Volume 7, No. 1

Galileo's Horoscope for Cosimo II de Medici

Guiseppe Righini

Editor's Note: Guiseppe Righini, who worked at the Arcetri-Florence Astrophysics department, found the original horoscope which Galileo composed for the young Cosimo II de Medici, in 1610 when he had just become Grand-Duke, and Galileo had just developed his telescope to behold Jupiter. Galileo was able to become court philosopher to the Medicis through his dedicating the four little moons of Jupiter to Cosimo. This was explained in the foreword of his classic Sidereus Nuncius. Righini apprehended the key position of Jupiter in this natal chart which he had discovered as being at the MC of Cosimo, and yet through a miscalculation his time of day erred by two hours. As to how that was possible, one could say that for an astronomer, house divisions did not signify very much. He ascertained that a page neither found in Galileo's Astrologia Nonulla nor published in Favaro's Opere was this key chart, as formed the basis for the Sidereus Nuncius dedication (Arcetri was where Galileo was kept, under house arrest, after his trial). Selected excepts are here cited. Later on, science historians figured out that the draft of a nativity by Galileo, on the same page as an excellent early Moon sketch, was an early version of this same chart. It is also included here.