Johannes Kepler was an astronomer and mathematician whose genius solved the mystery of planetary motion. Using the precise observational data of Tycho Brahe, Kepler abandoned the centuries-old belief that planets move in perfect circles. Instead, he formulated the Three Laws of Planetary Motion, demonstrating that planets move in ellipses with the Sun at one focus. His laws correctly described that planets speed up as they get closer to the Sun and provided a mathematical relationship between a planet's distance from the Sun and its orbital period. Kepler's work was the essential bridge between the observations of the Renaissance and the universal gravitation of Isaac Newton.