omnianasa/nasa-apod-metadata huggingface dataset:
Reflections on NGC 6188 (1999-08-25)
NGC 6188 is an interstellar carnival of young blue stars, hot red gas, and cool dark dust.  Located 4000 light years away in the disk of our Galaxy, NGC 6188 is home to the Ara OB1 association, a group of bright young stars whose nucleus forms the open cluster NGC 6193.  These stars are so bright that some of their blue light reflects off of interstellar dust forming the diffuse blue glow in the center of the above photograph.  Open cluster NGC 6193 formed about three million years ago from the surrounding gas, and appears unusually rich in close binary stars.   The red glow visible throughout the photograph arises from hydrogen gas heated by the bright stars in Ara OB1.  The dark dust that blocks much of NGC 6188's light was likely formed in the outer atmospheres of cooler stars and in supernovae ejecta.
Cassini Flyby (1999-08-26)
Connect the dots and you'll trace the path of the Cassini spacecraft as it took a final turn by Earth on its way to the outer solar system. The dots (in a horizontal row just below center) are actually successive images of the spacecraft. The picture was produced by making exposures at 10 minute intervals as Cassini moved rapidly through Earth's night sky on August 18 - around the time of its closest approach. Cassini's ultimate destination is Saturn, but so far its voyage has consisted of a series of fuel saving "gravity assist" flybys of Venus and Earth, each designed to result in an increase in the spacecraft's speed. During this Earth flyby Cassini received about a 12,000 mile- per-hour (5.5 km/sec) boost. Cassini is now being maneuvered toward yet another slingshot encounter, this time a December 2000 flyby of of gas giant Jupiter, to received a final boost toward Saturn. The wayfaring spacecraft is slated to arrive at long last in the Saturnian system in 2004.
Chandra's First Light: Cassiopeia A (1999-08-27)
Cosmic wreckage from the detonation of a massive star is the subject of this official first image from NASA's Chandra X-ray Observatory. The supernova remnant, known as Cassiopeia A, was produced when a star exploded around 300 years ago in this northern sky constellation. It is revealed here in unprecedented detail in the light of X-rays - photons with thousands of times the energy of visible light. Shock waves expanding at 10 million miles-per-hour are seen to have heated this 10 light-year diameter bubble of stellar debris to X-ray emitting temperatures of 50 million kelvins. The tantalizing bright speck near the bubble's center could well be the dense, hot remnant of the stellar core collapsed to form a newborn neutron star. With this and other first light images, the Chandra Observatory is still undergoing check out operations in preparation for its much anticipated exploration of the X-ray sky. Chandra was launched aboard the space shuttle Columbia in July.
X-Ray Pleiades (1999-08-28)
The Pleiades star cluster is one of the jewels of the northern sky. To the unaided eye it appears as an alluring group of stars in the constellation Taurus, while telescopic views reveal cluster stars surrounded by delicate blue wisps of dust-reflected starlight. To the X-ray telescopes on board the orbiting ROSAT observatory, the cluster also presents an impressive, but slightly altered, appearance. This false color image was produced from ROSAT observations by translating different X-ray energy bands to visual colors - the lowest energies are shown in red, medium in green, and highest energies in blue. (The green boxes mark the position of the seven brightest visual stars.) The Pleiades stars seen in X-rays have extremely hot, tenuous outer atmospheres called coronas and the range of colors corresponds to different coronal temperatures.
The Witch Head Nebula (1999-08-29)
Tomorrow's picture: Eclipsed Earth from Space  < 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.
Looking Back on an Eclipsed Earth (1999-08-30)
Here is what the Earth looks like during a solar eclipse.  The shadow of the Moon can be seen darkening part of Earth. This shadow moves across the Earth at nearly 2000 kilometers per hour. Only observers near the center of the dark circle see a  total solar eclipse - others see a partial eclipse where only part of the Sun appears blocked by the Moon.  This spectacular picture of the 1999 August 11 solar eclipse was one of the last ever taken from the Mir space station, as Mir is being decommissioned after more than ten years of productive use.
