juliensimon/nasa-apod huggingface dataset:
RCW 79: Stars in a Bubble (2007-07-14)

A cosmic bubble of gas and dust, RCW 79 has grown to about 70 light-years in diameter, blown by the winds and radiation from hot young stars. Infrared light from the dust embedded in the nebula is tinted red in this gorgeous false-color view from the Spitzer Space Telescope. A good 17 thousand light-years away in the grand southern constellation Centaurus, the expanding nebula itself has triggered star formation as it plows into the gas and dust surrounding it. In fact, this penetrating infrared picture reveals groups of new stars as yellowish points scattered along the bubble's edge. One remarkable group still lies within its own natal bubble at about 7 o'clock (lower left), while another can be seen near the upper gap at about 3 o'clock (right) from the bubble's center.
Aurora from Space (2007-07-15)

From the ground, spectacular auroras seem to dance high above. But the International Space Station (ISS) orbits at nearly the same height as many auroras, sometimes passing over them, and sometimes right through them.  Still, the auroral electron and proton  streams pose no direct danger to the ISS. In 2003, ISS Science Officer Don Pettit captured the green aurora, pictured above in a digitally sharpened image.  From orbit, Pettit reported that changing auroras appeared to crawl around like giant green amoebas.  Over 300 kilometers below, the Manicouagan Impact Crater can be seen in northern Canada, planet Earth.
The Lagoon Nebula in Gas, Dust, and Stars (2007-07-16)

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.  The light from M8 we see today left about 5,000 years ago. Light takes about 50 years to cross this section of M8.

Image credit: Antonio Fernandez
The Same Color Illusion (2007-07-17)

Are square A and B the same color? They are. Are too.  To verify this, click on the above image 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.
Planets over Pony Express Lake (2007-07-18)

Beautiful sunset sky colors are reflected in Pony Express Lake in this twilight skyview from northern Missouri, USA, planet Earth. Recorded on Monday, a two day old crescent Moon and brilliant planet Venus shine through thin clouds. Joining the conjunction on the right of the Moon's sunlit crescent is fellow wanderer Saturn, with Regulus, alpha star of the constellation Leo, above and right of Venus. Moonlight and Venus light streak the almost-calm lake waters.

Image credit: Dan Bush
(Missouri Skies)
The Hercules Cluster of Galaxies (2007-07-19)

These are galaxies of the Hercules Cluster, an archipelago of island universes a mere 500 million light-years away. Also known as Abell 2151, this cluster is loaded with gas and dust rich, star-forming spiral galaxies but has relatively few elliptical galaxies, which lack gas and dust and the associated newborn stars. The colors in this remarkably deep composite image clearly show the star forming galaxies with a blue tint and galaxies with older stellar populations with a yellowish cast. The sharp picture spans about 1/2 degree across the cluster center, corresponding to over 4 million light-years at the cluster's estimated distance. In the cosmic vista many galaxies seem to be colliding or merging while others seem distorted - clear evidence that cluster galaxies commonly interact. In fact, the Hercules Cluster itself may be seen as the result of ongoing mergers of smaller galaxy clusters and is thought to be similar to young galaxy clusters in the much more distant, early Universe.

Image credit: Tony Hallas
Apollo 11: East Crater Panorama (2007-07-20)

On July 20, 1969, Apollo 11 astronauts Neil Armstrong and Edwin "Buzz" Aldrin became the first to walk on the Moon. This panorama of their landing site sweeps across the magnificent desolation of the Moon's Sea of Tranquility, with their Lunar Module, the Eagle, in the background at the far left. East Crater, about 30 meters wide and 4 meters deep, is on the right (scroll right), and was so named because it is about 60 meters east of the Lunar Module. Armstrong had piloted the Eagle safely over the crater. Near the end of his stay on the lunar surface Armstrong strayed far enough from the Lunar Module to take the pictures used to construct this wide-angle view, his shadow appearing at the panorama's left edge. The object near the middle foreground is a stereo close-up camera.
Infrared Andromeda (2007-07-21)

