omnianasa/nasa-apod-metadata huggingface dataset:
A Galaxy is not a Comet (2002-04-12)
This gorgeous galaxy and comet portrait was recorded on April 5th in the skies over the Oriental Pyrenees near Figueres, Spain. From a site above 1,100 meters, astrophotographer Juan Carlos Casado used a guided time exposure, fast film, and a telephoto lens to capture the predicted conjunction of the bright Comet Ikeya-Zhang (right) and the Andromeda Galaxy (left). This stunning celestial scene would also have been a rewarding one for the influential 18th century comet hunter Charles Messier. While Messier scanned French skies for comets, he carefully cataloged positions of things which were fuzzy and comet-like in appearance but did not move against the background stars and so were definitely not comets. The Andromeda Galaxy, also known as M31, is the 31st object in his famous not-a-comet catalog. Not-a-comet object number 110, a late addition to Messier's catalog, is one of Andromeda's small satellite galaxies, and can be seen here just below M31. Our modern understanding holds that the Andromeda galaxy is a large spiral galaxy some 2 million light-years distant. The photogenic Comet Ikeya-Zhang, now a lovely sight in early morning skies, is about 80 million kilometers (4 light-minutes) from planet Earth.
Pwyll: Icy Crater of Europa (2002-04-13)
The impact crater Pwyll (a name from Celtic Mythology) is thought to represent one of the youngest features on the surface of Jupiter's moon Europa. A combination of color and high resolution black and white data from NASA's Galileo spacecraft was used to produce this view looking down on the crater with the sun illuminating the scene from the right. Pwyll's visible dark central region is about 26 kilometers in diameter, while brilliant white rays of debris blasted from the impact site extend outward for hundreds of kilometers. The white debris or ejecta clearly overlays everything else on the surface - indicating that this impact crater is younger than all surrounding features. The bright white color suggests a composition of water ice particles. Galileo's instruments have uncovered substantial evidence that water in liquid form exists below Europa's icy surface. If Europa has a subsurface ocean, could it harbor life?
RX J185635-375: Candidate Quark Star (2002-04-14)
Is RJX J185635-375 really so small?  Previously, this compact star held claim to being the closest neutron star -- only 150 light-years away.  Now new observations and analysis indicate not only a larger distance, roughly 450 light-years, but a very small radius for RXJ J185635-375, pictured above. One hypothesized solution holds hope a RJX J185635-375 is actually a not a neutron star but a quark star -- something new.  Now quark stars are truly strange -- some may have made a transition to type of matter known as strange quarks.  Quark stars, were they to exist, can be intermediate between neutron stars and black holes in size and density.  Quark stars can also be more compact and cool faster than neutron stars. In fact, some might even be ultracompact -- so dense that light itself can orbit.  Future observations will likely settle the controversial claims of RJX J185635-375's distance and radiative geometry, and hence determine if a previously undiscovered type of beast roams the sky.
A New Truss for the International Space Station (2002-04-15)
The International Space Station (ISS) is being fitted with a backbone.  During the present visit of Space Shuttle Atlantis, astronauts are installing a huge truss on the growing space outpost.  The truss is over 13 meters long and about 4.5 meters wide.  Dubbed Starboard 0, or S0 (pronounced S-Zero) for short, the truss will route electricity, vent excess heat, and allow for future ISS expansion.  Pictured above, the truss was lifted out of the shuttle's cargo bay by the station's robotic Canadarm2.
Millions of Stars in Omega Centauri (2002-04-16)
Pictured above is the largest ball of stars in our Galaxy.  About 10 million stars orbit the center of this globular cluster - named Omega Centauri - as this giant globular cluster orbits our Galactic center.  Recent evidence indicates that Omega Centauri is by far the most massive of the about 150 known globular clusters in the Milky Way.  Omega Centauri, cataloged as NGC 5139, spans about 150 light years across, lies about 15,000 light years away, and can be seen without visual aid toward the constellation of Centaurus. The stars in globular clusters are generally older, redder and less massive than our Sun.  Studying globular clusters tells us not only about the history of our Galaxy but also limits the age of the universe.
