Figure 1. The Copernican theory places the Sun (1) in the enter of the Solar System orbited by Mercury (2), Venus (3), the Earth (4), Mars (5), Jupiter (6), and Saturn (). His theory met strong opposition from the Church, and religious persecution persisted for a century. Copernicus retained both circular orbits and epicycles..
Figure 2. Diagram of the heliocentric universe, from De Revolutionibus Orbium Coelestium (1543). Image credit: Royal Astronomical Society.
The Copernican System is a heliocentric model of the Solar System introduced by Nicolaus Copernicus in the first half of the sixteenth century; despite causing little stir at the time, it laid the foundation for the revolution in astronomy that was realized through the work of Johannes Kepler and Galileo (but which is nevertheless referred to as the Copernican Revolution.)
Although modern in its reversal of roles for the Sun and Earth, the Copernican system owed much to the geocentric Ptolemaic system that it opposed. It still involved epicycles and circular orbits, and incorporated ideas from variations to the Ptolemaic model proposed by Arab astronomers. Its importance lay not in its improved accuracy – Kepler's elliptical orbits would be needed for that – but in its challenge to the orthodox view that Earth was at the center of the universe. A much earlier heliocentric scheme had been proposed by Aristarchus of Samos in the third century BC, a fact known to Copernicus but long ignored by others prior to him.