Copernican heliocentrism is the astronomical model developed by Nicolaus Copernicus and published in 1543. This model positioned the Sun at the center of the Universe, motionless, with Earth and the other planets orbiting around it in circular paths, modified by epicycles, and at uniform speeds. The Copernican model displaced the geocentric model of Ptolemy that had prevailed for centuries, which had placed Earth at the center of the Universe.
Although he had circulated an outline of his own heliocentric theory to colleagues sometime before 1514, he did not decide to publish it until he was urged to do so later by his pupil Rheticus. Copernicus's challenge was to present a practical alternative to the Ptolemaic model by more elegantly and accurately determining the length of a solar year while preserving the metaphysical implications of a mathematically ordered cosmos. Thus, his heliocentric model retained several of the Ptolemaic elements, causing inaccuracies, such as the planets' circular orbits, epicycles, and uniform speeds,[1] while at the same time using ideas such as:
- The Earth is one of several planets revolving around a stationary sun in a determined order.
- The Earth has three motions: daily rotation, annual revolution, and annual tilting of its axis.
- Retrograde motion of the planets is explained by the Earth's motion.
- The distance from the Earth to the Sun is small compared to the distance from the Sun to the stars.