juliensimon/nasa-apod huggingface dataset:
Analemma of the Moon (2005-07-13)

An analemma is that figure-8 curve you get when you mark the position of the Sun at the same time each day for one year. But the trick to imaging an analemma of the Moon is to understand that on average the Moon returns to the same position in the sky about 51 minutes later each day. So, if you photograph the Moon 51 minutes later on successive days, over one lunation or lunar month it will trace out an analemma-like curve as the actual position of the Moon wanders compared to the average -- due to the Moon's tilted and elliptical orbit. For this excellent demonstration of the lunar analemma, astronomer Rich Richins chose the lunar month containing this year's northern hemisphere summer solstice. The southernmost Full Moon rises at the lower right above the Organ Mountains in southern New Mexico, USA, with the New Moon phase at the upper left. The multiple exposure image required some digital manipulation, particularly to include thin crescent phases in daytime skies.

Image credit: Rich
Richins
Star Trails Over Vienna (2005-07-14)

As the Earth spins on its axis, the sky seems to rotate around us.  This motion, called diurnal motion, produces the beautiful concentric trails traced by stars during time exposures.  In the middle of the picture is the North Celestial Pole (NCP), easily identified as the point in the sky at the center of all the star trail arcs.  The star Polaris, commonly known as the North Star, made the very short bright circle near the NCP.  Full circle star trails are pictured over Vienna, Austria.   This image, a relatively short exposure followed by a digital trick, could not have been taken during a single night because 24-hours are needed for one full rotation, and the Sun is sure to dominate the frame at some time.

Image credit: Peter Wienerroither  
(U. Wien)
Reflections on the Inner Solar System (2005-07-15)

Only Mars is missing from this reflective view of the major rocky bodies of the inner solar system. Captured on July 8th, the serene, twilight picture looks out over the Flat Tops Wilderness area from near Toponas, Colorado, USA and includes planets Mercury, Venus, Earth, and Earth's large natural satellite, the Moon. The Moon is in a young crescent phase about three degrees above bright planet Venus. Forest fires contribute to a layer of smoke in Earth's sky that almost hides planet Mercury, still visible very near the horizon. Just a week earlier Venus and Mercury were joined by Saturn, forming a notable grouping in the west also enjoyed by skygazers across planet Earth.

Image credit: Jimmy
Westlake
(Colorado
Mountain College)
Galaxy Group HCG 87 (2005-07-16)

Posing for this cosmic family photo are the galaxies of HCG (Hickson Compact Group) 87, about four hundred million light-years distant toward the amphibious constellation Capricornus. The large edge-on spiral near picture center, the fuzzy elliptical galaxy immediately to its right, and the spiral near the top of the image are identified members of the group, while the small spiral galaxy in the middle is likely a more distant background galaxy. In any event, a careful examination of the deep image reveals other galaxies which certainly lie far beyond HCG 87. While not exactly locked in a group hug, the HCG 87 galaxies are interacting gravitationally, influencing their fellow group members' structure and evolution. This image is from the commissioning phase of an instrument on the Gemini Observatory's South Telescope at Cerro Pachon, Chile. It compares favorably with views of this photogenic galaxy group recorded by the Hubble Space Telescope.
The Center of Centaurus A (2005-07-17)

A fantastic jumble of young blue star clusters, gigantic glowing gas clouds, and imposing dark dust lanes surrounds the central region of the active galaxy Centaurus A.  This mosaic of Hubble Space Telescope images taken in blue, green, and red light has been processed to present a natural color picture of this cosmic maelstrom. Infrared images from the Hubble have also shown that hidden at the center of this activity are what seem to be disks of matter spiraling into a black hole with a billion times the mass of the Sun! Centaurus A itself is apparently the result of a collision of two galaxies and the left over debris is steadily being consumed by the black hole. Astronomers believe that such black hole central engines generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies. But for an active galaxy Centaurus A is close, a mere 10 million light-years away, and is a relatively convenient laboratory for exploring these powerful sources of energy.
Deep Impact on Comet Tempel 1 from Hubble (2005-07-18)

