Historical Excursus 2: Riccioli

Giovanni Battista Riccioli (17 April 1598 – 25 June 1671) was a seventeenth-century Jesuit astronomer. His most significant work was the Almagestum novum (1651), in which he attempted to bring all astronomical knowledge up to date in light of the new telescopic discoveries. (The title hearkens back to Ptolemy’s great second-century astronomical work, The Almagest.) With Francesco Maria Grimaldi, another Jesuit astronomer, he traced the topography of the moon and introduced much nomenclature still in use. He described sunspots, compiled star catalogs, identified the first double star (Mizar – Zeta UMa), noted the colored bands along Jupiter’s equator, and made careful observations of Saturn. Hoping to refute Galileo’s arguments on the motion of the Earth, Riccioli did experiments with falling bodies, intended to test primitive (pre-Newtonian) hypotheses on gravitation. Although initially inclined to reject the Earth’s motion, Riccioli published findings that confirmed Galileo’s concept of uniformly accelerated motion. (In one experiment, he demonstrated the acceleration of a falling body by noting that the loudness of a falling object when it hit the ground increased proportionately to the height from which it was dropped.) He is considered the most astute and intellectually vigorous of the seventeenth-century skeptics of heliocentrism.

from the Almagestum novum


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