omnianasa/nasa-apod-metadata huggingface dataset:
The Magnetic Carpet Of The Sun (1999-10-24)
The Sun has a magnetic carpet. Its visible surface appears to be carpeted with tens of thousands of magnetic north and south poles joined by looping field lines which extend outward into the Solar Corona. Recently, researchers have revealed maps of large numbers of these small magnetic concentrations produced using data and images from the space-based SOHO observatory. The above computer generated sunscape highlights these effects, with white and black field lines drawn in joining regions of strong magnetism. A close-up of the Solar surface is illustrated in the inset. These small magnetic regions emerge, fragment, drift, and disappear over periods of only 40 hours or so. Their origin is mystifying and their dynamic behavior is difficult to reconcile with present theories of rotationally driven large-scale solar magnetism.  Is some unknown process at work?  Possibly, but the source of this mystery may well be the solution to another -- the long standing mystery of why the outer Solar Corona is over 100 times hotter than the sun's visible surface! The SOHO data reveal that energy released as these loops break apart and interact seems to be heating the coronal plasma.
Neptune in Infrared (1999-10-25)
Neptune has never looked so clear in infrared light.  Neptune is the eighth most distant planet from the Sun, thirty times the Earth-Sun distance.  Neptune is the fourth largest planet, almost four times Earth's diameter.  Surprisingly, Neptune radiates about twice as much energy as it receives from the Sun.  A fascinating feature of the above photograph is that it was taken far from distant Neptune, through the Earth's normally blurry atmosphere.  The great clarity of this recently released image was made possible by "rubber mirror" adaptive optics technology.  Here, mirrors in the new Palomar High Angular Resolution Observer (PHARO) instrument connected to the 200-inch Hale Telescope flex to remove the effects of turbulence in the Earth's atmosphere.
30 Doradus: The Tarantula Nebula (1999-10-26)
30 Doradus is an immense star forming region in a nearby galaxy known as the Large Magellanic Cloud. Its spidery appearance is responsible for its popular name, the Tarantula Nebula, except that this tarantula is about 1,000 light-years across, and 165,000 light-years away in the southern constellation Dorado. If it were at the distance of the Orion Nebula, the nearest stellar nursery to Earth, it would appear to cover about 30 degrees on the sky or about 60 full moons. The above image was taken with the Big Throughput Camera and is shown in representative colors. The spindly arms of the Tarantula Nebula surround the NGC 2070 star cluster which contains some of the intrinsically brightest, most massive stars known. This celestial Tarantula is also seen near the site of the closest recent Supernova.
In the Heart of the Tarantula Nebula (1999-10-27)
Tomorrow's picture: X-Ray Jet From Centaurus A  < 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.
X-Ray Jet From Centaurus A (1999-10-28)
Spanning over 25,000 light-years, comparable to the distance from the Sun to the center of our own Milky Way galaxy, a cosmic jet seen in X-rays blasts from the center of Centaurus A. Only 10 million light-years away, Centaurus A is a giant elliptical galaxy - the closest active galaxy to Earth. This composite image illustrates the jumble of gas, dust, and stars visible in an optical picture of Cen A superposed on a new image recorded by the orbiting Chandra X-ray Observatory. The X-ray data is shown in red. Present theories hold that the X-ray bright jet is caused by electrons driven to extremely high energies over enormous distances. The jet's power source is likely to be a black hole with about 10 million times the mass of the Sun coincident with the X-ray bright spot at the galaxy's center. Amazingly, while some material in the vicinity of the black hole falls in, some material is blasted outward in energetic jets. Details of this cosmic power generator can be explored with the Chandra X-ray data.
