Abu Jafar Muhammad Ibn Muhammad Ibn al-Hasan Nasir al-Din al-Tusi (also known as Nasir al-Din Tusi) (1201–1274) was a Persian scientist, of Shi'a Islamic belief, born in Tus, Khorasan, Iran. He is known as a philosopher, mathematician, astronomer, theologian, physician, and a prolific writer, i.e., he was a polymath.

He was perhaps the first to treat trigonometry as a separate mathematical discipline and in his Treatise on the Quadrilateral he was the first to list the six distinct cases of a right angled triangle in spherical trigonometry.

As the armies of Genghis Khan swept his homeland, he fled to join the Ismailis and made his most important contributions in science during this time, while he was moving from one stronghold to another. He finally joined Hulagu's (Genghis Khan's son) ranks, after the invasion of the Alamut castle of the Hashshashin (Assassins) by Mongol forces.

The Mongol ruler, Hulagu Khan, built an observatory in Maragheh for Tusi. Tusi is considered the first of the Maragheh School of astronomers, who made significant contributions to the development of astronomy. Notable members of that school were Mu’ayyad al-Din al-’Urdi and Qutb al-Din al-Shirazi.

Tusi made very accurate tables of planetary movements as depicted in his book Zij-i ilkhani (the Ilkhanic Tables). This books contains astronomical tables for calculating the positions of the planets and the names of the stars. His planetary system was the most advanced of his period and was used extensively until the development of the heliocentric model in the time of Copernicus. Between Ptolemy and Copernicus, he is considered as the most eminent astronomer of his time.

He invented the geometrical technique called a Tusi-couple for his planetary models, which generates linear motion from the sum of two circular motions. He also calculated the value of 51" for the annual precession of the equinoxes and contributed to construction and usage of some astronomical instruments including astrolabe. He gave the first extant exposition of the whole system of plane and spherical trigonometry.

A 60-km diameter lunar crater located on the southern hemisphere of the moon is named after him as "Nasireddin".

See also

• Islamic scholars
• List of Iranian scientists

External links

• Biography by School of Mathematics and Statistics, University of St Andrews, Scotland
• History of Science Online: Islamic and Early Medieval Science, University of Oklahoma
• Islam Online.

Persian philosophers | Persian astronomers | 13th century mathematicians | Persian scientists | Persian mathematicians | Muslim scientists | 1201 births | 1274 deaths

Nəsirəddin Tusi | Nasir Al-din al-Tusi | Nasir al-Din al-Tusi | خواجه نصیر طوسی | Nasir ad-Din at-Tusi | Nasir al-Din al-Toesi | Nasir al-Din Tusi | Nasir at-Tusi