Ptolemy happened to be a citizen of Egypt, between 90AD and 168AD, during the Roman times and was of Greek Origins (University of Oregon, 2012). Ptolemy was known to be a versatile personality, who happened to be a mathematician, astrologer, geographer and astronomer.
Aristarchus was the first astronomer to propound the theory of heliocentricity, which regarded the sun to be a stationary star around which the earth revolved (V Archive, 2012). It was Aristarchus who calculated the diameter of the sun and estimated the volume of the sun on the basis of its diameter (V Archive, 2012). Many astronomers and physicists do believe that it was Aristarchus’ estimation of the superior volume of the sun as compared to the earth that led Aristarchus to conclude that the Sun constituted the center around which the earth revolved (V Archive, 2012). Though Aristarchus’ original treatise in which he noted down his discovery did not survive, references to his heliocentric theory do occur in the works of Archimedes (V Archive, 2012). It was Aristarchus who first proposed that the sun remained fixed and unmoved and the earth revolved around it in a circular orbit.
In the history of astronomy, Ptolemy is attributed the honor of developing a comprehensive arithmetical model for accurately calculating celestial motions and astronomical phenomena (University of Oregon, 2012). Ptolemy also propounded his geocentric theory, which the astronomers popularly refer to as Ptolemaic system. Ptolemy extended varied arguments to establish the fact that the earth constituted the center of the universe, and other heavenly bodies revolved around it (University of Oregon, 2012). It was primarily owing to the Ptolemaic system that the geocentric theory gained strong grounds in the Christendom for a long time, until it was eventually replaced by the heliocentric theory propounded by Copernicus (University of Oregon, 2012)). Ptolemy is also credited