juliensimon/nasa-apod huggingface dataset:
Southern Saturn from Cassini (2004-10-18)

What happens to Saturn's pervasive clouds at its South Pole?  Visible in the above image of Saturn are bright bands, dark belts and a dark spot right over the South Pole.  The above image in infrared light spans over 30,000 kilometers and was taken early last month by the robot Cassini spacecraft currently orbiting Saturn.  Saturn's atmosphere is about 75 percent hydrogen, 25 percent helium, and small amounts of heavier compounds including water vapor, methane, and ammonia.  The relatively low gravity at Saturn's cloud tops result in a thicker haze layer, which in turn makes atmospheric features blurrier than Jupiter.
Old Planetary Dust Disks Found by SST (2004-10-19)

Why are some older stars surrounded by dust?  Observations from the Spitzer Space Telescope by a team led by George Rieke (U. Arizona) were expected to show that young stars, on the order of one million years old, have large dust disks, while relatively older stars, between 10 and 100 million years old, have none.  The conventional wisdom was that the dust disks surrounding young stars were still forming planets, while in older systems these disks had dissipated after planets had already formed.  Unexpectedly, they found some older stars with the infrared glow of impressive rings or disks of dust.  A possible explanation is that the old disks are remnant debris from violent collisions between many forming planets of rock.  Resultant dust rings from such a scenario are depicted by an artist's illustration above.
NGC 281: Cluster, Clouds, and Globules (2004-10-20)

NGC 281 is a busy workshop of star formation.  Prominent features include a small open cluster of stars, a diffuse red-glowing emission nebula, large lanes of obscuring gas and dust, and dense knots of dust and gas in which stars may still be forming.  The open cluster of stars IC 1590 visible around the center has formed only in the last few million years.  The brightest member of this cluster is actually a multiple-star system shining light that helps ionize the nebula's gas, causing the red glow visible throughout.  The lanes of dust visible left of center are likely homes of future star formation.  Particularly striking in the above photograph are the dark Bok globules visible against the bright nebula.  The entire NGC 281 system lies about 10 thousand light years distant.

Image credit: Chris Sauer
Apogee Moon, Perigee Moon (2004-10-21)

Why don't these pieces fit? This third quarter Moon (left) and first quarter Moon were both photographed during the last lunar cycle or lunation with the same telescope and camera. But, simply combining the pictures into one sharp, full surface view would clearly be a problem. In fact, on October 6th the Moon's third quarter phase happened to occur near lunar apogee, the farthest point in the Moon's orbit. On September 21st, the first quarter phase fell close to lunar perigee, the Moon's closest approach to planet Earth. Viewed two weeks apart, the resulting difference in apparent sizes would not be noticed by casual skygazers, but the simultaneous side by side comparison makes it hard to ignore. Skygazers will likely notice the Moon next week though, as it slides through Earth's shadow during October 27th's total lunar eclipse.

Image credit: António Cidadão
SOFIA's Mirror (2004-10-22)

The candy-dish appearance of this high-tech astronomical mirror is striking. Made of a special glass ceramic material called Zerodur, it actually measures 2.7 meters across. The transparent surface has not yet received a reflective coating, so the weight-reducing internal honeycomb structure is visible with attractive blue and yellow tints provided by a protective tarp and background lighting. Recently unveiled, the telescope mirror is destined to fly on the Stratospheric Observatory For Infrared Astronomy (SOFIA). Since water vapor in Earth's troposphere tends to block infrared light, SOFIA will operate from a modified Boeing 747 jetliner at altitudes above 40,000 feet. As the largest airborne observatory in the world, SOFIA will explore a host of cosmic environments including sites of star birth and death, the formation of distant solar systems, and black holes in active galaxies.
Surveyor Slides (2004-10-23)

"Safe!" In September 1967, during regular season play, the Surveyor 5 lander actually slid several feet while making a successful soft landing on the Moon's Mare Tranquillitatis. Equipped with television cameras and soil sampling experiments, the US Surveyor spacecraft were intended to determine if the lunar surface at chosen locations was safe for the planned Apollo landings. Surveyor 5 touched down on the inside edge of a small crater inclined at about 20 degrees. Its footpad slipped and dug the trench visible in the picture. Covered with dusty lunar soil, the footpad is about half a meter in diameter.
Inside the Eagle Nebula (2004-10-24)

