omnianasa/nasa-apod-metadata huggingface dataset:
Galactic Supernova Remnant IC 443 (1999-07-21)
About 8000 years ago, a star in our Galaxy exploded.  Ancient humans might have noticed the supernova as a temporary star, but modern humans can see the expanding shell of gas even today.  In the above false-color infrared image of supernova remnant IC 443, blue denotes expanding gas where emission is dominated by excited iron atoms.  Of particular interest, though, are the wisps of IC 443 colored red, as they are impacting an otherwise normal molecular cloud.  Here emission from shock-excited molecular hydrogen is allowing astronomers to study how fast moving supernova gas affects star formation in the cloud.  Additionally, astronomers theorize that the impact accelerates some particles to velocities near the speed of light.  The horizontal line across the image is not part of the nebula.
Cosmic Collisions in a Galaxy Cluster (1999-07-22)
Hundreds of galaxies appear as faint smudges of light in this Hubble Space Telescope picture of galaxy cluster MS1054-03. Eight billion light-years away, the cluster is among the most distant known clusters of galaxies and is now reported to contain the largest number of colliding galaxies ever found in a cluster. Examples of these truly cosmic collisions are shown in the insets at the right. Disrupted by gravitational effects, the colliding galaxies are thought to merge over a billion years or so to form larger galaxies - a theory of galaxy formation which seems to be borne out by these results. Though galaxy collisions appear to have occurred much more frequently in the distant, early Universe, they are still seen to happen in the nearby, "close-to-present" Universe.
Infrared Saturn (1999-07-24)
This delightfully detailed false color image of Saturn was earmarked to celebrate the 8th anniversary of the orbiting Hubble Space Telescope. The picture is a combination of three images taken in January 1998 and shows the lovely ringed planet in reflected infrared light. Different colors indicated varying heights and compositions of cloud layers generally thought to consist of ammonia ice crystals. The eye-catching rings cast a shadow on Saturn's upper hemisphere, while the bright stripe seen within the left portion of the shadow is infrared sunlight streaming through the large gap in the rings known as the Cassini Division. Two of Saturn's many moons have also put in an appearance, Tethys just beyond the planet's disk at the upper right, and Dione at the lower left.
The Cygnus Loop (1999-07-25)
The shockwave from a 20,000 year-old supernova in the constellation of Cygnus supernova explosion is still expanding into interstellar space. The collision of this fast moving wall of gas with a stationary cloud has heated it causing it to glow in visible as well as high energy radiation, producing the nebula known as the Cygnus Loop (NGC 6960/95). The nebula is located about 2500 light-years away. The colors used here indicate emission from different kinds of atoms excited by the shock: oxygen-blue, sulfur-red, and hydrogen-green. This picture was taken with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope.
Noctilucent Clouds (1999-07-26)
Sometimes it's night on the ground but day in the air. As the Earth rotates to eclipse the Sun, sunset rises up from the ground. Therefore, at sunset on the ground, sunlight still shines on clouds above.  Under usual circumstances, a pretty sunset might be visible, but unusual noctilucent clouds float so high up they can be seen well after dark.  Pictured above, a network of noctilucent clouds casts a colorful but eerie glow visible above the dark.  Although noctilucent clouds are thought to be composed of small ice-coated particles, much remains unknown about them.
Chandra X Ray Telescope (1999-07-27)
Tomorrow's picture: Asia at Night  < Archive | Index | Search | Calendar | Glossary | Education | About APOD >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Asia at Night (1999-07-28)
This is what Asia looks like at night!  Can you find your favorite Asian city? Although not all of Asia is shown, city lights might make this task possible.  The above picture is actually a composite of over 200 images made by satellites orbiting the Earth.  Scans were made by the USAF Defense Meteorological Satellite Program (DMSP) Operational Linescan System.  The DMSP satellites continue to help in the understanding and prediction of weather phenomena as well as provide key information about population patterns, city light levels, and even rural forest fires.
