omnianasa/nasa-apod-metadata huggingface dataset:
Neutron Mars (2002-03-15)
Looking for water on Mars, researchers using detectors on board the orbiting Mars Odyssey spacecraft have created this false-color global map of energetic neutrons from the otherwise Red Planet. What do neutrons have to do with water? As cosmic rays from interplanetary space penetrate the thin martian atmosphere and reach the surface they interact with elements in the upper layer of soil, scattering neutrons back into space. But if the martian soil contains hydrogen, it seriously absorbs energetic scattered neutrons. Tracking variations in absorption, neutron detectors can map changes in surface hydrogen content from orbit. Hydrogen content is taken as a surrogate measure of frozen water (H20), the most likely form of hydrogen close to the martian surface. Blue shades in the above map correspond to large concentrations of hydrogen, indicating in particular that the martian south polar region has a high amount of water ice near the surface.
The Colorful Moon (2002-03-16)
Do you recognize the Earth's Moon when you see it? The crazy, patchwork appearance of the false-color image makes this almost full view of the Moon's familiar near side look very strange. The Sea of Tranquillity (Mare Tranquillitatis) is the bright blue area at right, the Ocean of Storms (Oceanus Procellarum) is the extensive blue and orange area on the left, and white lines radiate from the crater Tycho at bottom center. Recorded in 1992 by the Galileo spacecraft enroute to Jupiter, the picture is a mosaic of 15 images taken through three color filters. The image data were combined in an exaggerated color scheme to emphasize composition differences - blue hues reveal titanium rich areas while orange and purple colors show regions relatively poor in titanium and iron. Multicolor images exploring the Moon's global surface composition were made in 1994 by the Clementine spacecraft.
NGC 2244: A Star Cluster in the Rosette Nebula (2002-03-17)
In the heart of the Rosette Nebula lies a bright open cluster of stars that lights up the nebula.  The stars of NGC 2244 formed from the surrounding gas only four million years ago and emit light and wind that define the nebula's appearance today.  High energy light from the bright young stars of NGC 2244 ionizes the surrounding hydrogen gas clouds to create the red emission nebula appearance.  The hot wind of particles that streams away from the cluster stars contributes to an already complex menagerie of gas and dust filaments while slowly evacuating the cluster center.  NGC 2244 measures about 50 light-years across, lies about 4500 light-years away, and is visible with binoculars towards the constellation of Monoceros.
Comet Ikeya-Zhang's Busy Tail (2002-03-18)
One of the brightest comets of the past five years will likely reach its peak brightness this week.  Comet Ikeya-Zhang, officially known as C/2002 C1, can now be seen without aide from a dark location above the western horizon shortly after sunset.  Recent luminosity estimates for Comet Ikeya-Zhang place it between magnitudes three and four, making it brighter than most commonly visible stars.  The above picture was taken on March 11 near Tucson, Arizona, USA.  The image caught Comet Ikeya-Zhang showing a quite detailed ion tail, possibly disrupted by the magnetic field of the Sun's outwardly flowing particle wind.  As the activity of comets is notoriously hard to predict, Comet Ikeya-Zhang may still hold some surprises as it rounds the Sun this month and starts back out of the Solar System in April.
Breaking Distant Light (2002-03-19)
In the distant universe, time appears to run slow.  Since time-dilated light appears shifted toward the red end of the spectrum (redshifted), astronomers are able to use cosmological time-slowing to help measure vast distances in the universe.  Above, the light from distant galaxies has been broken up into its constituent colors (spectra), allowing astronomers to measure the redshift of known spectral lines.  The novelty of the above image is that the distance to hundreds of galaxies can now be measured on a single frame using the Visible MultiObject Spectrograph that has begun operating at the Very Large Telescope array in Chile.  Analyzing the space distribution of distant objects will allow insight into when and how stars, galaxies, and quasars formed, clustered, and evolved in the early universe.
Aurora Over Antarctica (2002-03-20)
Looking out from the bottom of the world, strange and spectacular sights are sometimes observed.  Such was the case during the long Antarctic night of 1998, as awesome aurora sub-storms were photographed above scientific outposts.  Visible in the left foreground of the above photograph is the Martin A. Pomerantz Observatory while the now defunct SPIREX telescope canvas dome is visible to its right.  The outside temperature at the time this photograph was taken was about -73 Celsius (-100 Fahrenheit), although a slightly heated box sheltered the camera.
