juliensimon/nasa-apod huggingface dataset:
Noctilucent Clouds Over Germany (2009-06-24)

Sometimes it's night on the ground but day in the air.  As the Earth rotates to eclipse the Sun, sunset rises up from the ground.  Therefore, at sunset on the ground, sunlight still shines on clouds above.   Under usual circumstances, a pretty sunset might be visible, but unusual noctilucent clouds float so high up they can be seen well after dark.   Pictured above last week, a network of noctilucent clouds cast an eerie white glow after dusk, beyond a local field near Potsdam, Germany.  Although noctilucent clouds are thought to be composed of small ice-coated particles, much remains unknown about them.  Satellites launched to help study these clouds include Sweden's Odin and NASA's AIM. Recent evidence indicates that at least some noctilucent clouds result from freezing water exhaust from Space Shuttles.

Image credit: Christoph Rollwagen
Sarychev Peak Volcano in Stereo (2009-06-25)

From 400 kilometers above planet Earth, the Expedition 20 Crew onboard the International Space Station (ISS) was able to witness a remarkable event from a remarkable vantage point -- the June 12 eruption of the Sarychev Peak Volcano. The active volcano is located in Russia's Kuril Island chain, stretching to the northeast of Japan. Emphasizing the orbital perspective, this stunning color stereo view was made by combining two images from the ISS and is intended to be viewed with red/blue glasses (red for the left eye). Punching upwards into the atmosphere at an early stage of the eruption, the volcanic plume features a brown column of ash topped with a smooth, bubble-like, white cloud that is likely water condensation. Below, a cloud of denser grey ash slides down the volcanic slope. About 1.5 kilometers of the island coastline is visible at ground level. The evolving ash plume posed no danger to the Expedition 20 crew, but commercial airline flights were diverted away from the region to minimize the danger of engine failures from ash intake.
Solstice to Solstice Solargraph (2009-06-26)

This six month long exposure compresses the time from solstice to solstice (~ December 21, 2008 to June 20, 2009) into a single point of view. Dubbed a solargraph, the unconventional picture was recorded with a pinhole camera made from an aluminum can lined with a piece of photographic paper. Fixed to a single spot for the entire exposure, the simple camera continuously records the Sun's daily path as a glowing trail burned into the photosensitive paper. Breaks and gaps in the trails are caused by cloud cover. In this case, the spot was chosen to look out from inside a radio telescope at the Ondrejov Observatory in the Czech Republic. At the end of the exposure, the paper was removed from the can and immediately scanned digitally. Contrasts and colors were then enhanced and added to the digital image. Of course, in December, the Sun trails begin lower down at the northern hemisphere's winter solstice. The trails climb higher in the sky as the June 21st summer solstice approaches.

Image credit: Maciej
Zapiór
Saharan Starry Night (2009-06-27)

This panoramic image of a starry night looks across a dry, desolate landscape. The magnificent view was recorded from Tassili National Park, in the heart of the Sahara desert in southern Algeria. Rising above eroded sandstone cliffs, the celestial menagerie of constellations includes Draco the Dragon, Cygnus the Swan, Aquila the Eagle, and Scorpius the Scorpion. Ruling planet Jupiter shines through clouds very close to the horizon near picture center, while star clouds of the Milky Way arc through Sagittarius above the rocks at the far right. Bright blue stars Deneb, in Cygnus, and Altair, in Aquila, also shine in the starry night along with Scorpius' bright yellowish star Antares, the rival of Mars. Prehistoric skygazers surely witnessed a similar sky. In addition to dramatic sandstone formations, the Tassili region is noted for rock art and archaeological sites dating to Neolithic times when the local climate was wetter.

