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Hassan Ibn Al Haitham was a physicist, mathematician and astronomer from the Islamic Golden Age and is known as the father of modern optics. He made significant contributions to the principles of optics and visual perception. Born in Basra, he spent most of his life in the Fatimid capital of Cairo in the neighborhood of the famous University of Al Azhar, and lived from the proceeds of his literary work until his death. His most influential work is titled the book of optics 1011-1021. Paved the way for the modern science of physical optics and was cited by scientists and physicists like Isaac Newton, Johannes Kepler, Christiaan Huygens and Galileo Galilei. During the Middle Ages, his books on cosmology were translated into English, Latin and other languages. Ibn Al Haytham was the first to correctly explain the theory of vision and to argue that vision occurs in the brain. He made major contributions to catopteryx and dioptrics by studying reflection, refraction and nature of images formed by light rays. He was an early advocate of the concept that hypotheses must be supported by experiments and mathematical reasoning five centuries before Renaissance scientists. Born in Basra, he spent most of his life in the Fatimid capital of Cairo in the neighborhood of the famous University of Al Azhar, and lived from the proceeds of his literary work until his death. Book of Optics Alhazin's most famous work is his seven volume treatise on optics, Kitab Al Manazir Book of Optics. Written in it, Ibn Al Haytham was the first to explain that vision occurs when light reflects from an object and then passes to one's eye. He also argued that vision occurs in the brain, pointing to observations, that it is subjective and affected by personal experience and differs from one person to another. Theory of Optics his most significant achievement was to come up with a theory that successfully combined parts of the mathematical ray arguments of Euclid, the medical tradition of Galen and Aristotle's intromission theories. What he needed was for each point on an object to correspond to one point only on the eye. He tried to resolve this by asserting that the eye would only see perpendicular rays from the object. For any one point on the eye, only the ray that reached it directly without being refracted by any other part of the eye would be detected. He argued, using a physical analogy, that perpendicular rays were more powerful than oblique rays in the same way that a ball thrown directly at a board might break the board. He also argued that a ball thrown sideways at the board would bounce off. Perpendicular rays were stronger than refracted rays and it was only perpendicular rays which were perceived by the eye, and there was only one perpendicular ray that would enter the eye and all these rays would converge on the eye's center. This allowed him to solve the issue of each point on an object, sending many rays to the eye, and the confusion could be resolved. He later explained in book seven of the Optics that other rays would be refracted through the eye and seen as if perpendicular. No other theory of the time was so detailed, and it was extremely influential, especially in Western Europe. His theory inspired much activity in optics between the 13th and 17th centuries. Kepler's theory of the retinal picture was built directly on the conceptual framework of Ibn Al Haytham theology Ibn Al Haytham was a Sunni Muslim. Alhazin wrote a book called Finding the Direction of Qibla by Calculation, in which he discussed finding the Qibla mathematically. The Qibla is a direction towards the Kabba in Mecca, Saudi Arabia, which is used by Muslims in various religious contexts, particularly the direction of prayer for the salah. Unconscious Interference Al Haytham explains the organ does not sense the forms that reach it from the visible objects until after it has been affected by these forms. This means that the last perception of color and light takes place at a time following that in which the form arrives from the surface of the organ to the cavity of the common eye. Color Constancy Ibn Al Haytham explained color constancy by observing that the light reflected from an object is modified by its color. He explained that the quality of the light and the object's color are mixed and the visual system separates light and color. In Book two, chapter three, he explains again the light does not travel from the colored object to the eye unaccompanied by the color, nor does the form of the color pass from the colored object to the eye unaccompanied by the light. Neither the form of the light nor that of the color existing and the colored object can pass except as mingled together, and the last sentient can only perceive them as mingled together. Nevertheless, the sentient perceives that the visible object is luminous luminous and that the light seen in the object is other than the color and that these are two properties. Legacy Ibn Al Haytham made important contributions to optics, number theory, geometry, astronomy and philosophy. A crater is named after the Arab Muslim scientist Ibn Al Haitham and was named Alhazen is a lunar impact crater that is located near the eastern side of the moon. He is also featured on the Iraqi 10,000 dinar banknote issued in 2003 and on 10 dinar notes from 1982. The 2015 International Year of Light by UNESCO celebrated the 1,000th anniversary of the works on optics by Ibn Al Haytham. Conclusion HJJ Winter, a British historian of science, summing up the significance of Ibn Al Haytham in the history of physics after the death of Archimedes, no really great physicists appeared until Ibn Al Haitham. If, therefore, we confine our interest only to the history of physics, there is a long period, over 1200 years, during which the Golden Age of Greece gave way to the era of Muslim scholasticism and the experimental spirit of the noblest physicist of antiquity lived again in the Arab scholar from Basra.
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