juliensimon/nasa-apod huggingface dataset:
Visitors' Galaxy Gallery (2001-04-27)

A tantalizing assortment of island universes is assembled here. From top left to bottom right are the lovely but distant galaxies M61, NGC 4449, NGC 4725, NGC 5068, NGC 5247, and NGC 5775/5774. Most are spiral galaxies more or less like our own Milky Way. The color images reveal distinct pink patches marking the glowing hydrogen gas clouds in star forming regions along the graceful spiral arms. While Virgo cluster galaxy M61 is perhaps the most striking of these spirals, the interesting galaxy pair NGC 5775/5774 neatly contrasts the characteristic spiral edge-on and face-on appearance. The one exception to this parade of photogenic spiral galaxies is the small and relatively close irregular galaxy NGC 4449 (top middle). Similar to the Large Magellanic Cloud, companion galaxy to the Milky Way, NGC 4449 also sports young blue star clusters and pink star forming regions. All the galaxies in this gallery were imaged with a small (16 inch diameter) reflecting telescope and digital camera by public participants in the Kitt Peak National Observatory Visitor Center's Advanced Observing Program.
The Moon and All the Crashes (2001-04-28)

Tomorrow's picture: Ice Fishing  < | 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.

Image credit: Tolga Topalhan &
Serkan Saygan
(Space Camp,
Turkey)
Ice Fishing for Cosmic Neutrinos (2001-04-29)

Scientists are melting holes in the bottom of the world. In fact, several holes have been melted near the South Pole, and they are now being used as astronomical observatories.  Astronomers with the Antarctic Muon and Neutrino Detector Array (AMANDA) lower into each vertical lake a string knotted with basketball-sized light detectors.  The water in each hole soon refreezes.  The detectors are sensitive to blue light emitted in the surrounding clear ice. Such light is expected from ice collisions with high-energy neutrinos emitted by objects or explosions out in the universe.  The above picture was taken 750 meters below the surface looking down into the abyss.  Instruments were lowered down past 2000 meters.  Data from AMANDA is currently being collected and analyzed.

Image credit: The AMANDA Collaboration
Approaching the International Space Station (2001-04-30)

rlier this month the crew of the US Space Shuttle Endeavor took in this view as they approached the developing International Space Station (ISS).  The Endeavor and ISS crew installed Italy's Raffaello, a Multi-Purpose Logistics Module and successfully deployed Canada's Canadarm2, a robot remote-controlled arm that can move about the outside of the station. The shuttle undocked from the ISS yesterday and is scheduled to return to Earth today.  A manned Russian Soyuz spacecraft is scheduled to dock with Earth's busiest orbiting outpost early today.
Antarctica Hears Little Normal Matter in the Big Bang (2001-05-01)

On the frozen ice near the bottom of our world, increasingly sophisticated instruments listen for a more precise echo of how our universe started.  Sunday, independent collaborations behind three such instruments announced evidence that overtones heard are consistent with our universe having only about five percent normal matter and 95 percent dark matter or dark energy.  This amount of normal matter was expected were our universe to have undergone a particularly explosive early phase of the big bang known as inflation.  The measurements were actually made on the angular scale of 1/10th degree by detecting slight fluctuations of microwave light that occur in cosmic background radiation.  These fluctuations are thought to be caused by sound waves moving through the early universe. Pictured above is the remote receiver for the Degree Angular Scale Interferometer (DASI) that recorded one of the data sets.  Similar results were reported Sunday by the BOOMERANG and MAXIMA collaborations.

Image credit: DASI, 
CARA, 
NSF
Planet Building in HD 100546 (2001-05-02)

More than 100 billion boulders may be swarming in the disk around nearby star HD 100546.  In a scene thought similar to the early years of our own Solar System, ever larger rocks are growing by colliding and accreting dust as the messy business of planet formation appears to be underway.  For an Earth-like planet in such a hostile environment, the sky would be lit continuously with streaking meteors and the ground would rumble continuously with impacts.  Pictured above, the swirling disk of dust, gas, and rocks of HD 100546 is visible as the dark region surrounding the image center.  The bright light and six-pointed diffraction spikes from the central star have been removed from the false-color image.  HD 100546 is visible with binoculars towards the southern constellation of Musca, and is a relatively nearby 335 light-years away.  Similar planet-building systems, dubbed proplyds, have recently been found in Orion, where many emerging planets there must survive the boiling radiations of neighboring bright stars.
Far Side of the Sun (2001-05-03)