Image credit: Babak
Tafreshi
Fresh Tiger Stripes on Saturn's Enceladus (2009-06-28)

Do underground oceans vent through the tiger stripes on Saturn's moon Enceladus?  Long features dubbed tiger stripes are known to be spewing ice from the moon's icy interior into space, creating a cloud of fine ice particles over the moon's South Pole and creating Saturn's mysterious E-ring.  Evidence for this has come from the robot Cassini spacecraft now orbiting Saturn.  Pictured above, a high resolution image of Enceladus is shown from a close flyby.  The unusual surface features dubbed tiger stripes are visible in false-color blue.  Why Enceladus is active remains a mystery, as the neighboring moon Mimas, approximately the same size, appears quite dead. Most recently, an analysis of dust captured by Cassini found evidence for sodium as expected in a deep salty ocean.  Conversely however, recent Earth-based observations of ice ejected by Enceladus into Saturn's E-Ring showed no evidence of the expected sodium.  Such research is particularly interesting since such an ocean would be a candidate to contain life.
Kaguya Spacecraft Crashes into the Moon (2009-06-29)

Japan's Kaguya spacecraft crashed into the Moon last week, as planned. Officially named the Selenological and Engineering Explorer (SELENE), the spacecraft was given the nickname Kaguya after the princess in the Japanese folklore story The Tale of the Bamboo Cutter. Pictured above is a movie taken by Kaguya during the last orbit of its twenty-month lunar mission. A desolate, hilly, and cratered terrain passes underneath as the spacecraft barely clears a few peaks.  At the movie's end, the spacecraft disappears into darkness near Gill crater. Robotic SELENE carried thirteen scientific instruments and two HDTV cameras. The groundbreaking mission took data on lunar topology and composition that are being used to better understand the origin and history of Earth's unique and ancient companion. Data and images from Kaguya and the recently launched Lunar Reconnaissance Orbiter could be used to choose good locations to land future Moon-exploring astronauts.

Image credit: SELENE
Team
The North America and Pelican Nebulae (2009-06-30)

Here are some familiar shapes in unfamiliar locations.  This emission nebula on the left is famous partly because it resembles Earth's continent of North America.  To the right of the North America Nebula, cataloged as NGC 7000, is a less luminous nebula that resembles a pelican dubbed the Pelican Nebula.  The two emission nebula measure about 50 light-years across, are located about 1,500 light-years away, and are separated by a dark absorption cloud.  This spectacular image captures the nebulas, bright ionization fronts, and fine details of the dark dust. The nebulae can be seen with binoculars from a dark location.  Look for a small nebular patch north-east of bright star Deneb in the constellation of Cygnus.  It is still unknown which star or stars ionize the red-glowing hydrogen gas.

Image credit: Danny Lee Russell �
Three Galaxies in Draco (2009-07-01)

This intriguing trio of galaxies is sometimes called the Draco Group, located in the northern constellation of (you guessed it) Draco. From left to right are edge-on spiral NGC 5981, elliptical galaxy NGC 5982, and face-on spiral NGC 5985 -- all within this single telescopic field of view spanning a little more than half the width of the full moon. While the group is far too small to be a galaxy cluster and has not been cataloged compact group, these galaxies all do lie roughly 100 million light-years from planet Earth. On close examination with spectrographs, the bright core of the striking face-on spiral NGC 5985 shows prominent emission in specific wavelengths of light, prompting astronomers to classify it as a Seyfert, a type of active galaxy. Not as well known as other tight groupings of galaxies, the contrast in visual appearance makes this triplet an attractive subject for astrophotographers. This impressively deep exposure of the region also reveals faint and even more distant background galaxies.

Image credit: Giovanni Benintende
Lyman Alpha Blob (2009-07-02)

Dubbed a Lyman-alpha blob, an enormous cloud of hydrogen gas spans several hundred thousand light-years in this remarkable image (left), a composite of x-ray, optical, and infrared data from space and ground based observatories. The gigantic, amoeba-like structure is seen as it was when the universe was a mere 2 billion years old (about 12 billion years ago). Lyman-alpha blobs are so called because they strongly emit radiation due to the Lyman-alpha emission line of hydrogen gas. Normally, Lyman-alpha emission is in the ultraviolet part of the spectrum, but Lyman-apha blobs are so distant, their light is redshifted to (longer) optical wavelengths. X-ray data (blue) indicates the presence of a supermassive black hole feeding at the center of an active galaxy embedded in the blob. Illustrated close up in the right hand panel, radiation and outflows from the active galaxy are thought to be a source for energizing and heating the blob's hydrogen gas. In fact, Lyman-alpha blobs could represent an early phase in galaxy formation where the heating is so great it begins to limit further rapid growth of active galaxies and their supermassive black holes.
Perihelion and Aphelion (2009-07-03)

