Geocentric model was gradually superseded by the heliocentric model of Copernicus, Galileo, and Kepler. There was much resistance to the transition between these two theories. Some Christian theologians were reluctant to reject a theory that agreed with Biblical passages. Others felt a new, unknown theory could not subvert an accepted consensus for geocentrism. The geocentric model entered Greek astronomy and philosophy at an early point; it can be found in pre-Socratic philosophy. In the 6th century BC, Anaximander proposed a cosmology with Earth shaped like a section of a pillar (a cylinder), held aloft at the center of everything. The Sun, Moon,
Geocentric model 1631). The change from circular orbits to elliptical planetary paths dramatically improved the accuracy of celestial observations and predictions. Because the heliocentric model devised by Copernicus was no more accurate than Ptolemy's system, new observations were needed to persuade those who still adhered to the geocentric model. However, Kepler's laws based on Brahe's data became a problem which geocentrists could not easily overcome. In 1687, Isaac Newton stated the law of universal gravitation, described earlier as a hypothesis by Robert Hooke and others. His main achievement was to mathematically derive Kepler's laws of planetary motion from the law of gravitation,