The laws of planetary motion were proposed by Johannes Kepler, a German astronomer and mathematician, in the early 17th century. His three laws describe the motion of planets around the Sun, radically changing our understanding of celestial dynamics. The first law, the law of ellipses, states that planets move in elliptical orbits with the Sun at one focus. The second law, the law of equal areas, indicates that a line segment joining a planet to the Sun sweeps out equal areas during equal intervals of time. The third law establishes a relation between the time a planet takes to orbit the Sun and its distance from it.