juliensimon/nasa-apod huggingface dataset:
Dust and Gas Surrounding Star R Coronae Australis (2000-10-16)

Young star R Coronae Australis has a dusty home.  The dust is so thick on the upper left of the above photograph that little light from background stars comes through.  Thinner dust near the stars reflects light from  R Coronae Australis (upper right) and neighbor TY Coronae Australis, giving their surroundings a flowing appearance.  Were these stars more massive they would emit light energetic enough to ionize much of the nearly invisible surrounding hydrogen gas, causing it to appear bright red.  The unusual structure above the center is a Herbig-Haro object, a knot of gas ejected from the star that has impacted surrounding gas.  R Coronae Australis is about 500 light-years away, while the region shown is about four light years across.
Gemini North Images Bow Shock Near Galactic Center (2000-10-17)

What's going on near the center of our Galaxy?  Glowing across the electromagnetic spectrum, the center of our Milky Way Galaxy is thought to be home to massive stars, rotating gas rings, and a massive black hole.  Now the central Galactic zoo just got larger.  The 8-meter Gemini North telescope in Hawaii in its first scientific observation has just imaged the Galactic Center and revealed a star only three light years out colliding with gas and dust.  The bow shock, similar to that caused by a boat moving through water, appears arrow-shaped and is visible on the upper right of the above photograph taken in representative infrared colors.  Gemini's new flexible-mirror technology has imaged this structure, known as IRS8, in finer detail than ever before.
The Space Shuttle Docking Ring (2000-10-18)

A space shuttle is again visiting the International Space Station (ISS).  The STS-92 crew aboard Discovery have already delivered and installed a truss and a docking port on the growing orbiting space station.  The station is being prepared for its first permanent crew, currently scheduled to be launched from Kazakstan on October 30.  Pictured above, the shuttle's docking ring is being extended to enable a stable connection to the space station.
The Farthest Explosion Yet Measured (2000-10-19)

It happened so far away that common human distance measures are inadequate to describe it.  Furthermore, astronomers do not even claim to know exactly what happened.  What is known is that satellites across our Solar System reported on 2000 January 31 a tremendous explosion of gamma rays had occurred towards some previously uninteresting direction.  Soon one of the largest optical telescopes on Earth, a VLT in Chile, began to peer in the direction of the gamma ray burst.  The VLT not only recorded an optical counterpart, shown above, but also was able to estimate that the cosmologically-induced redshift was an astonishing 4.5 -- placing GRB000131 farther across the universe than any explosion so measured.  This vast distance indicates that GRB000131 occurred just as galaxies like our Milky Way were forming, and so qualifies gamma ray bursts as unique probes of this ancient epoch.  This result bodes well for the recently launched HETE-2 satellite, which may record and help place more explosions in this distant and mysterious time-period of our universe.
North Pole Below (2000-10-20)

Orbiting over the north pole of planet Earth on May 5, the MODIS instrument on-board the Terra spacecraft, recorded this view of the ice cap 700 kilometers below. A radial grid centered on the pole is shown on top of the approximately true color image where each pixel covers about one square kilometer. Frozen sea ice appears whitish while open water or newly refrozen ice looks black. An impressive criss-crossing network of cracks in ice shifting above a liquid water ocean is visible, traced by the meandering dark lines. In fact, the dark network of cracks in the sea ice is reminiscent of another world in our solar system which may also harbor a liquid water ocean -- Jupiter's ice moon Europa.
The Averted Side Of The Moon (2000-10-21)

This vintage 60-kopek stamp celebrates a dramatic achievement. On the 7th of October, 1959 (7/X/1959), the Soviet interplanetary station which has come to be called "Luna 3" successfully photographed the far side of the moon giving denizens of planet Earth their first ever view of this hidden hemisphere. Lacking the digital image technology familiar now, Luna 3 took the pictures on 35mm film which was automatically developed on board. The pictures were then scanned and the signal transmitted to Earth days later in what was perhaps also the first interplanetary fax. In all, seventeen pictures were received providing enough coverage and resolution to construct a far side map and identify a few major features. Depicted on the stamp are regions dubbed the Sea of Moscow, the Soviet Mountains, the Bay of Astronauts, and the Sea of Dreams.
Wild Duck Open Cluster M11 (2000-10-22)

Many stars like our Sun were formed in open clusters.  The above open cluster, M11, contains thousands of stars and is just over three thousand light years distant.  The stars in this cluster all formed together about 150 million years ago.  The bright young stars in M11 appear blue.  Open clusters, also called galactic clusters, contain fewer and younger stars than globular clusters.  Also unlike globular clusters, open clusters are generally confined to the plane of our Galaxy. M11 is visible with binoculars towards the constellation of Scutum.