Hydrogen Blob N88A in the Small Magellanic Cloud (1999-07-29)
The bright blob of hydrogen gas cataloged as N88A is seen at the right. It measures a mere 3 light years across. Emerging from the cool, dusty interstellar medium in a nearby irregular galaxy known as the Small Magellanic Cloud, N88A hides hot young stars at its core. The false-color Hubble Space Telescope image was recorded in the characteristic "H-alpha" light emitted by hydrogen atoms as they are ionized by the young star's energetic ultraviolet light and then recombine. Other regions of ionized hydrogen (H II regions) which surround new born stars can be over a thousand light-years across but astronomers now recognize that these small ionized hydrogen blobs contain some of the most massive stars known.
The Sea of Tranquillity: 5 Seconds To Impact (1999-07-30)
On February 20th, 1965, the Ranger 8 spacecraft crashed into the Moon. Rapidly transmitting a series of pictures to ground controllers, its camera recorded this one at an altitude of about 11 kilometers, 5 seconds before impacting the lunar surface. Two kilometers across, with 4 meter sized objects visible, the picture is of an area in the Sea of Tranquillity north of the Apollo 11 landing site. The Ranger spacecraft represented the first attempts by the US to obtain high resolution photos of the Moon, flying a crash course toward selected areas and sending back pictures until the moment of impact. Tomorrow, another spacecraft will be intentionally crashed into the Moon. Its very successful mission in lunar orbit complete, the Lunar Prospector is scheduled to crash into a crater near the Moon's south pole in an effort to confirm the presence of water-ice by studying the impact's debris cloud.
X-Ray Triple Jet (1999-07-31)
Recorded on July 7, 1998, this animation using X-ray images of the Sun shows an amazing event - three nearly simultaneous jets connected with solar active regions. The two frames were taken several hours apart by the Soft X-ray Telescope on board the orbiting Yohkoh observatory. They have a "negative" color scheme, the darker colors representing more intense X-rays from the corona and active regions on the solar surface. The pictures clearly show two curving jets of X-ray hot plasma appearing above the solar equator and one below. A sharp vertical stripe near the jet above center is a digital blemish while the overall shift of the image is due to solar rotation. As the Sun is now approaching the active part of its 11 year cycle, numerous single jets have been seen. But the appearance of these three widely separated jets at once is considered an unlikely coincidence and has fueled current speculations about their origins.
Walking in Space (1999-08-01)
Pictured above is the first american astronaut to walk in space: Edward White.  White is seen floating outside the Gemini 4 capsule in 1965.  The term spacewalk is deceiving since astronauts do not actually walk - they float - usually without their feet touching anything solid. White was connected to the spaceship only by a thick tether.  He carried a Hand-Held Self-Maneuvering Unit which expelled gas allowing him to move around.  A maneuvering device is necessary in the free-fall of space since there is nothing (besides the spacecraft) to push off of to guide movements.
Regulus Occulted (1999-08-02)
Tomorrow's picture: Vela Expands  < Archive | Index | Search | Calendar | Glossary | Education | About APOD >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
The Vela Supernova Remnant Expands (1999-08-03)
Tomorrow's picture: Sail Titan  < Archive | Index | Search | Calendar | Glossary | Education | About APOD >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
The Surface of Titan (1999-08-04)
If sailing the hydrocarbon seas of Titan, beware of gasoline rain.  Such might be a travel advisory issued next millennium for adventurers visiting Titan, the largest moon of Saturn.   Images of Titan's surface were released last week from the Keck 10-meter telescope featuring the finest details yet resolved.  Peering into Titan's thick smog atmosphere with infrared light, complex features interpreted as oceans, glaciers, and rock became visible.  The high-resolution infrared image pictured above was made possible using an unblurring technique called speckle interferometry.  The interplanetary probe Cassini will reach Saturn and Titan in 2004 to better explore this unusual world.
