juliensimon/nasa-apod huggingface dataset:
Stephan's Quintet (2009-09-11)

The first identified compact galaxy group, Stephan's Quintet is featured in this stunning image from the newly upgraded Hubble Space Telescope. About 300 million light-years away, only four galaxies of the group are actually locked in a cosmic dance of repeated close encounters. The odd man out is easy to spot, though. The four interacting galaxies (NGC 7319, 7318A, 7318B, and 7317) have an overall yellowish cast and tend to have distorted loops and tails, grown under the influence of disruptive gravitational tides. But the bluish galaxy at the upper left (NGC 7320) is much closer than the others. A mere 40 million light-years distant, it isn't part of the interacting group. In fact, individual stars in the foreground galaxy can be seen in the sharp Hubble image, hinting that it is much closer than the others. Stephan's Quintet lies within the boundaries of the high flying constellation Pegasus.
Summer Night in Astronomy Town (2009-09-12)

This serene view records a late summer night sky over the rolling, green hills of planet Earth. It was taken near the rural village of Saadat Shahr, Fars province, in southern Iran. Saadat Shahr is also known as Astronomy Town, as the inhabitants have demonstrated a remarkable passion for sky gazing. Fittingly, this Astronomy Town sky view finds a lovely part of the Milky Way near picture center. The three brightest stars are the stars of the Summer Triangle, Deneb in Cygnus (top), Altair in Aquila (left), and Vega in Lyra (right). The foreground landscape, illuminated by Astronomy Town lights, includes a kind of wild pistachio tree common in the region. To identify the stars and constellations, just slide your cursor over the image.

Image credit: Babak
Tafreshi
The Holographic Principle (2009-09-13)

Is this picture worth a thousand words?  According to the Holographic Principle, the most information you can get from this image is about 3 x 1065 bits for a normal sized computer monitor.  The Holographic Principle, yet unproven, states that there is a maximum amount of information content held by regions adjacent to any surface.  Therefore, counter-intuitively, the information content inside a room depends not on the volume of the room but on the area of the bounding walls.  The principle derives from the idea that the Planck length, the length scale where quantum mechanics begins to dominate classical gravity, is one side of an area that can hold only about one bit of information.  The limit was first postulated by physicist Gerard 't Hooft in 1993.  It can arise from generalizations from seemingly distant speculation that the information held by a black hole is determined not by its enclosed volume but by the surface area of its event horizon.  The term "holographic" arises from a hologram analogy where three-dimension images are created by projecting light though a flat screen.  Beware, other people looking at the above image may not claim to see 3 x 1065 bits -- they might claim to see a teapot.

Image credit: E. Winfree,
K. Fleischer, A. Barr et al.
(Caltech)
The Center of Globular Cluster Omega Centauri (2009-09-14)

What is left over after stars collide?  To help answer this question, astronomers have been studying the center of the most massive ball of stars in our Milky Way Galaxy.  In the center of globular cluster Omega Centauri, stars are packed in 10,000 times more densely than near our Sun.  Pictured above, the newly upgraded Hubble Space Telescope has resolved the very center of Omega Centauri into individual stars.  Visible are many faint yellow-white stars that are smaller than our Sun, several yellow-orange stars that are Red Giants, and an occasional blue star.  When two stars collide they likely either combine to form one more massive star, or they stick, forming a new binary star system.  Close binary stars interact, sometimes emitting ultraviolet or X-ray light when gas falls from one star onto the surface of a compact companion such as a white dwarf or neutron star.  Two such binaries have now been located in Omega Centauri's center.  The star cluster lies about 15,000 light-years away and is visible toward the constellation of Centaurus.
NGC 6888: The Crescent Nebula (2009-09-15)

NGC 6888, also known as the Crescent Nebula, is a cosmic bubble about 25 light-years across, blown by winds from its central, bright, massive star. This beautiful portrait of the nebula is from the Isaac Newton Telescope at Roque de los Muchachos Observatory in the Canary Islands. It combines a composite color image with narrow band data that isolates light from hydrogen and oxygen atoms in the wind-blown nebula. The oxygen atoms produce the blue-green hue that seems to enshroud the detailed folds and filaments. NGC 6888's central star is classified as a Wolf-Rayet star (WR 136). The star is shedding its outer envelope in a strong stellar wind, ejecting the equivalent of the Sun's mass every 10,000 years.  The nebula's complex structures are likely the result of this strong wind interacting with material ejected in an earlier phase. Burning fuel at a prodigious rate and near the end of its stellar life this star should ultimately go out with a bang in a spectacular supernova explosion. Found in the nebula rich constellation Cygnus, NGC 6888 is about 5,000 light-years away.

