omnianasa/nasa-apod-metadata huggingface dataset:
Hoag's Object: A Strange Ring Galaxy (2004-08-15)
Is this one galaxy or two?  This question came to light in 1950 when astronomer Art Hoag  chanced upon this unusual extragalactic object.  On the outside is a ring dominated by bright blue stars, while near the center lies a ball of much redder stars that are likely much older.  Between the two is a gap that appears almost completely dark.  How Hoag's Object formed remains unknown, although similar objects have now been identified and collectively labeled as a form of ring galaxy.  Genesis hypotheses include a galaxy collision billions of years ago and perturbative gravitational interactions involving an unusually shaped core.  The above photo taken by the Hubble Space Telescope in July 2001 reveals unprecedented details of Hoag's Object and may yield a better understanding.   Hoag's Object spans about 100,000 light years and lies about 600 million light years away toward the constellation of  Serpens.  Coincidentally, visible in the gap (at about one o'clock) is yet another ring galaxy that likely lies far in the distance.
Close-Up of the Lagoon (2004-08-16)
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.  This spectacular portion of the Lagoon Nebula taken by the CFHT was created from light emitted by hydrogen (shown in red) and light emitted by oxygen (shown in green).  The light from M8 we see today left about 5000 years ago. Light takes about 50 years to cross this section of M8.
The Unusual Blueberries at Bylot Rock (2004-08-17)
Why aren't these Martian rocks round?  Small rocks dubbed blueberries have been found by the Opportunity rover all over Meridiani Planum on Mars, but the ones perched on Bylot rock have unusually non-spherical shapes.  The strangely shaped blueberry rocks are shown above in an image taken by Opportunity's microscopic imager on August 9.  Dark sand also covers much of Bylot rock.  One hypothesis for the lack of blueberry roundness here is a coating relatively resistant to erosion.  The average diameter of a blueberry is about 4 millimeters.  The study of these and other rock features is allowing a better understanding of the wet past of ancient Mars.
Lightning on Earth (2004-08-18)
Nobody knows what causes lightning.  It is known that charges slowly separate in some clouds causing rapid electrical discharges (lightning), but how electrical charges get separated in clouds remains a topic of much research.  Nevertheless, lightning bolts are common in clouds during rainstorms, and on average 6000 lightning bolts occur between clouds and the Earth every minute.  Above, several lightning strokes were photographed under a starry sky behind Kitt Peak National Observatory near Tucson, Arizona.  Lightning has also been found on the planets Jupiter,  Saturn, and Uranus.  NASA launched the TRMM mission in 1997 that continues to measure rainfall and lightning on planet Earth.
Windblown N44F (2004-08-19)
A fast and powerful wind from a hot young star has created this stunning bubble-shaped nebula poised on the end of a bright filament of hydrogen gas. Cataloged as N44F, the cosmic windblown bubble is seen at the left of this Hubble Space Telescope image. N44F lies along the northern outskirts of the N44 complex of emission nebulae in the Large Magellanic Cloud, a mere 160,000 light-years away. The bright, blue, hot star itself is just below the center of the bubble. Peering into the bubble's interior, the Hubble image reveals dramatic structures, including pillars of dust, aligned toward N44F's hot central star. Reminiscent of dust pillars in stellar nurseries within our Milky Way galaxy, they likely contain young stars at their tips. Expanding into the surrounding gas and dust at about 12 kilometers per second, N44F is around 35 light-years across.
Raining Perseids (2004-08-20)
Comet dust rained down on planet Earth last week, streaking through dark skies in the annual Perseid meteor shower. So, while enjoying the anticipated space weather, astronomer Fred Bruenjes recorded a series of many 30 second long exposures spanning about six hours on the night of August 11/12 using a wide angle lens. Combining those frames which captured meteor flashes, he produced this dramatic view of the Perseids of summer. Although the comet dust particles are traveling parallel to each other, the resulting shower meteors clearly seem to radiate from a single point on the sky in the eponymous constellation Perseus. The radiant effect is due to perspective, as the parallel tracks appear to converge at a distance. Bruenjes notes that there are 51 Perseid meteors in the composite image, including one seen nearly head-on.
