juliensimon/nasa-apod huggingface dataset:
All the Water on Europa (2012-05-24)

How much of Jupiter's moon Europa is made of water? A lot, actually. Based on the Galileo probe data acquired during its exploration of the Jovian system from 1995 to 2003, Europa possesses a deep, global ocean of liquid water beneath a layer of surface ice. The subsurface ocean plus ice layer could range from 80 to 170 kilometers in average depth. Adopting an estimate of 100 kilometers depth, if all the water on Europa were gathered into a ball it would have a radius of 877 kilometers. To scale, this intriguing illustration compares that hypothetical ball of all the water on Europa to the size of Europa itself (left) - and similarly to all the water on planet Earth. With a volume 2-3 times the volume of water in Earth's oceans, the global ocean on Europa holds out a tantalizing destination in the search for extraterrestrial life in our solar system.   Help Evaluate APOD: Is the text on APOD easy to read and understand?

Image credit: JPL/Caltech
Scorpius in Red and Blue (2012-05-25)

Cosmic dust clouds dim the light of background stars. But they also reflect the light of stars nearby. Since bright stars tend to radiate strongly in the blue portion of the visible spectrum, and the interstellar dust scatters blue light more strongly than red, the dusty reflection nebulae tend to be blue. Lovely examples are the wispy blue reflection nebulae near bright, hot stars Pi and Delta Scorpii (upper left and lower right) in this telescopic skyscape from the head of the constellation Scorpius. Of course, the contrasting red emission nebulae are also caused by the hot stars' energetic radiation. Ultraviolet photons ionize hydrogen atoms in the interstellar clouds producing the characteristic red hydrogen alpha emission line as the electrons recombine. About 600 light-years away, the nebulae are found in the second version of the Sharpless Catalog as Sh2-1 (left, with reflection nebulae VdB 99) and Sh2-7. At that distance, this field of view is about 40 light-years across.

Image credit: John Davis
At the Edge of NGC 891 (2012-05-26)

This sharp cosmic portrait features NGC 891. The spiral galaxy spans about 100 thousand light-years and is seen almost exactly edge-on from our perspective. In fact, about 30 million light-years distant in the constellation Andromeda, NGC 891 looks a lot like our Milky Way. At first glance, it has a flat, thin, galactic disk and a central bulge cut along the middle by regions of dark obscuring dust. The combined image data also reveal the galaxy's young blue star clusters and telltale pinkish star forming regions. And remarkably apparent in NGC 891's edge-on presentation are filaments of dust that extend hundreds of light-years above and below the center line. The dust has likely been blown out of the disk by supernova explosions or intense star formation activity. Faint neighboring galaxies can also be seen near this galaxy's disk.
Mercury Spotting (2012-05-27)

Can you spot the planet? The diminutive disk of Mercury, the solar system's innermost planet, spent about five hours crossing in front of the enormous solar disk in 2003, as viewed from the general vicinity of planet Earth. The Sun was above the horizon during the entire transit for observers in Europe, Africa, Asia, or Australia, and the horizon was certainly no problem for the sun-staring SOHO spacecraft. Seen as a dark spot, Mercury progresses from left to right (top panel to bottom) in these four images from SOHO's extreme ultraviolet camera. The panels' false-colors correspond to different wavelengths in the extreme ultraviolet which highlight regions above the Sun's visible surface. This was the first of 14 transits of Mercury which will occur during the 21st century. Next week, however, an event much more rare but easier to spot will occur -- a transit of Venus across the Sun. Need help spotting Mercury? Just click on the picture.   New Image Feeds: APOD River on Google Plus and APOD Sky on Facebook
Contemplating the Sun (2012-05-28)

Have you contemplated your home star recently? Pictured above, a Sun partially eclipsed on the top left by the Moon is also seen eclipsed by earthlings contemplating the eclipse below. The above menagerie of silhouettes was taken from the Glen Canyon National Recreation Area near Page, Arizona, USA, where park rangers and astronomers expounded on the unusual event to interested gatherers. Also faintly visible on the Sun's disk, just to the lower right of the dark Moon's disk, is a group of sunspots.  Although exciting, some consider this event a warm-up act for next week's chance to comtemplate the Sun -- a much more rare partial eclipse by the planet Venus.   Astronomy Seminar of the Week: The 2012 Transit of Venus

