fine tuning the size of the of the epicycle and deferent circles, the astronomers of that time could explain and predict the motions of the Moon and planets with some degree of accuracy (Chaisson 32-33). Figure 1: Epicycle (Ptolemy’s Devices 1)Astronomers sought to further fine tune the model of a geocentric universe as more observations and movements of the planets did not quite fit the existing models. One such astronomer was Ptolemy, who was of Greek nationality, but lived in Egypt in the second century A.D. Ptolemy’s system consisted of 80 epicycles, set into a complex pattern, to explain and justify the movements of the five known planets at that time, the Sun, and the Moon. Ptolemy published his model and explanation in a thirteen book set called Mathematical Syntaxis. This geocentric model of the universe, termed the Ptolemaic model, was the accepted standard for the motion of celestial bodies for over a thousand years. It has been suggested that Ptolemy devised this model as a method for calculating positions, but may not have believed in it’s absolute depiction of reality (Nineplanets 1-2).The Ptolemaic model, based upon the flawed premise that the earth was the center of the Universe, required a complex set of mathematical rules to explain the movements of the celestial bodies. Not all ancient astronomers agreed with the geocentric view, one notable exception was the Greek astronomer Aristarchus of Samos (310-230 B.C.). Aristarchus views stated that the Sun was the center, with the Earth and all the other planets revolving around the Sun. The strength of Aristarchus’ argument could not overcome Aristotle’s persuasive logical and philosophical reasoning that man and therefore the Earth, was the center of the Universe. Therefore, Aristotle’s philosophical argument supported by Ptolemy’s complex model remained the basis for the western world’s understanding of the Universe...
