juliensimon/nasa-apod huggingface dataset:
The South Pole of Asteroid Vesta (2011-09-19)

What created the circular structure around the south pole of asteroid Vesta? Pictured above, the bottom of the second largest object in the asteroid belt was recently imaged for the first time by the robotic Dawn satellite that arrived last month. A close inspection of the 260-meter resolution image shows not only hills and craters and cliffs and more craters, but ragged circular features that cover most of the lower right of the 500-kilometer sized object. Early speculation posits that the structure might have been created by a collision and coalescence with a smaller asteroid. Alternatively, the features might have originated in an internal process soon after the asteroid formed. New clues might come in the next few months as Dawn spirals down toward the rocky world and obtains images of increasingly high resolution.
Kepler-16b: A Planet with Two Suns (2011-09-20)

If you stay up long enough, you can watch both suns set. Such might be a common adage from beings floating in the atmosphere of Kepler 16b, a planet recently discovered by the space-based Kepler satellite. The above animated video shows how the planetary system might look to a visiting spaceship. Although multiple star systems are quite common, this is the first known to have a planet. Because our Earth is in the orbital plane of both stars and the planet, each body is seen to eclipse the others at different times, producing noticeable drop offs in the amount of light seen. The frequent eclipses have given Kepler 16b the most accurate mass and radius determination for a planet outside our Solar System. To find a planet like Saturn in an orbit like Venus -- so close to its binary star parents -- was a surprise and will surely become a focus of research.
Pleiades Deep Field (2011-09-21)

Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it like this: all dusty. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city.  With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The above exposure took about 30 hours and covers a sky area several times the size of the full moon.  Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus).  A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.   APOD Retrospective: The Pleiades Star Cluster

Image credit: Stanislav Volskiy
Arp 272 (2011-09-22)

Linking spiral arms, two large colliding galaxies are featured in this remarkable cosmic portrait constructed using image data from the Hubble Legacy Archive. Recorded in astronomer Halton Arp's Atlas of Peculiar Galaxies as Arp 272, the pair is otherwise known as NGC 6050 near center, and IC 1179 at upper right. A third galaxy, likely also a member of the interacting system, can be spotted above and left of larger spiral NGC 6050. They lie some 450 million light-years away in the Hercules Galaxy Cluster. At that estimated distance, the picture spans over 150 thousand light-years. Although this scenario does look peculiar, galaxy collisions and their eventual mergers are now understood to be common, with Arp 272 representing a stage in this inevitable process. In fact, the nearby large spiral Andromeda Galaxy is known to be approaching our own galaxy and Arp 272 may offer a glimpse of the far future collision between Andromeda and the Milky Way.
September's Aurora (2011-09-23)

September's equinox arrives today at 0905 UT. As the Sun crosses the celestial equator heading south, spring begins in the southern hemisphere and autumn in the north. And though the seasonal connection is still puzzling, both spring and autumn bring an increase in geomagnetic storms. So as northern nights grow longer, the equinox also heralds the arrival of a good season for viewing aurora. Recorded earlier this month, these curtains of September's shimmering green light sprawl across a gorgeous night skyscape. In the foreground lies Hidden Lake Territorial Park near Yellowknife, Northwest Territories, Canada. Calm water reflects the aurora, with bright star trails peering through the mesmerizing sky glow. Of course, shining at altitudes of 100 kilometers or so, planet Earth's auroras are visible from space.

Image credit: Yuichi Takasaka
Mangaia's Milky Way (2011-09-24)

From Sagittarius to Carina, the Milky Way Galaxy shines in this dark night sky above planet Earth's lush island paradise of Mangaia. Familiar to denizens of the southern hemisphere, the gorgeous skyscape includes the bulging galactic center at the upper left and bright stars Alpha and Beta Centauri just right of center. About 10 kilometers wide, volcanic Mangaia is the southernmost of the Cook Islands. Geologists estimate that at 18 million years old it is the oldest island in the Pacific Ocean. Of course, the Milky Way is somewhat older, with the galaxy's oldest stars estimated to be over 13 billion years old. (Editor's note: This image holds the distinction of being selected as winner in the Royal Observatory, Greenwich, Astronomy Photographer of the Year competition in the Earth and Space category.)

