Copernicus' heliocentric theory is an astronomical model developed by Nicolaus Copernicus and published in 1543. This theory positioned the Sun at the center of the Universe, motionless, with Earth and the other planets revolving around it in circular orbits with uniform speeds. It displaced the earlier geocentric model, which had Earth at the center. Key elements of Copernicus' theory included the idea that the Earth is one of several planets orbiting the Sun, the Earth's daily rotation and annual revolution, and that apparent retrograde motions of planets are explained by Earth's motion. The heliocentric model brought greater symmetry and simplicity to the understanding of celestial motions, even though it still retained some inaccuracies like circular orbits and epicycles.
