juliensimon/nasa-apod huggingface dataset:
Meteors and Northern Lights (2002-08-15)

Skygazers report that the annual Perseid meteor shower went pretty much as predicted, producing a meteor every few minutes during the dark early morning hours of August 12 and 13. And as the constellation Perseus rose above the horizon on the night of August 11, astrophotographer Wade Clark was anticipating recording images of the flashing meteor trails from the Mt. Baker Ski Area in northwest Washington, USA. But Clark was also treated to a colorful display of northern lights. As a result, the stars of Perseus are arrayed near the center of his well composed skyscape along with trails of Perseid meteors all viewed through the auroral glow. The alluring scene might look familiar to watchers of bygone Perseids. For many, views of the meteor shower in 2000 also coincided with auroral displays, courtesy of the active Sun.

Image credit: Wade B. Clark Jr.
Rainbow Perseid (2002-08-16)

While meteors do show colors, the colors aren't always seen with the unaided eye. Still, high speed color film recorded this rainbow-like trail as a meteor streaked through the early morning sky on August 13 above Sedona, Arizona, USA. Part of the annual Perseid meteor shower, this bit of dust from the tail of Comet Swift-Tuttle entered Earth's atmosphere at over 200,000 kilometers per hour. The trail it left glowed briefly as friction with the atmosphere vaporized the dust grain and ionized atoms along its path. The initial green color is thought to be the glow from oxygen in the atmosphere at altitudes above 100 kilometers or so, while sodium atoms and other constituents of the cometary dust grain itself contribute to the orange hues.

Image credit: Dirk Obudzinski
Asteroid 2002 NY40 (2002-08-17)

Asteroid 2002 NY40 will fly by planet Earth early in the morning August 18 Universal Time (late in the evening August 17 Eastern Daylight Time). Approaching to within about 530,000 kilometers or 1.3 times the Earth-Moon distance 2002 NY40 will definitely not be close enough to pose any danger of collision. But it will be close enough and just bright enough for experienced skygazers to see this 800 meter wide space rock in a small telescope or binoculars as it glides quickly through northern skies past the bright star Vega. It will also be close enough to ping with radar, and asteroid hunters using the large Arecibo radio telescope in Puerto Rico expect to determine the three dimensional outline of 2002 NY40. Similar investigations of other near Earth asteroids have revealed some surprising shapes. In this five minute time exposure, recorded at Cerro Tololo Inter-American Observatory on August 14, 2002 NY40 shows itself as a long smudge as it moves against a background of faint stars in the constellation Aquarius.
Earth's North Magnetic Pole (2002-08-18)

A magnetic compass does not point toward the true North Pole of the Earth.  Rather, it more closely points toward the North Magnetic Pole of the Earth.  The North Magnetic Pole is currently located in northern Canada.  It wanders in an elliptical path each day, and moves, on the average, more than forty meters northward each day.  Evidence indicates that the North Magnetic Pole has wandered over much of the Earth's surface in the 4.5 billion years since the Earth formed.  The Earth's magnetic field is created by Earth's partially ionized outer core, which rotates more rapidly than the Earth's surface.  Indicated in the above picture is Ellef Ringnes Island, the location of Earth's North Magnetic Pole in 1999.
Roque de los Muchachos Observatory (2002-08-19)

Above the clouds, atop an island off the coast of Africa, a group of cutting-edge telescopes inspects the universe.  Pictured above are telescopes at Roque de los Muchachos Observatory on La Palma, one of the Canary Islands, Spain.  The site is one of the premier observing locations on Earth.  The telescopes pictured are, from left to right, the Carlsberg Meridian Telescope, the 4.2-meter William Herschel Telescope, the Dutch Open Telescope, the Swedish Solar Tower, the 2.5-meter Isaac Newton Telescope, and the 1.0-meter Jacobus Kapteyn Telescope.  Pioneering observations made recently by these telescopes include stars and galaxies forming early in our universe, comets breaking up, and evidence for planets around Sun-like stars.
The Universe in Hot Gas (2002-08-20)