The USNO Millennium Time Ball (1999-10-29)
In the nineteenth century, dropping a time ball from a prominent location was a practical way of communicating the time to the surrounding country side and ships at sea. Initiating a fledgling time service for the United States, the U.S. Naval Observatory dropped a time ball at precisely noon every day begining in 1845. At the end of the twentieth century, in commemoration of this traditional method of disseminating time, the U.S. Naval Observatory has installed this ceremonial time ball atop its main building in Washington D.C. Dropping this time ball - at midnight Eastern Standard Time on New Year's Eve - will be the local culmination of a "round-the-world time ball drop" marking the beginning of the year 2000 and the beginning of the Third Millennium in 2001. Meanwhile, don't forget ... this year, in most of the U.S. Daylight Time ends at 2:00 am on Sunday, October 31.
Mars Rocks, Sojourner Rolls (1999-10-30)
This sharp color image featuring Mars rock Yogi and the rolling Sojourner robot shows off Yogi's two-toned surface. Yogi appears to be leaning into the prevailing winds causing some to suggest that its color contrast may be caused by the accumulation of rust colored dust on its windward face. The Pathfinder spacecraft, now the Sagan Memorial Station, has ended the primary mission phase after returning a scientific bonanza from the surface of Mars. The Sojourner robot rolled hundreds of feet on the martian surface, circumnavigated the lander, and produced a wealth of data and images. Mars Pathfinder and Soujourner landed on July 4, 1997 and lasted about 3 months, well beyond their designed lifetime.
The Cat's Eye Nebula (1999-10-31)
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. On planet Earth, of course, cats and other creatures may be on the prowl tonight. Keep your eyes peeled and have a safe and happy Halloween!
The Rotten Egg Planetary Nebula (1999-11-01)
Not all evolving stars eject gas clouds that look like people.  OH231.8+4.2 was a star much like our Sun that ran out of nuclear fuel to fuse in its core.  It has therefore entered the planetary nebula phase, where it throws off its outer atmosphere into space leaving a core that will become a white dwarf star.  Every Sun-like star creates a different planetary nebula though, and OH231.8+4.2's looks eerily like a person!  Spectacular jets of streaming gas can be seen in this recently released photograph by the Hubble Space Telescope. The gas cloud has been dubbed the Rotten Egg Planetary Nebula because it contains unusually high amounts of sulfur, an element that, when combined with other elements, can smell like a rotten egg.  This young planetary nebula will likely change its appearance over the next few thousand years and eventually disperse.
Aurora Through a Moonlit Sky (1999-11-02)
A night sky can glow in fascinating ways.  Through a clearing in the woods, the pictured sky above Alaska shines by reflected light from a nearby city, by the brightness of the Moon, and by aurora.  The night sky in or near a city appears to contain relatively few stars because lights there reflect off atmospheric particles, hiding stars in a diffuse glow.  The bright Moon also creates a diffuse sky glow, although much less bright than the analogous blue-sky glow created during the day by the Sun.  Particles from the Sun crashing into the Earth's atmosphere are seen here as bands of aurora.  These glows also illuminate visible clouds.  Auroral displays are becoming more frequent as the Sun approaches Solar Maximum.
M32: Blue Stars in an Elliptical Galaxy (1999-11-03)
cal galaxies are known for their old, red stars. But is this old elliptical up to new tricks?  In recent years, the centers of elliptical galaxies have been found to emit unexpectedly high amounts of blue and ultraviolet light.  Most blue light from spiral galaxies originates from massive young hot stars, in contrast to the red light from the old cool stars thought to compose ellipticals.  In the above recently released, false-color photograph by the Hubble Space Telescope, the center of nearby dwarf elliptical M32 has actually been resolved and does indeed show thousands of bright blue stars.  The answer is probably that these blue stars are also old and glow blue, reaching relatively high temperatures by the advanced process of fusing helium, rather than hydrogen, in their cores. M32 appears in many pictures as the companion galaxy to the massive Andromeda Galaxy (M31).
