Solar Eclipse Observations in the Time of Copernicus: Tradition or Novelty?
In Western astronomy before Tycho Brahe and Kepler, only a handful of astronomical observations were actually used to derive parameters in a theory or to test the structure of a theory. Those observations, usually quoted in scientific treatises, such as the Almagest or De revolutionibus, have been analysed by historians of astronomy who want to know how observations are to be tied to a theory. Not surprisingly, those records give us a very general picture of historical observational practice. However, there are still not fully explored series of observations that allow us to understand details of the observational methods used in the medieval and early modern period and the transmission of these methods. This paper will offer an examination of such a series of observations made in Frauenburg by Nicolaus Copernicus. The series was recorded by Copernicus in his copy of Johann Stoeffler's Calendarium Romanum magnum (Oppenheim, 1518), and concerns four partial solar eclipses that occurred in 1530, 1536, 1540, and 1541. It will be argued that Copernicus employed the camera obscura (pinhole camera) to measure the magnitude of these eclipses. This conclusion will allow us to strengthen a thesis previously proposed by Ludwik A. Birkenmajer, that the astronomical use of images formed through an aperture, which spread among European astronomers in the second half of the sixteenth century, may have its source in eclipse measurements made by Copernicus during the later years of his scientific activity.