Astronomical observations in Bologna, Montpellier, and Genoa in the early 14th century: Iohannes de Luna Theutonicus revisited

Abstract

MS Vienna, Österreichische Nationalbibliothek, 5311, fol. 137r, contains an unusual record of astronomical observations, among which are measurements of solar and stellar altitudes carried out with large quadrants in Bologna, Montpellier, and Genoa between 1305 and 1312. An analysis of this observational data reveals a high level of precision and accuracy, as the astronomer responsible achieved a mean error of only 0;2° during an extended run of measurements of solar noon altitudes made between December 1305 and March 1306. Other passages on the same manuscript page mention Johannes de Luna, a German astrologer-astronomer active in Bologna between c.1299 and 1312. References to his name in 14th-century manuscripts shed light on his involvement in contemporary attempts to correct the Toledan Tables and revise their model of precession on an observational basis.