Plato's Homework ProblemPlato gave his students a major problem to work on. Their task was to find a geometric explanation for the apparent motion of the planets, especially the strange retrograde motion. One key observation: as a planet undergoes retrograde motion (drifts westward with respect to the stars), it becomes brighter. Plato and his students were, of course, also guided by the Pythagorean Paradigm. This meant that regardless of the scheme they came up with, the Earth should be at the unmoving center of the planet motions. One student named Aristarchusviolated that rule and developed a model with the Sun at the center. His model was not accepted because of the obvious observations against a moving Earth. Some of the observations that convinced the Greeks that the Earth was not moving are 1.The Earth is not part of the heavens. Today the Earth is known to be just one planet of nine that orbit an average star in the outskirts of a large galaxy, but this idea gained acceptance only recently when telescopes extended our vision.
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