Nasir al-Din al-Tusi

Abu Ja’far Muhammad ibn Muhammad ibn al-Hasan Nasir al-Din al-Tusi was born in 1201 in the city of Tus in Khorasan, in what is now north-eastern Iran. His father was a jurist of the Twelver Shi’a school. Nasir al-Din began his studies in Tus, where his uncle taught him logic, physics and metaphysics, and continued in Nishapur with philosophy, medicine and mathematics, studying mathematics and astronomy under Kamal al-Din ibn Yunus.

As the Mongol conquests swept over the region, al-Tusi entered the service of the Ismaili governor of Quhistan, Nasir al-Din Abd al-Rahim ibn Abi Mansur, for whom he wrote the Persian work on ethics “Akhlaq-i Nasiri” around 1235. He later lived in the Nizari Ismaili strongholds of Alamut and Maymun-Diz and produced important works on logic, philosophy, mathematics and astronomy.

In 1256 the Mongol army under Hulegu captured Alamut and al-Tusi entered Hulegu’s service as a scientific adviser; he was with Hulegu in 1258 when Baghdad was taken. Historians judge his role in these events differently. He was later put in charge of religious endowments, and according to some accounts he helped to preserve libraries and scholarly institutions.

Al-Tusi persuaded Hulegu to build an observatory: construction near Maragha in Azerbaijan began in 1259, and the observatory was working by 1262. Scholars from different countries worked there, and a large library was assembled. Observations over twelve years produced the “Zij-i Ilkhani” (Ilkhanic Tables), completed in 1272. In his astronomical treatise “Al-Tadhkira fi ilm al-hay’a” he proposed planetary models that differed from Ptolemy’s and used the geometric device now called the Tusi couple.

In mathematics his “Treatise on the Quadrilateral” (“Shakl al-qatta’”) is regarded as one of the first works to present trigonometry as a discipline in its own right, separate from astronomy. He wrote commentaries on and edited the works of Euclid, Archimedes, Ptolemy and other Greek authors, and attempted a proof of Euclid’s fifth postulate.

Nasir al-Din al-Tusi died in 1274 in Kadhimiyya, near Baghdad. Some 150 works are ascribed to him, about twenty-five of them in Persian and the rest in Arabic. A lunar crater and the asteroid 10269 Tusi are named after him, and the manuscript collection of the Institute of Oriental Studies of the Academy of Sciences of Uzbekistan holds more than twenty rare copies of his works.