Image credit: Steven Gilbert
Sentinels of the Arctic (2012-05-29)

Who guards the north?  Judging from the above photograph, possibly giant trees covered in snow and ice. The picture was taken last winter in Finnish Lapland where weather can include sub-freezing temperatures and driving snow.  Surreal landscapes sometimes result, where common trees become cloaked in white and so appear, to some, as watchful aliens. Far in the distance, behind this uncommon Earthly vista, is a more common sight -- a Belt of Venus that divided a darkened from sunlit sky as the Sun rose behind the photographer. Of course, in the spring, the trees have thawed and Lapland looks much  different.   Astronomy Seminar of the Week: The 2012 Transit of Venus

Image credit: Niccol� Bonfadini
Looking Back at an Eclipsed Earth (2012-05-30)

What's that dark spot on planet Earth? It's the shadow of the Moon. The above image of Earth was taken last week by MTSAT during an annular eclipse of the Sun. The dark spot appears quite unusual as clouds are white and the oceans are blue in this color corrected image. Earthlings residing within the dark spot would see part of the Sun blocked by the Moon and so receive less sunlight than normal. The spot moved across the Earth at nearly 2,000 kilometers per hour, giving many viewers less than two hours to see a partially eclipsed Sun. MTSAT circles the Earth in a geostationary orbit and so took the above image from about three Earth-diameters away. Sky enthusiasts might want to keep their eyes pointed upward this coming week as a partial eclipse of the Moon will occur on June 4 and a transit of Venus across the face of the Sun will occur on June 5.   Note:  An APOD editor is scheduled to appear on Weekly Space Hangout tomorrow.
Lantern Saturn (2012-05-31)

Known for its bright ring system and many moons, gas giant Saturn looks strange and unfamiliar in this false-color view from the Cassini spacecraft. In fact, in this Visual and Infrared Mapping Spectrometer (VIMS) mosaic the famous rings are almost invisible, seen edge-on cutting across picture center. The most striking contrast in the image is along the terminator or boundary between night and day. To the right (day side) blue-green hues are visible sunlight reflected from Saturn's cloud tops. But on the left (night side) in the absence of sunlight, the lantern-like glow of infrared radiation from the planet's warm interior silhouettes features at Saturn's deeper cloud levels. The infrared glow also shines from the broad shadows of Saturn's rings sweeping across the planet's upper hemisphere.
A Sagittarius Triplet (2012-06-01)

These three bright nebulae are often featured in telescopic tours of the constellation Sagittarius and the crowded starfields of the central Milky Way. In fact, 18th century cosmic tourist Charles Messier cataloged two of them; M8, the large nebula left of center, and colorful M20 on the right. The third, NGC 6559, is above M8, separated from 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. M20's popular moniker is the Trifid. Glowing hydrogen gas creates the dominant red color of the emission nebulae, with contrasting blue hues, most striking in the Trifid, due to dust reflected starlight. This broad skyscape also includes one of Messier's open star clusters, M21, just above and right of the Trifid.

Image credit: Martin Pugh
M51: The Whirlpool Galaxy (2012-06-02)

Follow the handle of the Big Dipper away from the dipper's bowl until you get to the handle's last bright star. Then, just slide your telescope a little south and west and you might find this stunning pair of interacting galaxies, the 51st entry in Charles Messier famous catalog. Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also cataloged as NGC 5194. Its spiral arms and dust lanes clearly sweep in front of its companion galaxy (top), NGC 5195. The pair are about 31 million light-years distant and officially lie within the angular boundaries of the small constellation Canes Venatici. Though M51 looks faint and fuzzy to the human eye, deep images like this one can reveal the faint tidal debris around the smaller galaxy.