It was a human-made event visible across the Solar System.  At the direction of terrestrial scientists, a refrigerator-sized probe from the Deep Impact mission struck Comet Tempel 1 on July 4 at over 35,000 kilometers per hour.  The unexpectedly bright explosion was not nuclear but rather originated from a large plume that reflected back sunlight. Pictured above is how the event looked to the Earth-orbiting Hubble Space Telescope.  A large cloud of bright material is seen emanating from the comet's nucleus and then dispersing.  The area encompassing the comet became over two times brighter in the hours after the impact. Astronomers will continue to study the images and data returned by Deep Impact to better determine the nature of Comet Tempel 1 and discern clues about the formation dynamics of the early Solar System.  Norwegian APOD mirror now available
A Nearby Supernova in M51 (2005-07-19)

One of the nearest supernovas of recent years was discovered late last month in the bright nearby galaxy M51.  It is visible on the right of the above before and after images of the picturesque spiral.   Can you spot it? The supernova, discovered originally by Wolfgang Kloehr and now dubbed 2005cs, is still near its maximum brightness and visible with a telescope toward the constellation of the Hunting Dogs (Canes Venatici). The supernova has been identified as a Type II but has an unusual brightness history, creating speculation that is similar in nature to the brightest supernova of modern times: 1987A. The progenitor star has been identified as a bright blue star. Although hundreds of supernovas are discovered each year by automated searches, nearby supernova are rare and important because they frequently become bright enough to be studied by many telescopes and are near enough for their (former) host star and immediate surroundings to be spatially resolved. Supernova 2005cs may have left behind a core that has been compressed into a neutron star or black hole.

Image credit: R Jay GaBany 
(Cosmotography.com)
Water Ice in a Martian Crater (2005-07-20)

What lies on the floor of this Martian crater?  A frozen patch of water ice.  The robotic Mars Express spacecraft took the above image in early February.   The ice pocket was found in a 35-kilometer wide crater that resides 70 degrees north of the Martian equator.  There, sunlight is blocked by the 300-meter tall crater wall from vaporizing the water-ice on the crater floor into the thin Martian atmosphere. The ice pocket may be as deep as 200 meters thick.  Frost can be seen around the inner edge on the upper right part of the crater, while part of the lower left crater wall is bathed in sunlight.  The existence of water-ice pockets inside craters near the Martian North Pole, like that pictured above and others noted previously, give clues not only about surface conditions in the Martian past but also possible places where future water-based astronauts might do well to land.

Image credit: Nature
X-Ray Stars of 47 Tuc (2005-07-21)

Visible light images show the central region of globular cluster 47 Tucanae is closely packed, with stars less than a tenth of a light-year apart. This Chandra false-color x-ray view of central 47 Tuc also shows the cluster is a popular neighborhood for x-ray stars, many of which are "normal" stars co-orbiting with extremely dense neutron stars -- stars with the mass of the Sun but the diameter of Manhattan Island. One of the most remarkable of these exotic binary systems is cataloged as 47 Tuc W, a bright source near the center of this image. The system consists of a low mass star and a a neutron star that spins once every 2.35 milliseconds. Such neutron stars are known to radio astronomers as millisecond pulsars, believed to be driven to such rapid rotation by material falling from the normal star onto its dense companion. In fact, x-ray observations of the 47 Tuc W system link this spin-up mechanism observed to operate in other x-ray binary stars with fast rotating millisecond pulsars.
Tethys, Rings, and Shadows (2005-07-22)

Seen from ice moon Tethys, rings and shadows would play across fantastic views of the Saturnian system. Haven't dropped in on Tethys lately? Then this gorgeous ringscape from the Cassini spacecraft will have to do for now. Caught in sunlight just below and left of picture center, Tethys itself is about 1,000 kilometers in diameter and orbits not quite five saturn-radii from the center of the gas giant planet. At that distance (around 300,000 kilometers) it is well outside Saturn's main bright rings, but Tethys is still one of five major moons that find themselves within the boundaries of the faint and tenuous outer E ring. Discovered in the 1980s, two very small moons Telesto and Calypso are locked in stable locations along Tethys' orbit. Telesto precedes and Calypso follows Tethys as the trio circles Saturn.
Ringed Nebulae (2005-07-23)

