Qushji's most important astronomical work is Concerning the Supposed Dependence of Astronomy upon Philosophy. Under the influence of Islamic theologians who opposed the interference of Aristotelianism in astronomy, Qushji rejected Aristotelian physics and completely separated natural philosophy from Islamic astronomy, allowing astronomy to become a purely empirical and mathematical science. This allowed him to explore alternatives to the Aristotelian notion of a stationary Earth, as he explored the idea of a moving Earth instead (though Emilie Savage-Smith asserts that no Islamic astronomers proposed a heliocentric universe). He found empirical evidence for the Earth's rotation through his observation on comets and concluded, on the basis of empirical evidence rather than speculative philosophy, that the moving Earth theory is just as likely to be true as the stationary Earth theory.