On the Use of the “Southern Horizons Plate” (al-ṣafīḥa al-āfāqīya dhāt al-janūb)

In the following is edited an anonymous text, in twenty-one unnumbered chapters, on the use of the southern horizons plate, from a manuscript in Istanbul dated in Jumādā II 676/November 1277. The horizons plate is a drawing of the horizons engraved on one side of one of the plates of certain astrolabes. There existed —since the tenth century AD as it seems— some literature on the construction of such plates and on their use, but it has not been studied so far. The twenty-one chapters found in the Istanbul manuscript and edited here look rather like a fragment from a longer work. Most of the chapters describe astronomical applications of these plates, but some also their use for astrological purposes.