juliensimon/nasa-apod huggingface dataset:
Asteroids in the Distance (2002-06-23)

Rocks from space hit Earth every day.  The larger the rock, though, the less often Earth is struck.  Many kilograms of space dust pitter to Earth daily. Larger bits appear initially as a bright meteor.  Baseball-sized rocks and ice-balls streak through our atmosphere daily, most evaporating quickly to nothing.  Significant threats do exist for rocks near 100 meters in diameter, which strike the Earth roughly every 1000 years.  An object this size could cause significant tidal waves were it to strike an ocean, potentially devastating even distant shores.  A collision with a massive asteroid, over 1 km across, is more rare, occurring typically millions of years apart, but could have truly global consequences.  Many asteroids remain undiscovered.  In fact, one was discovered in 1998 as the long blue streak in the above archival image taken by the Hubble Space Telescope. Last week, the small 100-meter asteroid 2002 MN was discovered only after it whizzed by the Earth, passing well within the orbit of the Moon.  2002 MN passed closer than any asteroid since 1994 XM1.  A collision with a large asteroid  would not affect Earth's orbit so much as raise dust that would affect Earth's climate.  One likely result is a global extinction of many species of life, possibly dwarfing the ongoing extinction occurring now.
The Sun's Heliosphere & Heliopause (2002-06-24)

Where does the Sun's influence end? Nobody is sure.  Out past the orbits of Neptune and Pluto extends a region named the heliosphere where the Sun's magnetic field and particles from the Solar Wind continue to dominate.  The surface where the Solar Wind drops below sound speed is called the termination shock and is depicted as the inner oval in the above computer-generated illustration.  It is thought that this surface occurs as close as 75-90 AU -- so close that a Pioneer or Voyager spacecraft may soon glide through it as they exit the Solar System at about 3 AU/year.  The actual contact sheet between the Sun's ions and the Galaxy's ions is called the heliopause and is thought to occur at about 110 AU.  It is depicted above as the middle surface.  The Sun's heliopause moves through the local interstellar medium much as a boat moves on water, pushing a bow shock out in front, thought to occur near 230 AU.

Image credit: P. C. Frisch 
(U. Chicago) 
et al., 
U. Indiana
Venus and Jupiter Over Belfast (2002-06-25)

Venus and Jupiter appeared to glide right past each other earlier this month.  In a slow day-by-day march, Jupiter sank into the sunset horizon while Venus remained high and bright.  The conjunction ended the five-planet party visible over the last two months.  Jupiter, of course, is much further away from the Earth and Sun than Venus, so the passing was really just an angular illusion.  Pictured above on June 3, a fading sunset finds Venus shining over Jupiter above clouds, mountains, and the city lights of Belfast, Northern Ireland.
In the Center of the Trifid Nebula (2002-06-26)

Clouds of glowing gas mingle with lanes of dark dust in the Trifid Nebula, a star forming region toward the constellation of Sagittarius.  In the center, the three huge dark dust lanes that give the Trifid its name all come together. Mountains of opaque dust appear on the lower left, while filaments of dust are visible threaded throughout the nebula.  A single massive star visible near the center causes much of the Trifid's glow.  The Trifid, also known as M20, is only about 300,000 years old, making it among the youngest emission nebula known.  The nebula lies about 5000 light years away and part pictured above spans about 20 light years.  The above false-color digitally enhanced image was taken with the Gemini North telescope earlier this month.
Carving Ma'adim Vallis (2002-06-27)

Just as erosion from the Colorado River carved the Grand Canyon on Earth, a river of flood water may have carved Ma'adim Vallis, one of the largest canyons on Mars. Researchers have presented strong evidence for such a scenario based on elevation data recorded by the MOLA (Mars Orbiter Laser Altimeter) experiment on the Mars Global Surveyor spacecraft. This false-color, detailed, topographical map of MOLA data shows in blue the area of an enormous complex of lakes that are thought to have existed over three and a half billion years ago in the southern highlands of Mars. As the largest lake spilled over the low point in its boundary a torrential flood would have moved north, along the direction indicated by the arrow, carving the sinuous Ma'adim Vallis. At the north end of Ma'adim Vallis, the flood waters would have poured into large, round Gusev Crater. Since standing bodies of surface water are thought to be favorable for ancient martian microbial life, Gusev Crater has been suggested as a landing site for future Mars missions.
Lunar Module at Taurus-Littrow (2002-06-28)

