juliensimon/nasa-apod huggingface dataset:
Americans Defeat Russians in First Space Quidditch Match (2001-04-01)

A historic first Space Quidditch match came to a spectacular conclusion last night as astronaut Michael Lopez-Alegria caught the Golden Snitch to give the Americans a hard fought victory over the Russians.  "The Russians used brilliant strategy, but only NASA had the T2KQMU (Thunderbolt 2000 Quidditch Maneuvering Unit)," commented Lopez-Alegria, pictured above squeezing the elusive Golden Snitch in his left hand. Happy April Fools Day from the folks at APOD.  In reality, Astronauts Jeff Wisoff and Lopez-Alegria are shown space-walking last October during a space shuttle mission to help build the International Space Station.
Aurora Over Clouds (2001-04-02)

Aurorae usually occur high above the clouds.  The auroral glow is created when fast-moving particles ejected from the Sun impact air molecules high in the Earth's atmosphere.  An oxygen molecule, for example, will glow in a green light when reacquiring an electron lost during a collision with a solar particle.  The lowest part of an aurora will typically occur at 100 kilometers up, while most clouds usually exist only below about 10 kilometers.  The relative heights of clouds and aurorae are shown clearly in the above picture from Iceland, where aurorae are relatively common.  Over the past weekend, one of the largest sunspot groups ever recorded has been associated with explosive solar activity and expansive terrestrial aurora displays.  Although in Earth's northern hemisphere aurorae are usually seen only in the far north, these aurorae were so prevalent they were imaged by a continuous nighttime camera operating in southern Arizona!

Image credit: Sigurdur H. Stefnisson
New Stars Destroying NGC 1748 (2001-04-03)

NGC 1748 cannot contain all the new stars it has formed.  The young stars, the most massive of which are bright blue, emit so much energy they are pushing out and dispersing the gas and dust that comprise this star forming nebula.  Within only the past hundred thousand years, these stars have altered the bubble-like shape of the nebula and will likely destroy the nebula over the next few million years.  Of particular interest is a bright region surrounded by a pink ring of dust and gas visible on the left of the above recently released picture by the Hubble Space Telescope.  The center of this region is being evacuated by the wind of the brightest star in the nebula.  A lane of cooler dust connects NGC 1748 to a larger more diffuse nebula seen on the right.  NGC 1748 spans about 25 light-years in diameter and can be found in our galactic neighbor: the Large Magellanic Cloud.
Distant Supernova, Dark Energy (2001-04-04)

A pinpoint of light from a star that exploded over 10 billion light-years away is centered in the panel at the lower right, a cosmic snapshot of the most distant supernova.  The ancient stellar detonation was detected by digitally subtracting before and after images of a faint, yellowish, elliptical galaxy included in the Hubble Space Telescope Deep Field image illustrated at the top and left. Remarkable in itself as the farthest known supernova, its measured brightness provides astounding evidence for a strange universe - one which eventually defies gravity and expands at an accelerating rate. The unseen force driving this expansion is attributed to "dark energy" and discovering the fundamental nature of dark energy has been called the challenge of this millennium.
On the Origin of Gold (2001-04-05)

Where did the gold in your jewelry originate?  No one is completely sure.  The relative average abundance in our Solar System appears higher than can be made in the early universe, in stars, and even in typical supernova explosions.  Some astronomers now suggest that neutron-rich heavy elements such as gold might be most easily made in rare neutron-rich explosions such as the collision of neutron stars.  Pictured above is a computer-animated frame depicting two neutron stars spiraling in toward each other, just before they collide.  Since neutron star collisions are also suggested as the origin of gamma-ray bursts, it is possible that you already own a souvenir from one of the most powerful explosions in the universe.
Aurora Over New Zealand (2001-04-06)

Last weekend skygazers at middle and high latitudes around the globe were treated to expansive auroral displays as a magnetic storm raged around planet Earth. The storm was triggered by a solar coronal mass ejection associated with the giant sunspot group cataloged as active region number 9393. For example, pictured here in the early morning hours of April 1, the skies over New Zealand are alive with "southern lights". In the wide-angle time exposure, a towering red aurora is visible suspended above the foreground of a well lit lumber yard, train station, church steeple and buildings of the city of Dunedin. On April 2, the largest solar flare of the last 25 years also erupted near active region 9393, but because of its position near the Sun's edge the effects were largely directed away from our fair planet. However, all the recent solar activity underscores the fact that the solar maximum is still with us.

