| Astronaut |
| Astronaut, individual involved in flight beyond the Earth's atmosphere. Yuri Gagarin of the Soviet Union rode the first manned Earth-orbiting spacecraft, launched on 12 April 1961. The first American to orbit the... |
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| Astronomy |
| Astronomy, science that studies the SUN, the solar system, the remote stars, distant GALAXIES and all other detectable bodies in the universe. Its major subdisciplines include astrophysics, the closely related... |
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| Astrophysics |
| Astrophysics is the study of the physical makeup and behaviour of celestial objects. Astrophysics and ASTRONOMY are not sharply distinguished. If one wishes to emphasize the application of physical laws or the... |
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| Balloon |
| Balloon, vehicle that can rise within Earth's atmosphere because its total weight is less than that of the air it displaces. This principle was first enunciated by Greek mathematician and inventor Archimedes. The... |
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| Black Hole |
| The notion of black holes originated near the end of the eighteenth century with the English physicist John Michell and then later by the French mathematician Pierre Simon de Laplace, who realized that if light was... |