The Copernican System: A Detailed Synopsis
By John A. Kramer
Oglethorpe Journal of Undergraduate Research, Vol. 5:1 (2015)
Introduction: Dissatisfied with the problems of the geocentric system inherited from Claudius Ptolemy, Nicholas Copernicus began the change from geocentrism to heliocentrism. His eponymous system was expounded first in the Commentariolus (written about 1508 and circulated privately in manuscript form) and then more fully and finally in his book, De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Orbs) published as he lay dying in 1543.
Recognizing three motions of the Earth where Ptolemy, following Aristotle, could admit none, he claimed to then be able to greatly simplify the heavenly motions. The motion of the stars, he said, is only apparent and is occasioned by the daily rotation of Earth on its north/south axis. The Earth also revolves about the Sun annually causing the 7 wanderers (“planets”) to seem to move around the Zodiac. More subtly, he reinterpreted the “precession of the equinoxes,” discovered by Hipparch plane of the “motion” of the Sun about 1 per century. Copernicus recognized this appearance as the consequence of a precession (a rotating tipping) of the axis of rotation of the Earth revolving about once every 26,000 years.