Image credit: Tunç Tezel
A Large Tsunami Shock Wave on the Sun (2011-09-25)

Tsunamis this large don't happen on Earth.  During 2006, a large solar flare from an Earth-sized sunspot produced a tsunami-type shock wave that was spectacular even for the Sun.  Pictured above, the tsunami wave was captured moving out from active region AR 10930 by the Optical Solar Patrol Network (OSPAN) telescope in New Mexico, USA.  The resulting shock wave, known technically as a Moreton wave, compressed and heated up gasses including hydrogen in the photosphere of the Sun, causing a momentarily brighter glow.  The above image was taken in a very specific red color emitted exclusively by hydrogen gas.  The rampaging tsunami took out some active filaments on the Sun, although many re-established themselves later.  The solar tsunami spread at nearly one million kilometers per hour, and circled the entire Sun in a matter of minutes.
Dry Ice Pits on Mars (2011-09-26)

Part of Mars is defrosting. Around the South Pole of Mars, toward the end of every Martian summer, the warm weather causes a section of the vast carbon-dioxide ice cap to evaporate.  Pits begin to appear and expand where the carbon dioxide dry ice sublimates directly into gas. These ice sheet pits may appear to be lined with gold, but the precise composition of the dust that highlights the pit walls actually remains unknown.  The circular depressions toward the image center measure about 60 meters across. The HiRISE camera aboard the Mars-orbiting Mars Reconnaissance Orbiter captured the above image in late July.  In the next few months, as Mars continues its journey around the Sun, colder seasons will prevail, and the thin air will turn chilly enough not only to stop the defrosting but once again freeze out more layers of solid carbon dioxide.
Flying Over Planet Earth (2011-09-27)

Have you ever dreamed of flying high above the Earth? Astronauts visiting the International Space Station do this every day, circling our restless planet twice every three hours. A dramatic example of their view was compiled in the above time-lapse video from images taken earlier this month. As the ISS speeds into the nighttime half of the globe, familiar constellations of stars remain visible above.  An aerosol haze of Earth's thin atmosphere is visible on the horizon as an thin multi-colored ring. Many wonders whiz by below, including vast banks of white clouds, large stretches of deep blue sea, land lit up by the lights of big cities and small towns, and storm clouds flashing with lightning. The video starts over the northern Pacific Ocean and then passes from western North America to western South America, ending near Antarctica as daylight finally approaches.
Violent Sunspot Group AR 1302 Unleashes a Flare (2011-09-28)

One of the most active sunspot groups in years is currently crossing the Sun. AR 1302 first came around the Sun's edge last week and is so large it can be seen without a telescope.  Coronal Mass Ejections from AR 1302 have already caused strong geomagnetic storms including notable aurora activity around both of Earth's poles. Pictured above, plasma was left magnetically hanging above the Sun's surface after AR 1302 emitted an X-class solar flare last Thursday.  Earth is illustrated in the inset for a size comparison. Although another X-class flare was emitted on Saturday, no flares from AR 1302 have been aimed directly at the Earth, as yet. The AR 1302 sunspot group will continue to evolve but likely remain visible on the Sun for the next week.   Instant Gallery: See recent pictures of sunspot group AR 1302.
Cocoon Nebula Wide Field (2011-09-29)

In this crowded starfield spanning some 3 degrees within the high flying constellation Cygnus, the eye is drawn to the Cocoon Nebula. A compact star forming region, the cosmic Cocoon punctuates a long trail of obscuring interstellar dust clouds. Cataloged as IC 5146, the nebula is nearly 15 light-years wide, located some 4,000 light years away. Like other star forming regions, it stands out in red, glowing, hydrogen gas excited by the young, hot stars and blue, dust-reflected starlight at the edge of an otherwise invisible molecular cloud. In fact, the bright star near the center of this nebula is likely only a few hundred thousand years old, powering the nebular glow as it clears out a cavity in the molecular cloud's star forming dust and gas. But the long dusty filaments that appear dark in this visible light image are themselves hiding stars in the process of formation, seen at infrared wavelengths.

