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A Medieval Arabic Reform of the Ptolemaic Lunar Model

In a previous article, published in 1979, I have described in some detail the planetary model of Mu'ayyad al-Din al-Tlrdi of Damascus (d. A.D.1266).1 In that article I published a working edition of the relatively short Arabic text describing the model, and appended to it an English translation and a commentary. The purpose of that article was to show that the planetary model, hitherto ascribed to Qutb al-Din al-Shirazi (d. A.D. 1311), was in fact due to the Damascene astronomer Mu'ayyad al-Din al-Tlrdi. In contrast, the remaining models of Mu'ayyad al-Din al-Tlrdi, namely his models for the Moon and Mercury, have received no attention beyond a brief mention here and there in public lectures. The most recent brief description of these models has now been incorporated in a chapter on Islamic planetary theories in a forthcoming trilingual book (English, Arabic and French) on Arabic science." The main purpose of this paper is to describe at some length the lunar model of Mu'ayyad al-Din al-Tlrdi, in order to "demonstrate one of the several attempts, produced by medieval Arabic astronomers, all expressly aiming to reform the Ptolemaic lunar model, and to make the contributions of Mu'ayyad al-Din al-Tlrdi more accessible to students of the history of Arabic science. After some hesitation the scheme followed in the previous article on the planetary model, namely to present an edition of the Arabic source, an English translation and a commentary, had to be abandoned here for the simple practical reason that the lunar model in 'Urdi's work occupies a considerably much larger space, and thus makes the reproduction of an edited Arabic text in the form of an article indeed prohibitive. For purposes of comparison, the planetary model in 'Urdi's text takes up some two-and-a-half folios, while that of the Moon is spread over a space of some thirteen folios.'