Grimaldi and Riccioli also made a calculation of gravity at the Earth's surface by recording the oscillations of an accurate pendulum.

[2] In astronomy, he built and used instruments to measure lunar mountains as well as the height of clouds, and drew an accurate map or, selenograph, which was published by Riccioli and now adorns the entrance to the National Air and Space Museum in Washington D.C.

He discovered and was the first to make accurate observations on the diffraction of light[3][4] (although by some accounts Leonardo da Vinci had earlier noted it[5]), and coined the word 'diffraction'.

In his book Physico-Mathesis de Lumine, Coloribus et Iride (1665), he stated the theory of the reconstitution of sunlight from refracted coloured light.

In the work, he was mainly concerned with two questions: He argued that light is probably a subtle fluid (thus a substance), though it might still be an accident (as Aristotelians believed).