omnianasa/nasa-apod-metadata huggingface dataset:
Impact Moon (1999-03-26)
The Moon's surface is covered with craters, scars of frequent impacts during the early history of the solar system. Now, recent results from the Lunar Prospector spacecraft support the idea that the Moon itself formed from the debris of a giant impact of a mars-sized planetary body with the Earth nearly 4.5 billion years ago. The impact theory of lunar origin can explain, for example, why Moon rocks returned by the Apollo missions have the same isotopic ratios as Earth rocks while the Moon seems deficient in heavy elements like iron. It can also explain a critical finding of the Lunar Prospector experiments - that the Moon's core is proportionally very small. If the Moon formed simply as a "sister world", its origin paralleling Earth's formation from the primordial solar nebula, it should have similar iron content and relative core size. But material blasted from the surface of Earth by an impacting body would lack the iron and heavy elements which had settled to the Earth's core yet retain similar ratios of chemical isotopes. A fraction of this debris cloud would remain in Earth orbit ultimately forming the Moon.
Stars Without Galaxies (1999-03-27)
Galaxies are made up of stars, but are all stars found within galaxies? Using the Hubble Space Telescope, researchers exploring the Virgo Cluster of galaxies have now found about 600 red giant stars adrift in intergalactic space. Above is an artist's vision of the sky from a hypothetical planet of such a lonely sun. The night sky on a world orbiting an intergalactic star would be a stark contrast to Earth's - which features a spectacle of stars, all members of our own Milky Way galaxy. As suggested by the illustration, a setting swollen red sun would leave behind a dark sky flecked only with faint, fuzzy, apparitions of Virgo Cluster galaxies. Possibly ejected from their home galaxies during galaxy-galaxy collisions, these isolated suns may well represent part of a large, previously unseen stellar population, filling the space between Virgo Cluster galaxies.
The Coma Cluster of Galaxies (1999-03-28)
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.
NGC 1850: Gas Clouds and Star Clusters (1999-03-29)
There's nothing like it in our own Galaxy.  Globular clusters as young as NGC 1850 don't exist here.  Globular clusters only 40 millions of years old can still be found in the neighboring LMC galaxy, though, but perhaps none so unusual as NGC 1850.  Close inspection of the above photograph will reveal two clusters.  Below and right of the main group of stars known as NGC 1850A is a smaller, still younger group dubbed NGC 1850B.  This cluster is made of stars only about four million years old. The large red cloud of gas surrounding the clusters may have been predominantly created by supernovae explosions of stars in the younger cluster.  The red supernova remnant N57D is visible on the upper left.
An Anomalous SETI Signal (1999-03-30)
No one knows for sure what caused this signal. The bright colors on the blue background indicate that an anomalous signal was received here on Earth by a radio telescope involved in a Search for Extraterrestrial Intelligence (SETI).  A search for these signals is ongoing by several groups including volunteer members of the SETI League.  Time labels the vertical axis of the above plot, and frequency marks the horizontal axis.  Although this strong signal was never positively identified, astronomers have identified in it many attributes characteristic of a man-made satellite in low Earth orbit.  Many unusual signals from space remain unidentified.  No signal has yet been strong enough or run long enough to be unambiguously identified as originating from an extraterrestrial intelligence.
PG 1115+080: A Gravitational Cloverleaf (1999-03-31)
All four blue images in the above photograph are the same object. The gravitational lens effect of the red, foreground, elliptical galaxy visible near image center creates a cloverleaf image of the single distant quasar.  Light from the quasar is pulled around the massive galaxy in different paths, corresponding to different images.  Light takes many billions of years to reach us from this quasar.  Since light takes a different amount of time to traverse each path, each image shows the quasar as it appeared at a slightly different time in the past, creating time delays on the time scale of days.  Since these time delays are influenced by the expansion rate of the universe, analysis of this image helps reveal Hubble's constant, the parameter that calibrates universe expansion.  This recent picture by the new Subaru Telescope is perhaps the clearest image yet of this famous optical mirage.
