c. 1305-c. 1375

Arab astronomer who sought to restore uniform circular motion to planetary theory by replacing Ptolemy's eccentric deferent and equant with secondary epicycles. This eliminated a major defect of Ptolemaic lunar theory by reducing the variation of the Moon's distance. Though developed within a geocentric framework, Ibn al-Shatir's models are mathematically equivalent to those later developed by Nicolaus Copernicus; however, no direct influence has been established. Ibn al-Shatir also constructed various instruments, including sundials, astrolabes, and quadrants.