omnianasa/nasa-apod-metadata huggingface dataset:
Where is Upsilon Andromedae? (1999-04-22)
Astronomers recently announced the detection of three large planets orbiting the star Upsilon Andromedae - the first planetary system known to orbit a normal star other than our Sun. These planets were not directly photographed but found through a Doppler technique developed to use large telescopes to search nearby stars for wobbling planetary signatures. However, Upsilon And itself is visible to the unaided eye shining in Earth's sky in the northern constellation Andromeda at about 4th magnitude. This deep photographic image shows Upsilon And along with fainter stars and "deep sky" objects including the famous Andromeda spiral galaxy or M31 (right), the Triangulum galaxy or M33 (below), and the star cluster NGC 752 (left). About 44 light-years distant, Upsilon And is a star only a little more massive and just slightly hotter than the Sun.
Io Shadow (1999-04-23)
Orbiting Jupiter once every 43 hours, the volcanic moon Io cruises 500,000 kilometers above swirling, banded cloud-tops. Orbiting Earth once every 1.5 hours, the Hubble Space Telescope watched as Io accompanied by its shadow crossed the face of the reigning gas giant planet in 1997. This and other sharp false-color images have recently been chosen to celebrate the ninth anniversary of the Hubble's launch (April 24, 1990). Reflective patches of sulfur dioxide "frost" are visible on Io's surface while Io's round dark shadow is seen passing over brownish white regions of Jupiter's high altitude haze and clouds. In October and November of this year, the Galileo spacecraft currently operating in the Jovian system is scheduled to make two daring close approaches to Io, possibly flying through a volcanic plume.
Barsoom (1999-04-24)
"Yes, I have been to Barsoom again ..." begins John Carter in Edgar Rice Burroughs' 1913 science fiction classic "The Gods of Mars". In Burroughs' novels describing Carter's adventures on Mars, "Barsoom" is the local inhabitants' name for the Red Planet. Long after Burroughs' stories were published, Mars continues to inspire Earthdwellers' interests and imagination. Soon it will again be invaded by spacecraft from Earth. This dramatic picture of a crescent Mars was taken by NASA's Viking 2 spacecraft in 1976.
Mimas: Small Moon with a Big Crater (1999-04-25)
Mimas is one of the smaller moons of Saturn but shows one of the largest impact craters. In fact, if the impact had been much greater, it would have disrupted the entire satellite.  The large crater has been named Herschel after the 1789 discoverer of Mimas, Sir William Herschel. Mimas' low mass produces a surface gravity just strong enough to create a spherical body but weak enough to allow such relatively large surface features.  Mimas is made of mostly water ice with a smattering of rock - so it is accurately described as a big dirty snowball.  Voyager 1 flew by in 1980 and took the above picture.
USNO-A2.0 Catalog: A Digital Sky (1999-04-26)
Here lie 526,230,881 of the brightest stars known.  The US Naval Observatory has deployed their monster Precision Measuring Machine to digitize photographic plates covering the whole sky and creating the above map.  Yellow corresponds to 150,000 stars per square degree, while dark blue corresponds to only 500 stars per square degree.  (For comparison, the Full Moon takes up about 1/4 of a square degree.)  The most striking feature on this whole sky projection is the central disk of our Milky Way Galaxy, which stretches across the middle.  Dark dust lanes are evident there by the great number of stars they obscure.  The two bright spots seen south of the Milky Way's disk are the neighboring Magellanic Cloud galaxies.  Anyone can order a free copy of this data, but not everyone can fit data from all 526,230,881 stars on their hard-drive.
Introducing Comet Lee (1999-04-27)
Another large snowball is falling toward the Sun.  Comet Lee was discovered two weeks ago by Steve Lee (AAO) in Australia, and is expected to brighten as it approaches the inner Solar System.  Comet Lee is not expected to become a naked-eye object, though, with recent projections guessing it will peak at magnitude 7 in July.  Starting in May, the large piece of dirty ice officially known as Comet C/1999 H1 Lee will be visible to northern observers. Comet Lee is the fuzzy patch in the above picture taken on April 16 from Loomberah, Australia.
A Sundial for Mars (1999-04-28)
When Mars Surveyor arrives at Mars in 2002, it will carry a sundial.  Even though batteries and a solar array will power the Mars Surveyor Lander, the sundial has been included to allow a prominent public display of time. The sundial idea was the brainchild of Bill Nye the Science Guy, who noticed that a post originally used for camera calibration could be redesigned.   Millennia ago, sundials were state-of-the-art timekeepers for humans on Earth.  Since the Sun casts similar shadows on Mars and Earth, accurate calibration of the shadow placement on the Martian Sundial will tell a curious inspector of returned images both the time of day and the season.
