(b. Ṭūs [?]. Iran; d. Iran, ca. 1213/1214)

astronomy, mathematics.

The name of Sharaf al-Dīn’s birthplace, Tūs, refers both to a city and to its surrounding region, which with Mashhad and Nīshāpur formed a very prosperous area in the twelfth century. ^{internal text/xml point ancestor::gift-doc:document//*[@id="asaen1"] self 1} A century earlier, Tūs had given Islam one of its most profound thinkers, al-Ghazālī (d. 1111); and it was soon to produce a great astronomer and theologian, Naṣīr al-Dīn (d. 1274). Nothing is known about the first years of al-Ṭūsī’s life; but it is reported that, faithful to the tradition of medieval scholars, he went on a long journey to some of the major cities of the time. His itinerary can be reconstructed from undated information preserved in biographies of his contemporaries.

Al-Ṭūsī taught at Damascus, probably about 1165. ^{internal text/xml point ancestor::gift-doc:document//*[@id="asaen2"] self 2} His most distinguished student there was Abu’l-Fadl (b. ca. 1135). an excellent carpenter who helped make the wood paneling of the Bīmāristān al-Nūrī (1154-1159) before discovering the joys of Euclid and Ptolemy. ^{internal text/xml point ancestor::gift-doc:document//*[@id="asaen3"] self 3} Al-Ṭūsī most probably then stayed at Aleppo, where one of his pupils was a respected member of the city’s Jewish community, Abu’l-Fadl Binyāmīn (d. 1207/1208), whom he instructed in the science of numbers, the use of astronomical table, and astrology, and, at a less advanced level, in the other rational sciences. ^{internal text/xml point ancestor::gift-doc:document//*[@id="asaen4"] self 4} From the nature of these courses, it is reasonable to suppose that they lasted about three years.

Al-Ṭūsī’s most outstanding pupil, however, was Kamāl al-Dīn Ibn Yūnus (d. 1243) of Mosul, through whom al-Ṭūsī’s teachings passed to Nasīr al-Dīn and Athīr al-Dīn al-Abharī (d. 1263/1265). ^{internal text/xml point ancestor::gift-doc:document//*[@id="asaen5"] self 5} Al-Ṭūsī was apparently in Mosul in the years preceding 1175, ^{internal text/xml point ancestor::gift-doc:document//*[@id="asaen6"] self 6} for around this date two physicians from Damascus went there to study with him, but he had already left. ^{internal text/xml point ancestor::gift-doc:document//*[@id="asaen7"] self 7} One of them then went to the neighboring city of irbil, where he became a pupil of Ibn al-Dahhān. ^{internal text/xml point ancestor::gift-doc:document//*[@id="asaen8"] self 8} About this time, however, the latter left Irbil to join Saladin, who had just seized Damascus (1174). ^{internal text/xml point ancestor::gift-doc:document//*[@id="asaen9"] self 9} Al-Ṭūsī returned to Iran, where he died around 1213, at an advanced age.

Al-Ṭūsī is known for his linear astrolabe (al-Ṭūsī’s staff), a simple wooden rod with graduated markings but without sights. It was furnished with a plumb line and a double cord for making angular measurements and bore a perforated pointer. This staff reproduced, in concrete form, the meridian line of the plane astrolabe-that is, the line upon which the engraved markings of that instrument are projected. (These markings are of stars, circles of declination, and heights.) Supplementary scales indicate the right ascensions of the sun at its entry into the signs of the zodiac as well as the hourly shadows....