Image credit: D. F. Malin, 
AAO
Dwarf Elliptical Galaxy NGC 205 in the Local Group (2000-10-23)

Our Milky Way Galaxy is not alone.  It is part of a gathering of about 25 galaxies known as the Local Group.  Members include the Great Andromeda Galaxy (M31), M32, M33, the Large Magellanic Cloud, the Small Magellanic Cloud, Dwingeloo 1, several small irregular galaxies, and many dwarf elliptical and dwarf spheroidal galaxies.  Pictured on the lower left is one of the many dwarf ellipticals: NGC 205.  Like M32, NGC 205 is a companion to the large M31, and can sometimes be seen to the south of M31's center in photographs.  The above image shows NGC 205 to be unusual for an elliptical galaxy in that it contains at least two dust clouds (at 1 and 4 o'clock - they are visible but hard to spot) and signs of recent star formation.  This galaxy is sometimes known as M110, although it was actually not part of Messier's original catalog.
Io Rotating (2000-10-24)

The surface of Io is continually changing.  Jupiter's moon is the home to many powerful volcanoes so active they are effectively turning the moon inside out.  The above time-lapse sequence is a composite of images taken during two space missions that approached the violent moon: Voyager and Galileo.  The sequence shows Io during a complete rotation, which corresponds to a complete revolution around Jupiter since Io always keeps the same face toward the giant planet. The rampant volcanism is thought to be caused by Jupiter's more distant Galilean Moons (Europa, Ganymede, and Callisto) pulling on Io and continually distorting its shape, causing internal frictional heating.  Io is composed mostly of rock, with the yellow color originating from sulfur.  The causes of many of the other colors remain a topic of research.

Image credit: Calvin J. Hamilton, 
Voyager Team, 
Galileo Team, 
NASA
The Nebula And The Neutron Star (2000-10-25)

The lonely RX J1856.5-3754 was formed from the collapsed core of an exploding star. At a distance of 180 light-years it is the closest known neutron star. More massive than the Sun but only 20 kilometers across, this tiny stellar juggernaut plows through the hydrogen gas and dust clouds of interstellar space at about 200 kilometers per second. The surface of the neutron star is fantastically hot, around 700,000 degrees Celsius, making it detectable with orbiting x-ray telescopes. But optical astronomers were recently surprised to discover that RX J1856.5-3754 is also surrounded by a cone-shaped nebula. Indicated in this deep image from the European Southern Observatory's Kueyen telescope, the nebula glows in the red light of ionized hydrogen atoms recombining with electrons. Its cone shape is analogous to the bow wave of a ship plowing through water. A faint blue dot near the tip of the cone is the neutron star itself. The nebula appears to have formed very near the surface of the neutron star and astronomers are trying to determine if the observed densities and temperatures can indeed explain the nebula's appearance.
The Map Of Eros (2000-10-26)

This map of Eros was constructed from a mosaic of images recorded by the NEAR Shoemaker spacecraft, currently orbiting the 40 x 14 x 14 kilometer asteroid. A simple cylindrical projection of an irregularly shaped world, the map's individual images don't always match up at the edges. Shown here, place names have been proposed to describe the geography of Eros with a fitting theme, though. They are based on romantic figures in the history and literature of the cultures of planet Earth. The largest feature, Himeros, is a depression about 10 kilometers wide. In Greek mythology, Himeros was an attendant of Eros and the personification of the longing of love. Today, after safely surveying Eros for the past eight months, NEAR Shoemaker is scheduled to make a daring close approach to the asteroid, briefly flying to within about 6 kilometers of its surface. Images returned from that distance are expected to show features less than 1 meter across.
Close To Eros (2000-10-27)

