1201-1274
Astronomer

Life. Born in Tus, Khorasan, al-Tusi became astrologer to the Ismaili governor of Persia at a time when the Mongol armies were advancing on the Muslim empire. After the Mongol ruler Hulagu conquered Persia, al-Tusi offered his services to him, hoping to diminish the usual destruction of libraries that accompanied Mongol onslaughts. He was able to gain the confidence of Hulagu, who supported al-Tusi's every scientific effort, including the establishment of the Maraghah observatory, where al-Tusi headed a large team of astronomers and mathematicians.

Writings. At this observatory al-Tusi and his team created the Ilkhanid astronomical star tables, which later had a major influence on European Renaissance studies of astronomy. Al-Tusi also wrote extensively on how the movements of the earth, sun, and moon were related, a study that led him to a scientific explanation for eclipses and a means of determining the...