Image credit: Daniel López
The Tarantula Zone (2009-09-16)

The Tarantula Nebula is more than 1,000 light-years in diameter -- a giant star forming region within our neighboring galaxy the Large Magellanic Cloud (LMC). That cosmic arachnid lies left of center in this sharp, colorful telescopic image taken through narrow-band filters. It covers a part of the LMC over 2,000 light-years across. Within the Tarantula (NGC 2070), intense radiation, stellar winds and supernova shocks from the central young cluster of massive stars, cataloged as R136, energize the nebular glow and shape the spidery filaments. Around the Tarantula are other violent star-forming regions with young star clusters, filaments and bubble-shaped clouds. The rich field is about as wide as the full Moon on the sky, located in the southern constellation Dorado.

Image credit: John P. Gleason
Ultraviolet Andromeda (2009-09-17)

Taken by a telescope onboard NASA's Swift satellite, this stunning vista represents the highest resolution image ever made of the Andromeda Galaxy (aka M31) - at ultraviolet wavelengths. The mosaic is composed of 330 individual images covering a region 200,000 light-years wide. It shows about 20,000 sources, dominated by hot, young stars and dense star clusters that radiate strongly in energetic ultraviolet light. Of course, the Andromeda Galaxy is the closest large spiral galaxy to our own Milky Way, at a distance of some 2.5 million light-years. To compare this gorgeous island universe's appearance in optical light with its ultraviolet portrait, just slide your cursor over the image.
Take My Hand (2009-09-18)

Get out your red/blue glasses and check out this close-up of spacesuited NASA astronaut John Olivas outside the International Space Station. Carefully constructed from two photographs (ISS020-E-038481, ISS02-0E-038482) taken during space shuttle orbiter Discovery's latest visit to the orbiting outpost, the 3D anaglyph creates the compelling illusion that you can actually reach out and take his gloved hand. The photographer, fellow spacewalker ESA astronaut Christer Fuglesang, along with ISS structures and planet Earth's horizon, are reflected in Olivas' helmet visor. Last Friday, the two returned to Earth along with the rest of Discovery's crew, landing at Edwards Air Force base in California.
NGC 3621: Far Beyond the Local Group (2009-09-19)

Far beyond the local group of galaxies lies NGC 3621, some 22 million light-years away. Found in the multi-headed southern constellation Hydra, the winding spiral arms of this gorgeous island universe are loaded with luminous young star clusters and dark dust lanes. Still, for earthbound astronomers NGC 3621 is not just another pretty face-on spiral galaxy. Some of its brighter stars have been used as standard candles to establish important estimates of extragalactic distances and the scale of the Universe. This beautiful image of NGC 3621 traces the loose spiral arms far from the galaxy's brighter central regions that span some 100,000 light-years. Spiky foreground stars in our own Milky Way Galaxy and even more distant background galaxies are scattered across the colorful skyscape.

Image credit: Robert Gendler
Ganymede Enhanced (2009-09-20)

What does the largest moon in the Solar System look like? Ganymede, larger than even Mercury and Pluto, has a surface speckled with bright young craters overlying a mixture of older, darker, more cratered terrain laced with grooves and ridges. Like Earth's Moon, Ganymede keeps the same face towards its central planet, in this case Jupiter. In this historic and detailed image mosaic taken by the Galileo spacecraft that orbited Jupiter from 1995 to 2003, the colors of this planet-sized moon have been enhanced to increase surface contrasts. The violet shades extending from the top and bottom are likely due to frost particles in Ganymede's polar regions. Possible future missions to Jupiter are being proposed that can search Europa and Ganymede for deep oceans that may harbor elements thought important for supporting life.
Abell 370: Galaxy Cluster Gravitational Lens (2009-09-21)

