Born in Perinaldo (modern Liguria) he was the nephew of Giovanni Cassini, and worked most of his life at the Paris Observatory (1687 – 1718).
[better source needed] His most famous astronomical discovery was that the ice caps on Mars are not exactly on the rotational poles of that body.
He also recognized (in May 1724) that the corona visible during a solar eclipse belongs to the Sun not to the Moon,[1] and he discovered R Hydrae as a variable star.
In 1723[2] he also confirmed earlier (1715) discovery of his pupil Joseph-Nicolas Delisle of what is usually referred to as Poisson's spot, an observation that was unrecognized until its rediscovery in the early 19th century by Dominique Arago.
At the time of Arago's discovery, Poisson's spot gave convincing evidence for the contested wave nature of light.