This year Aphelion, the point in Earth's elliptical orbit when it is farthest from the Sun, occurs tomorrow, July 4th. Of course, that doesn't affect the seasons on our fair planet. Those are determined by the tilt of Earth's axis of rotation and not Earth's distance from the Sun, so July is still winter in the south and summer in northern hemisphere. But it does mean that on July 4th the Sun will be at its smallest apparent size. This composite neatly compares two pictures of the Sun taken with the same telescope and camera on the dates of Perihelion (closest approach) and Aphelion in 2008. The image labels include Earth's distance in kilometers from the Sun on the two dates. Otherwise difficult to notice, the change in the Sun's apparent diameter between Perihelion and Aphelion is clear. The difference amounts to a little over 3 percent.

Image credit: Enrique Luque Cervigón
Mount Rushmore's Starry Night (2009-07-04)

This starry night sky sparkles above the Black Hills of South Dakota and the United States' Mount Rushmore National Park. The historic site features enormous sculptures of four US presidents; George Washington, Thomas Jefferson, Theodore Roosevelt and Abraham Lincoln, carved into the southeast face of granite cliffs. Above the monumental symbols of the country's independence and early history, the night features stars and constellations familiar to northern skygazers around the world. Most noticeable are the stars of Ursa Major and the asterism known as the Big Dipper, almost resting upright along the cliff edge near picture center. Follow the arc of the Big Dipper's handle to get to Arcturus, the bright yellowish star in the lower left corner. Of course, a line extending through the dipper's two right most stars points to the upper right toward Polaris, planet Earth's North Star.

Image credit: Wally Pacholka
Genesis Mission's Hard Impact (2009-07-05)

A flying saucer from outer space crash-landed in the Utah desert in 2004 after being tracked by radar and chased by helicopters.  No space aliens were involved, however.  The saucer, pictured above, was the Genesis sample return capsule, part of a human-made robot Genesis spaceship launched in 2001 by NASA itself to study the Sun.  The unexpectedly hard landing at over 300 kilometers per hour occurred because the parachutes did not open as planned.  The Genesis mission had been orbiting the Sun collecting solar wind particles that are usually deflected away by Earth's magnetic field. Despite the crash landing, many return samples remained in good enough condition to analyze and research is ongoing.  So far, discoveries include new details about the composition of the Sun and the effects of the solar wind on unprotected material.
Unknown Dark Material on Mercury (2009-07-06)

What is that strange material on Mercury? When flying by Mercury last October, the robotic MESSENGER spacecraft imaged much of the solar system's innermost planet in unprecedented detail.  As common in science, new data bring new mysteries.  Pictured above on the lower right, a large crater -- about 100 kilometers across -- has unusual dark material of unknown composition near its center. The material's darkness does not appear to be caused by shadows, as the Sun was near zenith when the image was taken. One origin hypothesis is that the dark material was uncovered from beneath Mercury's surface during the impact that created the surrounding crater.  If so, the composition of the dark mound might be similar to the composition of some mysterious dark rings also recently discovered on Mercury.  Alternatively, the dark material could be related to an unusual composition of the impacting rock.  MESSENGER will buzz past Mercury again later this year before entering orbit in 2011.
The Trifid Nebula in Stars and Dust (2009-07-07)

Unspeakable beauty and unimaginable bedlam can be found together in the Trifid Nebula. Also known as M20, this photogenic nebula is visible with good 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 M20 were created in the atmospheres of cool giant stars and in the debris from supernovae explosions. Which bright young stars light up the blue reflection nebula is still being investigated. The light from M20 we see today left perhaps 3,000 years ago, although the exact distance remains unknown. Light takes about 50 years to cross M20.

Image credit: Adam Block
The Dark River to Antares (2009-07-08)

Connecting the Pipe Nebula to the colorful region near bright star Antares is a dark cloud dubbed the Dark River,  flowing from the picture's left edge. Murky looking, the Dark River's appearance is caused by dust obscuring background starlight, although the dark nebula contains mostly hydrogen and molecular gas.  Surrounded by dust, Antares, a red supergiant star, creates an unusual bright yellowish reflection nebula. Above it, bright blue double star Rho Ophiuchi is embedded in one of the more typical bluish reflection nebulae, while red emission nebulae are also scattered around the region. Globular star cluster M4 is just seen above and right of Antares, though it lies far behind the colorful clouds, at a distance of some 7,000 light-years. The Dark River itself is about 500 light years away.  The colorful skyscape is a mosaic of telescopic images spanning nearly 10 degrees (20 Full Moons) across the sky in the constellation Scorpius.