Image credit: Chris Petrich
Stereo Sun (2001-04-07)

This week's stereo offering features the now famous Active Region 9393, the largest sunspot group in the last 10 years. Viewed with red/blue glasses, the stereo pair of images merges into one 3D representation of the Sun with AR9393 above and right of center. The images were recorded in extreme ultraviolet light and AR9393 is seen as an extensive array of bright patches laced with large graceful loops of arcing plasma. In the extreme ultraviolet, active regions outshine the solar surface, just the reverse of their appearance as dark sunspots against a bright photosphere when viewed in visible light. Recorded 96 minutes apart on March 30 by the space-based SOHO EIT camera, the pair produces an exaggerated but pleasing stereo effect due to solar rotation -- the Sun's surface moving slightly between the two exposures to offer different perspectives.
The Big Corona (2001-04-08)

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 of a total eclipe that occurred in August of 1999.  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 next total solar eclipse will be visible from parts of Africa on June 21.

Image credit: Fred Espenak 
(NASA/GSFC)
Mars Odyssey Lifts Off for Mars (2001-04-09)

Tomorrow's picture: Messy Spiral  < | 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.
M51: The Whirlpool Galaxy in Dust and Stars (2001-04-10)

The Whirlpool Galaxy is a classic spiral galaxy.  At only 30 million light years distant and fully 60 thousand light years across, M51, also known as NGC 5194, is one of the brightest and most picturesque galaxies on the sky.  The above image is a digital combination of a ground-based image from the 0.9-meter telescope at Kitt Peak National Observatory and a space-based image from the Hubble Space Telescope highlighting sharp features normally too red to be seen. Anyone with a good pair of binoculars, however, can see this Whirlpool toward the constellation of Canes Venatici.  M51 is a spiral galaxy of type Sc and is the dominant member of a whole group of galaxies.  Astronomers speculate that M51's spiral structure is primarily due to its gravitational interaction with a smaller galaxy just off the top of this image.
Large Sunspot Group AR 9393 (2001-04-11)

The largest sunspot group of the past ten years crossed the surface of the Sun late last month and early this month.  The group was designated Active Region 9393 as it was the 9393rd region identified since counting officially began in 1973.  The number of active regions on the Sun is high recently because the Sun is reaching the maximum of its current 11-year cycle of magnetic activity. The above time-lapse sequence shows AR 9393 as it evolved from 27 March to April 2 to become over 10 times larger than our Earth. Just after the end of the movie, on April 2, AR 9393 unleashed the largest solar flare of the last 25 years.  Luckily, the flare was not pointed toward the Earth, or flare particles might have damaged satellites or even caused local electrical blackouts. Yesterday morning, however, a less powerful flare was ejected from a different sunspot group (AR 9415) toward Earth that has already caused radio interference. This and solar activity from Monday should cause significant aurorae over the next two nights. Will the above sunspot group remain as its region rotates back into view in a few days, or will it break up on the far side of the Sun?  Currently, no one knows for sure.
STS-1: First Shuttle Launch (2001-04-12)

