# Kepler's laws

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**Kepler's laws of planetary motion**, or simply **Kepler's laws**, are three laws stated by the German astronomer Johannes Kepler. These laws govern the motion of the planets around the Sun. Stated briefly, the laws are:

- The orbit of a planet is elliptical, with the sun at one of the two foci of the ellipse.
- The line joining a planet and the Sun sweeps out equal areas in equal intervals of time.
- The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its (elliptical) orbit.

Note that planetary orbits can be circular, as a circle is a special case of an ellipse. In this case, the sun is located at the center of the circle, and the semi-major axis is simply the circle's radius.