Where is most of the normal matter in the Universe?  Recent observations from the Chandra X-ray Observatory confirm that it is in hot gas filaments strewn throughout the universe.  "Normal matter" refers to known elements and familiar fundamental particles.  Previously, the amount of normal matter predicted by the physics of the early universe exceeded the normal matter in galaxies and clusters of galaxies, and so was observationally unaccounted for.  The Chandra observations found evidence for the massive and hot intergalactic medium filaments by noting a slight dimming in distant quasar X-rays likely caused by hot gas absorption.  The above image derives from a computer simulation showing an expected typical distribution of hot gas in a huge slice of the universe 2.7 billion light-years across and 0.3 billion light years thick.  The distribution of much more abundant dark matter likely mimics the normal matter, although the composition of the dark matter remains mysterious.  Both the distribution and the nature of the even more abundant dark energy also remain unknown.

Image credit: James Wadsley 
(McMaster U.) et al.
Spiral Galaxy NGC 300 (2002-08-21)

NGC 300 is so interesting because it is so normal.  An Sc-type spiral galaxy in the nearby Sculptor group of galaxies, NGC 300 shows typical flowing blue spiral arms, an expected compact nucleus, and the requisite amount of stars, star clusters, and nebulae.  Therefore, studying NGC 300 should indicate how, exactly, a normal spiral galaxy works.  Toward this goal, NGC 300 and the surrounding area were studied in exquisite detail, creating and combining a series of high-resolution images to create the above conglomerate picture. NGC 300 lies only 7 million light years away, spans nearly the same amount of sky as the full moon, and is visible with a small telescope toward the constellation of Sculptor.
Shell Game in NGC 300 (2002-08-22)

Featured in color in yesterday's episode, big, beautiful, face-on spiral galaxy NGC 300 is seen here through a narrow filter that transmits only the red light of hydrogen atoms. Ionized by energetic starlight, a hydrogen atom emits the characteristic red H-alpha light as its single electron is recaptured and transitions to lower energy states. As a result, this image of NGC 300 is dominated by regions filled with massive, young stars and shell-shaped clouds of hydrogen gas hundreds to thousands of light-years across. Formed in groups called OB associations, the stars are likely only a few million years young. The hydrogen clouds are glowing nebulae or HII regions that have been sculpted by the strong stellar winds and ultraviolet radiation. While picking out your favorite cosmic shell in this picture, don't be misled by the relatively bright foreground stars located in our own Milky Way galaxy. They often show spikes and rings caused by the telescope and camera system.
Island Universe, Cosmic Sand (2002-08-23)

On August 13, while counting Perseid meteors under dark, early morning Arizona skies, Rick Scott set out to photograph their fleeting but fiery trails. The equipment he used included a telephoto lens and fast color film. After 21 pictures he'd caught only two meteors, but luckily this was one of them. Tracking the sky, his ten minute long exposure shows a field of many stars in our own Milky Way galaxy, most too faint to be seen by the unaided eye. Flashing from lower left to upper right, the bright meteor would have been an easy eyeful though, as friction with Earth's atmosphere vaporized the hurtling grain of cosmic sand, a piece of dust from Comet Swift-Tuttle. Just above and left of center, well beyond the stars of the Milky Way, lies the island universe known as M31 or the Andromeda galaxy. The visible meteor trail begins about 100 kilometers above Earth's surface, one of the closest celestial objects seen in the sky. In contrast, Andromeda, about 2 million light-years away, is the most distant object easily visible to the naked-eye.

