juliensimon/nasa-apod huggingface dataset:
Hurricane Ivan from the Space Station (2008-01-13)

Ninety percent of the houses on Grenada were damaged by the destructive force of Hurricane Ivan.  At its peak, Ivan was a Category 5 hurricane, the highest power category on the Saffir-Simpson Scale, and created sustained winds in excess of 200 kilometers per hour.  Ivan was the largest hurricane to strike the US in 2004, and, so far, the 10th most powerful in recorded history.  As it swirled in the Atlantic Ocean, the tremendous eye of Hurricane Ivan was photographed from above by the orbiting International Space Station. The name Ivan has now been retired from Atlantic Ocean use by the World Meteorological Organization.   Note: Astronomy lectures by an APOD editor are now available as a free podcast.
The Cocoon Nebula from CFHT (2008-01-14)

What creates the colors of the Cocoon Nebula? The Cocoon Nebula, cataloged as IC 5146, is a strikingly beautiful nebula located about 4,000 light years away toward the constellation of the Swan (Cygnus).  Inside the Cocoon Nebula is a newly developing open cluster of stars.  Like other stellar nurseries, the Cocoon Nebula holds, at the same time, a bright red emission nebula, blue reflection nebulas, and dark absorption nebulas.  Given different mixtures, these three processes create a host of colors in this image taken recently by the Canada-France-Hawaii Telescope (CFHT) in Hawaii, USA.  Speculation based on recent measurements holds that the massive star towards the left of the picture opened a hole in an existing molecular cloud through which much of the glowing material flows.  The same star, which formed about 100,000 years ago, now provides the energy source for much of the emitted and reflected light from this nebula.

Image credit: Jean-Charles
Cuillandre
Double Supernova Remnants DEM L316 (2008-01-15)

Are these two supernova shells related?  To help find out, the 8-meter Gemini Telescope located high atop a mountain in Chile was pointed at the unusual, huge, double-lobed cloud dubbed DEM L316.  The resulting image, shown above, yields tremendous detail.  Inspection of the image as well as data taken by the orbiting Chandra X-Ray Observatory indicate how different the two supernova remnants are.  In particular, the smaller shell appears to be the result of Type Ia supernova where a white dwarf exploded, while the larger shell appears to be the result of a Type II supernova where a massive normal star exploded. Since those two stellar types evolve on such different time scales, they likely did not form together and so are likely not physically associated.   Considering also that no evidence exists that the shells are colliding, the two shells are now hypothesized to be superposed by chance.  DEM L316 lies about 160,000 light years away in the neighboring Large Magellanic Cloud (LMC) galaxy, spans about 140 light-years across, and appears toward the southern constellation of the Swordfish (Dorado).

Image credit: Gemini Observatory
MESSENGER Passes Mercury (2008-01-16)

Two days ago, the MESSENGER spacecraft became only the second spacecraft in human history to swoop past Mercury.  The last spacecraft to visit the Sun's closest planet was Mariner 10 over 35 years ago.  Mariner 10 was not able to photograph Mercury's entire surface, and the images it did send back raised many questions.  Therefore, much about planet Mercury remains unknown.  This week's flyby of MESSENGER was only the first of three flybys.  Over the next few years MESSENGER will swing past twice more and finally enter Mercury's orbit in 2011. MESSENGER is currently moving too fast to enter orbit around Mercury now.   The above image was taken two days ago during MESSENGER's flyby and shows part of Mercury's surface that has never been imaged in detail before. Many more detailed images of Mercury are expected to be sent back over the next few days.  The data acquired by MESSENGER will hopefully help scientists better understand how Mercury's surface was formed, and why it is so dense.    Note: Today's APOD image has been updated.  The latest MESSENGER images are here.
Thor's Emerald Helmet (2008-01-17)

This helmet-shaped cosmic cloud with wing-like appendages is popularly called Thor's Helmet. Heroically sized even for a Norse god, Thor's Helmet is about 30 light-years across. In fact, the helmet is actually more like an interstellar bubble, blown as a fast wind from the bright, massive star near the bubble's center sweeps through a surrounding molecular cloud. Known as a Wolf-Rayet star, the central star is an extremely hot giant thought to be in a brief, pre-supernova stage of evolution. Cataloged as NGC 2359, the nebula is located about 15,000 light-years away in the constellation Canis Major. The sharp image captures striking details of the nebula's filamentary structures and also records an almost emerald color from strong emission due to oxygen atoms in the glowing gas.

