juliensimon/nasa-apod huggingface dataset:
Eris: The Largest Known Dwarf Planet (2006-09-18)

Is Pluto the largest dwarf planet? No!  Currently, the largest known dwarf planet is (136199) Eris, renamed last week from 2003 UB313.   Eris is just slightly larger than Pluto, but orbits as far as twice Pluto's distance from the Sun. Eris is shown above in an image taken by a 10-meter Keck Telescope from Hawaii, USA.  Like Pluto, Eris has a moon, which has been officially named by the International Astronomical Union as (136199) Eris I (Dysnomia).  Dysnomia is visible above just to the right of Eris.   Dwarf planets Pluto and Eris are trans-Neptunian objects that orbit in the Kuiper belt of objects past Neptune.  Eris was discovered in 2003, and is likely composed of frozen water-ice and methane. Since Pluto's recent demotion by the IAU from planet to dwarf planet status, Pluto has recently also been given a new numeric designation: (134340) Pluto.   Currently, the only other officially designated "dwarf planet" is (1) Ceres.

Image credit: W. M. Keck Observatory
Beagle Crater on Mars (2006-09-19)

What have we found on the way to large Victoria Crater?  Smaller Beagle Crater.  The robotic Opportunity rover rolling across Mars stopped at Beagle Crater early last month and took an impressively detailed 360-degree panorama of the alien Martian landscape.  Beagle crater appears in the center as a dip exposing relatively dark sand. Surrounding 35-meter Beagle Crater are many of the rocks ejected during its creation impact.  Opportunity's detailed images show significant erosion on the rocks and walls of Beagle Crater, indicating that the crater is not fresh. Beagle Crater's unofficial name derives from the ship HMS Beagle where Charles Darwin observations led him to postulate his theory of natural selection.  That ship was named after the dog breed of beagle.  Opportunity is scheduled to roll up to expansive Victoria Crater this week.
The International Space Station Expands Again (2006-09-20)

The developing International Space Station (ISS) has changed its appearance again.  Over the past few days, the Space Shuttle Atlantis visited the ISS and added pieces of the  Integrated Truss Structure, including an impressively long array of solar panels.  These expansive solar panels are visible extending from the lower right of the above image taken by the Shuttle Atlantis Crew after leaving the ISS to return to Earth. The world's foremost space outpost can be seen developing over the past several years by comparing the above image to past images.  Also visible above are many different types of modules, a robotic arm, another impressive set of  solar panels, and a supply ship.  Construction began on the ISS in 1998.
Sharp Silhouette (2006-09-21)

Though it's 93 million miles away, the Sun still hurts your eyes when you look at it. But bright sunlight (along with accurate planning and proper equipment!) resulted in this sharp silhouette of spaceship and space station. The amazing telescopic view, recorded on September 17, captures shuttle orbiter Atlantis and the International Space Station in orbit over planet Earth. At a range of 550 kilometers from the observing site near Mamers, Normandy, France, Atlantis (left) has just undocked and moved about 200 meters away from the space station. Tomorrow, yet another satellite of planet Earth can be seen in silhouette - the Moon will eclipse the Sun. This last eclipse of 2006 will be seen as an annular solar eclipse along a track that crosses northern South America and the south Atlantic.

Image credit: Thierry Legault
Central IC 1805 (2006-09-22)

Cosmic clouds seem to form fantastic shapes in the central regions of emission nebula IC 1805. Of course, the clouds are sculpted by stellar winds and radiation from massive hot stars in the nebula's newborn star cluster (aka Melotte 15). About 1.5 million years young, the cluster stars appear in this colorful skyscape, along with dark dust clouds silhouetted against glowing atomic gas. A composite of narrow band telescopic images, the view spans about 15 light-years and shows emission from hydrogen in green, sulfur in red, and oxygen in blue hues. Wider field images reveal that IC 1805's simpler, overall outline suggests its popular name - The Heart Nebula. IC 1805 is located about 7,500 light years away toward the constellation Cassiopeia.

