Aristotle's picture of the heavens described a series of 55 concentric spheres composed of an incorruptible element called "aether." These spheres contained the sun, moon, planets, stars and other heavenly bodies that circled the spherical Earth.
Aristotle's view of the universe relied on the idea of elements. He believed in four terrestrial elements: earth, air, fire and water. The natural tendencies of these elements shaped the reality of the planet Earth. The heaviest element, earth, naturally moved to the center of the system followed by the second heaviest, water. Air, the third-lightest element, made up the atmosphere followed by a layer of fire, the lightest element.
A fifth element, aether, made up the spheres circling the Earth and the celestial bodies attached to them. The closest sphere contained the moon, while the furthest sphere contained the stars. Outside of the celestial system lay the sphere of the "Prime Mover," which moved at a constant angular velocity, providing motion to the entire system.
Although modern science eventually disproved Aristotle's geocentric model of the universe, it remained the basic picture of the heavens from the 3rd century BC until the 16th century AD, and it functioned well for astronomers attempting to predict planetary movement and celestial events.