Asteroid 9969 Braille (1999-08-05)
NASA probe Deep Space 1 zoomed past asteroid 9969 Braille last week as it continued to test its new ion drive in the inner Solar System.  The flyby was the closest approach a spacecraft has ever made to an asteroid.  Looking back afterwards, DS1 took the above picture. Formerly known as 1992 KD, the 9969th asteroid discovered was renamed in honor of Louis Braille, a pioneer in written communication for the blind.  9969 Braille is thought by some to have collided with asteroid Vesta in the distant past and broken up, providing debris for many of the meteorites that fall to Earth.  Asteroid 9969 Braille rotates only once in 9 days, and has an orbit greatly tilted relative to the ecliptic plane of the planets.
Hubble Tracks Jupiters Great Red Spot (1999-08-06)
Tomorrow's picture: An Asteroid's Moon  < Archive | Index | Search | Calendar | Glossary | Education | About APOD >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Ida and Dactyl: Asteroid and Moon (1999-08-07)
This asteroid has a moon! The robot spacecraft Galileo currently exploring the Jovian system, encountered and photographed two asteroids during its long journey to Jupiter. The second asteroid it photographed, Ida, was discovered to have a moon which appears as a small dot to the right of Ida in this picture. The tiny moon, named Dactyl, is about one mile across, while the potato shaped Ida measures about 36 miles long and 14 miles wide. Dactyl is the first moon of an asteroid ever discovered. The names Ida and Dactyl are based on characters in Greek mythology. Do other asteroids have moons?
Comet Hale-Bopp Over Val Parola Pass (1999-08-08)
Comet Hale-Bopp became much brighter than any surrounding stars. It was seen even over bright city lights. Out away from city lights, however, it put on quite a spectacular show.  Here Comet Hale-Bopp was photographed above Val Parola Pass in the Dolomite mountains surrounding Cortina d'Ampezzo, Italy.  Comet Hale-Bopp's blue ion tail was created when fast moving particles from the solar wind struck expelled ions from the comet's nucleus.  The white dust tail is composed of larger particles of dust and ice expelled by the nucleus that orbit behind the comet.  Observations showed that Comet Hale-Bopp's nucleus spins about once every 12 hours.
A Martian Dust Storm Approaches (1999-08-09)
Tomorrow's picture: Sun Block  < Archive | Index | Search | Calendar | Glossary | Education | About APOD >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
A Total Eclipse for Europe (1999-08-10)
The last total solar eclipse of this millennium will be visible for a few minutes tomorrow from a narrow path in Europe and Asia.  There, millions of sightseers will witness the Moon move directly between the Earth and Sun, covering up the Sun completely.  Observers not besieged by clouds may get to see the Sun's large and flowing corona first hand.  A partial eclipse of the Sun, where part of the Sun is still visible, can be witnessed throughout the rest of Europe and much of Northern Africa and Asia.  Precise locations of total and partial eclipse are shown on the above map.  In modern times, eclipses are precisely predicted and well understood.  In fact, anyone can see this total solar eclipse live on the web.  In ancient times, though, eclipses frequently startled large populations, who interpreted them in ways that changed the course of wars and empires.
A Meteor Over the Anza-Borrego Desert (1999-08-11)
Meteors will be flashing across your skies over the next two nights.  Specifically, the Perseid Meteor Shower should be at its best just before each morning's dawn.  Observers at dark locations might see as much as a meteor a minute.  Perseid meteors are bits of dirt that blew off Comet Swift-Tuttle and that burn up as they fall to Earth.  Exciting expectations of a new filament in the Perseids might be tested this year.  Pictured above is a meteor from the most active meteor shower of last year: the Leonids.  Pictured above, a Leonid meteor was caught in November outshining even the brightest stars over the Anza-Borrego Desert in California. The Leonids will peak again this November and might provide an ever better show.