Can the Hubble Space Telescope take a picture that shows the Apollo lunar modules on the Moon? With its 2.4 meter diameter mirror, the smallest object that the Hubble can resolve at the Moon's distance of around 400,000 kilometers is about 80 meters across. So, from low Earth orbit even Hubble's sharp vision can not image the Apollo lunar module descent stages, at most a few meters across, left behind at the lunar landing sites. A space telescope over ten times the size of Hubble could ... or a much smaller telescope in close lunar orbit. In fact, this picture does just resolve Apollo 17's Lunar Module, Challenger, and its shadow on the cratered floor of the Taurus-Littrow valley in the Moon's Mare Serenitatis. It was taken in 1972 from the Apollo 17 Command Module, America, orbiting about 100 kilometers above the Moon's surface and covers an area about 1.1 kilometers wide. Using a web site created by Dan Durda of Southwest Research Institute, armchair astronauts can explore orbital views of this and the 5 other Apollo lunar landing sites.
A Deep Field In The Southern Sky (2002-06-29)

This deep view of the cosmos is the sequel to the 1995 hit Hubble Space Telescope Deep Field. Billed as the Hubble Deep Field South, it was produced by pointing the space telescope toward a patch of sky in the southern constellation Tucana. Over a period of 10 days, many separate exposures were accumulated and combined to reveal progressively fainter galaxies. The original deep field was constructed by observing a piece of sky in the northern constellation Ursa Major. Both stare down 12 billion light-year long tunnels to far-off and still mysterious times when young galaxies inhabited an infant universe. Hubble Deep Field South observations were released to an enthusiastic audience on November 23, 1998.
Ida and Dactyl: Asteroid and Moon (2002-06-30)

This asteroid has a moon! The robot spacecraft Galileo currently exploring the Jovian system, encountered and photographed two asteroids during its long journey to Jupiter. The second asteroid it photographed, Ida, was discovered to have a moon which appears as a small dot to the right of Ida in this picture. The tiny moon, named Dactyl, is about one mile across, while the potato shaped Ida measures about 36 miles long and 14 miles wide. Dactyl is the first moon of an asteroid ever discovered. The names Ida and Dactyl are based on characters in Greek mythology. Other asteroids are now known to have moons.
The Fox Fur Nebula (2002-07-01)

The nebula surrounding bright star S Mon is filled with dark dust and glowing gas.  The strange shapes originate from fine interstellar dust reacting in complex ways with the energetic light and hot gas being expelled by the young stars.  The region just below S Mon, the bright star in the above picture, is nicknamed the Fox Fur Nebula for its color and texture.  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.  S Mon is part of a young open cluster of stars named NGC 2264, located about 2500 light years away toward the constellation of Monoceros, just north of the Cone Nebula.

Image credit: Anglo-Australian Observatory
The Average Color of the Universe (2002-07-02)

What color is the universe?  More precisely, if the entire sky was smeared out, what color would the final mix be?  This whimsical question came up when trying to determine what stars are commonplace in nearby galaxies. The answer, depicted above, is a conditionally perceived shade of beige.  To determine this, astronomers computationally averaged the light emitted by one of the largest sample of galaxies yet analyzed: the 200,000 galaxies of the 2dF survey.  The resulting cosmic spectrum has some emission in all parts of the electromagnetic spectrum, but a single perceived composite color.  This color has become much less blue over the past 10 billion years, indicating that redder stars are becoming more prevalent.   In a contest to better name the color, notable entries included skyvory, univeige, and the winner: cosmic latte.
Interstellar Dust Bunnies of NGC 891 (2002-07-03)

What is going on in NGC 891?  This galaxy appeared previously to be very similar to our own Milky Way Galaxy: a spiral galaxy seen nearly edge-on.  However, recent high-resolution images of NGC 891's dust show unusual filamentary patterns extending well away from its Galactic disk.  This interstellar dust was probably thrown out of the galactic disk toward the halo by stellar supernovae explosions.  Because dust is so fragile, its appearance after surviving disk expulsion can be very telling. Newly discovered phenomena, however, sometimes appear so complex that more questions are raised than are answered.

Image credit: Jean-Charles Cuillandre
Young Star Clusters in an Old Galaxy (2002-07-04)

cal galaxy NGC 4365 is old, probably about 12 billion years old. Like most elliptical galaxies, this galaxy was thought to be full of old stars too, its burst of star forming activity having long since ended. But combining data from the Hubble Space Telescope and the European Southern Observatory's ground-based Antu Telescope, a team of European and US astronomers discovered NGC 4365's surprising secret -- some of its star clusters are young. In this composite image, the galaxy's bright nucleus is at the upper left. NGC 4365's star clusters themselves appear as bright dots against a diffuse glow of unresolved starlight and fuzzy, distant background galaxies. The notched border outlines Hubble's WFPC2 camera field. Moving the cursor over the image identifies individual star clusters, with the relatively young (few billion year-old) clusters circled in blue, and the anticipated 12 billion year-old clusters circled in red. NGC 4365 is 60 million light-years away in the Virgo galaxy cluster.
Many Moons (2002-07-05)