This wide, detailed Spitzer Space Telescope view features infrared light from dust (red) and old stars (blue) in Andromeda, a massive spiral galaxy a mere 2.5 million light-years away. In fact, with over twice the diameter of our own Milky Way, Andromeda is the largest nearby galaxy. Andromeda's population of bright young stars define its sweeping spiral arms in visible light images, but here the infrared view clearly follows the lumpy dust lanes heated by the young stars as they wind even closer to the galaxy's core. Constructed to explore Andromeda's infrared brightness and stellar populations, the full mosaic image is composed of about 3,000 individual frames. Two smaller companion galaxies, NGC 205 (below) and M32 (above) are also included in the combined fields. The data confirm that Andromeda (aka M31) houses around 1 trillion stars, compared to 4 hundred billion for the Milky Way.
The Flight of Helios (2007-07-22)

An example of solar-powered flight, NASA's Helios aircraft flew almost one hundred years after the Wright brothers' historic flight on December 17, 1903. Pictured here at 10,000 feet in in skies northwest of Kauai, Hawaii in August 2001, the remotely piloted Helios is traveling at about 25 miles per hour. Essentially an ultralight flying wing with 14 electric motors, the aircraft was built by AeroVironment Inc. Covered with solar cells, Helios' impressive 247 foot wide wing exceeded the wing span and even overall length of a Boeing 747 jet airliner. Climbing during daylight hours, the prototype aircraft ultimately reached an altitude just short of 100,000 feet, breaking records for non-rocket powered flight. Helios was intended as a technology demonstrator, but in the extremely thin air 100,000 feet above Earth's surface, the flight of Helios also approached conditions for winged flight in the atmosphere of Mars.
Verona Rupes: Tallest Known Cliff in the Solar System (2007-07-23)

Could you survive a jump off the tallest cliff in the Solar System?  Quite possibly.  Verona Rupes on Uranus' moon Miranda is estimated to be 20 kilometers deep -- ten times the depth of the Earth's Grand Canyon.   Given Miranda's low gravity, it would take about 12 minutes for a thrill-seeking adventurer to fall from the top, reaching the bottom at the speed of a racecar -- about 200 kilometers per hour.   Even so, the fall might be survivable given proper airbag protection.  The above image of Verona Rupes was captured by the passing Voyager 2 robotic spacecraft in 1986.  How the giant cliff was created remains unknown, but is possibly related to a large impact or tectonic surface motion.
Spiral Galaxy M83: The Southern Pinwheel (2007-07-24)

M83 is one of the closest and brightest spiral galaxies on the sky. Visible with binoculars in the constellation of Hydra, majestic spiral arms have prompted its nickname as the Southern Pinwheel. Although discovered 250 years ago, only much later was it appreciated that M83 was not a nearby gas cloud, but a barred spiral galaxy much like our own Milky Way Galaxy.  M83, pictured above, is a prominent member of a group of galaxies that includes Centaurus A and NGC 5253, all of which lie about 15 million light years distant.  Several bright supernova explosions have been recorded in M83.  An intriguing double circumnuclear ring has been discovered at the center of M83.

Image credit: Robert Gendler and
Stephane Guisard
Global Dust Storms Threaten Mars Rovers (2007-07-25)

Will global dust storms terminate the robotic Martian rovers? Over the past month, windy dust storms have blocked much needed sunlight from reaching the solar panels of both the Spirit and Opportunity rovers exploring Mars.  At times, as much as 99 percent of direct sunlight has been obscured, causing worry that the batteries might run out of energy before the storms end -- which may be as long as weeks. In an effort to weather these storms, Earth controllers have programmed the rovers to restrict movements and to use as little power as possible.  Although the rovers have been working for a remarkable three years past their planned three month lifetimes, their immediate future is now uncertain.  Pictured above, the Opportunity rover perched on the edge of Victoria Crater peered for a month into the distance as dust made the Martian air increasingly opaque.
Hot Stars in the Rosette Nebula (2007-07-26)

