Giacomo F. Maraldi’s most famous astronomical discovery…

Giacomo F. Maraldi’s most famous astronomical discovery is that the ice caps on Mars are not exactly on the rotational poles of that body.

He also recognizes (in May 1724) that the corona visible during a solar eclipse belongs to the Sun not to the Moon, and he discovers R Hydrae as a variable star.

He also helps with the survey based on the Paris Meridian.

He is also credited for the first observation (1723) of what is usually referred to as Poisson's spot, an observation that is unrecognized until its rediscovery in the early nineteenth century by Dominique Arago.

At the time of Arago's discovery, Poisson's spot, a bright point that appears at the center of a circular object's shadow due to Fresnel diffraction, gives convincing evidence for the contested wave nature of light.