noun Astronomy.
- See under Kepler’s laws.
noun Astronomy.
- 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).