But Still, It Moves: Tides, Stellar Parallax, and Galileo’s Commitment to the Copernican Theory

Galileo found the Copernican heliocentric theory of the universe so persuasive owing to its mathematical elegance that he embraced it even when his theory of the tides stood in opposition to it. Further support for Galileo’s deep commitment to the Copernican heliocentric theory is found in his recently discovered unpublished observations of the double star Mizar in 1617, which exhibited no annual stellar parallax and hence indicated that the Earth does not move, in contradiction to the Copernican heliocentric theory. Further, Galileo did not mention this contradiction in his Dialogue Concerning the Two Chief World Systems of 1632. I conclude that he was so deeply committed to the Copernican heliocentric theory that he was unswayed even when observations undermined it, and I suggest that if he had published his observations on the double star Mizar, general acceptance of the Copernican heliocentric theory by astronomers would have been delayed even more than it was.