You may think it's impossible to see through the Sun, but maps of the Sun's far side are now made routinely by instruments on board the sun-staring SOHO spacecraft. This is one such map from April 12. At right, is a map projection of calculated magnetic field strengths on the Earth-facing solar hemisphere with yellow and red indicating high magnetic fields characteristic of solar active regions. At left is a similar map of the solar hemisphere opposite planet Earth, which shows the large active region AR9393 as the 27-day solar rotation carried it across the far side. The largest sunspot group in a decade, AR9393 was easily seen as it tracked across the Sun's Earth-facing hemisphere in late March. When AR9393 swung around to the Sun's far side, SOHO's Michelson Doppler Interferometer (MDI) instrument continued to map its position by measuring changes in motions caused by solar sound waves - transmitted through the Sun and influenced by the active region's strong magnetic fields. Known as helioseismology, analyzing solar sound waves is like using seismological records of earthquakes to probe the interior of the Earth.  On the Sun, sound waves are produced by turbulent convection cells seen on the surface as dynamic solar granules.
Protoplanetary Survivors in Orion (2001-05-04)

The Orion Nebula is a nuturing stellar nursery filled with hot young stars and their natal clouds of gas and dust. But for planetary systems, the active star-forming region can present a hazardous and inhospitable birthplace. While the formation of dusty protoplanetary disks seems common in Orion, these Hubble Space Telescope close-up images dramatically reveal the torturous conditions they must face while trying to grow into full-fledged planetary systems. In each case, a central young star is surrounded by a disk substantially wider than our solar system. The disks likely contain material in the process of planet formation. However, withering ultraviolet radiation from one of Orion's nearby hot stars is rapidly destroying the disks -- ultimately creating the comet-shaped clouds of glowing gas seen engulfing the protoplanetary systems. Planet formation must occur quickly here, if at all. Researchers estimate that about 90 percent of Orion's youngest protoplanetary disks will not survive the next 100,000 years.
Shepard Flies Freedom 7 (2001-05-05)

Forty years ago today (May 5, 1961), at the dawn of the space age, NASA controllers "lit the candle" and sent Alan Shepard arcing into space atop a Redstone rocket. The picture shows the pressure-suited Shepard before launch in his cramped space capsule dubbed "Freedom 7". Broadcast live to a global television audience, the flight of Freedom 7 - the first space flight by an American - followed less than a month after the first human venture into space by Soviet Cosmonaut Yuri Gagarin. Freedom 7's historic flight was suborbital, lasting only about 15 minutes, but during it Shepard demonstrated manual control of his capsule. Naval aviator Shepard was chosen as one of the original seven Mercury Program astronauts. He considered this first flight the greatest challenge and actively sought the assignment. Shepard's career as an astronaut spanned a remarkable period in human achievement and in 1971 he walked on the moon as commander of the Apollo 14 mission. A true pioneer and intrepid explorer, Alan Shepard died in 1998 at age 74.
The Pleiades Star Cluster (2001-05-06)

It is the most famous star cluster on the sky. The Pleiades can be seen without binoculars from even the depths of a light-polluted city.  Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters.   The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across.  Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars.  Low mass, faint, brown dwarfs have recently been found in the Pleiades.

Image credit: AAO
One Hundred-Kilometer Terrain on Venus (2001-05-07)

ven the hot and cracked surface of Venus has rolling hills.  Although never actually photographed from up-close, images of the Venusian surface like that shown above have been constructed in recent years by digitally merging distant photographs from height-sensitive radar.  Isolated above is a 100-kilometer wide swath inside a volcanic region known as Yavine Corona.  Visible in the frame are numerous fractures in the surface.  Data is missing from the dark lane on the upper right.  The surface of Venus is so hot and oppressive that robot spacecraft landed there have lasted for only a few hours.
GRO J1655-40: Evidence for a Spinning Black Hole (2001-05-08)

