Talk abstract details

The Astronomy of Maimonides and Its Arabic Sources
Ari Belenkiy


In 1949 paper “Astronomy of Maimonides and its Sources” Otto Neugebauer discovered that the mean lunisolar conjunction set by Maimonides in his Code of Jewish Law, Mishneh Torah, differs from the molad (Jewish calendar conjunction) by 1 hour and 17 minutes. Several explanations written by Jewish researchers seem unsatisfactory and brought us to a further examination of Maimonides’ sources on the one hand and to a clarification of the notion of molad on the other. We split the problem into two - geographical and astronomical.
First we conjecture that a difference of circa 50 minutes between the epochs of Maimonides and al­-Battānī came from a geographical manuscript that was different than al-Battānī’s treatise, translated by Carlo Nallino in 1903 under the title Opus Astronomicum, and which (manuscript) quoted an unreasonably high longitude for the city of Raqqa (the location of al-Battānī’s observations) compared with Jerusalem’s longitude. After analysis of Abū ’l-Fidā’s compendium of medieval geographical manuscripts we suggest at least two plausible sources, Atwāl (of unknown origin) and/or Canon, coming either from Habash or Al-Bīrūnī.
Second, examination of a time difference between al-Battānī’s mean lunisolar conjunction and the molad brings it close to 27 minutes. Taking into consideration a rounding-up procedure this confirms that the interval of 1 hour and 17 minutes between Maimonides’ conjunction and the molad consists of only two parts and does not require the additional assumptions made by previous researchers.
We conclude by a brief discussion whether Maimonides’ new moon’s visibility criteria could come from Arabic sources as well, like Hekemite Tables composed by Ibn Yūnus, and not from Babylonian heritage as Neugebauer suggested.