  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.