Image credit: Ken Crawford  
(Rancho Del Sol Observatory)
Triple Sunrise (2006-09-23)

Today, the Sun rises due east at the Equinox, a geocentric astronomical event that occurs twice a year. To celebrate, consider this view of the rising Sun and a lovely set of ice halos recorded on a cold winter morning near Green Bay, Wisconsin, USA, planet Earth. Produced by sunlight shining through common atmospheric ice crystals with hexagonal cross-sections, such halos can actually be seen more often than rainbows. The remarkable sunrise picture captures a beautiful assortment of the types most frequently seen, including a sun pillar (center) just above the rising Sun surrounded by a 22 degree halo arc. Completing a triple sunrise illusion, sundogs appear at the far left and far right edges of the 22 degree arc. An upper tangent arc is also just visible at the very top of the view.

Image credit: Jim Hoida
NGC 1499: The California Nebula (2006-09-24)

What's California doing in space?  Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud by chance echoes the outline of California on the west coast of the United States. Our own Sun also lies within the Milky Way's Orion Arm, only about 1,500 light-years from the California Nebula. Also known as NGC 1499, the classic emission nebula is around 100 light-years long. It glows with the red light characteristic of hydrogen atoms recombining with long lost electrons, stripped away (ionized) by energetic starlight. In this case, the star most likely providing the energetic starlight is the bright, hot, bluish Xi Persei, just right of the nebula and above picture center. Fittingly, this composite picture was made with images from a telescope in California - the 48-inch (1.2-meter) Samuel Oschin Telescope - taken as a part of the second National Geographic Palomar Observatory Sky Survey.
Mars Express Close-Up of the Face on Mars (2006-09-25)

Wouldn't it be fun if clouds were turtles?  Wouldn't it be fun if the laundry on the bedroom chair was a friendly  monster?  Wouldn't it be fun if rock mesas on Mars were faces or interplanetary monuments?  Clouds, though, are small water droplets, floating on air.  Laundry is cotton, wool, or plastic, woven into garments.  Famous Martian rock mesas known by names like the Face on Mars appear quite natural when seen more clearly, as the above recently-released digital-perspective image shows.  Is reality boring?  Nobody knows how clouds make lightning.  Nobody knows the geological history of Mars.  Nobody knows why the laundry on the bedroom chair smells like root beer.   Understanding reality brings more questions.  Mystery and adventure are never far behind.  Perhaps fun and  discovery are  just beginning.
Mars Express: Return to Cydonia (2006-09-26)

The unusual stone mesas of the Cydonia region on Mars are quite striking in appearance.  Last week, the Mars Express project released a new close-up image of a portion of the Cydonia region on Mars. This new image, taken by the robotic Mars Express spacecraft now orbiting Mars,  shows an area about 90 kilometers wide.  In the far lower right of the above image, a particularly picturesque mesa can be seen as the upper right of the two mesas visible there.  This mesa, when lit from just the right sun angle, can appear similar to a human face and became famous as the Face on Mars in 1976 Viking orbiter images. Better images show it to be just an interesting mesa.  Such complex looking landforms in the Cydonia region are thought to be the result of landslides and erosion of the ancient Martian crust.
Earth from Saturn (2006-09-27)

What's that pale blue dot in this image taken from Saturn?  Earth.  The robotic Cassini spacecraft looked back toward its old home world earlier this month as it orbited Saturn.  Using Saturn itself to block the bright Sun, Cassini imaged a faint dot on the right of the above photograph.  That dot is expanded on the image inset, where a slight elongation in the direction of Earth's Moon is visible.  Vast water oceans make Earth's reflection of sunlight somewhat blue.  Earth is home to over six billion humans and over one octillion Prochlorococcus.
RCW 86: Historical Supernova Remnant (2006-09-28)

In 185 AD, Chinese astronomers recorded the appearance of a new star in the Nanmen asterism - a part of the sky identified with Alpha and Beta Centauri on modern star charts. The new star was visible for months and is thought to be the earliest recorded supernova. Data from two orbiting X-ray telescopes of the 21st century, XMM-Newton and Chandra, now offer evidence that supernova remnant RCW 86 is indeed the debris from that stellar explosion. Their composite, false-color view of RCW 86 shows the expanding shell of material glowing in x-rays with high, medium, and low energies shown in blue, green, and red hues. Shock velocities measured in the x-ray emitting shell and an estimated radius of about 50 light-years can be used to find the apparent age of the remnant. The results indicate that light from the initial explosion could well have first reached planet Earth in 185 AD. Near the plane of our Milky Way Galaxy, RCW 86 is about 8,200 light-years away.
NGC 5905 and 5908 (2006-09-29)