What is that strange arc? While imaging the cluster of galaxies Abell 370, astronomers had noted an unusual arc to the right of many cluster galaxies.  Although curious, one initial response was to avoid commenting on the arc because nothing like it had ever been noted before.  In the mid-1980s, however, better images allowed astronomers to identify the arc as a prototype of a new kind of astrophysical phenomenon -- the gravitational lens effect of entire cluster of galaxies on background galaxies. Today, we know that this arc actually consists of two distorted images of a fairly normal galaxy that happened to lie far behind the huge cluster.  Abell 370's gravity caused the background galaxies' light -- and others -- to spread out and come to the observer along multiple paths, not unlike a distant light appears through the stem of a wine glass. In mid-July, astronomers used the just-upgraded Hubble Space Telescope to image Abell 370 and its gravitational lens images in unprecedented detail.  Almost all of the yellow images pictured above are galaxies in the Abell 370 cluster. An astute eye can pick up many strange arcs and distorted arclets, however, that are actually images of more distant galaxies. Studying Abell 370 and its images gives astronomers a unique window into the distribution of normal and dark matter in galaxy clusters and the universe.
Aurora Over Yellowknife (2009-09-22)

Sometimes, after your eyes adapt to the dark, a spectacular sky appears. In this case, a picturesque lake lies in front of you, beautiful green auroras flap high above you, brilliant stars shine far in the distance, and a brilliant moon shines just ahead of you. This digitally fused panorama was captured earlier this month from Yellowknife, Northwest Territories, Canada, and includes the Pleiades open cluster of stars just to the upper right of the Moon. Since auroras are ultimately started by solar activity, this current flurry of auroras is somewhat surprising, given the historic lack of sunspots and other activity on the Sun over the past two years. This time of year is known as aurora season, however, for noted average increases in auroras. The reason for the yearly increase is not known for sure, but possibly relates to the tilt of the Earth creating a more easily traversable connection between the Earth's magnetic field and the magnetic field of the Sun's changing wind streams.

Image credit: Yuichi Takasaka
(Blue Moon Promotions),
TWAN
CoRoT Satellite Discovers Rocky Planet (2009-09-23)

How similar is exoplanet CoRoT-7b to Earth?  The newly discovered  extra-solar planet is the closest physical match yet, with a mass about five Earths and a radius of about 1.7 Earths. Also, the home star to CoRoT-7b, although 500 light years distant, is very similar to our Sun. Unfortunately, the similarities likely end there, as CoRoT-7b orbits its home star well inside the orbit of Mercury, making its year last only 20 hours, and making its peak temperature much hotter than humans might find comfortable. CoRoT-7b was discovered in February by noting a predictable slight decrease in the brightness of its parent star.  Pictured above, an artist's depiction shows how CoRoT-7b might appear in front of its parent star.  The composition of CoRoT-7b remains unknown, but given its size and mass, it cannot be a gas giant like Jupiter, and is very likely composed predominantly of rock.  Future observations will likely narrow the composition of one of the first known rocky planets discovered outside of our Solar System.
Equinox Sunset (2009-09-24)

Often inspiring, or offering a moment for contemplation, a sunset is probably the most commonly photographed celestial event. But this uncommonly beautiful sunset picture was taken on a special day, the Equinox on September 22. Marking the astronomical change of seasons, on that day Earth dwellers experienced nearly 12 hours of daylight and 12 hours of darkness (an equal night).  Reflected in the calm waters of Lake Balaton with a motionless sailboat in silhouette, the Sun is setting due west and heading south across the celestial equator. In the background lies the Benedictine Archabbey of Tihany, Hungary.

Image credit: Tamas Ladanyi
Gigagalaxy Zoom: Galactic Center (2009-09-25)

From Sagittarius to Scorpius, the central Milky Way is a truly beautiful part of planet Earth's night sky. The gorgeous region is captured here, an expansive gigapixel mosaic of 52 fields spanning 34 by 20 degrees in 1200 individual images and 200 hours of exposure time. Part of ESO's Gigagalaxy Zoom Project, the images were collected over 29 nights with a small telescope under the exceptionally clear, dark skies of the ESO Paranal Observatory in Chile. The breathtaking cosmic vista shows off intricate dust lanes, bright nebulae, and star clusters scattered through our galaxy's rich central starfields. Starting on the left, look for the Lagoon and Trifid nebulae, the Cat's Paw, the Pipe dark nebula, and the colorful clouds of Rho Ophiuchi and Antares (right).