Solar Sail (2004-08-21)
Could solar sailing become a future Olympic sport? Nearly 400 years ago astronomer Johannes Kepler observed comet tails blown by a solar breeze and suggested that vessels might likewise navigate through space using appropriately fashioned sails. It is now widely recognized that sunlight does indeed produce a force which moves comet tails and a large, reflective sail could be a practical means of propelling a spacecraft. In fact, the illustration above represents a concept explored by NASA for an interstellar probe pushed along by sunlight reflected from an ultrathin sail. Nearly half a kilometer wide, the delicate solar sail would be unfurled in space. Continuous pressure from sunlight would ultimately accelerate the craft to speeds about five times higher than possible with conventional rockets. While not quite ready for the Olympics, NASA has recently tested solar sail technologies on earth and the Japanese Space Agency ISAS has deployed solar sail material in space. The Planetary Society in collaboration with the Space Research Institute (IKI) in Moscow and partners is preparing to launch Cosmos 1, a solar sail powered spacecraft.
Earth at Night (2004-08-22)
This is what the Earth looks like at night.  Can you find your favorite country or city?  Surprisingly, city lights make this task quite possible.  Human-made lights highlight particularly developed or populated areas of the Earth's surface, including the seaboards of Europe, the eastern  United States, and Japan.  Many large cities are located near rivers or oceans so that they can exchange goods cheaply by boat.  Particularly dark areas include the central parts of South America, Africa, Asia, and Australia.  The above image is actually a composite of hundreds of pictures made by the orbiting DMSP satellites. (Editor's note: This image has become an email-attachment phenomenon! It has also generated many print requests. Unfortunately, we do not sell prints. However, a high-resolution digital version of the image is available (click here or here).
Looking Out Over Mars (2004-08-23)
What would it be like to climb a hill and look out over Mars?  That opportunity was afforded the Spirit rover earlier this month as it rolled to a high perch in the Columbia Hills.  Peering out, the rolling robot spied the interior plains and distant rim of Gusev Crater, beyond an outcrop of rocks called Longhorn.  Spirit continues to find evidence that many rock shapes have been altered by ancient water.  Both Spirit and her sister robot Opportunity have completed their primary three-month mission but remain in good enough condition to continue to explore Mars.
Supply Ship Approaches the Space Station (2004-08-24)
The crew on board the International Space Station sometimes needs supplies.  As the US Space Shuttle fleet prepares to return to flight, supplies usually now come from a robot Progress supply vessel launched from Kazakhstan.  Pictured above, a Progress ship approaches the ISS on May 27, delivering over 2,500 kilograms of food, water, fuel and other important items.  The supply ship soon docked with the Zvezda Service Module while orbiting the Earth over 300 kilometers over central Asia.
Zodiacal Light and the False Dawn (2004-08-25)
Tomorrow's picture: Cas A  < | 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.
Cassiopeia A in a Million (2004-08-26)
One million seconds of x-ray image data were used to construct this view of supernova remnant Cassiopeia A, the expanding debris cloud from a stellar explosion. The stunningly detailed image from the Chandra Observatory will allow an unprecedented exploration of the catastrophic fate that awaits stars much more massive than the Sun. Seen in false-color, Cas A's outer green ring, 10 light-years or so in diameter, marks the location of the expanding shock from the original supernova explosion. At about 10 o'clock around the ring, a structure extends beyond it, evidence that the initial explosion may have also produced energetic jets. Still glowing in x-rays, the tiny point source near the center of Cas A is a neutron star, the collapsed remains of the stellar core. While Cas A is about 10,000 light-years away, light from the supernova explosion first reached Earth just over 300 years ago.
