Three laws devised by Johannes Kepler todefinethe mechanics ofplanetary motion. The first law states thatplanetsmove in an elliptical orbit, with the Sun being one focus of the ellipse. This law identifies that the distance between the Sun and Earthisconstantly changing as the Earth goes around its orbit.

Kepler's three laws ofplanetary motioncan be stated as follows: (1) Allplanetsmove about the Sun in elliptical orbits, having the Sun as one of the foci. (2) A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time.

Kepler’s laws of planetary motion, inastronomyand classicalphysics, laws describing the motions of theplanetsin thesolar system. They were derived by the German astronomerJohannes Kepler, whose analysis of the observations of the 16th-century Danish astronomerTycho Braheenabled him to announce his first two laws in the year 1609 and a third law nearly a decade later, in 1618. Kepler himself never numbered these laws or specially distinguished them from his other discoveries.