The Glory (2002-04-17)
Looking out the window of an airplane, you might be lucky enough to see "the glory" in the direction directly opposite the Sun.  Before airplanes, the phenomenon, known to some as the heiligenschein or the Specter of the Brocken, was sometimes seen from mountaintops.  There, when conditions were right, one could look away from the Sun and see what appeared to be the shadow of a giant surrounded by a bright halo.  The giant turns out to be the observer, as in the modern version a silhouette of an plane frequently occupies the glory's center.  Pictured above, several concentric rings of the glory were photographed.  The cause of the glory has only been understood recently and is relatively complex.  Briefly, small droplets of water reflect, refract, and diffract sunlight backwards towards the Sun.  The phenomenon has similar counterparts in other branches of science including astronomy, where the looking out from the Earth in the direction opposite the Sun yields a bright spot called the gegenschein.
Planets in the West (2002-04-18)
Have you seen any bright planets lately? Chances are if you've been outside under clear skies just after sunset, then you have. Now shining in the west as bright "stars" in the night sky, are all five planets of the solar system known to ancient astronomers - Mercury, Venus, Mars, Saturn, and Jupiter. Recorded from Holt, Michigan, USA about 40 minutes after sunset on April 14th, this digital image captures three of them, Venus, Mars, and Saturn, along with a young crescent Moon. Also indicated are the Pleiades star cluster and bright red giant star Aldebaran in Taurus.  Mercury, setting, is lost in the trees and glow along the horizon, while Jupiter is off the top of this view. The coming weeks will see photo opportunities galore as all five planets gradually move closer together, posing after sunset with the Moon and stars in the western sky. Venus, Mars, and Saturn will form the closest trio, drawing within a 5 degree circle (about the apparent size of your fist with arm extended) above Aldebaran by May 3rd.
The Old Moon in the New Moon's Arms (2002-04-19)
Also known as the Moon's "ashen glow" or "the old Moon in the new Moon's arms", Earthshine is Earthlight reflected from the Moon's night side. This dramatic image of Earthshine and a young crescent Moon was taken by astrophotographer and APOD translator Laurent Laveder from the remote Pic du Midi Observatory on planet Earth. But the view from the Moon would have been stunning too. When the Moon appears in Earth's sky as a slender crescent, a dazzlingly bright, nearly full Earth would be seen from the lunar surface. The Earth's brightness, due to reflected sunlight, is strongly influenced by cloud cover and recent studies of Earthshine indicate that it is more pronounced during April and May. A description of Earthshine, in terms of sunlight reflected by Earth's oceans in turn illuminating the Moon's dark surface, was written 500 years ago by Leonardo da Vinci.
Orion Nebula: The 2MASS View (2002-04-20)
Few astronomical sights excite the imagination like the nearby stellar nursery known as the Orion Nebula. The Nebula's glowing gas surrounds hot young stars at the edge of an immense interstellar molecular cloud only 1,500 light-years away. This distinctively detailed image of the Orion Nebula was constructed using data from the 2 Micron All Sky Survey or 2MASS. Using telescopes in the Northern and Southern Hemispheres of planet Earth, the 2MASS project has mapped the entire sky in infrared light. The wavelength of infrared light is longer than visible light but more easily penetrates obscuring dust clouds. 2MASS cameras were sensitve to near infrared wavelengths around 2 microns or about 0.00008 inches. Visible light has a wavelength of about 0.00002 inches. Survey observations in three infrared bands were translated to blue, green, and red colors to produce this composite image.
The Center of Centaurus A (2002-04-21)
A fantastic jumble of young blue star clusters, gigantic glowing gas clouds, and imposing dark dust lanes surrounds the central region of the active galaxy Centaurus A. This mosaic of Hubble Space Telescope images taken in blue, green, and red light has been processed to present a natural color picture of this cosmic maelstrom. Infrared images from the Hubble have also shown that hidden at the center of this activity are what seem to be disks of matter spiraling into a black hole with a billion times the mass of the Sun! Centaurus A itself is apparently the result of a collision of two galaxies and the left over debris is steadily being consumed by the black hole. Astronomers believe that such black hole central engines generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies. But for an active galaxy Centaurus A is close, a mere 10 million light-years away, and is a relatively convenient laboratory for exploring these powerful sources of energy.
