The Online Encyclopedia and Dictionary






Giovanni Domenico Cassini

Giovanni Domenico (Jean-Dominique) Cassini
Giovanni Domenico (Jean-Dominique) Cassini

Giovanni Domenico Cassini (June 8, 1625 - September 14, 1712) was an Italian-French astronomer and engineer. Cassini was born in Perinaldo , Genoa.

Astronomy and astrology

Cassini was an astronomer at the Panzano Observatory , from 1648 to 1669. He was a professor of astronomy at the University of Bologna and became, in 1671, director of the Paris Observatory. He thoroughly adopted his new country, to the extent that he became interchangeably known as Jean-Dominique Cassini.

Along with Hooke, Cassini is given credit for the discovery of the Great Red Spot on Jupiter (~1665). Cassini was the first to observe four of Saturn's moons; he also discovered the Cassini Division (1675). Around 1690, Cassini was the first to observe differential rotation within Jupiter's atmosphere.

In 1672 he sent his colleague Jean Richer to Cayenne, French Guiana, while he himself stayed in Paris. The two made simultaneous observations of Mars and thus found its parallax to determine its distance, thus measuring for the first time the true dimensions of the solar system.

Cassini was the first to make successful measurements of longitude by the method suggested by Galileo, using eclipses of the satellites of Jupiter as a clock.

Attracted to the heavens in his youth, his first interest was in astrology rather than astronomy. Later in his life he focused almost exclusively on astronomy alone and all but denounced astrology as he became more and more involved in the scientific revolution and ultra-rational thought of the day. While young he read widely on the subject of astrology, and soon he was very knowledgeable about it; strangely enough, it was his extensive knowledge of astrology that led to his first appointment as an astronomer.

In 1644 the Marquis Cornelio Malvasia, who was a senator of Bologna with a great interest in astrology, invited Cassini to Bologna and offered him a position in the Panzano Observatory which he was constructing at that time. Most of their time was spent calculating newer, better, and more accurate ephemerides for astrological purposes using the rapidly advancing astronomical methods and tools of the day.

In 1669 Cassini moved to France and through a grant from Louis XIV of France helped to set up the Paris Observatory which opened in 1671; Cassini would remain the director of it for the rest of his career until his death in 1712. While in France Cassini also served as the court astronomer/astrologer of Louis XIV of France ("The Sun King") for 41 years, serving the expected dual role yet focusing the overwhelming majority of his time on astronomy rather than the astrology he had studied so much of in his youth.


Cassini was employed by Pope Clement IX in regard to fortifications, river management , and flooding of the Po.

Named after Cassini

Last updated: 07-31-2005 11:58:10
Last updated: 09-12-2005 02:39:13