing white and interstellar dust appearing red.
NGC 7009: The Saturn Nebula (1997-12-30)

The layers of the Saturn Nebula give a complex picture of how this planetary nebula was created. The above picture, taken in April 1996 and released last week, allows a better understanding of the mysterious process that transformed a low-mass star into a white dwarf star.  A computer model indicates that the central star of NGC 7009 first expelled the green gas that now appears barrel shaped.  This green gas now confines stellar winds flowing from the central star, creating a jet which forms the ansae that appear in red at the tips.  Much remains unknown, including why the gas has not become turbulent.
NGC 5307: A Symmetric Planetary Nebula (1997-12-31)

Some stellar nebulae are strangely symmetric. For example, every major blob of gas visible on the upper left of NGC 5307 appears to have a counterpart on the lower right.  This picture taken by the Hubble Space Telescope was released last week. NGC 5307 is an example of a planetary nebula with a spiral shape.  Spiral planetary nebulae are thought to be caused by a bright central white dwarf star expelling a symmetric wobbling jet of rapidly moving gas.  It takes light about 10,000 years to reach us from NGC 5307, and about 6 months just to go from one side to the other.  In contrast, light takes only about 8 minutes to reach Earth from the Sun.
The Largest Rock Known (1998-01-01)

There, that faint dot in the center - that's the largest rock known.  It is larger than every known asteroid, moon, and comet nucleus.  It is larger than any other rocky planet. (Nobody knows for sure what size rocks lie at the cores of Jovian planets, or orbit other stars.) The Voyager 1 spacecraft took this picture in 1990 from the outer Solar System.  This rock is so large its gravity makes it nearly spherical, and holds heavy gases near its surface. Today, this rock starts another orbit around its parent star, for roughly the 5 billionth time, spinning over 350 times during each trip.  Happy Gregorian Calendar New Year to all the human inhabitants of this rock we call Earth.
Europa's Disconnected Surface (1998-01-02)

Jupiter's moon Europa is so exciting that the Galileo spacecraft orbiting Jupiter has now embarked on an extended mission to study it.  Oceans that might exist beneath Europa's surface are thought to be one of the best places to look for life in our Solar System. The Galileo Europa Mission has planned eight close fly-bys  frozen moon. The first close encounter of this extended mission occurred last December and the next will occur in February.  The above enhanced color picture shows a small region of Europa's Conamara region.  The white and blue colors highlight regions covered by ice dust from the collision that created the Pwyll Crater.  Disconnected islands of ice are visible that have apparently rafted to new positions.
The Barren Moon (1998-01-03)

The above photo, taken as the Apollo 17 astronauts orbited the Moon in 1972, depicts the stark lunar surface around the Eratosthenes and Copernicus craters. Many similar images of a Moon devoid of life are familiar to denizens of the space age. Contrary to this modern perception, life on the Moon was reported in August of 1835 in a series of sensational stories first published by the New York Sun - apparently intended to improve the paper's circulation. These descriptions of lunar life received broad credence and became one of the most spectacular hoaxes in history. Supposedly based on telescopic observations, the stories featured full, lavish accounts of a Moon with oceans and beaches, teeming with plant and animal life and climaxing with the report of sightings of groups of winged, furry, human-like creatures resembling bats! Within a month the hoax had been revealed but the newspaper continued to enjoy an increased readership. Though barren, the Moon remains a popular setting for science fiction stories and extra-terrestrial adventures. It has now been 25 years since Apollo 17 ended an era of human exploration of Earth's Moon.
Fractal Interstellar Dust Up-Close (1998-01-04)

Our universe is a very dusty place.  Dust usually shows its presence by blocking out light emitted from stars or nebulae behind it, sometimes creating the illusion of a horse's head or a sombrero hat. But nobody really knows what a typical interstellar dust grain looks like. By studying how dust absorbs, emits, and reflects light, astronomers do know that interstellar dust is much different than the cell and lint based dust found around a typical house. Interstellar dust grains are composed mostly of carbon, silicon, and oxygen and are usually less than about 1/1000 of a millimeter across. Recent work indicates that most dust grains are not spherical. The above picture shows the result of a fractal adhesion model for dust grains involving random conglomerates of spherical compounds of different properties, here artificially highlighted by different colors.

Image credit: E. L. Wright (UCLA)
Earth's Richat Structure (1998-01-05)

What on Earth is that? The Richat Structure in the Sahara Desert of Mauritania is easily visible from space because it is nearly 50 kilometers across.  Once thought to be an impact crater, the Richat Structure's flat middle and lack of shock-altered rock indicates otherwise. The possibility that the Richat Structure was formed by a volcanic eruption also seems improbable because of the lack of a dome of igneous or volcanic rock.  Rather, the layered sedimentary rock of the Richat structure is now thought by many to have been caused by uplifted rock sculpted by erosion.  Why the Richat Structure is nearly circular remains a mystery.
The Red Spider Planetary Nebula (1998-01-06)

Oh what a tangled web a planetary nebula can weave. The Red Spider Planetary Nebula shows the complex structure that can result when a normal star ejects its outer gases and becomes a white dwarf star. Officially tagged NGC 6537, this two-lobed symmetric nebula houses one of the hottest white dwarfs ever observed, probably as part of binary star system. Internal winds emanating from the central stars, shown in the central inset, have been measured in excess of 300 kilometers per second.  These hot winds expand the nebula, flow along the nebula's walls, and cause gas and dust to collide.  Atoms caught in these colliding shocks radiate light shown in the above representative-light picture.
The Colorful Moon (1998-01-07)

