ASTR 101 Lecture Notes - Lecture 10: Orbital Eccentricity, Orbital Period, Blue Arrow
14 Apr 2016
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Kepler wanted to use the extensive data sets provided by tycho to work out the shapes and relative sizes of all the planetary orbits. First, he assumed that the sun was at the centre of the solar system; in other words, he accepted the copernican notion. Secondly, he assumed that the earth"s orbit around the sun is a circle. This simplified his further calculations of the orbits of the other planets. It can be justified by the fact that the sun looks roughly the same size at all times of year so our orbit must be nearly circular in fact. If you think about it there are three obvious questions you could ask about the nature of the orbits followed by planets around the sun. The answers to each of these led to one of kepler"s famous three laws. The first question is to inquire about the shape of the orbits of planets around the sun.
