Although usually known as Nasir al-Din al-Tusi, his proper name was Abu jafar Muhammad ibn Muhammad ibn al-Hasan Nasir al-Din al-Tusi. In fact al-Tusi was known by a number of different names during his lifetime such as Muhaqqiq-i Tusi, Khwaja-yi Tusi and Khwaja Nasir.
He was born in Tus, Khurasan in 1201 C.E. which lies close to Meshed in northeastern Iran high up in the valley of the Kashaf River. He was born at the beginning of a century which would see conquests across the whole of the Islamic world from close to China in the east to Europe in the west. It was the era when the vast military power of the Mongols would sweep across the vast areas of the Islamic world displaying a bitter animosity towards Islam and cruelly massacring people. This was a period in which there would be little peace and tranquillity for great scholars to pursue their works.
He learnt sciences and philosophy from Kamal al-Din Ibn Yunus and
others. He was one of those who were kidnapped by Hasan Bin Sabah's agents and sent to
Almut, Hasan's stronghold.
In 1256 when Almut was conquered by the Mongols, Nasir al-Din
joined Halagu's service. Halagu Khan was deeply impressed by his knowledge, including his
astrological competency; appointed him as one of his ministers, and, later on, as
administrator of Auqaf. He was instrumental in the establishment and progress of the
observatory at Maragha. In his last year of life he went to Baghdad and died there.
Nasir al-Din was one of the greatest scientists, philosophers, mathematicians,
astronomers, theologians and physicians of the time and was a prolific writer.
He made
significant contributions to a large number of subjects, and it is indeed difficult to
present his work in a few words. He wrote one or several treatises on different sciences
and subjects including those on geometry, algebra, arithmetic, trigonometry, medicine,
metaphysics, logic, ethics and theology. In addition he wrote poetry in Persian.
In mathematics, his major contribution would seem to be in trigonometry, which was
compiled by him as a new subject in its own right for the first time. He also developed
the subject of spherical trigonometry, including six fundamental formulas for the solution
of spherical right-angled triangles.
As the chief scientist at the observatory established under his supervision at Maragha,
Tusi made significant contributions to astronomy.
The observatory was equipped with the best
possible instruments, including those collected by the Mongol armies from Baghdad and
other Islamic centres. The instruments included astrolabes, representations of
constellations, epicycles, shapes of spheres, etc. He himself invented an instrument
'turquet' that contained two planes. After the devoted work of 12 years at the observatory
and with the assistance of his group, he produced new astronomical tables called Al-Zij-Ilkhani
dedicated to Ilkhan (Halagu Khan). Although Tusi had contemplated completing the
tables in 30 years, the time required for the completion of planetary cycles, but he had
to complete them in 12 years on orders from Halagu Khan. The tables were largely based on
original observations, but also drew upon the then existing knowledge on the subject.
The Zij Ilkhani became the most popular tables among astronomers and remained so
till the 15th century. Nasir al-Din pointed out several serious shortcomings in Ptolemy's
astronomy and foreshadowed the later dissatisfaction with the system that culminated in
the Copernican reforms.
In philosophy, apart from his contribution in logic and meta- physics, his work on
ethics entitled Akhlaq-i-Nasri became the most important book on the subject, and
remained popular for centuries. His book Tajrid-al-'Aqaid was a major work on al-Kalam
(Islamic Scholastic Philosophy) and enjoyed widespread popularity. Several commentaries
were written on this book and even a number of supercommentaries on the major
commentaries, Sharh Qadim and Sharh Jadid.
The list of his known treatises is exhaustive; Brockelmann lists 56 and Sarton 64.
About one-fourth of these concern mathe- matics, another fourth astronomy, another fourth
philosophy and religion, and the remainder other subjects. The books, though originally
written in Arabic and Persian, were translated into Latin and other European languages in
the Middle Ages and several of these have been printed.
Tusi's influence has been significant in the development of science, notably in
mathematics and astronomy. His books were widely consulted for centuries and he has been
held in high repute for his rich contributions.