From 1700 until 1718 he worked on a catalog of fixed stars, and from 1672 until 1719 he studied Mars extensively.[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. He also helped with the survey based on the Paris Meridian.
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.[3]
^Maraldi, G.F. (1723). "Diverses expèriences d'optique" [Various optical experiments]. Histoire de l'Académie Royale des Sciences ... Avec les Mémoires de Mathématique & de Physique (in French): 111–143. From p. 140: "La lumiere plus grande au milieu des boules plus petites, fait voir qu'elle circule en plus grande abondance & plus facilement autour des petites boules qu'autour des grandes." (More light in the middle of the smaller balls shows that it [i.e., light] spreads in greater abundance and more easily around small balls than around big [ones].) Fig. 8 on Plate 6 (following p. 142) shows light at the center of a ball's shadow.