Gamma-Ray Bursting (1999-11-04)
Using graphics and data from NASA's Compton Gamma Ray Observatory, this animation illustrates one of the most exciting mysteries of modern astrophysics, gamma-ray bursts. Incredibly gamma-ray bursts, sudden flashes of radiation with over 100,000 times the energy of visible light photons, occur several times a day. They typically last from fractions of a second to many minutes and appear from random directions, unexpectedly triggering space-based gamma-ray instruments. At left a burst suddenly appears, flickers and fades in a false-color gamma-ray all-sky map, briefly overwhelming all other sources of celestial gamma-rays. The graph at right shows the corresponding response of an orbiting gamma-ray detector as its counting rate suddenly climbs and falls recording the passage of the mysterious burst. Originating far across the Universe, gamma-ray bursts are now known to be the most powerful explosions since the big bang and may yet prove to be useful tools for exploring the distant cosmos. Future space and ground-based observatories will also work to discover the nature of the bursters and the source of their extreme energy.
The Shadow Of Phobos (1999-11-05)
Hurtling through space above the Red Planet, potato-shaped Phobos completes an orbit of Mars in less than eight hours. In fact, since its orbital period is shorter than the planet's rotation period, Mars-based observers see Phobos rise in the west and set in the east - traveling from horizon to horizon in about 5 1/2 hours. These three images from the Mars Global Surveyor (MGS) spacecraft record the oval shadow of Phobos racing over western Xanthe Terra on August 26, 1999. The area imaged is about 250 kilometers across and is seen in panels from left to right as red filter, blue filter, and combined color composite views from the MGS wide-angle camera system. The three dark spots most easily seen in the red image are likely small fields of dark sand dunes on crater floors. Standing in the shadow of Phobos, you would see the Martian version of a solar eclipse!
X-ray Transit of Mercury (1999-11-06)
This sequence of false color X-ray images captures a rare event - the passage or transit of planet Mercury in front of the Sun. Mercury's small disk is silhouetted against the bright background of X-rays from the hot Solar Corona. It appears just to the right of center in the top frame and moves farther right as the sequence progresses toward the bottom. The dark notch is a coronal hole near the Solar South Pole, while a flaring coronal bright point can be seen to the left of the notch in the top frames. The frames were recorded on November 6, 1993 by the Soft X-ray Telescope on board the orbiting Yohkoh satellite. Transits of Mercury (and Venus) were historically used to discover the geometry of the solar system and to map planet Earth itself. The next transit of Mercury will occur on November 15.
The Heart Of NGC 4261 (1999-11-07)
Who knows what evil lurks in the hearts of galaxies? The Hubble knows.  This Hubble Space Telescope picture of the center of the nearby elliptical galaxy NGC 4261 tells one dramatic tale. The gas and dust in this disk are swirling into what is almost certainly a massive black hole. The disk is probably what remains of a smaller galaxy that fell in hundreds of millions of years ago. Collisions like this may be a common way of creating such active galactic nuclei as quasars.  Strangely, the center of this fiery whirlpool is offset from the exact center of the galaxy - for a reason that for now remains an astronomical mystery.
Lunation (1999-11-08)
Our Moon's appearance changes nightly.  This slow-loading time-lapse sequence shows what our Moon looks like during a lunation, a complete lunar cycle.  As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible.  The Moon always keeps the same face toward the Earth.  The Moon's apparent size changes slightly, though, and a slight wobble called a libration is discernable as it progresses along its elliptical orbit. During the cycle, sunlight reflects from the Moon at different angles, and so illuminates different features differently.  A full lunation takes about 29.5 days, just under a month (moon-th).
Spiral Galaxies in Collision (1999-11-09)
Billions of years from now, only one of these two galaxies will remain.  Until then, spiral galaxies NGC 2207 and IC 2163 will slowly pull each other apart, creating tides of matter, sheets of shocked gas, lanes of dark dust, bursts of star formation, and streams of cast-away stars.  Astronomers predict that NGC 2207, the larger galaxy on the left, will eventually incorporate IC 2163, the smaller galaxy on the right.  In the most recent encounter that peaked 40 million years ago, the smaller galaxy is swinging around counter-clockwise, and is now slightly behind the larger galaxy.  The space between stars is so vast that when galaxies collide, the stars in them usually do not collide.