Comet and Aurora Over Alaska (2002-04-22)
Can you spot the comet?  Flowing across the frozen Alaskan landscape is an easily visible, colorful aurora.  Just to the lower left, however, well in the background, is something harder to spot: Comet Ikeya-Zhang, the brightest comet of recent years.  Although the aurora faded in minutes, the comet is just now beginning to fade.  It remains just barely visible without aid, however, before sunrise in the East.  The comet is actually a giant dirt-covered snowball that spends most of its time in the outer Solar System -- to where it is now returns.  The above photograph was taken on March 20 when Comet Ikeya-Zhang was near its brightest.  Careful inspection of the photo will uncover several other sky delights, including the giant galaxy M31.
The Newly Expanded International Space Station (2002-04-23)
What does the developing International Space Station (ISS) look like now?  After delivering and deploying a crucial first backbone-like component last week, the Space Shuttle Atlantis took an inspection lap around the space station.  The newly installed truss is visible toward the center of the above image.  Also visible are many different types of modules, a robotic arm, several wing-like solar panels, and a supply ship.  Construction began on the ISS in 1998 and the core structure should be in place before 2005.
The Trifid Nebula from AAO (2002-04-24)
Unspeakable beauty and unimaginable bedlam can be found together in the Trifid Nebula. Also known as M20, this photogenic nebula is visible with good binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos.  The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas.  The dark dust filaments that lace M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions.  Which bright young stars light up the blue reflection nebula is still being investigated.  The light from M20 we see today left perhaps 3000 years ago, although the exact distance remains unknown.  Light takes about 50 years to cross M20.
Southern Cross in Mauna Loa Skies (2002-04-25)
Gazing across this gorgeous skyscape, the Southern Cross and stars of the constellation Centaurus are seen above the outline of Mauna Loa (Long Mountain), planet Earth's largest volcano. Unfamiliar to sky gazers north of about 25 degrees north latitude, the Southern Cross, constellation Crux, is near the horizon to the left of Mauna Loa's summit. A compact constellation of bright stars, the long axis of the cross conveniently points south toward the southern celestial pole. The top of the cross is marked by the lovely pale red star Gamma Crucis, which is in fact a red giant star about 120 light-years distant. Stars of the grand constellation Centaurus almost engulf the Southern Cross with blue giant Beta Centauri, and yellowish Alpha Centauri, appearing as the brightest stars to the left of Gamma Crucis. At a distance of 4.3 light-years, Alpha Centauri, the closest star to the Sun, is actually a triple star system which includes a star similar to the Sun. But what caused the reddish streaks in the foreground of this time exposure? Alas, it is the mundane glow of lights from cars (not molten lava!) traveling the road to Hilo, Hawaii.
Comet Ikeya-Zhang Meets The ISS (2002-04-26)
Still catching the Sun's rays, the International Space Station (ISS) cruises across the early evening sky above Tomahawk, Wisconsin, USA. Recorded on April 9 around 9 pm CDT in a 30 second exposure, the sunlit space station traced this bright streak moving east (right) through the constellation Cassiopeia. Below lies Comet Ikeya-Zhang sporting a visible tail. But while this photogenic comet is now fading from view, the ISS will be getting brighter. Hours after this picture was taken, the Space Shuttle Atlantis docked with the ISS, bringing another structure to add to the growing orbital outpost.
Hawaii (2002-04-27)
Aloha! With the graceful arc of Earth's limb in the background, the Hawaiian Island archipelago is visible in this stunning photo taken by the astronauts onboard the shuttle Discovery in October of 1988. Along with popular beaches and tropical resorts, these volcanic islands offer extreme elevations with dark, dry, cloudless skies. Consequently they have also become popular sites for large and sophisticated ground based telescopes. The peak of Mauna Kea, on the Big Island (upper left), boasts an impressive array of astronomical instruments including twin Kecks, the Canada-France-Hawaii Telescope, the NASA IRTF, the JCMT and UKIRT, the Subaru and the Gemini Telescope Project. The dormant volcanic cone of Haleakala on Maui (just below the Big Island) is home to the Air Force Maui Optical Station and the Mees Solar Observatory. Mahalo nui loa!
