From: The Journal of the American Oriental Society | Date: April 1, 1997| Author: Kennedy, E.S. | COPYRIGHT 1997 American Oriental Society. This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan.  All inquiries regarding rights should be directed to the Gale Group.Copyright information

Medieval Muslim astronomers criticized the models of planetary motion invented by Ptolemy (fl. 150 A.D.) on the grounds that they violated the principle of uniform circularity. This held that the position of any celestial body must be the product of a combination of uniform circular motions. In the thirteenth century, Mu ayyad al-Din al- Urdi (d. 1266), Nasir al-Din al-Tusi (d. 1274), and Qutb al-Din al-Shirazi (d. 1311), all three working at the Maragha observatory in northwestern Ir...