In the center of a swirling whirlpool of hot gas is likely a beast that has never been seen directly: a black hole.   Studies of the bright light emitted by the swirling gas frequently indicate not only that a black hole is present, but also likely attributes.  The gas surrounding GRO J1655-40, for example, has recently been found to display an unusual flickering at a rate of 450 times a second.  Given a previous mass estimate for the central object of seven times the mass of our Sun, the rate of the fast flickering can be explained by a black hole that is rotating very rapidly.  What physical mechanisms actually cause the flickering -- and a slower quasi-periodic oscillation (QPO) -- in accretion disks surrounding black holes and neutron stars remains a topic of much research.
Space Station Shows Off New Robot Arm (2001-05-09)

The International Space Station (ISS) continues to grow.  Last month, the crew of the Space Shuttle Endeavor delivered new Logistics Modules and installed the new Canadarm2 on the growing outpost. The ISS -- complete with its new arm -- was photographed 400 kilometers above planet Earth by the Space Shuttle Endeavor crew soon after they undocked.  The shuttle then flew around the station for a survey.  Three members of the Expedition Two Crew remain aboard the ISS running scientific experiments and unpacking over two tons of material delivered by the shuttle.  The next shuttle scheduled to visit the ISS will be Atlantis in June.
Spirals On Edge (2001-05-10)

Spiral galaxies viewed face-on display a grand design, with graceful spiral arms traced by bright star clusters and glowing stellar nurseries. When seen edge-on, their appearance is very different but no less striking as their central regions bulge and dark cosmic dust lanes appear silhouetted against starlight from flattened galactic disks. This masterful mosaic of digital images shows nine prominent edge-on spirals arranged as follows: top; NGC2683, M104, NGC4565, middle; NGC891, NGC4631, NGC3628, and bottom; NGC5746, NGC5907, and NGC4217. Perhaps the best known of these is M104 (NGC4594) whose more descriptive moniker is the Sombrero Galaxy. Notably, the edge-on perspective of these galaxies allows a measurement of their galactic rotation speed using the Doppler effect. Plotting rotation speed versus distance from the center determines a galaxy's gravitational mass and historically led to premier evidence for mysterious Dark Matter.

Image credit: Robert Gendler
X-Ray Rainbows (2001-05-11)

A drop of water or prism of glass can spread out visible sunlight into a rainbow of colors. In order of increasing energy, the well known spectrum of colors in a rainbow runs red, orange, yellow, green, blue, indigo, violet. X-ray light too can be spread out into a spectrum ordered by energy ... but not by drops of water or glass. Instead, the orbiting Chandra X-ray Observatory uses a set of 540 finely ruled, gold gratings to spread out the x-rays, recording the results with digital detectors. The resulting x-ray spectrum reveals much about the compositions, temperatures, and motions within cosmic x-ray sources. This false color Chandra image shows the x-ray spectrum of a star system in Ursa Major cataloged as XTE J1118+480 and thought to consist of a sun-like star orbiting a black hole. Unlike the familiar appearance of a prism's visible light rainbow, the energies here are ordered along radial lines with the highest energy x-rays near the center and lowest energies near the upper left and lower right edges of the image. The central spiky region itself is created by x-rays from the source which are not spread out by the array of gratings.
Shuttle Moon (2001-05-12)

As a gorgeous full Moon rose above the eastern horizon on February 7, the Space Shuttle Atlantis streaked skyward towards an orbital rendezvous with the International Space Station. Watching from Orlando, Florida, about 60 miles west of the Kennedy Space Center launch site, photographer Tony DeVito captured this digital image, one of a series of pictures of the shuttle's fiery climb. While foreground street lights flickered on and a clear evening sky grew dark, the shuttle's path just grazed the bright lunar disk.  On this mission, STS-98, Atlantis carried the U.S. Destiny laboratory module to be added to the expanding orbital outpost. Atlantis is currently scheduled to return to the space station next month.

