On the Heavens is a treatise written by Aristotle in which he explores the nature and motion of the celestial bodies. In this work, Aristotle argues that the heavens are eternal, unchanging, and composed of a fifth element called aether. He distinguishes between the sublunary world, which is subject to change and decay, and the celestial realm, which is perfect and immutable. On the Heavens is a significant work in the history of astronomy and natural philosophy, and it had a profound influence on later thinkers such as Ptolemy and Galileo. Read in English, unabridged.