This gorgeous celestial vista is centered on one of the Milky Way's own planetary nebulae, M57, the famous Ring Nebula. The wide view is a composite of three exposures; one to record the details of the inner roughly one light-year span of the familiar nebula, one to record the surprisingly intricate but faint outer rings of glowing hydrogen gas, and one to pick up the rich assortment of distant background galaxies. By chance, one of the background galaxies, IC 1296 at the upper left, is close enough to show its barred, spiral structure making an attractive visual comparison with M57. Interestingly, though IC 1296 is 200 million light-years away compared to only 2 thousand light-years for M57, a faint ring is also apparent around the outer reaches of the distant spiral galaxy.

Image credit: Tony and Daphne Hallas
A Chicago Meteorite Fall (2005-07-24)

If you wait long enough, a piece of outer space itself will come right to you.  As Colby Navarro worked innocently on the computer, a rock from space crashed through the roof, struck the printer, banged off the wall, and came to rest near the filing cabinet.  This occurred around midnight on March 26, 2003 in Park Forest, Illinois, USA, near Chicago.  The meteorite, measuring about 10 cm across, was one of several that fell near Chicago that day as part of a tremendous fireball.  Pictured above is the resulting hole in the ceiling, while the inset image shows the wall dent and the meteorite itself.  Although the vast majority of meteors is much smaller and burn up in the Earth's atmosphere, the average homeowner should expect to repair direct meteor damage every hundred million years.

Image credit: Ivan and Colby Navarro
Unusual Gas Filaments Surround Galaxy NGC 1275 (2005-07-25)

How were the unusual gas filaments surrounding galaxy NGC 1275 created?  No one is sure. Galaxy NGC 1275 is the central dominant galaxy of the Perseus Cluster of Galaxies, a cluster with many member galaxies visible in the above image.  In visible light, NGC 1275 appears to show a spectacular collision between two distinct galaxies.  The galaxy and cluster are also bright emitters of X-rays.  The unusual gas filaments are shown above in a very specific color of light emitted by hydrogen, here artificially colored pink.  Possible origins for the filaments may involve details of the collision between the two galaxies, or alternatively, interactions between a galactic center black hole and the surrounding intracluster gas.  NGC 1275, pictured above, spans about 100,000 light years and lies about 230 million light years distant toward the constellation of Perseus.

Image credit: C. Conselice
Hyperion: Sponge Moon of Saturn (2005-07-26)

Why is Saturn's moon Hyperion textured like a sponge?  Recent high-resolution images from the robot Cassini spacecraft orbiting Saturn show Hyperion to be an even stranger place than thought before.  Previously, it was known that the length of a day on Hyperion is unpredictable.  The moon's highly elliptical orbit around Saturn, its highly non-spherical shape, and its locked 4:3 orbital resonance with Titan torque Hyperion around so much it is hard to predict when the Sun will rise next.  The newly imaged craters on the unusually coarse surface are surely the result of impacts, but for some reason have dark centers.  The low density of Hyperion indicates it might even be a spelunker's paradise, riddled with tremendous caverns.
America Returns to Human Space Flight (2005-07-27)

NASA's launch of the massive Space Shuttle Discovery yesterday brought a nation known for its tremendous space program back to human space flight.  Shuttle flights had been suspended for over two years previously following the tragic loss of the Space Shuttle Columbia crew on 2003 February 1.  The complex, powerful Space Shuttle Discovery lifted a crew of seven into an Earth orbit that will bring them to the International Space Station (ISS).  The shuttle crew will deliver supplies to the ISS, perform repairs, and test new methods for inspecting and repairing the shuttle's thermal protection system.  Three space walks are planned.  This Return to Flight Mission STS-114 is pictured above launching from Pad 39B on Cape Canaveral, Florida.
Spherical Planetary Nebula Abell 39 (2005-07-28)

Ghostly in appearance, Abell 39 is a remarkably simple, spherical nebula about five light-years across. Well within our own Milky Way galaxy, the cosmic sphere is roughly 7,000 light-years distant toward the constellation Hercules. Abell 39 is a planetary nebula, formed as a once sun-like star's outer atmosphere was expelled over a period of thousands of years. Still visible, the nebula's central star is evolving into a hot white dwarf. Although faint, the nebula's simple geometry has proven to be a boon to astronomers exploring the chemical abundances and life cycles of stars. In this deep image recorded under dark night skies, very distant background galaxies can be found -- some visible right through the nebula itself.