From afar, the whole thing looks like an Eagle.  A closer look at the Eagle Nebula, however, shows the bright region is actually a window into the center of a larger dark shell of dust.  Through this window, a brightly-lit workshop appears where a whole open cluster of stars is being formed.  In this cavity tall pillars and round globules of dark dust and cold molecular gas remain where stars are still forming.  Already visible are several young bright blue stars whose light and winds are burning away and pushing back the remaining filaments and walls of gas and dust.  The Eagle emission nebula, tagged M16, lies about 6500 light years away, spans about 20 light-years, and is visible with binoculars toward the constellation of Serpens.  The above picture combines three specific emitted colors and was taken with the 0.9-meter telescope on Kitt Peak, Arizona, USA.

Image credit: T. A. Rector
The Perseus Cluster of Galaxies (2004-10-25)

Here is one of the largest objects that anyone will ever see on the sky.  Each of the fuzzy blobs in the above picture is a galaxy, together making up the Perseus Cluster, one of the closest clusters of galaxies.  The cluster is seen through the foreground of faint stars in our own Milky Way Galaxy.  It takes light roughly 300 million years to get here from this region of the Universe, so we see this cluster as it existed before the age of the dinosaurs.  Also known as Abell 426, the center of the Perseus Cluster is a prodigious source of X-ray radiation, and so helps astronomers explore how clusters formed and how gas and dark matter interact.  The Perseus Cluster of Galaxies is part of the Pisces-Perseus supercluster of galaxies, which spans over 15 degrees and contains over 1000 galaxies.
Titan Through the Haze (2004-10-26)

What are these surface features on Titan?  This planet-sized moon of Saturn had much of its south polar surface imaged during an initial flyby by the Saturn-orbiting Cassini spacecraft back in early July.  The above image mosaic was digitally stitched together from pictures taken at a very specific color of polarized infrared light, a color not absorbed and little scattered by Titan's methane haze.  Visible are light and dark regions that are not yet understood.  Surface features as small as 10 kilometers are resolved from about 340,000 kilometers away.  The white region near Titan's South Pole, left of center, is unusually thick clouds also thought to be composed of methane.  Today Cassini will swoop to within 1,500 kilometers above Titan and may return data and images that help humanity better understand this strange world.
Total Lunar Eclipse Tonight (2004-10-27)

Go outside tonight and see the total lunar eclipse.  Tonight's eclipse is easy and convenient for much of the world to see.  Anyone who can spot a full Moon can see it fade out as the Earth's shadow engulfs it.  No protective glasses or expensive telescopes are needed, just a little moxie.  The above illustration shows how the eclipse will appear across the Earth.  The total lunar eclipse starts at 9:14 pm Eastern Daylight Time, equivalent to 1:14 am UT in the morning for sky enthusiasts in the United Kingdom.  From the moment the first part of the Moon disappears to the moment that the last part of the Moon reappears will be 3 hours and 40 minutes.  For those unfortunate enough to suffer clouds, the eclipse can also be followed over several live webcasts.   World Series Lunar Eclipse: Live TV shot makes this eclipse possibly the most seen live eclipse ever.
Tantalizing Titan (2004-10-28)

Normally hidden by a thick, hazy atmosphere, tantalizing features on Titan's surface appear in this false-color view. The image was recorded as the Cassini spacecraft approached its first close flyby of Saturn's smog-shrouded moon on October 26. Here, red and green colors represent specific infrared wavelengths absorbed by Titan's atmospheric methane while bright and dark surface areas are revealed in a more penetrating infrared band. Ultraviolet data showing the extensive upper atmosphere and haze layers are seen as blue. Sprawling across the 5,000 kilometer wide moon, the bright continent-sized feature known as Xanadu is near picture center, bordered at the left by contrasting dark terrain. Saturn orbiter Cassini and Titan lander Huygens plan further explorations, but for now the origin and nature of Titan's surface features remain unknown.
Red Moon Triple (2004-10-29)

Some thought of baseball and some thought of Halloween during October 27th's widely viewed total lunar eclipse. Sliding through Earth's shadow, the Moon turned haunting shades of red and orange during the eclipse's total phase. The reddish hues are caused by sunlight scattered and refracted by the atmosphere into the Earth's otherwise dark central shadow region. Enjoying the show from Dunkirk, Maryland, USA, astronomer Fred Espenak recorded the images used in this composite photo. The picture shows the Moon at the beginning (right), middle (center) and end (left) of totality which lasted about 81 minutes. Though lunar eclipses can occur twice a year, this eclipse is perhaps remarkable for being the first total lunar eclipse to occur during a World Series baseball game.