S is for Sun (2002-03-21)
Taken yesterday from the SOHO spacecraft, this false-color image shows the active Sun near the March Equinox, the beginning of Autumn in the south and Spring in the northern hemisphere. Recorded in a band of extreme ultraviolet light emitted by highly ionized iron atoms, the Sun's upper atmosphere or solar corona shines with an array of active regions and plasma loops suspended in magnetic fields. The bright coronal structures and loops seen here have temperatures of about 1.5 million kelvins. By chance, the Sun's earth-facing side also seems to be marked with a twisting complex of dark filament channels shaped like a giant "S". Filaments represent relatively (!) cool material in the corona which show up as prominences when seen at the Sun's edge. For planet Earth, recent solar activity has made auroral displays likely around this year's March Equinox.
Odyssey Over Mars (2002-03-22)
Scroll right and journey for 300 kilometers over Terra Sirenum in the cratered highlands of southern Mars. The infrared view, 32 kilometers wide, was recently recorded by the THEMIS camera on board the orbiting Mars Odyssey spacecraft. Beginning at the north (left) edge, the scene sweeps across the floor and over the rim of Koval'sky Crater. Continuing southward (right) of the crater's rim are lava flows exhibiting fractures and numerous smaller impact craters. The infrared image was made in daylight hours, so sun-facing slopes are still warm and bright while shadowed areas are cool and dark. But rocky regions also tend to remain cooler and darker than their surroundings, likely corresponding to the dark blotchy terrain along the Koval'sky Crater floor and dark rings of rocky ejecta surrounding some of the smaller craters.
The Water Vapor Channel (2002-03-23)
What alien planet's bizarre landscape lurks below these fiery-looking clouds? It's only planet Earth, of course ... as seen on the Water Vapor Channel. Hourly, images like this one (an infrared image shown in false-color) are brought to you by the orbiting Geostationary Operational Environmental Satellites' (GOES) multi-channel imagers. These instruments can produce images at the infrared wavelength of 6.7 microns or about 10 times the wavelength of visible light, recording radiation absorbed by water vapor in the upper troposphere. In this picture, the planet's dark regions correspond to high concentrations of water vapor over storms and high cloud tops, while bright areas are relatively dry. The dominant bright feature seen here is a persistent region of dry descending air extending west into the Pacific off the Peruvian coast. Atmospheric water vapor is otherwise invisible to the eye and produced by evaporation from the oceans.  Editor's note: Thanks to Don Garlick (Humboldt State Univ.) for corrections to the original text.
The Cat's Eye Nebula (2002-03-24)
Three thousand light-years away, a dying star throws off shells of glowing gas.  This image from the Hubble Space Telescope reveals the Cat's Eye Nebula to be one of the most complex planetary nebulae known.  In fact, the features seen in the Cat's Eye are so complex that astronomers suspect the bright central object may actually be a binary star system. The term planetary nebula, used to describe this general class of objects, is misleading. Although these objects may appear round and planet-like in small telescopes, high resolution images reveal them to be stars surrounded by cocoons of gas blown off in the late stages of stellar evolution.
An Unusual Globule in IC 1396 (2002-03-25)
Is there a monster in IC 1396?  Known to some as the Elephant's Trunk Nebula, parts of gas and dust clouds of this star formation region may appear to take on foreboding forms, some nearly human.  The only real monster here, however, is a bright young star too far from Earth to hurt us.  Energetic light from this star is eating away the dust of the dark cometary globule near the top of the above image.  Jets and winds of particles emitted from this star are also pushing away ambient gas and dust.  Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a much larger region on the sky than shown here, with an apparent width of more than 10 full moons.
Comet Ikeya-Zhang Over Tenerife (2002-03-26)
Comet Ikeya-Zhang has become bright enough to stand out in the night sky.  Discovered February 1, the comet has now just rounded the Sun and has likely attained its peak brightness.  The comet appears near the Sun and over the next week moves from the evening sky (just after sunset) to the morning sky (just before sunrise).  Many observers report a current brightness approaching third magnitude.  The comet is actually a giant snowball created during the early days of our Solar System and pushed out by the gravitational tugs by massive planets.  Comet Ikeya-Zhang has been back to the inner Solar System at least once before in 1661.  Above, the comet was photographed above Tenerife, one the Canary Islands, Spain.