Image credit: Jim Misti 
(Misti
Mountain Observatory)
ISS and Discovery Transit the Sun (2005-07-29)

That large sunspot near the right edge of the Sun is actually not a sunspot at all. It's the International Space Station (ISS) and the Space Shuttle Discovery on mission STS-114. In the past, many skygazers have spotted the space station and space shuttles as bright stars gliding through twilight skies, still glinting in the sunlight while orbiting 200 kilometers or so above the Earth's surface. But here, astronomer Anthony Ayiomamitis took advantage of a rarer opportunity to record the spacefaring combination moving quickly in silhouette across the solar disk. He snapped the picture on Thursday, July 28th from Athens, Greece. Launched on Tuesday, Discovery joined with the ISS Thursday, making the already large space station seem to loom even larger.

Image credit: Anthony Ayiomamitis
M106 in Canes Venatici (2005-07-30)

Close to the Great Bear (Ursa Major) and surrounded by the stars of the Hunting Dogs (Canes Venatici), this celestial nebula was discovered in 1781 by the metric French astronomer Pierre Mechain. Later, it was added to the catalog of his friend and colleague Charles Messier as M106. Modern deep telescopic views reveal it to be an island universe -- a spiral galaxy around 30 thousand light-years across located only about 21 million light-years beyond the stars of the Milky Way. Youthful blue star clusters and reddish stellar nurseries trace the striking spiral arms of M106. Seen so clearly in this beautiful image, the galaxy's bright core is also visible across the spectrum from radio to x-rays, making M106 a nearby example of the Seyfert class of active galaxies. The bright core of a Seyfert galaxy is believed to be powered by matter falling into a massive central black hole.   News Flash: Object Larger than Pluto Discovered in Distant Solar System
Solar System Object Larger than Pluto Discovered (2005-07-31)

Is that a tenth planet?  A faint, slowly moving dot discovered by computer shows clear signs of being a deep Solar System object at least as large as Pluto.  The object, designated 2003 UB313, is currently situated nearly 100 times the Earth-Sun distance -- over twice the average Pluto-Sun distance.  That far out, the only way a single round object could be as bright as 2003 UB313 would be if it is at least as large as Pluto and completely reflective.  Since 2003 UB313 is surely not completely reflective, it could be substantially larger.  One of the discovery frames is shown above digitally expanded and artificially brightened.  2003 UB313 was identified initially on frames taken by the automated 1.2-meter Samuel Oschin Telescope at Palomar Observatory in California, USA.
2003 UB313: A Tenth Planet? (2005-08-01)

Has a tenth planet been discovered?  A newly discovered object, designated 2003 UB313 and located more than twice the distance of Pluto, is expected to be at least as large as Pluto and probably larger, given current measurements. 2003 UB313's dimness and highly tilted orbit (44 degrees) prevented it from being discovered sooner.  Many astronomers speculate that numerous other icy objects larger than Pluto likely exist in the Kuiper Belt of the far distant Solar System.  If so, and if some are found closer in than 2003 UB313, it may be premature to call 2003 UB313 the tenth planet. Illustrated above is an artist's drawing showing how 2003 UB313 might look.  The unusually bright star on the right is the Sun.  Much of the world eagerly await the decision by the International Astronomical Union on whether 2003 UB313 will be designated a planet or given a name without subscripts.
A Shuttle Back Flip at the Space Station (2005-08-02)

