Today in Astronomy

Giovanni Domenico Cassini died on this day in 1712 in Paris. He was an Italian mathematician, astronomer, engineer, and astrologer. Cassini, also known as Giandomenico Cassini, was born on June 8, 1625 in Perinaldo, near Sanremo, at that time in the Republic of Genoa.

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 —although that is also the name of his great-grand-son.

Along with Robert Hooke, Cassini is given credit for the discovery of the Great Red Spot on Jupiter (ca. 1665). Cassini was the first to observe four of Saturn's moons, which he called Sidera Lodoicea; 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.

Named after Cassini

• Cassini-Huygens Mission to Saturn
• The Cassini Division in Saturn's rings
• Cassini Regio, dark area on Iapetus
• Cassini crater on Mars
• Cassini crater on the Moon
• Cassini's Laws
• 24101 Cassini, an asteroid
• Cassini's identity for Fibonacci numbers
• Cassini oval
• Cassini Web Server

For more information visit the Astronomy Compendium.