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The Astronomy of Maimonides and Its Arabic Sources

2009, COSMOLOGY ACROSS CULTURES. SEAC 2008 Proceedings, ASP Series

In this paper, I analyze the fact discovered by Otto Neugebauer in a 1949 paper explaining why the mean lunisolar conjunction set by Maimonides in his Code of Jewish Law, Mishneh Torah, differs from the mo-lad (Jewish calendar conjunction) by 1 hour and 17 minutes. I also address Neugebauer's fundamental question of whether the molad is a mean conjunction. This problem leads me to a further examination of Maimonides' sources on the one hand and to a clarification of the notion of molad on the other. First I conjecture that a difference of circa 50 minutes between the epochs of Maimonides and al-Battânˆı came from a geographical manuscript that was different than al-Battânˆı's treatise (translated by Carlo Nallino in 1903) and which quoted an unreasonably high longitude for Raqqa (the location of al-Battânˆı's observations) compared with Jerusalem's longitude. Second, examination of a time difference between al-Battânˆı's mean lunisolar conjunction and the molad shows an additional circa 27-minute difference. This proves 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. I conclude by reiterating that molad is Ptolemaic mean lunisolar conjunction while Maimonides used al-Battânˆı's mean lunisolar conjunction.