Galileo could have safely proposed heliocentricity as a theory or a method to more simply account for the planets’ motions. His problem arose when he stopped proposing it as a scientific theory and began proclaiming it as truth, though there was no conclusive proof of it at the time. Even so, Galileo would not have been in so much trouble if he had chosen to stay within the realm of science and out of the realm of theology. But, despite his friends’ warnings, he insisted on moving the debate onto theological grounds. …Many people wrongly believe
Galileo proved heliocentricity. He could not answer the strongest argument against it, which had been made nearly two thousand years earlier by Aristotle: If heliocentrism were true, then there would be observable parallax shifts in the stars’ positions as the earth moved in its orbit around the sun. However, given the technology of Galileo’s time, no such shifts in their positions could be observed. It would require more sensitive measuring equipment than was available in Galileo’s day to document the existence of these shifts, given the stars’ great distance. Until then, the available evidence suggested that the stars were fixed in their positions relative to the earth, and, thus, that the earth and the stars were not moving in space—only the sun, moon, and planets were.