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Ibn al-Haytham

Ibn al-Haytham

c. 965 CE–c. 1040 CE · Basra

Ibn al-Haytham (Latinized as Alhazen, after a 1572 European edition by Friedrich Risner) was one of the most influential scientists of the medieval Islamic world. His full name is given as Abu Ali al-Hasan ibn al-Hasan ibn al-Haytham. He was born around 965 CE (354 AH) in Basra, in present-day Iraq, then under Buyid rule, and is traditionally reported to have held an administrative post there before turning to mathematics.

According to a widely repeated account, the Fatimid caliph al-Hakim bi-Amr Allah summoned him to Egypt to study regulating the Nile's annual flood with a dam near the site of modern Aswan. Tradition holds that after fieldwork convinced him the scheme was unworkable, he feared the caliph's anger and feigned madness, living under a form of house arrest until al-Hakim's death around 1021; this dramatic episode is reported by later sources ("legend has it," "he is said to") rather than firmly attested. During and after this period in Cairo he composed his seven-volume Kitab al-Manazir (Book of Optics).

In that work he argued that vision results from light entering the eye from objects (rejecting older "emission" theories), and tested claims about reflection, refraction, and the camera obscura through controlled observation—an approach later writers credit as an early form of experimental method. He spent his last years in Cairo, near the al-Azhar mosque, supporting himself by copying and writing texts. He died around 1040 CE (c. 430 AH); sources give 1039, 1040, or 1041.

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Did you know?

  • He built optics on experiment, in a Cairo dark room

    Ibn al-Haytham (c. 965–1040), writing his Book of Optics in Cairo around 1011–1021, argued that vision results from light entering the eye and gave one of the first clear descriptions of the camera obscura, the darkened chamber that projects an inverted image through a small hole. Translated into Latin as De aspectibus, his work later informed European students of light including Johannes Kepler (1571–1630).

    How we know

    Ibn al-Haytham b. c.965 Basra, d. c.1040/1041 Cairo; Kitāb al-Manāẓir (Book of Optics) written in Cairo c.1011–1021; intromission theory + dark-room (al-bayt al-muẓlim) camera-obscura description; Latin De aspectibus (late 12th–early 13th c.) influenced Bacon, Witelo, Kepler (1571–1630, optical work c.1604).

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Stop 1 of 2965Born

BasraבצרהSouthern Iraq — Persian Gulf port

What they did here

Ibn al-Haytham was born around 965 CE (c. 354 AH) in Basra, then under Buyid rule; the nisba 'al-Basri' reflects this birthplace. He is traditionally reported to have held an administrative post and to have been known there for applied mathematics, though the details of his Basra years are thinly documented.

About Basra

Basra hosted one of the oldest Babylonian-Jewish communities, with continuous residence from the Talmudic era until the mid-20th century. R. Yosef Hayyim of Baghdad (Ben Ish Hai) maintained extensive correspondence with the Basra rabbinic court.

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The world in their lifetime

Thinkers and teachers of other traditions whose lives overlapped with Ibn al-Haytham’s — a glimpse of the wider world they lived in. Drawn purely from recorded birth and death years.

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