juliensimon/nasa-apod huggingface dataset:
Footprints on Another World (2002-07-20)

On July 20th, 1969, humans first set foot on the Moon. Taken from a window of their Apollo 11 lunar module, the Eagle, this picture shows the footprints in the powdery lunar soil made by astronauts Neil Armstrong and Buzz Aldrin. It has been estimated that one billion people on planet Earth watched Armstrong step from the lander onto the surface of another world, making this live transmission one of the highest rated television shows ever.  In the foreground at right, a rocket nozzle on the side of the Eagle is seen in silhouette, while beyond an unfurled United States flag is the television camera, remounted on a stand to better view the landing area. The Apollo missions to the Moon have been described as the result of the greatest technological mobilization in history.
Nearby Spiral Galaxy NGC 4945 (2002-07-21)

For such a close galaxy, NGC 4945 is easy to miss.  NGC 4945 is a spiral galaxy in the Centaurus Group of galaxies, located only six times farther away than the prominent Andromeda Galaxy. The thin disk galaxy is oriented nearly edge-on, however, and shrouded in dark dust.  Therefore galaxy-gazers searching the southern constellation of Centaurus need a telescope to see it.  The above picture was taken with a large telescope testing a new wide-angle, high-resolution CCD camera.  Most of the spots scattered about the frame are foreground stars in our own Galaxy, but some spots are globular clusters orbiting the distant galaxy.  NGC 4945 is thought to be quite similar to our own Milky Way Galaxy.  X-ray observations reveal, however, that NGC 4945 has an unusual, energetic, Seyfert 2 nucleus that might house a large black hole.
Open Cluster NGC 6520 from CFHT (2002-07-22)

Did you ever have a day when it felt like a dark cloud was following you around?  For the open cluster of stars NGC 6520, every day is like this. On the left of the above picture are many of NGC 6520's bright blue stars.  They formed only millions of years ago - much more recently than our ancient Sun which formed billions of years ago.  On the right is an absorption nebula, molecular cloud Barnard 86, from which the stars of NGC 6520 surely formed.  This nebula contains much opaque dust that blocks light from the many stars that would have been visible in the background.  Surrounding NGC 6520 is part of the tremendously dense starscape in the bulge of our Milky Way Galaxy, the extended halo of stars that surrounds the center of our Galaxy. NGC 6520 spans about 10 light years and lies about 5500 light years away toward the direction of Sagittarius.

Image credit: Jean-Charles Cuillandre
The View from Everest (2002-07-23)

What would it be like to stand atop the tallest mountain on Earth?  To see a full panoramic vista from there, scroll right.  Visible are snow peaked mountains near and far, tremendous cliffs, distant plateaus, the tops of clouds, and a dark blue sky.  Mt. Everest stands 8.85 kilometers above sea level, roughly the maximum height reached by international airplane flights, but much less than the 300 kilometers achieved by a space shuttle.  Hundreds of people have tried and failed to climb the behemoth by foot, a feat first accomplished successfully in 1953.  About 1000 people have now made it to the summit.  Roddy Mackenzie, who climbed the mountain in 1989, captured the above image. Mt. Everest lies in the Himalayan mountains in the country of Nepal.  In the native language of Nepal, the mountain's name is "Sagarmatha" which means "goddess of the sky."

Image credit: Roddy Mackenzie
Our Busy Solar System (2002-07-24)

Our Solar System is a busy place.  Although the major planets get the most press, a swarm of rocks, comets, and asteroids also exist. The above plot shows the placement of known inner Solar System objects on 2002 July 20.  The light blue lines indicate the orbits of planets.  The green dots indicate asteroids, officially known as minor planets.  The red dots indicate asteroids that come within 1.3 Earth-Sun distances (AU) of the Sun and so pose an increased (although small) collision risk with the Earth.   Comets appear as dark blue squares, while dark blue points are Jupiter Trojans, asteroids that orbit just ahead of, or just behind Jupiter.  Note that most asteroids of the inner Solar System orbit between Mars and Jupiter in the main asteroid belt.  Every day this plot shifts with objects nearer the Sun typically shifting the most.  The current locations of these objects can be found here.