Looking Into an Io Volcano (2002-03-27)
What would it look like to peer into one of the volcanoes currently active on Jupiter's moon Io?  The caldera of Tupan Patera, named after a Brazilian thunder god, reveals itself to be a strange and dangerous place, replete with hot black lava, warm red sulfur deposits likely deposited from vented gas, and hilly yellow terrain also high in sulfur.  The robot spacecraft Galileo currently orbiting Jupiter provided the above vista late last year when it swooped by the active world.  Tupan Patera is actually a volcanic depression, surrounded by cliffs nearly a kilometer high.  The width of the depression is about 75 kilometers.  As Galileo has filled its mission objectives and is running low on maneuvering fuel, NASA plans to crash the spacecraft into Jupiter during 2003.
Centaurus Galaxy Cluster in X-Rays (2002-03-28)
The Centaurus Cluster is a swarm of hundreds of galaxies a mere 170 million light-years away. Like other immense galaxy clusters, the Centaurus Cluster is filled with gas at temperatures of 10 million degrees or more, making the cluster a luminous source of cosmic x-rays. While individual galaxies are not seen here, this false-color x-ray image from the Chandra Observatory does reveal striking details of the central region's hot cluster gas, including a large twisted plume about 70,000 light-years long. Colors represent temperatures indicated by the x-ray data with red, yellow, green, and blue shades ranging in order from cool to hot. The plume of gas alone is estimated to contain material equivalent to about one billion times the mass of the Sun. It may be a wake of gas condensing and cooling along the path of the massive, dominant central galaxy moving through the cluster.
NGC 4631: The Whale Galaxy (2002-03-29)
NGC 4631 is a big beautiful spiral galaxy seen edge-on only 25 million light-years away towards the small northern constellation Canes Venatici. This galaxy's slightly distorted wedge shape suggests to some a cosmic herring and to others the popular moniker of The Whale Galaxy. Either way, it is similar in size to our own Milky Way. In this gorgeous color image, the Whale's dark interstellar dust clouds, young bright blue star clusters, and purplish star forming regions are easy to spot. A companion galaxy, the small elliptical NGC 4627 appears above the Whale Galaxy. Out of view off the lower left corner of the picture lies another distorted galaxy, the hockey stick-shaped NGC 4656. The distortions and mingling trails of gas and dust detected at other wavelengths suggest that all three galaxies have had close encounters with each other in their past. The Whale Galaxy is also known to have spouted a halo of hot gas glowing in x-rays.
Venus Unveiled (2002-03-30)
The surface of Venus is perpetually covered by a veil of thick clouds and remains hidden from even the powerful telescopic eyes of earth-bound astronomers. But in the early 1990s, using imaging radar, the Venus orbiting Magellan spacecraft was able to lift the veil from the face of Venus and produced spectacular high resolution images of the planet's surface. Colors used in this computer generated picture of Magellan radar data are based on color images from the surface of Venus transmitted by the Soviet Venera 13 and 14 landers. The bright area running roughly across the middle represents the largest highland region of Venus known as Aphrodite Terra.
The Mysterious Rings of Supernova 1987A (2002-03-31)
What's causing those odd rings in supernova 1987A?  In 1987, the brightestsupernova in recent history occurred in the Large Magellanic Clouds.  At the center of the picture is an object central to the remains of the violent stellar explosion. When the Hubble Space Telescope was pointed at the supernova remnant in 1994, however, the existence of  curious rings was confirmed.  The origins of these rings still remains a mystery. Speculation into the cause of the rings includes  beamed jets emanating from a dense star left over from the supernova, and a superposition of two stellar winds ionized by the supernova explosion.
Hubble Resolves Expiration Date For Green Cheese Moon (2002-04-01)
Using the new camera on the recently refitted Hubble Space Telescope, astronomers have been able to confirm that the Moon is made of green cheese.  The telling clue was the resolution of a numeric date after which the Moon may go bad.  Controversy still exists, however, over whether the date resolved is truly an expiration date or just a "sell by" date.  "To be cautious, we should completely devour the Moon by tomorrow," a spokesperson advised.  Happy April Fool's Day from the folks at APOD.  The above image (slightly altered) was actually taken in 1965 by the Ranger 9 probe minutes before impact.  The popular "Moon is made of Green Cheese" myth can be traced back almost 500 years.  It has been used historically in context to indicate a claim so clearly false that no one -- not even April Fools -- will believe it.
