"Ibn al-Shatir’s forgotten model was rediscovered in the late 1950’s by E. S. Kennedy. .. In a preliminary work, the Commentariolus, he [Copernicus] employed an arrangement equivalent to Ibn al-Shatir's. Later, in De revolutionibus, he reverted to the use of eccentric orbits, adopting a model that was the sun-centered equivalent of the one developed at Maragha. Could Copernicus have been influenced by the Maragha astronomers or by Ibn al-Shatir? ...some of the al-Tusi material is known to have reached Rome in the 15th century (many Greek manuscripts were carried west after the fall of Constantinople in 1453), but there is no evidence that Copernicus ever saw It... . I personally believe he could have invented the method independently."