Image credit: Robert Gendler
Supernova Factory NGC 2770 (2008-01-18)

The stellar explosions known as supernovae are among the most powerful events in the universe. Triggered by the collapsing core of a massive star or the nuclear demise of a white dwarf, supernovae occur in average spiral galaxies only about once every century. But the remarkable spiral galaxy NGC 2770 has lately produced more than its fair share. Two still bright supernovae and the location of a third, originally spotted in 1999 but now faded from view, are indicated in this image of the edge-on spiral. All three supernovae are now thought to be of the core-collapse variety, but the most recent of the trio, SN2008D, was first detected by the Swift satellite at more extreme energies as an X-ray flash (XRF) or possibly a low-energy version of a gamma-ray burst on January 9th. Located a mere 90 million light-years away in the northern constellation Lynx, NGC 2770 is now the closest galaxy known to host such a powerful supernova event.
Starry Night Castle (2008-01-19)

The tantalizing Pleiades star cluster seems to lie just beyond the trees above a dark castle tower in this dramatic view of The World at Night. Recorded earlier this month, the starry sky also features bright star Aldebaran below the Pleiades and a small, faint, fuzzy cloud otherwise known as Comet Holmes near picture center at the top of the field. Starry Night Castle might be an appropriate name for the medieval castle ruin in the foreground. But its traditional name is Mörby Castle, found north of Stockholm, near lake Skedviken in Norrtälje, Sweden.

Image credit: P-M Hedén
Comet McNaught Over Chile (2008-01-20)

Comet McNaught was perhaps the most photogenic comet of our time.  After making quite a show in the northern hemisphere in early January, the comet moved south and developed a long and unusual dust tail that dazzled southern hemisphere observers.  In this image, Comet McNaught was captured one year ago above Chile.  The bright comet dominates on the left while part of its magnificent tail spreads across the entire picture.   From this vantage point in the Andes Mountains, one looks up toward Comet McNaught and a magnificent sky, across at a crescent moon, and down on clouds, atmospheric haze, and the city lights of Santiago. Comet McNaught has glided into the outer Solar System and is now only visible as a speck in a large telescope.  The other spectacular comet of 2007, Comet Holmes, has also faded from easy view.

Image credit: St�phane Guisard
Mercury's Horizon from MESSENGER (2008-01-21)

What would it look like to fly past Mercury?  Just such an adventure was experienced last week by the MESSENGER spacecraft during its first flyby of the strange moon-like world nearest the Sun.  Pictured above is the limb of Mercury seen by MESSENGER upon approach, from about 1 1/2 Earth diameters away.  Visible on the hot and barren planet are many craters, many appeared to be more shallow than similarly sized craters on the Moon.  The comparatively high gravity of Mercury helps flatten tall structures like high crater walls.  MESSENGER was able to take over 1,000 images of Mercury which will be beamed back to Earth for planetary geologists to study.  The robotic MESSENGER spacecraft is scheduled to fly past Mercury twice more before firing its thrusters to enter orbit in 2011.
Shelf Cloud Over Saskatchewan (2008-01-22)

Perhaps it's time to go inside.  Such thoughts might occur to people witnessing the approach of an impressive shelf cloud.  Shelf clouds are typically seen leading thunderstorms, although they may precede any well defined front of relatively cold air.  Shelf clouds differ from roll clouds because shelf clouds are attached to a larger cloud system lurking above.  Similarly, shelf clouds differ from wall clouds because wall clouds typically trail storm systems.  The above pictured shelf cloud was photographed toward the southwest during a trip crossing the prairies of Saskatchewan, Canada on the Trans-Canada Highway in 2001 August.  A rising Sun illuminated the impressive cloud from the east as it advanced from the west.
Orbiting Astronaut Reflects Earth (2008-01-23)