The Belt of Venus (1999-11-10)
Although you've surely seen it, you might not have noticed it.  During a cloudless twilight, just before sunrise or after sunset, part of the atmosphere above the horizon appears slightly off-color, slightly pink.  Visible in the above photograph, this off-color band between the dark eclipsed sky and the blue sky can best be seen in the direction opposite the Sun and is called the Belt of Venus.  Straight above, blue sky is normal sunlight reflecting off the atmosphere.  In the Belt of Venus, however, the atmosphere reflects light from the setting (or rising) Sun which appears more red.  The Belt of Venus can be seen from any location with a clear horizon.
Mercury And The Moon (1999-11-11)
Mercury is the closest planet to the Sun and never moves far from our parent star in Earth's sky. Racing around its tight orbit, this well-done world is a little over 1/3 the diameter of Earth and is often lost to our view in the solar glare. But, just one day before the August 11 total solar eclipse, astronomer Tunc Tezel captured this fleeting view of a close conjunction of Mercury and the soon to be silhouetted Moon as seen from Turkey. Mercury at the lower right shines brightly in reflected sunlight while only a thin crescent of the almost new Moon is directly illuminated. The rest of the lunar nearside is faintly visible though, illuminated by light from an almost full Earth. On Monday, November 15th, Mercury will actually be seen to transit or pass across the disk of the Sun for well placed observers in the pacific hemisphere.
1998 Leonid Fireball (1999-11-12)
Will this be the year? Last year's Leonid meteor shower did not produce the meteor storm many had hoped for. Still, it put on a dazzling show with many bright fireball meteors. For example, this Leonid fireball, photographed through light clouds, eerily flashed across the skies of Monteromano, Italy on November 17, 1998. This year, the chances for a storm with thousands of meteors per hour are considered good ... but experts are quick to acknowledge that such predictions are tricky. Want to see for yourself? The predicted peak should occur on early Thursday, November 18 (UTC) but meteor activity will certainly be observable days before and after. If the night is clear, just grab a lawn chair and a warm jacket, go outside and look up!
Tempel-Tuttle: The Leonid Comet (1999-11-13)
Star trails streak this composite time exposure of Comet Tempel-Tuttle recorded by T. Puckett on January 26, 1998. Then passing through the inner solar system on its 33 year orbit around the Sun, Tempel-Tuttle brightened unexpectedly, but binoculars or small telescopes were still required to visually observe it. Tempel-Tuttle is also called "the Leonid Comet" as the yearly Leonid meteor shower results when the Earth crosses this comet's orbital plane and encounters cometary dust. So, while not rivaling spectacular naked-eye comets like Hyakutake or Hale-Bopp, Tempel-Tuttle still puts on a show. When the Earth plunges through Tempel-Tuttle's debris tail in November of this year, many sky-watchers are anticipating an extremely active meteor shower to result, perhaps even a meteor storm!
M31: The Andromeda Galaxy (1999-11-14)
Andromeda is the nearest major galaxy to our own Milky Way Galaxy.  Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies.  The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it.  The several distinct stars that surround Andromeda's image are actually stars in our Galaxy that are well in front of the background object.  Andromeda is frequently referred to as M31 since it is the 31st object on Messier's list of diffuse sky objects.  M31 is so distant it takes about two million years for light to reach us from there.  Much about M31 remains unknown, including why the center contains two nuclei.
In the Shade of a Historic Planet (1999-11-15)
For the first time, astronomers have recovered independent evidence that distant planetary systems exist.  Last Friday, a team led by G. W. Henry (Tenn. State) and G. Marcy (UC Berkeley) announced the discovery of a shadow of a planet crossing a distant star.  Little known HD 209458, a Sun-like star 150 light-years away, had been suspected of harboring planets from a slight wobble found in its motion.  Henry et al. now find that this wobble exactly corresponds to a planet crossing the face of the star, creating the slight dimming effect of a partial eclipse.  The astronomers were then able to make a groundbreaking estimate of the mass and radius of the extra-solar planet, which they find to have about two-thirds the mass of Jupiter but about 60 percent larger radius.  The drawing above is an artist's depiction of a planetary eclipse in the HD 209458 system.