Symbiotic Star Bubbles (1999-08-31)
The two stars at the center of this nebula are very different.  One is a white dwarf star with a mass similar to our Sun but with a radius as small as our Earth.  The other star is a red giant, a star also with mass near our Sun but with a radius so large it could fill the orbit of the Earth.  The strange symbiotic relationship between these two stars in the He2-104 system has created a planetary nebula shaped like an hourglass within an hourglass.  The red giant star turns out to be a Mira variable, a pulsating star that is dumping mass into an accretion disk surrounding the white dwarf.  Astronomers speculate that when enough mass falls onto the white dwarf, a thermonuclear explosion occurs creating another expanding hourglass-shaped nebula.  The above photograph was taken with the WFPC2 instrument onboard the Hubble Space Telescope.  The hourglasses from the two most recent explosions are visible with the last one highlighted in the inset.
1999 JM8: A Rock Too Close (1999-09-01)
Nearly four kilometers across, the huge rock known as 1999 JM8 silently passed only 8.5 million kilometers from the Earth in early August.  The small asteroid was completely unknown before May.  Every few centuries, a rock like this impacts the Earth, with the potential to disrupt modern civilization. Radar from two of the largest radio telescopes, Arecibo and Goldstone, tracked and imaged the Apollo asteroid as it approached to only 22 times the distance to the Moon.  Although 1999 JM8 missed the Earth, thousands of similar but unknown asteroids likely exist that cross Earth's orbit.  In fact, four asteroids have passed inside the orbit of the Moon within the last decade.  Possibly of larger concern to humanity are the more numerous rocks near 100 meters across. Were one of these to strike an ocean, a dangerous tidal wave might occur.
Eclipse Over The Mountain (1999-09-02)
Undaunted by world wide anticipation of the August 11 total solar eclipse, the moon also performed a lunar eclipse just two weeks earlier, on July 28. Crossing the edge of Earth's shadow the moon was only partially eclipsed - but the spectacle could be seen by observers located across the Earth's night side. For example, this photo was taken in early morning hours shortly after the mid-point of the eclipse as seen from Cody, Wyoming, USA. Still illuminating the landscape and obscured by a wisp of cloud, the moon is setting behind Sheep Mountain, west of Cody. Enjoying the celestial display, astrophotographer Mack Frost reported fairly clear skies tinged with a little smoke from area grass fires.
Venus Falls Out of the Evening Sky (1999-09-03)
Tomorrow's picture: The Water Vapor Channel  < 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 Water Vapor Channel (1999-09-04)
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 emitted by water vapor in the upper troposphere. Bright regions correspond to high concentrations of water vapor while dark spots are relatively dry areas. Atmospheric water vapor is invisible to the eye and produced by evaporation from the oceans. Convected upward in the tropical zones it affects the climate by contributing substantially to the greenhouse effect.
The Universe Evolves (1999-09-05)
Scroll right and watch the universe evolve.  Above is a computer simulation depicting the evolution of our entire universe.  On the far left is a slice of the universe soon after the Big Bang - over 10 billion years ago.  As time progresses toward the right, the initially smooth universe can be seen becoming more and more clumpy. The vertex near the far right marks the present day.  The largest slice of the universe actually surveyed is simulated to the vertex's right. This artificial universe, called a Hubble Volume, was designed to mimic what humanity might see were we to have powerful enough telescopes.  By comparing different computer simulations to reality, we might be able to better tell what kind of universe we live in.