Astronaut self-portraits can be particularly interesting.  Visible in the above picture, working in from the outer borders, are the edges of the reflecting helmet of a space suit, modules of the International Space Station (ISS), the Earth, the arms of Expedition 15 astronaut Clay Anderson, and the digital camera used to snap the image.  This picture was taken during the shuttle orbiter Endeavour's mission to expand the space station last August.  The large curvature of the Earth appearing in the visor reflection is not the true curvature of our spherical Earth, but rather an artifact of the curve of the space helmet.  Earth's horizon appears only slightly curved when viewed from the height of the ISS -- approximately 400 kilometers.  The next space shuttle mission to the space station is currently expected to take place next month and includes the installation of the scientific Columbus Laboratory.
Andromeda Island Universe (2008-01-24)

The most distant object easily visible to the unaided eye is M31, the great Andromeda Galaxy some two and a half million light-years away. But without a telescope, even this immense spiral galaxy - spanning over 200,000 light years - appears as a faint, nebulous cloud in the constellation Andromeda. In contrast, a bright yellow nucleus, dark winding dust lanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital mosaic. While even casual skygazers are now inspired by the knowledge that there are many distant galaxies like M31, astronomers seriously debated this fundamental concept less than 90 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis debate of 1920, which was later resolved by observations of M31 in favor of Andromeda, island universe.

Image credit: Tony Hallas
Winter Night at Pic du Midi (2008-01-25)

This dreamlike view looking south from the historic mountain top Pic du Midi Observatory combines moonlit domes, a winter night sky, and the snowy peaks of the French Pyrenees. Encroaching on the night, lights from the La Mongie ski resort illuminate the mountain slopes nearby while the glow along the distant horizon is from urban areas in southern France and Spain. The night sky features stars of the constellations Orion and Gemini with a bright planet Mars very near the top edge, left of center. The three prominent domes visible (from left to right) house a 0.6 meter telescope reserved for amateur astronomers, a 1 meter telescope that was used to support the Apollo lunar landing missions, and the new, Sun-watching CLIMSO.

Image credit: picdumidi.org
Crescent Mercury in Color (2008-01-26)

Hard to spot against the twilight glow near planet Earth's horizon, a crescent Mercury was imaged close up by the MESSENGER spacecraft early last week. Colors in this remarkable picture were created using data recorded through infrared, red, and violet filters. The combination enhances color differences otherwise not visible to the eye across the innermost planet's cratered surface. In this view, light bluish material seems to surround relatively new craters, contrasting with the mostly drab, brown terrain. Mercury itself is 4,880 kilometers in diameter. The full resolution image shows features as small as 10 kilometers across.
Mercury on the Horizon (2008-01-27)

Have you ever seen the planet Mercury?  Because Mercury orbits so close to the Sun, it never wanders far from the Sun in Earth's sky. If trailing the Sun, Mercury will be visible low on the horizon for only a short while after sunset. If leading the Sun, Mercury will be visible only shortly before sunrise. So at certain times of the year an informed skygazer with a little determination can usually pick Mercury out from a site with an unobscured horizon. Above, a lot of determination has been combined with a little digital trickery to show Mercury's successive positions during March of 2000.  Each picture was taken from the same location in Spain when the Sun itself was 10 degrees below the horizon and superposed on the single most photogenic sunset.  Mercury is currently visible in the western sky after sunset, but will disappear in the Sun's glare after a few days.

Image credit: Juan Carlos Casado
A Solar Eclipse Painting from the 1700s (2008-01-28)

Is this painting the earliest realistic depiction of a total eclipse of the Sun?  Some historians believe it is.  The above painting was completed in 1735 by Cosmas Damian Asam, a painter and architect famous in early eighteenth century Germany.  Clearly drawn is not only a total solar eclipse, but the solar corona and the diamond ring effect visible when sunlight flows only between mountains on the Moon.  The person depicted viewing these eclipse phenomena is St. Benedict. Roberta J. M. Olson and Jay Pasachoff have hypothesized that Asam himself may have seen first hand one or all of the total solar eclipses of May 1706, 1724, and 1733.  Many facts about our astronomical universe that are taken for granted today have been known -- or accurately recorded -- only during the last millennium.  Asam's painting currently hangs in Weltenburg Abbey in Bavaria, Germany.

