juliensimon/nasa-apod huggingface dataset:
NGC 4013 and the Tidal Stream (2008-02-07)

Nearly 50 million light-years away in the constellation Ursa Major, NGC 4013 was long considered an isolated island universe. Seen edge-on, the gorgeous spiral galaxy was known for its flattened disk and central bulge of stars, cut by silhouetted dust lanes. But this deep color image of the region reveals a previously unknown feature associated with NGC 4013, an enormous, faint looping structure extending (above and toward the left) over 80 thousand light-years from the galaxy's center.  A detailed exploration of the remarkable structure reveals it to be a stream of stars originally belonging to another galaxy, likely a smaller galaxy torn apart by gravitational tides as it merged with the larger spiral. Astronomers argue that the newly discovered tidal stream also explains a warped distribution of neutral hydrogen gas seen in radio images of NGC 4013 and offers parallels to the formation of our own Milky Way galaxy.

Image credit: R Jay Gabany
(Blackbird Observatory) - collaboration;
D.Martínez-Delgado(IAC,
MPIA),

M.Pohlen (Cardiff),
S.Majewski (U.Virginia),
J.Peñarrubia
(U.Victoria),
C.Palma (Penn State)
The Bay of Rainbows (2008-02-08)

Dark, smooth regions that cover the Moon's familiar face are called by Latin names for oceans and seas. The naming convention is historical, though it may seem a little ironic to denizens of the space age who recognize the Moon as a mostly dry and airless world, and the smooth, dark areas as lava-flooded impact basins. For example, this elegant lunar vista, a careful mosaic of telescopic images, looks across the expanse of the northwestern Mare Imbrium, or Sea of Rains, into the Sinus Iridum - the Bay of Rainbows. Ringed by the Jura Mountains (montes), the bay is about 250 kilometers across, bounded at the bottom of the rugged arc by Cape (promontorium) Laplace. The cape's sunlit face towers nearly 3,000 meters above the bay's surface. At the top of the arc is Cape Heraclides, at times seen as a moon maiden.

Image credit: Alan Friedman
Atlantis on Pad 39A (2008-02-09)

An intricate network of lighting plays across the 130 foot high Rotating Service Structure (RSS) in this dramatic night view of the Space Shuttle Atlantis on the Kennedy Space Center's launch pad 39A. Small human figures visible in silhouette emphasize the structure's enormous scale. Seen here after rolling back before Thursday's shuttle launch, the RSS provides pre-launch access to the orbiter and its payload. For this mission to the International Space Station, STS-122, Atlantis' payload is the European Space Agency's Columbus science laboratory. During the mission, three space walks are planned to attach the Columbus lab. Atlantis is expected to dock with the space station today.
Abell 2218: A Galaxy Cluster Lens (2008-02-10)

Gravity can bend light, allowing huge clusters of galaxies to act as telescopes.  Almost all of the bright objects in this Hubble Space Telescope image are galaxies in the cluster known as Abell 2218.  The cluster is so massive and so compact that its gravity bends and focuses the light from galaxies that lie behind it.  As a result, multiple images of these background galaxies are distorted into long faint arcs -- a simple lensing effect analogous to viewing distant street lamps through a glass of wine.  The cluster of galaxies Abell 2218 is itself about three billion light-years away in the northern constellation of the Dragon (Draco). The power of this massive cluster telescope has allowed astronomers to detect a galaxy at redshift 5.58, the most distant galaxy yet measured.  This young, still-maturing galaxy is faintly visible to the lower right of the cluster core.
Saturn's Moon Epimetheus from the Cassini Spacecraft (2008-02-11)

How did Epimetheus form?  No one is yet sure.  To help answer that question, this small moon has recently been imaged again in great detail by the robot spacecraft Cassini now orbiting Saturn.  Epimetheus sometimes orbits Saturn in front of  Janus, another small satellite, but sometimes behind. The above image, taken last December, shows a surface covered with craters indicating great age.  Epimetheus spans about 115 kilometers across.  Epimetheus does not have enough surface gravity to restructure itself into a sphere. The flattened face of Epimetheus shown above might have been created by a single large impact.
Echoes from RS Pup (2008-02-12)

