Alhazen, Ibn al-Haytham (c. 965-1038)

(Abu al-Hassan ibn al-Haytham) Arab scientist, author of the Kitab al-Manazir/Book of Optics, translated into Latin as Opticae thesaurus (1572). For centuries it remained the most comprehensive and authoritative treatment of optics in both East and West. Alhazen was born in Basra (now in Iraq). He made many contributions to optics, contesting the Greek view of Hero and Ptolemy that vision involves rays that emerge from the eye and are reflected by objects viewed. Alhazen postulated that light rays originate in a flame or in the Sun, strike objects, and are reflected by them into the eye. He studied lenses and mirrors, working out that the curvature of a lens accounts for its ability to focus light. He measured the refraction of light by lenses and its reflection by mirrors, and formulated the geometric optics of image formation by spherical and parabolic mirrors. He constructed a camera obscura. He also tried to account for the occurrence of rainbows, appreciating that they are formed in the atmosphere, which he estimated extended for about 15 km/9 mi above the ground.