As far as I can tell, this is an excellent summary of the issues, but this caught my attention (my emphasis): If the earth were whipping around the sun, we sho

As far as I can tell, this is an excellent summary of the issues, but this caught my attention (my emphasis): If the earth were whipping around the sun, we should see parallax among the fixed stars, but do not. The Copernicans answered, "Well, yeah, but maybe the stars aren't just far away but really really far away." But you cannot save an unproven hypothesis by asserting a second unproven hypothesis. The stars had to be relatively close because otherwise their observed diameters would mean they were ginormous entities. Some Copernicans embraced this and said "Goddidit!" Who cared how enormous the stars were, since God was infinite. You can 'save' a hypothesis as a hypothesis by showing that the objection is incomplete, and this is what happened here: the stars are indeed so far away that parallax was not then observable. The apparent corollary, that the stars must therefore be enormous, turned out to be false for a reason not suspected by either side: the apparent angular size of stars as observed by telescope is due to diffraction (the Airy disc.) The author picks up this thread in the comments, saying ...it was not evident at the time which model was more true nor even why one model ought to be more true. That was the contribution of Newton's theory of universal gravitation... Stellar parallax was not observed, however, until 1832, and the Airy disc was not explained until 1834, while Newton's gravitational explanation became widely known in 1686. Furthermore, neither Newton nor any of his contemporaries explained gravitation (Newton himself saying that he "brooked no hypothesis" in that regard), or presented any evidence independent of astronomical observations (i.e. the phenomena to be explained) for either its universality or that it follows an inverse-square law. It turned out, therefore, that what was arguably the strongest objection to heliocentricity was put aside, not because it had been explained away, but because it paled into relative insignificance in comparison to the explanatory power of Newton's theory. In this view, Galileo, for all his faults, was not just a self-aggrandizing promoter who happened to latch on to what turned out to be a correct theory; he was a respectable scientist of his day who had what turned out to have good (mostly) intuitions about which ideas were on the right track. For a more general moral, it is probably this just this: read Kuhn - and probably also Popper, who, at least according to David Deutsch, presents explanation as the ultimate goal of science.