Image credit: Jay Pasachoff
West Valley Panorama from the Spirit Rover on Mars (2008-01-29)

What does Mars look like from here? Last September, before hiking across rugged and slippery terrain to reach its winter hibernation point, the robotic Spirit rover climbed a small plateau known as Home Plate and captured the spectacular vista pictured above.  Part of the curious flat-topped Home Plate is visible as the light colored landscape across the panorama's foreground.   On the image left, visible about eight kilometers in the distance, is Grissom Hill, while on the left foreground is rock strewn Tsiolkovski Ridge.  On the right, at about 800 meters distant, is Husband Hill, already explored by Spirit and notable as the highest point visible in the westward looking panorama. In the inset is a close-up of a tiny motionless feature informally dubbed Little Bigfoot that has drawn some attention for it superficial appearance to a humanoid life form.  Tenacious image explorers might locate Little Bigfoot towards the front left of the high resolution panorama.  Spirit successfully reached its energy-conserving winter haven in December.
Asteroid 2007 TU24 Passes the Earth (2008-01-30)

Asteroid 2007 TU24 passed by the Earth yesterday, posing no danger.  The space rock, estimated to be about 250 meters across, coasted by just outside the orbit of Earth's Moon.   The passing was not very unusual -- small rocks strike Earth daily, and in 2003 a rock the size of a bus passed inside the orbit of the Moon, being detected only after passing. TU24 was notable partly because it was so large.  Were TU24 to have struck land, it might have caused a magnitude seven earthquake and left a city-sized crater.  A perhaps larger danger would have occurred were TU24  to have struck the ocean and raised a large tsunami. This radar image was taken two days ago.  The Arecibo Radio Telescope in Puerto Rico broadcast radar that was reflected by the asteroid and then recorded by the Byrd Radio Telescope in Green Bank, West Virginia.  The resulting image shows TU24 to have an oblong and irregular shape. TU24 was discovered only three months ago, indicating that other potentially hazardous asteroids might lurk in our Solar System currently undetected.  Objects like TU24 are hard to detect because they are so faint and move so fast.  Humanity's ability to scan the sky to detect, catalog, and analyze such objects has increased notably in recent years.
Young Star Cluster Westerlund 2 (2008-01-31)

Dusty stellar nursery RCW 49 surrounds young star cluster Westerlund 2 in this remarkable composite skyscape from beyond the visible spectrum of light. Infrared data from the Spitzer Space Telescope is shown in black and white, complimenting the Chandra X-ray image data (in false color) of the hot energetic stars within the cluster's central region. Looking toward the grand southern constellation Centaurus, both views reveal stars and structures hidden from optical telescopes by obscuring dust. Westerlund 2 itself is a mere 2 million years old or less, and contains some of our galaxy's most luminous, massive and therefore short-lived stars. The infrared signatures of proto-planetary disks have also been identified in the intense star forming region. At the cluster's estimated distance of 20,000 light-years, the square marking the Chandra field of view would be about 50 light-years on a side.
The First Explorer (2008-02-01)

Fifty years ago (on January 31, 1958) the First Explorer, was launched into Earth orbit by the Army Ballistic Missile Agency. Inaugurating the era of space exploration for the United States, Explorer I was a thirty pound satellite that carried instruments to measure temperatures, and micrometeorite impacts, along with an experiment designed by James A. Van Allen to measure the density of electrons and ions in space. The measurements made by Van Allen's experiment led to an unexpected and startling discovery -- an earth-encircling belt of high energy electrons and ions trapped in the magnetosphere now known as the Van Allen Radiation Belt. Explorer I ceased transmitting on February 28, 1958, but remained in orbit until March of 1970. Pioneering space scientist James Van Allen died on August 9th, 2006 at the age of 91.
Venus and Jupiter in Morning Skies (2008-02-02)

These two celestial beacons shining brightly in the east before sunrise are actually children of the Sun, the planets Venus and Jupiter. The second and third brightest objects in the sky at Night after the Moon, Venus and Jupiter appeared separated by about 2 degrees when this picture was taken on January 30th, but closed to within nearly half a degree early yesterday morning. In the serene foreground is the shoreline along the Miankaleh Peninsula and Gorgan Bay, an important bird and wildlife refuge in the southeastern Caspian Sea. Over the next two days, early morning risers around the globe will be able to enjoy a close pairing of Venus and Jupiter with an old crescent Moon.