Image credit: Rick Scott
Cas A Supernova Remnant in X-Rays (2002-08-24)

The complex shell of a star seen to explode 300 years ago is helping astronomers to understand how that star exploded.  This Chandra Observatory image of supernova remnant Cassiopeia A (Cas A) shows unprecedented detail in three x-ray colors.  The relationship between brightness, color, and position of material in the image indicates where in the star this material was just before the explosion.  Bright knots on the left, for example, contain little iron, and so are hypothesized to originate from a higher layer than outer red filaments, which are iron rich.  The blue region on the right is seen through absorbing dust, and so appears depleted of low-energy x-rays.  It takes light ten years to cross the gas shell of the Cas A supernova remnant, which is 10,000 light-years distant. Most of the elements that make people and planets were produced in supernova explosions.
Nebula Nova Cygni Turns On (2002-08-25)

Old photographs show no evidence of the above nebula.  In 1992, a white dwarf star toward the constellation of Cygnus blew off its outer layers in a classical nova explosion: an event called Nova Cygni 1992.  Light flooded the local interstellar neighborhood, illuminated this existing gas cloud, excited the existing hydrogen, and hence caused the red emission.  The only gas actually expelled by the nova can be seen as a small red ball just above the photograph's center.  Eventually, light from the nova shell will fade, and this nebula will again become invisible!
The Mysterious Voynich Manuscript (2002-08-26)

The ancient text has no known title, no known author, and is written in no known language: what does it say and why does it have many astronomy illustrations?  The mysterious book was once bought by an emperor, forgotten on a library shelf, sold for thousands of dollars, and later donated to Yale.  Possibly written in the 15th century, the over 200-page volume is known most recently as the Voynich Manuscript, after its (re-)discoverer in 1912.  Pictured above is an illustration from the book that appears to be somehow related to the Sun.  The book labels some patches of the sky with unfamiliar constellations.  The inability of modern historians of astronomy to understand the origins of these constellations is perhaps dwarfed by the inability of modern code-breakers to understand the book's text.  The book remains in Yale's rare book collection under catalog number "MS 408."

Image credit: B. E. Schaefer 
(U. Texas)
Valles Marineris: The Grand Canyon of Mars (2002-08-27)

The largest canyon in the Solar System cuts a wide swath across the face of Mars.  Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep.  By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep.  The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled.  Recently, several geologic processes have been identified in the canyon.  The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.
3D Mars: Northern Terra Meridiani (2002-08-28)

In this spectacular 3D stereoscopic view from orbit, steep-sided, flat-topped hills stand above the Terra Meridiani region of Mars. Seen best with red/blue glasses (red for the left eye), the structures are reminiscent of buttes and mesas found in southwestern areas of the North American continent on planet Earth. Like their terrestrial counterparts, these layered martian outcrops apparently formed of hard sedimentary rocks with surrounding softer material eroded away. The possibility that surface water laid down the formations makes the Terra Meridiani region a tempting target for future exploration by Mars landers. But alternative explanations include material deposited by wind or accumulations of volcanic ash. The area pictured is about 3 kilometers across, maybe a thirty minute walk over flat ground. Terrestrial rock climbers take note; you and your equipment would only weigh around 1/3 as much in the lower martian surface gravity.
The Pelican in the Swan (2002-08-29)

The Pelican Nebula, also known as IC 5070, lies about 2,000 light-years away in the high and far-off constellation of Cygnus, the Swan. This picture spans a portion of the magnificent nebula about 30 light-years wide. Fittingly, this cosmic pelican is found just off the east "coast" of the North America Nebula, another surprisingly familiar looking emission nebula in Cygnus. In fact, the Pelican and North America nebulae are part of the same large star forming region. The two glowing nebulae appear separated from our vantage point by a large obscuring dust cloud running across the upper left corner in this gorgeous color view. Within the Pelican Nebula, dark dust clouds also help define the eye and long bill, while a bright front of ionized gas suggests the curved shape of the head and neck. Even though it is almost as close as the Orion Nebula, the stellar nursery marked by the Pelican and North America nebulae has proven complex and difficult to study.