Image credit: Osservatorio MTM
A Picturesque Venus Transit (2012-06-03)

The rare transit of Venus across the face of the Sun in 2004 was one of the better-photographed events in sky history.  Both scientific and artistic images flooded in from the areas that could see the transit: Europe and much of Asia, Africa, and North America.  Scientifically, solar photographers confirmed that the black drop effect is really better related to the viewing clarity of the camera or telescope than the atmosphere of Venus. Artistically, images might be divided into several categories.  One type captures the transit in front of a highly detailed Sun.  Another category captures a double coincidence such as both Venus and an airplane simultaneously silhouetted, or Venus and the International Space Station in low Earth orbit. A third image type involves a fortuitous arrangement of interesting looking clouds, as shown by example in the above image taken from North Carolina, USA. Sky enthusiasts worldwide are abuzz about the coming transit of Venus on Tuesday. It is perhaps interesting to wonder whether any person will live to see -- and remember seeing -- both Tuesday's Venus transit and the next one in 2117.   Best of APOD: Gallery of previous Mercury and Venus Transit images

Image credit: David Cortner
Milky Way Galaxy Doomed: Collision with Andromeda Pending (2012-06-04)

Will our Milky Way Galaxy collide one day with its larger neighbor, the Andromeda Galaxy? Most likely, yes.  Careful plotting of slight displacements of M31's stars relative to background galaxies on recent Hubble Space Telescope images indicate that the center of M31 could be on a direct collision course with the center of our home galaxy. Still, the errors in sideways velocity appear sufficiently large to admit a good chance that the central parts of the two galaxies will miss, slightly, but will become close enough for their outer halos to become gravitationally entangled. Once that happens, the two galaxies will become bound, dance around, and eventually merge to become one large elliptical galaxy -- over the next few billion years. Pictured above is an artist's illustration of the sky of a world in the distant future when the central parts of each galaxy begin to destroy each other. The exact future of our Milky Way and the entire surrounding Local Group of Galaxies is likely to remain an active topic of research for years to come.   Partial Lunar Eclipse Galleries: Today's Lunar Eclipse and a Collection of Past APOD Lunar Eclipse Images
Live: Watching for Venus to Cross the Sun (2012-06-05)

Today Venus moves in front of the Sun. One way to follow this rare event is to actively reload the above live image of the Sun during the right time interval and look for an unusual circular dark dot. The smaller sprawling dark areas are sunspots. The circular dot is the planet Venus. The dark dot will only appear during a few very specific hours, from about 22:10 on 2012 June 5 through 4:50 2012 June 6, Universal Time. This transit is the rarest type of solar eclipse known -- much more rare than an eclipse of the Sun by the Moon or even by the planet Mercury. In fact, the next transit of Venus across the Sun will be in 2117. Anyone with a clear view of the Sun can go outside and carefully view the transit for themselves by projecting sunlight through a hole in a card onto a wall. Because this Venus transit is so unusual and visible from so much of the Earth, it is expected to be one of the more photographed celestial events in history. The above live image on the Sun is being taken by the Earth-orbiting Solar Dynamics Observatory and can be updated about every 15 minutes. Editor's note: Since the transit has ended, the live image was replaced by one taken just before Venus crossed out of Sun.    Gallery: Browse the latest Venus transit images
Eclipsed Moon Over Wyoming (2012-06-06)

A setting full moon rarely looks like this. Monday morning just before a fully lit Strawberry Moon dropped behind the Absaroka Mountain Range near Cody, Wyoming, USA, the shadow of the Earth got in the way. A similarly setting partial lunar eclipse was visible throughout most of North and South America, while simultaneously the same partially darkened moon was visible throughout eastern Asia. Pictured in the foreground is a snowbank formation known as the Horse's Head off a tributary of the Shoshone River. Lunar eclipses occur about twice a year, and the next one -- a penumbral eclipse -- will occur in late November.   Venus Transit Gallery:  Browse or Contribute!

Image credit: Mack H. Frost
Venus Transit 2012 (2012-06-07)

Occurring in pairs separated by over a hundred years, there have now been only eight transits of Venus since the invention of the telescope in 1608. The next will be in December of 2117. But many modern telescopes and cameras were trained on this week's Venus transit, capturing the planet in rare silhouette against the Sun. In this sharp telescopic view from Georgia, USA, a narrowband H-alpha filter was used to show the round planetary disk against a mottled solar surface with dark filaments, sunspots, and prominences. The transit itself lasted for 6 hours and 40 minutes. Historically, astronomers used timings of the transit from different locations to triangulate the distance to Venus, while modern astronomers actively search for planets that transit distant suns.

