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Tolbert7 - Astronomy September 16, 2008 Lecture 7 Greeks...

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Astronomy September 16, 2008 Lecture 7 Greeks came up with a model for how the sky worked. It involved everything circling the earth. If you watch the objects move however, planets will go backwards while the stars keep moving in the same direction. This retrograde motion presented a problem for the Greeks since they viewed the sky to be perfect. o To alleviate this problem, invented the circular epicycles. However, this soon proved ineffective. Aristarchus- by measuring the length of time it took the moon to transverse through an eclipse was able to judge the size of earth to moon was about 4 to 1. By looking at phases, he was able to judge the sun was 15x further away from the moon. The sun is 4x roughly larger from the earth. Ptolemy summarized all this in the Almagest (?). He summarized the Greek knowledge of astronomy. Equant- point slightly off center about which the motions of the planet would appear constant. If you live on the equant, and you look at the sun, the time from the vernal equinox to the atumnal equinox would be the same.
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This note was uploaded on 10/16/2008 for the course ASTR 121 taught by Professor Tolbert during the Spring '08 term at UVA.

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Tolbert7 - Astronomy September 16, 2008 Lecture 7 Greeks...

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