On April 12, 1981, twenty years ago today, the space shuttle orbiter Columbia became the first shuttle to orbit the Earth. In this gorgeous time exposure, flood lights play on the Columbia and service structures (left) as it rests atop Complex 39's Pad A at Kennedy Space Center in preparation for first launch. Flown by Commander John W. Young and Pilot Robert L. Crippen, Columbia spent 2 days aloft on its check-out mission, STS-1, which ended in a smooth landing, airplane-style, at Edwards Air Force Base in California. Ferried back to Kennedy by a modified Boeing 747, Columbia was launched again seven months later on STS-2, becoming the first piloted reuseable orbiter. The oldest operating shuttle orbiter, Columbia's 1981 debut was followed by Challenger in 1982 (destroyed in 1986), Discovery in 1983, Atlantis in 1985, and Challenger's replacement Endeavour in 1991. This shuttle orbiter fleet has now accomplished over 100 orbital missions. Today also marks the 40th anniversary of the first human in space, Yuri Gagarin.
GRB010222: Gamma-Ray Burst, X-Ray Afterglow (2001-04-13)

A fading afterglow from one of the most powerful explosions in the universe is centered in this false color image from the spacebased Chandra X-ray Observatory. The cosmic explosion, an enormously bright gamma-ray burst (GRB), originated in a galaxy billions of light-years away and was detected by the BeppoSAX satellite on February 22. GRB010222 was visible for only a few seconds at gamma-ray energies, but its afterglow was followed for days by x-ray, optical, infrared and radio instruments. These Chandra observations of the GRB's x-ray glow hours after the initial explosion suggest an expanding fireball of material moving at near light speed has hit a wall of relatively dense gas. While the true nature of gamma-ray bursters remains unknown, the mounting evidence from GRB afterglows does indicate that the cosmic blasts may be hypernovae -- the death explosions of very massive, short-lived stars embedded in active star forming regions. As the hypernova blasts sweep up dense clouds of material in the crowded star forming regions they may also trigger more star formation.
Man Enters Space (2001-04-14)

Forty years ago, on April 12, 1961, Soviet cosmonaut Yuri Alexseyevich Gagarin became the first human in space. His remotely controlled Vostok 1 spacecraft lofted him to an altitude of 200 miles and carried him once around planet Earth. Gagarin was strictly a passenger on this flight. As a precaution against the unknown physiological effects of spaceflight on piloting skills and judgement, his onboard controls were locked out by a secret combination. In case of emergency he carried the combination in a sealed envelope. After reentry, Gagarin ejected from the Vostok at an altitude of 20,000 feet and parachuted to Earth. How was the first view from space? He reportedly commented, "The sky is very dark; the Earth is bluish. Everything is seen very clearly". Coupled with other accomplishments, this flight confirmed the early Soviet lead in the space race -- the first US astronaut would not be launched until almost a month later and then on a comparatively short suborbital flight. Born on March 9, 1934, Gagarin was an air force jet pilot before being chosen for the first group of cosmonauts in 1960. As a result of his historic flight he became an international hero and legend. Killed when his MIG jet crashed during a training flight on March 27, 1968, Gagarin was given a hero's funeral, his ashes interred in the Kremlin Wall.
Diffraction Spikes: When Stars Look Like Crosses (2001-04-15)

Unusual appendages around bright stars are commonplace, but never seem to be mentioned. What are they?   First, a telescope brings starlight falling over a large area to a small area.  To get at this small area, however, one must go inside a reflecting telescope, and one good way to do this is to use support rods,  which are right in the view of the telescope.  The wave nature of light causes it to deflect when passing near these rods.  Light scatters away from the original destination point ending up elsewhere and appearing as "diffraction spikes."   These annoying spikes steal precious light from the central image and hide light from fainter, more interesting stars.  Above, astronomers are more interested in the half-circled point near the image center, than the cool-looking diffraction spikes from the bright star at the bottom.  Apparently, that half-circle is a new stellar system forming in the Lagoon Nebula.
The Hydra Cluster of Galaxies (2001-04-16)

The Hydra Cluster of Galaxies contains well over 100 bright galaxies - but perhaps fewer galaxies than might be expected from its mass.  Clusters of galaxies are the largest gravitationally bound objects in the universe.  Most of a cluster's mass, however, appears to be in a form too dark to see, as analyses of the distribution of X-ray light, gravitational lensing, and internal motions indicate. Abell 1060, as the above cluster is also known, appears to have an even higher fraction of dark matter than seen in a similar cluster, a situation astronomers cannot easily reconcile with both clusters forming solely from gravitational attraction.  The Hydra Cluster of Galaxies, named for its home constellation, spans about ten million light years.

