On the Heavens

Main Ideas

• Aristotle examines the nature of celestial bodies and their movement, asserting that the heavens consist of a special fifth element — aether, which is different from the four earthly elements (earth, water, air, fire).
• He claims that celestial bodies move in circular orbits because circular motion is perfect and natural for heavenly objects.
• Aristotle divides the universe into two parts: the sublunary world, where changes and movement occur, and the superlunary world, where everything is eternal and unchanging.
• He views Earth as the center of the universe, around which all celestial bodies revolve, supporting the geocentric model.
• Aristotle discusses the nature of comets, asserting that they are atmospheric phenomena rather than celestial bodies.
• He analyzes the causes of eclipses and the movement of planets, explaining them within his geocentric model.
• Aristotle also considers the nature of time and eternity, linking them to the movement of celestial bodies.