In the history of Islamic astronomy the thirteenth century was the most important. It witnessed the founding of the Maragha Observatory, the most advanced scientific institution in the Eurasian world. Lavishly funded, Maragha had an extensive library and a large staff. And its head astronomer, Nasir al-Din Tusi (1201–74), compiled the most complete and up-to-date zij yet available, while also composing ground-breaking works in mathematics and astronomy. Because, however, the Reconquista had ended intellectual exchange between the Islamic and Christian worlds, the discoveries of Tusi and the Maragha astronomers remained unknown in Europe for more than two hundred years.

Nasir al-Din Tusi was one of the great polymaths of medieval Islam. He wrote more than one hundred and fifty works in both Persian and Arabic, covering an impressive range of subjects. Expert in both the traditional and the rational sciences, he completed treatises on law, Shi‘ite theology, Sufism, logic, ethics, medicine, and metallurgy. He wrote critical summaries of the major Greek mathematicians and philosophers and composed original works in arithmetic, geometry, trigonometry, astrology, and astronomy. His fame stretched from Baghdad in the West to China in the East. Known in his time as ‘Khwaja’ (distinguished teacher), he was later given the title of ‘third teacher’ – after Aristotle and Abu Nasr Muhammad ibn Muhammad al-Farabi (872–950). Ibn Khaldun considered him the greatest of the later Persian scholars.

Born into a family of Twelver, or Imami, Shi‘ites in Tus, a town in eastern Iran, Nasir al-Din studied the traditional sciences with his father, a scholar of Imami law, logic, and natural philosophy, and metaphysics with his uncle. In Tus he also received basic instruction in algebra and geometry. In 1213 he travelled to Nishapur to read philosophy with Farid al-Din al-Damad and medicine with Qutb al-Din al-Masri. Later during the 1220s he travelled to Mosul in northern Iraq to study mathematics and astronomy with Kamal al-Din ibn Yunus (1156–1242).

By the time he had finished his formal education the Islamic world had been thrown into chaos by the Mongol hordes of Chinghiz Khan (1206–7). The steppe warriors of the great Khan had conquered an enormous swath of territory from the Pacific in the East to the Caspian in the West.