Do you recognize the Earth's Moon when you see it? The crazy, patchwork appearance of this false color image makes this nearly full view of our Moon's familiar nearside look very strange. The image was taken in 1992 by the Galileo spacecraft enroute to Jupiter. The Sea of Tranquillity (Mare Tranquillitatis) is the blue area at right, the Ocean of Storms (Oceanus Procellarum) is the extensive blue and orange area on the left, and white lines radiate from the crater Tycho at bottom center. Three filters were used to make three separate exposures, combined in an exaggerated color scheme to emphasize composition differences - blue hues reveal titanium rich areas while orange and purple colors show regions relatively poor in titanium and iron. NASA soon plans to conduct an extensive remote exploration of the lunar surface, including a search for water ice near the lunar South Pole, with the Lunar Prospector spacecraft.
Destination: Moon (1998-01-08)

Tuesday, January 6, at 9:28 p.m. EST, NASA's Lunar Prospector spacecraft climbed into the sky above Cape Canaveral Air Station riding an Athena II rocket. Representing NASA's first Moon mission since the 1972 flight of Apollo 17, this launch also occurred on the 30th anniversary of the launch of the Surveyor 7 lunar lander. The three stage launch vehicle's fiery trail is in the foreground of this time exposure while the Moon, near first quarter phase, is shown in the background some 250,000 miles from the Cape. Prospector will cover that distance in about 5 days, entering lunar orbit on Sunday. Prospector carries no cameras to image the well-photographed lunar surface. Instead, its array of instruments will map the lunar gravity, magnetic field, internal structure, and surface composition. The result, a detailed global view of current lunar properties, is expected to dramatically impact humanity's understanding of the origins of the Moon and the Solar System. From its vantage point in polar orbit, only 63 miles above the lunar surface, Prospector will also conduct a sensitive search for water ice which may be preserved in permanent shadow at the Moon's South Pole.
Saturnian Aurora (1998-01-09)

Girdling the second largest planet in the Solar System, Saturn's Rings are one of the most spectacular sights for earthbound telescopes. This recently released image, from the orbiting Hubble Space Telescope's STIS instrument, offers a striking view of another kind of ring around Saturn - pole encircling rings of ultraviolet aurora. Towering more than 1,000 miles above the cloud tops, these Saturnian auroral displays are analogous to Earth's. Energetic charged particles in the Solar Wind are funneled by the planet's magnetic field into polar regions where they interact with atmospheric gases. Following the ebb and flow of Saturn's aurora, researchers can remotely explore the planet's atmosphere and magnetic field. In this false color image, the dramatic red aurora identify emission from atomic hydrogen, while the more concentrated white areas are due to hydrogen molecules. In 2004, NASA plans to begin making close-up studies of the Saturnian system with the Cassini Spacecraft.
Disorder in Stephan's Quintet (1998-01-10)

What are five closely grouped galaxies doing in this image? The grouping is commonly known as Stephan's Quintet. Four of the galaxies show essentially the same redshift suggesting that they are at the same distance from us. The large bluish spiral below and left of center actually has a smaller redshift than the others, indicating it is much closer. It is probably a foreground object which happens to lie along the line of sight to the more distant galaxies. Of the four distant galaxies, three seem to be colliding, showing serious distortions due to gravitational tidal forces. The fourth is a normal appearing elliptical galaxy (at the lower right edge of the field). Recent results suggest that collisions play an important role in the life cycles of galaxies.
Abell 2218: A Galaxy Cluster Lens (1998-01-11)

Gravity can bend light. Almost all of the bright objects in this Hubble Space Telescope image are galaxies in the cluster known as Abell 2218. The cluster is so massive and so compact that its gravity bends and focuses the light from galaxies that lie behind it. As a result, multiple images of these background galaxies are distorted into faint stretched out arcs - a simple lensing effect analogous to viewing distant street lamps through a glass of wine. The Abell 2218 cluster itself is about 3 billion light-years away in the northern constellation Draco.
The Keyhole Nebula (1998-01-12)

The dark dusty Keyhole Nebula gets its name from its unusual shape. Officially designated NGC 3324, the Keyhole Nebula is a smaller region superposed on the larger Eta Carina Nebula. These nebulae were created by the dying star Eta Carina, which is prone to violent outbursts during its final centuries.  Noted and discussed as early as 1840 when a spectacular explosion became visible, the Eta Carina system now appears to be undergoing an unusual period of change. An emission nebula that contains much dust, the Keyhole Nebula is roughly 9,000 light years distant. This photogenic nebula can be seen in the south with even a small telescope. The Keyhole Nebula was recently discovered to contain highly structured clouds of molecular gas.

Image credit: AURA, all rights reserved.
El Niño Water Rhythm (1998-01-13)

This year's El Niño is the strongest ever recorded.  The large amount of warm water in the Pacific Ocean near the equator is causing unusual weather all over planet Earth.  The above false-color images of Earth show the relative levels of warm water between normal (upper left) and the comparatively mild El Niño of 1995 - 1996. Red indicates a high water level.  Detailed measurements of this years El Niño indicate the warm water level is rising and falling in rhythmic fashion, possibly in response to changing wind patterns.