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Aristotelian Model of the Universe

In the sublunary region, substances were made up of the four elements, earth, water, air, and fire. Earth was the heaviest, and its natural place was the center of the cosmos; for that reason the Earth was situated in the center of the cosmos. The natural places of water, air, and fire, were concentric spherical shells around the sphere of earth. Things were not arranged perfectly, and therefore areas of land protruded above the water. Objects sought the natural place of the element that predominated in them. Thus stones, in which earth predominated, move down to the center of the cosmos, and fire moves straight up.
The heavens, on the other hand, were made up of an entirely different substance, the aether or quintessence (fifth element), an immutable substance. Heavenly bodies were part of spherical shells of aether. These spherical shells fit tightly around each other, without any spaces between them, in the following order: Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, fixed stars. Each sphere had its particular rotation, all perfectly circular, and controled by God.
Aristotle and his peers tried to explain the inconsistencies in their theory and their observations with very complicated explainations. However, because they were so "sure" that the Earth was the center of the universe, the theory was doomed to fail from the beginning.

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