This is a repository copy of Reversals in Wartime : Alcuin and Charlemagne discuss Retrograde Motion. White Rose Research Online URL for this paper: https://eprints.whiterose.ac.uk/172393/ Version: Accepted Version Article: Garrison, Mary orcid.org/0000-0003-0236-2374 and McLeish, Thomas Charles orcid.org/0000-0002-2025-0299 (Accepted: 2019) Reversals in Wartime : Alcuin and Charlemagne discuss Retrograde Motion. Interfaces.. (In Press) Reuse This article is distributed under the terms of the Creative Commons Attribution (CC BY) licence. This licence allows you to distribute, remix, tweak, and build upon the work, even commercially, as long as you credit the authors for the original work. More information and the full terms of the licence here: https://creativecommons.org/licenses/ Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing
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[email protected] https://eprints.whiterose.ac.uk/ 1 FINAL Reversals in Wartime: Alcuin and Charlemagne discuss Retrograde Motion Tom McLeish and Mary Garrison Departments of Physics and History Centre For Medieval Studies University of York Abstract The apparent retrograde motion of the planets was a puzzle for astronomers from the ancient world to the final establishment of heliocentric cosmology in the early modern period, but enjoyed an especially rich discussion in the Carolingian Renaissance. We explore the first stirrings of an eighth-century response to this epistemological challenge in a remarkable series of letters between Alcuin of York and Charlemagne, sent while the latter was on campaign against the Saxons in 798 A.D.