Johannes Kepler (1571-1630),the German astronomer who devised the three basic laws of planetary motion. These were based on detailed observations of the planets made by Tycho Brahe and himself. Kepler's 1st law states that the planets orbit the Sun in elliptical paths,with the Sun at one focus of the ellipse. The 2nd law states that a line joining a planet to the Sun sweeps out equal areas in equal times (meaning that the nearer a planet is to the Sun,the faster it moves). The 3rd law states that the cube of a planet's mean distance from the Sun is proportional to the square of its orbital period. Newton used these ideas to help formulate his theory of gravity | |
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