The
astronomer Johannes Kepler's main contribution to
astronomy was his three laws of planetary motion. They predate
Isaac Newton and provide the foundation for his work, and can be derived from his
laws of motion and
gravity. Kepler's laws not only caused the theories of
Copernicus to find wider acceptance, they also formed a basis for the theories of
Newton, who proved that Kepler's Laws could be directly derived from the mathematics of an inverse-square law gravitation force.
Kepler's First Law: Planets move in ellipses, with the sun located on one focus of the ellipse.
Kepler's Second Law: A line between a planet and the sun will sweep out equal areas over equals times.
Kepler's Third Law: The square of the semimajor axis of the orbit of a planet is proportional to the cube of the time it takes to orbit the sun (its period).