Mysterious Black Water in Florida Bay (2002-04-02)
What is causing the water in Florida Bay to turn black?  The mysterious black color could be seen as early as last December in images taken by the SeaWIFS instrument on board the Earth-orbiting SeaStar satellite.  During the darkest period in February, when the above image was taken, visibility in the usually transparent/turquoise water dropped below three meters.  Samples have been taken and are currently being analyzed.  Early tests show the black water has normal salinity and oxygen and might be an unusual nontoxic algae bloom.  Whatever the cause, the black water has real ecological and economic consequences, as normally abundant fish are completely absent.  More recent SeaWIFS images show the black water to be breaking up into smaller pockets.
NGC 4414: A Flocculent Spiral Galaxy (2002-04-03)
How much mass do flocculent spirals hide?  The above true color image of flocculent spiral galaxy NGC 4414 was taken with the Hubble Space Telescope to help answer this question.  Flocculent spirals -- galaxies without well defined spiral arms -- are a quite common form of galaxy, and NGC 4414 is one of the closest.  Stars and gas near the visible edge of spiral galaxies orbit the center so fast that the gravity from a large amount of unseen dark matter must be present to hold them together.  Pictured above is the photogenic center of NGC 4414.  A bright foreground star from our Milky Way Galaxy shines in the foreground of the image.  Although NGC 4414's center likely holds little dark matter, understanding its matter distribution helps calibrate the rest of the galaxy and, by deduction, flocculent spirals in general.  By determining a precise distance to NGC 4414, astronomers also hope to help calibrate the scale to the more distant universe.
Ikeya-Zhang: Comet Over Colorado (2002-04-04)
Comet Ikeya-Zhang ("ee-KAY-uh JONG") has become a most photogenic comet. This lovely early evening view of the comet in Rocky Mountain skies looks northwest over ridges and low clouds. The time exposure was recorded on March 31st from an 8,000 foot elevation near Yampa, Colorado, USA. Sporting a sweeping yellowish dust tail and blue ion tail eight to ten degrees long, Ikeya-Zhang is nestled near the horizon in the northern constellation of Andromeda. To the comet's left is the bright star Mirach or Beta Andromedae while the stretched celestial fuzzball to the comet's right is M31 or the Andromeda galaxy, the nearest bright spiral galaxy to our own Milky Way. As the days pass, Comet Ikeya-Zhang's apparent motion through the sky is towards the right in this image. Tonight, comet-watchers blessed with clear skies should find Ikeya-Zhang posing perfectly for binoculars and cameras just above M31, less than two degrees from the center of the bright galaxy.
Gamma-Ray Burst Afterglow: Supernova Connection (2002-04-05)
What causes the mysterious gamma-ray bursts? Indicated in this Hubble Space Telescope exposure of an otherwise unremarkable field in the constellation Crater, is the dwindling optical afterglow of a gamma-ray burst first detected by the Beppo-SAX satellite on 2001 December 11. The burst's host galaxy, billions of light-years distant, is the faint smudge extending above and to the left of the afterglow position. After rapidly catching the fading x-ray light from the burst with the orbiting XMM-Newton observatory, astronomers are now reporting the telltale signatures of elements magnesium, silicon, sulphur, argon, and calcium - material most likely found in an expanding debris cloud produced by the explosion of a massive star. The exciting result is evidence that the gamma-ray burst itself is linked to a very energetic supernova explosion which may have preceded the powerful flash of gamma-rays by up to a few days.
Vintage Gamma Rays (2002-04-06)
Gamma-rays are the most energetic form of electromagnetic radiation. But these high energy photons penetrate and interact in normal materials and cannot be focused by lenses and mirrors like those in optical telescopes. So how do you make an image in gamma-ray light? One way is to use a patterned mask of material which can cast gamma-ray shadows on a digital detector array. The mask is called a coded aperture and the resulting shadow patterns can be used to construct a gamma-ray image of the source. For example, consider the picture above. In place of a coded mask, familiar objects were positioned in front of a detector array and illuminated with gamma-rays in a laboratory test. Do you recognize the shadow image? (Click on the picture for the focused visible light image.) Destined to fly on the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) satellite scheduled for launch in October of this year, the detector array is part of the imaging gamma-ray telescope, IBIS.
