From: Thomas Hockey et al. (eds.). The Biographical Encyclopedia of Astronomers, Springer Reference. New York: Springer, 2007, pp. 460-461
Ḥajjāj ibn Yūsuf ibn Maṭar
Flourished Baghdad, (Iraq), 786–830
We know next to nothing about Ḥajjāj's personal life, his family, his friends, or his training; we do know that he was one of the most influential translators of the late 8th and early 9th centuries in Baghdad, then the capital of the ʿAbbāsid Empire.
Ḥajjāj translated Ptolemy's Megále Sýntaxis (later known as the Almagest) and Euclid's Elements. In the early 9th century, he translated the Elements, apparently on the basis of a single Greek manuscript, into Arabic for Yaḥyā ibn Khālid (died: 805), the Vizier of Caliph Hārūn al‐Rashīd. In the 820s, Ḥajjāj revised his translation and produced for the then ruling ʿAbbāsid Caliph Maʾmūn (reigned: 813–833) a new version described as more sophisticated than his original translation. When and for whom he translated the Almagest is unknown. Two manuscripts of Ḥajjāj's translation of Ptolemy's major work are today extant, one of them complete, the second containing only Books I–IV.
Ḥajjāj's translations exercised a long‐lasting influence upon the community of Arabic, Persian, Hebrew, and Latin students of Ptolemy's and Euclid's books. It can be detected in the manuscripts representing the second major tradition in the Arabic transmission of the Almagest and the Elements (and in that of its later offspring in Latin and Hebrew). This second tradition was started by Isḥāq ibn Ḥunayn's translations of the Almagest and the Elements into Arabic and continued with Thābit ibn Qurra's edition of the two translations. Several of the ten manuscripts of the Arabic Almagest extant today and representing this tradition contain some portions of the Ḥajjāj translation, in particular the star catalog. Manuscripts of both traditions, including manuscripts having parts of each, were studied in Andalusia (Spain), in northern Africa, the central lands of the Middle East, Central Asia, and India. Important scholars such as Abū ʿAlī ibn Sīnā (in Central Asia and Iran;), Jābir ibn Aflaḥ (in al‐Andalus), and Naṣīr al‐Dīn al‐Ṭūsī (in Iran) knew and worked with manuscripts of both traditions and commented, sometimes critically, upon them. In the 12th century, Gerard of Cremona translated the Almagest in Toledo from Arabic into Latin using manuscripts representing the two Arabic traditions. Books I–IX of his translation are based on the work of Ḥajjāj except for the star catalog in the books VII.5–VIII.1, which represents a text mixing the two Arabic traditions. The remaining three books of Gerard's translation are derived from the work of Isḥāq ibn Ḥunayn and Thābit ibn Qurra (Ptolemäus, Vol. 2, p. 3, 1990).
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——— (2001). “A Hitherto Unknown Arabic Manuscript of the Almagest.” Zeitschrift für Geschichte der Arabisch‐Islamischen Wissenschaften 14: 31–37.
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Ptolemäus, Claudius (1986–1991). Der Sternkatalog des Almagest: Die arabisch‐mittelalterliche Tradition, edited by Paul Kunitzsch. 3 Vols. Wiesbaden: Otto Harrassowitz.