juliensimon/nasa-apod huggingface dataset:
Galileo's Europa (2003-09-19)

Launched in 1989 and looping through the jovian system since late 1995, the voyage of NASA's Galileo spacecraft will soon come to an end. The spacecraft has been targeted to plunge directly into Jupiter this Sunday, September 21st, at about 30 miles per second. Its components will be vaporized in the gas giant's outer atmosphere. While Galileo's long voyage of exploration has resulted in a spectacular scientific legacy, the spacecraft's ultimate fate is related to perhaps its most tantalizing discovery -- strong evidence for a liquid ocean beneath the frozen surface of Jupiter's moon Europa. Galileo is now almost completely out of fuel for maneuvers, so this intentional collision with Jupiter will prevent any unintentional future collision with Europa and the possibility of contaminating the jovian moon with microbes from Earth hardy enough to survive in interplanetary space. Color image data from the Galileo mission recorded between 1995 and 1998 was used to create this depiction of Europa's cracked and icy surface. The inset shows dark reddish, disrupted regions dubbed Thera and Thrace.
Apollo 11: Catching Some Sun (2003-09-20)

Bright sunlight glints and long dark shadows dramatize this image of the lunar surface taken by Apollo 11 astronaut Neil Armstrong, the first to walk on the Moon. Pictured is the mission's lunar module, the Eagle, and spacesuited lunar module pilot Buzz Aldrin unfurling a long sheet of foil also known as the Solar Wind Collector. Exposed facing the Sun, the foil trapped atoms streaming outward in the solar wind, ultimately catching a sample of material from the Sun itself. Along with moon rocks and lunar soil samples, the solar wind collector was returned for analysis in earthbound laboratories.
Inside the Eagle Nebula (2003-09-21)

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
Opportunity Rockets Toward Mars (2003-09-22)

Next stop: Mars.  Two months ago, the second of two missions to Mars was launched from Cape Canaveral, Florida, USA above a Boeing Delta II rocket. The Mars Exploration Rover dubbed Opportunity is expected to arrive at the red planet this coming January.  Pictured above, an attached RocketCam (TM) captures Opportunity separating from lower booster stages and rocketing off toward Mars. Upon arriving, parachutes will deploy to slow the spacecraft and surrounding airbags will inflate.  The balloon-like package will then bounce around the surface a dozen times or more before coming to a stop.  The airbags will then deflate, the spacecraft will right itself, and the Opportunity rover will prepare to roll onto Mars.  A first rover named Spirit was successfully launched on June 10 and will arrive at Mars a few weeks earlier.  The robots Spirit and Opportunity are expected to cover as much as 40 metres per day, much more than Sojourner, their 1997 predecessor.  Spirit and Opportunity will search for evidence of ancient Martian water, from which implications might be drawn about the possibility of ancient Martian life.
Egging On the Autumnal Equinox (2003-09-23)

Today is the autumnal equinox -- should eggs be able to stand on end?  This long-standing myth loses much of its mystique after a demonstration that eggs can be made to stand on end during any day of the year.  Pictured above, Dr. Phil Plait (Sonoma St. U.) acting as the Bad Astronomer balanced three raw eggs on end in late October 1998.  Later, more modestly, his wife balanced five more.  The little-appreciated fact that most eggshells have small bumps on them makes this seemingly impossible task achievable.  Although, during an equinox, every place on Earth experiences an equal length day and night (12 hours each), this fact has no practical effect on egg stability.
M33: Spiral Galaxy in Triangulum (2003-09-24)

The small constellation Triangulum in the northern sky harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33's diameter spans over 50,000 light-years, making it third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 lies very close to the Andromeda Galaxy and observers in these two galaxies would likely have spectacular views of each other's grand spiral star systems. As for the view from planet Earth, this sharp 27 frame mosaic of M33 nicely shows off blue star clusters and pinkish star forming regions which trace the galaxy's loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region seen here, visible along an arm arcing above and to the right of the galaxy center. Like M31, M33's population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.

