The Copernican world system or Copernican heliocentrism is the name given to the astronomical model developed by Nicolaus Copernicus and published in 1543 in his book De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres). It positioned the Sun near the center of the Universe, motionless, with Earth and the other planets rotating around it in circular paths modified by epicycles and at uniform speeds. The Copernican model departed from the Ptolemaic system that prevailed in Western culture for centuries, placing Earth at the center of the Universe, and is often regarded as the launching point to modern astronomy and the Scientific Revolution.