Image credit: Tony Hallas
Cloudy Night of the Northern Lights (2011-09-30)

On September 26, a large solar coronal mass ejection smacked into planet Earth's magnetosphere producing a severe geomagnetic storm and wide spread auroras. Captured here near local midnight from Kvaløya island outside Tromsø in northern Norway, the intense auroral glow was framed by parting rain clouds. Tinted orange, the clouds are also in silhouette as the tops of the colorful shimmering curtains of northern lights extend well over 100 kilometers above the ground. Though the auroral rays are parallel, perspective makes them appear to radiate from a vanishing point at the zenith. Near the bottom of the scene, an even more distant Pleiades star cluster and bright planet Jupiter shine on this cloudy northern night.

Image credit: Fredrick Broms
Asteroids Near Earth (2011-10-01)

Though the sizes are not to scale, the Sun and planets of the inner solar system are shown in this illustration, where each red dot represents an asteroid. New results from NEOWISE, the infrared asteroid hunting portion of the WISE mission, are shown on the left compared to old population projections of mid-size or larger near-Earth asteroids from surveys at visible wavelengths. And the good news is, NEOWISE observations estimate there are 40 percent fewer near-Earth asteroids that are larger than 100 meters (330 feet), than indicated by visible light searches. Based on infrared imaging, the NEOWISE results are more accurate as well. Heated by the Sun, asteroids of the same size radiate the same amount of infrared light, but can reflect very different amounts of visible sunlight depending on how shiny their surface is, or their surface albedo. That effect can bias surveys based on optical observations. NEOWISE results reduce the estimated number of mid-size near-Earth asteroids from about 35,000 to 19,500, but the majority still remain undiscovered.
Tunguska: The Largest Recent Impact Event (2011-10-02)

Yes, but can your meteor do this?  The most powerful natural explosion in recent Earth history occurred on 1908 June 30 when a meteor exploded above the Tunguska River in Siberia, Russia.  Detonating with an estimated power 1,000 times greater than the atomic bomb dropped over Hiroshima, the Tunguska event leveled trees over 40 kilometers away and shook the ground in a tremendous earthquake.  Eyewitness reports are astounding.  The above picture was taken by a Russian expedition to the Tunguska site almost 20 years after the event, finding trees littering the ground like toothpicks. Estimates of the meteor's size range from 60 meters to over 1000 meters in diameter.  Recent evidence suggests that nearby Lake Cheko may even have been created by the impact. Although a meteor the size of the Tunguska can level a city, metropolitan areas take up such a small fraction of the Earth's surface that a direct impact on one is relatively unlikely.  More likely is an impact in the water near a city that creates a dangerous tsunami.  One focus of modern astronomy is to find Solar System objects capable of creating such devastation well before they impact the Earth.
Dark Matter Movie from the Bolshoi Simulation (2011-10-03)

What if you could fly through the universe and see dark matter? While the technology for taking such a flight remains under development, the technology for visualizing such a flight has taken a grand leap forward with the completion of the Bolshoi Cosmological Simulation. After 6 million CPU hours, the world's seventh fastest supercomputer output many scientific novelties including the above flight simulation. Starting from the relatively smooth dark matter distribution of the early universe discerned from the microwave background and other large sky data sets, the Bolshoi tracked the universe's evolution to the present epoch shown above, given the standard concordance cosmology. The bright spots in the above video are all knots of normally invisible dark matter, many of which contain normal galaxies.  Long filaments and clusters of galaxies, all gravitationally dominated by dark matter, become evident. Statistical comparison between the Bolshoi and current real sky maps of actual galaxies show good agreement. Although the Bolshoi simulation bolsters the existence of dark matter, many questions about our universe remain, including the composition of dark matter, the nature of dark energy, and how the first generation of stars and galaxies formed.   Astrophysicists: Browse the Astrophysics Source Code Library
QR Codes: Not for Human Eyes (2011-10-04)

