Abu 'Ali al-Hasan ibn al-Haytham
The Arab physicist, astronomer, and mathematician Abu 'Ali al-Hasan ibn al-Haytham (ca. 966-1039), or Alhazen, established the theory of vision that prevailed till the 17th century. He also defended a theory of the physical reality of Ptolemy's planetary models.
Al-Hasan was born at Basra in southern Iraq, where he must have received all his education. He gained sufficient fame for his knowledge of physics in his youth that he was called to Egypt by the Fatimid ruler al-Hakim to attempt to regulate the flow of the Nile. Failing in this effort, he was disgraced and established himself as a copyist of mathematical manuscripts; there still exists in Istanbul a manuscript of the Banu Musa's version of Apollonius's Conics copied by him in 1024. He continued to practice the scribal art in Cairo for the remainder of his life.
He did not cease to pursue his scientific studies, however, and published a large number of highly original works. He produced two catalogs of his own work, which are preserved by Ibn abi Usaybia. The first of these, compiled in 1027, comprises 25 books on mathematics and 44 on physics and metaphysics, including On the Structure of the World. The second, supplementary catalog was complied in 1028.
Work in Astronomy
The primary interest of al-Hasan was the explanation of phenomena by both mathematical and physical hypotheses. His interest in astronomy was motivated by the discrepancy between the Aristotelian physical and mechanistic model of the celestial spheres and the Ptolemaic mathematical model. On the Structure of the World, of which only the Latin translation has been published, describes the Aristotelian sublunar world of four elements and the Ptolemaic celestial spheres in all their complexity (his only change is to accept the theory that the solar apogee is fixed with respect to the fixed stars) as if they were material. He inserts a discussion of the perception of lunar and solar eclipses based on the assumption that the moon and sun are solid physical bodies.
This problem al-Hasan takes up again in On the Light of the Moon, in which he refutes the ancient theory that the moon reflects the sun's light like a mirror.