NGC 2266: Old Cluster in the New General Catalog (1999-04-29)
The New General Catalog of star clusters and nebulae really isn't so new. In fact, it was published in 1888 - an attempt by J. L. E. Dreyer to consolidate the work of astronomers William, Caroline, and John Herschel along with others into a useful single, complete catalog of astronomical discoveries and measurements. Dreyer's work was successful and is still important today as this famous catalog continues to lend its acronym "NGC" to bright clusters, galaxies, and nebulae. Take for example this star cluster known as NGC 2266 (item number 2,266 in the NGC compilation). It lies about 10,000 light-years distant in the constellation Gemini and represents an open or galactic cluster. With an age of about 1 billion years, NGC 2266 is old for a galactic cluster. Its evolved red giant stars are readily apparent in this gorgeous three-color image.
Solar Shock Wave (1999-04-30)
On September 24, 1997 a shock wave blasted across the surface of the sun at speeds of 250 to 600 kilometers per second. On planet Earth, observer Barry Reynolds photographed the expanding shock front (left) in the light emitted by hydrogen atoms at the solar surface. His discovery image was nicely confirmed by a space-based extreme ultraviolet image (right) of the shock ramming through the sun's upper atmosphere as recorded by the SOHO satellite observatory. In both pictures a bright solar flare is seen near the center of a circular arc-like feature representing a shock front. The shock front is dark in the ground based photo and bright in the ultraviolet image. These shock fronts are believed to be tracers of a 3-dimensional disturbance caused by the flare but researchers are uncertain as to the exact physical mechanisms which produced it. Along with other violent events called coronal mass ejections, solar flares are known to generate streams of energetic particles which can affect the Earth's magnetosphere and Earth orbiting satellites.
Lunar Dust and Duct Tape (1999-05-01)
Why is the Moon dusty? On Earth, rocks are weathered by wind and water, creating soil and sand. On the Moon, the long history of micrometeorite bombardment has blasted away at the rocky surface creating a layer of powdery lunar soil or regolith. This lunar regolith could be a scientific and industrial bonanza. But for the Apollo astronauts and their equipment, the pervasive, fine, gritty dust was definitely a problem. On the lunar surface in December 1972, Apollo 17 astronauts Harrison Schmitt and Eugene Cernan needed to repair one of their lunar rover's fenders in an effort to keep the "rooster tails" of dust away from themselves and their gear. This picture reveals the wheel and fender of their dust covered rover along with the ingenious application of spare maps, clamps, and a grey strip of "duct tape".
Stars from Eagle's Eggs (1999-05-02)
Newborn stars are forming in the Eagle Nebula.  This image, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs) emerging from pillars of molecular hydrogen gas and dust.  The giant pillars are light years in length and are so dense that interior gas contracts gravitationally to form stars.  At each pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed. The Eagle Nebula, associated with the open star cluster M16, lies about 7000 light years away.
Loop I in the Northern Sky (1999-05-03)
One of the largest coherent structures on the sky is known simply as Loop I and can best be seen in radio and X-ray maps.  Spanning over 100 degrees, part of Loop I appears so prominent in northern sky maps that it is known as the North Polar Spur (NPS).  Loop I, shown above in X-ray light, is a thin bubble of gas about 700 light-years across with a center located only about 400 light-years away.  Surprisingly, the cause of this immense structure is still debated, but is possibly related to expanding gas from a million-year old supernova.  Loop I gas is impacting the nearby Aquila Rift molecular cloud, and may create relatively dense fragments of the local interstellar medium.  Were our Sun to pass through one of these fragments in the next few million years, it might affect Earth's climate.
Magnetic Mars (1999-05-04)
Mapping Mars from orbit, instruments on the Mars Global Surveyor (MGS) spacecraft have recently revealed banded magnetic field patterns - a startling and unanticipated suggestion that the Red Planet was more Earth-like in its distant past. The red and blue regions within the MGS orbital tracks across this portion of southern Mars indicate adjacent areas of crust where magnetic fields point in opposite directions. The bands seem to run east-west and are about 100 miles wide and 600 miles long. Such patterns are known to be produced on Earth by plate tectonics. As the crustal plates spread apart along the mid-ocean ridges, they carry a progressive banded record of Earth's changing magnetic field. The similar patterns on Mars are seen as evidence that it too once had moving crustal plates and a changing magnetic field, although both processes - still active on the larger planet Earth - are thought to have long since died away. These high resolution measurements of martian magnetism were made possible by the revised, close aerobraking orbits of the MGS spacecraft and not originally planned.