Ski Mars! (1999-04-01)
These brightly reflecting fields of snow or frost are on the slopes of a crater rim in the northern hemisphere of Mars. They are 500 meters or so long and have lasted through about eight months of the Red Planet's spring and summer weather. Recently imaged by the Mars Global Surveyor spacecraft, they also seem to be relatively uncrowded ... suggesting to some on April 1st, that lift tickets on Mars are extremely expensive. Of course, a vacation on the Red Planet could still offer some advantages to skiing and snowboarding enthusiasts. For example, Mars' low gravity - only about 3/8ths Earth's gravity - would definitely tend to reduce sore muscles and fall-related injuries. Happy April Fools day from APOD.
Stars of NGC 206 (1999-04-02)
Nestled within the dusty arms of the large spiral galaxy Andromeda (M31), the star cluster NGC 206 is one of the largest star forming regions known in our local group of galaxies. The beautiful bright blue stars of NGC 206 betray its youth - but close, systematic studies of variable stars in and around NGC 206 will also accurately reveal its distance. Astronomers are searching for variable stars in NGC 206, particularly pulsating stars known as Cepheids and eclipsing binary star systems. Distances for these types of stars can be effectively determined by following the periodic changes in their brightness and spectra. About 3 million light-years away, an accurately known distance to NGC 206 and thus M31 is critical to the larger understanding of galaxy formation, galaxy evolution, and ultimately the distance scale of the Universe.
The Radio Sky: Tuned to 408MHz (1999-04-03)
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.
Hot Gas and Dark Matter (1999-04-04)
Is the gravity of the galaxies seen in this image high enough to contain the glowing hot gas? Superposed on an optical picture of a group of galaxies is an image taken in X-ray light.  This picture, taken by ROSAT, shows confined hot gas highlighted in false red color, and provides clear evidence that the gravity exerted in groups and clusters of galaxies exceeds all the individual component galaxies combined.  The extra gravity is attributed to dark matter, the nature and abundance of which is one of the biggest mysteries in astronomy today.
The Launch of STARDUST (1999-04-05)
NASA launches powerful rockets. One such rocket, the Delta II, recently lofted the STARDUST mission into the nearby Solar System.  STARDUST is expected to photograph Comet Wild in 2004 as it zooms by, and return interstellar dust samples to Earth in 2006.  Currently, much remains unknown about the size distribution, primordial composition, and even shapes of these dust grains. Above, a side-mounted camera photographed the separation of the solid rocket boosters above the receding Earth.
NGC 6334: The Bear Claw Nebula (1999-04-06)
NGC 6334 is a cloud of gas and dust that appears to be forming massive stars.  At 5500 light-years away, the Bear Claw Nebula, as it has also been dubbed, is more than three times as distant as the Orion Nebula, but still close enough for detailed study.  The Bear Claw Nebula can be found towards the constellation of Scorpius.  In visible light, ionized gas makes NGC 6334 look quite red.  The above false-color photograph, however, was taken in infrared light. There, the glow of starlight absorbing dust is more apparent (depicted in blue).  Current research indicates that the bright sources are very young and massive stars.  These stars emit light so energetic and intense that it destroys fine grains of dust in their immediate vicinity, creating an abundance of ionized gas (depicted in red).
Denizen of the Tarantula Nebula (1999-04-07)
The star cluster at lower right, cataloged as Hodge 301, is a denizen of the Tarantula Nebula. An evocative nebula in the southern sky, the sprawling cosmic Tarantula is an energetic star forming region some 168,000 light-years distant in our neighboring galaxy the Large Magellanic Cloud. The stars within Hodge 301 formed together tens of millions of years ago and as the massive ones quickly exhaust their nuclear fuel they explode. In fact, the red giant stars of Hodge 301 are rapidly approaching this violent final phase of stellar evolution - known as a supernova. These supernova blasts send material and shock waves back into the nebular gas to create the Tarantula's glowing filaments also visible in this Hubble Space Telescope Heritage image. But these spectacular stellar death explosions signal star birth as well, as the blast waves condense gas and dust to ultimately form the next generation of stars inside the Tarantula Nebula.