Image credit: Robert Gendler
Logarithmic Spirals Isabel and M51 (2003-09-25)

Uncomfortably close hurricane Isabel (left) and 30 million light-year distant galaxy M51 actually don't have much in common. For starters, Isabel was hundreds of miles across, while M51 (the Whirlpool Galaxy) spans about 50,000 light-years making them vastly dissimilar in scale, not to mention the extremely different physical interactions which control their formation and evolution. But they do look amazingly alike, both exhibiting the shape of a simple and beautiful mathematical curve known as a logarithmic spiral, a spiral whose separation grows in a geometric way with increasing distance from the center. Also known as the equiangular spiral, growth spiral, and Bernoulli's spiral or spira mirabilis, this curve's rich properties have fascinated mathematicians since its discovery by 17th century philosopher Descartes. Intriguingly, this abstract shape is much more abundant in nature than suggested by the striking visual comparison above. Logarithmic spirals also describe, for example, the arrangement of sunflower seeds, the shapes of nautilus shells, and ... cauliflower.
IC1340 in the Eastern Veil (2003-09-26)

These ghostly filaments of interstellar gas are just a small part of the expansive Veil Nebula, seen against a rich field of background stars in the long-necked constellation Cygnus. Also known as the Cygnus Loop, the Veil Nebula is a supernova remnant, the expanding debris cloud created by a stellar explosion whose light first reached planet Earth from 5,000 to 10,000 years ago. About 1,400 light-years away, the entire nebula now appears to span over 3 degrees on the sky, nearly 6 times the apparent size of the full moon, but is faint and can be difficult to see in small telescopes. The region captured in this beautiful, deep, color image is located at the southern tip of the Veil's eastern crescent. It covers about 10 light-years at the distance of the Veil and is cataloged as IC1340.

Image credit: StarryScapes
Surveyor Slides (2003-09-27)

"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 20 inches in diameter.
Our Galaxy in Stars, Gas, and Dust (2003-09-28)

The disk of our Milky Way Galaxy is home to hot nebulae, cold dust, and billions of stars.   The red nebulae visible in the above contrast-enhanced picture are primarily emission nebulae, glowing clouds of hydrogen gas heated by nearby, bright, young stars.  The blue nebulae are primarily reflection nebulae, clouds of gas and fine dust reflecting the light of nearby bright stars.  Perhaps the most striking, though, are the areas of darkness, including the Pipe Nebula visible on the image top left.  These are lanes of thick dust, many times containing relatively cold molecular clouds of gas.  Dust is so plentiful that it obscures the Galactic Center in visible light, hiding its true direction until discovered early last century.  The diffuse glow comes from billions of older, fainter stars like our Sun, which are typically much older than any of the nebulae.  Most of the mass of our Galaxy remains in a form currently unknown.

Image credit: John P. Gleason,
Steve Mandel
Aurora Over the Chugach Mountains (2003-09-29)

Tomorrow's picture: Through the Milky Way  < | Archive | Index | Search | Calendar | Glossary | Education | About APOD | >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Web Site Statements, Warnings, and Disclaimers NASA Official: Jay Norris. Specific rights apply. A service of: LHEA at NASA / GSFC & Michigan Tech. U.

Image credit: Calvin Hall 
(Alaska's Aurora)
The Sagittarius Dwarf Tidal Stream (2003-09-30)

Is our Milky Way Galaxy out to lunch?  Recent wide field images and analyses now indicate that our home galaxy is actually still in the process of devouring its closest satellite neighbor.  This unfortunate neighbor, the Sagittarius Dwarf galaxy, is now seen to be part of a larger Sagittarius Tidal Stream, a loose filament of stars, gas, and possibly dark matter that entangles the Milky Way.  An artist's depiction of the stream is shown above.  Speculation also holds that the Sagittarius Dwarf was once pulled through the Milky Way disk very close to our Sun's current location.  An important resulting realization is that galaxies contain a jumble of clumps and filaments of both dim and dark matter.

