Ibn al-Haytham, known to the west as Alhazen, was born in Basra where he studied mathematics and other sciences. He flourished in Egypt under al-Hakim (996-1220 CE) and died in Cairo in 430H (1039 CE) or soon after. The first great physicist and the greatest investigator of optics in the history of science, he wrote about 200 works on mathematics, physics, astronomy and medicine. An accurate observer, experimenter and a great theoretician, he wrote a number of treatises on geometry also which he used in his studies on optics. The problems of optics which he solved in consonance with geometry gave rise to such unique geometrical problems that associated his name with them forever, the problems are known as the ‘problems of Alhazen.’ As a physician, he wrote commentaries on Aristotle and Galen.
Though Ibn al-Haytham wrote numerous works on optics and related phenomena like the atmosphere, his Magnum opus on the subject is Kitab al-Manazir (Optical Thesaurus), which had great influence on Western science. His highly advanced methods in performing experiments as explained in the book show his scientific outlook. His competence in medicine as well as in physics is obvious from the book. He begins with the study of anatomy and physiology of the eye and traces the optic nerves beginning from the brain to the eye of which the entire structure he masterly describes pointing out the function of each part of the eye in the process of vision. He explains the inter-relationship between different parts of the eye and how the eye acts as a unitary organ and dioptric system during the process of vision. Ibn al-Haytham, like Ibn Sina and several other Muslim scientists, did not hold that rays issue from the eye but on the contrary they issue forth from the object and enter our eyes so that we are able to see the object. Ibn al-Haytham was the first to refute the doctrine of Euclid and Ptolemy that the eyes emit rays to receive the images of objects to see them. This reversal of the doctrine heralded new fields of research and laid the foundation of modern optics. His vision of the eye lens to be the sensitive part that focuses the incoming rays on the retina established the fundamental basis which eventually led to the discovery of magnifying lenses in Italy.
The earliest scientific accounts of atmospheric refraction given by Ibn al-Haytham that contains geometrical solution to the problem of finding the focal point of concave mirror could be possible because of his extensive use and sound knowledge of geometry and mathematics. Theorem of radical axis and many other original theorems were discovered and solved by him. The problem of the aplanatic surface for reflection was solved through his sound mathematical knowledge. Halo, rainbow, eclipses, shadows, problems of spherical and parabolic mirrors and doctrines related to all of them owe to the sound mathematical and geometrical knowledge of Ibn al-Haytham. His tables of corresponding angles of incidence and refraction show how he nearly discovered the laws of the ratio of sins for any given pair of media, later attributed to Snell. He investigated the twilight relating it to atmospheric refraction by estimating the sun’s height to be 19 degrees below the horizon. The figures generally accepted now are 18 degrees.