ASTR 101 Lecture Notes - Lecture 6: Geocentric Model, Ptolemaic Dynasty, Deferent And Epicycle

• School: University of Victoria
• Department: Astronomy
• Course: ASTR 101
• Professor: Travis Martin

Document Summary

Sun is very small in comparison to some stars in the universe! Planets do not look significantly different than stars - advanced that ancient greeks could tell the difference. Planets remained close to the ecliptic path the sun takes across the sky. The moon doesn"t follow the ecliptic path at all. Mars and jupiter move in one direction across sky, then move opposite direction. Why stars move altogether, all at once uniformly across the sky. Why moon was sometimes visible during the day, why height of sun changed. Why planets varied in brightness over the years. Explanation of the heavens must use the "perfect form": the circle. Idea that the earth is at the center of everything and everything comes to rest - heavens are moving around us following the perfect form. Perfect form could not be challenged - aristotle thought it was definitely true. Deferent: main circle that goes around the earth.