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Aaristotle

Aristotle's Model of the Universe
It is important to point out that Aristotle used his theory of violent motion to develop a model for the Universe. Aristotle, and philosophers before him, knew that the night sky experienced many different cycles: day and night, monthly phases of the moon and the yearly cycle of the Sun (seasons). Thus they thought the celestial objects must be on perfect crystalline spheres (the circle and sphere were thought to be perfect shapes that repeated in space, with no beginning or end).Aristotle thought that the Earth was at the center of the Universe since it could not move. He reasoned that if it did move, all the water in the ocean and air in the sky would be left behind. He also could not imagine a force which could violently push the Earth through space. All other objects in the heavens moved on crystalline spheres where the Earth would be the center of the sphere. Aristotle developed one of the first geocentric (Earth centered) models of the Universe. Ptolemy later improved on the model by placing the planets on epicycles while keeping the Earth at the center. This model survived until the Renaissance, when Copernicus proposed the Heliocentric (Sun centered) model of the Universe.
Heliocentric Model
Copernicus is often credited for starting the Renaissance with his Heliocentric model of the Universe.Copernicus became interested in astronomy after studying mathematics. He was fascinated with Ptolemy's geocentric model of the Universe and tried to create a simpler method to calculate the positions of the planets. Copernicus did not initially think that the Earth orbited the Sun. He just found the mathematical calculations for planetary positions easier if all objects went in circles around the Sun rather than the Earth. Seeing how successful and simple this heliocentric model was, he soon came to realize that it must be true. To have the Earth go around the Sun violated Aristotle's theory of violent motion since the Earth must...