Armed with Tycho Brahe?s very accurate observations of the planets and his own painstaking measurements, the German astronomer Johannes Kepler discovered what we now call Kepler?s laws of planetary motion. These three laws precisely describe the motions of the planets around the sun.
Kepler?s first law states that planets move in elliptical orbits around the sun. This overturned the ancient dogma that the planets move in perfect circles. His second law describes how a planet travels faster in its orbit when it is closer to the sun. The third law describes how the orbital periods of the planets increase with the size of their orbits.
Kepler?s laws were based on the Copernican view of a heliocentric universe. Newton relied on them when he developed his more general law of universal gravitation.