Alun Salt is doing what historians are not supposed to do and indulging in counterfactual speculations. He asks the question, “Would Copernicus have been more convincing if he’d been more accurate?” He continues:
[…] I was wondering if Copernicus would have been more convincing if he’d used ellipses in his model instead of circles. By using circles Copernicus had to use epicycles like Ptolemy, though not so many1. Still, it gave the impression that epicycles were necessary. If that’s the case then why not have a stationary Earth as well? The discovery that planetary motion would be better described by ellipses didn’t come about till Kepler’s work almost a century later.
His own answer is in the negative as he argues that it would have been too much change at one go and even less people would have accepted his work than the handful, who did in reality in the first decades after publication. I think he is wrong and I would like to explain why.
First of all in reality Copernicus could not have used elliptical orbits as the data that was available to him was too inaccurate for him or anybody else to calculate the very small eccentricity that differentiates the elliptical planetary orbits from circles. However to pursue Alun’s hypothetical we will assume that a Tycho had lived before Copernicus and he had had the necessary data available to carry out Kepler’s calculations and deduce the existence of the elliptical orbits; if this had indeed been the case then I’m relative certain that his system would have found substantially more acceptance. Why?
To understand we first have to examine the function of astronomical systems both in antiquity and in the Renaissance. Astronomical systems were expected to deliver accurate prognoses of the positions of celestial objects and the occurrences of celestial occurrences such as eclipses. A system was judged by its accuracy in this regard. The Ptolemaic system was actually quite good in this respect but over the centuries the fundamental data delivered by Ptolemaeus became more and more corrupt due to constant copying of manuscripts and so the accuracy of the prognoses was below that wished for. When Copernicus originally published the De revolutionibus it was greeted very warmly by the astronomical community because they hoped it would deliver more accurate prognoses than the Ptolemaic system. Unfortunately being based on the sane degenerate data it could not deliver, so initial enthusiasm turned into disappointment. As a historical footnote Tycho was one of those disappointed by the equal inaccuracy of both systems and this is why he set out on his amazing programme of observational astronomy to deliver new, accurate basic data on which to model astronomical systems.
Kepler’s system based on Tycho’s data delivered the required accuracy and was therefore accepted despite the fact that it had abandoned the 2000-year-old tradition of the Platonic axioms that required circular orbits with uniform motion for celestial objects. If Copernicus had been able to calculate and use the accurate elliptical orbits then his system would also have delivered accurate prognoses and have found widespread acceptance within the astronomical community.
1) I should point out that Copernicus wanted to use circles because he wished to restore the purity of the Platonic axioms that he saw as violated by Ptolemaeus’ use of the equant point. Secondly his system actually required more circles than Peuerbach’s version of Ptolemaeus’ geocentric system in use at the time.