1625-1712

Italian-French Astronomer

Giovanni Domenico Cassini made the first accurate determination of the dimensions of the solar system. A gifted observationalist, he was an extremely conservative theorist, refusing to accept Nicolaus Copernicus's (1473-1543) heliocentric view and opposing Isaac Newton's (1642-1727) gravitational theory.

Cassini was born June 8, 1625, in Perinaldo, near Nice (then in Italy). His early education was completed at Genoa. He later became Professor of Astronomy at the University of Bologna (1650), where his scientific reputation was established through a series of solar and planetary observations. This prompted an invitation to France, where he became director of the Royal Observatory (1671). He observational work and duties as director ceased after he went blind in 1710. He died September 11, 1712, in Paris.

At Bologna, Cassini produced new tables of the Sun's motion (1662). In 1664 he determined Jupiter's rotational period to within a few minutes and detected bands and a red...