Whimsical and creative, this multiple exposure suggests that planet Earth's sky could be very dramatic indeed if it were graced by many moons. And in James Thurber's well-known children's story, Princess Lenore was comfortable with the idea of many moons, even if the wise men of the King's court failed to understand. But just for the Royal Astronomer and Mathematician, this picture has an explanation. On 2001 July 8, three days past full moon, astrophotographer Corrado Alesso loaded his camera with high-speed film and set it up in the province of Cuneo, Italy. With the shutter open, he recorded four separate one second long exposures on the same frame, covering the wide-angle lens for about 30 minutes between each exposure as the inconstant moon drifted through the night.

Image credit: Corrado Alesso
Io: Moon Over Jupiter (2002-07-06)

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.
The Galactic Center Across the Infrared (2002-07-07)

The center of our Galaxy is obscured in visible light by dark dust that rotates with the stars in the Galactic Plane.  In this century, however, sensors have been developed that can detect light more red that humans can see - light called infrared.  The above picture shows what the Galactic Center looks like in three increasingly red bands of near-infrared light.  The picture results from a digital combination of data recently taken by the 2MASS and MSX Galactic surveys.  In near-infrared light (shown in blue) the dust is less opaque and many previously shrouded red giant stars become visible.  In the mid-infrared (shown in red) the dust itself glows brightly, but allows us a view very close to our tumultuous and mysterious Galactic Center.
Weighing Empty Space (2002-07-08)

Sometimes staring into empty space is useful.  Pictured above is a region of sky that was picked because it had, well, nothing: no bright stars, no bright galaxies, and no picturesque nebulas.  What could not be avoided, however, were a few stars in our own Galaxy, and many distant galaxies strewn across the universe.  Now the more distant galaxies have their light slightly deflected by the gravity of more nearby galaxies, causing them to appear slightly distorted.  By analyzing these gravitational lens distortions, nearby mass concentrations can be found, regardless of how bright they appear.  Using this method, astronomers can now weigh entire clusters of galaxies and search for large groupings of relatively dark matter.  Circled in the lower right of the above image is a cluster of galaxies that was found not by its light, but by its mass.

Image credit: Bell Labs-Lucent Technologies
Analemma (2002-07-09)

Tomorrow's picture: southwest of the big dipper  < | 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: Vasilij Rumyantsev
(Crimean Astrophysical Obsevatory)
M51: Cosmic Whirlpool (2002-07-10)

Follow the handle of the Big Dipper away from the dipper's bowl, until you get to the handle's last bright star. Then, just slide your telescope a little south and west and you'll likely find this stunning pair of interacting galaxies, the 51st entry in Charles Messier's famous catalog. Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also cataloged as NGC 5194. Its spiral arms and dust lanes clearly sweep in front of its companion galaxy (left), NGC 5195. The pair are about 37 million light-years distant and officially lie within the boundaries of the small constellation Canes Venatici. While M51 is visible as a faint, fuzzy patch in binoculars, this sharp color picture was made with a 14 inch telescope and combines digital camera exposures totaling 3 hours and 42 minutes.

Image credit: Tony and Daphne Hallas
M51: X-Rays from the Whirlpool (2002-07-11)

Fresh from yesterday's episode, a popular pair of interacting galaxies known as the Whirlpool debut here beyond the realm of visible light -- imaged at high energies by the orbiting Chandra X-ray Observatory. Still turning in a remarkable performance, over 80 glittering x-ray stars are present in the Chandra image data from the region. The number of luminous x-ray sources, likely neutron star and black hole binary systems within the confines of M51, is unusually high for normal spiral or elliptical galaxies and suggests this cosmic whirlpool has experienced intense bursts of massive star formation. The bright cores of both galaxies, NGC 5194 and NGC 5195 (right and left respectively), also exhibit high-energy activity in this false-color x-ray picture showing a diffuse glow from multi-million degree gas. An expanded view of the region near the core of NGC 5194 reveals x-rays from a supernova remnant, the debris from a spectacular stellar explosion, first detected by earthbound astronomers in 1994.
Recycling Cassiopeia A (2002-07-12)

For billions of years, massive stars in our Milky Way Galaxy have lived spectacular lives.  Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation begins anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant was probably first seen in planet Earth's sky just over 300 years ago, although it took that light more than 10,000 years to reach us. In this gorgeous Hubble Space Telescope image of cooling filaments and knots in the Cas A remnant, light from specific elements has been color coded to help astronomers understand the recycling of our galaxy's star stuff. For instance, red regions are dominated by emission from sulfur atoms while blue shades correspond to oxygen. The area shown is about 10 light-years across.
Apollo 12: Stereo View Near Surveyor Crater (2002-07-13)