Image credit: Babak Tafreshi
Light Echoes from V838 Mon (2008-02-03)

What caused this outburst of V838 Mon?  For reasons unknown, star V838 Mon's outer surface suddenly greatly expanded with the result that it became the brightest star in the entire Milky Way Galaxy in January 2002.  Then, just as suddenly, it faded.  A stellar flash like this has never been seen before -- supernovas and novas expel matter out into space.  Although the V838 Mon flash appears to expel material into space, what is seen in the above image from the  Hubble Space Telescope is actually an outwardly moving light echo of the bright flash.  In a light echo, light from the flash is reflected by successively more distant rings in the complex array of ambient interstellar dust that already surrounded the star.  V838 Mon lies about 20,000 light years away toward the constellation of the unicorn (Monoceros), while the  light echo above spans about six light years in diameter.
A Spider Shaped Crater on Mercury (2008-02-04)

Why does this crater on Mercury look like a spider?  When the robotic MESSENGER spacecraft glided by the planet Mercury last month, it was able to image portions of the Sun's closest planet that had never been seen before. When imaging the center of Mercury's extremely large Caloris Basin, MESSENGER found a crater, pictured above, with a set of unusual rays emanating out from its center.  A crater with such troughs has never been seen before anywhere in our Solar System. What isn't clear is the relation of the crater to the radial troughs. Perhaps the crater created the radial rays, or perhaps the two features appear only by a chance superposition -- the topic is sure to be one of future research. MESSENGER is scheduled to fly past Mercury twice more before firing its thrusters to enter orbit in 2011.
Three Month Composite of Comet Holmes (2008-02-05)

How has Comet Holmes changed? Since brightening unexpectedly by nearly one million fold in late October, the last three months have found the coma of Comet 17P/Holmes both expanding and fading. This spectacular composite image shows how the coma and tail of Comet Holmes have changed. Due to Earth's changing vantage point, Comet Holmes, out beyond the orbit of Mars, was seen in November nearly head-on, but in recent months is seen more from the side. Additionally, the comet's motion, when combined with Earth's changing perspective, has caused the comet to have shifted relative to the background stars. The curved path of Comet Holmes shows it to be undergoing apparent retrograde motion as the Earth orbits quickly in front of it. The extent of the coma currently makes Comet Holmes over five times the physical size of our Sun. Anecdotal evidence holds that the comet is hard to see without long photographic exposures, but on such exposures the comet may still be an impressive sight.

Image credit: John Pane
Sunspot in the Old Solar Cycle (2008-02-06)

A new cycle has begun on our Sun.  Over the past year, the Sun's magnetic field has reset and now a new 11 year period is beginning.  Pictured above in a specific color of light emitted by hydrogen is sunspot 10982, one of the last sunspots of the old solar cycle.   The two dark lines visible just above and to either side of the bright sunspot are cool filaments held aloft by the Sun's magnetic field.  Hot and cold regions are shown as regions of relative light and dark, respectively. A solar cycle is caused by the changing magnetic field, and varies from solar maximum, when sunspot, coronal mass ejection, and flare phenomena are most frequent, to solar minimum, when such activity is relatively infrequent. Solar minimums occurred in 1996 and 2007, while the last solar maximum occurred in 2001.     Editor's note: This APOD originally ran under the title "A Sunspot in the New Solar Cycle." But even though the new solar cycle has begun, the old one has not ended yet and may run concurrently with the new cycle for up to a year or so. This sunspot is now thought to belong to the old cycle, not the new one, based on its measured magnetic polarity and location.

Image credit: Greg Piepol