The Sedna Scenario (2004-08-27)
The discovery of Sedna (aka 2003 VB12), the most distant known object orbiting the Sun, presents a mystery. Pluto's orbit averages about 40 AU in radius, where an AU (Astronomical Unit) is the Earth-Sun distance. But the closest point in Sedna's eccentric orbit scarcely comes within 75 AU, while its farthest point extends to nearly 1,000 AU. So how did something as large as Sedna get so far out there? Exploring the problem with computer simulations, astronomers Alessandro Morbidelli and Harold Levison suggest that while Sedna was not formed in its current location, it was also not moved there by encounters with other solar system objects. Instead, they find it more likely that Sedna resides in its present orbit because of an encounter with another star. In one scenario, objects like Sedna are yanked out of closer orbits by the gravitational pull of a Sun-sized star passing near the solar system during its formative years. Alternatively Sedna could have formed of material from another system entirely, captured during an early encounter with a much smaller star. Both Sedna-forming stellar encounter scenarios are consistent with idea that the Sun itself was born in an ancient, dense, cluster of stars.
M17: A Hubble Close-Up (2004-08-28)
Sculpted by stellar winds and radiation, these fantastic, undulating shapes lie within the stellar nursery known as M17, the Omega Nebula, some 5,500 light-years away in the nebula-rich constellation Sagittarius. The lumpy features in the dense cold gas and dust are illuminated by stars off the upper left of the image and may themselves represent sites of future star formation. Colors in the fog of surrounding hotter material indicate M17's chemical make up. The predominately green glow corresponds to abundant hydrogen, with trace sulfur and oxygen atoms contributing red and blue hues. The picture spans about 3 light-years and was released in the thirteenth year of the Hubble Space Telescope's cosmic voyage of exploration.
Lunation (2004-08-29)
Our Moon's appearance changes nightly.  This time-lapse sequence shows what our Moon looks like during a lunation, a complete lunar cycle.  As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible.  The Moon always keeps the same face toward the Earth.  The Moon's apparent size changes slightly, though, and a slight wobble called a libration is discernable as it progresses along its elliptical orbit. During the cycle, sunlight reflects from the Moon at different angles, and so illuminates different features differently.  A full lunation takes about 29.5 days, just under a month (moon-th).
Announcing Comet C/2003 K4 (LINEAR) (2004-08-30)
A comet discovered last year has brightened unexpectedly and now may become visible to the unaided eye within the next month.  Designated Comet C/2003 K4 (LINEAR), the comet was discovered in 2003 May by project LINEAR.  Many reports already place the comet as brighter than magnitude 7, meaning that it can now be seen with binoculars.  Reports also indicate the comet already has a visible tail nearly the length of a full Moon.  Since predicting the future brightness of comets is a very tricky business, there remains the possibility that K4 might never become very bright.  Current predictions, however, estimate the comet may approach fifth magnitude in October.  K4 passes closest to the Sun on October 12 and then closest to the Earth on December 23.  Comet K4 was photographed above from Van Buren, Arkansas, USA on August 17.
The Dotted Dunes of Mars (2004-08-31)
What causes the black dots on dunes on Mars?  As spring dawns on the Northern Hemisphere of Mars, 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.  By summer, the spots will have expanded to encompass the entire dunes that will then be 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.  Meanwhile, in the Southern Hemisphere of Mars, the Earth-sent robot Martian rovers will try to survive through Martian winter, which peaks in mid-September.
An Inner Neptune for 55 Cancri (2004-09-01)
Is our Solar System unique?  The discovery of a Neptune-mass planet in an sub-Mercury orbit around nearby Sun-like star 55 Cancri, announced yesterday along with the discovery of other similar systems, gives a new indication that planetary systems as complex as our own  Solar System likely exist elsewhere.  The planet, discovered in data from the Hobby-Eberly telescope in Texas, the Lick Observatory in California, and the orbiting Hubble Space Telescope, is one of four planets now known to orbit  55 Cancri -- the others being similar in mass to Jupiter.  The finding involved noting subtle changes in the speed of the star caused by its orbiting planets.  The above drawing depicts what this planet might look like, assuming a mass similar to Neptune, but a composition similar to Earth.  The star 55 Cancri, only 40 light-years distant, is visible with binoculars towards the constellation of Cancer.