Image credit: Stéphane Guisard
Gigagalaxy Zoom: Milky Way (2009-09-26)

Our magnificent Milky Way Galaxy sprawls across this ambitious all-sky panorama. In fact, at 800 million pixels the full resolution mosaic strives to show all the stars the eye can see in planet Earth's night sky. Part of ESO's Gigagalaxy Zoom Project, the mosaicked images were recorded over several months of 2008 and 2009 at exceptional astronomical sites; the Atacama Desert in the southern hemisphere and the Canary Islands in the northern hemisphere. Also capturing bright planets and even a comet, the individual frames were stitched together and mapped into a single, flat, apparently seamless 360 by 180 degree view. The final result is oriented so the plane of our galaxy runs horizontally through the middle with the bulging Galactic Center at image center. Below and right of center are the Milky Way's satellite galaxies, the Magellanic Clouds.

Image credit: Serge Brunier
To Fly Free in Space (2009-09-27)

At about 100 meters from the cargo bay of the space shuttle Challenger, Bruce McCandless II was farther out than anyone had ever been before.  Guided by a Manned Maneuvering Unit (MMU), astronaut McCandless, pictured above, was floating free in space. McCandless and fellow NASA astronaut Robert Stewart were the first to experience such an "untethered space walk" during Space Shuttle mission 41-B in 1984.  The MMU works by shooting jets of nitrogen and has since been used to help deploy and retrieve satellites.  With a mass over 140 kilograms, an MMU is heavy on Earth, but, like everything, is weightless when drifting in orbit. The MMU was replaced with the SAFER backpack propulsion unit.
Water Discovered on the Moon (2009-09-28)

Water has been discovered on the surface of the Moon.  No lakes have been found, but rather NASA's Moon Mineralogy Mapper aboard India's new Chandrayaan-1 lunar orbiter radios back that parts of the Moon's surface absorb a very specific color of light identified previously only with water. Currently, scientists are trying to fit this with other facts about the Moon to figure out how much water is there, and even what form this water takes.  Unfortunately, even the dampest scenarios leave our moon dryer than the driest of Earth's deserts.  A fascinating clue being debated is whether the water signal rises and falls during a single lunar day.   If true, the signal might be explainable by hydrogen flowing out from the Sun and interacting with oxygen in the lunar soil.  This could leave an extremely thin monolayer of water, perhaps only a few molecules thick. Some of the resulting water might subsequently evaporate away in bright sunlight. Pictured above, the area near a crater on the far side of the Moon shows a relatively high abundance of water-carrying minerals in false-color blue.  Next week, the new LCROSS satellite will release an impactor that will strike a permanently shadowed crater near the lunar south pole to see if any hidden water or ice sprays free there.
Orion in Gas, Dust, and Stars (2009-09-29)

The constellation of Orion holds much more than three stars in a row.  A deep exposure shows everything from dark nebula to star clusters, all imbedded in an extended patch of gaseous wisps in the greater Orion Molecular Cloud Complex.  The brightest three stars on the far left are indeed the famous three stars that make up the belt of Orion.  Just below Alnitak, the lowest of the three belt stars, is the Flame Nebula, glowing with excited hydrogen gas and immersed in filaments of dark brown dust.  Below the frame center and just to the right of Alnitak lies the Horsehead Nebula, a  dark indentation of dense dust that has perhaps the most recognized nebular shapes on the sky. On the upper right lies M42, the Orion Nebula, an energetic caldron of tumultuous gas, visible to the unaided eye, that is giving birth to a new open cluster of stars.  Immediately to the left of M42 is a prominent bluish reflection nebula sometimes called the Running Man that houses many bright blue stars.  The above image, a digitally stitched composite taken over several nights, covers an area with objects that are roughly 1,500 light years away and spans about 75 light years.