Image credit: Chris Hetlage
When Venus Rises with the Sun (2012-06-08)

This dramatic telephoto view across the Black Sea on June 6 finds Venus rising with the Sun, the planet in silhouette against a ruddy and ragged solar disk. Of course, the reddened light is due to scattering in planet Earth's atmosphere and the rare transit of Venus didn't influence the strangely shaped and distorted Sun. In fact, seeing the Sun in the shape of an Etruscan Vase is relatively common, especially compared to Venus transits. At sunset and sunrise, the effects of atmospheric refraction enhanced by long, low, sight lines and strong atmospheric temperature gradients produce the visual distortions and mirages. That situation is often favored by a sea horizon.

Image credit: Emil Ivanov
Venus at the Edge (2012-06-09)

As its June 6 2012 transit begins Earth's sister planet crosses the edge of the Sun in this stunning view from the Hinode spacecraft. The timing of limb crossings during the rare transits was used historically to triangulate the distance to Venus and determine a value for the Earth-Sun distance called the astronomical unit. Still, modern space-based views like this one show the event against an evocative backdrop of the turbulent solar surface with prominences lofted above the Sun's edge by twisting magnetic fields. Remarkably, the thin ring of light seen surrounding the planet's dark silhouette is sunlight refracted by Venus' thick atmosphere.
Two New Hubble-Quality Telescopes Gifted to NASA (2012-06-10)

What if you were given a new Hubble telescope for free? How about two?  The astronomical community is abuzz with just this opportunity as the US National Reconnaissance Office has unexpectedly transferred ownership of two space-qualified Hubble-quality telescopes to NASA. The usefulness of these telescopes in addressing existing science priorities has begun, but preliminary indications hold that even one of these telescope could be extremely useful in searching for extrasolar planets as well as distant galaxies and supernovas that could better explore the nature of dark energy. Although they start out as free, making even one telescope operational and fitting it with useful cameras would be quite expensive, so NASA is being decidedly careful about how to fit these new telescopes into its existing budget. Pictured above, the original Hubble Space Telescope floats high above the Earth during a servicing mission in 2002.   Prefer Spanish?: Follow APOD's new Facebook feed "Universo"
A Venus Transit Music Video from SDO (2012-06-11)

What's that black dot moving across the Sun? Venus. Possibly the clearest view of Venus crossing in front of the Sun last week was from Earth orbit. The Solar Dynamics Observatory obtained an uninterrupted vista recording it not only in optical light but also in bands of ultraviolet light. Pictured above is a composite movie of the crossing set to music. Although the event might prove successful scientifically for better determining components of Venus' atmosphere, the event surely proved successful culturally by involving people throughout the world in observing a rare astronomical phenomenon. Many spectacular images of this Venus transit from around (and above) the globe are being proudly displayed.   Astronomy Seminar of the Week: Introduction to Dark Matter
Thackeray's Globules (2012-06-12)

These are larger dust bunnies than you will find under your bed. Situated in rich star fields and glowing hydrogen gas, these opaque clouds of interstellar dust and gas are so large they might be able to form stars. Their home is known as IC 2944, a bright stellar nursery located about 5,900 light years away toward the constellation of Centaurus. The largest of these dark globules, first spotted by South African astronomer A. D. Thackeray in 1950, is likely two separate but overlapping clouds, each more than one light-year wide. Along with other data, the above representative color image from the 4-m Blanco telescope at Cerro Tololo, Chile indicates that Thackeray's globules are fractured and churning as a result of intense ultraviolet radiation from young, hot stars already energizing and heating the bright emission nebula. These and similar dark globules known to be associated with other star forming regions may ultimately be dissipated by their hostile environment -- like cosmic lumps of butter in a hot frying pan.   3x the Astronomy Images:  Follow cool APOD submissions on Facebook and Google Plus.

