Ptolemaic system. Diagram of the Ptolemaic universe, an attempt at modelling the motions of heavenly bodies. This is a geocentric model, with Earth at the centre and the Sun, planets and stars orbiting it. Based on earlier astronomers' work, the theory was finally completed by Ptolemy in the 2nd century AD in his Almagest. It was translated into Latin in about 1160 AD and was the basis of astronomy until challenged by Copernicus (1473-1543). Diagram from 'A Short Introduction to Natural Philosophy' (1720) by John Questebrune.