Winds and radiation from massive hot stars in the Rosette Nebula have cleared the natal gas and dust from the center of the nearby star-forming region. They also pose a danger to planet forming disks around young, cooler stars in the neighborhood. This Spitzer Space Telescope infrared image of dust clouds near the Rosette's central region, shows the cleared-out cavity. The view spans about 45 light-years at the the nebula's estimated distance of 5,200 light-years. Putting your cursor over the false color picture will highlight the dangerous hot stars, classified as O stars with surface temperatures of 25,000 kelvins or higher. Astronomers calculate that cool stars wandering within about 1.6 light-years of the Rosette's O stars are in danger of having their planet forming disks destroyed.
The Tidal Tail of NGC 3628 (2007-07-27)

A mere 30 million light-years away, large spiral galaxy NGC 3628 (center) shares its neighborhood in the local Universe with two other large spirals, in a magnificent grouping otherwise known as the Leo Triplett. In fact, fellow trio member M65 is near the bottom edge of this deep cosmic group portrait, with M66, just above it and to the left. But, perhaps most intriguing is the spectacular tail stretching up and to the left for about 300,000 light-years from NGC 3628's warped, edge-on disk. Known as a tidal tail, the structure has been drawn out of the galaxy by gravitational tides during brief but violent past interactions with its large neighbors. Not often imaged so distinctly, the tidal tail is composed of young bluish star clusters and star-forming regions.

Image credit: Steve Mandel
(Galaxy Images)
Full Moondark (2007-07-28)

The brilliant full Moon might not look quite like this to skygazers next Monday, but the image is a mosaic of 18 digital frames recorded when the Moon was only about seven hours past its exact full phase or time of maximum illumination as viewed from Earth. Here, the pixel values corresponding to light and dark areas have been translated in reverse, or inverted, producing a false-color representation reminiscent of a black and white photographic negative. Normally bright rays from the large crater Tycho dominate the southern (bottom) features as easily followed dark lines emanating from the 85 kilometer diameter impact site. Normally dark lunar mare appear light and silvery. Traditionally, astronomical images recorded on photographic plates were directly examined in this negative color scheme, which can help the eye pick out faint details.

Image credit: Frank Barrett
The Center of Centaurus A (2007-07-29)

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.
The Four Suns of HD 98800 (2007-07-30)

How would it look to have four suns in the sky? Planets of the HD 98800 system, if they exist, would experience such a view.  HD 98800 is a  multiple star system about 150 light years from Earth -- right in our section of the Milky Way Galaxy.  For years it has been known that HD 98800 consists of two pairs of double stars, with one pair surrounded by a disk of dust.   The star pairs are located about 50 AU from each other -- in comparison just outside the orbit of Pluto.  Recent data from the Earth-trailing Spitzer Space Telescope in infrared light, however, indicate that the dust disk has gaps that appear consistent with being cleared by planets orbiting in the disk.  If so, one planet appears to be orbiting at a distance similar to Mars of our own Solar System.  Pictured above is an artist's drawing of how the HD 98800 system might appear to a nearby observer.
A Laser Strike at the Galactic Center (2007-07-31)

Why are these people shooting a powerful laser into the center of our Galaxy?  Fortunately, this is not meant to be the first step in a Galactic war.  Rather, astronomers at the Very Large Telescope (VLT) site in Chile are trying to measure the distortions of Earth's ever changing atmosphere.  Constant imaging of high-altitude atoms excited by the laser -- which appear like an artificial star -- allow astronomers to instantly measure atmospheric blurring.   This information is fed back to a VLT telescope mirror which is then slightly deformed to minimize this blurring.  In this case, a VLT was observing our Galaxy's center, and so Earth's atmospheric blurring in that direction was needed.  As for inter-galaxy warfare, when viewed from our Galaxy's center, no casualties are expected.  In fact, the light from this powerful laser would combine with light from our Sun to together appear only as bright as a faint and distant star.