Image credit: Fred Espenak
Pumpkin Moon (2004-10-30)

Does this look familiar? Red and orange hues haunting the face of the Moon should remind you of the October 27th total lunar eclipse. Created from exposures taken at intervals of 8.5 minutes during the total eclipse phase, the midpoint of the eclipse corresponds to the central exposure. The play of light across the lunar surface nicely demonstrates that the Earth's shadow is not uniformly dark as it extends into space. In fact, lunar maria and montes are still visible in the dimmed, reddened sunlight scattered into the cone-shaped shadow region, or umbra, by the atmosphere. Still, while processing the pictures into this composite image, astronomer Sebastien Gauthier was reminded of another haunting orange face. Have a safe and happy Halloween!

Image credit: Sebastien Gauthier
Halloween and the Ghost Head Nebula (2004-10-31)

Halloween's origin is ancient and astronomical.  Since the fifth century BC, Halloween has been celebrated as a cross-quarter day, a day halfway between an equinox (equal day / equal night) and a solstice (minimum day / maximum night in the northern hemisphere).  With our modern calendar, however, the real cross-quarter day will occur next week.  Another cross-quarter day is Groundhog's Day. Halloween's modern celebration retains historic roots in dressing to scare away the spirits of the dead.  Perhaps a fitting modern tribute to this ancient holiday is the above-pictured Ghost Head Nebula taken with the Hubble Space Telescope.  Appearing similar to the icon of a fictional ghost, NGC 2080 is actually a star forming region in the Large Magellanic Cloud, a satellite galaxy of our own Milky Way Galaxy.  The Ghost Head Nebula spans about 50 light-years and is shown in representative colors.
Spooky Star Forming Region DR 6 (2004-11-01)

How could stars form such a spooky and familiar shape as a human skull?  First, the complex process of star formation creates nebulas of many shapes and sizes -- it is human perception that identifies the skull shape.  Next, the physical reasons for the large nearly empty cavities that resemble the skull's eyes and mouth in nebula DR 6 are the strong stellar winds and energetic light emanating from about ten bright young stars in the nebula's central "nose".  The length of the central nasal bridge is about 3.5 light years.  Star forming nebula DR 6 is located about 4000 light years away toward the constellation of Cygnus.  The Spitzer Space Telescope took the above image last year in four infrared colors.  The perhaps-perceived eeriness of nebula DR 6 commemorates today being historically spooky All Hallow's Day, which follows All Hallow's Eve or "Halloween".
Storm Alley on Saturn (2004-11-02)

What causes storms on Saturn?  To help find out, scientists commanded the robot Cassini spacecraft now orbiting Saturn to inspect a circulating band of clouds nicknamed "Storm Alley."  This westwardly moving cloud ring has been unusually active since the beginning of 2004, spawning white swirling storms and dark storms ringed by sprawling white clouds all cascading around the gas giant.  The rogue band, as well as other parts of south Saturn, were imaged in stunning detail in a very specific band of infrared light that passes through Saturn's upper haze relatively unblurred.  The result was then digitally sharpened, showing more cloud detail but creating fake image artifacts such as a surrounding ring.  Speculation on the nature of past Saturn storms included convective motions of small amounts of ammonia and water, seasons, and shadowing effects of the great ring system.  Although the above image provides data and clues, the power behind Saturn's storms still remains a mystery.
A Time-Lapse Lunar Eclipse (2004-11-03)

During last week's lunar eclipse, our Moon appeared to disappear.  As the Earth moved between the Moon and the Sun, the Earth's shadow fell on the moon, making it quite dark.  In the above picture the Earth's rotation, multiple exposures, and digital enhancements are used to create a time-lapse effect that dramatizes how the Moon looked as it faded out and re-appeared during the three hour lunar eclipse.  As the Earth's shadow engulfed the Moon, the lunar images became less and less bright, practically disappearing during totality.  At this time, the Moon, which normally shines by reflecting direct sunlight, shone only by sunlight refracted through the Earth's atmosphere.  The next total lunar eclipse won't be visible from Earth until 2007.

