Fatimid supremacy on the seas was possible due to their knowledge of astronomy and geography. The Fatimid Caliphs were great patrons of science and learning, thus encouraging research in astronomy and geography. There were big observatories in Cairo where scholars could follow the movement of the stars. Ibn Yunus, who worked in these observatories, is considered one of the greatest astronomers of the Islamic World. An astrolabe (instrument for measuring altitude of the sun and stars at sea) developed in the time of Imam Moiz is still kept in the British Museum in London. Geography formed an important part of the curriculum at the Al-Azhar. The Caliph Moiz was greatly interested in geography and commended a piece of silk to be made at Tustar in Persia, representing, in gold and colours, a map of the world, which cost him 22,000 Dinars

Sherali Alladina, “Ismaili Navigation”, Ismaili Mirror, Dec ’74, p.11

http://www.ancientworlds.net/aw/Post/667573

http://www.lacma.org/islamic_art/ema.htm