The changes which occurred in man's view of the solar system from the time of Ptolemy to that of Galileo are presented. Contained is a brief review of the chain of events which resulted in the acceptance of a heliocentric system. Ptolomy's theory is described and a diagram illustrates the paths of the epicycle of Mars according to his geocentric model. Challenges of the theory from prominent men such as Heraclides, Aristarchus, Copernicus, Brahe, Kepler, Tycho, and Galileo are discussed. A bibliography is included. (SA)