Space exploration began with the launch of Sputnik and Astrophysics was born as the application of physics to the phenomena observed by Astronomy, which etymologically means laws of the stars.
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| Deferent |
A basic circular orbit, which, in combination with the epicycle, was necessary to the theory of planetary motions developed by Ptolemy in the second century AD. The planets were supposed to travel uniformly around a small, circular epicycle, the centre of which in turn moved around a larger circle, called the deferent.
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