Kepler's laws

Century Dictionary and Cyclopedia

1. See law.

Wiktionary

1. n. astronomy The three laws of planetary motion discovered by Kepler in the early 17th century.

GNU Webster's 1913

1. n. (Astron.) three important laws or expressions of the order of the planetary motions, discovered by John Kepler. They are these: (1) The orbit of a planet with respect to the sun is an ellipse, the sun being in one of the foci. (2) The areas swept over by a vector drawn from the sun to a planet are proportioned to the times of describing them. (3) The squares of the times of revolution of two planets are in the ratio of the cubes of their mean distances.