This communication was not meant for human eyes. It was not even meant for aliens eyes. It's an attempt to communicate directly with your smartphone. Cameras on many smartphones can image the above Quick Response (QR) code and then common applications can tell you what it means.  Sometimes the deciphered code will reveal a web site address, prompting the smartphone to then ask you if you want to access this address to learn more about the object. QR codes are two-dimensional analogs of bar codes that can be scanned in any orientation and tolerate several types of errors. These codes are being used increasingly as doors between real objects and web-based information about those objects, and so are popping up increasingly in unexpected places.  Anyone can create a QR code from any of several free online services, print it out, and affix it to an object. Although not meant to communicate with aliens, QR codes employ several attributes common to famous alien communication attempts.  Can you -- or a local smartphone -- figure out what the above QR code means?
Comet and CME on the Sun (2011-10-05)

Did a sun-diving comet just cause a solar explosion? Probably not.  This past weekend a comet dove toward the Sun and was followed very quickly by a Coronal Mass Ejection (CMEs) from the other side of the Sun. The first two sequences in the above video shows the spectacular unfolding of events as seen by the Sun-orbiting SOHO satellite, while the same events were also captured by both Sun-orbiting STEREO satellites. Now sungrazer comets that break up as they pass near the Sun are not all that rare -- hundreds have been cataloged over the past few years. CMEs are even more common, with perhaps three lesser events occurring even during the eight hours of the above time-lapse movie. Therefore, the best bet of solar scientists is that the two events were unrelated. Another basis for this judgment is that CMEs are caused by rapid changes in the Sun's magnetic field, changes that a small comet seem unlikely to make.  Such coincidences are even more likely during periods of high activity on the Sun's surface -- like now.
M82: Starburst Galaxy with a Superwind (2011-10-06)

Also known as the Cigar Galaxy for its elongated visual appearance, M82 is a starburst galaxy with a superwind. In fact, through ensuing supernova explosions and powerful winds from massive stars, the burst of star formation in M82 is driving the prodigous outflow of material. Evidence for the superwind from the galaxy's central regions is clear in this sharp composite image, based on data from small telescopes on planet Earth. The composite highlights emission from filaments of atomic hydrogen gas in reddish hues. The filaments extend for over 10,000 light-years. Some of the gas in the superwind, enriched in heavy elements forged in the massive stars, will eventually escape into intergalactic space. Triggered by a close encounter with nearby large galaxy M81, the furious burst of star formation in M82 should last about 100 million years or so. M82 is 12 million light-years distant, near the northern boundary of Ursa Major.   Memorial: Aden Meinel (1922 - 2011 Oct 2), first director of Kitt Peak

Image credit: Dietmar Hager
The Comet Hartley 2 Cruise (2011-10-07)

rly last November, small but active Comet Hartley 2 (103/P Hartley) became the fifth comet imaged close-up by a spacecraft from planet Earth. Still cruising through the solar system with a 6 year orbital period, Hartley 2 is making astronomical headlines again. New Herschel Space Observatory measurements indicate that the water found in this comet's thin atmosphere or coma has the same ratio of the hydrogen isotope deuterium (in heavy water) as the oceans of our fair planet. Hartley 2 originated in the distant Kuiper Belt, a region beyond the orbit of Neptune that is a reservoir of icy cometary bodies and dwarf planets. Since the ratio of deuterium is related to the solar system environment where the comet formed, the Herschel results indicate that Kuiper Belt comets could have contributed substantial amounts of water to Earth's oceans. Comet Hartley 2 appears in this starry skyscape from last November sporting a tantalizing greenish coma appropriately sailing through the nautical constellation Puppis. Below the comet are open star clusters M47 (right) and M46 (left).

