The Starry Universe of Jacques Cassini: Century-old Echoes of Kepler

Abstract

This paper discusses measurements of the apparent diameter and parallax of the star Sirius, made in the early 18th century by Jacques Cassini, and how those measurements were discussed by other writers. Of particular interest is how other writers accepted Cassini’s measurements, but then discussed Sirius and other stars as though they were all the same size as the sun. Cassini’s measurements, by contrast, required Sirius and other stars to dwarf the sun—something Cassini explicitly noted, and something that echoed the ideas of Johannes Kepler more than a century earlier.