juliensimon/nasa-apod huggingface dataset:
Going Wild (2004-03-19)

Dynamic jets of gas and dust surround one of the most active planetary surfaces in the solar system in this wild-looking picture of a comet nucleus. The comet's designation is 81P/Wild 2 of course (sounds like "vilt 2"), and the picture is a composite of two images recorded by the Stardust spacecraft's navigation camera during its January 2nd flyby. The composited images consist of a short exposure recording startling surface details of Wild 2's nucleus and a longer exposure, taken 10 seconds later, revealing material streaming from the surface. The left edge of the nucleus appears extremely jagged due to a strong shadow. Pitted and eroded after billions of years of outgassing and meteorite impacts, the nucleus pictured is only about 5 kilometers in diameter, while the jets of dust and gas ultimately leave trails millions of kilometers long. Stardust is scheduled to return samples of Wild 2's cometary dust, picked up during the flyby, to Earth in January 2006.
Equinox + 1 (2004-03-20)

Twice a year, at the Spring and Fall equinox, the Sun rises due east. In an emphatic demonstration of this celestial alignment, photographer Joe Orman recorded this inspiring image of the Sun rising exactly along the east-west oriented Western Canal, in Tempe,Arizona, USA. But he waited until March 21st, one day after the northern Spring equinox in 2001, to photograph the striking view. Why was the rising Sun due east one day after the equinox? At Tempe's latitude the Sun rises at an angle, arcing southward as it climbs above the horizon. Because the distant mountains hide the true horizon, the Sun shifts slightly southward by the time it clears the mountain tops. Waiting 24 hours allowed the Sun to rise just north of east and arc back to an exactly eastern alignment for the photo. Today's equinox finds the Sun on the celestial equator at 0649 Universal Time.

Image credit: Joe Orman
A Green Flash from the Sun (2004-03-21)

Many think it is just a myth.  Others think it is true but its cause isn't known.  Adventurers pride themselves on having seen it.  It's a green flash from the Sun.  The truth is the green flash does exist and its cause is well understood.  Just as the setting Sun disappears completely from view, a last glimmer appears startlingly green.  The effect is typically visible only from locations with a low, distant horizon, and lasts just a few seconds.  A green flash is also visible for a rising Sun, but takes better timing to spot.  A dramatic green flash was caught in the above photograph in 1992 from Finland. The Sun itself does not turn partly green, the effect is caused by layers of the Earth's atmosphere acting like a prism.

Image credit: Pekka Parviainen 
(Polar Image)
Asteroid 2004 FH Whizzes By (2004-03-22)

Last week, a small asteroid approached unusually close to the Earth.  Asteroid 2004 FH posed no danger, but became bright enough to see with binoculars.  Passing only 7 Earth radii away, this asteroid pass was the closest yet that was previously predicted, although it was discovered only two days before. Pictured above, the 30-meter sized 2004 FH was imaged from Switzerland crossing the sky on March 18, near its closest approach.  The asteroid, centered in the above time-lapse movie covering about 30 minutes, changes in brightness as it tumbles by.  An asteroid this size passes this close to Earth about every two years.  Were 2004 FH to have struck the Earth, it would have likely burned up in the atmosphere. Large impact features on the Earth are testaments, however, to larger asteroids and comets that actually impacted the Earth in the distant past.  Astronomers continue to discover, track, and study potentially hazardous asteroids with a goal of making planet Earth a safer place.

Image credit: S. Sposetti & R. Behrend 
(Geneva Obs.)
Lava Flows on Venus (2004-03-23)

The hot surface of Venus shows clear signs of ancient lava flows.  Evidence of this was bolstered by the robot spacecraft Magellan, which orbited Venus in the early 1990s.  Using imaging radar, Magellan was able to peer beneath the thick perpetual clouds that cover Earth's closest planetary neighbor.  Picture above, lava apparently flowed down from the top of the image and pooled in the light colored areas visible across the image middle and bottom. The lava cut a channel across the darker ridge that runs horizontally across the image center.  The picture covers about 500 kilometers across.  The lava originates from a caldera named Ammavaru that lies about 300 kilometers off the image top.  The hot dense climate makes Venus a more difficult planet on which to land spacecraft and rovers.  Venus currently sparkles as the brightest object in the western sky after sunset.
Intriguing Dimples Near Eagle Crater on Mars (2004-03-24)

