ASTR 101 Lecture Notes - Lecture 9: Physical Law, Orbital Eccentricity, Solar System
6 Sep 2016
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He wanted to use tycho"s data to work out the shapes and relative sizes of all the planetary orbits. He assumed a heliocentric model (sun at center) He assumed that the earth"s orbit around the sun is a circle. This can be justified by the fact that the. Sun seems to look roughly the same size at all times of year. Three obvious questions you could ask about the nature of the orbits followed by the planets around the sun. These led to three important findings: kepler"s laws. Any given planet moves in a path that is an ellipse. Ellipse has nothing to do with eclipses, or the ecliptic. Also discovered the sun is at one focus of the ellipse. An ellipse has two foci (singular = focus). The sun sits at one of the foci of the ellipse, with a planet moving around and around.