Image credit: Robert Gendler
Semeis 147: Supernova Remnant (2002-08-30)

It's easy to get lost following the intricate filaments in this stunningly detailed image of faint supernova remnant Simeis 147. Seen towards the constellation Taurus it covers nearly 3 degrees (6 full moons) on the sky corresponding to a width of 150 light-years at the stellar debris cloud's estimated distance of 3,000 light-years. On three separate nights in December 2001 and January 2002 astronomer Steve Mandel accumulated a total of over eight hours of exposure time to compose this image. He used an astronomical CCD camera, telephoto lens, and his specially designed adapter to allow such wide-field digital imaging. He also used a narrow H-alpha filter to transmit only the the light from recombining hydrogen atoms in the expanding nebulosity, defining the regions of shocked, glowing gas. This supernova remnant has an apparent age of about 100,000 years (light from the original explosion first reached Earth 100,000 years ago) but it is not the only aftermath of the massive stellar explosion. The cosmic catastrophe also left behind a spinning neutron star or pulsar, all that remains of the star's dense core.

Image credit: Steve Mandel
The Voyagers' Message in a Bottle (2002-08-31)

Launched twenty-five years ago, NASA's Voyager 1 and 2 spacecraft are now over 10 billion kilometers from the Sun. Still operational, the Voyagers are being tracked and commanded through the Deep Space Network. Having traveled beyond the outer planets, these remarkable spacecraft are only the third and fourth human built artifacts to escape our solar system, following in the footsteps of Pioneer 10 and 11. A 12-inch gold plated copper disk containing recorded sounds and images representing human cultures and life on Earth, is affixed to each Voyager - a message in a bottle cast into the cosmic sea. The recorded material was selected by a committee chaired by the late Carl Sagan. Simple diagrams on the cover (visible above) represent symbolically the spacecraft's origin and give instructions for playing the disk. The exotic construction of the disks should provide them with a long lifetime as they coast through interstellar space. The two spacecraft will not make a close approach to another planetary system for at least 40,000 years.
The Hubble Deep Field (2002-09-01)

Galaxies like colorful pieces of candy fill the Hubble Deep Field - one of humanity's most distant optical views of the Universe. The dimmest, some as faint as 30th magnitude (about four billion times fainter than stars visible to the unaided eye), are very distant galaxies and represent what the Universe looked like in the extreme past, perhaps less than one billion years after the Big Bang. To make the Deep Field image, astronomers selected an uncluttered area of the sky in the constellation Ursa Major (the Big Bear) and pointed the Hubble Space Telescope at a single spot for 10 days accumulating and combining many separate exposures. With each additional exposure, fainter objects were revealed. The final result has been used to explore the mysteries of galaxy evolution and the infant Universe.
Colorful Light Pillars (2002-09-02)

How can an aurora appear so near the ground? Pictured above are not aurora but nearby light pillars, a local phenomenon that can appear as a distant one.  In most places on Earth, a lucky viewer can see a Sun-pillar, a column of light appearing to extend up from the Sun caused by flat fluttering ice-crystals reflecting sunlight from the upper atmosphere.  Usually these ice crystals evaporate before reaching the ground.  During freezing temperatures, however, flat fluttering ice crystals may form near the ground in a form of light snow, sometimes known as a crystal fog.  These ice crystals may then reflect ground lights in columns not unlike a Sun-pillar.  In the above picture, the colorful lights causing the light pillars surround a ice-skating rink in Fairbanks, Alaska.

Image credit: Walter Tape 
(Alaska Fairbanks), 
Figure 8-1, 
Atmospheric Halos
A Dust Devil on Mars (2002-09-03)

Does the surface of Mars change?  When inspecting yearly images of the Martian surface taken by the robot spacecraft Mars Global Surveyor currently orbiting Mars, sometimes new dark trails are visible.  Although originally a mystery, the culprit is now usually known to be a dust devil, a huge swirling gas-cloud with similarities to a terrestrial tornado.  Pictured above, a recent image has not only captured a new dark trail but the actual dust devil itself climbing a crater wall.  Dust devils are created when Martian air is heated by a warm surface and begins to spin as it rises.  Dust devils can stretch 8 kilometers high but usually last only a few minutes.
Halo of the Cat's Eye (2002-09-04)