This dusty reflection nebula surrounds pulsating star RS Pup, some 10 times more massive than the Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid type variable star; a class of stars whose brightness is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance scale. As RS Pup pulsates over a period of about 40 days, its regular changes in brightness are also seen along the nebula delayed in time, effectively a light echo. The otherwise overwhelming light from RS Pup itself is hidden behind the dark central stripe in the color image. Using new measurements of the time delay and angular size of the nebula, the known speed of light allows astronomers to geometrically determine the distance to RS Pup to be 6,500 light-years, with a remarkably small error of plus or minus 90 light-years. An impressive achievement for stellar astronomy, the echo-measured distance also more accurately establishes the true brightness of RS Pup, and by extension other Cepheid stars, improving the knowledge of distances to galaxies beyond the Milky Way.
Elliptical Galaxy NGC 1132 (2008-02-13)

NGC 1132 is one smooth galaxy -- but how did it form? As an elliptical galaxy, NGC 1132 has little dust and gas, and few stars have formed in it recently. Although many elliptical galaxies are in clusters of galaxies, NGC 1132 appears as a large, isolated galaxy toward the constellation of the River (Eridanus).  To probe the history of this intriguing trillion-star ball, astronomers imaged NGC 1132 in both visible light with the Hubble Space Telescope and X-ray light with the Chandra X-ray Observatory.  In this composite false-color image, visible light is white, while the X-ray light is blue and indicates the unusual presence of very hot gas.  The X-ray light also likely traces out the location of dark matter. One progenitor hypothesis is that NGC 1132 is the result of a series of galaxy mergers in what once was a small group of galaxies.  NGC 1132 is over 300 million light years away, so the light we see from it today left before dinosaurs roamed the Earth.   Many fascinating background galaxies can be seen far in the distance.
Long Stem Rosette (2008-02-14)

The Rosette Nebula (aka NGC 2237) is not the only cosmic cloud of gas and dust to evoke the imagery of flowers. But it is the one most often suggested as a suitable astronomy image for Valentine's Day. Of the many excellent Rosette Nebula pictures submitted to APOD editors, this view seemed most appropriate, with a long stem of glowing hydrogen gas in the region included in the composition. At the edge of a large molecular cloud in Monoceros, some 5,000 light years away, the petals of this rose are actually a stellar nursery whose lovely, symmetric shape is sculpted by the winds and radiation from its central cluster of hot young stars. The stars in the energetic cluster, cataloged as NGC 2244, are only a few million years old, while the central cavity in the Rosette Nebula is about 50 light-years in diameter. Happy Valentine's Day!

Image credit: Caelum
Observatory
Young Stars in the Rho Ophiuchi Cloud (2008-02-15)

Cosmic dust clouds and embedded newborn stars glow at infrared wavelengths in this tantalizing false-color view from the Spitzer Space Telescope. Pictured is of one of the closest star forming regions, part of the Rho Ophiuchi cloud complex some 400 light-years distant near the southern edge of the pronounceable constellation Ophiuchus. The view spans about 5 light-years at that estimated distance. After forming along a large cloud of cold molecular hydrogen gas, newborn stars heat the surrounding dust to produce the infrared glow. An exploration of the region in penetrating infrared light has detected some 300 emerging and newly formed stars whose average age is estimated to be a mere 300,000 years -- extremely young compared to the Sun's age of 5 billion years.
Large Binocular Telescope (2008-02-16)

With moonlight on the horizon, a starry sky and the northern Milky Way provide the background for this dramatic view of the World at Night. The imposing structure in the foreground houses the Large Binocular Telescope (LBT), on Mount Graham, Arizona. Inside, the two 8.4 meter diameter mirrors of the LBT really are side-by-side on a common mount, an arrangement mimicking the design of more modest optical equipment usually carried around the neck. While not exactly portable, the benefits of the large scale binocular configuration adopted include an increase in sensitivity over a single mirror telescope and high resolution imaging for faint objects over a relatively wide field of view. An international collaboration operates the LBT Observatory.

