Ibn al-Haytham Born
Ibn al-Haytham, known in Latin Europe as Alhazen, was born around 965 AD in Basra, in what is now southern Iraq. He became one of the most influential figures in the history of science. His Book of Optics, written in the early eleventh century, transformed the understanding of vision and light, and it set a standard for testing ideas through experiment that later thinkers would build on. The birth year is approximate, since medieval biographical records are imprecise, but it is traditionally placed in the mid-960s.
He was born into a world in which Baghdad's Abbasid court supported a vast movement to translate and extend Greek, Persian, and Indian learning. Basra was a thriving intellectual center, and Ibn al-Haytham grew up with access to works by Euclid, Ptolemy, Galen, and Aristotle. Earlier theories of vision disagreed sharply. Some thinkers, including Euclid and Ptolemy, argued that the eye sends out rays to touch objects, while Aristotle and others held that objects send something into the eye. Ibn al-Haytham would later help settle that debate.
Accounts of his life, written generations later, say he worked in government service before moving to Fatimid Cairo. One often-repeated story claims he promised to regulate the flooding of the Nile, realized the task was impossible, and feigned madness to escape the caliph's anger, spending years under house arrest. Historians treat this tale cautiously, as it comes from later sources. What seems clear is that he spent much of his mature career in Cairo, copying texts and writing on mathematics, astronomy, and optics.
His Book of Optics argued that vision occurs when light reflected from objects enters the eye. He studied the eye's anatomy, reflection, refraction, shadows, and the camera obscura, using carefully designed experiments to test his claims. He insisted that conclusions should rest on observation and reasoning rather than authority alone. Calling him the inventor of the scientific method, as is sometimes done, overstates the case, since others before him also valued empirical inquiry, but his systematic approach was unusually rigorous for his time.
The book's legacy was long and wide. Translated into Latin around the twelfth or thirteenth century, it influenced European scholars such as Roger Bacon, Witelo, and later Johannes Kepler, whose work on the retinal image drew on this tradition. Its ideas helped lay groundwork for the development of lenses, spectacles, and eventually modern optics. Today Ibn al-Haytham is honored across the world as a foundational figure in physics, and the United Nations marked 2015 as the International Year of Light partly in recognition of his contributions.