ASTR 101 Chapter Notes -Retrograde And Prograde Motion, Equant, Deferent And Epicycle

• School: Queen's University
• Department: Physics, Engineering Physics and Astronomy
• Course: ASTR 101
• Professor: Prof.

Document Summary

Earth was the center of the universe and everything orbited around it in circular patterns (since circles kept occurring in nature like planet shape, sun shape, etc) Orbits of the sun, planets, and moon are independent of one another and occur at uniform speed. Problems with greek cosmology: the movements of the sun and moon are not uniform as their speeds against background stars are not constant. Modern understanding: the earth does not orbit the sun at constant speed; neither does the moon orbit the earth at constant speed! The apparent motion of the sun across the field of remote stars is caused by our changing perspective as we orbit around it. Our orbit is not a perfect circle centred on the sun, and we move faster when we are close to the sun in january than when we are farther away from it, say in.