Image credit: Stefan Seip
M1: The Crab Nebula from Hubble (2008-02-17)

This is the mess that is left when a star explodes.  The Crab Nebula, the result of a supernova seen in 1054 AD, is filled with mysterious filaments.  The filaments are not only tremendously complex, but appear to have less mass than expelled in the original supernova and a higher speed than expected from a free explosion.  The above image, taken by the Hubble Space Telescope, is presented in three colors chosen for scientific interest.  The Crab Nebula spans about 10 light-years.  In the nebula's very center lies a pulsar: a neutron star as massive as the Sun but with only the size of a small town.  The Crab Pulsar rotates about 30 times each second.
BLG-109: A Distant Version of our own Solar System (2008-02-18)

How common are planetary systems like our own? Perhaps quite common, as the first system of planets like our own Solar System has been discovered using a newly adapted technique that, so far, has probed only six planetary systems.  The technique, called gravitational microlensing, looks for telling brightness changes in measured starlight when a foreground star with planets chances almost directly in front of a more distant star. The distant star's light is slightly deflected in predictable ways by the gravity of the closer system. Recently a detailed analysis of microlensing system OGLE-2006-BLG-109 has related brightness variations to two planets that are similar to Jupiter and Saturn of our own Solar System.  This discovery carries the tantalizing implication that interior planets, possibly including Earth-like planets, might also be common. Pictured above is an artistic conception of how the BLG-109 planetary system might look.
Columbus Laboratory Installed on Space Station (2008-02-19)

The International Space Station (ISS) has been equipped with a powerful new scientific laboratory. The Space Shuttle Atlantis delivered the Columbus Laboratory to the ISS and installed the seven meter long module over the past week. Columbus has ten racks for experiments that can be controlled from the station or the Columbus Control Center in Germany.  The first set of experiments includes the Fluid Science Laboratory that will explore fluid properties in the microgravity of low Earth orbit, and Biolab which supports experiments on microorganisms. Future Columbus experiments include an atomic clock that will test minuscule timing effects including those expected by Einstein's General Theory of Relativity.  Pictured above, mission specialist Hans Schlegel works on the outside of Columbus.  Scientists from all over the world may propose and carry out experiments to be done on the laboratory during its ten year mission.    Watch the Total Lunar Eclipse the night of Feb. 20/21.
Moon Slide Slim (2008-02-20)

No special filters - or even a telescope - are required to enjoy a leisurely lunar eclipse. In fact, watched from all over the night side of planet Earth, these regular celestial performances have entertained many casual skygazers. Still, this eye-catching picture of a lunar eclipse may look unfamiliar. To make it, astroimager Stefan Seip set his camera on a tripod and locked the shutter open during the total lunar eclipse of March 3, 2007. The resulting image records the trail of the Moon (and narrower trails of stars) sliding through the night. Reddish hues common during the total phase of a lunar eclipse, are evident along the darker, slimmer portion of the Moon trail. At least part of tonight's lunar eclipse will be visible in clear skies over the Americas, Europe, Africa and western Asia. The eclipse lasts over three hours from start to finish, with about 50 minutes of totality. Tonight's eclipse is the last total lunar eclipse until December of 2010.    Lunar eclipse: Times | Webcast | Photo Tips

Image credit: Stefan Seip
Orion's Horsehead Nebula (2008-02-21)

The Horsehead Nebula is one of the most famous nebulae on the sky.  It is visible as the dark indentation to the red emission nebula seen just below and left of center in the this photograph.  The brightest star on the left is located in the belt of the familiar constellation Orion. The horse-head feature is dark because it is really an opaque dust cloud that lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance.  After many thousands of years, the internal motions of the cloud will alter its appearance.  The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms.  Also visible in the picture are blue reflection nebulae that preferentially reflect the blue light from nearby stars.

Image credit: Victor Bertol
Eclipsed Moonlight (2008-02-22)

Moon watchers blessed with clear skies over the Americas, Europe, Africa and western Asia enjoyed a total lunar eclipse this week. Catching eclipsed moonlight, astroimager Jerry Lodriguss offers this view of the inspiring celestial event with the shadowed Moon accompanied by wandering planet Saturn at the left, and bright Regulus, alpha star of the constellation Leo, above. The engaging composite picture was made by combining a filtered, telephoto image of the Moon and surrounding starfield with a telescopic exposure. The combination dramatizes the reddened moonlight while clearly showing the variation of brightness and color in Earth's not-so-dark shadow across the lunar surface.