Image credit: Yuri Beletsky
(ESO)
Unusual Cratering on Saturn's Dione (2007-08-01)

Why does one half of Dione have more craters than the other? Start with the fact that Saturn's moon Dione always has one side that faces Saturn, and always has one side that faces away.  This is similar to Earth's Moon. This tidal locking means that one side of Dione always leads as the moon progresses in its orbit, while the other side always trails.  Dione should therefore have undergone a significant amount of impacts on its leading half. But the current leading half of Dione is less cratered than the trailing half!  A possible explanation is that some impacts were so large they spun Dione, sometimes changing the part that suffered the highest impact rate before the moon's spin again became locked.  Pictured above, it is the top part of Dione that appears significantly more cratered than the bottom half.
M64: The Black Eye Galaxy (2007-08-02)

This bright, beautiful spiral galaxy is Messier 64, sometimes known as the Black Eye Galaxy. M64 lies about 17 million light-years distant in the otherwise well-groomed northern constellation Coma Berenices. The dark clouds along the near-side of M64's central region that give the galaxy its black-eye appearance are enormous obscuring dust clouds associated with star formation, but they are not the galaxy's only peculiar feature. Observations show that M64 is actually composed of two concentric, counter-rotating systems of stars, one in the inner 3,000 light-years and another extending to about 40,000 light-years and rotating in the opposite direction. The dusty black eye and bizarre rotation is likely the result of a merger of two different galaxies.

Image credit: Andrea Tamanti
NGC 7293: The Helix Nebula (2007-08-03)

A mere seven hundred light years from Earth, in the constellation Aquarius, a sun-like star is dying. Its last few thousand years have produced the Helix Nebula (NGC 7293), a well studied and nearby example of a Planetary Nebula, typical of this final phase of stellar evolution.  Nearly 11 hours of exposure time have gone in to creating this remarkably deep view of the nebula. It shows details of the Helix's brighter inner region, about 3 light-years across, but also follows fainter outer halo features that give the nebula a span of well over six light-years. The white dot at the Helix's center is this Planetary Nebula's hot, central star. A simple looking nebula at first glance, the Helix is now understood to have a surprisingly complex geometry.

Image credit: Imaging - Josch Hambsch,

Processing - Karel Teuwen
Sagittarius Triplet (2007-08-04)

These three bright nebulae are often featured in telescopic tours of the constellation Sagittarius and the crowded starfields of the central Milky Way. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the nebula below and right of center, and colorful M20 at the upper right. The third, NGC 6559, is left of M8, separated from the the larger nebula by a dark dust lane. All three are stellar nurseries about five thousand light-years or so distant. The expansive M8, over a hundred light-years across, is also known as the Lagoon Nebula while M20's popular moniker is the Trifid. This stunning digital view is actually a collaborative composite recorded by 2 cameras and 2 telescopes about 2 thousand miles apart. The deep, wide image field was captured under dark Arizona skies. Both M8 and M20 were recorded in more detail from an observatory in Pennsylvania. Glowing hydrogen gas creates the dominant red color of the emission nebulae, with contrasting blue hues, most striking in the Trifid, due to dust reflected starlight.

Image credit: Steve Mazlin,
Jim Misti
The Dotted Dunes of Mars (2007-08-05)

What causes the black dots on dunes on Mars?  As spring dawned on the Northern Hemisphere of Mars in 2004, dunes of sand near the poles begin to defrost.  Thinner regions of ice typically thaw first revealing sand whose darkness soaks in sunlight and accelerates the thaw.  The process might involve sandy jets exploding through the thinning ice.  By summer, the spots expanded to encompass the entire dunes that were then completely thawed and dark. The carbon dioxide and water ice actually sublime in the thin atmosphere directly to gas.  Taken in mid-July, the above image shows a field of spotted polar dunes spanning about 3 kilometers near the Martian North Pole.  Today, the future of Mars rovers Spirit and Opportunity remains unknown windy dust storms continue to starve them of needed sunlight.