Image credit: Anthony DeVito
Crater Copernicus (2001-05-13)

One of the more prominent craters on the Moon is named Copernicus.  Copernicus is a large young crater visible with binoculars slightly northwest of the center of the Moon's Earth-facing hemisphere.  Copernicus is distinguished by its size and by the many bright rays pointing out from it.  Although Copernicus is relatively young for a lunar crater, it was formed nearly a billion years ago by a colossal impact. The center of Copernicus is about 93 kilometers across.  The above picture was taken in 1972 by the last human mission to the moon: Apollo 17.  The prospects for a return have been boosted recently with increased evidence of ice deposits near the lunar poles.
A Cerro Tololo Sky (2001-05-14)

High atop a Chilean mountain lies one of the premier observatories of the southern sky: Cerro Tololo.  Pictured above is one of the premier telescopes of the Cerro Tololo Inter-American Observatory (CTIO) and of the past quarter-century: the 4-meter Blanco Telescope.  Far behind the telescope are thousands of individual stars and diffuse light from three galaxies: the Small Magellanic Cloud (upper left), the Large Magellanic Cloud (lower left), and our Milky Way Galaxy (right).  Visible just to Blanco's right is the famous superposition of four bright stars known as the Southern Cross. The observatory structures are lit solely by starlight.

Image credit: Roger Smith
A Radar Image of Venus (2001-05-15)

The largest radio telescopes in the world are working together to create a new map of the surface of Venus.  The surface of Venus is unusually hidden by a thick atmosphere of mostly carbon dioxide gas.  These thick clouds are transparent, however, to radar signals sent and received from Earth.  The two radio telescopes generating the most powerful radar ever are the Arecibo Telescope in Puerto Rico and the new Robert C. Byrd Green Bank Telescope in West Virginia.  The new survey will resolve details as fine a one-kilometer across, and will be inspected for changes since the last major radar map was made by NASA's Magellan spacecraft that orbited Venus from 1990 to 1994.  Pictured above is part of a preliminary image showing details as small as five-kilometers across.
The Center of the Circinus Galaxy in X-Rays (2001-05-16)

Are black holes the cause of X-rays that pour out from the center of the Circinus galaxy?   A new high-resolution image from the orbiting Chandra X-ray Observatory has resolved the inner regions of this nearby galaxy into several smaller sources.  The image is shown above in representative-color.  Extended X-ray emission from the center appears to match optical light and appears consistent with a model where hot gas is escaping from a supermassive black hole at Circinus' center.  At least one of the other sources varies its X-ray brightness as expected from a binary star system, indicating that the system is small yet massive, and giving credence to a model where a black hole is surrounded by doughnut-shaped ring.  The region shown spans about 5000 light-years across.
Solar Neutrino Astronomy (2001-05-17)

Neutrinos are subatomic particles generated by the nuclear reactions which power stars like our Sun. Flying outward from the Sun's core, they easily pass through the Sun (and almost anything else!) unimpeded and should be detectable by earth-based neutrino "telescopes". Still, to the long-standing consternation of astrophysicists, the observed flux of solar neutrinos is less than expected. In a new twist to this solar neutrino saga, an analysis of data from the GALLEX / GNO neutrino detector finds a solar neutrino flux that varies over about 27 days ... approximately matching the Sun's rotation period. In fact, since different parts of the Sun rotate at different rates, the neutrino flux variations match most exactly the rotation rates of the areas shown in red on this colorful cross-sectional map of the solar interior rotation. So how could solar rotation affect the neutrino flux? Some theoretical models say that neutrinos can change quantum properties when they interact with tangled solar magnetic fields and become particles that the neutrino experiments were not designed to detect. Then, as the Sun rotates, the neutrinos sometimes come to us unaffected and sometimes come through magnetic fields, diminishing the flux that can be measured.
HD 82943: Planet Swallower (2001-05-18)

Stars like HD 82943 are main sequence G dwarf stars with temperatures and compositions similar to the Sun. Also like the Sun, HD 82943 is known to have at least two giant planets, but unlike gas giants in our solar system their orbits are not nearly circular and bring them closer to the parent star. Astronomers now point to strong observational evidence that HD 82943 used to have more planets ... but swallowed them in the past. Such a cosmic cataclysm is illustrated above in an artist's dramatic vision. As a result, planetary debris would contaminate the outer layers of HD 82943. Researchers using a high resolution spectrograph at the European Southern Observatory's Kueyen telescope believe they have seen a clear signature of this contamination by identifying the isotope Lithium-6 in this sun-like star's spectrum. Because the light element Lithium-6 is so readily destroyed in nuclear reactions during star formation, no significant Lithium-6 should now exist in HD 82943. Startlingly, perhaps the most likely explanation for the presence of Lithium-6 today is that it is left over from planetary material which formed separately and was then absorbed by the parent star.
Damage to Apollo 13 (2001-05-19)