Image credit: Catching the Light
Stereo Space Station (2008-02-23)

Get out your red-blue glasses and float next to the International Space Station (ISS), planet Earth's largest artificial moon. This fun stereo view was constructed from parts of two separate images (S122-E-009880, S122-E-009893) and an additional background recorded as the shuttle orbiter Atlantis undocked from the ISS on February 18. Atlantis and the ISS were traveling over 7,500 meters per second at an altitude of about 350 kilometers. The shiny, 7 meter long module extending from the station at the lower right is ESA's Columbus Laboratory, delivered by Atlantis and installed by spacewalking astronauts. After a successful 13 day mission to the ISS, Atlantis landed at Kennedy Space Center on Wednesday.
NGC 4676: When Mice Collide (2008-02-24)

These two mighty galaxies are pulling each other apart.  Known as " The Mice" because they have such long tails, each spiral galaxy has likely already passed through the other. They will probably collide again and again until they coalesce.  The long tails are created by the relative  difference between gravitational pulls on the near and far parts of each galaxy.  Because the distances are so large, the cosmic interaction takes place in slow motion -- over hundreds of millions of years.  NGC 4676 lies about 300 million light-years away toward the constellation of Bernice's Hair (Coma Berenices) and are likely members of the Coma Cluster of Galaxies.  The above picture was taken with the Hubble Space Telescope's Advanced Camera for Surveys which is more sensitive and images a larger field than previous Hubble cameras.  The camera's increased sensitivity has imaged, serendipitously, galaxies far in the distance scattered about the frame.
Dawn of the Large 
Hadron Collider (2008-02-25)

Why do objects have mass?  To help find out, Europe's CERN has built the Large Hadron Collider (LHC), the most powerful particle accelerator yet created by humans.   This May, the LHC is scheduled to start smashing protons into each other with unprecedented impact speeds.  The LHC will explore the leading explanation that mass arises from ordinary particles slogging through an otherwise invisible but pervasive field of virtual Higgs particles.   Were high energy colliding particles to create real Higgs bosons, the Higgs mechanism for mass creation may be bolstered.   LHC will also look for micro black holes, magnetic monopoles, and explore the possibility that every type of fundamental particle we know about has a nearly invisible supersymmetric counterpart.  The LHC@Home project will allow anyone with a home computer to help LHC scientists search archived LHC data for these strange beasts. Pictured above, a person stands in front of the huge ATLAS detector, one of six detectors being attached to the LHC.

Image credit: CERN
Mysterious Acid Haze on Venus (2008-02-26)

Why did an acidic haze spread across Venus?  The unusual clouds were discovered last July by ESA's robotic Venus Express spacecraft currently orbiting Venus.  The bright and smooth haze was found by Venus Express to be rich in sulfuric acid, created when an unknown process lifted water vapor and sulphur dioxide from lower levels into Venus' upper atmosphere.  There, sunlight broke these molecules apart and some of them recombined into the volatile sulfuric acid.  Over the course of just a few days last July, the smooth acidic clouds spread from the South Pole of Venus across half the planet.  The above false-color picture of Venus was taken last July 23rd in ultraviolet light, and shows the unusual haze as relatively smooth regions across the image bottom. The cause of the dark streaks in the clouds is also not yet understood and is being researched.
The Eagle Nebula in Hydrogen, Oxygen, and Sulfur (2008-02-27)

Bright blue stars are still forming in the dark pillars of the Eagle Nebula.  Made famous by a picture from the Hubble Space Telescope in 1995, the Eagle Nebula shows the dramatic process of star formation.  The above picture taken by a 0.8-meter telescope in the Canary Islands captures part of M16, the open cluster of stars that is being created.  The high amount of detail in the above image results from it being taken only in specific colors of light emitted by hydrogen, oxygen, and sulfur.  The bright blue stars of M16 have been continually forming over the past 5 million years, most recently in the famous central gas and dust columns that have been informally dubbed the Pillars of Creation and the Fairy. Light takes about 7,000 years to reach us from M16, which spans about 20 light years and can be seen with binoculars toward the constellation of the Serpent (Serpens).