Image credit: Rogelio Bernal Andreo
(Deep Sky Colors)
Saturn at Equinox (2009-09-30)

How would Saturn look if its ring plane pointed right at the Sun? Before last month, nobody knew.  Every 15 years, as seen from Earth, Saturn's rings point toward the Earth and appear to disappear. The disappearing rings are no longer a mystery -- Saturn's rings are known to be so thin and the Earth is so near the Sun that when the rings point toward the Sun, they also point nearly edge-on at the Earth. Fortunately, in this third millennium, humanity is advanced enough to have a spacecraft that can see the rings during equinox from the side. Last month, that Saturn-orbiting spacecraft, Cassini, was able to snap a series of unprecedented pictures of Saturn's rings during equinox. A digital composite of 75 such images is shown above. The rings appear unusually dark, and a very thin ring shadow line can be made out on Saturn's cloud-tops.  Objects sticking out of the ring plane are brightly illuminated and cast long shadows.  Inspection of these images may help humanity understand the specific sizes of Saturn's ring particles and the general dynamics of orbital motion.
Carina Pillar and Jets (2009-10-01)

This cosmic pillar of gas and dust is nearly 2 light-years wide. The structure lies within one of our galaxy's largest star forming regions, the Carina Nebula, shining in southern skies at a distance of about 7,500 light-years. The pillar's convoluted outlines are shaped by the winds and radiation of Carina's young, hot, massive stars. But the interior of the cosmic pillar itself is home to stars in the process of formation. In fact, placing your cursor over this visible light image will reveal a penetrating near-infrared view of the pillar - now dominated by two, narrow, energetic jets blasting outward from a still hidden infant star. Both visible light and near-infrared images were made using the Hubble Space Telescope's newly installed Wide Field Camera 3.
Comet and Orion (2009-10-02)

These colorful panels both feature a familiar astronomical sight: the stellar nursery known as the Great Orion Nebula. They also offer an intriguing and unfamiliar detail of the nebula rich skyscape -- a passing comet. Recorded this weekend with a remotely operated telescope in New Mexico, the right hand image was taken on September 26 and the left on September 27. Comet 217P Linear sports an extended greenish tail and lies above the bluish Running Man reflection nebula near the top of both frames. Nearby and moving rapidly through the night sky, the comet's position clearly shifts against the cosmic nebulae and background stars from one night to the next. In fact, the comet was a mere 5 light-minutes away on September 27, compared to 1,500 light-years for the Orion Nebula. Much too faint to be seen with the unaided eye, Comet 217P Linear is a small periodic comet with an orbital period of about 8 years. At its most distant point from the Sun, the comet's orbit is calculated to reach beyond the orbit of Jupiter At its closest point to the Sun, the comet still lies just beyond the orbit of planet Earth.

Image credit: CARA Project
Old Faith-Full Moon (2009-10-03)

Scheduled to illuminate the landscape throughout the night tomorrow, October's bright Full Moon will also be called the Harvest Moon. Traditionally, the Harvest Moon is the Full Moon closest to the autumnal equinox. But in this vacation snapshot, the Full Moon could be called the "Old Faith-Full Moon". Taken on September 4, the picture combines the regularly occurring lunar phase with Old Faithful Geyser in Yellowstone National Park, named for its dependable erruptions. Shining on the well-known geyser's towering pillar from behind, the moonlight creates an eerie halo surrounding convoluted shapes. Faithfully, the Full Moon itself is bright enough to be seen through the dense swirling steam near the top.

Image credit: Westlake
The Same Color Illusion (2009-10-04)

Are square A and B the same color? They are. Are too.  To verify this, click here to see them connected.  The above illusion, called the same color illusion, illustrates that purely human observations in science may be ambiguous or inaccurate.  Even such a seemingly direct perception as relative color.  Similar illusions exist on the sky, such as the size of the Moon near the horizon, or the apparent shapes of astronomical objects.  The advent of automated, reproducible, measuring devices such as CCDs have made science in general and astronomy in particular less prone to, but not free of, human-biased illusions.
The International Space Station Over Earth (2009-10-05)

After undocking, the space shuttle Discovery crew got a memorable view of the developing International Space Station (ISS). Pictured orbiting high above Earth last month, numerous solar panels, trusses, and science modules of the ISS were visible.  The Discovery crew brought mission specialist Nicole Stott to the ISS, and returned astronaut Timothy Kopra to Earth. Among the many mission and expedition accomplishments of the Discovery crew included delivering and placing the Fluids Integrated Rack and the Materials Science Research Rack in the Destiny module as well as the Minus Eighty Degree Laboratory Freezer in the Kibo module.  Better known, however, was the delivery of the COLBERT treadmill for keeping astronauts fit.  Over this past week the Soyuz TMA-16 spacecraft carrying three more astronauts docked with the ISS as Expedition 21 is set to begin.  The next shuttle trip to the ISS is currently scheduled for 2009 November 12.