HCG 87: A Small Group of Galaxies (1999-09-06)
Sometimes galaxies form groups. For example, our own Milky Way Galaxy is part of the Local Group of Galaxies.  Small, compact groups, like Hickson Compact Group 87 (HCG 87) shown above, are interesting partly because they slowly self-destruct.  Indeed, the galaxies of HCG 87 are gravitationally stretching each other during their 100-million year orbits around a common center.  The pulling creates colliding gas that causes bright bursts of star formation and feeds matter into their active galaxy centers.  HCG 87 is composed of a large edge-on spiral galaxy visible on the lower left, an elliptical galaxy visible on the lower right, and a spiral galaxy visible near the top.  The small spiral near the center might be far in the distance.  Several stars from our Galaxy are also visible in the foreground.  The above picture was taken in July by the Hubble Space Telescope's Wide Field Planetary Camera 2.  Studying groups like HCG 87 allows insight into how all galaxies form and evolve.
Water Found in Space Rock (1999-09-07)
What would you do if it rained blue water from space?   On 1998 March 22, no umbrella was needed, as the blue water came attached to a stony meteorite that landed in Monahans, Texas.  The meteorite fall was seen by several boys, and was being carefully scrutinized by NASA scientists within 72 hours.  The scientists discovered an unusual patch of salt crystals on the meteorite's surface, turned blue by radiation in space.  Inside the blue crystals was an even bigger surprise - small droplets of water.  One of these water droplets is visible near the very center of the above photograph.  Water is a key factor in life, and this drop of water most likely dates from 4.5 billion years ago - from the early days of the Solar System.  How salt and water came to be attached to this asteroid chip still remains speculative.  What did the boys do with the meteorite? First they lent it to NASA.  Then they sold it on the Internet.
A Superior Conjunction Of Mercury (1999-09-08)
In astronomical parlance, an interior planet is at superior conjunction when it is located on the opposite side of the Sun from Earth. Mercury, the solar system's innermost planet, zips past this point in its orbit today. In fact, this recent picture from a solar coronagraph on board the the space-based SOHO observatory shows Mercury positioned very close to the Sun as seen from a near Earth vantage point. The coronagraph uses an internal occulting disk to block the intense solar glare which otherwise hides this sight from ground-based observers. The shadow of the occulting disk is at the center with the Sun's size and position indicated by the white circle. Mercury is the bright dot with a horizontal line (a digital artifact), while faint dots scattered throughout the field are stars. Bright regions of the sun's outer atmosphere are also visible. As Mercury continues in its orbit, on November 15 it will actually appear to cross the disk of the Sun as viewed from Earth.
Comet Hale-Bopp Over the Superstition Mountains (1999-09-09)
Four years ago, Comet Hale-Bopp was discovered out near Jupiter falling toward the inner Solar System.   Two years ago, it provided spectacular pictures as it neared its closest approach to the Sun.  Still today, spectacular pictures of the brightest comet of the 1990s are surfacing.  Above, Comet Hale-Bopp was photographed in 1997 behind the Superstition Mountains in Arizona.  Clearly visible are the comets white dust tail that shines by reflected sunlight, and the blue ion tail that shines by glowing gas.  Currently, there are several comets visible from the proper location with a small telescope.  A comet visible to the unaided eye appears about once every five years.
Cassini Images The Moon (1999-09-10)
On August 18, the Cassini spacecraft flew by the Earth and Moon, then continued on its way to the outer solar system. Near its closest approach to the Moon, a distance of about 377,000 kilometers, controllers tested Cassini's imaging systems on this most familiar celestial body. This composite picture shows three resulting lunar images from the green, blue, and ultraviolet regions of the spectrum (left to right). Prominant in the upper right of each image is the dark, round Mare Crisium (Sea of Crises) at the eastern edge of the Moon's near side. With its cameras clearly functioning well, Cassini's next way-point will be Jupiter in December 2000. It is expected to arrive at its final destination, the Saturnian system, in 2004.
The Annotated Galactic Center (1999-09-11)
The sky toward the center of our Galaxy is filled with a wide variety of celestial wonders. Many are easily visible with binoculars.   Constellations near the galactic center include Sagittarius, Libra, Scorpius, Scutum, and Ophiuchus.  Nebulae include Messier Objects M8, M16, M17, M20 and the Pipe Nebula.  Open star clusters include M6, M7, M18, M21, M23, M24, M25.   Globular star clusters include M9, M22, M28, M54, M69, M70.  And don't forget Baade's Window.  Click on the photo to get the un-annotated version.