In April of 1970, after an oxygen tank exploded and crippled their service module, the Apollo 13 astronauts were forced to abandon plans to make the third human lunar landing. The extent of the damage is revealed in this grainy, grim photo, taken as the service module was drifting away -- jettisoned only hours prior to the command module's reentry and eventual safe splashdown. An entire panel on the side of the service module has been blown away and extensive internal damage is apparent. Visible below the gutted compartment is a radio antenna and the large, bell-shaped nozzle of the service module's rocket engine.
Sagittarius Star Cloud (2001-05-20)

Stars come in all different colors. The color of a star indicates its surface temperature, an important property used to assign each star a spectral type. Most stars in the above Sagittarius Star Cloud are orange or red and relatively faint, as our Sun would appear. The blue and greenish stars are hotter, many being relatively young and massive.  The bright red stars are cool Red Giants, bloated stars once similar to our Sun that have entered a more advanced stage of evolution.  Stars of this Sagittarius Cloud lie towards the center of our Galaxy - tantalizing cosmic jewels viewed through a rift in the dark, pervasive, interstellar dust. This famous stellar grouping houses some of the oldest stars known.
Another Comet LINEAR Breaks Up (2001-05-21)

Last year, a different comet LINEAR (C/1999 S4) broke up.  This year, a comet first imaged by the Lincoln Near Asteroid Research (LINEAR) telescope in New Mexico on 2001 January 3, is also breaking up.   This new Comet LINEAR (C/2001 A2) unexpectedly brightened to the edge of naked-eye visiblilty a few weeks ago when its nucleus broke in two.  Observations taken just last week now indicate that one of the two remaining nuclear fragments has again fragmented.  The first piece to break off is visible on the upper left of the above false-color image by a Very Large Telescope, while additional fragmentation is inferred from the brightness and elongation of the spot on the lower right.  When a comet nucleus splits, new surfaces are exposed and previously trapped ice and gas are released that evaporate and brighten in the energetic sunlight.  Comet LINEAR may remain visible with little or no optical aid into early June.  In contrast, at least two other much dimmer Comet LINEARs discovered recently appear stable.
Spiral Galaxy NGC 1232 (2001-05-22)

Galaxies are fascinating not only for what is visible, but for what is invisible.  Grand spiral galaxy NGC 1232, captured in detail by one of the new Very Large Telescopes, is a good example.  The visible is dominated by millions of bright stars and dark dust, caught up in a gravitational swirl of spiral arms rotating about the center.  Open clusters containing bright blue stars can be seen sprinkled along these spiral arms, while dark lanes of dense interstellar dust can be seen sprinkled between them.  Less visible, but detectable, are billions of dim normal stars and vast tracts of interstellar gas, together wielding such high mass that they dominate the dynamics of the inner galaxy.  Invisible are even greater amounts of matter in a form we don't yet know - pervasive dark matter needed to explain the motions of the visible in the outer galaxy.  What's out there?
Strange Orange Soil on the Moon (2001-05-23)

How did orange soil appear on the Moon?  This mystery began when astronaut Harrison Schmidt noticed the off-color patch near Apollo 17's Taurus-Littrow landing site in 1972.  Schmidt and fellow astronaut Eugene Cernan scooped up some of the unusual orange soil for detailed inspection back on Earth.  Pictured above is a return sample shown greatly magnified, with its discovery location shown in the inset.  The orange soil contains particles less than 0.1 millimeter across, some of the smallest particles yet found on the Moon.  Lunar geologists now think that the orange soil was created during an ancient fire-fountain.  Detailed chemical and dating analyses indicate that during an explosive volcanic eruption 3.64 billion years ago, small drops of molten rock cooled rapidly into the nearly spherical colored grains.  The origin of some of the unusual elements found in the soil, however, remains unknown.