Image credit: Forrest J. Egan
(Digital Astro)
NGC 7023: The Iris Nebula (2004-11-04)

Like delicate cosmic petals, these clouds of interstellar dust and gas have blossomed 1,300 light-years away in the fertile star fields of the constellation Cepheus. Sometimes called the Iris Nebula and dutifully cataloged as NGC 7023, this is not the only nebula in the sky to evoke the imagery of flowers. Still, the beautiful digital image shows off the Iris Nebula's range of colors and symmetries in impressive detail. Within the Iris, dusty nebular material surrounds a massive, hot, young star in its formative years. Central filaments of cosmic dust glow with a reddish photoluminesence as some dust grains effectively convert the star's invisible ultraviolet radiation to visible red light. Yet the dominant color of the nebula is blue, characteristic of dust grains reflecting starlight. Dark, obscuring clouds of dust and cold molecular gas are also present and can lead the eye to see other convoluted and fantastic shapes. Infrared observations indicate that this nebula may contain complex carbon molecules known as PAHs. As shown here, the Iris Nebula is about 6 light-years across.

Image credit: Jim Misti
(acquisition),
Robert Gendler
(processing)
Supernova Remnant Imaged in Gamma Rays (2004-11-05)

Gamma rays are the most energetic form of light. With up to a billion times the energy of ordinary "medical" x-rays, they easily penetrate telescope lenses and mirrors, making it very difficult to create gamma-ray images of cosmic sources. Still, an array of large telescopes designed to detect gamma-ray induced atmospheric flashes - the HESS (High Energy Stereoscopic System) experiment - has produced this historic, resolved image of a supernova remnant at extreme gamma-ray energies. Astronomers note that the premier gamma-ray view of the expanding stellar debris cloud is clearly similar to x-ray images of the remnant and convincingly supports the idea that these sites of powerful shock waves are also sources of cosmic rays within our galaxy. The gamma-ray intensity is color-coded in the picture, shown with dark contour lines that trace levels of x-ray emission from the object. At an estimated distance of 3,000 light-years, the supernova remnant measures about 50 light-years across and lies near the galactic plane.
X-Rays from the Galactic Core (2004-11-06)

Using the orbiting Chandra X-ray Observatory, astronomers have taken this long look at the core of our Milky Way galaxy, some 26,000 light-years away. The spectacular false-color view spans about 130 light-years. It reveals an energetic region rich in x-ray sources and high-lighted by the central source, Sagittarius A*, known to be a supermassive black hole with 3 million times the mass of the Sun. Given its tremendous mass, Sagittarius A* is amazingly faint in x-rays in comparison to central black holes observed in distant galaxies, even during its frequent x-ray flares. This suggests that this supermassive black hole has been starved by a lack of infalling material. In fact, the sharp Chandra image shows clouds of multi-million degree gas dozens of light-years across flanking (upper right and lower left) the central region -- evidence that violent events have cleared much material from the vicinity of the black hole.
The Galactic Center in Infrared (2004-11-07)

The center of our Galaxy is a busy place. In visible light, much of the  Galactic Center is obscured by opaque dust.  In infrared light, however, dust glows more and obscures less, allowing nearly one million stars to be recorded in the above photograph.  The Galactic Center itself appears on the right and is located about 30,000 light years away towards the constellation of Sagittarius.  The Galactic Plane of our Milky Way Galaxy, the plane in which the Sun orbits, is identifiable by the dark diagonal dust lane.  The absorbing dust grains are created in the atmospheres of cool red-giant stars and grow in molecular clouds.  The region directly surrounding the Galactic Center glows brightly in radio and high-energy radiation, and is thought to house a large black hole.
Jupiter and Venus at Sunrise (2004-11-08)

What are those bright objects in the morning sky?  Early morning dog walkers, among many others across our world's Northern Hemisphere, have likely noticed tremendously bright Venus hanging in the eastern sky just before sunrise.  Looking a bit like an approaching airplane, Venus holds its place in the sky and never seems to land.  Last week, impressive but less bright Jupiter appeared within a degree of the Venusian orb, creating a dazzling sky that you might appreciate a bit more than your dog.  This night sky early show will change slightly over the next week, with the planets moving past each other, Mars moving into the picture, guest stars like Spica appearing to shift in the background, and even a crescent Moon stopping in for a cameo.  Pictured above last week, Jupiter and Venus were photographed rising before the Sun over the city of Bursa, Turkey.