Image credit: AAO
Colorful Water Clouds Over Mars (2001-04-17)

One place where water can be found on Mars is in clouds.  In the above picture colorful water clouds are visible just after sunrise in and around a maze of canyons known as Noctis Labyrinthus (the labyrinth of the night).  Scientists don't yet know, however, why these clouds formed, and why some stick to the canyons.  One exciting possibility is that water sometimes condenses in shaded regions of the canyons, only to evaporate into clouds when exposed to the morning Sun.  Water in any form on the Martian surface might be important to sustaining life and possible future human exploration.  Viking Orbiter 1, which visited Mars in 1976, took the above picture.  The region shown is about 100 kilometers across.
A Higher Dimensional Universe? (2001-04-18)

Does our universe have higher but unusual spatial dimensions? This idea has been gaining popularity to help explain why vastly separated parts of our universe appear so similar, and why the geometry of our universe does not seem to result naturally from the amounts of matter it seems to contain.  In a new incarnation of an old extra-dimensional idea, some astrophysicists hypothesize that we live in a universe dubbed Ekpyrotic, where our four dimensions (three spatial plus one time) resulted from the fiery collision of two four-dimensional spaces (branes) in a five-dimensional universe.  This big-bang hypothesis is meant to compete with another big-bang hypothesis that our universe underwent a superluminal inflation event in the distant past, and does make distinct testable predictions.  Above, a dynamic three-dimensional drawing (two spatial plus one time) of a four-dimensional depiction of a five-dimensional cube (a hypercube with four spatial dimensions is also known as a tesseract) is shown.  Donning red-blue glasses will give the best multi-dimensional perspective.

Image credit: Mark Newbold
Sunspot Stack (2001-04-19)

Welcome to multiwavelength astronomy! From top to bottom, these stacked panels show the largest sunspot group in a decade in visible, extreme ultraviolet, and x-ray light. All were taken on March 29, around the time the famous solar active region, cataloged as AR 9393, was at its peak size -- over 10 times the size of planet Earth. The panels illustrate how the "appearance" of the active region changes, when imaged in electromagnetic radiation (light) of progressively shorter wavelengths. In the visible light panel, dark islands of sunspots stand out against the bright solar surface, but the situation seems to be reversed in the extreme ultraviolet panel with a bright active region seen against a darker background. Finally, the x-ray panel reveals majestic loops of glowing plasma arcing far above the sunspot group. Why do pictures of the same part of the Sun look so different? Made at different wavelengths, each panel actually records a different layer in the solar atmosphere. Top to bottom, the altitude of each layer (along with temperature) increases; starting with the Sun's visible surface or photosphere (about 5 thousand kelvins), then the chromosphere / transition region (ten to a hundred thousand kelvins), and finally the solar corona (millions of kelvins).
Io: Moon Over Jupiter (2001-04-20)

How big is the Jovian moon Io? The most volcanic body in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite. Gliding past Jupiter at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view of active Io with the largest gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size. Although in the picture Io appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter. That puts it nearly 350,000 kilometers above Jupiter's cloud tops, roughly equivalent to the distance between Earth and Moon. The Cassini spacecraft itself was about 10 million kilometers from Jupiter when recording the image data.
Apollo 12: Stereo View Near Surveyor Crater (2001-04-21)

This weekend's stereo picture finds Apollo 12 astronaut Pete Conrad standing on the lunar surface near the southern rim of Surveyor Crater in November of 1969. With red/blue glasses you can gaze beyond the spacesuited Conrad across the magnificent desolation of the Moon's Ocean of Storms. Conrad stands next to large chunks of loose rock, debris from the small impact crater. A sampling scoop is in his right hand and a specially designed tool carrier rests by his left foot as he poses for the picture. His photographer, fellow astronaut Al Bean, captured two separate images (cataloged as AS12-49-7318 and AS12-49-7319) by doing something like a stereo "cha-cha" ... taking the first picture while resting his weight on his right foot and the second after shifting to his left. With the first tinted blue and second red, the pair of pictures were offset and combined to create a 3D anaglyph. Donning red/blue glasses allows the result to be viewed with stereo vision.
Globular Cluster 47 Tucanae (2001-04-22)

