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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The Oort cloud (artist's rendering pictured) is a hypothesized spherical cloud of comets that may lie nearly a light-year from the Sun. It is thought to comprise two separate regions: a spherical outer Oort cloud and a disc-shaped inner Oort cloud, or Hills cloud; the outer extent of the cloud defines the boundary of the Solar System. Objects in the Oort cloud are largely composed of ices, such as water, ammonia, and methane and are thought to have formed close to the Sun, later being scattered into space by the gravitational effects of the giant planets early in the Solar System's evolution. Although no confirmed direct observations of the Oort cloud have been made, astronomers believe that it is the source of all long-period and Halley-type comets entering the inner Solar System, as well as many of the Centaurs and Jupiter-family comets.
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Credit: Eugene Alvin Villar
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Animation of the night sky showing the apparent retrograde motion of the planet Mars in August and September of 2003 in the constellation Aquarius. The time period depicted spans from June 15, 2003 to November 18, 2003 in 2-day increments where each day is at 00:00 UTC. All stars brighter than 5.0 magnitude are shown and labelled. The animation period also encompasses the time that Mars was at its closest approach to Earth in nearly 60,000 years.
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