The World-System of Giovanni Battista Riccioli and the Phases of Venus and Mercury

Abstract

The Jesuit astronomer Giovanni Battista Riccioli (1598-1671) proposed an original astronomical system as an intermediate solution between the Copernican and the Ptolemaic systems. Many scholars describe his system as “geocentric”, and so does Riccioli. He uses the Tychonic solution by adding a lot of differences, for instance, the order of the orbits and the movement of Jupiter and Mars. In his astronomical work, Riccioli is rigorous and serious and offers a great quantity of observational data. The analysis of these results is crucial to understand the evolution of the Copernican question during the first half of the XVII century. The article will look at some general lines of Riccioli’s system, to understand how an astronomer of the XVII century really worked and to understand which problems the Copernican system could not resolve. Finally, I will try to consider some philosophical implications of this historical case.