Image credit: Jason Jennings
Fermi's Gamma-ray Pulsars (2009-07-09)

Born in supernovae, pulsars are spinning neutron stars, collapsed stellar cores left from the death explosions of massive stars. Traditionally identified and studied by observing their regular radio pulsations, two dozen pulsars have now been detected at extreme gamma-ray energies by the Fermi Gamma-ray Space Telescope. The detections include 16 pulsars identified by their pulsed gamma-ray emission alone. This gamma-ray all-sky map, aligned with the plane of our Milky Way Galaxy, shows the pulsar positions, with the 16 new Fermi pulsars circled in yellow (8 previously known radio pulsars are in magenta). Bizarre stellar corpses, the Vela, Crab, and Geminga pulsars on the right are the brightest ones in the gamma-ray sky. Pulsars Taz, Eel, and Rabbit are named for the nebulae they are now known to power. The Gamma Cygni and CTA 1 pulsars at the left also reside within expanding supernova remnants of the same name.
The Pillars of Eagle Castle (2009-07-10)

What lights up this castle of star formation?  The familiar Eagle Nebula glows bright in many colors at once.  The above image is a composite of three of these glowing gas colors.  Pillars of dark dust nicely outline some of the denser towers of star formation.  Energetic light from young massive stars causes the gas to glow and effectively boils away part of the dust and gas from its birth pillar.  Many of these stars will explode after several million years, returning most of their elements back to the nebula which formed them.  This process is forming an open cluster of stars known as M16.

Image credit: Emanuele Colognato & Jim Wood
(Backyard Skies)
Noctilucent Cloud Storm Panorama (2009-07-11)

Noctilucent or night-shining clouds lie near the edge of space. From about 80 kilometers above Earth's surface, the icy clouds can still reflect sunlight even though the Sun itself is below the horizon as seen from the ground. Usually occurring at high latitudes in summer months, the diaphanous apparitions are also known as polar mesospheric clouds and may be connected to global change in the lower atmosphere. This impressive 360 degree panorama made from 34 separate images captures an impressive display of noctilucent clouds all over the sky. It was recorded last month from Vallentuna, Sweden. The photographer reports that the display was like a noctilucent cloud storm, one of the best he's ever witnessed.
A Cosmic Call to Nearby Stars (2009-07-12)

If Earth received this message from deep space, could we decode it? The people from the Cosmic Call project sent the above image as the first page of a longer message.  The message was broadcast toward local stars by radio telescope during the summer of 1999.  Another message was sent in 2003. The single-dish, 70-meter diameter telescope that send the messages is located in Ukraine on the Crimean peninsula near the town of Yevpatoria. This first page of the Cosmic Call 1999 message, shown above, involves only numbers and so is easier for puzzle solvers to decode than a more famous message broadcast toward distant star cluster M13 in 1974.  (The solution is here.)

Image credit: Yuvan Dutil & Stephane Dumas
Erupting Volcano Anak Krakatau (2009-07-13)

A volcano on Krakatoa is still erupting. Perhaps most famous for the powerfully explosive eruption in 1883 that killed tens of thousands of people, ash from a violent eruption might also have temporarily altered Earth's climate as long as 1500 years ago. In 1927, eruptions caused smaller Anak Krakatau to rise from the sea, and the emerging volcanic island continues to grow at an average rate of 2 cm per day.  The latest eruption of Anak Krakatau started in 2008 April and continues today.  In this picture, Anak Krakatau is seen erupting from Rakata, the main island of the Krakatoai group.  High above, stars including the Big Dipper are clearly apparent.

Image credit: Marco Fulle
Moons and Jupiter (2009-07-14)

rth's Moon and planet Jupiter made a beautiful pairing in the night sky late last week. This skyscape recorded on July 11 from Brittany in north western France captures the bright conjunction through a cloud bank. The clouds add drama and mystery to the scene but they were also positioned to reduce the intense moonlight. As a result, the exposure captures Jupiter's own Galilean moons (lower right) as tiny pinpricks of light, lined up and hugging both sides of the solar system's ruling gas giant.  Later this week, the Moon is headed for a conjunction with Mars and Venus in the dawn sky.

