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The source material for the study of medieval oriental astronomy consists of Byzantine Greek, Sanscrit, Hebrew, Arabic, Persian, and Turkish astronomical and astrological manuscripts. If one desires to build up a detailed picture of Islamic astronomy, one can choose material from these available manuscripts. Of these manuscripts it is possible to isolate a group of works, the "zijes". A "zij" consists of the numerical tables and accompanying explanation sufficient to measure time and to compute planetary and stellar positions, appearance, and eclipses. This paper is a survey of the number, distribution, contents, and relations between "zijes" written in Arabic or Persian during the period from the 8th through the 15th centuries. Illustrations. Oversize.