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Notes and Reflections on Books and Media

by Hannah Leitheiser

Inaccuracy of Epicycles

#astronomy #epicycle #Ptolemy #Kepler

The Remarkable Science of Ancient Astronomy

Dr. Bradley Schaefer




A path given by a circle within a circle can create an elliptical orbit (proof left to the reader), but will not follow Kepler's second law requiring equal areas swept in equal time. However a Ptolemaic system of circles can be worked out with a bit of algebra, a ruler, and protractor. The planetary orbits are nearly circular, so a few arcminutes will be the extent of your reward for doing Newton's differential calculus.