Last week, crew members of the International Space Station (ISS) watched carefully as the Space Shuttle Discovery did a planned but unusual back flip upon approach.  Discovery Commander Eileen Collins guided the shuttle through the flip, which was about 200 meters from the ISS when the above picture was taken.  The ISS crew took detailed images of the dark heat shield tiles underneath during a 90-second photo shoot.   The images are being analyzed to assess the condition of the dark heat shield.  Later the shuttle docked with the space station.  On the more usually photographed top side of the Space Shuttle, the above image shows Discovery's cargo bay doors open toward a distant Earth below.
The Busy Center of the Lagoon Nebula (2005-08-03)

Stars are battling gas and dust in the Lagoon Nebula but the photographers are winning. Also known as M8, this photogenic nebula is visible even without binoculars towards the constellation of Sagittarius. The energetic processes of star formation create not only the colors but the chaos.  The red-glowing gas results from high-energy starlight striking interstellar hydrogen gas.  The dark dust filaments that lace M8 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions.  This spectacular portion of the Lagoon Nebula was created in scientifically-assigned colors from light emitted in very specific colors by hydrogen, silicon, and oxygen.  The light from M8 we see today left about 5000 years ago. Light takes about 50 years to cross this section of M8.

Image credit: Michael Sherick
Stars Young and Old (2005-08-04)

Galactic or open star clusters are relatively young swarms of bright stars born together near the plane of our Milky Way Galaxy. Separated by about a degree on the sky, two nice examples are M46 (upper left) 5,400 light-years in the distance and M47 (lower right) only 1,600 light-years away toward the nautical constellation Puppis. Around 300 million years young M46 contains a few hundred stars in a region about 30 light-years across. Aged 80 million years, M47 is a smaller but looser cluster of about 50 stars spanning 10 light-years. But this portrait of stellar youth also contains an ancient interloper. The small, colorful patch of glowing gas in M46 is actually the planetary nebula NGC 2438 - the final phase in the life of a sun-like star billions of years old. NGC 2438 is estimated to be only 3,000 light-years distant and likely represents a foreground object, only by chance appearing along our line of sight to youthful M46.

Image credit: Chris Hetlage
HD 188753: Triple Sunset (2005-08-05)

Although it looks like fiction, this artist's vision of sunset on an alien world is based on fact -- the recent discovery of a hot, jupiter-sized planet orbiting in triple star system HD 188753. Only 149 light-years away in the constellation Cygnus, HD 188753's massive planet was detected by astronomer Maciej Konacki after analyzing detailed spectroscopic data from the Keck Observatory. The large planet itself is depicted at the upper left in this imagined view from the well-illuminated surface of a hypothetical rocky moon. From this perspective, the closest, hottest and most massive star in the triple system, a star only a little hotter than the Sun, has set below distant peaks. The two other suns nearing the horizon are both cooler and farther from the large planet. While other hot, jupiter-like planets are known to orbit nearby stars, the "crowded" multiple star nature of this system challenges current theories of planet formation.
Raining Perseids (2005-08-06)

Comet dust rained down on planet Earth last August, streaking through dark skies in the annual Perseid meteor shower. So, while enjoying the anticipated space weather, astronomer Fred Bruenjes recorded a series of many 30 second long exposures spanning about six hours on the night of August 11/12 using a wide angle lens. Combining those frames which captured meteor flashes, he produced this dramatic view of the Perseids of summer. Although the comet dust particles are traveling parallel to each other, the resulting shower meteors clearly seem to radiate from a single point on the sky in the eponymous constellation Perseus. The radiant effect is due to perspective, as the parallel tracks appear to converge at a distance. Bruenjes notes that there are 51 Perseid meteors in the composite image, including one seen nearly head-on. This year, the Perseids Meteor Shower will peak in the early morning hours on Friday, August 12.

Image credit: Fred Bruenjes
Dueling Auroras (2005-08-07)

Will it be curtains for one of these auroras?   A quick inspection indicates that it is curtains for both, as the designation "curtains" well categorizes the type of aurora pattern pictured.  Another (informal) type is the corona. The above auroras resulted from outbursts of ionic particles from the Sun during the last week of 2001 September.  A polarity change in the solar magnetic field at the  Earth then triggered auroras over the next few days. The above picture was taken on 2001 October 3 as fleeting space radiation pelted the Earth's atmosphere high above the Yukon in  Canada.

Image credit: Phil Hoffman