A Solar System Portrait (1999-05-05)
As the Voyager 1 spacecraft headed out of our Solar System, it looked back and took a parting family portrait of the Sun and planets.  From beyond Pluto, our Solar System looks like a bright star surrounded by faint dots. In the  above picture, the Sun is so bright it is blocked out for contrast.  The innermost dots visible, labeled E and V for Earth and Venus, are particularly hard to discern.  Gas giants Jupiter (J) and Saturn (S) are much more noticeable.  The outermost planets visible are Uranus (U) and Neptune (N).  Each planet is shown labeled and digitally enhanced in an inset image. Voyager 1 is only one of four human-made objects to leave our Solar System, the other three being Voyager 2, and Pioneer 10 and Pioneer 11.
Liberty Bell 7 (1999-05-06)
Today, the space capsule Liberty Bell 7 rests about 3 miles below the surface of the Atlantic Ocean. But on July 21, 1961, astronaut Virgil I. "Gus" Grissom rode this tiny craft 118 miles above the Earth to become the second American in space. Grissom's flight was suborbital - like fellow Mercury astronaut Alan Shepard's first flight - however his capsule was different, with a window, a new manual spacecraft control system, and an explosive hatch. Unfortunately, after Grissom brought Liberty Bell 7 to a successful splash down in the planned area, the hatch blew prematurely and rough seas began to flood the capsule. While Grissom was able to get out, the military recovery helicopter could not lift the waterlogged spacecraft. This dramatic picture was taken from the helicopter shortly before Liberty Bell 7 was released and sank.
Hot Stars in the Southern Milky Way (1999-05-07)
Hot blue stars, red glowing hydrogen gas, and dark, obscuring dust clouds are strewn through this dramatic region of the Milky Way in the southern constellation of Ara (the Altar). About 4,000 light-years from Earth, the stars at the left are young, massive, and energetic. Their intense ultraviolet radiation is eating away at the nearby star forming cloud complex - ionizing the hydrogen gas and producing the characteristic red "hydrogen-alpha" glow. At right, visible within the dark dust nebula, is small cluster of newborn stars. This beautiful color picture is a composite of images made through blue, green, and hydrogen-alpha filters.
Moon Occults Saturn (1999-05-08)
On September 18, 1997, many stargazers in the U. S. were able to watch a lovely early morning lunar occultation as a bright Moon passed in front of Saturn. Using a 1.2 meter reflector, astronomer Kris Stanek had an excellent view of this dream-like event from the Whipple Observatory atop Arizona's Mount Hopkins. This animated gif image was constructed by Wes Colley from 4 frames taken by Stanek at 35 second intervals as the ringed planet emerged from behind the Moon's dark limb. While lunar occultations of fairly bright stars and planets are not extremely rare events, their exact timing depends critically on the observer's location.
Fractal Interstellar Dust Up-Close (1999-05-09)
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.
Polar Ring Galaxy NGC 4650A (1999-05-10)
Tomorrow's picture: A Black Cloud  < 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.
Molecular Cloud Barnard 68 (1999-05-11)
Where did all the stars go?  What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud.  Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars.  The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe.  One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured above.  That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across.  It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form.
Warped Spiral Galaxy ESO510-13 (1999-05-12)
How did spiral galaxy ESO510-13 get bent out-of-shape?  The disks of many spirals are thin and flat, but not solid.  Spiral disks are loose conglomerations of billions of stars and diffuse gas all gravitationally orbiting a galaxy center.  A flat disk is thought to be created by sticky collisions of large gas clouds early in the galaxy's formation.  Warped disks are not uncommon, though, and even our own Milky Way Galaxy is thought to have a small warp.  The causes of spiral warps are still being investigated, but some warps are thought to result from interactions or even collisions between galaxies.  ESO510-13, pictured above, is about 150 million light years away and about 100,000 light years across.
Mars Volcano Apollinaris Patera (1999-05-13)
Dwarfed by Olympus Mons and the other immense shield volcanos on Mars, Apollinaris Patera rises only 3 miles or so into the thin martian atmosphere, but bright water-ice clouds can be still be seen hovering around its summit. Mars' volcanic structures known as "paterae" are not only smaller than its shield volcanos but older as well, with ages estimated to be around 3 billion years. Like Apollinaris Patera, narrow furrows typically extend from their central craters or calderas. It is thought that the paterae represent broad piles of easily eroded volcanic ash. This wide angle view of Apollinaris Patera was recorded last month by the Mars Global Surveyor spacecraft. The large central crater is about 50 miles across.
