This collaborative project will bring to light an overlooked astronomical controversy of previously unsuspected importance for the interpretation of the Copernican revolution. Johannes Regiomontanus was the leading mathematical astronomer of the fifteenth century; his critical analysis of Ptolemy's `Almagest` provided an important stimulus for Copernicus's development of his sun-centered model of the solar system. Regiomontanus's `Defense of Theon against George of Trebizond` is a very rich but completely unstudied 573-page attack on Trebizond's presentation of the `Almagest,` the work that Copernicus would eclipse. This work of Regiomontanus's illuminates the most important known clue about the emergence of Copernicus's cosmology, for it fleshes out Regiomontanus's reasoning in proposing the alternative models that Copernicus would later use. In this collaborative project the PIs will transcribe and analyze Regiomontanus's lengthy text, present their most important results in four preliminary articles, and begin the monograph they will write about this astronomical controversy and its significance in the history of cosmology. The project will be done in collaboration with Richard Kremer at Dartmouth College, who is funded separately for this work through grant SBR9720672.
