An Etymological Dictionary of Astronomy and Astrophysics
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A model of the Solar System proposed by Copernicus in which the Sun lies at the center with the planets orbiting around it. In this model, the Earth is a planet, and the Moon is in orbit around the Earth, not the Sun. The stars are distant objects that do not revolve around the Sun. Instead, the Earth is assumed to rotate once in 24 hours, causing the stars to appear to revolve around the Earth in the opposite direction. This model readily explained both the varying brightness of the planets and the → retrograde motion. In the Copernican model the planets executed uniform circular motion about the Sun. As a consequence, the model could not explain all the details of planetary motions on the celestial sphere without → epicycles of the → Ptolemaic system. However, the Copernican system required many fewer epicycles than its predecessor because it moved the Sun to the center. Hence, Copernicus borrowed elements from variants of the Ptolemaic system developed by Middle Eastern astronomers, mainly the Iranian Nasireddin Tusi (1201-1274) and the Damascene Ibn al-Shatir (1304-1375), which Copernicus apparently knew about.

Nicolaus Copernicus (1473-1543), the L. rendition of the Polish original name Mikołaj Kopernik, author of the epoch making work De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), published in 1543, in which he exposed his heliocentric system; → model.