These two beautiful galaxies, NGC 5905 (left) and NGC 5908 lie about 140 million light-years distant in the northern constellation Draco. Separated by about 500,000 light-years, the pair are actually both spiral galaxies and nicely illustrate the striking contrasts in appearance possible when viewing spirals from different perspectives. Seen face-on, NGC 5905 is clearly a spiral galaxy with bright star clusters tracing arms that wind outward from a prominent central bar. Oriented edge-on to our view, the spiral nature of NGC 5908 is revealed by a bright nucleus and dark band of obscuring dust characteristic of a spiral galaxy's disk. In fact, NGC 5908 is similar in appearance to the well studied edge-on spiral galaxy M104 - The Sombrero Galaxy.

Image credit: Stefan Seip
STS-115: Stereo Portrait (2006-09-30)

On September 12, astronaut Heidemarie Stefanyshyn-Piper snapped photos of her colleague Joseph Tanner during the STS-115 mission. At the time, the spacesuited pair were working outside the shuttle orbiter Atlantis, some 300 kilometers above planet Earth. Portions of two of the pictures (S115-E-05750 and S115-E-05753) have been combined in this spectacular 3D image - a stereo anaglyph intended to be viewed with red/blue glasses. Included in the scene reflected in Tanner's visor is Stefanyshyn-Piper herself and the Sun shining above the Earth's distant horizon.
Earth at Night (2006-10-01)

This is what the Earth looks like at night.  Can you find your favorite  country or city?  Surprisingly, city lights make this task quite possible.  Human-made lights highlight particularly developed or populated areas of the Earth's surface, including the seaboards of Europe, the eastern United States, and Japan.  Many large cities are located near rivers or oceans so that they can exchange goods cheaply by boat.  Particularly dark areas include the central parts of South America, Africa, Asia, and Australia.  The above image is actually a composite of hundreds of pictures made by the orbiting DMSP satellites. (Editor's note: This image has generated many print requests. Unfortunately, we do not sell prints. However, a high-resolution digital version of the image is available here.
Victoria Crater on Mars (2006-10-02)

Scroll right to see the largest crater yet visited by a rover on Mars.  Reaching the expansive Victoria Crater has been a goal for the robotic Opportunity rover rolling across Mars for the past 21 months.  Opportunity reached Victoria last week, and is cautiously probing the stadium-sized crevice.  It is hoped that Victoria Crater will show a deep stack of layers uncovered by the initial impact, and hence new clues into the ancient surface history of Mars. Visible in the distance of the above image mosaic is the far rim of Victoria Crater, lying about 800 meters away and rising about 70 meters above the crater floor.  The alcove in front has been dubbed Duck Bay.  Victoria crater has about five times the diameter of Endurance Crater, which Opportunity spent six months exploring.  If a safe path is found, Opportunity may actually attempt to enter Victoria Crater.
Light from the Heart Nebula (2006-10-03)

What powers the Heart Nebula?  The large emission nebula dubbed IC 1805 looks, in whole, like a human heart.  The nebula glows brightly in red light emitted by its most prominent element: hydrogen.  The red glow and the larger shape are all created by a small group of stars near the nebula's center.  A close up spanning about 30 light years contains many of these stars is shown above . This open cluster of stars contains a few bright stars nearly 50 times the mass of our Sun, many dim stars only a fraction of the mass of our Sun, and an absent microquasar that was expelled millions of years ago.  The Heart Nebula is located about 7,500 light years away toward the constellation of Cassiopeia.

