Observations and Theories of Planetary Motion The crescent Venus seen with the naked eye Owen Gingerich - Empirical proof and/or persuasion — lecture on Galileo's observation of the phases of Venus from a renowned historian of science YouTube animation of the phases of Venus predicted by the pure geocentric Ptolemaic model YouTube animation of the phases of Venus predicted by the heliocentric model (and implicitly also by the geo-heliocentric models such as the Tychonic)