Nasir al-Din al-Tusi

He married a Mongol in 1256, after being accepted by Hulagu Khan.

In 1274, he went to Baghdad with a group of his students, where he died on June 26, at the age of 73.

A lunar crater, measuring 60-km in diameter, on the southern hemisphere of moon has been named as ‘Nasireddin’.

Khwaja Muhammad ibn Muhammad ibn al-Hasan al-Tusi, or Nasir al-Din al-Tusi for short, was born on February 18, 1201, in Tus, medieval Kharasan (now north-eastern Iran), into a wealthy and learned Twelver Shi’ah family.

After losing his father as a child, he devoted his entire life in accomplishing his father’s dream of becoming a learned scholar.

His education started in Tus where he was taught physics, logic and metaphysics by his uncle, while he learnt mathematics under other teachers.

He moved to Nishapur, a prominent learning center, as a teenager to study more advanced topics in mathematics, philosophy and medicine. Thereafter, he went to Mosul to take mathematics and astronomy lectures.

While studying at Mosul, he completed a small booklet of philosophical Sufi compositions ‘Awsaf al-Ashraf’ (The Attributes of the Illustrious).

After completing his education in the early 1230s, he took refuge from the Mongols, who had invaded Tus, at the Isma’ili fort, where he spent the next 25 years researching on philosophy, astronomy, logic and mathematics.

In 1247, he authored ‘Tahrir al-Majisti’ (Commentary on the Almagest) as an introduction to trigonometry and showed various methods to calculate sine tables.

While he was at the Isma’ili capital, Alamut, in 1256, the Mongols, led by Hulagu Khan, invaded and captured him. However, he was appointed Hulagu’s scientific advisor due to his knowledge, talent and abilities.

In 1259, he began the construction of Rasad Khaneh Observatory in Maragha, after seeking Hulagu’s consent and served as its director till his death. It was equipped with the best instruments and included a library and school as well.

He pioneered in building an astronomical observatory in Maragha, where he spent 12 years in producing an accurate table for planetary movements, which were used by astrologers till the 1600s.

He is credited with inventing the Tusi-couple, a geometrical technique for solving the problematic equant of Ptolemy. His invention was later used by famous astrologers – Ibn al-Shatir and Nicolaus Copernicus.

His ‘Treatise of the Quadrilateral’ is regarded as his best work on mathematics, where he differentiates between spherical trigonometry and astronomy, thus declaring trigonometry a branch of mathematics, distinct from astronomy.

He was the first astronomer to describe the Milky Way’s composition of numerous small and tightly-clustered stars, which was proved by Galileo Galilei three centuries later in 1610, using a telescope.