Landsat 7 Views Planet Earth (1999-05-14)
Launched last month, NASA's Landsat 7 spacecraft now orbits planet Earth. Looking down from an altitude of 700 km, Landsat 7 can map the planet's surface in visible and infrared bands and resolve features 30 meters across or smaller. For example, this striking engineering test image is a natural-looking color composite of 3 different visible wavelength bands. It nicely shows details of urban areas around San Francisco, California, USA, nestled in the surrounding terrain (north is up). Flowing blue-green colors track the spring runoff from the Sierras to the west and neighboring mountains into the bay and out into the Pacific ocean. Landsat 7 is currently performing well in its check out phase and controllers are preparing the satellite for regular operations.
Star Wars in NGC 664 (1999-05-15)
Long ago in a galaxy far, far away, locked in their final desperate struggle against the force of gravity ... two stars exploded! stellar explosions - Supernovae - are among the most powerful events in the Universe, estimated to release an equivalent energy of up to 1 million trillion trillion (1 followed by 30 zeros) megatons of TNT. After the explosion, an expanding supernova envelope is observed to brighten over a a period of days to a maximum light output which rivals that of an entire galaxy before fading from view over the following months. Triggered by the collapsing core of a massive star or the nuclear demise of a white dwarf supernovae occur in average spiral galaxies only about once every 25-100 years. But a recent observation of NGC 664, a spiral galaxy about 300 million light years distant, captured a rare and colorful performance - two supernovae from the same galaxy. In this monitoring exposure the two supernovae, one reddish yellow and one blue, form a close pair just below the image center (to the right of the galaxy nucleus). The color difference is due to temperature - blue is hotter.
Europe at Night (1999-05-16)
This is what Europe looks like at night! Can you find your favorite European city? Although not all of Europe 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.
How to Search for Aliens (1999-05-17)
"Mom, can I use our computer to search for aliens?"  Last week, the SETI@home project released free software that enables many home computers to search for signals from intelligent extra-terrestrials.  These signals may have already been detected by the huge Arecibo radio telescope, but gone unnoticed due to the large amount of data that has been accumulating.  SETI enthusiasts David Gedye and Craig Kasnoff realized that the enormous amount of computing power in people's homes might help.  The resulting software can work as a screensaver and so after downloading a chunk of data, will only search for alien signals when the computer is otherwise idle.  When running, the software will generate images like that shown above: a changing Fast Fourier Transform plot highlighting strong periodic signals.  Although more likely to find false-alarms like known Earth-orbiting satellites, if your computer finds a true ET signal, SETI@home promises that you will be given due credit.
A Laguna Triangle (1999-05-18)
Tomorrow's picture: The Horsehead 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.
The Horsehead Nebula (1999-05-19)
One of the most identifiable nebulae in the sky, the Horsehead Nebula in Orion, is part of a large, dark, molecular cloud.  Also known as Barnard 33, the unusual shape was first discovered on a photographic plate in the late 1800s.  The red glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis.  The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead's neck casts a shadow to the left.  Streams of gas leaving the nebula are funneled by a strong magnetic field.  Bright spots in the Horsehead Nebula's base are young stars just in the process of forming.  Light takes about 1500 years to reach us from the Horsehead Nebula.  The above image was taken with the 0.9-meter telescope at Kitt Peak National Observatory.
Cyclone on Mars (1999-05-20)
Late last month a team of Mars-watching astronomers sighted an immense cyclonic storm system raging near the Red Planet's north pole. Their discovery picture, made with the Hubble Space Telescope on April 27, is seen at left while the projected insets (right) show closeups of the storm and surrounding areas. Shrunken to its martian midsummer state, Mars' north polar cap appears at the top of the discovery picture. The polar cap is clearly smaller than the storm just below it and farther left.  Similar to the "spiral storms" detected on Mars over 20 years ago by the Viking spacecraft, this storm was marked by a system of swirling bright water-ice clouds instead of the billowing dust of a more typical martian wind storm. Measuring roughly 1,000 miles across, with a cloud-free central eye spanning about 200 miles, it was comparable in size to cyclones seen in planet Earth's polar regions. The storm system was imaged once more, hours later, but then was not seen again and may have had a lifetime of only a few days.
Star Party Trails (1999-05-21)
Stargazing is fun! If you'd like to try it, this weekend may be your chance as many astronomy clubs and organizations will be hosting public celebrations of Astronomy Day on Saturday, May 22nd. In recent years, open house nights at observatories, astronomy club gatherings, and star parties have become increasingly popular. They offer great opportunities for beginners to view the sky through a variety of telescopes and veterans to swap stories and ideas. This time exposure of star trails was made last month at the Sentinel, Arizona "Stargaze" star party. On the right, a brilliant trail tracks the setting evening star, Venus. Stars in Orion are near the center and bright Sirius produced the prominent trail at the left. City lights from nearby Yuma glow on the horizon while party-goers' red filtered flashlights create the eerie foreground effect. The red flashlights are courteously used to provide a safe level of illumination but still preserve night vision for enjoyable stargazing.