Qushji: an anti-Aristotelian astronomer, a Muslim genius of Hagia Sophia

Ali al-Qushji left an important mark in the field of astronomy in the 15th century. The son of the royal falconer who served the legendary astronomer Ulugh Beg, Qushji took courses in the linguistic sciences, mathematics, and astronomy as well as other sciences taught by Beg and his proteges. 

In 1420, he secretly moved to Kirman where he studied astronomy and mathematical sciences. When he returned to Samarkand in 1428, he presented his master Ulugh Beg with a monograph, “Hall ishkal al-mu’addil li-l-masir,” in which he solved the problems related to the planet Mercury. It impressed Beg so much that he began to refer to his disciple as Qushji, which means his ‘virtuous son’. 

When Beg, who was also known as ‘the prince of stars’, passed away, Qushji left the Timurid palace and went to Tabriz (a city in modern Iran) where he met with the king of Akkoyunlu State, Long Hasan. 

From that moment, Long Hasan admired Qushji’s wisdom and sent him as an ambassador to Mehmed the Conqueror of the Ottoman Empire. He was tasked with settling a dispute between the two emperors. 

As he approached Istanbul, Sultan Mehmed sent a group of scholars to welcome Qushji. According to some historical accounts, while crossing the Bosphorus to enter Istanbul, a discussion ensued about the causes of the strait's ebb and flow. When he arrived at the Ottoman Palace, he presented a mathematical piece of work titled “Al‐Muḥammadiyya fi al‐ḥisab” to the Sultan, which was named in Mehmed's honour. 

Following Sultan Mehmed’s offer, Ali Qushji decided to stay in Istanbul and became lecturer at the Hagia Sophia Madrassa in 1473, a year that became a turning point for astronomy and mathematics in Istanbul.

During that period, Ali Qushji took care of the Madrasa coursework along with Mullah Husrev. He corrected the wrong value of Istanbul’s geographic longitude from 60 degrees to 59, and detected the latitude as 41 degrees and 14 minutes. 

He spent the last three years of his life in Istanbul and first taught in the Sahn-i Thaman Madrassa which was founded by the sultan. Afterwards, he became the head of Hagia Sophia Madrassa. In a short period of time, he educated and influenced a large number of students and scholars who were believed to have then had themselves a huge impact on the future generations of the Ottoman Empire.

A remarkable polymath, he excelled in several disciplines including language and literature, philosophy and theology. His commentaries became more popular than the original texts, and they became the subject of numerous commentaries. Thousands of copies of Qūshjī's works were taught in the madrassas. 

Qushji wrote five books on mathematics: one in Persian and four in Arabic. The one in Persian, ‘Risala dar ‘ilm al -hisab’ became a mid-level textbook in Ottoman madrassas.  In them, in accordance with the principles he laid down in the Sharḥ al‐Tajrīd, he tried to free mathematics from hermetic–Pythagorean mysticism. As a result, Ottoman mathematics took on a practical character which hindered traditional studies such as the theory of numbers. 

As a philosopher–theologian, mathematician, astronomer, and linguist who produced original studies in both observational and theoretical astronomy within 15th‐century Islamic and Ottoman astronomy, he contributed to the preparation of Ulugh Beg's Zīj (astronomical handbook) at the Samarqand Observatory,  in which he insisted on the possibility of the Earth's motion, asserting the need for the purification of all the scientific disciplines right from the Aristotelian physics to metaphysics. 

Qushji's scientific philosophy, which was a major contribution to astronomy, laid down the principles of concepts such as existence, existents, nature, knowledge, and language. 

Qushji sought to define body (jism) as being predominantly mathematical in character, arguing that the essence of a body is composed of discontinuous (atomic) quantity, while its form consists of continuous (geometrical) quantity. When a body is a subject of the senses, it then gains its natural properties (qualifications). 

One consequence of Qushji's anti‐Aristotelian views was his striking assertion that it might well be possible that the Earth is in motion. Here Qushji followed a long line of Islamic astronomers who rejected Ptolemy's observational proofs for geostasis; Qushji, though, refused to follow them in depending on Aristotle's philosophical proofs, thus opening up the possibility for a new physics in which the Earth was in motion. 

His views were debated for centuries after his death, and he exerted a profound influence on Ottoman–Turkish thought and scientific inquiry, in particular through the madrassa and its curriculum. His influence also extended to Central Asia and Iran, and it has been argued that he may well have had an influence, either directly or indirectly, upon early modern European science to which his ideas bear a striking resemblance. 

In the field of astronomy, one of Qushji's most important contributions is in the observational program for the Zīj‐i Ulugh Beg and in his corrections to the work, both before and after publication. 

In addition, he published nine works on astronomy: two in Persian and seven in Arabic. Some of them are original contributions while others are pedagogical. In his theoretical monograph entitled, “Ḥall ishkal al‐muʿaddil li‐l‐masir”, he criticises and corrects opinions and ideas pertaining to Mercury's motions mentioned in Ptolemy's Almagest. Another work, “Risala fī anna asl al‐kharij yumkinu fī al‐sufliyayn”, deals with the possibility of using an eccentric model for Mercury and Venus, which, as he says, goes against both Ptolemy and Quṭb al‐Din al‐Shirazi. 

His “Risala dar ʿilm al‐hayʾa written in Persian in Samarqand in 1458, was commonly used as a teaching text; there are eighty manuscript copies in existence in libraries throughout the world. It was also translated into Turkish. Two commentaries were written on it, one by Muṣliḥ al‐Din al‐Lari, the other by an anonymous author. 

Lari’s commentary was widely taught in Ottoman madrassas. Qushji's Risala was also translated into Sanskrit and thus represents the transmission of Islamic astronomy to the Indian subcontinent. Qushji wrote an enlarged version of the work in Arabic under the name, al‐Fatḥiyya fī ʿilm al‐hayʾa, which was presented to Sultan Mehmed in 1473.

Ali Qushji was buried in the cemetery of the Eyyub mosque in Istanbul in 1474.