Stars come in bunches. Of the over 200 globular star clusters that orbit the center of our Milky Way Galaxy, 47 Tucanae is the second brightest globular cluster (behind Omega Centauri).  Known to some affectionately as 47 Tuc or NGC 104, it is only visible from the Southern Hemisphere.  Light takes about 20,000 years to reach us from 47 Tuc which can be seen near the SMC in the constellation of Tucana.  Red Giant stars are particularly easy to see in this picture.  The dynamics of stars near the center of 47 Tuc are not well understood, particularly why there are so few binary systems there.
Space Shuttle Lifts Off for Space Station (2001-04-23)

Last Thursday, Space Shuttle Endeavor lifted off on course for the latest round of building the International Space Station (ISS) in orbit around Earth.  One of the highlights of the 11-day mission promises to be the installation of Canadarm2, a robotic arm that will assist in the future construction and utilization of the ISS.  Canadarm2, a larger and more sophisticated version of the shuttle's own robotic arm, will be able to move around the station's exterior.  This is the ninth shuttle mission to build the ISS --  many more are planned over the next several years.  When completed, the ISS should enclose about the same room as the passenger cabin of a 747 jet.
NGC 2264: Stars, Dust, and Gas (2001-04-24)

The nebula surrounding bright star S Mon is filled with dark dust and glowing gas.  The strange shapes that haunt this star forming region originate from fine interstellar dust reacting in complex ways to the energetic light and hot gas being expelled by the young stars.  The above picture, in representative color, isolates the northern part of a greater nebula designated NGC 2264, which lies about 2500 light-years away and includes the Cone Nebula.  The blue glow directly surrounding S Mon results from reflection, where neighboring dust reflects light from the bright star.  The more diffuse red glow results from emission, where starlight ionizes hydrogen gas.  Pink areas are lit by a combination of the two processes.  A small group of stars surrounds S Mon, the brightest star in the picture and a star visible with the naked eye toward the constellation of Monoceros.

Image credit: Michael Bessell 
(RSAA, ANU), 
MSO
Space Laser Creates Artificial Star (2001-04-25)

Some astronomers don't like stars.  Bright star fluctuations can indicate how the Earth's atmosphere is changing, but many times no bright star exists in the direction where atmospheric information is needed.  So rather than try to eradicate existing stars with a laser, these astronomers create an artificial star of their own right where they need it -- with a laser.  Subsequent observations of the artificial laser guide star can reveal information so detailed about the blurring effects of the Earth's atmosphere that much of this blurring can be removed by rapidly flexing the mirror.  Such adaptive optic techniques allow high-resolution ground-based observations of real stars, planets, and nebulae.  Above, an artificial star was created with a four-watt laser at Richard B. Dunn Solar Telescope on Sacramento Peak in New Mexico.

Image credit: Fang Shi 
(U. Chicago) et al., 
AURA, 
NSO, 
NOAO, 
NSF
Horsehead Rides Again (2001-04-26)

Difficult to see in small telescopes, the Horsehead nebula was recently selected by internet voters as a target for the Hubble Space Telescope. Above (top) is Hubble's detailed view of the dark cosmic dust cloud, released to celebrate the 11th anniversary of the workhorse orbiting observatory. Below it is a stunning ground-based view from the NOAO 0.9 meter telescope at Kitt Peak National Observatory which shows the dark Horsehead against a wider edge-on expanse of glowing gas. Dramatic dust and gas clouds in and around the Horsehead are part of a large, complex stellar nursery seen towards the constellation of Orion. This star forming region is about 1,500 light-years distant and includes the well known Orion nebula. The Horsehead nebula is found just south of Zeta Orionis, the easternmost star in Orion's belt.

Image credit: selected by internet voters