Johannes Kepler's theories of the universe were notable for hypothesizing that the universe was created on April 27, 4977 B.C. and that the planets orbit in an elliptical pattern rather than a circular pattern. His theory superseded previous theories which postulated that planets move in circular orbits at constant speeds.
Kepler based his theories on the ideas of Copernicus, who had previously proposed that the sun, rather than the Earth, was the center of the solar system. Working from this perspective, Kepler began to carefully observe the motion of the planets, particularly Mars. After obtaining a telescope from Galileo Galilei and improving its design, he realized that the orbit of Mars did not fit into a circular pattern. From this observation, he began to formulate his theory that the planets moved in ellipses rather than circles.
This theory led to his later theories of planetary motion, which stated that the speed of a planet's motion is determined by its distance from the sun. Although his theory about the origin of the universe has been discredited by modern astronomy, his laws of planetary motion have proven widely influential in the development of later scientific theories, including Isaac Newton's law of gravity.