Speaker
Description
The most important astronomical themes in the years spent by Cassini in Bologna concerned the problem of the “World Systems” and the physics that justified them.
His works were an important part of this history, making him one of the greatest astronomers of the seventeenth century.
A few decades had passed since the condemnation of Galileo, of his anti-Peripatetic physics and of the new heliocentric cosmos. Especially in environments such as the main university of the Papal States, it was not easy to delve into those themes with a critical and unconventional spirit.
Cassini entered into those discussions with attention to drawing conclusions only from “facts” – observations and measurements – rather than from unjustified assumptions, philosophical elaborations or theological prejudices.
Although with a certain “dissimulation”, typical of the time, the projects of his observations and measurements were aimed at verifying the supremacy of the World System of the “novatores” and of the new physics, with respect to geostatic systems and Scholastic physics.
The construction of the great sundial, in San Petronio was one of the first and most important steps in this direction – with the first observational verification of Kepler’s second law – together with the demonstration that comets were celestial bodies orbiting the Sun beyond the Moon, and with the rotation measures of Sun and planets. The tables of Jupiter’s satellites in 1668 Ephemerides Bononienses Mediceorum Syderum were then so important in tackling an ancient and difficult problem, the measurement of longitude, that Louis XIV called him to Paris to deal with the construction and management of the Observatoire Royal, thus making him abandon the city of Bologna and his University forever.
