# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Astro*Dictionary by Michael Erlewine





1 article for "Cassini, Giovanni Domenico"

Cassini, Giovanni Domenico [Astro*Index]

(1625-1712) Italian-French astronomer. Born at Perinaldo (near Nice); died at Paris.

Often considered a French astronomer, his first names are frequently given as Jean Dominique. He is reported to have studied astronomy in order to be able to disprove astrology. He measured the rotation of Jupiter and Mars, published an ephemeris of the moons of Jupiter (which led Roemer to his discovery of the Velocity of Light), and was first to study the Zodiacal Light. He discovered four new satellites of Saturn: Iapetus, Rhea, Dione, and Tethys. He noted a division in the rings of Saturn (which is now known as the Cassini Division), and suggested that the rings might be composed of small particles. His most important contribution was the determination of an accurate value for the parallax of Mars, which led to a determination of the AU (the Astronomical Unit), yielding a value of 93 million miles (still too low by 7%). Aristarchus had obtained a value of 5 million, Poseidonius gave 40 million, and Kepler had obtained 15 million.

See also:
♦ Roemer, Olaus ♦ Kepler, Johannes


Astro*Index Copyright © 1997 Michael Erlewine