His most important astronomical treatise was kitab nihayat al-sul fi tashih al-usul ("The Final Quest Concerning the Rectification of Principles"). In it he drastically reformed the Ptolemaic models of the Sun, Moon and planets, eliminating the eccentric and equant by introducing extra epicycles.
Although his system was firmly geocentric (he had eliminated the Ptolemaic eccentrics), the mathematical details of his system were identical to those in Copernicus'sDe revolutionibus. It is unknown whether Copernicus read ibn al-Shatir.
^The model Copernicus used in his earlier Commentariolus differs in minor detail from that of ibn al-Shatir. V. Roberts and E. S. Kennedy, "The Planetary Theory of Ibn al-Shatir", Isis, 50(1959):232-234. jstor