Image credit: CARA Project
MESSENGER's First Day (2011-10-08)

One solar day on a planet is the length of time from noon to noon. A solar day lasts 24 hours on planet Earth. On Mercury a solar day is about 176 Earth days long. And during its first Mercury solar day in orbit the MESSENGER spacecraft has imaged nearly the entire surface of the innermost planet to generate a global monochrome map at 250 meters per pixel resolution and a 1 kilometer per pixel resolution color map. Examples of the maps, mosaics constructed from thousands of images made under uniform lighting conditions, are shown (monochrome at left), both centered along the planet's 75 degrees East longitude meridian. The MESSENGER spacecraft's second Mercury solar day will likely include more high resolution targeted observations of the planet's surface features. (Editor's note: Due to Mercury's 3:2 spin-orbit resonance, a Mercury solar day is 2 Mercury years long.)
Nobels for a Strange Universe (2011-10-09)

Thirteen years ago results were first presented indicating that most of the energy in our universe is not in stars or galaxies but is tied to space itself.  In the language of cosmologists, a large cosmological constant is directly implied by new distant supernova observations.  Suggestions of a cosmological constant (lambda) were not new -- they have existed since the advent of modern relativistic cosmology. Such claims were not usually popular with astronomers, though, because lambda is so unlike known universe components, because lambda's value appeared limited by other observations, and because less-strange cosmologies without lambda had previously done well in explaining the data. What is noteworthy here is the seemingly direct and reliable method of the observations and the good reputations of the scientists conducting the investigations. Over the past thirteen years, independent teams of astronomers have continued to accumulate data that appears to confirm the existence of dark energy and the unsettling result of a presently accelerating universe. This year, the team leaders were awarded the Nobel Prize in Physics for their work.  The above picture of a supernova that occurred in 1994 on the outskirts of a spiral galaxy was taken by one of these collaborations.
A Strange Sunrise Over Argentina (2011-10-10)

Why would a rising Sun look so strange? No one is yet sure.  What is clear is that the above unusual sunrise was captured last month from Buenos Aires, Argentina. The body of water in the foreground is Rio de La Plata, considered by many to be the widest river in the world. Although the above image is actually a combination of a normal and a very short exposure needed to avoid oversaturating the bright Sun, the photographer saw this unusual structure with his own eyes, indicating that this effect was caused by neither reflections nor distortions in the camera or lens. What looks like arms on this monster illusion might actually be, for example, low level clouds just thick enough to scatter sunlight without completely blocking the Sun. Additionally, the distortion visible on the lower part of the Sun's image might indicate a Etruscan Vase or Fata Morgana mirage possibly created by a curious refracting layer of air over the water. Unusual atmospheric phenomena are frequently thrilling to see personally, and although most can be traced to well known phenomena, others, for lack of more data, remain mysterious.

Image credit: Luis Argerich
NGC 7635: The Bubble Nebula (2011-10-11)

It's the bubble versus the cloud. NGC 7635, the Bubble Nebula, is being pushed out by the stellar wind of massive central star BD+602522. Next door, though, lives a giant molecular cloud, visible to the right. At this place in space, an irresistible force meets an immovable object in an interesting way. The cloud is able to contain the expansion of the bubble gas, but gets blasted by the hot radiation from the bubble's central star. The radiation heats up dense regions of the molecular cloud causing it to glow. The Bubble Nebula, pictured above in scientifically mapped colors to bring up contrast, is about 10 light-years across and part of a much larger complex of stars and shells. The Bubble Nebula can be seen with a small telescope towards the constellation of the Queen of Aethiopia (Cassiopeia).

Image credit: Larry Van Vleet