Rounding numbers: Ptolemy’s calculation of the Earth–Sun distance

Abstract

In this paper I analyze the coincidence of the prediction of the Earth-Sun distance carried out by Ptolemy in his Almagest and the one he carried out, with another method, in the Planetary Hypotheses. In both cases, the values obtained for the Earth-Sun distance are very similar, so that the great majority of historians have suspected that Ptolemy altered or at least selected the data in order to obtain this agreement. In this paper I will provide a reconstruction of some way in which Ptolemy could have altered or selected the data and subsequently will try to argue in favor of its historical plausibility.