From Infogalactic: the planetary knowledge core
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The Space Portal
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Space (or outer space) describes the vast empty regions between and around planets and stars. The study of these, and other, astronomical objects is called astronomy, one of the oldest sciences. It is often said that space exploration began with the launch of Sputnik 1, the first man-made object to orbit the Earth. Then, in an almost unbelievable feat of human achievement, in 1969 Neil Armstrong and Buzz Aldrin travelled to the Moon and set foot on the surface during the Apollo 11 mission. Recently, it has become clear that the possibility of space colonization may no longer be exclusively reserved for science-fiction stories, and many controversial issues surrounding space have come to light, including commercial spaceflight, space laws and space weapons.
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 Callisto is a moon of the planet Jupiter, discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. It is not a part of the orbital resonance that affects three inner Galilean satellites—Io, Europa and Ganymede—and thus does not experience appreciable tidal heating. Callisto rotates synchronously with its orbital period, so the same hemisphere is always turned toward Jupiter. It is composed of approximately equal amounts of rock and ices, with a mean density of about 1.83 g/cm3. Compounds detected spectroscopically on the surface include water ice, carbon dioxide, silicates, and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto may have only partially differentiated interior covered by a thick icy crust and possibly a subsurface ocean of liquid water at depths greater than 100 km. Prominent surface features include multi-ring structures, variously shaped impact craters, and chains of craters and associated scarps, ridges and deposits. Callisto is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen, as well as by a rather dense ionosphere.
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A composite photo of the Orion Nebula, the closest region of star formation to Earth. It is composed of 520 separate images and NASA calls it "one of the most detailed astronomical images ever produced". The nebula is located below Orion's Belt and is visible to the naked eye at night. It is one of the most scrutinized and photographed objects in the night sky, and is among the most intensely-studied celestial features.
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