Image credit: Matt Russell
Comet SWAN Brightens (2006-10-04)

A newly discovered comet has brightened enough to be visible this week with binoculars. The picturesque comet is already becoming a favored target for northern sky imagers.  Pictured above just last week, Comet SWAN showed a bright blue-green coma and an impressive tail. Comet C/2006 M4 (SWAN) was discovered in June in public images from the Solar Wind Anisotropies (SWAN) instrument of NASA and ESA's Sun-orbiting SOHO spacecraft. Comet SWAN, near magnitude six, will be visible with binoculars in the northeastern sky not far from the Big Dipper over the next few days before dawn.  The comet is expected to reach its peak brightness this week. Passing its closest to the Sun two days ago, Comet SWAN and will be at its closest to the Earth toward the end of this month.   Comet SWAN's unusual orbit appears to be hyperbolic, meaning that it will likely go off into interstellar space, never to return.

Image credit: Michael J�ger  & 
Gerald Rhemann
Hidden Galaxy IC 342 (2006-10-05)

Similar in size to other large, bright spiral galaxies IC 342 is a mere 7 million light-years distant in the long-necked, northern constellation Camelopardalis. A sprawling island universe, IC 342 would otherwise be a prominent galaxy in our night sky, but it is almost hidden from view behind the veil of stars, gas and dust clouds in the plane of our Milky Way galaxy. Even though IC 342's light is dimmed by intervening cosmic clouds, this remarkably sharp telescopic image traces the galaxy's own obscuring dust, blue star clusters, and glowing pink star forming regions along spiral arms that wind far from the galaxy's core. IC 342 may have undergone a recent burst of star formation activity and is close enough to have gravitationally influenced the evolution of the local group of galaxies and the Milky Way.

Image credit: Robert Gendler
Dusty NGC 1333 (2006-10-06)

Dusty NGC 1333 is seen in visible light as a reflection nebula, dominated by bluish hues characteristic of starlight reflected by dust. But at longer infrared wavelengths, the interstellar dust itself glows. Moving your cursor over the picture will match up a visible light view with a false-color infrared image of the region from the Spitzer Space Telescope. The penetrating infrared view unmasks youthful stars that are otherwise obscured by the dusty clouds that formed them. Also revealed are greenish streaks and splotches that seem to litter the region. The structures trace the glow of cosmic jets blasting away from emerging young stellar objects and plowing into the cold cloud material. In all, the chaotic environment likely resembles one in which our own Sun formed over 4.5 billion years ago. NGC 1333 is a mere 1,000 light-years distant in the constellation Perseus.
COBE All-Sky Map (2006-10-07)

This historic all-sky map is based on the first two years of data from NASA's COsmic Background Explorer (COBE) satellite, launched in November of 1989. The map shows minute temperature variations (red is hotter) imprinted on the Cosmic Microwave Background (CMB) radiation by structures in the early Universe. These detailed measurements of the CMB and other COBE results ushered in an age of precision cosmology, and exactly confirmed the predictions of the Big Bang theory. Playing leading roles in the COBE project, for their resulting discoveries John C. Mather (NASA, Goddard Space Flight Center), and George F. Smoot (UC Berkeley) were selected to receive the 2006 Nobel Prize in Physics.
CMBR Dipole: Speeding Through the Universe (2006-10-08)

Our Earth is not at rest.   The Earth moves around the Sun.   The Sun orbits the center of the Milky Way Galaxy.   The Milky Way Galaxy orbits in the Local Group of Galaxies.   The Local Group falls toward the Virgo Cluster of Galaxies.   But these speeds are less than the speed that all of these objects together move relative to the cosmic microwave background radiation (CMBR).   In the above all-sky map from the COBE satellite, radiation in the Earth's direction of motion appears blueshifted and hence hotter, while radiation on the opposite side of the sky is redshifted and colder.   The map indicates that the Local Group moves at about 600 kilometers per second relative to this primordial radiation.   This high speed was initially unexpected and its magnitude is still unexplained.   Why are we moving so fast?   What is out there?  Note: Playing leading roles in the COBE project, for their resulting discoveries John C. Mather (NASA, Goddard Space Flight Center ), and George F. Smoot (UC Berkeley) were selected to receive the 2006 Nobel Prize in Physics.
Mars Rover at Victoria Crater Imaged from Orbit (2006-10-09)

