Using astronomy as an aid to dating manuscripts The example of the Leiden Aratea planetarium

Using tables of planetary, lunar and solar positions, the planetary configuration of the Leiden Aratea-manuscript (MS Leiden, UB Voss. lat. Q 79, fo. 93v) can be dated as 18 March 816, in preference to an earlier calculation, which gave 28 March 579. This new date accords very well with the date of the manuscript itself. The authors suggest that the manuscript was produced at the imperial court at Aachen. The method used might prove useful to date other manuscripts with similar illustrations which are otherwise undatable.