Johannes Kepler was a German astronomer who discovered the three laws of planetary motion. The first law states that planets orbit the sun in ellipses, with the sun located at one focus. The second law describes how a line connecting a planet to the sun sweeps out equal areas in equal times. Kepler's third law relates the orbital period of a planet to its average distance from the sun. These laws helped usher in the modern era of astronomy and supported the Copernican model of a sun-centered solar system.