AST 111 Lecture Notes - Lecture 3: Apparent Retrograde Motion, Copernican Revolution, Orbital Period

• School: Tunxis Community College
• Department: Astronomy
• Course: AST 111
• Professor: Reynolds

Document Summary

First believe the earth is flat, with the sky being a dome surrounding them. Then adopt the geocentric view: that earth was the centre of the universe. When trying to explain planetary motion, they modeled the heavens to be a series of spheres, like russian dolls; but that didn"t explain apparent retrograde motion. Came up with the complex and tedious ptolemaic model: each planet moved on a small circle whose centre moved around earth on a larger circle. Adopted the sun-centered idea, allowing him to calculate each planet"s orbital period, each planet"s relative distance from the sun, and explained retrograde motion. Problem: was still holding to the ancient belief that heavenly motion must occur in perfect circles, which forced him to add numerous complexities to his system that were incorrect. Model made the sun orbited earth, while all the other planets orbited the sun.