With an exceptionally good eye, he observed planets using refractor telescopes whose lenses were made in Rome by Eustachio Divini or Giuseppe Campani. He thus discovered Iapetus, then three other Saturnian moons. Until then, the only known satellite of the planet was Titan, discovered in Holland by Christiaan Huygens (1629-1695). Huygens, like Cassini, was invited to the Observatory and appointed to the Royal Academy at its creation by Colbert. He remained in Paris from 1666 to 1684.

caption : Cassini observation journal - copyright : Observatoire de Paris