To the modern reader, Aristotle's views on astronomy, as presented in Metaphysics, Physics, De Caelo (On the Heavens) and Simplicius' Commentary, will most likely seem very bizarre, as they are based more on a priori philosophical speculation than empirical observation. Although Aristotle acknowledged the importance of "scientific" astronomy - the study of the positions, distances and motions of the stars - he nevertheless treated astronomy in the abstract, linking it to his overall philosophical world picture. As a result, the modern distinction between physics and metaphysics is not present in Aristotle, and in order to fully appreciate him we must