Abū 'Alī al-Hasan ibn al-Hasan ibn al-Haytham as shown on the obverse of the 1982 Iraqi 10 dinar note
Abu Ali al-Hasan (Alhazen) (965-1039 AD) was a Muslim mathematician and astronomer born in Basra. He made numerous discoveries in optics, astronomy, and mathematics, and wrote commentaries on Aristotle, Ptolemy, and Euclid. He also wrote on methods of discovery. He was the first to argue that the centre of optical activity in the perception of the object was the object itself, that when illuminated produces rays of light in every direction, contrary to the widely-held theory that the eye itself is the source of emissions, or the Aristotelian theory that in the presence of light the eye perceives an object by taking on its form.
Alhazen’s investigations into human visual perception led him to the camera obscura and to image inversion in the eye. He advocated the use of mathematical and quantitative methods in determining phenomena, particularly visual phenomena. He was led in this way to investigations of fourth order equations in algebra, and to techniques to find their roots. His commentary on Ptolemy’s astronomy insisted that his models of moons orbiting on epicycles about the Earth should be understood realistically, rather than as abstract ideas, and as accountable to universal laws. His Model of the Motions of Each of the Seven Planets was written in about 1038; only the introduction has survived. Whilst he embraced Ptolemy’s geocentric system, he eliminated his use of the equant. In this he was followed by Copernicus, who saw in the elimination of the equant the chief virtue of his heliocentric system.