Galileo’s Trattato della sfera ovvero cosmografia and Its Sources

This paper studies Galileo Galilei’s Trattato della sfera ovvero cosmografia, which was written before 1600. It is a geocentric astronomical treatise that follows the main structure of Johannes de Sacrobosco’s Tractatus de sphæra. This paper analyzes some peculiarities of Galileo’s treatise, comparing it to several other vernacular astronomical works of the sixteenth century and discussing its likely sources. Contrary to previous claims, we argue that Christoph Clavius’ commentary on Sacrobosco’s Sphæra cannot be regarded as its only or main influence. A likely inspiration for Galileo’s treatise is Alessandro Piccolomini’s Sfera del mondo, a work that anticipated several specific features of the Trattato della sfera. This influence is corroborated by Galileo’s copious marginal notes found in a copy of Piccolomini’s book.