Qadi Zada al-Rumi

Salah al-Din Musa ibn Muhammad ibn Mahmud was born in Bursa, in present-day Turkey. The year of his birth is not known exactly: 1364 is the date most often given, while some sources say about 1359. The epithet Qadi Zada (“son of the judge”) goes back to his grandfather, the well-known judge of Bursa Mahmud Chelebi, who brought him up after his father’s death; “al-Rumi” points to Asia Minor, the land the East called Rum. He studied the religious and rational sciences with his grandfather and with the famous scholar Molla Fenari.

In the early fifteenth century, encouraged by Fenari and against the wishes of his family, he set out for Khurasan and Transoxiana. According to the sources he was in Samarkand from 1411, when the theologian and mathematician al-Sayyid al-Sharif al-Jurjani was lecturing there. But Qadi Zada judged every question by mathematical standards, disagreed with al-Jurjani and gave up his lessons.

In 1412 he wrote a commentary on Mahmud al-Jaghmini’s astronomical “Mulakhkhas” and a commentary on Shams al-Din al-Samarqandi’s geometrical “Ashkal al-ta’sis”, and presented both to the young Ulugh Beg. Ulugh Beg became his pupil and later spoke of his teacher with respect in his “Zij”. When Ulugh Beg built a madrasa in Samarkand in 1417–1420, Qadi Zada became its head teacher; Ulugh Beg himself regularly attended his lectures.

Together with Ghiyath al-Din Jamshid al-Kashi he supervised the building of Ulugh Beg’s Samarkand observatory. After al-Kashi’s death in 1429 he remained one of the directors of the observatory, took part in observations and calculations, and contributed to Ulugh Beg’s astronomical tables, the “Zij-i Gurgani”. He edited and developed al-Kashi’s unfinished treatise on calculating the sine of one degree.

His pupils included Ali Qushji and Fathallah al-Shirwani, both of whom later taught in Anatolia. Qadi Zada’s son married Qushji’s daughter, and their son was Miram Chelebi, a noted Ottoman scholar.

Qadi Zada died in Samarkand. Older reference works give 1436–1437 as the year of his death, but a licence (ijaza) he issued to a student in September 1440 survives, so he lived beyond that date. He is buried in a mausoleum in the Shah-i-Zinda complex. His commentaries on al-Jaghmini and al-Samarqandi were studied as textbooks in Ottoman madrasas for centuries.