What are those unusual looking dimples?  Looking back toward Eagle crater, its landing place on Mars, the robot rover Opportunity has spotted some unusual depressions in the Martian soil.  The dimples, visible above on the image left, each measure about one meter across and appear to have light colored rock in their interior.  The nearest dimple has been dubbed "Homeplate", while the next furthest one out is called "First Base."  Scrolling right will reveal a magnificent panorama including the rover in the foreground, the backshell and parachute that detached from Opportunity before it landed near the horizon, Eagle crater in the center, Opportunity's tracks as it rolled away from Eagle crater, and wind blown ripples of Martian soil in every direction.  Further analysis of rocks photographed by Opportunity has yielded evidence that Opportunity has landed on an evaporated shoreline of an ancient salt-water ocean.
An Orion of a Different Color (2004-03-25)

Look up into the sky tonight, and even with a good telescope you won't come across a sight quite like this one. It is a familiar object though, the grand stellar nursery known as the Orion Nebula. But the striking picture combines images taken through three separate filters, each designed to record different emission lines - light from Sulfur, Oxygen, and Hydrogen atoms glowing in the tenuous nebular gas. At such low densities, Sulfur and Hydrogen atoms emit red colors while Oxygen glows green. To distinguish their contributions in the final image, Sulfur was assigned to red, Hydrogen to green, and Oxygen to blue, a color scheme used in mapped-color images of other astronomical nebulae as well. While the result is very different from what the eye might see, the image is still both beautiful and scientifically valuable, tracing elements and conditions within the nearby star forming region.

Image credit: Russell Croman
Moon and Planets Sky (2004-03-26)

Look up into the sky tonight and without a telescope or binoculars you might have a view like this one of Moon, planets and stars. The lovely photo was taken on March 23rd, and captures the crescent Moon on the horizon with Venus above it. Both brilliant celestial bodies are over-exposed. Farther above Venus is the tinted glow of Mars with the Pleiades star cluster just to the red planet's right. The V-shaped arrangement of stars to the left of Mars is the Hydaes star cluster. Bright red giant Aldebaran, not itself a member of the Hyades cluster, marks the top left of the V. During the next week, all five naked-eye planets, Mercury, Venus, Mars, Jupiter, and Saturn, along with the Moon will grace the evening sky together - a lunar and planetary spectacle that can be enjoyed by skygazers around the world. But look just after sunset, low on the western horizon, to see Mercury before it sets. The next similar gathering of the planets will be in 2008.
Mir Dreams (2004-03-27)

This dream-like image of Mir was recorded by astronauts as the Space Shuttle Atlantis approached the Russian space station prior to docking during the STS-76 mission. Sporting spindly appendages and solar panels, Mir resembles a whimsical flying insect hovering about 350 kilometers above New Zealand's South Island and the city of Nelson near Cook Strait. In late March 1996, Atlantis shuttled astronaut Shannon W. Lucid to Mir for a five month visit, increasing Mir's occupancy from 2 to 3. It returned to pick Lucid up and drop off astronaut John Blaha during the STS-79 mission in August of that year. Since becoming operational in 1986, Mir has been visited by over 100 spacefarers from the nations of planet Earth including, Russia, the United States, Great Britain, Germany, France, Japan, Austria, Kazakhstan and Slovakia.  After joint Shuttle-Mir training missions in support of the International Space Station, continuous occupation of Mir ended in August 1999. The Mir was deorbited in March 2001.
Stars and the Bubble Nebula (2004-03-28)

Seemingly adrift in a cosmic sea of stars and gas, this delicate, floating apparition is cataloged as NGC 7635 -- The Bubble Nebula. In this wide-angle view, the Bubble nebula lies at the center of a larger complex of shocked glowing gas about 11,000 light-years distant in the fair constellation Cassiopeia. NGC 7635 really is an interstellar bubble, blown by winds from the brightest star visible within the bubble's boundary. The bubble's expansion is constrained by the surrounding material. About 10 light-years in diameter, if the Bubble nebula were centered on the Sun, the Sun's nearest stellar neighbor, Alpha Centauri, would also be enclosed. This breathtaking picture is a combination of telescopic digital images made through broad color filters along with a narrow filter intended to transmit only the red light emitted by excited hydrogen atoms.

