How Marius Was Right and Galileo Was Wrong Even Though Galileo Was Right and Marius Was Wrong

Abstract

Astronomers in the early 17th century misunderstood the images of stars that they saw in their telescopes. For this reason, the data a skilled observer of that time acquired via telescopic observation of the heavens appeared to support a geocentric Tychonic (or semi-Tychonic) world system, and not a heliocentric Copernican world system. Galileo Galilei made steps in the direction of letting observations lead him towards a Tychonic or semi-Tychonic world system. However, he ultimately backed the Copernican system, against the data he had on hand. By contrast, the German astronomer Simon Marius understood that data acquired by telescopic observation supported a Tychonic world system.