Image credit: Anne Riou
The Chameleon's Dark Nebulae (2009-07-15)

The Chameleon is a small constellation near the south celestial pole. Boasting no bright stars, it blends inconspicuously with the starry southern sky. But, taken in dark skies over Namibia, this image reveals a stunning aspect of the shy constellation -- a field of dusty nebulae and colorful stars. Blue reflection nebulae are scattered through the scene, but most eye-catching is the complex of silvery dust clouds that only faintly reflect starlight, punctuated by dense dark nebulae. The dark nebulae stand out because they block out background stars. This view of the cosmic dust clouds spans about 4 degrees on the sky.

Image credit: Andrey Kuznetsov
The Hercules Cluster of Galaxies (2009-07-16)

These are galaxies of the Hercules Cluster, an archipelago of island universes a mere 500 million light-years away. Also known as Abell 2151, this cluster is loaded with gas and dust rich, star-forming spiral galaxies but has relatively few elliptical galaxies, which lack gas and dust and the associated newborn stars. The colors in this remarkably deep composite image clearly show the star forming galaxies with a blue tint and galaxies with older stellar populations with a yellowish cast. The sharp picture spans about 3/4 degree across the cluster center, corresponding to over 6 million light-years at the cluster's estimated distance. In the cosmic vista many galaxies seem to be colliding or merging while others seem distorted - clear evidence that cluster galaxies commonly interact. In fact, the Hercules Cluster itself may be seen as the result of ongoing mergers of smaller galaxy clusters and is thought to be similar to young galaxy clusters in the much more distant, early Universe.

Image credit: Tony Hallas
Starburst Galaxy M94 (2009-07-17)

Beautiful island universe M94 lies a mere 15 million light-years distant in the northern constellation of the hunting dogs, Canes Venatici. A popular target for earth-based astronomers, the face-on spiral galaxy is about 30,000 light-years across. Its remarkable features include prominent dust lanes, a bright, point-like nucleus, and a bright, bluish ring dominated by the light of young, massive stars. The massive stars in the ring are all likely less than 10 million years old, indicating the galaxy experienced a well-defined era of rapid star formation. As a result, while the small, bright nucleus is typical of the Seyfert class of active galaxies, M94 is also known as a starburst galaxy. Because M94 is relatively nearby, astronomers can explore in detail reasons for the galaxy's burst of star formation.

Image credit: Marcin Paciorek
Planets, Great Wall, and Solar Eclipse (2009-07-18)

This dramatic skyscape was recorded during the August 2008 total solar eclipse. The Moon's silhouette surrounded by a glistening solar corona hangs above the Jiayuguan Fort along the western edge of the Great Wall of China. Lined-up along the ecliptic plane, all the planets of the inner solar system, Mercury, Venus, Mars, (and Earth!) can also be seen along with Saturn and bright star Regulus, as the Moon's shadow tracks across the landscape. Beyond the Moon's shadow, outside the total eclipse track, sunlight still brightens the sky over mountains on the horizon 30 - 50 kilometers away.  Much anticipated, the 2009 July 22nd total solar eclipse will again be visible from China. Planets and bright stars will briefly appear in darkened daytime skies, though a total eclipse won't be seen from the Great Wall. Still, major cities and populated areas lie along the 2009 total eclipse track that begins in India and sweeps eastward across Asia and into the Pacific Ocean.

Image credit: Terry Cuttle
From the Moon to the Earth (2009-07-19)

After the most famous voyage of modern times, it was time to go home.  After proving that humanity has the ability to go beyond the confines of planet Earth, the first humans to walk on another world -- Neil Armstrong and Buzz Aldrin -- flew the ascent stage of their Lunar Module back to meet Michael Collins in the moon-orbiting Command and Service Module. Pictured above on 1969 July 21, the ascending spaceship was captured by Collins making its approach, with the Moon below, and Earth far in the distance.  Tomorrow marks the 40th anniversary of the first human moon landing. Recently, NASA's moon-orbiting Lunar Reconnaissance Orbiter sent back the first pictures of most of the Apollo landing sites -- including Apollo 11 -- with enough resolution to see the Lunar Module descent stages left behind.