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.
The Crab Nebula from VLT (2002-07-14)

The Crab Nebula, filled with mysterious filaments, is the result of a star that was seen to explode in 1054 AD.  This spectacular supernova explosion was recorded by Chinese and (quite probably) Anasazi Indian astronomers.  The filaments are mysterious because they appear to have less mass than expelled in the original supernova and higher speed than expected from a free explosion. In the above picture taken recently from a Very Large Telescope, the color indicates what is happening to the electrons in different parts of the Crab Nebula. Red indicates the electrons are recombining with protons to form neutral hydrogen, while blue indicates the electrons are whirling around the magnetic field of the inner nebula.  In the nebula's very center lies a pulsar: a neutron star rotating, in this case, 30 times a second.
Proxima Centauri: The Closest Star (2002-07-15)

What is the closest star to our Sun?  It is Proxima Centauri, the nearest member of the Alpha Centauri triple star system.  Light takes only 4.22 years to reach us from Proxima Centauri.  This small red star, captured in the center of the above image,  is so faint that it was only discovered in 1915 and is only visible through a telescope.  Stars of all types from our Milky Way Galaxy are visible in the background.   The brightest star in the Alpha Centauri system is quite similar to our Sun, has been known as long as recorded history, and is the third brightest star in the night sky.  The Alpha Centauri system is primarily visible from Earth's Southern Hemisphere.

Image credit: David Malin
Outbound from Mercury (2002-07-16)

After just passing Mercury, the robot spacecraft Mariner 10 looked back.  The above picture is what it saw.  Mercury, the closest planet to the Sun, is heavily cratered much like Earth's Moon.  As Mercury slowly rotates, its surface temperature varies from an unbearably cold -180 degrees Celsius in the half facing away from the Sun, to an unbearably hot 400 degrees Celsius in the half facing toward the Sun.  Mercury is slightly larger than Earth's Moon and much denser.   The Mariner 10 spacecraft swooped by Mercury three times in its journey around the inner Solar System in the mid-1970s.  This outbound view has similarities to the inbound view.  Nearly half of Mercury's surface has yet to be photographed in detail.
Star-Forming Region RCW38 from 2MASS (2002-07-17)

The star cluster in RCW38 was hiding.  Looking at the star forming region RCW38 will not normally reveal most of the stars in this cluster.  The reason is that the open cluster is so young that it is still shrouded in thick dust that absorbs visible light.  This dust typically accompanies the gas that condenses to form young stars.  When viewed in infrared light, however, many stars in RCW38 are revealed, because dust is less effective at absorbing infrared light. The above representative-color image mosaic of RCW38 taken by the 2MASS sky survey in infrared light shows not only many bright blue stars from the star cluster but clouds of brightly emitting gas and dramatic lanes of dark dust. RCW38 spans about 10 light-years and is located about 5500 light years away towards the constellation of Vela.
Sunspot Region 30 (2002-07-18)

The solar active region designated number 10030 (or simply region 30) is now appearing on the visible hemisphere of the closest star. Dwarfed by the Sun's disk, the group of sunspots which make up region 30 actually cover an enormous area -- nearly 10 times the size of Earth. The panels above were recorded July 15, 16, and 17 (top to bottom) by the MDI instrument on the space-based SOHO Observatory as the solar rotation slowly carried the large, dynamic sunspot group across the Sun's nearside. On July 15, a powerful solar flare erupted from this region followed by a coronal mass ejection. The energetic cloud of electrically charged particles swept past our fair planet yesterday, and as a result enhanced auroral activity is possible.
Counting Stars in the Infrared Sky (2002-07-19)

The bulging center of our Milky Way Galaxy, dark cosmic clouds, the thin galactic plane, and even nearby galaxies are easy to spot in this sky view. But each pixel in the digital image is actually based on star counts alone -- as derived from the Two Micron All Sky Survey (2MASS) database. In 2001, the 2MASS project completed a ground-based survey of the entire sky and cataloged upwards of 250 million stars. Their full all-sky picture assigns a brightness and color to individual pixels based on corresponding star counts in each of the survey's three near-infrared bands. In this cropped image, the star-packed galactic center is toward the upper left, with the bright plane of our Galaxy running horizontally through it. Dense regions of interstellar dust clouds, still opaque to penetrating near-infrared light, appear dark by reducing the 2MASS star counts. Our fuzzy neighboring galaxies, the large and small Magellanic Clouds, are at the lower right, while scattered single bright spots correspond to the intense concentrations of stars in the Milky Way's large globular star clusters.