Maimonides and Māshāʾallāh on the Ninth Orb of the Signs and Astrology

This paper is mainly concerned with the reception of the theory of a starless ninth orb by Maimonides (1138–1204). Maimonides addressed this topic in two of his works: first, in the third chapter of the Laws of the Foundation of the Torah, part of his code of Jewish law, the Mishneh Torah; and, at a later date, in the Guide of the Perplexed. I begin with the approach to the ninth orb in the Laws of the Foundation of the Torah, where it is presented as a starless orb divided into twelve signs named for the twelve zodiacal constellations. My contention is that Maimonides extracted the ideas about the ninth orb from a cosmological work ascribed to Māshāʾallāh, an early Abbasid astrologer, or from some later work derived from Māshāʾallāh’s cosmology. I also clarify the unusual features of this model as presented by Māshāʾallāh and try to determine the rationale behind its inclusion in Māshāʾallāh’s cosmology as well as in Maimonides’ Mishneh Torah. This, I maintain, has to do not only with cosmological but also and especially with astrological considerations. Then I briefly study the approach to the ninth orb in the Guide, where it is incorporated in its “classical” form, i.e., as the all-encompassing orb imparting the diurnal motion to all the other motions, and weigh the difference between this and the Mishneh Torah. Last, in a short postscript, I broaden the scope to show that Māshāʾallāh’s cosmology, particularly the ninth starless orb divided into twelve signs, was widely known in the Arabic world before Maimonides, especially among Jewish intellectuals in Muslim Spain.