Image credit: David Martinez-Delgado
(MPIA) & 
Gabriel Perez
(IAC)
An Unusual Event Over South Wales (2003-10-01)

Jon Burnett, a teenager from South Wales, UK, was photographing some friends skateboarding last week when the sky did something very strange.  By diverting his camera, he was able to document this rare sky event and capture one of the more spectacular sky images yet recorded.  Roughly four minutes later, he took another picture of the dispersing trail.  What is it? Experts disagree. The first guess was a sofa-sized rock that exploded as a daytime fireball, but perhaps a better hypothesis is an unusual airplane contrail reflecting the setting Sun. Bright fireballs occur over someplace on Earth nearly every day.  A separate bolide, likely even more dramatic, struck India only a few days ago.   Editor's note: The APOD text was updated on Oct. 1.

Image credit: Jon Burnett
Reflections on the 1970s (2003-10-02)

The 1970s are often overlooked. In particular, the beautiful grouping of reflection nebulae NGC 1977, NGC 1975, and NGC 1973 in Orion are often overlooked in favor of the substantial stellar nursery better known as the Orion Nebula. Found along the sword of Orion just north of the bright Orion Nebula complex, these nebulae are also associated with Orion's giant molecular cloud which lies about 1,500 light-years away, but are dominated by the characteristic blue color of interstellar dust reflecting light from hot young stars. In this sharp color image a portion of the Orion Nebula appears along the bottom border with the cluster of reflection nebulae at picture center. NGC 1977 stretches across the field just below center, separated from NGC 1973 (above right) and NGC 1975 (above left) by dark regions laced with faint red emission from hydrogen atoms. Taken together, the dark regions suggest to many the shape of a running man.

Image credit: Dean Jacobsen
Cold Comet Halley (2003-10-03)

While this may not be the most esthetic image of Comet Halley that you have ever seen, it is likely the most unique. The tiny cluster of pixels circled is the famous comet along its orbit over 4 billion (4,000,000,000) kilometers or 28 AU from the Sun -- a record distance for a comet observation. Its last passage through our neck of the woods in 1986, Comet Halley presently cruises through the dim reaches of the outer solar system, almost as far away as outermost gas giant Neptune, and shows no sign of activity. Captured in March, this negative image is a composite of digital exposures made with three of ESO's Very Large Telescopes. The exposures are registered on the moving comet, so the picture shows background stars and galaxies as elongated smudges. An earth-orbiting satellite appears as a dark streak at the top. Comet Halley is clearly extremely faint here, but large earthbound telescopes will be able to follow it as it grows fainter still, reaching the most distant point in its orbit, more than 5 billion kilometers (35 AU) from the Sun, in 2023.
X-Ray Moon (2003-10-04)

This x-ray image of the Moon was made by the orbiting ROSAT (Röntgensatellit) Observatory in 1990. In this digital picture, pixel brightness corresponds to x-ray intensity. Consider the image in three parts: the bright hemisphere of the x-ray moon, the darker half of the moon, and the x-ray sky background. The bright lunar hemisphere shines in x-rays because it scatters x-rays emitted by the sun. The background sky has an x-ray glow in part due to the myriad of distant, powerful active galaxies, unresolved in the ROSAT picture but recently detected in Chandra Observatory x-ray images. But why isn't the dark half of the moon completely dark? New Chandra results also suggest that a few x-rays only seem to come from the shadowed lunar hemisphere. Instead, they originate in Earth's geocorona or extended atmosphere which surrounds the orbiting x-ray observatories.
Apollo 12 Visits Surveyor 3 (2003-10-05)

