is the foundation of the modern study of medieval Islamic astronomy. (, “The book of the science of the ascensions of the signs of the zodiac in the spaces between the quadrants of the celestial sphere”) may have been about calculations relating to the zodiac. The work is mentioned in a work by Ibn al-Nadim, and is probably identical with chapter 55 of al-Battānī's . It provided methods of calculation needed in the astrological problem of finding (directio). Other works ("On the astrological indications of conjunctions and eclipses") is a treatise on horoscopes and astrology in connection with conjunctions of Saturn and Jupiter that occurred during the earliest period of Islam. The extant manuscript is held in the İsmail Saib Library at Ankara University. (, "Commentary on Ptolemy's Tetrabiblos") is a commentary on the in the version of Abu as-Salt. Al‐Battānī mentions two earlier treatises that are likely identical to two chapters of the . It is extant in the manuscripts Berlin Spr. 1840 (Ahlwardt #5875) and Escorial árabe 969/2. (, "Four discourses") was a commentary on Ptolemy’s , known as the . The 10th-century encyclopedist Ibn Nadim in his , lists al-Battānī among a number of authors of commentaries on this work. (, "Knowledge of the rising-places of the zodiacal signs"). (), an astrological treatise on the four "quarters of the sphere". Legacy Medieval period The was renowned by medieval Islamic astronomers; the Arab polymath al-Bīrūnī wrote ("Elucidation of genius in al‐Battānī's Zīj"), now lost. Al-Battānī's work was instrumental in the development of science and astronomy in the west. Once it became known, it was used by medieval European astronomers and during the Renaissance. He influenced Jewish rabbis and philosophers such as Abraham ibn Ezra and Gersonides. The 12th-century scholar Moses Maimonides, the intellectual leader of medieval Judaism, closely followed al-Battānī. Hebrew editions of the were produced by the 12th-century Catalan astronomer Abraham bar Hiyya and the 14th-century French mathematician Immanuel Bonfils. Copernicus referred to "al-Battani the Harranite" when discussing the orbits of Mercury and Venus. He compared to his own value for the sidereal year with those obtained by al-Battānī, Ptolemy and a value he attributed to the 9th-century scholar Thabit ibn Qurra. The accuracy of al-Battānī's observations encouraged Copernicus to pursue his ideas about the heliocentric nature of the cosmos, and in the book that initiated the Copernican Revolution, the , al-Battānī is mentioned 23 times. 16th