Giovanni Domenico Casini, late 17th century.
© Science Museum / Science & Society Picture Library
Photograph of a painting. Italian-born French astronomer Casini (1625-1712), became profesor of astronomy at Bologna in 1650, and in 1699 became the first director of the Paris Observatory. He was responsible for greatly extending knowledge of the Sun's parallax and the periods of Jupiter, Mars and Venus, along with many planetary discoveries.