Stonehenge: Ancient Monument to the Sun (1999-09-12)
Stonehenge consists of large carved stones assembled about 4000 years ago.  Long before modern England was established, ancient inhabitants somehow moved 25 ton rocks nearly 20 miles to complete it.  From similar constructs of the era, people could learn the time of year by watching how the Sun and Moon rose and set relative to accurately placed stones and pits.  The placement of the boulders at Stonehenge, however, is not impressively accurate by today's standards, nor even by the standards of that time.  Therefore, modern scholars interpret Stonehenge as a colossal monument to the Sun in celebration of the predictability of the seasons.
Supernova Remnant N132D in X-Rays (1999-09-13)
Thousands of years after a star explodes, an expanding remnant may still glow brightly.  Such is the case with N132D, a supernova remnant located in the neighboring Large Magellanic Cloud galaxy.  The expanding shell from this explosion now spans 80 light-years and has swept up about 600 Suns worth of mass.  The bright regions surrounding the lower right of this X-ray image result from a collision with an even more massive molecular cloud.  Towards the upper left, the supernova remnant expands more rapidly into less dense region of space.  This image is one of the first ever taken with the High Resolution Camera onboard the orbiting Chandra X-ray Observatory, and records details being analyzed for the first time.
The Colorful Orion Nebula (1999-09-14)
Tomorrow's picture: The Big Corona  < 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 Big Corona (1999-09-15)
Most photographs don't adequately portray the magnificence of the Sun's corona.  Seeing the corona first-hand during a total solar eclipse is best.  The human eye can adapt to see features and extent that photographic film usually cannot.  Welcome, however, to the digital age.  The above picture is a combination of twenty-two photographs that were digitally processed to highlight faint features.  The outer pictures of the Sun's corona were digitally altered to enhance dim, outlying waves and filaments.   The inner pictures of the usually dark Moon were enhanced to bring out its faint glow from doubly reflected sunlight.  Shadow seekers need not fret, though, since as yet there is no way that digital image processing can mimic the fun involved in experiencing a total solar eclipse.
The Incredible Expanding Cat's Eye (1999-09-16)
Watch closely. As this animation blinks between two Hubble Space Telescope images of NGC 6543 - the first from 1994 and the second from 1997 - the intricate filaments of this nebula are seen to shift. The shift is due to the actual expansion of this gaseous shroud shed by a dying star! NGC 6543 is more popularly known as the Cat's Eye Nebula. Classified as a "planetary nebula", its complex, interwoven shells of expanding gas have been castoff by the central star as it evolves from a red giant to its final white dwarf phase. The planetary nebula phase of a star's life is known to be relatively brief, lasting 10,000 years or so. In fact, combined with other data, this nebula's detectable shift over a three year period allows the expansion age of its bright inner shells to be estimated at only around 1,000 years while its distance can be gauged at about 3,000 light-years.
M3: Half A Million Stars (1999-09-17)
This immense ball of half a million stars older than the sun lies 30,000 light-years above the plane of our Galaxy. Cataloged as M3 (and NGC 5272), it is one of about 250 globular star clusters which roam our galactic halo.  Individual stars are difficult to distinguished in the densely packed core but colors are apparent for the bright stars on the cluster's outskirts. M3's many cool "red" giant stars take on a yellowish cast in this lovely composite image while hotter giants and pulsating variable stars look light blue.
Mercury Astronauts and a Redstone (1999-09-18)
Space suited project Mercury astronauts John H. Glenn, Virgil I. Grissom, and Alan B. Shepard Jr. (left to right) are posing in front of a Redstone rocket in this vintage 1961 NASA publicity photo. Project Mercury was the first U.S. program designed to put humans in space. It resulted in 6 flights using one-man capsules and Redstone and Atlas rockets. Shortly after the first U.S. manned flight on May 5, 1961, a suborbital flight piloted by Alan Shepard, President Kennedy announced the goal of a manned lunar landing by 1970. This goal was achieved by NASA's Apollo program and Shepard himself walked on the moon as commander of the Apollo 14 mission. Alan Shepard passed away in 1998. Virgil Grissom died in a tragic fire during an Apollo launch pad test in 1967. Senator John Glenn flew again on the 25th voyage of the Space Shuttle Discovery.