Scroll right and fly close over asteroid Eros! This long mosaic was constructed of images returned yesterday by the NEAR Shoemaker spacecraft as it orbited to within 6.4 kilometers of a spot in the southern hemisphere of the rotating asteroid's surface. That distance (about 21,000 feet) is less than the cruising altitude of most commercial airline flights. The digital images show that while many regions appear smooth with craters filled in by an accumulation of loose regolith, much of Eros' surface is littered with rocks and boulders. The large boulder glinting in the sunlight at the far left, just above the center of the mosaic, spans approximately 25 meters. In the high-resolution view, the smallest rocks visible are roughly human-sized at about 1.4 meters (5 feet) across. The car-sized Near Shoemaker spacecraft is now on its way to a higher, more stable orbit about 200 kilometers above asteroid Eros.
Moonset, Planet Earth (2000-10-28)

During the Astro-1 astronomy mission of December, 1990, Space Shuttle astronauts photographed this stunning view of the setting full moon above the Earth's limb. In the foreground, towering clouds of condensing water vapor mark the extent of the troposphere, the lowest layer of the planet's life-sustaining atmosphere. Strongly scattering blue sunlight, the upper atmospheric layer, the stratosphere, fades dramatically to the black background of space. Moon and clouds are strong visual elements of many well known portraits of planet Earth, including Ansel Adams' famous "Moonrise, Hernandez, New Mexico", photographed in 1941.
Microwave Hotspots: The Oldest Structures Known (2000-10-29)

These spots are the oldest, most distant structures known. They are seen on the above two images of the microwave sky, north and south of our galaxy's equator, based on four-year's worth of data from NASA's COsmic Background Explorer (COBE) satellite (1989-1993).  The spots represent temperature variations in the early universe.  As our universe expanded and cooled, conglomerations of mass formed.  These COBE images confirmed that only a million years after the big-bang - which occurred roughly 15 billion years ago - parts of the universe were visibly hotter than other parts.  By studying the size and distribution of the spots found on the microwave background, astronomers hope to learn what matter and processes caused the spots to form - and hence determine the composition, density, and future of our Universe.  Results from recent measurements of the cosmic microwave background are consistent with a universe stranger than previously thought, possibly filled with unexpected forms of dark matter and dark energy.  A more detailed analysis might result after NASA's Microwave Anisotropy Probe is launched in 2001.
A Step Toward Gravitational Wave Detection (2000-10-30)

Accelerate a charge and you'll get electromagnetic radiation: light.  But accelerate any mass and you'll get gravitational radiation.  Light is seen all the time, but, so far, a confirmed direct detection of gravitational radiation has yet to be made.  When absorbed, gravitational waves (GWs) create a tiny symmetric jiggle similar to squashing a rubber ball and letting go quickly.  Separated detectors can be used to discern GWs from everyday bumps.  Powerful astronomical GW sources would coincidentally jiggle even detectors on opposite ends of the Earth.  Pictured above are the two-kilometer-long arms of one such detector: the LIGO Hanford Observatory in Washington, which recently achieved a phase-lock milestone to future GW detection.  When it and its sister interferometer in Louisiana come online in 2002, they may see a GW sky so strange it won't be immediately understood.  APOD mourns the recent passing of Joseph Weber, a visionary thinker and pioneer in gravitational wave detection.
The Perseus Cluster's X-Ray Skull (2000-10-31)

This haunting image from the orbiting Chandra Observatory reveals the Perseus Cluster of Galaxies in x-rays, photons with a thousand or more times the energy of visible light. Three hundred twenty million light-years distant, the Perseus Cluster contains thousands of galaxies, but none of them are seen here. Instead of mere galaxies, a fifty million degree cloud of intracluster gas, itself more massive than all the cluster's galaxies combined, dominates the x-ray view. From this angle, voids and bright knots in the x-ray hot gas cloud lend it a very suggestive appearance. Like eyes in a skull, two dark bubbles flank a bright central source of x-ray emission. A third elongated bubble (at about 5 o'clock) forms a toothless mouth. The bright x-ray source is likely a supermassive black hole at the cluster center with the bubbles blown by explosions of energetic particles ejected from the black hole and expanding into the immense gas cloud. Fittingly, the dark spot forming the skull's "nose" is an x-ray shadow ... the shadow of a large galaxy inexorably falling into the cluster center. Over a hundred thousand light-years across, the Perseus Cluster's x-ray skull is a bit larger than skulls you may see tonight. Have a safe and happy Halloween!
Double Asteroid 90 Antiope (2000-11-01)

