A quantitative analysis of David Fabricius’ astronomical observations

David Fabricius, a Reformed pastor in Ostfriesland, was highly regarded by Kepler as an exceptional observer, second only to Tycho Brahe. From 1596 to 1609, Fabricius engaged in extensive correspondence, exchanging numerous letters with Brahe and subsequently with Kepler. These communications also provided values for direct observations on meridian altitudes of planets and stars, as well as elongations between a planet and a star or between two stars. We provide a detailed summary of Fabricius’s observations and compare them with the prediction of twenty-first-century models. The analysis indicates that under specific conditions, his observations exhibit sub-arcminute deviations in relation to those calculated from modern theories. Our findings preliminarily indicate that Fabricius’ astronomical observational abilities were comparable to, an occasionally superior to, those of Brahe himself. We provide machine-readable tables of his observations.