A RADARSAT Map of Antarctica (1999-11-16)
It's not easy to make a map of Antarctica.  Earth's southern most continent is so cold and inhospitable that much of it remains unexplored.  From space, though, it is possible to map this entire region by radar: by systematically noting how long it takes for radio waves to reflect off the terrain.  The Canadian satellite RADARSAT has been orbiting the Earth for the past five years making radar maps, and has recently released the most detailed map of Antarctica ever created.  Above is a computer-generated map of Antarctica at relatively low resolution.  From the RADARSAT map, scientists have been able to better study this mysterious continent, including information about how ancient ice-shelves are crumbling.
A Leonid Meteor Explodes (1999-11-17)
Tonight, a lucky few may see a meteor explode.  Over the next 36 hours the Earth will pass unusually close to debris expelled from Comet Tempel-Tuttle, causing many sand-sized particles from this comet to enter and burn up in the Earth's atmosphere.  This yearly phenomenon is known as the Leonids Meteor Shower, but the location the Earth passes through this year holds promise to provide particularly high activity.  The 1998 Leonids was noteworthy for its many bright meteors.  In the above slow-loading sequence, a 1998 Leonid was caught exploding over Los Alamos, New Mexico.  In the last one-minute exposure, another Leonid streaks past.  If tonight is clear, just grab a lawn chair and a warm jacket, go outside, and look up!
A Sirius Leonid Meteor (1999-11-18)
In the sky or on the web, did you watch this year's Leonid meteor shower? If you did, meteors flashing through the night sky should be a familiar sight. Recorded last year during the 1998 apparition of the Leonids, this time-exposure of the sky around the constellation Canis Major (big dog) shows the trail of a spectacular fireball meteor. The meteor, by chance, seems to leap from the constellation's brightest star Sirius, near the top right. In the foreground is the beautiful desert scenery of Joshua Tree National Park. At this year's peak of the cosmic dust storm, observers in Europe and Africa reported intense rates of over 1600 meteors per hour for a brief period near 0215 November 18 (UTC). Awe inspiring as they were, the Leonids posed no danger to earthbound skywatchers.
Mercury And The Sun (1999-11-19)
Just days before the peak of the Leonid meteor shower, skywatchers were offered another astronomical treat as planet Mercury crossed the face of the Sun on November 15. Viewed from planet Earth, a transit of Mercury is not all that rare. The last occurred in 1993 and the next will happen in 2003. Enjoying a mercurial transit does require an appropriately filtered telescope, still the event can be dramatic as the diminutive well-done world drifts past the dominating solar disk. This slow loading gif animation is based on images recorded by the earth-orbiting TRACE satellite. The false-color TRACE images were made in ultraviolet light and tend to show the hot gas just above the Sun's visible surface. Mercury's disk is silhouetted against the seething plasma as it follows a trajectory near the edge of the Sun.
Small Star (1999-11-20)
A dim double star system cataloged as Gliese 623 lies 25 light-years from Earth, in the constellation of Hercules. The individual stars of this binary system were distinguished for the first time when the Hubble Space Telescope's Faint Object Camera recorded this image in June 1994. They are separated by 200 million miles - about twice the Earth/Sun distance. On the right, the fainter Gliese 623b is 60,000 times less luminous than the Sun and approximately 10 times less massive. The fuzzy rings around its brighter companion, Gliese 623a, are image artifacts. The lowest mass stars are classified as red dwarf stars, but even red dwarfs are massive enough to trigger hydrogen fusion in their cores to sustain their feeble starlight. Slightly less massive objects, known as brown dwarfs, can shine only briefly as their central temperatures are too low to utilize hydrogen as nuclear fuel. The present estimates of the mass of Gliese 623b are right at this red dwarf/brown dwarf border but future observations should help clarify the nature of one of our Galaxy's small stars. Dim and difficult to detect, an abundance of objects like Gl623b has been proposed as a possible solution to the mystery of "Dark Matter" in the Universe.