The Large Cloud of Magellan (2004-09-02)
Portuguese navigator Fernando de Magellan and his crew had plenty of time to study the southern sky during the first circumnavigation of planet Earth. As a result, two fuzzy cloud-like objects easily visible for southern hemisphere skygazers are known as the Clouds of Magellan. Of course, these star clouds are now understood to be dwarf irregular galaxies, satellites of our larger spiral Milky Way galaxy. The Large Magellanic Cloud (LMC) pictured above is only about 180,000 light-years distant in the constellation Dorado. Spanning about 15,000 light-years or so, it is the most massive of the Milky Way's satellite galaxies and is the site of the closest supernova in modern times.  The prominent red knot on the right is 30 Doradus, or the Tarantula Nebula, a giant star-forming region in the Large Magellanic Cloud.
Hurricane Frances Approaches Florida (2004-09-03)
A major hurricane is heading for Florida.  Hurricane Frances, one of the stronger storm systems of modern times, may cross the eastern coast of Florida sometime tomorrow.  Those in the path of a hurricane should take precautions.  For example, NASA's Kennedy Space Center has completely shut down.  The orbiting GOES-12 satellite took the above image of Hurricane Frances early yesterday. Hurricanes are huge swirling storms with cloud systems typically larger than a state.  Tropical cyclones, called hurricanes in Earth's Western Hemisphere and typhoons in the Eastern Hemisphere, get their immense energy from warm evaporated ocean water.  As this water vapor cools and condenses, it heats the air, lowers pressure and hence causes cooler air to come swooshing in.  Winds can reach over 250 kilometers per hour and become very dangerous.  Much remains unknown about cyclones, including how they are formed and the exact path they will take.
Neutron Mars (2004-09-04)
Looking for water on Mars, researchers using detectors on board the orbiting Mars Odyssey spacecraft have created this false-color global map of energetic neutrons from the otherwise Red Planet. What do neutrons have to do with water? As cosmic rays from interplanetary space penetrate the thin martian atmosphere and reach the surface they interact with elements in the upper layer of soil, scattering neutrons back into space. But if the martian soil contains hydrogen, it seriously absorbs energetic scattered neutrons. Tracking variations in absorption, neutron detectors can map changes in surface hydrogen content from orbit. Hydrogen content is taken as a surrogate measure of frozen water (H20), the most likely form of hydrogen close to the martian surface. Thus, bluer shades in the above map correspond to larger presumed concentrations of near-surface water ice. Water ice at the martian poles came as no surprise, but significant concentrations also seem to be present at lower latitudes. The melting of such near-surface ice could be responsible for the formation of martian gullies.
M51: The Whirlpool Galaxy in Dust and Stars (2004-09-05)
The Whirlpool Galaxy is a classic spiral galaxy.  At only 30 million light years distant and fully 60 thousand light years across, M51, also known as  NGC 5194, is one of the brightest and most picturesque galaxies on the sky.  The above image is a digital combination of a ground-based image from the 0.9-meter telescope at Kitt Peak National Observatory and a space-based image from the Hubble Space Telescope highlighting sharp features normally too red to be seen. Anyone with a good pair of binoculars, however, can see this Whirlpool toward the constellation of Canes Venatici.  M51 is a spiral galaxy of type Sc and is the dominant member of a whole group of galaxies.  Astronomers speculate that M51's spiral structure is primarily due to its gravitational interaction with a smaller galaxy just off the top of this digitally sharpened image.