This eight-frame animation is based on the first ever images of a double asteroid! Formerly thought to be a single enormous chunk of rock, asteroid 90 Antiope resides in the solar system's main asteroid belt between Mars and Jupiter. Now, these premier images reveal Antiope to actually consist of two 50 mile wide asteroids separated by about 100 miles. Like weights on each end of an elastic string, the pair mutually orbit their center of mass, or balance point in the space between them, once every 16.5 hours. Binary asteroids and asteroids with moons are believed to be rare, but observations of their orbits allow a direct determination of asteroid masses and densities. Surprisingly, Antiope and known asteroid-moon systems are found to have densities closer to ice than rock, despite their relatively dark and unreflective surfaces. These sharp images were made at the Keck Observatory atop the Hawaiian volcano Mauna Kea using newly developed adaptive optics technology to overcome the blurring effect of Earth's atmosphere.
A Galaxy Collision in NGC 6745 (2000-11-02)

Galaxies don't normally look like this.  NGC 6745 actually shows the results of two galaxies that have been colliding for only hundreds of millions of years.  Just off the above photograph to the lower right is the smaller galaxy, moving away.  The larger galaxy, pictured above, used to be a spiral galaxy but now is damaged and appears peculiar.  Gravity has distorted the shapes of the galaxies.  Although it is likely that no stars in the two galaxies directly collided, the gas, dust, and ambient magnetic fields do interact directly. In fact, a knot of gas pulled off the larger galaxy on the lower right has now begun to form stars.  NGC 6745 spans about 80 thousand light-years across and is located about 200 million light-years away.
New Moons For Saturn (2000-11-03)

Tomorrow's picture: Self-Portrait  < | 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.
Apollo 12: Self-Portrait (2000-11-04)

Is it art? In November of 1969, Apollo 12 astronaut-photographer Charles "Pete" Conrad recorded this masterpiece while documenting colleague Alan Bean's lunar soil collection activities on the Oceanus Procellarum. The image is dramatic and stark. Bean is faceless. The harsh environment of the Moon's Ocean of Storms is echoed in his helmet's perfectly composed reflection of Conrad and the lunar horizon. Works of photojournalists originally intent on recording the human condition on planet Earth, such as Lewis W. Hine's images from New York City in the early 20th century, or Margaret Bourke-White's magazine photography are widely regarded as art. Similarly many documentary astronomy and space images can be appreciated for their artistic and esthetic appeal.
Jupiter Swallows Comet Shoemaker Levy 9 (2000-11-05)

What happens when a comet encounters a planet?  If the planet has a rocky surface, a huge impact feature will form.  A giant planet like Jupiter, however, is mostly gas.  When Comet Shoemaker-Levy 9 struck Jupiter in 1994, each piece was swallowed into the vast Jovian atmosphere.  Pictured above is a time-lapse sequence of the result of two fragments striking Jupiter. As the comet plunged in, it created large dark marks that gradually faded.  The high temperature of gas under Jupiter's cloud tops surely caused the comet fragment to melt before it plunged very far.  Because Jupiter is much more massive than any comet, the orbit of Jupiter around the Sun did not change noticeably.
Heaven on Earth (2000-11-06)

Tomorrow's picture: The Gum Nebula  < | 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.