Deploying Spartan (1999-08-12)
Last October the Space Shuttle Discovery deployed Spartan 201, a spacecraft that monitored the corona of the Sun.  Instruments on Spartan 201 were used to estimate the density of electrons emitted into the solar corona, calibrate data from the Solar and Heliospheric Observatory (SOHO) satellite, and study how the Sun is changing as it reaches maximum activity over the next few years.  Pictured above, the space shuttle's robot arm (top left) releases Spartan (center) into space.  The tail fin of the space shuttle is visible on the right, while the Earth hovers in the background.  Spartan floated near the shuttle for two days before it was picked up again and returned to Earth.
Eclipse In The Shade (1999-08-13)
Near the shadow of the moon under a shady tree, dozens of images of a 1994 solar eclipse in progress are visible in this striking picture from the campus of Northwestern University in Evanston, Illinois. What creates the multiple images? Any small gap between leaves can act like a pin-hole camera, projecting a discernible image of the crescent sun onto the shaded sidewalk below. This tree's height and multitude of leaves combine dramatically to produce the large size and number of images. On August 11, many throughout Europe and Asia had the chance to enjoy similar views of the last total solar eclipse of the millennium as the moon's shadow raced across densely populated regions of the globe.
A String Of Pearls (1999-08-14)
Comet Shoemaker-Levy 9, named after its co-discoverers, was often referred to as the "string of pearls" comet. It is famous for its suggestive appearance as well as its collision with the planet Jupiter! The comet's original single nucleus was torn to pieces by Jupiter's strong gravity during a close encounter with the solar system's largest planet in 1992. The pieces are seen in this composite of Hubble Space Telescope images to be "pearls" strung out along the comet's orbital path. In July of 1994 these pieces collided with Jupiter in a rare and spectacular series of events.
M104: The Sombrero Galaxy (1999-08-15)
What's going on in the center of this spiral galaxy? Named the Sombrero Galaxy for its hat-like resemblance, M104 features a prominent dust lane and a bright halo of stars and globular clusters.  Something truly energetic is going on in the Sombrero's center, as it not only appears bright in visible light, but glows prodigiously in X-ray light as well. This X-ray emission coupled with unusually high central stellar speeds cause many astronomers to speculate that a black hole lies at the Sombrero's center - a black hole possibly a billion times the mass of our Sun.
Mars Weather Watch (1999-08-16)
Mars may be a cold, dry planet but its weather is dynamic. On June 30, wide angle cameras on board the Mars Global Surveyor (MGS) spacecraft watched the development of this large scale storm system above Mars' north polar area. These frames were recorded on successive mapping orbits at intervals of about 2 hours, with the white north polar cap near the center of each. High winds seem to mix the brownish dust clouds and white water-ice clouds as the curling storm front churns over the extreme northern martain landscape. The MGS cameras have watched similar storms in this region during the months of July and August revealing surprisingly complex weather. Mars Climate Orbiter will join the MGS spacecraft in martian orbit in late September, and in December Mars Polar Lander is scheduled to touch down near the Red Planet's south pole.
A Crescent Sunrise (1999-08-17)
Normally, the Moon shows phases, but the Sun does not.  The reason is founded in the fact that the Moon shines only by reflected sunlight.  When the Moon is closer to the Sun than the Earth, only part of it appears to be lit - resulting in a familiar crescent-shaped phase.  Last Wednesday, however, many viewers in eastern North America were treated to an unusual sunrise where the Sun appeared to itself rise in a crescent phase.  Nothing was wrong with Sun - viewers were witnessing the end of a solar eclipse.   This unusual sight was caught above during a cloudy morning in Quebec.  A similar sunrise eclipse recorded almost 3000 years ago has allowed historians to attempt to match ancient and modern calendars.
