Astronomy then developed in India from about AD 400. Greek science also came to Islam through Persia. In 773, a man from India appeared before al-Mansur, the Caliph of Baghdad. This man knew the stars and could calculate eclipses. The caliph ordered that the Indian books be translated into Arabic.
Good maps mean good measurement of latitude and longitude.
Without accurate portable clocks, longitude can only be found by sighting a star in two different places at the same time. A lunar eclipse gives astronomers in two places a natural way of adjusting their clocks to the same time. The first astronomical tables were published in the next century by the scientist and mathematician al-Khwarizmi . They were used to find days of new moon, rising and setting times of the sun, moon, and planets, and to predict eclipses. Because they made these calculations easier, the tables served the same function as today s computers.