Image credit: Naoyuki Kurita
The Gum Nebula Supernova Remnant (2000-11-07)

Because the Gum Nebula is the closest supernova remnant, it is actually hard to see.  Spanning 40 degrees across the sky, the nebula is so large and faint it is easily lost in the din of a bright and complex background.  The Gum Nebula, highlighted nicely in the above wide angle photograph, is so close that we are much nearer the front edge than the back edge, each measuring 450 and 1500 light years respectively.  The complex nebula lies in the direction of the constellations of Puppis and Vela.  Oddly, much remains unknown about the Gum Nebula, including the timing and even number of supernova explosions that formed it.

Image credit: John Gleason 
(Celestial Images)
October Skylights (2000-11-08)

Tomorrow's picture: XRB  < | 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.

Image credit: Wade Clark Jr.
The Cosmic X-Ray Background (2000-11-09)

rly on, x-ray satellites revealed a surprising cosmic background glow of x-rays and astronomers have struggled to understand its origin. Now, peering through a hole in the obscuring gas and dust of our own Milky Way Galaxy, the powerful orbiting XMM-Newton telescope has recorded this deep image of the x-ray sky, resolving some of the mysterious background into many faint individual sources. The tantalizing image is color-coded, with red representing relatively low energy x-rays, photons with 500 or so times the energy of visible light. Green and blue colors correspond to increasingly energetic x-rays with up to about 10,000 times visible light energies. Notably, the faint sources tend to be green and blue, showing x-ray characteristics of huge amounts of material falling into massive black holes in very distant galaxies. Do massive black holes reside in the hearts of all large galaxies? The XMM-Newton results add to the growing consensus that they do and that, from across the universe, x-rays produced as matter feeds these black holes account for the cosmic x-ray background.
X-Ray Cygnus A (2000-11-10)

Amazingly detailed, this false-color x-ray image is centered on the galaxy Cygnus A. Recorded by the orbiting Chandra Observatory, Cygnus A is seen here as a spectacular high energy x-ray source. But it is actually more famous at the low energy end of the electromagnetic spectrum as one of the brightest celestial radio sources. Merely 700 million light-years distant, Cygnus A is the closest powerful radio galaxy and the false-color radio image (inset right) shows remarkable similarity to Chandra's x-ray view. Central in both pictures, the center of Cygnus A shines brightly while emission extends 300,000 light-years to either side along the same axis. Near light speed jets of atomic particles produced by a massive central black hole are believed to cause the emission. In fact, the x-ray image reveals "hot spots" suggestive of the locations where the particle jets are stopped in surrounding cooler, denser gas. The x-ray image also shows that the jets have cleared out a huge cavity in the surrounding gas. Bright swaths of emission within the cavity likely indicate x-ray hot material ... swirling toward the central black hole.
The First Lunar Observatory (2000-11-11)

The first, and so far only, lunar astronomical observatory was deployed by the Apollo 16 crew in 1972. The Far Ultraviolet Camera / Spectrograph used a 3-inch diameter Schmidt telescope to photograph the Earth, nebulae, star clusters, and the Large Magellanic Cloud.  The tripod mounted astronomical equipment is seen above, placed in the shadow of the Lunar Module (right) so it would not overheat. Also in the shadow is astronaut Charles Duke with the lunar rover in the background. The Far Ultraviolet Camera took pictures in ultraviolet light which would normally be blocked by the Earth's atmosphere.  It was created by George Carruthers (NRL), had a field of view of twenty degrees, and could detect stars having visual magnitude brighter than eleven. One hundred seventy-eight images were recorded in a film cartridge which the astronauts returned to Earth. The observatory still stands on the Moon today.
The Lyman Alpha Forest (2000-11-12)

We live in a forest.  Strewn throughout the universe are "trees" of hydrogen gas that absorb light from distant objects.  These gas clouds leave numerous absorption lines in a distant quasar's spectra, together called the Lyman-alpha forest.  Distant quasars appear to be absorbed by many more Lyman-alpha clouds than nearby quasars, indicating a Lyman-alpha thicket early in our universe.  The above image depicts one possible computer realization of how Lyman-alpha clouds were distributed at a redshift of 3.  Each side of the box measures 30 million light-years across.  Much remains unknown about the Lyman-alpha forest, including the real geometry and extent of the clouds, and why there are so many fewer clouds today.

Image credit: J. Shalf, Y. Zhang 
(UIUC) et al., 
GCCC