Muhammad ibn Muhammad ibn al-Hasan al-Tūsī, better known as Nasir al-Din al-Tusi, was a Persian polymath, architect, philosopher, physician, scientist, and theologian. Nasir al-Din al-Tusi was a well published author, writing on subjects of maths, engineering, prose, and mysticism. He made invaluable contributions to astronomy and later served as a scientific advisor of the Mongols. One of his notable written works was Akhlaq-i Nasiri.
Naṣīr al-Dīn al-Ṭūsī, in full Muḥammad ibn Muḥammad ibn al-Ḥasan al-Ṭūsī, was an outstanding Persian philosopher, scientist, and mathematician.
Educated first in Ṭūs, where his father was a jurist in the Twelfth Imam school, the main sect of Shīʾite Muslims, al-Ṭūsī finished his education in Neyshābūr, about 75 kilometres to the west. (This Ismāʿīlīte state began in 1090 with the conquest of Alamūt by Ḥasan-e Ṣabbāḥ and ended with the fall of the city to the Mongols in 1256.) During this period, al-Ṭūsī wrote on Ismāʿīlīte theology , logic “Foundations of Inference”), and mathematics; “Commentary on the Almagest”
With the fall in 1256 of Alamūt to Hülegü Khan (c. 1217–1265), grandson of Genghis Khan, al-Ṭūsī immediately accepted a position with the Mongols as a scientific adviser. (The alacrity with which he went to work for them fueled accusations that his conversion to the Ismāʿīlīte faith was feigned, as well as rumours that he betrayed the city’s defenses.) Al-Ṭūsī married a Mongol and was then put in charge of the ministry of religious bequests. Profiting from Hülegü’s belief in astrology, al-Ṭūsī obtained support in 1259 to build a fine observatory (completed in 1262) adjacent to Hülegü’s capital in Marāgheh. More than an observatory, Hülegü obtained a first-rate library and staffed his institution with notable Islamic and Chinese scholars. Funded by an endowment, research continued at the institution for at least 25 years after al-Ṭūsī’s death, and some of its astronomical instruments inspired later designs in Samarkand.
He wrote approximately 150 books in Arabic and Persian and edited the definitive Arabic versions of the works of Euclid, Archimedes, Ptolemy, Autolycus, and Theodosius. He also made original contributions to mathematics and astronomy. His Zīj-i Ilkhānī (1271; “Ilkhan Tables”), based on research at the Marāgheh observatory, is a splendidly accurate table of planetary movements. Al-Ṭūsī’s most influential book in the West may have been Tadhkirah fi ʿilm al-hayʿa (“Treasury of astronomy”), which describes a geometric construction, now known as the al-Ṭūsī couple, for producing rectilinear motion from a point on one circle rolling inside another. By means of this construction, al-Ṭūsī succeeded in reforming the Ptolemaic planetary models, producing a system in which all orbits are described by uniform circular motion. Most historians of Islamic astronomy believe that the planetary models developed at Marāgheh found their way to Europe (perhaps via Byzantium) and provided Nicolaus Copernicus (1473–1543) with inspiration for his astronomical models.
In the East, al-Ṭūsī is an example par excellence of the ḥakīm, or wise man.
Tusi has about 150 works, of which 25 are in Persian and the remaining are in Arabic,[27] and there is one treatise in Persian, Arabic and Turkish.[28]

A Treatise on the Astrolabe by Tusi, Isfahan 1505
Sayr wa-Suluk (The Voyage) – Autobiography[26]
Kitāb al-Shakl al-qattāʴ Book on the complete quadrilateral. A five-volume summary of trigonometry.
Al-Tadhkirah fi’ilm al-hay’ah – A memoir on the science of astronomy. Many commentaries were written about this work called Sharh al-Tadhkirah (A Commentary on al-Tadhkirah) – Commentaries were written by Abd al-Ali ibn Muhammad ibn al-Husayn al-Birjandi and by Nazzam Nishapuri.
Akhlaq-i Nasiri – A work on ethics.
al-Risalah al-Asturlabiyah – A Treatise on the astrolabe.
Zij-i Ilkhani (Ilkhanic Tables) – A major astronomical treatise, completed in 1272.
Sharh al-Isharat (Commentary on Avicenna’s Isharat)
Awsaf al-Ashraf a short mystical-ethical work in Persian.[29]
Tajrīd al-Iʿtiqād (Summation of Belief) – A commentary on Shia doctrines.
Talkhis al-Muhassal (summary of summaries).
Maṭlūb al-muʾminīn (Desideratum of the Faithful)[20]
Aghaz u anjam – Esoteric interpretation of the Quran[21]
In 1214, when al-Tusi was 13 years old, Genghis Khan, who was the leader of the Mongols, turned away from his conquests in China and began his rapid advance towards the west. It would not be too long before al-Tusi would see the effects of these conquests on his own regions, but before that happened he was able to study more advanced topics. From Tus, al-Tusi went to Nishapur which is 75 km west of Tus. Nishapur was a good choice for al-Tusi to complete his education since it was an important centre of learning. There al-Tusi studied philosophy, medicine and mathematics. In particular he was taught mathematics by Kamal al-Din ibn Yunus, who himself had been a pupil of Sharaf al-Din al-Tusi. While in Nishapur al-Tusi began to acquire a reputation as an outstanding scholar and became well known throughout the area.

