Ibn al-Haytham
Abū ʿAlī al-Ḥasan ibn al-Haytham (c. 965–c. 1040), known in Latin Europe as Alhazen, was a mathematician, astronomer, and physicist who worked in Basra and in Fatimid Cairo. His seven-volume Kitāb al-Manāẓir (Book of Optics), composed around 1011–1021, argued that vision occurs when light rays reflected from objects enter the eye — overturning the ancient emission theory of Euclid and Ptolemy — and combined systematic experiment with geometrical reasoning. He wrote on reflection and refraction, discussed the camera obscura, framed the problem of reflection on curved mirrors that still bears his Latinized name, and criticized Ptolemy's astronomy. His Optics reached the Latin West in translation and shaped the optics of Roger Bacon, Witelo, and Johannes Kepler. His life is documented only through late and contradictory accounts — notably the 13th-century historian Ibn al-Qifṭī — so the Nile episode, the feigned madness, and popular claims that he 'invented the scientific method' must be handled with care.