Cassini, Gian Domenico

(born June 8, 1625, Perinaldo, Republic of Genoa—died Sept. 14, 1712, Paris, France) Italian-born French astronomer. His early studies were mainly observations of the Sun, but, after obtaining more powerful telescopes, he turned his attention to the planets. He calculated Jupiter's and Mars's rotational periods and compiled a table of the positions of Jupiter's satellites. His observations of the Moon (1671–79) led to his compiling a large map. In 1683, after a study of the zodiacal light, he concluded it was of cosmic origin. He discovered four of Saturn's moons: Iapetus (1671), Rhea (1672), Tethys (1684), and Dione (1684). The dark gap between two of Saturn's main rings (Cassini's division) is named for him.

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