In 1420, he founded in Samarkand a madrasa where mathematics and astronomy were among the most important subjects taught. The most prominent teacher was Qāḍīzāde al-Rūmī, who was joined somewhat later by Kāshī. In 1423 he founded his famous astronomical observatory (which stayed in operation for over 30 years); Ulugh Beg was the director of the Samarqand observatory, Kāshī was in charge of observations until his death in 1429, after which he was succeeded by Qāḍīzāde, who died after 1440. The observational program was completed by Qūshjī. [BEA, van Dalen]