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K-12 Science

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Sci fair neatness. Cogitations. The Universe of Aristotle and Ptolemy. The celestial sphere that we introduced previously is a convenient fiction to locate objects in the sky. However, the Greek philosopher Aristotle (many of Aristotles works are available at the Internet Classics Archive) proposed that the heavens were literally composed of 55 concentric, crystalline spheres to which the celestial objects were attached and which rotated at different velocities (but the angular velocity was constant for a given sphere), with the Earth at the center.

The following figure illustrates the ordering of the spheres to which the Sun, Moon, and visible planets were attached. (The diagram is not to scale, and the planets are aligned for convenience in illustration; generally they were distributed around the spheres.) There were additional "buffering" spheres that lay between the spheres illustrated. By adjusting the velocities of these concentric spheres, many features of planetary motion could be explained. Epicycles and Planetary Motion. Wave on a String 2.04.