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(;  ), also known by the LatinizationAlhazen or Alhacen, was an Arab or Persian scientist, mathematician, astronomer, and philosopher. Ibn al-Haytham made significant contributions to the principles of optics, astronomy, mathematics, meteorology, visual perception, and the scientific method. He was the first to explain that vision occurs when light bounces on an object and then is directed to one's eyes. He spent most of his life close to the court of the Fatimid Caliphate in Cairo and earned his living authoring various treatises and tutoring members of the nobilities.

Ibn al-Haytham is widely considered to be one of the first theoretical physicists, and an early proponent of the concept that a hypothesis must be proved by experiments based on confirmable procedures or mathematical evidence—hence understanding the scientific method 200 years before Renaissance scientists.

In medieval Europe, Ibn al-Haytham was honored as (the "Second Ptolemy") or simply called "The Physicist". He is also sometimes called al-Baṣrī after his birthplace Basra in Iraq, or al-Miṣrī ("of Egypt").

Alhazen (crater)

Alhazen is a lunar impact crater that lies near the eastern limb of the Moon's near side. Just to the south-southeast is the crater Hansen, and to the west is the Mare Crisium. The rim of Alhazen is nearly circular, but appears highly oblong when viewed from the Earth due to foreshortening. The inner walls and the crater floor are rugged and irregular. A low ridge joins the south rim of Alhazen with the nearby Hansen. The crater is named after the Arab Medieval scientist, Ibn al-Haytham.