Image credit: IAC, 
Daniel Lopez
ISS: Sunlight to Shadow (2008-02-28)

Orbiting 400,000 kilometers above the Earth, the Moon slid into Earth's shadow to begin last week's total lunar eclipse. Of course the International Space Station (ISS) slides into Earth's shadow every 90 minutes, the time it takes it to complete one orbit at an altitude of about 400 kilometers. Recorded near sunset on February 7, looking toward the north, this composite of 70 exposures shows the trail of the ISS (with gaps between exposures) as it moved left to right over the city of Tübingen in southern Germany. Beginning in sunlight on the left, the ISS vanishes as it enters Earth's shadow at the far right, above the northeastern horizon. As seen from Tübingen, the passage took about 4 minutes. Clicking on the image will download a time-lapse animation (mpg file) based on the individual exposures that includes a plane flying along the horizon.

Image credit: Till Credner
Twelve Lunar Eclipses (2008-02-29)

Welcome to the extra day in the Gregorian Calendar's leap year 2008! To celebrate, consider this grid of lunar eclipse pictures - starting in leap year 1996 and ending with February's eclipse - with the date in numerical year/month/day format beneath each image. Mostly based on visibility from a site in Turkey, the 3x4 matrix includes 11 of the 13 total lunar eclipses during that period, and fills out the grid with the partial lunar eclipse of September 2006. Still, as the pictures are at the same scale, they illustrate a noticeable variation in the apparent size of the eclipsed Moon caused by the real change in Earth-Moon distance around the Moon's elliptical orbit. The total phases are also seen to differ in color and darkness. Those effects are due to changes in cloud cover and dust content in the atmosphere reddening and refracting sunlight into Earth's shadow. Of course, the next chance to add a total lunar eclipse to this grid will come at the very end of the decade.

Image credit: Tunç Tezel
Mauna Kea Shadow Play (2008-03-01)

Just opposite the setting Sun, the already-eclipsed Moon rose over the Hawaiian Islands on February 20. A view near the 14,000 foot peak of volcanic Mauna Kea on the Big Island, a popular spot for astronomers, offered this remarkable play of shadows and sunlight. With snowy cinder cones in the foreground, the Moon lies within the shadow cast by the mountain -- a shadow extending across a lower cloud deck and on through Earth's dense atmosphere. As the lunar eclipse is drawing to a close, the curved shadow of the limb of planet Earth itself can also be traced across the Moon's surface, some 400,000 kilometers away.

Image credit: Alex Mukensnable
Comet Hale-Bopp Over Val Parola Pass (2008-03-02)

Comet Hale-Bopp, the Great Comet of 1997, became much brighter than any surrounding stars. It was seen even over bright city lights. Away from city lights, however, it put on quite a spectacular show. Here Comet Hale-Bopp was photographed above Val Parola Pass in the Dolomite mountains surrounding Cortina d'Ampezzo, Italy. Comet Hale-Bopp's blue ion tail, consisting of ions from the comet's nucleus, is pushed out by the solar wind. The white dust tail is composed of larger particles of dust from the nucleus driven by the pressure of sunlight, that orbit behind the comet. Observations showed that Comet Hale-Bopp's nucleus spins about once every 12 hours.

Image credit: A. Dimai, (Col Druscie Obs.),
AAC
Sand Dunes Thawing on Mars (2008-03-03)

What are these strange shapes on Mars?  Defrosting sand dunes. As spring now dawns on the Northern Hemisphere of Mars, dunes of sand near the pole, as pictured above, are beginning to thaw.  The carbon dioxide and water ice actually sublime in the thin atmosphere directly to gas.  Thinner regions of ice typically defrost first revealing sand whose darkness soaks in sunlight and accelerates the thaw.  The process might even involve sandy jets exploding through the thinning ice.  By summer, spots will expand to encompass the entire dunes.  The Martian North Pole is ringed by many similar fields of barchan sand dunes, whose strange, smooth arcs are shaped by persistent Martian winds.
NGC 6334: The Cat's Paw Nebula (2008-03-04)

Nebulae are perhaps as famous for being identified with familiar shapes as perhaps cats are for getting into trouble.  Still, no known cat could have created the vast  Cat's Paw Nebula visible in Scorpius.  At 5,500 light years distant, Cat's Paw is an emission nebula with a red color that originates from an abundance of ionized hydrogen atoms.  Alternatively known as the Bear Claw Nebula or NGC 6334, stars nearly ten times the mass of our Sun have been born there in only the past few million years. Pictured above, the end of the Cat's Paw nebula was imaged from the Blanco 4-meter Telescope in Chile.

Image credit: T. A. Rector