Image credit: MPC, 
CBAT, 
Harvard CfA, 
IAU
NGC 1569: Heavy Elements from a Small Galaxy (2002-07-25)

For astronomers, elements other than hydrogen and helium are sometimes considered to be simply "heavy elements". It's understandable really, because even lumped all together heavy elements make up an exceedingly small fraction of the Universe. Still, heavy elements can profoundly influence galaxy and star formation ... not to mention the formation of planets and people. In this tantalizing false-color x-ray image from the orbiting Chandra Observatory, small dwarf galaxy NGC 1569 is surrounded by x-ray emitting clouds of gas thousands of light-years across. The gas has recently been observed to contain significant concentrations of astronomers' heavy elements such as oxygen, silicon, and magnesium, supporting the idea that dwarf galaxies, the most common type of galaxy in the Universe, are largely responsible for heavy elements in intergalactic space. A mere 7 million light-years distant toward the long-necked constellation Camelopardalis, NGC 1569 has undergone a recent burst of star formation and stellar supernova explosions. The furious cosmic activity has heated the expanding gas clouds to temperatures of millions of degrees while enriching them with newly synthesized heavy elements.
Clearing Skies (2002-07-26)

Clear evening skies are a welcome sight for stargazers worldwide, but clearing skies are good too. Just such a glorious occasion was recorded in this dramatic photo taken by Dominic Cantin during a recent gathering of Canadian astronomers at St-N�r�e Observatory, located about 60 kilometers southeast of the city of Quebec. Looking toward the west on July 13th, the exposure captured a distant lightning flash from a passing thunderstorm at the far left. On the right, the storm clouds' retreat has uncovered an overexposed crescent Moon sharing the evening twilight with bright Venus only a few degrees away (below and far right). In the darkening sky above the young Moon is a familiar right triangle of stars in the constellation Leo. Cantin reports that clear skies followed, all night long.

Image credit: Dominic Cantin
Apollo 11: Catching Some Sun (2002-07-27)

Bright sunlight glints and long dark shadows dramatize this image of the lunar surface taken by Apollo 11 astronaut Neil Armstrong, the first to walk on the Moon. Pictured is the mission's lunar module, the Eagle, and spacesuited lunar module pilot Buzz Aldrin unfurling a long sheet of foil also known as the Solar Wind Collector. Exposed facing the Sun, the foil trapped atoms streaming outward in the solar wind, ultimately catching a sample of material from the Sun itself. Along with moon rocks and lunar soil samples, the solar wind collector was returned for analysis in earthbound laboratories.
An Anomalous SETI Signal (2002-07-28)

No one knows for sure what caused this signal.  There is a slight possibility that it just might originate from an extraterrestrial intelligence. The bright colors on the blue background indicate that an anomalous signal was received here on Earth by a radio telescope involved in a Search for Extraterrestrial Intelligence (SETI).  A search for these signals is ongoing by several groups including volunteer members of the SETI League.  Time labels the vertical axis of the above plot, and frequency marks the horizontal axis.  Although this strong signal was never positively identified, astronomers have identified in it many attributes characteristic of a more mundane and ultimately terrestrial origin.  In this case, a leading possibility is that the signal originates from an unusual modulation between a GPS satellite and an unidentified Earth-based source. Many unusual signals from space remain unidentified.  No signal has yet been strong enough or run long enough to be unambiguously identified as originating from an extraterrestrial intelligence.

Image credit: SETI League
A Setting Sun Trail (2002-07-29)

The Sun appears to move on the sky because the Earth rotates.  The extreme brightness of the Sun, however, makes it difficult to capture a sun-trail -- the path the Sun traces on the sky.  To capture the above picture, a very dark filter covered the camera lens for most of the time, allowing only a trifle of light from the bright Sun to peek through.   Just after the Sun had dipped below the horizon but before it was completely dark, the thick filter was removed and the pretty foreground scene was captured.  Slight flares appeared when the Sun went behind thin clouds.  Star-trails and planet-trails are much easier to image, and a similar Moon trail has also recently been imaged.