Doomed Star Eta Carinae (2002-04-28)
Carinae may be about to explode.  But no one knows when - it may be next year, it may be one million years from now.  Eta Carinae's mass - about 100 times greater than our Sun - makes it an excellent candidate for a full blown supernova. Historical records do show that about 150 years ago Eta Carinae underwent an unusual outburst that made it one of the brightest stars in the southern sky.  Eta Carinae, in the Keyhole Nebula, is the only star currently thought to emit natural LASER light.  This image, taken in 1996, resulted from sophisticated image-processing procedures designed to bring out new details in the unusual nebula that surrounds this rogue star.  Now clearly visible are two distinct lobes, a hot central region, and strange radial streaks.  The lobes are filled with lanes of gas and dust which absorb the blue and ultraviolet light emitted near the center.  The streaks remain unexplained. Will these clues tell us how the nebula was formed?  Will they better indicate when Eta Carinae will explode?
Dusk of the Planets (2002-04-29)
Tomorrow's picture: More than 1000 Words (Usually)  < | 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 Holographic Principle (2002-04-30)
Is this image worth a thousand words?  According to the Holographic Principle, the most information you can get from this image is about 3 x 1065 bits for a normal sized computer monitor.  The Holographic Principle, yet unproven, states that there is a maximum amount of information content held by regions adjacent to any surface.  Therefore, counter-intuitively, the information content inside a room depends not on the volume of the room but on the area of the bounding walls.  The principle derives from the idea that the Planck length, the length scale where quantum mechanics begins to dominate classical gravity, is one side of an area that can hold only about one bit of information.  The limit was first postulated by physicist Gerard 't Hooft in 1993.  It can arise from generalizations from seemingly distant speculation that the information held by a black hole is determined not by its enclosed volume but by the surface area of its event horizon.  The term "holographic" arises from a hologram analogy where three-dimension images are created by projecting light though a flat screen.  Beware, other people looking at the above image may not claim to see 3 x 1065 bits -- they might claim to see a teapot.
In the Center of the Omega Nebula (2002-05-01)
In the depths of the dark clouds of dust and molecular gas known as the Omega Nebula, stars continue to form.  The above image from the Hubble Space Telescope's newly installed Advanced Camera for Surveys shows unprecedented detail in the famous star-forming region.  The dark dust filaments that lace the center of Omega Nebula were created in the atmospheres of cool giant stars and in the debris from supernova explosions.  The red and blue hues arise from glowing gas heated by the radiation of massive nearby stars.  The points of light are the young stars themselves, some brighter than 100 Suns.  Dark globules mark even younger systems, clouds of gas and dust just now condensing to form stars and planets.  The Omega Nebula lies about 5000 light years away toward the constellation of Sagittarius.  The region shown spans about 3000 times the diameter of our Solar System.
Arp 188 and the Tadpole's Tidal Tail (2002-05-02)
In this stunning vista recorded with the Hubble Space Telescope's new advanced camera, distant galaxies form a dramatic backdrop for disrupted spiral galaxy Arp 188, the Tadpole Galaxy. The cosmic Tadpole is a mere 420 million light-years distant toward the northern constellation Draco. Its eye-catching tail is about 280 thousand light-years long and features massive, bright blue star clusters. One story goes that a more compact intruder galaxy crossed in front of Arp 188 - from left to right in this view - and was slung around behind the Tadpole by their gravitational attraction. During the close encounter, tidal forces drew out the spiral galaxy's stars, gas, and dust forming the spectacular tail. The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the Tadpole, can be seen through foreground spiral arms at the upper left. Following its terrestrial namesake, the Tadpole Galaxy will likely lose its tail as it grows older, the tail's star clusters forming smaller satellites of the large spiral galaxy.
