Interpretatio B5

Models and Precision: The Quality of Ptolemy’s Observations and Parameters


 This work, originally published in 1992, addresses the ancient and widely held view that Ptolemy was an inferior practical astronomer who manipulated the observations to fit his models. Examining the solar and lunar observations found in Almagest and the parameters of the models ostensibly derived from them, it finds scant evidence to support this view. Ptolemy’s lunar observations are no less accurate than those of his predecessors, and the individual errors of the lunar observations are as a whole consistent with what we would expect from naked eye observations. The parameters derived from these observations, moreover, are in every instance more accurate than we would expect given the errors of the observations. Thus, it appears that Ptolemy had more observations at his disposal than he reports, and that he was more skilled than has been recognized at deriving accurate parameters from them.



Date Mounted: 

Tuesday, March 29, 2016




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