Ali Qushji

Ala al-Din Ali ibn Muhammad Qushji was born around 1403, probably in Samarkand; some sources give his kunya as Abu’l-Qasim. His father, Muhammad, was Ulugh Beg’s falconer, in charge of the court’s hunting birds, which is how the family came by the name Qushji (“falconer”). Ali learned the foundations of mathematics and astronomy in Samarkand from Ulugh Beg himself and from Qadizada al-Rumi and Ghiyath al-Din Jamshid al-Kashi.

According to tradition, eager to learn more, he left for Kerman in Iran without telling his teachers; there he studied astronomy and other sciences and came to know Nasir al-Din al-Tusi’s “Tajrid”. Returning to Samarkand in the late 1420s, he presented Ulugh Beg with a treatise he had written in Kerman and won his praise. He then worked at Ulugh Beg’s observatory, and after the death of Qadizada al-Rumi Ulugh Beg put him in charge of the observations there. Qushji took part in compiling and correcting Ulugh Beg’s “Zij-i Sultani”. The sources also say that Ulugh Beg sent him to China.

After Ulugh Beg was murdered in 1449, Qushji left Samarkand with his family and students and spent a long time in Herat. In these years he presented his great commentary on al-Tusi’s “Tajrid” to the Timurid sultan Abu Sa’id. When Abu Sa’id was defeated by the Aq Qoyunlu ruler Uzun Hasan in 1469, the scholar moved to Tabriz. Uzun Hasan received him with honour and sent him as his envoy to the Ottoman sultan Mehmed II the Conqueror.

Around 1472 Qushji settled in Istanbul for good, with his family and students; the sultan had him welcomed with ceremony. He dedicated to Mehmed II his treatise on arithmetic, “Al-Risala al-Muhammadiyya”. In 1473 he accompanied the sultan on his campaign against Uzun Hasan and marked the victory with a treatise on astronomy, “Al-Risala al-Fathiyya”. In Istanbul he taught first at the Sahn-ı Seman madrasas built by Mehmed II and was then appointed head teacher (mudarris) of the Hagia Sophia madrasa. He determined the latitude of Istanbul as 41°14′ and corrected its longitude.

Qushji left dozens of works on mathematics, astronomy, theology, the principles of law and linguistics. His Persian “Risala dar ilm al-hay'a” and “Risala dar ilm al-hisab”, together with their enlarged Arabic versions, “Al-Fathiyya” and “Al-Muhammadiyya”, served as textbooks in Ottoman madrasas. In his commentary on the “Tajrid” he argued that astronomy should not rest on Aristotle’s natural philosophy and that observation cannot rule out the Earth’s daily rotation about its axis. He proposed a model for the motion of Mercury that differs from Ptolemy’s, and in his “Commentary on Ulugh Beg’s Zij” he explained how the tables were built and pointed out some of their errors.

Ali Qushji died in Istanbul on 5 Sha’ban 879 AH, in mid-December 1474, and was buried in the cemetery around the tomb of Eyüp Sultan. Of the students he trained in Istanbul, Molla Lutfi became well known; commentaries on “Al-Fathiyya” were written by his descendant, the mathematician Mirim Chelebi, and by his student Sinan Pasha. Manuscripts of his works are kept in libraries in Tashkent, St Petersburg, Istanbul, Oxford and elsewhere. In 2020 a mosque opened near Istanbul Airport was named after him.