Image credit: Brian Lula
NASA's X-43A Scramjet Sets Air Speed Record (2004-03-29)

Using oxygen from the air itself, a NASA experimental jet propelled itself past Mach 7 in the atmosphere above the Pacific Ocean this weekend.  The small automated X-43A Hyper-X craft was dropped from a huge converted B-52 bomber and then accelerated by a standard Pegasus rocket.  At Mach 7, seven times the speed of sound, the X-43A separated and the novel scramjet kicked in.  Atmospheric oxygen was then scooped up, combined with onboard hydrogen, and combusted in flight to propel the X-43A to record air speeds during maneuvers over the next 10 seconds.  Engines of ramjet design have been suggested as a satellite launch method without heavy fuel tanks and even romanticized for interstellar space travel.  The previously acknowledged air-speed record for jet-powered flight was Mach 3.3 for the decommissioned SR-71.  Re-entering space rockets can start as high as Mach 36 before the atmosphere decelerates them.  The X-43A, depicted in the artist's illustration above, might well propel itself past Mach 10 in future tests.
A Prominent Solar Prominence from SOHO (2004-03-30)

One of the most spectacular solar sights is a prominence.  A solar prominence is a cloud of solar gas held above the Sun's surface by the Sun's magnetic field.  Last month, NASA's Sun-orbiting SOHO spacecraft imaged an impressively large prominence hovering over the surface, pictured above.  The Earth would easily fit under the hovering curtain of hot gas.  A quiescent prominence typically lasts about a month, and may erupt in a Coronal Mass Ejection (CME) expelling hot gas into the Solar System.  Although somehow related to the Sun's changing magnetic field, the energy mechanism that creates and sustains a Solar prominence is still a topic of research.
M39: Open Cluster in Cygnus (2004-03-31)

Lying just at the limit of human perception is a picturesque starfield containing one of the larger open clusters on the northern sky.  Spanning an angle larger than the Moon, M39's relatively few stars lie only about 800 light years distant toward the constellation of Cygnus.  The above picture of M39 is a mosaic of 33 images taken by the WIYN telescope on Kitt Peak in Arizona, USA.  The stars in M39 are all about 300 million years old, much younger than the 5000 million years of our Sun.  Open clusters, also called galactic clusters, contain fewer and younger stars than globular clusters.  Also unlike globular clusters, open clusters are generally confined to the plane of our Galaxy.

Image credit: Heidi Schweiker
April Fools Day More Intense On Mars (2004-04-01)

Today, April 1st, astrophysicists have announced a surprising discovery - April Fools Day is more intense on Mars! Though the discovery is contrary to accepted theories of April Fools Day, researchers note that there are several likely causes for the severe martian April Fools phenomenon. For starters, gravity, the force that opposes comedy throughout the universe, is only about 3/8ths as strong on Mars' surface as it is on planet Earth. Also, a martian day, called a sol, lasts nearly 40 minutes longer than an earth day. And furthermore ... well, as soon as they think of some more reasons, they've promised to tell us. Happy April Fools day from the editors at APOD! Editors note: Mars rover Spirit recorded this image looking out toward the eastern horizon and the Columbia Hills over 2 kilometers in the distance. Its journey across this rocky martian terrain could take from 60 to 90 sols.
Mercury and Venus in the West (2004-04-02)

Doing their part in the ongoing dance of the planets, Mercury and Venus both reached their greatest elongation or maximum apparent distance from the Sun only a few days ago, on March 29th. Eager to record their celestial accomplishment, astronomer Jimmy Westlake snapped this view of the two inner most planets shining in western twilight skies above Yampa, Colorado, USA. The picture was taken using a digital camera mounted on a tripod. Mercury is easily the brightest celestial object near the horizon, appearing to the right of the foreground structure and just above a thin cloud silhouetted by fading sunlight. Still, near the top of the picture brilliant Venus dominates the scene as the magnificent evening star. After climbing in western skies throughout the month of March, Venus lies just below the Pleiades star cluster. Tonight and tomorrow night, skygazers can spot Venus at the southern edge of the Pleiades.

