- See under Kepler's laws.
- any one of three laws governing planetary motion: each planet revolves in an ellipse, with the sun at one focus; the line connecting a planet to the sun sweeps out equal areas in equal periods of time (law of areas); or the square of the period of revolution of each planet is proportional to the cube of the semimajor axis of the planet's orbit (harmonic law).
Origin of Kepler's law
after J. Kepler
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