Occultation records in the Royal Frankish Annals for A.D. 807: Knowledge transfer from Arabia to Frankia?

Abstract

The Royal Frankish Annals (RFA) report under A.D. 807 three lunar and one solar eclipse (complete and dated correctly), a lunar occultation of Jupiter, and “a small spot” on the Sun interpreted as Mercury transit. This transmission is embedded between texts on the landing of diplomatic delegates from Baghdad and Jerusalem in Venice and on their meeting with Charlemagne. Technology transfer is explicitly mentioned (a mechanical water clock). The interpretation of a spot on the Sun as planetary transit is attested in Arabic reports since A.D. 840. The Jupiter occultation by the Moon is dated “Luna 17,” correctly counted in Muslim calendar practice since the first crescent detection. Eclipse predictions and records by astronomers from the cAbbasid caliphate using Ptolemy’s Almagest are extant from the early ninth century. There are time-spans of 6 months each between the three reported lunar eclipses (806 Sep 1/2, 807 Feb 25/26, Aug 21/22), a period of possible repetition given in the Almagest, but not known to the Carolingians. The 6-month rule for lunar eclipses might be preserved in the Carolingian Seven Book Computus. We present multiple evidence that visitors from Baghdad brought new insight and fostered the Carolingian progress in astronomy.