Cassini, Giovanni Domenico (Jean Dominique) (1625-1712), an Italian astronomer. As a skilled observer using the most accurate telescopes available at the time, Cassini made many important discoveries about the planets of the solar system.
From 1650 to 1669, Cassini was professor of astronomy at the University of Bologna. During this time he accurately determined the rotation period of Jupiter to be 9 hours and 56 minutes. In 1669, he was persuaded to leave Bologna and join the new Academy of Sciences in Paris. Cassini never returned to Italy. In Paris he began observations of Saturn that led him to discover four of its satellites. In 1675 he observed a dark band in what was thought to be a single ring around Saturn. This gap is now known as the Cassini division.
Cassini lost his sight in 1710, and his son Jacques continued his work.