diversity and variety of hayʾa books in islamic civilization

once the greek astronomy's most worthy masterpiece, ptolemy’s almagest, was translated into arabic, many scientific works were produced in islamic civilization. the genre known as hayʾa, which deals with the cosmological aspect of astronomy, gradually seperated itself from other astronomical branches. while these branches were in relation with each other, their goals were different. computational astronomy, known as science of “zijes”, was developed to produce arithmetical tables to forecast the position of the heavenly bodies in any given time. the science of astronomical instruments and science of timekeeping were two of the other branches of astronomy. science of hay'a uaully presents a non-technical descrpition of the large scale structure of the universe, i.e. the earth and its position, configuration and size of the celestial spheres and the planets. in this article almost all of the hayʾa books of islamic civilization are listed and classified. based on their manuscripts we mention their scientific specifications and compare them with each other. the golden age of these works in 12th century is studied in more details.