Image credit: T. Rector
A Venus Transit Over the Baltic Sea (2012-06-13)

Waiting years and traveling kilometers -- all to get a shot like this. And even with all of this planning, a good bit of luck was helpful. As the Sun rose over the Baltic Sea last Wednesday as seen from Fehmarn Island in northern Germany, photographer Jens Hackmann was ready for the very unusual black dot of Venus to appear superimposed. Less expected were the textures of clouds and haze that would tint different levels of the Sun various shades of red.  And possibly the luckiest gift of all was a flicker of a rare green flash at the very top of the Sun. The above image is, of course, just one of many spectacular pictures taken last week of the last transit of the planet Venus across the face of the Sun for the next 105 years.   Vote: APOD entered in Three Quarks Daily 2012 Science Writing Contest

Image credit: Jens Hackmann
M13: The Great Globular Cluster in Hercules (2012-06-14)

In 1716, English astronomer Edmond Halley noted, "This is but a little Patch, but it shews itself to the naked Eye, when the Sky is serene and the Moon absent." Of course, M13 is now modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Telescopic views reveal the spectacular cluster's hundreds of thousands of stars. At a distance of 25,000 light-years, the cluster stars crowd into a region 150 light-years in diameter, but approaching the cluster core upwards of 100 stars could be contained in a cube just 3 light-years on a side. For comparison, the closest star to the Sun is over 4 light-years away. Along with the cluster's dense core, the outer reaches of M13 are highlighted in this sharp color image. The cluster's evolved red and blue giant stars show up in yellowish and blue tints.

Image credit: Martin Pugh
M65 and M66 (2012-06-15)

Nearby and bright, spiral galaxies M65 (top) and M66 stand out in this engaging cosmic snapshot. The pair are just 35 million light-years distant and around 100,000 light-years across, about the size of our own spiral Milky Way. While both exhibit prominent dust lanes sweeping along their broad spiral arms, M66 in particular is a striking contrast in red and blue hues; the telltale pinkish glow of hydrogen gas in star forming regions and young blue star clusters. M65 and M66 make up two thirds of the well-known Leo Triplet of galaxies with warps and tidal tails that offer evidence of the group's past close encounters. The larger M66 has been host to four supernovae discovered since 1973.

Image credit: Bill Snyder
APOD Turns 17 (2012-06-16)

The first APOD appeared seventeen years ago today, on 1995 June 16.  Although garnering only 14 page views on that day, we are proud to estimate that APOD has now served over one billion space-related images over the last 1.7 decades.  That early beginning, along with a nearly unchanging format, has allowed APOD to be a consistent and familiar site on a web frequently filled with change.   Many people don't know, though, that APOD is now translated daily into many major languages and featured on social media sites and smartphone applications. We again thank our readers and NASA for their continued support, as well as the folks who created the great pictures -- many times with considerable effort -- that APOD has been fortunate enough to feature over the years.  Many can be contacted by following links found in the credit line under the image.  Today's birthday collage includes numerous galaxies captured by the Hubble Space Telescope.   Vote: APOD entered in Three Quarks Daily 2012 Science Writing Contest  APOD Retrospectives: Anniversary day today and every day.

Image credit: Judy Schmidt
Jupiter's Rings Revealed (2012-06-17)

Why does Jupiter have rings?  Jupiter's rings were discovered in 1979 by the passing Voyager 1 spacecraft, but their origin was a mystery.  Data from the Galileo spacecraft that orbited Jupiter from 1995 to 2003 later confirmed that these rings were created by meteoroid impacts on small nearby moons.  As a small meteoroid strikes tiny Adrastea, for example, it will bore into the moon, vaporize, and explode dirt and dust off into a Jovian orbit.  Pictured above is an eclipse of the Sun by Jupiter, as viewed from Galileo.  Small dust particles high in Jupiter's atmosphere, as well as the dust particles that compose the rings, can be seen by reflected sunlight.   APOD Retrospective: Today and Every Day
Milky Way Above Easter Island (2012-06-18)

Why were the statues on Easter Island built? No one is sure.  What is sure is that over 800 large stone statues exist there.  The Easter Island statues, stand, on the average, over twice as tall as a person and have over 200 times as much mass.  Few specifics are known about the history or meaning of the unusual statues, but many believe that they were created about 500 years ago in the images of local leaders of a lost civilization.  Pictured above, some of the stone giants were illuminated in 2009 under the central band of our Milky Way Galaxy.   Help Evaluate APOD: Does viewing APOD make you more interested in science?

Image credit: Manel Soria