Image credit: Jimmy Westlake
(Colorado
Mountain College)
A Mystery In Gamma Rays (2004-04-03)

Gamma rays are the most energetic form of light, packing a million or more times the energy of visible light photons. If you could see gamma rays, the familiar skyscape of steady stars would be replaced by some of the most bizarre objects known to modern astrophysics -- and some which are unknown. When the EGRET instrument on the orbiting Compton Gamma-ray Observatory surveyed the sky in the 1990s, it cataloged 271 celestial sources of high-energy gamma-rays. Researchers identified some with exotic black holes, neutron stars, and distant flaring galaxies. But 170 of the cataloged sources, shown in the above all-sky map, remain unidentified. Many sources in this gamma-ray mystery map likely belong to already known classes of gamma-ray emitters and are simply obscured or too faint to be otherwise positively identified. However, astronomers have called attention to the ribbon of sources winding through the plane of the galaxy, projected here along the middle of the map, which may represent a large unknown class of galactic gamma-ray emitters. In any event, the unidentified sources could remain a mystery until the planned launch of the more sensitive Gamma-ray Large Area Space Telescope in 2007.
The Lost World of Lake Vida (2004-04-04)

A lake hidden beneath 19 meters of ice and gravel has been found near the bottom of the world that might contain an ecosystem completely separate from our own.  In a modern version of Sir Arthur Conan Doyle's classic book Lost World, NASA funded scientists are now plotting a mission to drill down into the lake and remove a sample of water from the lake for analysis.  Lake Vida, buried under Antarctic ice for over 2,500 years, is liquid only because of a high salt content that results from salt being expelled from water above as it turns to ice.  Previously, scientists drilled to within a few meters of the lake and indeed found frozen microbes.  Their existence bolsters speculation that similar microorganisms could be found in frozen brine beneath the surface of Mars.  If living organisms are found in Lake Vida, they may give an indication that life might even still exist under similar frozen ice-sheets, such as under the larger Lake Vostok, parts of Mars, and even moons of Jupiter such as Europa.  Pictured above, a robot meteorological station continues to monitor surface conditions over the ice-sealed lake.

Image credit: Thomas Nylen & 
Andrew Fountain 
(PSU), 
NASA, 
NSF
Russell Croman
A Berry Bowl of Martian Spherules (2004-04-05)

How were these unusual Martian spherules created?  Thousands of unusual gray spherules, made of iron and rock but dubbed blueberries, were found embedded in and surrounding rocks near the landing site of the robot Opportunity rover on Mars.  To help investigate their origin, Opportunity found a surface dubbed the Berry Bowl with an indentation that was rich in the Martian orbs.  The Berry Bowl is pictured above, imaged during rover's 48th Sol on Mars.  The average diameter of a blueberry is only about 4 millimeters.  By analyzing a circular patch in the rock surface to the left of the densest patch of spherules, Opportunity obtained data showing that the underlying rock has a much different composition than the hematite rich blueberries.  This information contributes to the growing consensus is that these small, strange, gray orbs were slowly deposited from a bath of dirty water.
Unusually Strong Cyclone Off the Brazilian Coast (2004-04-06)

How did this huge cyclone form?  An unusually strong storm -- perhaps the strongest storm in the recorded history of the South Atlantic Ocean -- crossed the coast of Brazil last week.  Cyclones this powerful, classified by some as the first ever Category 1 Hurricane, are very rare in the South Atlantic.  Tropical cyclones are large regions of low pressure with little vertical wind shear that typically form over regions of warm water, which power the cyclone through evaporation.  Reports of relatively cold air in the center indicate, however, that this storm was extratropical.  The storm was dubbed Caterina by local meteorologists, although no formal naming precedents exist in this part of the world.
Unusual Spiral Galaxy M66 (2004-04-07)

Why isn't spiral galaxy M66 symmetric?  Usually density waves of gas, dust, and newly formed stars circle a spiral galaxy's center and create a nearly symmetric galaxy.  The differences between M66's spiral arms and the apparent displacement of its nucleus are all likely caused by the tidal gravitational pull of nearby galaxy neighbor M65. Spiral galaxy M66, pictured above, spans about 100,000 light years, lies about 35 million light years distant, and is the largest galaxy in a group including M65 and NGC 3628 known as the Leo Triplet.  Like many spiral galaxies, the long and intricate dust lanes of M66 are seen intertwined with the bright stars and nebulas that light up the spiral arms.