Apollo 12: Surveyor 3 and Intrepid (1999-04-08)
On April 20, 1967, NASA's robot spacecraft Surveyor 3 landed on the moon, touching down on the inside slope of a small lunar crater in the Ocean of Storms. Over 2 1/2 years later, on November 19, 1969, the lunar module Intrepid, piloted by Apollo 12 astronauts Pete Conrad and Alan Bean, flew overhead and landed nearby in the second visit by humans to the lunar surface. Intrepid touched down about 600 feet away and the moon walking astronauts were easily able to reach the Surveyor and examine the remote explorer that had preceded them. Intrepid is seen in the background of this striking high resolution picture of Surveyor 3. Surveyor's leftmost foot pad appears dug in while its foreground foot pad has made two distinct imprints in the powdery lunar soil - clear indications that the Surveyor slid and bounced on landing. Using bolt cutters, the astronauts removed Surveyor's TV camera (the cylinder shape at the right of the tall solar panel mast) and its sampling scoop (on the arm extended to the right), returning them to Earth for study.
WR 104: Pinwheel Star (1999-04-09)
Like a cosmic lawn sprinkler, dust streaming from a rotating star system creates a pinwheel pattern in this false color infrared image. Astronomers discovered the surprising star dust scenario using a sophisticated interferometer and the 10 meter Keck I telescope to observe the bright Wolf-Rayet star WR 104. Wolf-Rayet stars are thought to be massive objects on the brink of a cataclysmic supernova explosion - having grown so hot and bright that their intense light begins to drive material away in a stellar wind. The problem is, their starlight would also be so intense that any dust flakes should be destroyed! A possible solution to this dusty dilemma is that a companion star exists hidden in the bright central region, generating wind interactions which shield a relatively narrow dust forming region from the light of WR 104. As the binary system rotates, the spray of surviving dust particles appears to spiral outward.
Canaries Sky (1999-04-10)
This gorgeous view of stars, nebulae, and the Milky Way comes from the dark night sky above the lovely island of La Palma in the Canaries archipelago. The picture was made by a group of experienced astrophotographers who traveled there to take advantage of the ideal observing conditions near La Palma's Observatorio del Roque de los Muchachos. Skygazers can easily pick out several of their favorite astronomical objects in this wide angle time exposure which covers about 40 degrees on winter the sky. Faint stars along the plane of our Galaxy compose the delicate, luminous band of the Milky Way stretching across the image from the bottom left. The familiar constellation of Orion the hunter is also easy to find, with glowing nebulae highlighting the hunter's belt and sword. Orion's famous red giant star Betelgeuse, near picture center, has a yellowish cast and Rigel is the bright star in Orion at lower right. Brilliant white Sirius, near the bottom, is the brightest star in the picture (and in Earth's night sky). Sirius, is part of the constellation Canis Major (Big Dog). Across the Milky Way, above and to the left of Sirius, is slightly less brilliant Procyon, brightest star of Canis Minor. A V-shaped group of yellowish stars at the upper right, part of Taurus the bull, is dominated by the red giant Aldebaran.
Liftoff of Space Shuttle Columbia (1999-04-11)
Tomorrow's picture: A Shy Galaxy  < 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.
