The two views differed radically. Ptolemy believed still that the earth was the center of the universe whereas Copernicus, Galileo and Kepler discovered that the sun is actually the center of the universe. This new understanding mainly came from Copernicus and Galileo but Kepler discovered that the planets have elliptical orbits and realized there must be a force controlling the movement of the planets around the sun. Newton discovered what this force was ie the force of gravity.