Cone Nebula Close-Up (2002-05-03)
Cones, pillars, and majestic flowing shapes abound in stellar nurseries where natal clouds of gas and dust are buffeted by energetic winds from newborn stars. A well-known example, the Cone Nebula within the bright galactic star-forming region NGC 2264, was captured in this close-up view from the Hubble Space Telescope's newest camera. While the Cone Nebula, about 2,500 light-years away in Monoceros, is around 7 light-years long, the region pictured here surrounding the cone's blunted head is a mere 2.5 light-years across. In our neck of the galaxy that distance is just over half way from the Sun to its nearest stellar neighbor, Alpha Centauri. The massive star NGC 2264 IRS, seen by Hubble's infrared camera in 1997, is the likely source of the wind sculpting the Cone Nebula and lies off the top of the image. The Cone Nebula's reddish veil is produced by glowing hydrogen gas.
The Moons of Earth (2002-05-04)
While orbiting the planet during their June 1998 mission, the crew of the Space Shuttle Discovery photographed this view of two moons of Earth. Thick storm clouds are visible in the lovely blue planet's nurturing atmosphere and, what was then Earth's largest artificial moon, the spindly Russian Mir Space Station can be seen above the planet's limb. The bright spot to the right of Mir is Earth's very large natural satellite, The Moon. The Mir orbited planet Earth once every 90 minutes about 200 miles above the planet's surface or about 4,000 miles from Earth's center. The Moon orbits once every 28 days at a distance of about 250,000 miles from the center of the Earth.
The M7 Open Star Cluster in Scorpius (2002-05-05)
M7 is one of the most prominent open clusters of stars on the sky.  The cluster, dominated by bright blue stars, can be seen with the naked eye in a dark sky in the tail of the constellation of Scorpius.  M7 contains about 100 stars in total, is about 200 million years old, spans 25 light-years across, and lies about 1000 light-years away.   This color picture was taken in 1995 at the Burrell-Schmidt Telescope at Kitt Peak National Observatory in Arizona.  The M7 star cluster has been known since ancient times, being noted by Ptolemy in the year 130 AD.  Also visible is a dark dust cloud near the bottom of the frame, and literally millions of unrelated stars towards the Galactic center.
NGC 4676: When Mice Collide (2002-05-06)
These two galaxies are pulling each other apart.  Known as "The Mice" because they have such long tails, each spiral galaxy has likely already passed through the other and will probably collide again and again until they coalesce.  The long tails are created by the relative difference between gravitational pulls on the near and far parts of each galaxy.  Scrolling right will show the very long tail of one of the galaxies.  Because the distances are so large, the whole thing takes place in slow motion -- over hundreds of millions of years.  NGC 4676 lies about 300 million light-years away toward the constellation of Coma Berenices and are likely members of the Coma Cluster of Galaxies.  The above picture was taken with the Hubble Space Telescope's new Advanced Camera for Surveys which is more sensitive and images a larger field than previous Hubble cameras.  The camera's increased sensitivity has imaged, serendipitously, galaxies far in the distance scattered about the frame.
Smog Over New York (2002-05-07)
What is not pretty about the above picture?  In a word: smog.  In 2000 October the orbiting Space Shuttle Discovery photographed upstate New York just at sunset.  Visible is golden sunlight reflecting from two of the Great Lakes (Erie and Ontario), and several of the Finger Lakes.  Between the clouds at the top and ground at the bottom, however, is a trapped layer of smog.  Smog is mostly ozone but may contain small amounts of volatile organic compounds.  As opposed to "good smog" in the upper atmosphere, "bad smog" near the ground is created mostly by humans.  In the upper atmosphere, ozone reflects back harmful ultraviolet radiation, but when it occurs near the ground, it can be inhaled.  Smog continues to be studied with an eye for how it develops and how it affects human health.
Sunspot Loops in Ultraviolet (2002-05-08)
It was a quiet day on the Sun.  The above image shows, however, that even during off days the Sun's surface is a busy place.  Shown in ultraviolet light, the relatively cool dark regions have temperatures of thousands of degrees Celsius.  Large sunspot group AR 9169 is visible as the bright area near the horizon.  The bright glowing gas flowing around the sunspots has a temperature of over one million degrees Celsius.  The reason for the high temperatures is unknown but thought to be related to the rapidly changing magnetic field loops that channel solar plasma.  Sunspot group AR 9169 moved across the Sun during 2000 September and decayed in a few weeks.