ESHS/HSS Annual Meeting

A Newly Discovered Mercator Star Catalogue (ca. 1550) and Its Genealogy from Ptolemy to Copernicus

• In Event: Tabular Practices and the Cross-cultural Exchange of Knowledge in Ancient in Medieval Astronomy 2

English Abstract

This paper introduces a newly identified Mercator manuscript, dated to approximately 1550, which comprises c. 50 folios including three star tables, as well as instructions for constructing and using astronomical instruments. The focus of this contribution is on the first star catalogue, which lists 130 stars and—exceptionally for the period—provides both ecliptic and equatorial coordinates for the epoch 1550. Coordinate listings in equatorial coordinates are otherwise only known from specialised astrolabe-related tables (using Declination and Mediant), besides Kunitzsch’s Type II and Stöffler’s Almanach nova (1499), using Declination and Right Ascension.
The study situates this catalogue within the broader genealogical development of astronomical tables. A comparative analysis shows that Mercator’s dataset derives from a distinctive chain of transmission: beginning with the Almagest, mediated through a Greek manuscript rooted in the Alexandrian tradition, filtered via George Valla’s humanist translation from Greek to Latin (1501), reframed through Copernicus’ reanchoring the Ptolemaic longitudes, and finally adapted for precession by Mercator (1550), who selectively employed Ptolemaic coordinates beside the Copernican ones. This reconstruction elucidates the compilation process behind Mercator's elaborate star catalogue and clarifies his position within late medieval and early Renaissance computational practices.
The paper further argues that this catalogue represents preparatory computational work for Mercator’s 1551 celestial globe and for a related astrolabe, attributed to him, now preserved in Florence. Together, the findings underscore the manuscript’s significance as a crucial link in understanding Mercator’s astronomical methods and their role in the evolving tradition of early modern stellar cartography.

Author

• Yves Charles Verspreet, University of Hasselt