FIG. 1. COPERNICUS' HELIOCENTRIC THEORY , as illustrated in his De revolutionibus orbium coelestium ("On the Revolutions of Heavenly Bodies"), 1543. Although suggested by Greek philosophers, the heliocentric theory was not adopted until the Ptolemaic geocentric view proved incapable of explaining observed motions of the heavenly bodies. Copernicus' work was carried on by Kepler and Galileo.