An unusual spot has been found on Mars that scientists believe is not natural in origin.  The spot appears mobile and is now hypothesized to be a robot created by an intelligent species alien to Mars.  In fact, the spot appears to be NASA's robotic Opportunity rover currently rolling across Mars. The ability to see the Martian rover from orbit has recently been demonstrated by the High Resolution Imaging Science Experiment on NASA's Mars Reconnaissance Orbiter (MRO).   The new spacecraft achieved orbit around Mars in 2006 March. Last week, MRO imaged the location of Victoria Crater and the rover Opportunity that had just arrived there.  In the above image at spectacularly high resolution, objects about one meter in size are resolved, and this includes the rolling rover.  Such images may help scientists better determine if any safe path exists for Opportunity to enter large crater.  In the inset image on the upper left, the whole of Victoria Crater was also imaged by MRO.
Reflection Nebulas in Orion (2006-10-10)

In the vast Orion Molecular Cloud complex, several bright blue nebulas are particularly apparent.  Pictured above are two of the most prominent reflection nebulas - dust clouds lit by the reflecting light of bright embedded stars.  The more famous nebula is M78, near the image center, cataloged over 200 years ago.  On the upper left is the lesser known NGC 2071.  The image was taken with the Mayall 4-meter telescope on Kitt Peak, Arizona, USA. Astronomers continue to study these reflection nebulas to better understand how interior stars form.  The Orion complex lies about 1500 light-years distant, contains the Orion and  Horsehead nebulas, and covers much of the constellation of Orion.

Image credit: T. Rector
Markarian's Chain of Galaxies (2006-10-11)

Across the heart of the Virgo Cluster of Galaxies lies a striking string of galaxies known as Markarian's Chain.  The chain, pictured above, is highlighted on the lower right with two large but featureless lenticular galaxies, M84 and M86, and connects through several large spiral to the upper left, including M88.  The home Virgo Cluster is the nearest cluster of galaxies, contains over 2,000 galaxies, and has a noticeable gravitational pull on the galaxies of the Local Group of Galaxies surrounding our Milky Way Galaxy.  The center of the Virgo Cluster is located about 70 million light years away toward the constellation of Virgo.  At least seven galaxies in the chain appear to move coherently, although others appear to be superposed by chance.  The above image is just a small part of a mosaic dubbed the Big Picture taken by the Samuel Oschin Telescope at Palomar Observatory, in California, USA.  A mural of the Big Picture will be displayed at the newly renovated Griffith Observatory near Los Angeles, California.

Image credit: The Palomar-Quest Survey Team, 
CalTech
Saturn's Infrared Glow (2006-10-12)

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 thermal infrared glow is also apparent in the broad bands of ring shadows draped across the northern hemisphere of Saturn.
The Hubble SWEEPS Field (2006-10-13)

This crowded star field towards the center of our Milky Way Galaxy turns out to be a great place to search for planets beyond our solar system. In fact, repeatedly imaging about 180,000 stars in the field over a one week period, the Hubble Space Telescope enabled astronomers to conduct the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). Their search looked for brief, periodic dips in brightness caused as a large planet eclipses or transits its parent star. Since chances of seeing such an eclipse are slim, it was a definite advantage to examine as many stars as possible. In the end, SWEEPS astronomers found 16 candidate stars (green circles identify 11 in this cropped picture) that are likely closely orbited by large Jupiter-sized planets with periods of a few days or less. Large planets orbiting so close to their stars are termed hot Jupiters. Kepler, a future NASA mission, is intended to extend the transit technique to search for Earth-sized planets.
Full Moon Crossing (2006-10-14)

On October 6th, a nearly full perigee Moon shone in Earth's night sky. The bright moonlight, accurate planning, and proper equipment resulted in this amazing composite featuring sharp silhouettes of the International Space Station (ISS) as it rapidly crossed (right to left) in front of the lunar disk. The picture was constructed using six video frames recorded from a site just outside Tracy, California, USA. Sporting newly deployed solar arrays, the ISS was at a range of about 260 miles from the telescope/video camera setup. In the background, about a thousand times more distant than the ISS, lies bright lunar ray crater Tycho.

Image credit: Ed Morana