A theory is either true or false  Galileo' s observations of Jupiter' s satellites showed that the Ptolemaic theory of the motion of celestial bodies is false
Ttherefore, since the Copernican theory of planetary motion is inconsistent with the Ptolemaic account, Galileo' s observations of Jupiter' s satellites proved the truth of the Copernican theory
the Ptolemaic and Copernican theories, being inconsistent, cannot both be based on exactly the same evidence