Known as Arzachel to the western world, Ibrahim al-Zarqali was a leading Muslim astronomer who left an indelible mark on the global stage. One of the craters on the Moon carries his name. He built a water clock, perfected the astrolabe, and corrected Ptolemy and al-Khwarizmi's geographical data. Copernicus also made mention of al-Zarqali while explaining his heliocentric theory. He was also regarded as one of the leading numerologists of his time.