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Astronomy Picture Of the Day (APOD)
Starburst Ring in Galaxy NGC 1317
11.12.1996
Where do stars form? A typical place is an area of dense nebular gas common to arms in spiral galaxies. Sometimes, however, a burst of star formation can occur with unusual geometry. Nearby galaxy NGC 1317 shows such an unusual ring of star formation surrounding its barred nucleus.
Comet Halley's Nucleus
10.12.1996
Here is what a comet nucleus really looks like. For all active comets except Halley, it was only possible to see the surrounding opaque gas cloud called the coma. During Comet Halley's most...
Callisto Full Face
9.12.1996
Callisto's surface shows its age. While probably formed at the same time as Io, the difference between the surfaces of these two moons of Jupiter could hardly be greater. Io's surface is young, shows practically no impact craters, and is continually being repaved by the lava exploding from its many large volcanoes.
Degas Ray Crater on Mercury
8.12.1996
Like the Earth's Moon, Mercury is scarred with craters, testifying to an intense bombardment during the early history of the Solar System. In 1974, the Mariner 10 spacecraft surveyed this innermost planet up close, producing the only detailed images of its tortured surface.
Planetary Systems Now Forming in Orion
7.12.1996
How do planets form? Astronomers are finding out by studying one of the most interesting of all astronomical nebulae known, the Great Nebula in Orion. Insets to above mosaic show several planetary systems in formation. The bottom left insert shows the relative size of our own Solar System. The Orion Nebula contains many stellar nurseries.
Globular Cluster M3
6.12.1996
This huge ball of stars predates our Sun. Long before mankind evolved, before dinosaurs roamed, and even before our Earth existed, ancient globs of stars condensed and orbited a young Milky Way Galaxy.
Io's Giant Volcano Pele
5.12.1996
Io has some very large volcanoes. One of the largest is evident near the center of the above photograph and named Pele, for the mythological Polynesian fire goddess. The Galileo spacecraft now orbiting Jupiter took this picture of Jupiter's most active moon in June, although it was released just last week.
Ice at the Lunar South Pole
4.12.1996
Ice on the Moon? The prospecting Clementine spacecraft may well have discovered it. In 1994, Clementine spent 70 days in lunar orbit mapping the Moon's surface. Shown above is a dramatically detailed composite view centered on the Lunar South Pole - constructed from 1500 Clementine images.
Cocoon of a New White Dwarf
3.12.1996
Like a butterfly, a white dwarf star begins its life by casting off a cocoon that enclosed its former self. In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all!
Orion's Star Colors
2.12.1996
What determines a star's color? Its temperature. Red stars are cool, with temperatures of around 3,000 degrees Kelvin (K), while blue stars are hotter and can have temperatures over 30,000 degrees K. Our own lovely yellow Sun's temperature is a comforting 6,000 degrees K.
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