   During the European Middle Ages, the Islamic world was the center of astronomical thought and activity. During the ninth century several aspects of Ptolemy’s solar theory were recalculated. Ibn al-Haytham in the tenth-eleventh century wrote a scathing critique of Ptolemy’s work: “Ptolemy assumed an arrangement that cannot exist, and the fact that this arrangement produces in his imagination the motions that belong to the planets does not free him from the error he committed in his assumed arrangement, for the existing motions of the planets cannot be the result of an arrangement that is impossible to exist” (quoted in Rosen 1984, 174). Swerdlow and Neugebauer (46–48) stressed that the thirteenth-century Maragha school was also important in finding errors and correcting Ptolemy: “The method of the Maragha planetary models was to break up the equant motion in Ptolemy’s models into two or more components of uniform circular motion, physically the uniform rotation of spheres, that together control the direction and distance of the center of the epicycle, so that it comes to lie in nearly the same position it would have in Ptolemy’s model, and always moves uniformly with respect to the equant.” They found that Copernicus used devices that had been developed by the Maragha astronomers Nasir al-Din Tusi (1201-1274), Muayyad al-Din al-Urdi (d. 1266), Qutb al-Din al-Shirazi (1236-1311), and Ibn al-Shatir (1304–1375). In addition, Ragep, 2005, has shown that a theory for the inner planets presented by Regiomontanus that enabled Copernicus to convert the planets to eccentric models had been developed by the fifteenth-century, Samarqand-trained astronomer ali Qushji  (1403–1474).[4] 