Interstellar Dust Bunnies of NGC 891 (1999-09-19)
Tomorrow's picture: Io in True Color  < 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.
Io in True Color (1999-09-20)
The strangest moon in the Solar System is bright yellow.  This recently released picture, showing Io's true colors, was taken in July by the Galileo spacecraft currently orbiting Jupiter.  Io's colors derive from sulfur and molten silicate rock.  The unusual surface of Io is kept very young by its system of active volcanoes.  The intense tidal gravity of Jupiter stretches Io and damps wobbles caused by Jupiter's other Galilean moons.  The resulting friction greatly heats Io's interior, causing molten rock to explode through the surface.  Io's volcanoes are so active that they are effectively turning the whole moon inside out. Some of Io's volcanic lava is so hot it glows in the dark.
The Quintuplet Star Cluster (1999-09-21)
Bright clusters of stars form and disperse near the center of our Galaxy.   Four million years ago the Quintuplet Cluster, pictured above, formed and is now slowly dispersing.  The Quintuplet Cluster is located within 100 light-years of the Galactic center, and is home to the brightest star yet cataloged in our Galaxy: the Pistol Star.  Objects near our Galactic center are usually hidden from view by opaque dust. This recently-released picture was able to capture the cluster in infrared light, though, with the NICMOS camera onboard the orbiting Hubble Space Telescope.  The young Quintuplet Cluster is one of the most massive open clusters yet discovered, but still much less massive than the ancient globular clusters that orbit in the distant halo.  Some of the bright white stars visible above may be on the verge of blowing themselves up in a spectacular supernova.
Halos Around the Ring Nebula (1999-09-22)
What's happened to the Ring Nebula?  The familiar Ring that can be seen with a small back-yard telescope takes on a new look when viewed in dim light.  The above recently-released, false-color image taken by the giant Subaru Telescope shows details of  giant halos of diffuse gas that are seen to envelop the entire structure.  The Ring Nebula, also known as M57, is an elongated planetary nebula, a type of nebula that is created when a Sun-like star evolves to throw off its outer atmosphere and becomes a white dwarf.  The Ring Nebula is about 2000 light-years away, and the main ring spans about one light-year.  The origin and future evolution of the Ring Nebula's outer halos is still being investigated.
Equinox and Eruptive Prominence (1999-09-23)
Today, the Sun crosses the celestial equator and seasons change from Summer to Fall in the north and Winter to Spring in the southern hemisphere.  Defined by the Sun's position in sky the event is known as an equinox - the length of daylight is equal to the length of night. Just last week the active Sun produced the dramatic eruptive prominence seen in this extreme ultraviolet picture from the space-based SOHO observatory.  The hot plasma is lofted above the solar surface by twisting magnetic fields. How big is the prominence? Click on the image to view the larger full-sun picture. At the same scale, planet Earth would likely still appear smaller than your cursor.
Cometary Globules In Orion (1999-09-24)
Intense ultraviolet light from massive, hot stars in the Orion region has sculpted and compressed clouds of dust and gas in to distinctively shaped Cometary Globules. Seen in this IRAS infrared image recorded at a wavelength sensitive to emission from dust, the elongated globules are easily visible along with a bright region which corresponds to the Trapezium star cluster. Otherwise known as the Witch Head Nebula, IC 2118 is the string of globules near the middle right. Suggestively similar to comets in general appearance only, Cometary Globules are interstellar condensations on a vastly different scale. These are likely related to star formation episodes in the Orion molecular cloud. Besides those indicated by the arrows, more comet-shaped clouds or globules are present in this image.