Timeline of astronomy Rectification of Planetary Theory", eliminated the need for an equant by introducing an extra epicycle, departing from the Ptolemaic system in a way very similar to what Copernicus later also did. Ibn al-Shatir proposed a system that was only approximately geocentric, rather than exactly so, having demonstrated trigonometrically that the Earth was not the exact center of the universe. His rectification is later used in the Copernican model. Nicolaus Copernicus publishes "De revolutionibus orbium coelestium" containing his theory that Earth travels around the Sun. However, he complicates his theory by retaining Plato's perfect circular orbits of the planets. A brilliant
Analogy of the sun the Good, we would only be able to see with our physical eyes and not the "mind's eye". The sun bequeaths its light so that we may see the world around us. If the source of light did not exist we would be in the dark and incapable of learning and understanding the true realities that surround us. Incidentally, the metaphor of the sun exemplifies a traditional interrelation between metaphysics and epistemology: interpretations of fundamental existence create—and are created by—ways of knowing. It also neatly sums up two views for which Plato is recognized: his rationalism and his realism (about