Le fonti di Galileo Galilei per le Lezioni e studi sulla stella nuova del 1604

The surviving text of Galileo Galilei’s lectures and studies on the “new star” is incomplete, fragmentary and time-stratified with respect to its content. This text was initially intended only to be the script for his Latin lectures held in the Paduan Studio at the end of 1604, but later he developed it, adding observational notes in view of its possible publication, which, however, was never realized under his own name. In his preparatory work Galileo made explicit or implicit references to a variety of sources. The main sources were: Seneca and the ancient Pythagoreans; his correspondent Ilario Altobelli; the astronomers Tycho Brahe, Joachim Camerarius, and perhaps Thomas Digges and Christopher Rothmann (by way of Brahe). Also a short, albeit significant, reference to Kepler’s De Stella nova in Pede Serpentarii (Prague 1606) should be included in this list. An analysis of these references shows that Galileo intended to center his argument on the evidence of the superlunary position of the nova, while also prudently proposing conjectures on its alleged motion and its physical (light-reflecting) constitution. At the same time, the selection and application of these sources indicate that Galileo set his interpretation of the phaenomenon within a Copernican framework precisely to establish an early proof for the revolutionary motion of the Earth around the Sun by measuring the expected annual parallax of the star. Two diagrams hand-drawn by Galileo confirm his original intent.