Nearby Spiral Galaxy NGC 4945 (1999-04-12)
For such a close galaxy, NGC 4945 is easy to miss.  NGC 4945 is a spiral galaxy in the Centaurus Group of galaxies, located only six times farther away than the prominent Andromeda Galaxy. The thin disk galaxy is oriented nearly edge-on, however, and shrouded in dark dust.  Therefore galaxy-gazers searching the southern constellation of Centaurus need a telescope to see it.  The above picture was taken with a large telescope testing a new wide-angle, high-resolution CCD camera.  Most of the spots scattered about the frame are foreground stars in our own Galaxy, but some spots are globular clusters orbiting the distant galaxy.  NGC 4945 is thought to be quite similar to our own Milky Way Galaxy.  X-ray observations reveal, however, that NGC 4945 has an unusual, energetic, Seyfert 2 nucleus that might house a large black hole.
The Case of the Missing Supernova (1999-04-13)
Would you notice a second Moon in the sky?  About 700 years ago, light from a tremendous explosion reached Earth that should have appeared almost as bright as a full Moon.  The bright spot should have lasted for weeks, yet no notation of such an occurrence has been found in historical records.  The mystery was uncovered by Wan Chen and Neil Gehrels (NASA/GSFC) when studying the source of radioactive elements toward the Vela supernova remnant.  They deduced that an explosion much younger and closer than the supernova that caused Vela must have occurred, and even computed explosion characteristics from the amounts of radioactive elements present.  They calculate that GRO/RX J0852 should have dazzled medieval stargazers.  Perhaps people were too busy, surviving records are too incomplete, or the explosion was somehow too dim.  The above picture of GRO/RX J0852 was taken in gamma-ray light with the Compton Gamma-Ray Observatory and is shown in false-color. Astronomers and historians continue to contemplate the clues.
The Backyard Universe (1999-04-14)
How far can you see from your own backyard?  Across the Solar System, even across our Galaxy, these sights are not difficult.  Recently, however, amateur Paul Boltwood gazed across the universe. His record setting image is shown above in false color.  Boltwood imaged sources more faint than magnitude 24 in response to a challenge made to amateur astronomers by Yale Astronomy Professor Bradley Schaefer.  Objects this dim tend to be galaxies billions of light years away.  Although professionals have recently recovered objects as dim as magnitude 30, Boltwood's image rivals even the best professional efforts of only a few decades ago.  Since then, photon-catching Charge Coupled Devices (CCDs) have allowed high efficiency frames to be added together.  As evidence, Boltwood used only a 16-inch telescope, but co-added 767 exposures each lasting only two minutes.
Apollo 17's Moonship (1999-04-15)
Awkward and angular looking, Apollo 17's lunar module Challenger was designed for flight in the vacuum of space. This sharp picture from the command module America, shows Challenger's ascent stage in lunar orbit. Small reaction control thrusters are at the sides of the moonship with the bell of the ascent rocket engine itself underneath. The hatch allowing access to the lunar surface is visible in the front and a round radar antenna appears at the top. This spaceship performed gracefully, landing on the moon and returning the Apollo astronauts to the orbiting command module in December of 1972 - but where is Challenger now? Its descent stage remains at the Apollo 17 landing site, Taurus-Littrow. The ascent stage crashed nearby after being jettisoned from the command module prior to the astronauts' return to planet Earth. Apollo 17's mission was the sixth and last time astronauts have landed on the moon.
Upsilon Andromedae: An Extra-Solar System (1999-04-16)
Yesterday, astronomers announced the discovery of the first system of planets around a normal star other than our Sun.  Previously, only single planet star systems had been found.  Subtle changes in the wobble of Upsilon Andromedae, a Sun-like star in the constellation of Andromeda, allowed astronomers led by R. Paul Butler (AAO) and Geoffrey W. Marcy (SFSU /UCB) to make the breakthrough.  This star system is quite different from our own Solar System, however.  All three detected planets have masses near or above Jupiter. The discovery implies that multiple-planet systems are quite common, increasing speculation that life-bearing planets similar to Earth may one day be found.  The drawing above is an artist's depiction of the Upsilon Andromedae system and its innermost planet.  This planet orbits unexpectedly close to its parent star.
