If you are going to commit the ultimate heresy of challenging the prevailing beliefs of your times, you need to have some solid equipment to back you up. As it turns out, not only was Galileo a brilliant mathematician and astronomer. He was also a brilliant technological innovator who increased the magnification of his telescope by a factor of 21.
In order for this to be possible, argue Yaakov Zik and Giora Hon at the University of Haifa in Israel, Galileo needed "a new theory of optics as revolutionary as the device itself."
This theory, Zik and Hon argue, must have been kept secret.