Image credit: Anglo-Australian Observatory
A Star Cluster in Motion (2002-07-30)

Star clusters are a swarm of complex motions.  The stars that compose globular clusters and many open clusters all orbit the cluster center, occasionally interacting, gravitationally, with a close-passing star.  The orbits of stars around the cluster are typically not as circular as the orbits of planets in our solar system.  Cluster stars frequently fall more directly toward the center and many times trace out unusual and complex loops.  The vast space inside a cluster results in stars colliding only rarely.   The above computer animation, derived from a type of computer code called an N-body simulation, shows 100 identical stars in a time-lapse movie where hundreds of years pass in one second.
Henize 3-401: An Elongated Planetary Nebula (2002-07-31)

How do dying stars eject their outer layers?  Stars that create elegant planetary nebulas like Henize 3-401, pictured above, are not unusual, causing speculation that, one day, our own Sun may look like this.  Henize 3-401 is one of the most elongated planetary nebulas yet discovered, a particularly odd feat for a seemingly round star.  Perhaps, some astronomers hypothesize, the elongated shape gives a clue to the expulsion mechanism.  Genesis hypotheses include that the outer layers of gas are funneled out by the star's own magnetic field, and that a second unseen star is somehow involved.  After the gas disperses in a few thousand years, only a white dwarf star will remain.  Henize 3-401 lies about 10,000 light years away toward the constellation of Carina.
Sunspots and Solar Active Regions (2002-08-01)

July was a good month for sunspots ... really big sunspots. In fact, the full disk and inset pictures above show three large groups of spots, photographed only a few days ago on July 28. Together the sunspots span a region about thirty times the diameter of planet Earth. Now rotating behind the Sun's visible edge, these groups followed close on the heels of another enormous sunspot group which appeared in mid July. All of July's monster sunspot groups could be viewed without magnification, using safe solar observing methods of course. While individual sunspots are not numbered or cataloged, groups of sunspots, designated solar active regions, are given consecutive numbers as they appear on the visible solar disk. That numbering began on January 5, 1972 and on June 14, 2002, reached active region number 10,000. At the 10k mark no door prizes were given and no disasters plagued our fair solar system. But since June 14, active region reports often drop at least the leading digit, making these three active regions AR 0050, AR 0039, and AR 0044 (top left to bottom right).

Image credit: Fred Espenak (courtesy of
www.MrEclipse.com)
Comet 57P Falls to Pieces (2002-08-02)

Comet 57P has fallen to pieces, at least 19 of them. Orbiting the Sun every 6 years or so this faint comet - also christened Comet 57P/du Toit-Neujmin-Delporte for its three 1941 co-discoverers - is simply 57th on the list of comets known to be periodic, beginning with Comet 1P/Halley. In mid July, responding to reports of a new object possibly associated with Comet 57P, astronomers were able to construct this mosaic of deep sky images identifying a surprising 19 fragments (circled) strung out behind the cometary coma and nucleus itself (far left). The full mosaic spans about a million kilometers at the distance of the comet, while the individual pieces detected are probably a few tens to a few hundred meters across. Stress produced as sunlight warmed the icy, rocky nucleus likely contributed to the fragmentation. In fact, when last seen passing through the inner solar system in 1996, Comet 57P brightened unexpectedly, indicating a sudden increase in surface activity.
The Galactic Center - A Radio Mystery (2002-08-03)

Tuning in to the center of our Milky Way galaxy, radio astronomers explore a complex, mysterious place. A premier high resolution view, this startlingly beautiful picture covers a 4x4 degree region around the galactic center. It was constructed from 1 meter wavelength radio data obtained by telescopes of the Very Large Array near Socorro, New Mexico, USA. The galactic center itself is at the edge of the extremely bright object labeled Sagittarius (Sgr) A, suspected of harboring a million solar mass black hole. Along the galactic plane which runs diagonally through the image are tortured clouds of gas energized by hot stars and bubble-shaped supernova remnants (SNRs) - hallmarks of a violent and energetic cosmic environment. But perhaps most intriguing are the arcs, threads, and filaments which abound in the scene. Their uncertain origins challenge present theories of the dynamics of the galactic center.
Spiral Galaxy NGC 2997 from VLT (2002-08-04)

