Browse NASA Astronomy Picture of the Day archive by date and media: Archive Discoveries
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Pwyll: Icy Crater of Europa
Explanation : The impact crater Pwyll ( a name from Celtic Mythology ) is thought to represent one of the youngest features on the surface of Jupiter's moon Europa . A combination…
A Star Cluster Through Hale-Bopp's Tail
Explanation : Comet Hale-Bopp continues to look impressive. The photograph above captured the comet on April 7 th passing nearly in front of M34 , a star cluster in the…
Hale-Bopp and the Plateau de Bure Interferometer
Explanation : Comet Hale-Bopp is being observed by many different telescopes. Here the comet is pictured behind the array of radio telescopes which compose the Plateau de Bure…
Hale-Bopp's Hoods
Explanation : Comet Hale-Bopp is spinning. The nucleus of the comet is a dirty snowball about 25 miles in diameter that spins about once every 12 hours . As Comet Hale-Bopp spins,…
Jets from SS433
Explanation : SS433 is one of the most exotic star systems known. Its unremarkable name stems from its inclusion in a catalog of stars which emit radiation characteristic of…
Arecibo: The Largest Telescope
Explanation : The Arecibo radio telescope is currently the largest single-dish telescope in the world. First opening in 1963, this 305 meter (1000 foot) radio telescope resides in…
The Sun Puffs
Explanation : The Earth has once again endured a burst of particles from the Sun. The latest storm , which began Monday, was one of the best documented solar storms to date. At 10…
Europa's Ice Rafts
Explanation : The surface of Jupiter 's moon Europa has shifted. Photographs released yesterday of Europa's surface taken by the spacecraft Galileo show that the smooth moon's icy…
Oceans Under Jupiter's Europa?
Explanation : Is there life beneath Europa? Today, new results are being announced (at about 2 pm EST) about the possibility of oceans under Jupiter 's moon Europa . The existence…
Comet Hale-Bopp Over New York City
Explanation : What's that point of light above the World Trade Center ? It's Comet Hale-Bopp ! Both faster than a speeding bullet and able to “leap” tall buildings in its single…
GRB970228: What's There?
Explanation : Could this fuzzy blob be the key to the whole gamma-ray burst (GRB) mystery ? Astronomers the world over are now scrambling to determine the true nature of the…
Mercury Astronauts and a Redstone
Explanation : Space suited project Mercury astronauts John H. Glenn , Virgil I. Grissom , and Alan B. Shepard Jr. (left to right) are pictured here posing in front of a Redstone…
A Black Hole in M87?
Explanation : The center of nearby giant galaxy M87 is a dense and violent place. In this 1994 photograph by the Hubble Space Telescope , a disk of hot gas was found to be…
Hale-Bopp in Stereo
Explanation : This stereo pair of Hale-Bopp images combines two pictures from slightly different viewing angles. Simulating stereo vision , the difference was generated by the…
Earth, Clouds, Sky, Comet
Explanation : Does a comet's dust tail always orbit behind it? Since comets rotate, they shed gas and dust in all directions equally. Small ice and dust particles expelled by the…
A Complete Aurora
Explanation : Aurora frequently make complete rings around a pole of the Earth. This particular “ crown ”, visible in orange near the top of this image , was taken by the orbiting…
Hale-Bopp and Andromeda
Explanation : Which is closer: the comet or the galaxy? Answer: the comet. In its trek through the inner Solar System , Comet Hale-Bopp has passed nearly in front of the Andromeda…
NGC 3242: The 'Ghost of Jupiter' Planetary Nebula
Explanation : It's a weed , it's Jupiter , no it's - actually planetary nebula NGC 3242. After a star like our Sun completes fusion in its core, it throws off its outer layers it…
Dusty Galaxy Centaurus A
Explanation : One of the most unusual galaxies known , Centaurus A , is pictured above. Cen A is marked by dramatic dust lanes that run across the galaxy's center. These dust…
The Closest Galaxy: The Sagittarius Dwarf
Explanation : What's the closest galaxy to our Milky Way ? For many years astronomers thought it was the Large Magellanic Cloud (LMC). But the seemingly insignificant fuzzy patch…
A Comet In The Sky
Explanation : It has been suggested that Comet Hale-Bopp will become the most viewed comet in Human history . Presently, for denizens of the Earth's northern hemisphere, this…
Comet Country
Explanation : Moonlight illuminates the landscape and lends a painterly quality to this beautiful photograph of the Absaroka mountain range , located along the Montana-Wyoming…
The City Comet
Explanation : Undaunted by the artificial glow from one of the most famous urban skylines on Earth, comet Hale-Bopp shines above the city of New York, USA . Photographed on March…
Hale-Bopp Brightest Comet This Century
Explanation : A comet as bright as Comet Hale-Bopp is very rare indeed. No comet has emitted or reflected this much light since possibly the Great Comet of 1811 . However, since…
Viewing discoveries from 17 April 1997 through 25 March 1997.