NGC 2392 from Hubble (2002-04-07)
In 1787, astronomer William Herschel discovered  NGC 2392.  From the ground, NGC 2392 resembles a person's head surrounded by a parka hood.  In 2000, the Hubble Space Telescope imaged  NGC 2392.   From space, the nebula displays gas clouds so complex they are not fully understood.   NGC 2392 is clearly a planetary nebula, and the gas seen above composed the outer layers of a Sun-like star only 10,000 years ago.  The inner filaments visible above are being ejected by strong wind of particles from the central star.  The outer disk contains unusual light-year long orange filaments.  NGC 2392 lies about 5000 light-years away and is visible with a small telescope in the constellation of Gemini.
NGC 2787: A Barred Lenticular Galaxy (2002-04-08)
Lenticular galaxies aren't supposed to be photogenic.  Like spiral galaxies, they contain a disk, but like elliptical galaxies, they are usually short on dust, gas, and pretty spiral arms.  Lenticulars are relatively little studied, possibly because of their seemingly benign nature.  Famous galaxies historically classified as lenticular include M84, M85, and M86.  Recent pictures and evidence, however, indicate that lenticulars can be both photogenic and scientifically interesting.  For example, the above image of NGC 2787 taken with the Hubble Space Telescope shows that the center of this lenticular galaxy has interesting structure.  The image was taken to help determine how lenticular galaxies formed, and what happens in their centers.  The span of NGC 2787 in the above image is about 4500 light years, while the galaxy lies about 25 million light years away toward the constellation of Ursa Major.
The Snake Nebula from CFHT (2002-04-09)
What slithers overhead? The dark winding lanes visible in part of the constellation of Ophiuchus belong to the Snake Nebula.  Also known as Barnard 72, the Snake Nebula is a series of dark absorption clouds made up of molecular gas and interstellar dust.  Interstellar dust grains - composed predominantly of carbon - absorb visible starlight and reradiate much of it in the infrared.  This absorption causes stars behind the clouds to be obscured from view, hence the appearance of starless voids on the sky.  Molecular clouds like the Snake Nebula are places where new stars are likely to form.  The Snake Nebula, pictured above, lies about 650 light-years away and spans the angular width of a full moon.
Unusual Rocks in Death Valley (2002-04-10)
How did those big rocks end up on that strange terrain? One of the more unusual places here on Earth occurs inside Death Valley, California, USA.  There a dried lakebed named Racetrack Playa exists that is almost perfectly flat, with the odd exception of some very large stones, one of which is pictured above.  Now the flatness and texture of large playa like Racetrack are fascinating but not scientifically puzzling -- they are caused by mud flowing, drying, and cracking after a heavy rain.  Only recently, however, has a viable scientific hypothesis been given to explain how 300-kilogram stones ended up near the middle of such a large flat surface.  Unfortunately, as frequently happens in science, a seemingly surreal problem ends up having a relatively mundane solution.  It turns out that high winds after a rain can push even heavy rocks across a momentarily slick lakebed.
Antennae Galaxies in Near-Infrared (2002-04-11)
What happens when galaxies collide? One of the best studied examples of the jumble of star clusters, gas, and dust clouds produced by such a cosmic train wreck is the interacting galaxy pair NGC 4038 / NGC 4039, the Antennae Galaxies, only sixty million light-years away. In visible light images, long, luminous tendrils of material seem to reach out from the galactic wreckage, lending the entwined pair an insect-like appearance. But this penetrating view from the new Wide-field InfraRed Camera (WIRC) attached to the Palomar Observatory's 200 inch Hale telescope shows, in false-color, details of some otherwise hidden features. The large central nuclei of the two original galaxies dominate the near-infrared scene speckled with other bright sources which are themselves giant, newly formed star clusters. Remarkably the northern (topmost) nucleus, obscured in optical images, is also revealed here to have a barred, mini-spiral structure reminiscent of many "single" spiral galaxies.