Apollo 12 was the second mission to land humans on the Moon. The landing site was picked to be near the location of Surveyor 3, a robot spacecraft that had landed on the Moon three years earlier. In the above photograph, taken by lunar module pilot Alan Bean, mission commander Pete Conrad jiggles the Surveyor spacecraft to see how firmly it is situated. The lunar module is visible in the distance.  Apollo 12 brought back many photographs and moon rocks.  Among the milestones achieved by Apollo 12 was the deployment of the Apollo Lunar Surface Experiments Package, which carried out many experiments including one that measured the solar wind.
A Near Record Ozone Hole in 2003 (2003-10-06)

As expected, the ozone hole near Earth's South Pole is back again this year. This year's hole, being slightly larger than North America, is larger than last year but short of the record set on 2000 September 10. Ozone is important because it shields us from damaging ultraviolet sunlight.  Ozone is vulnerable, though, to CFCs and halons being released into the atmosphere.  International efforts to reduce the use of these damaging chemicals appear to be having a positive effect on their atmospheric abundance.  The relatively large size of the ozone hole this year, however, is attributed partly to colder than normal air in the surrounding stratosphere.  The above picture of the ozone hole was taken on September 11 by  TOMS on board the orbiting Earth Probe satellite.
The Colorful Horsehead Nebula (2003-10-07)

Tomorrow's picture: Galaxy Hat  < | Archive | Index | Search | Calendar | Glossary | Education | About APOD | >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Web Site Statements, Warnings, and Disclaimers NASA Official: Jay Norris. Specific rights apply. A service of: LHEA at NASA / GSFC & Michigan Tech. U.

Image credit: Canada-France-Hawaii Telescope
The Sombrero Galaxy from HST (2003-10-08)

Why does the Sombrero Galaxy look like a hat?  Reasons include the Sombrero's unusually large and extended central bulge of stars, and dark prominent dust lanes that appear in a disk that we see nearly edge-on.  Billions of old stars cause the diffuse glow of the extended central bulge.  Close inspection of the bulge in the above photograph shows many points of light that are actually globular clusters. M104's spectacular dust rings harbor many younger and brighter stars, and show intricate details astronomers don't yet fully understand.  The very center of the Sombrero glows across the electromagnetic spectrum, and is thought to house a large black hole.  Fifty million-year-old light from the Sombrero Galaxy can be seen with a small telescope towards the constellation of Virgo.
Radio Jupiter (2003-10-09)

This view of gas giant Jupiter, made from data recorded at the Very Large Array radio observatory near Socorro, New Mexico, may not look too familiar. In fact, there is no sign of a bright, round planet striped with cloud bands, sporting a Great Red Spot. Instead, the radio waves mapped in this false-color image are produced by energetic electrons trapped within Jupiter's intense magnetic field. The radio emitting region extends far beyond Jupiter's cloud tops, to over twice the visible radius of the planet, and surrounds Jupiter like an oversized version of Earth's Van Allen radiation belt. While it glows strongly at radio wavelengths, Jupiter's radiation belt is invisible in the more familiar optical and infrared views which show the Jovian cloud tops and atmospheric features in reflected sunlight.
Peculiar Arp 295 (2003-10-10)

A spectacular bridge of stars and gas stretches for nearly 250,000 light-years and joins this famous peculiar pair of galaxies cataloged as Arp 295. The cosmic bridge between the galaxies and the long tail extending below and right of picture center are strong evidence that these two immense star systems have passed close to each other in the past, allowing violent tides induced by mutual gravity to create the eye-catching plumes of stellar material. While such interactions are drawn out over billions of years, repeated close passages should ultimately result in the merger of this pair of galaxies into a larger single galaxy of stars. Although this scenario does look peculiar, galactic mergers are thought to be common, with Arp 295 representing an early stage of this inevitable process. The Arp 295 pair are the largest of a loose grouping of galaxies about 270 million light-years distant toward the constellation Aquarius. This deep color image of the region was recorded in September using the USNO 1 meter telescope near Flagstaff, Arizona.
Moonrise Over Seattle (2003-10-11)

