Kepler's laws of planetary motion

Johannes Kepler's primary contributions to astronomy/astrophysics were his three laws of planetary motion. Kepler, a nearly blind though brilliant German mathematician, derived these laws, in part, by studying the observations of the keen-sighted Danish astronomer Tycho Brahe. The article on Johannes Kepler gives a less mathematical description of the laws, as well as a treatment of their historical and intellectual context.

Kepler's laws of planetary motion

• Kepler's first law (1609): The orbit of a planet about a star is an ellipse with the star at one focus.
• Kepler's second law (1609): A line joining a planet and its star sweeps out equal areas during equal intervals of time.
• Kepler's third law (1618): The square of the sidereal period of an orbiting planet is directly proportional to the cube of the orbit's semimajor axis.