Astronomy is often considered the zenith of ‘the exact sciences’ in antiquity. Highly mathematical, it is quite distinct from cosmology, and was more concerned with modelling celestial phenomena than with speculation about why the heavens appeared as they did. In modelling the heavens astronomers sought to ‘save the phenomena’, that is, to ‘explain’ observations by means of a mathematical construction which located certain celestial bodies at certain places and certain times. Each construction aimed to be systematic – even axiomatic in the Euclidean style – and leave as few as possible ‘anomalies’, i.e., unexplained phenomena. After centuries of effort by mathematicians and astronomers, Claudius Ptolemy synthesized and developed their achievements to produce the Almagest. This is the Arabic name by which his Mathematical Syntax, the rules of the motion of the heavens, is better known. It became the bible of astronomy in the West and the Islamic world for the next 1500 years, until displaced in the Copernican Revolution.