The Mongol invasion reached the area of Tus around 1220 and there was much destruction. Genghis Khan turned his attention again towards the east leaving his generals and sons in the west to continue his conquests. There was, amid the frequent fighting in the region, peaceful havens which attracted al-Tusi. The Assassins, who practised an intellectual form of extremist Shi’ism, controlled the castle of Alamut in the Elburz Mountains, and other similar impregnable forts in the mountains. When invited by the Isma’ili ruler Nasir ad-Din ‘Abd ar-Rahim to join the service of the Assassins, al-Tusi accepted and became a highly regarded member of the Isma’ili Court. Whether he would have been able to leave, had he wished to, is not entirely clear. However, al-Tusi did some of his best work while moving round the different strongholds, and during this period he wrote important works on logic, philosophy, mathematics and astronomy. The first of these works, Akhlaq-i nasiri, was written in 1232. It was a work on ethics which al-Tusi dedicated to the Isma’ili ruler Nasir ad-Din ‘Abd ar-Rahim.

In 1256 al-Tusi was in the castle of Alamut when it was attacked by the forces of the Mongol leader Hulegu, a grandson of Genghis Khan, who was at that time set on extending Mongol power in Islamic areas. Some claim that al-Tusi betrayed the defences of Alamut to the invading Mongols. Certainly Hulegu’s forces destroyed Alamut and, Hulegu himself being himself interested in science, he treated al-Tusi with great respect. It may be that indeed al-Tusi felt that he was being held in Alamut against his will, for certainly he seemed enthusiastic in joining the victorious Mongols who appointed him as their scientific advisor. He was also put in charge of religious affairs and was with the Mongol forces under Hulegu when they attacked Baghdad in 1258.

Al-Musta’sim, the last Abbasid caliph in Baghdad, was a weak leader and he proved no match for Hulegu’s Mongol forces when they attacked Baghdad. After having laid siege to the city, the Mongols entered it in February 1258 and al-Musta’sim together with 300 of his officials were murdered. Hulegu had little sympathy with a city after his armies had won a battle, so he burned and plundered the city and killed many of its inhabitants. Certainly al-Tusi had made the right move as far as his own safety was concerned, and he would also profit scientifically by his change of allegiance.

Hulegu was very pleased with his conquest of Baghdad and also pleased that such an eminent scholar as al-Tusi had joined him. So, when al-Tusi presented Hulegu with plans for the construction of a fine Observatory, Hulegu was happy to agree. Hulegu had made Maragheh his capital . Maragheh was in the Azerbaijan region of northwestern Iran, and it was at Maragheh that the Observatory was to be built. Construction of the Observatory began in 1259 west of Maragheh, and traces of it can still be seen there today.

The observatory at Maragheh became operational in 1262. Interestingly the Persians were assisted by Chinese astronomers in the construction and operation of the observatory. It had various instruments such as a 4 metre wall quadrant made from copper and an azimuth quadrant which was the invention of Al-Tusi himself. Al-Tusi also designed other instruments for the Observatory which was far more than a centre for astronomy. It possessed a fine library with books on a wide range of scientific topics, while work on science, mathematics and philosophy were vigorously pursued there.

Al-Tusi put his Observatory to good use, making very accurate tables of planetary movements. He published Zij-i ilkhani (the Ilkhanic Tables), written first in Persian and later translated into Arabic, after making observations for 12 years. This work contains tables for computing the positions of the planets, and it also contains a star catalogue. This was not the only important work which al-Tusi produced in astronomy. It is fair to say that al-Tusi made the most significant development of Ptolemy’s model of the planetary system up to the development of the heliocentric model in the time of Copernicus.