NGC 2997 is a grand design spiral galaxy.  Its small nucleus and sprawling spiral arms give it a type Sc designation.  NGC 2997, pictured above, is speeding away from us at about 1100 kilometers per second, which would place it at about 55 million light years distant, given current estimates of the expansion rate of our universe.  NGC 2997 is thought to have a mass of about 100 billion times that of our Sun, but is probably less massive than our own Milky Way galaxy.  NGC 2997 is not seen face-on - it is thought tilted by about 45 degrees.  NGC 2997 is particularly notable for a nucleus surrounded by a chain of hot giant clouds of ionized hydrogen.
Rays from an Unexpected Aurora (2002-08-05)

This aurora was a bit of a surprise.  For starters, last Friday morning, no intense auroral activity was expected at all.  Possibly more surprising, however, the aurora appeared to show an usual structure of green rays from some locations.  In the above image, captured from North Dakota, USA, a picket fence of green rays stretches toward the horizon.  Mirroring the green rays is a red band, somewhat rare in its own right.  Lights from the cities of Bismarck and Mandan are visible near the horizon.  Large sunspot groups indicate that activity from the currently active Sun is relatively likely, possibly causing other streams of energetic particles to cascade onto the Earth and so causing more auroras.

Image credit: Lyndon Anderson 
(Prairie Journal)
Muon Wobble Possible Door to Supersymmetric Universe (2002-08-06)

How fast do fundamental particles wobble?  A surprising answer to this seemingly inconsequential question is coming out of Brookhaven National Laboratory in New York, USA and may not only indicate that the Standard Model of Particle Physics is incomplete but also that our universe is filled with a previously undetected type of fundamental particle.  Specifically, the muon, a particle with similarities to a heavy electron, has had its relatively large wobble under scrutiny since 1999 in an experiment known as g-2 (gee-minus-two), pictured above.  The result galvanizes other experimental groups around the world to confirm it, and pressures theorists to better understand it.  The rate of wobble is sensitive to a strange sea of virtual particles that pop into and out of existence everywhere.  The unexpected wobble rate may indicate that this sea houses virtual particles that include nearly invisible supersymmetric counterparts to known particles.  If so, a nearly invisible universe of real supersymmetric particles might exist all around us.
Gomez's Hamburger: A Proto-Planetary Nebula (2002-08-07)

What, in heaven, is that?  Sometimes astronomers see things on the sky they don't immediately understand.  In 1985 this happened to Arturo Gomez, and the object became known as Gomez's Hamburger for its distinctive yet familiar shape.  After some investigation, the object was identified as a proto-planetary nebula, a gas cloud emitted by a Sun-like star just after its central hydrogen fuel has all been fused to helium.  Gomez's Hamburger is on its way to becoming a full-fledged planetary nebula in a few thousand years.  The light seen (the bun) is reflected by dust from the central star, although the star itself is obscured by a thick dust disk that runs across the middle (the patty).  Gomez's Hamburger, pictured above in a recent image from the Hubble Space Telescope, is only a fraction of a light year across but located approximately 10,000 light years away towards the constellation of Sagittarius.
Ancient Volcanos of Mars (2002-08-08)

Findings of ancient martian microbial fossils in meteorites and liquid water related features on Mars' surface are currently controversial issues. But one thing long established by space-based observations of the Red Planet is the presence of volcanos, as Mars supports some of the largest volcanos in the solar system. This synthetic color picture recorded in March by the Mars Global Surveyor spacecraft shows two of them, Ceraunius Tholus (leftmost) and Uranius Tholus. Found north of the Tharsis region of truly large martian volcanos, these are actually two relatively small volcanos, Ceraunius Tholus being only about the size of the Big Island of Hawaii on planet Earth. Impact craters which overlay the volcanic martian terrain indicate that these volcanos are themselves ancient and inactive. North is to the right and the scene is illuminated by sunlight from the top left. A light region of dust deposited by recent global dust storms lies on the lower left flank of Ceraunius Tholus, whose summit crater is about 25 kilometers across.
Fireworks and Shooting Stars (2002-08-09)

erimenting with a new telescope and camera, photographer Jim Steele captured this surreal but festive image of fireworks in the night sky above Ashland, Oregon. The date was July 4th and the fiery streaks were part of the traditional annual celebration of independence day in the United States. Fiery streaks from another annual event will revisit dark skies this weekend, as shooting stars arc through the night during the much anticipated Perseid Meteor Shower. Perseid meteors are actually bits of dust from the periodic Comet Swift-Tuttle and once each year planet Earth orbits through Swift-Tuttle's cometary dust stream. As the comet dust enters Earth's atmosphere traveling at tens of kilometers per second, the particles are vaporized leaving bright and sometimes colorful trails. While Perseid meteors can be viewed over the next few nights, this year's shower is expected to peak on August 12 and 13 with a rate of dozens or more meteors per hour visible in moonless early morning skies.

