Some of the great Western astronomers were al-Farghani (Abu'l-Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani), and al-Khwarizmi (Abu Ja'far Muhammad ibn Musa Al-Khwarizmi).
al-Khwarizmi (Abu Ja'far Muhammad ibn Musa Al-Khwarizmi) was one of the greatest Islamic astronomers. He lived in the 9th century. al-Khwarizmi invented algebra which he based the system on the Indian numbers borrowed by the Arabs known as arabic numerals. He developed this mathematical device without mathematical expressions but completely in words. He performed a number of eclipse calculations and calculated the positions of the Moon, Sun and planets. He also made an early world map by constructing a table of longitudes and latitudes of 2,402 cities and landmarks.