Ulugh Beg
With the instruments located in the observatory in Samarkand, Ulugh Beg composed a star catalogue consisting of 1018 stars, which is eleven fewer stars than are present in the star catalogue of Ptolemy. Ulugh Beg utilized dimensions from al-Sufi and based his star catalogue on a new analysis that was autonomous from the data used by Ptolemy. Throughout his life as an astronomer, Ulugh Beg came to realize that there were multiple mistakes in the work and subsequent data of Ptolemy that had been in use for many years.