Image credit: Canada-France-Hawaii Telescope
Elusive Jellyfish Nebula (2004-04-08)

Normally faint and elusive, the Jellyfish Nebula is caught in the net of this spectacular wide-field telescopic view. Flanked by two yellow-tinted stars at the foot of a celestial twin - Mu and Eta Geminorum - the Jellyfish Nebula is the brighter arcing ridge of emission with dangling tentacles just right of center. Here, the cosmic jellyfish is seen to be part of bubble-shaped supernova remnant IC 443, the expanding debris cloud from an exploded star some 5,000 light-years away. Also in view, emission nebula IC 444 nearly fills the field to the upper left, dotted with small blue reflection nebulae. Like its cousin in astrophysical waters, the Crab Nebula, IC 443 is known to harbor a neutron star, the collapsed core of the massive star that exploded over 30,000 years ago.

Image credit: Johannes Schedler
(Panther Observatory)
NGC 4565: Galaxy on the Edge (2004-04-09)

Magnificent spiral galaxy NGC 4565 is viewed edge-on from planet Earth. Also known as the Needle Galaxy for its narrow profile, bright NGC 4565 is a stop on many springtime telescopic tours of the northern sky as it lies in the faint but well-groomed constellation Coma Berenices. This sharp color image reveals the galaxy's bulging central core dominated by light from a population of older, yellowish stars. The core is dramatically cut by obscuring dust lanes which lace NGC 4565's thin galactic plane. A large island universe similar to our own Milky Way Galaxy, NGC 4565 is only about 30 million light-years distant, but over 100,000 light-years in diameter.  In fact, some consider NGC 4565 to be a prominent celestial masterpiece Messier missed.
Facing NGC 6946 (2004-04-10)

From our vantage point in the Milky Way Galaxy, we see NGC 6946 face-on. The big beautiful spiral galaxy is located just 10 million light-years away, behind a veil of foreground stars in the high and far-off constellation of Cepheus. Looking from the bright core outward along the loose, fragmented spiral arms, the galaxy's colors show a striking change from the yellowish light of old stars in the galaxy's center to young blue star clusters and reddish star forming regions. NGC 6946 is also bright in infrared light and rich in gas and dust, exhibiting a high star birth and death rate. In fact, during the 20th century, at least six supernovae, the death explosions of massive stars, were discovered in NGC 6946. In this sharp composite color digital image, a small barred structure is just visible at the gorgeous galaxy's core.

Image credit: Robert Gendler
Journey to the Center of the Galaxy (2004-04-11)

In Jules Verne's science fiction classic A Journey to the Center of the Earth, Professor Liedenbrock and his fellow explorers encounter many strange and exciting wonders. What wonders lie at the center of our Galaxy? Astronomers know of some of the bizarre objects that exist there, like vast cosmic dust clouds, bright star clusters, swirling rings of gas, and even a supermassive black hole. Much of the Galactic Center is shielded from our view in visible light by the intervening dust and gas, but it can be explored using other forms of electromagnetic radiation. This haunting wide angle image of the Galactic Center region in infrared light was constructed using data from the Midcourse Space Experiment (MSX) satellite. The image maps three mid-infrared bands, otherwise invisible to human eyes, into visible blue, green, and red colors revealing the thermal emission from dust clouds near the galactic center that have been heated by starlight. The galactic plane runs along the middle of this image while the galactic center itself is the bright spot at picture center. The field of view of this cropped picture is about 1.5 by 2.5 degrees.
Apollo 17 Panorama: Astronaut Running (2004-04-12)

What would it be like to explore the surface of another world? In 1972 during the Apollo 17 mission, astronaut Harrison Schmitt found out first hand.  In this case, the world was Earth's own Moon.  In this recently compiled panorama of lunar photographs originally taken by astronaut Eugene Cernan, the magnificent desolation of the barren Moon is apparent.  Visible above and by scrolling right are lunar rocks in the foreground, lunar mountains in the background, some small craters, a lunar rover, and astronaut Schmidt on his way back to the rover. A few days after this image was taken, humanity left the Moon and has yet to return.

Image credit: M. Constantine (moonpans.com)