The Cat's Eye Nebula (NGC 6543) is one of the best known planetary nebulae in the sky. Its haunting symmetries are seen in the very central region of this stunning false-color picture, processed to reveal the enormous but extremely faint halo of gaseous material, over three light-years across, which surrounds the brighter, familiar planetary nebula. Made with data from the Nordic Optical Telescope in the Canary Islands, the composite picture shows emission from nitrogen atoms as red and oxygen atoms as green and blue shades. Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star. Only much more recently however, have some planetaries been found to have halos like this one, likely formed of material shrugged off during earlier active episodes in the star's evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years.
Voyager Views Titan's Haze (2002-09-05)

Launched in 1977, 25 years ago today, the Voyager 1 spacecraft's historic tour of the outer Solar System took it past Saturn in late 1980. On November 12, 1980, Voyager 1 recorded this view looking across the edge of Titan, Saturn's largest moon, from a distance of about 22,000 kilometers. Seen in false color, the moon's hazy atmosphere appears orange with further layers of blue haze suspended above. Titan's mostly nitrogen atmosphere, denser than planet Earth's, also contains methane and is thought to be laced with more complex hydrogen and carbon compounds. The composition is likened to Earth's atmosphere before life began. Spotted by Voyager, the detached layers of haze hundreds of kilometers above the surface, along with details of Titan's atmospheric chemistry, have intrigued earth-bound researchers who have recently proposed a model that links seasonal variations in the haze, winds, and sunlight. Their model accounts for the early Voyager observations as well as subsequent studies. Further tests of the model are anticipated when the Huygens probe, carried by the saturn-bound Cassini spacecraft, enters Titan's atmosphere in 2005.
HESS Gamma-Ray Telescope (2002-09-06)

Most ground-based telescopes with lenses and mirrors are hindered by the Earth's nurturing, protective atmosphere that blurs images and scatters and absorbs light. But this telescope was designed to detect extreme gamma rays - photons with over 100 billion times the energy of visible light - and actually requires the atmosphere to operate. As the gamma rays impact the upper atmosphere they produce air showers of high-energy particles. Adorned with 382 separate mirrors each 60 centimeters in diameter and equipped with a fast camera, the telescope records in detail the brief flashes of optical light, called Cherenkov light, created by the air shower particles. The telescope pictured here was inaugurated this week and is intended to operate as part of the High Energy Stereoscopic System (HESS) array under construction in Namibia. The initial phase of HESS will consist of four telescopes working in concert to provide multiple stereoscopic views of the air showers, relating them to the energies and directions of the incoming cosmic gamma rays.
Stereo Saturn (2002-09-07)

Get out your red/blue glasses and launch yourself into this stereo picture of Saturn! The picture is actually composed from two images recorded weeks apart by the Voyager 2 spacecraft during its visit to the Saturnian System in August of 1981. Traveling at about 35,000 miles per hour, the spacecraft's changing viewpoint from one image to the next produced this exaggerated but pleasing stereo effect. Saturn is the second largest planet in the Solar System, after Jupiter. Its spectacular ring system is so wide that it would span the space between the Earth and Moon. Although they look solid here, Saturn's rings consist of individually orbiting bits of ice and rock ranging in size from grains of sand to barn-sized boulders.
Too Close to a Black Hole (2002-09-08)

What would you see if you went right up to a black hole?  Above are two computer generated images highlighting how strange things would look.  On the left is a normal star field containing the constellation Orion.  Notice the three stars of nearly equal brightness that make up Orion's Belt.  On the right is the same star field but this time with a black hole superposed in the center of the frame.  The black hole has such strong gravity that light is noticeably bent towards it - causing some very unusual visual distortions. In the distorted frame, every star in the normal frame has at least two bright images - one on each side of the black hole.  In fact, near the black hole, you can see the whole sky - light from every direction is bent around and comes back to you.  Black holes are thought to be the densest state of matter, and there is indirect evidence for their presence in stellar binary systems and the centers of globular clusters, galaxies, and quasars.

Image credit: Robert Nemiroff
(MTU)