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Back to Book List# Inaccuracy of Epicycles

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Notes and Reflections on Books and Media

by Hannah Leitheiser

#astronomy #epicycle #Ptolemy #Kepler

The Remarkable Science of Ancient Astronomy | Dr. Bradley Schaefer | 2016 | Link |

2019-12-30

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.