Ptolemy
Ptolemy believed that Earth was the center of the universe and that everything revolved around it. He believed that the stars were lights attached to a crystal sphere that spun around the Earth. He thought that the planets traveled on spheres of their own. To account for the more subtle motions, Ptolemy believed that each planet also moved on a smaller sphere - an epicycle.
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Two commonly made observations supported the idea that Earth was the center of the Universe. The first observation was that the stars, the sun, and planets appear to revolve around Earth each day, making Earth the center of that system. Further, every star was on a "stellar" or "celestial" sphere, of which the earth was the center, that rotated each day, using a line through the north and south pole as an axis. The stars closest to the equator appeared to rise and fall the greatest distance, but each star circled back to its rising point each day.[2] The second common notion supporting the geocentric model was that the Earth does not seem to move from the perspective of an Earth bound observer, and that it is solid, stable, and unmoving. In other words, it is completely at rest.
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PTOLEMAIC MODEL
In the Ptolemaic system, each planet is moved by a system of two or more spheres: one called its deferent, the others, its epicycles. The deferent is a circle whose center point exists halfway between the equant and the earth, marked by the X in the picture to the right where the equant is the solid point opposite the earth. Another sphere, the epicycle, is embedded inside of the deferent and is represented by the smaller dotted line to the right. A given planet then moves along the epicycle at the same time the epicycle moves along the path marked by the deferent. These combined movements cause the given planet to move closer to and further away from the Earth at different points in its orbit, and
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Two commonly made observations supported the idea that Earth was the center of the Universe. The first observation was that the stars, the sun, and planets appear to revolve around Earth each day, making Earth the center of that system. Further, every star was on a "stellar" or "celestial" sphere, of which the earth was the center, that rotated each day, using a line through the north and south pole as an axis. The stars closest to the equator appeared to rise and fall the greatest distance, but each star circled back to its rising point each day.[2] The second common notion supporting the geocentric model was that the Earth does not seem to move from the perspective of an Earth bound observer, and that it is solid, stable, and unmoving. In other words, it is completely at rest.
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PTOLEMAIC MODEL
In the Ptolemaic system, each planet is moved by a system of two or more spheres: one called its deferent, the others, its epicycles. The deferent is a circle whose center point exists halfway between the equant and the earth, marked by the X in the picture to the right where the equant is the solid point opposite the earth. Another sphere, the epicycle, is embedded inside of the deferent and is represented by the smaller dotted line to the right. A given planet then moves along the epicycle at the same time the epicycle moves along the path marked by the deferent. These combined movements cause the given planet to move closer to and further away from the Earth at different points in its orbit, and