Image credit: Tun� Tezel
A Full Sky Multicolored Auroral Corona (2004-11-09)

On some nights the sky is the most interesting show in town.  This fisheye picture captures a particularly active and colorful auroral corona that occurred two days ago over l'Observatoire de la Decouverte in Val Belair near Quebec, Canada.  The above spectacular aurora has an unusually high degree of detail, range of colors, and breadth across the sky.  The vivid green, red, and blue auroral colors are likely caused by high atmospheric oxygen and hydrogen reacting to incoming electrons.  The trigger events were magnetically induced explosions on the Sun from sunspot region 696 over the past few days.  Continued activity from this active solar region could mean more auroras visible to northern observers over the next few days.  Early in the morning but far in the background, planets, stars and the Moon will be simultaneously putting on their own show.

Image credit: Philippe
Moussette
(Obs. Mont
Cosmos)
Leo A: Nearby Dwarf Irregular Galaxy (2004-11-10)

Why isn't this small galaxy simple?  The above image and contemporary observations of small nearby galaxy Leo A were supposed to show it has a simple structure.  Now Leo A is known to be a dwarf irregular galaxy - one of the most common types of galaxies in the universe and a type that is likely a building block of more massive galaxy like our Milky Way Galaxy.  In general, larger galaxies have recently been shown to continually eat, and be primarily composed of, many of the smaller satellite galaxies that have surrounded them.  Leo A's surprising complexity indicates that that it, and possibly many small galaxies, have formation histories nearly as complex as large galaxies.  Leo A spans about 10,000 light years and lies about 2.5 million light years away toward the constellation of Leo.

Image credit: IoP Lithuania
Pastel Planet, Triple Eclipse (2004-11-11)

This false-color image of banded gas giant Jupiter shows a triple eclipse in progress on March 28 - a relatively rare event, even for a large planet with many moons. Captured by the Hubble Space Telescope's near-infrared camera are shadows of Jupiter's moons Ganymede (left edge), Callisto (right edge) and Io, three black spots crossing the sunlit Jovian cloud tops. In fact, Io itself is visible as a white spot near picture center with a bluish Ganymede above and to the right, but Callisto is off the right hand edge of the scene. Viewed from Jupiter's perspective, these shadow crossings would be seen as solar eclipses, analogous to the Moon's shadow crossing the sunlit face of planet Earth. Historically, timing the eclipses of Jupiter's moons allowed astronomer Ole Roemer to make the first accurate measurement of the speed of light in 1676.
Missouri's Green Ribbon Sky (2004-11-12)

The critics rave - "Amazing!", "Unbelievable!", "The best I've ever seen!" They aren't talking about a movie, though. Instead, even casual sky critics are remarking on November's stunning auroral displays, visible with surprising intensities well beyond the confines of high latitudes where auroral activity is normally observed. In fact, in this example of an unforgettable performance a green ribbon of auroral light stretches from horizon to horizon - recorded on November 7th with a fisheye lens near Warrensburg, Missouri, USA. Want to see an aurora? Relatively wide-spread displays may continue, triggered by activity from an energetic sunspot region.

Image credit: Vic & Jen Winter 
(ICSTARS Astronomy)
Moon Over Shiraz (2004-11-13)

rly morning risers around the world have enjoyed the sight of bright planets in this week's predawn skies - further enhanced by the celestial spectacle of the waning crescent Moon. From some locations the Moon was seen to pass in front of Jupiter or Venus, a lunar occultation. Recorded near sunrise on November 10th from Shiraz, Iran, this eastern horizon view finds Jupiter (top) and a brilliant Venus in line with the Moon, a lovely conjunction of the three brightest objects in the night sky. Although the Moon has now fallen out of the early morning scene, Venus and Jupiter (along with a much fainter Mars) still precede the rising Sun above the eastern horizon.

Image credit: Ahmad Karimi,