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Ibn al-Haytham (ĭbˈən äl-hĪth-ämˈ) [key] or Alhazen ălhəzĕnˈ, 965–c.1040, Arab mathematician. Ibn al-Haytham was born in Basra, but made his career in Cairo, where he supported himself copying scientific manuscripts. Among his original works, only those on optics, astronomy, and mathematics survive. His *Optics,* which relied on experiment rather than on past authority, introduced the idea that light rays emanate in straight lines in all directions from every point on a luminous surface. Latin editions of the *Optics,* available from the 13th cent. on, influenced Kepler and Descartes. As a cosmologist, al-Haytham tried to find mechanisms by which the heavenly bodies might be shown to follow the paths determined by Ptolemaic mathematics. In mathematics, al-Haytham elucidated and extended Euclid's *Elements* and suggested a proof of the parallel postulate.

*The Columbia Electronic Encyclopedia,* 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.