born in modern Turkey; also known by the Latinized name Albategnius. He was one of the first Arab astronomers to grasp the importance of accurate observations. He produced a set of tables, including a catalogue of star positions more accurate than those in Ptolemy’s Almagest, that was to influence medieval European astronomers. Al-Battānī refined the values of the precession of the equinoxes, the obliquity of the ecliptic, and the length of the tropical year, and found that over the course of the year the Earth–Sun distance varies.