Astronomy 1021 Lecture Notes - Lecture 5: Nicolaus Copernicus, Axial Precession, Star Catalogue

• School: Western University
• Department: Astronomy
• Course: Astronomy 1021
• Professor: Robert Cockcroft

Document Summary

Aristarchus: sizes and distances for/between sun, moon, earth; suggested heliocentrism. Hipparchus: star catalogue; brightness system; axial precession. 1542 published on the revolution of the heavenly spheres . Mercury and venus close to sun. Nearby objects have a larger parallax than more distant objects. Parallax can be used to measure distances. Sun is at one focus of the ellipse. Sun-planet line sweeps out equal areas during equal intervals of time. Planet moves faster when closer, and slower when further. More distant planets orbit the sun at slower average speeds. P is the planet"s orbital period in years a is the average distance from the sun in au. Planets will either have too much speed or too little speed: Second law: planets move faster in their orbits are ellipses orbits when they"re closer to the sun. Third law: more distant planets move more slowly. Aristotle: if earth moves birds, falling stones and clouds would be left behind.