Image credit: Jim Steele
Earth at Night (2002-08-10)

This is what the Earth looks like at night.  Can you find your favorite country or city?  Surprisingly, city lights make this task quite possible.  Human-made lights highlight particularly developed or populated areas of the Earth's surface, including the seaboards of Europe, the eastern United States, and Japan.  Many large cities are located near rivers or oceans so that they can exchange goods cheaply by boat.  Particularly dark areas include the central parts of South America, Africa, Asia, and Australia.  The above image is actually a composite of hundreds of pictures made by the orbiting DMSP satellites. (Editor's note: This image has become an email-attachment phenomenon! It has also generated many print requests. Unfortunately, we do not sell prints. However, a high-resolution digital version of the image is available (click here or here).
A Perseid Meteor (2002-08-11)

The ongoing Perseid Meteor Shower should be at its strongest on August 12 and 13. The best time to watch will be between 2:00 AM and dawn on Monday morning (so plan on setting your alarm tonight!) and then again on Tuesday. In dark, moonless, predawn skies you may see dozens of meteors per hour. Grains of cosmic sand and gravel shed from Comet Swift-Tuttle will streak across the sky as they vaporize during entry into Earth's atmosphere. Tracing the meteor trails backwards, experienced skygazers will find they converge on the constellation Perseus, thus this annual meteor shower's name. Pictured above is a Perseid meteor from 1993. The colors are representative but digitally enhanced. As the meteor streaked across the night sky, different excited atoms emitted different colors of light.  The origin of the green tinge visible at the right is currently unknown, however, and might result from oxygen in Earth's atmosphere.

Image credit: S. Kohle & B. Koch,
Bonn University
The Colors and Mysteries of Centaurus A (2002-08-12)

Why is spiral galaxy Centaurus A in so much turmoil?  The above composite image shows different clues to the unusual galaxy's past in different bands of light.  In low energy radio waves, shown in red, lobes across the thick swath of dust glow brightly.  In more energetic radio waves, depicted in green, a bright jet is seen emanating from the galaxy's center.  In optical light, shown in white, the stars that compose much of the galaxy are visible.  Recently, Centaurus A has recently been imaged in X-ray light by the Chandra X-ray Observatory.  The X-rays, depicted in blue, show arcs of hot gas shooting out from the center in an explosion that likely happened about 10 million years ago.  One hypothesis that would explain the turmoil would be if Centaurus A devoured a smaller galaxy about 100 million years ago.
Contemplating the Sky (2002-08-13)

Have you contemplated your sky recently?  Last night was a good one for midnight meditators at many northerly locations as meteors from the Perseid meteor shower frequently streaked through.  The Perseid meteor shower has slowly been building to a crescendo but should continue to be rewarding tonight and into the week.  Pictured above on August 1, a group of celestial sightseers near Quebec, Canada are treated to a dark and wondrous night sky that contained bright stars, green auroras, the band of our Milky Way galaxy, a majestic Moon rising, the International Space Station slowly gliding by, and the occasional flash of a Perseid meteor.  Although no meteors were caught in this frame, the Big Dipper remained quite prominent.

Image credit: Sebastien Giguere
(Astrolab du Parc du Mont-Megantic)
Giant Emission Nebula NGC 3603 in Infrared (2002-08-14)

NGC 3603 is the largest region of glowing gas in our Milky Way galaxy.   Spanning over 20 light years across, the giant emission nebula (HII region) is home to a massive star cluster, thick dust pillars, and a star about to explode.  NGC 3603 was captured above in infrared light by a Two Micron All Sky Survey (2MASS) telescope.  The young star cluster near the center heats the region's mostly hydrogen gas.  Many stars in the cluster are estimated to be about one million years old, much less than the five billion-year age of our Sun.  NGC 3603 lies approximately 20,000 light years away toward the constellation of Carina.