Sun Block (1999-08-18)
During a total solar eclipse, Earth's moon blocks the sun - almost exactly. While the sun is about 400 times wider than the moon, it is also about 400 times farther away and each appears to be half a degree or so in diameter. On August 11, this remarkable coincidence in the apparent size of two vastly different celestial bodies produced tantalizing solar spectacles for denizens of Europe and Asia. For example, prominences along the sun's limb peer around the moon's dark edge in this dramatic picture of totality recorded as the lunar shadow swept across Hungary. Subtle structures in the sun's inner corona are also visible streaming beyond the silhouetted moon. This total eclipse of the sun was the last to grace planet Earth's skies for this millennium. Although four partial eclipses will occur in the year 2000, the next total eclipse will not be until 2001 June 21.
Light From The Dark Sun (1999-08-19)
Only in the fleeting darkness of a total solar eclipse is the light of the solar corona easily visible from Earth. Normally overwhelmed by the bright solar disk, the expansive corona, the sun's outer atmosphere, is an alluring sight. But the subtle details and extreme ranges in the corona's brightness discernible to the eye are notoriously difficult to photograph. In this series of images recorded from Siofok, Hungary during the total phase of the August 11 eclipse, progressively longer exposures (top left to bottom center) have been used to more faithfully capture different regions of the elusive solar corona. The final image (at bottom right) shows light from the solar disk emerging from behind the moon's edge at the end of totality.
At The Suns Edge (1999-08-20)
Tomorrow's picture: Galaxies Away  < Archive | Index | Search | Calendar | Glossary | Education | About APOD >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.
Galaxies Away (1999-08-21)
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.
The Center of Centaurus A (1999-08-22)
A fantastic jumble of young blue star clusters, gigantic glowing gas clouds, and imposing dark dust lanes surrounds the central region of the active galaxy Centaurus A. This mosaic of Hubble Space Telescope images taken in blue, green, and red light has been processed to present a natural color picture of this cosmic maelstrom. Infrared images from the Hubble have also shown that hidden at the center of this activity are what seem to be disks of matter spiraling into a black hole with a billion times the mass of the Sun! Centaurus A itself is apparently the result of a collision of two galaxies and the left over debris is steadily being consumed by the black hole. Astronomers believe that such black hole "central engines" generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies. But for an active galaxy Centaurus A is close, a mere 10 million light-years away, and is a relatively convenient laboratory for exploring these powerful sources of energy.
Sundogs over the VLA (1999-08-23)
What if you woke up one morning and saw more than one Sun in the sky?  Most probably, you would be seeing sundogs, extra-images of the Sun created by falling ice-crystals in the Earth's atmosphere.  As water freezes in the atmosphere, small, flat, six-sided, ice crystals might be formed.  As these crystals flutter to the ground, much time is spent with their faces flat, parallel to the ground.  An observer may pass through the same plane as many of the falling ice crystals near sunrise or sunset.  During this alignment, each crystal can act like a miniature lens, refracting sunlight into our view and creating parhelia, the technical term for sundogs.  Sundogs were photographed here in a cloudy sky above the Very Large Array of radio telescopes.  The real Sun is near the center above the train tracks. A bright sundog is visible on the far right, and a dim one on the far left.   Ice-crystals can create other strange illusions of the Sun and Moon including halos and pillars
A Network of Microlensing Caustics (1999-08-24)
A virtual sky map like this would be of interest to astronomers studying gravitational microlensing. In microlensing, the gravity of stars near the line of sight can act to magnify the light of background objects such as distant stars, or quasars. Nowhere is this magnification greater than near a gravitational lensing caustic. In the above computer simulated map, caustics are discernible as the sharp bright curved lines. When a background quasar moves across a microlensing caustic, it can appear dramatically brighter. Many astronomers thought microlensing events practically immeasurable even ten years ago, but within the past five years now hundreds have been found. Precise measurements of microlensing are now providing unique information about the composition and distribution of matter in galaxies and the universe. Some astronomers now predict that future microlensing searches might even isolate planets orbiting distant stars.