Sharaf al-Dīn al-Ṭūsī

Born Ṭūs, (Ira), circa1135

Died (Iran), 1213

Although Sharaf al-Dīn al-Ṭūsī is known especially for his mathematics (in particular his novel work on the solutions of cubic equations), he was also the inventor of the linear astrolabe, a tool that derives from the planispheric astrolabe but is more easily constructed. From his name we may infer that Sharaf al-Dīn was born in the region of Ṭūs, in northeastern Iran. He spent a major part of his early career as a teacher of the sciences, including astronomy and astrology, in Damascus and Aleppo; he also taught in Mosul. Among his students was Kamāl al-Dīn ibn Yūnus, who would eventually teach Sharaf’s namesake, the great Naṣīr al-Dīn al- Ṭūsī .

Sharaf al-Dīn al-Ṭūsī devoted several treatises to the linear astrolabe, sometimes called the staff of al-Ṭūsī. Its principle is simple – many of the important circles on the planispheric astrolabe, especially the almucantars (altitude circles) and the circles of declination, are centered on the...