Trepidation or Precession: The Turning Point in a Tradition

Tanner, Brian; McLeish, Thomas; Nothaft, Philipp

Abstract

This chapter provides historical and scientific commentary on the reference in On the Sphere to the very slow movement of the equinoxes as identified by the change in stellar positions measured in different centuries. It discusses the two different models: Ptolemaic Precession and Toledan Trepidation, and why the latter was preferred by Grosseteste, who attributed it to the Sabean mathematician Thābit ibn Qurra, although other authors are more likely. A novel graphical presentation of the predictions of the two models, together with the data available on stellar positions to the Latin West of the early 13th century, makes clear why Trepidation could be accepted as the better explanation at that time, but not a century later. Grosseteste’s main reason for preferring Trepidation arises from climate change; the chapter ends by explaining his reasoning, and relating it to the modern understanding of Milankovitch cycles.

Citation

Tanner, B., McLeish, T., & Nothaft, P. (2023). Trepidation or Precession: The Turning Point in a Tradition. In G. E. Gasper, T. C. McLeish, S. Olsen Sønnesyn, & H. E. Smithson (Eds.), Mapping the Universe: Robert Grosseteste’s De sphera - On the Sphere (279-304). Oxford: Oxford University Press

• Publication Date: 2023
• Deposit Date: Jan 17, 2024
• Pages: 279-304
• Series Title: The Scientific Works of Robert Grosseteste
• Series Number: Vol 2
• Book Title: Mapping the Universe: Robert Grosseteste’s De sphera - On the Sphere
• Chapter Number: 8
• ISBN: 978-0-19-880552-6
• Public URL: https://durham-repository.worktribe.com/output/2149572