With the advent of the Scientific Revolution and the heliocentric model of Copernicus, Galileo, and Kepler, use of the term "planet" changed from something that moved around the sky relative to the fixed star to a body that orbited the Sun, directly (a primary planet) or indirectly (a secondary or satellite planet). Thus the Earth was added to the roster of planets, and the Sun was removed. The Copernican count of primary planets stood until 1781, when William Herschel discovered Uranus.