Image credit: Malin Space Science Systems,
MOC,
MGS,
JPL, 
NASA
CG4: A Ruptured Cometary Globule (2007-08-06)

Can a gas cloud eat a galaxy?  It's not even close.  The odd looking "creature" or "hand" extending down from the top of the above photo is a gas cloud known as a cometary globule.  This globule, however, has ruptured.  Cometary globules are typically characterized by dusty heads and elongated tails.  These features cause cometary globules to have visual similarities to comets, but in reality they are very much different.  Globules are frequently the birthplaces of stars, and many show very young stars in their heads. The reason for the rupture in the head of this object is not completely known.  The galaxy to the near the bottom of the image is huge, very far in the distance, and only placed near CG4 by chance superposition.   News Flash: Phoenix Spacecraft Launches to Mars

Image credit: Josch Hambsch
Old Faithful Below a Yellowstone Sky (2007-08-07)

You don't have to be at Yellowstone to see a sky this beautiful, but it helps. Only at Yellowstone National Park in Wyoming, USA, would you see the picturesque foreground of the famous Old Faithful Geyser erupting in front an already picturesque sky.  Old Faithful Geyser, visible in the foreground, is seen propelling a stream of hot water over 30 meters in the air. This happens predictably for a few minutes about every 90 minutes.  Also predictable are the brightest orbs that populate the nighttime sky, although those visible at any one time keep changing.  Visible far in the background sky of this mid-July image are the plane of our Milky Way Galaxy on the left, and the bright planet Jupiter on the right.  Jupiter is the brightest celestial object in the entire image. Old Faithful has been erupting at least since the late 1800s.

Image credit: Wally Pacholka 
(Astropics.com)
Phoenix Rises Toward Mars (2007-08-08)

Can Mars sustain life?  To help answer this question, last week NASA launched the Phoenix mission to Mars. In May 2008, Phoenix is expected to land in an unexplored north polar region of Mars that is rich in water-ice.  Although Phoenix cannot move, it can deploy its cameras, robotic arm, and a small chemistry laboratory to inspect, dig, and chemically analyze its landing area.  One hope is that Phoenix will be able to discern telling clues to the history of ice and water on Mars.  Phoenix is also poised to explore the boundary between ice and soil in hopes of finding clues of a habitable zone there that could support microbial life. Phoenix has a planned lifetime of three months on the Martian surface.
Star Cluster Messier 67 (2007-08-09)

Gathered at the center of this sharp skyview are the stars of Messier 67, one of the oldest known open star clusters. In fact, though open star clusters are usually much younger, the stars of M67 are likely around 4 billion years old, about the same age and with about the same elemental abundances as the Sun. Open clusters are almost always younger because they are dispersed over time as they encounter other stars, interstellar clouds, and experience gravitational tides while orbiting the center of our galaxy.  Still, M67 contains over 500 stars or so and lies some 2,800 light-years away in the constellation Cancer. At that estimated distance, M67 would be about 12 light-years across.

Image credit: Processing - Noel Carboni,

Imaging - Greg Parker
Star Factory Messier 17 (2007-08-10)

Sculpted by stellar winds and radiation, the star factory known as Messier 17 lies some 5,500 light-years away in the nebula-rich constellation Sagittarius. At that distance, this 30 arcminute field of view spans almost 50 light-years. Stellar winds and energetic light from hot, massive stars formed from M17's stock of cosmic gas and dust have slowly carved away at the remaining interstellar material producing the cavernous appearance and undulating shapes. Colors in the gorgeous image were picked to emphasize light emitted by specific elements in the nebula excited by the energetic starlight. Red indicates emission from sulfur, green from hydrogen, and blue from oxygen. M17 is also known as the Omega Nebula or the Swan Nebula.

Image credit: Ignacio de la Cueva
Torregrosa