Gamma Ray Moon (1999-04-17)
What if you could see gamma rays (photons with more than 40 million times the energy of visible light)? If you could, the Moon would appear brighter than the Sun! This startling notion is demonstrated by this image of the Moon from the Energetic Gamma Ray Experiment Telescope (EGRET) onboard NASA's orbiting Compton Gamma Ray Observatory. The most sensitive instrument of its kind, even EGRET can not see the quiet Sun which is faint at extreme gamma-ray energies. Why is the Moon so bright in gamma rays? High energy charged particles known as cosmic rays, constantly bombard the unprotected lunar surface generating gamma rays. EGRET's gamma-ray vision is not sharp enough to resolve a lunar disk or any surface features but its sensitivity reveals the bright gamma-ray moonglow against a background of gamma rays from our Milky Way galaxy, gamma-ray quasars and some still mysterious unidentified sources. The image was generated from eight exposures made during 1991-1994. A wide-angle picture, it covers a roughly 40x40 degree field of view with gamma-ray intensity represented in false color.
Moon Over California (1999-04-18)
The Moon, Saturn, and Venus shine above while city lights twinkle below in the deepening twilight of March 19.  Taken from outside Indio, California, the photo shows the city lights of Indio and nearby Palm Springs. The brilliant lunar crescent is over exposed here with Saturn about 4 degrees away to the upper right and bright Venus still farther to the right only another 2 degrees or so. This Sunday evening, April 18, another dramatic lunar spectacle should be easily visible to stargazers in the western and midwestern US when the crescent moon passes in front of the bright star Aldebaran.
The Full Moon (1999-04-19)
rth has one moon. A symbol in famous love songs, movies, poems, and folklore, many myths about the Moon date back to ancient history.  In fact, the name Monday originates from Moon-day.  The Moon glows by light it reflects from the Sun and is frequently the brightest object in the night sky.  The Moon orbits the Earth about once a month (moon-th) from about 1 light second away. The above-pictured Full Moon occurs when the Moon is nearly opposite to the Sun in its orbit.  The Moon's diameter is about 1/4 that of the Earth, and from the Earth's surface appears to have almost exactly the same angular size as the Sun. Recent evidence indicates that the Moon formed from a colossal impact on the Earth about 4.5 billions of years ago, and therefore has a similar composition to the Earth.  Humans walked on the Moon for the first time in 1969.
Candidates for a Hypernova (1999-04-20)
What created these huge explosion remnants? Speculation has been building recently that outbursts even more powerful than well-known supernovae might occur.  Dubbed hypernovae, these explosions might result from high-mass stars and liberate perhaps ten times more energy than conventional supernovae. A hypernova was originally postulated to explain the great amount of energy seemingly liberated in a gamma-ray burst.  A search for visible remnants of hypernovae has now yielded the above two candidates.  Nearby spiral galaxy M101, shown on the right, has two large expanding shells that might have originated from a hypernova. Remnant NGC 5471B on the upper left and MF83 below were identified by the unusually high amount of X-ray radiation they emit.  MF83 is also one of the largest expanding shells ever found.  Research continues into the possible nature and visibility of hypernovae and the gas shells they likely leave behind.
The Nearest Stars (1999-04-21)
Which stars are closest to the Sun?  The closest is Proxima Centauri, one of three stars that orbit each other about 4 light-years away in the Alpha-Centauri system.  Alpha Centauri is easily visible from Earth's Southern Hemisphere. Next is Barnard's Star, a dim star visible with a telescope in the constellation of Ophiuchus.  Sirius, the brightest star in the night sky, is part of the fifth closest star system, from which light takes 8.6 years to reach us.  The nearest 25 star systems are shown on the above map, out to 13 light-years.  Past that there are probably stars so dim that their proximity has not yet been discovered. Research continues in trying to identify an estimated 130 missing star systems out to 32 light-years.