C153 Takes the Plunge (2004-09-06)
A comet-like tail of glowing gas, 200,000 light-years long, streams from galaxy C153 as it plunges through galaxy cluster Abell 2125 at nearly 8 million kilometers per hour. Itself a member of the giant cluster of galaxies, C153 may once have been a spiral galaxy like the Milky Way. But this remarkable series of images, false-color composites of x-ray and optical data, zooms in on the galaxy's fate. A headlong passage through the hot intracluster gas in the central regions of Abell 2125 is seen to be stripping C153 of its own star forming material and distorting its shape. As other galaxies in the cluster suffer a similar fate, the hot gas collecting in the cluster's core should become enriched in heavy elements. The violent spectacle was taking place about 3 billion light-years from Earth and is thought to illustrate a common process in the cosmic evolution of large clusters of galaxies.
A Supernova in Nearby Galaxy NGC 2403 (2004-09-07)
The closest and brightest supernova in over a decade was recorded just over a month ago in the outskirts of nearby galaxy NGC 2403.  Officially tagged SN 2004dj, the Type IIP explosion likely annihilated most of a blue supergiant star as central fusion could no longer hold it up.  The supernova can be seen as the bright object in the above image in the direction of the arrow.  The home galaxy to the supernova, spiral galaxy NGC 2403, is located only 11 million light years away and is visible with binoculars toward the northern constellation of Camelopardalis (the Giraffe).  The supernova is fading but still visible with a telescope, once peaking at just brighter than magnitude 12.  Supernovas of this type change brightness in a predictable way and may be searched for in the distant universe as distance indicators.
Molecular Torus Surrounds Black Hole (2004-09-08)
Why do some black hole surroundings appear brighter than others?  In the centers of active galaxies, supermassive black holes at least thousands of times the mass of our Sun dominate.  Many, called Seyfert Type I, are very bright in visible light.  Others, called Seyfert Type II, are rather dim.  The difference might be caused by some black holes accreting much more matter than others.  Alternatively, the black holes in the center of Seyfert Type II galaxies might be obscured by a surrounding torus.  To help choose between these competing hypotheses, the nearby Seyfert II galaxy NGC 4388 has been observed in X-ray light recently by many recent Earth-orbiting X-ray observatories, including CGRO, SIGMA, BeppoSAX, INTEGRAL, Chandra, and XMM-Newton.  Recent data from INTEGRAL and XMM-Newton have found that the X-ray flux in some X-ray colors varies rapidly, while flux in other X-ray colors is quite steady.  The constant flux and apparent absorption of very specific X-ray colors by cool iron together give evidence that the central black hole in NGC 4388 is seen through a thick torus composed of molecular gas and dust.
Sagittarius Triplet (2004-09-09)
These three bright nebulae are often featured in telescopic tours of the constellation Sagittarius and the view toward the center of our Milky Way galaxy. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the nebula above and left of center, and colorful M20 at the lower left. The third, NGC 6559, is at the right 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. In this gorgeous digital composition, the dominant red color of the emission nebulae is due to glowing hydrogen gas energized by the radiation of hot, young stars. The contrasting blue hues, most striking in the Trifid as well as NGC 6559, are due to dust reflected starlight.
Cat's Eye (2004-09-10)
Staring across interstellar space, the alluring Cat's Eye nebula lies three thousand light-years from Earth. A classic planetary nebula, the Cat's Eye (NGC 6543) represents a final, brief yet glorious phase in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells by shrugging off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood. Seen so clearly in this sharp Hubble Space Telescope image, the truly cosmic eye is over half a light-year across.  Of course, gazing into the Cat's Eye, astronomers may well be seeing the fate of our sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.
The Star Trails of Kilimanjaro (2004-09-11)
The night had no moon, but the stars were out. And camped at 16,000 feet on Mt. Kilimanjaro, photographer Dan Heller recorded this marvelous 3 1/2 hour long exposure. Here the landscape is lit mostly by the stars. Flashlights give the tents an erie internal radiance while the greenish glow from the distant city lights of Moshi, Tanzania filter through the clouds below. The view from this famous equatorial African mountain is toward the south, putting the South Celestial Pole close to the horizon on the far left, near the center of the graceful concentric star trail arcs. In the thin air and clear dark skies, even the ghostly Milky Way left a faint triangular glow as it swept across the middle of the dreamlike scene.