Is the Moon larger when near the horizon?  No -- as shown above, the Moon appears to be very nearly the same size no matter its location on the sky.  Oddly, the cause or causes for the common Moon Illusion are still being debated. Two leading explanations both hinge on the illusion that foreground objects make a horizon Moon seem farther in the distance.  The historically most popular explanation then holds that the mind interprets more distant objects as wider, while a more recent explanation adds that the distance illusion may actually make the eye focus differently.  Either way, the angular diameter of the Moon is always about 0.5 degrees.  In the above time-lapse sequence taken near the end of 2001, the Moon was briefly re-imaged every 2.5 minutes, with the last exposure of longer duration to bring up a magnificent panorama of the city of Seattle.

Image credit: Shay Stephens
The Coma Cluster of Galaxies (2003-10-12)

Almost every object in the above photograph is a galaxy.  The Coma Cluster of Galaxies pictured above is one of the densest clusters known - it contains thousands of galaxies.  Each of these galaxies houses billions of stars - just as our own Milky Way Galaxy does.  Although nearby when compared to most other clusters, light from the Coma Cluster still takes hundreds of millions of years to reach us.  In fact, the Coma Cluster is so big it takes light millions of years just to go from one side to the other!  Most galaxies in Coma and other clusters are  ellipticals, while most galaxies outside of clusters are spirals.  The nature of Coma's X-ray emission is still being investigated.

Image credit: O. Lopez-Cruz   
(INAOEP) et al., 
AURA,
NOAO, 
NSF
Pelican Nebula Ionization Front (2003-10-13)

What's happening to the Pelican Nebula?  The light from young energetic stars is slowly transforming the Pelican's cold gas to hot gas, with the advancing boundary between the two known as an ionization front.  Most of these bright stars lie off the top of the image, but part of the bright ionization front crosses on the upper right. Particularly dense and intricate filaments of cold gas are visible along the front.  Millions of years from now this nebula might no longer be known as the Pelican, as the balance and placement of stars and gas will leave something that appears completely different.  The above image was taken with the Mayall 4-meter telescope at Kitt Peak National Observatory in Arizona, USA.  The large circular artifact below the image center is not real. The nebula, also known as IC 5070, spans about 30 light years and lies about 1800 light years away toward the constellation of Cygnus.
Iridescent Clouds Over Aiguille de la Tsa (2003-10-14)

Before the sun rose over the mountains, iridescent colors danced across the sky.  The unexpected light show was caused by a batch of iridescent clouds, and captured on film in early September in Arolla, Wallis, Switzerland.  The peak in the foreground of the above image is Aiguille de la Tsa.  Iridescent clouds contain patches of water droplets of nearly identical size that can therefore diffract sunlight in a nearly uniform manner.   Different colors will be deflected by different amounts and so come to the observer from slightly different directions.  Iridescent clouds are best seen outside the glare of the direct Sun although they can occasionally be seen to encircle the Sun.

Image credit: Ute Esser
(U. Heidelberg)
Space Rock SQ222 Noticed After Pass (2003-10-15)

Why didn't we see it?  An undetected asteroid zipped past the Earth undetected last month in the closest near miss yet recorded -- within a quarter of the distance to the Moon.  Such a close call is actually quite common -- what was new was that we did see it, although the detection occurred hours after it happened. In fact, a rock this size strikes the Earth roughly once a year and smaller rocks strike the Earth daily.  The global danger from the bus-sized space rock was minimal. Robert Cash of Minor Planet Research Inc. discovered asteroid  2003 SQ222 in data from the sky-scanning Lowell Observatory Near Earth Object Search (LONEOS). Pictured above is the discovery image sequence of SQ222, shown stretched vertically to be more easily viewable. Objects like SQ222 are hard to detect because they are so faint and move so fast.  An ability to scan the sky to detect, catalog, and analyze such objects has been increasing notably in recent years.

Image credit: LONEOS,
Lowell Observatory