Ibn al-Haitham Al Hazan Biography

As Europe was nearing the end of the dark ages, science flourished in the Arab world. From Baghdad to Cairo, scholars studied the science of the ancient Greeks and expanded on it with new investigations. Ibn al-Haitham Al Hazan, often referred to as Alhazen or Alhazan, was one of the great Arab experimentalists and a pioneer of optical science.

Al Hazan, who was born in 965, was commonly called al-Basri, indicating that he was from Basra, Iraq. He also was known as al-Misri, meaning "of Egypt." Although his earliest studies were of a religious nature, he soon turned to mathematics, physics, philosophy, and the works of Aristotle. The details of Al Hazan's life are unclear. According to one source, the caliph al-Hakim, who had founded the "House of Science" in Cairo, summoned Al Hazan to Fatimid, Egypt, after hearing of his plan to control the periodic flooding of the Nile River. When Al Hazan's plan failed, al-Hakim gave him a post in a government office. But fearing for his life, Al Hazan feigned insanity until the caliph's death in 1021. Other sources, however, contend that Al Hazan was a government minister in Basra, who feigned madness so as to be relieved of his duties. According to these accounts, Al Hazan did not go to Egypt until after al-Hakim's death. In either case, he spent the remaining years of his life in Cairo, teaching, writing, and earning his living by copying scientific books, until his death about 1040.

Al Hazan's most important work, Optics, consisted of seven volumes of experiments, mathematics, and inductive reasoning, without reliance on previous authorities. Euclid, Ptolemy, and other ancient Greek scientists had believed that vision resulted from light rays emitted by the eye. Al Hazan originated the theory that vision was the result of illuminated rays reaching the eye. He believed that light rays emanated in straight lines, in a spherical direction, from every point of a luminous object. He studied the properties of various types of lenses, mirrors, and magnifying glasses and conducted major studies on refraction, the angle at which light is bent when passing from one medium to another. Latin translations of Optics influenced European scientists, such as Roger Bacon, Johannes Kepler, Pierre de Fermat, and René Descartes, from the end of the twelfth century into the seventeenth century.

Al Hazan addressed the "moon illusion," the ancient question of why the sun and moon appear larger near the horizon. He suggested that objects on the horizon influence our optical perception of the moon. Although the illusion holds even at sea where there are no objects on the horizon, he was correct in considering it to be a problem of visual perception, wherein the brain is unable to accurately interpret optical information about size and distance.

Al Hazan wrote at least 92 works on mathematics, physics, and metaphysics, as well as treatises on logic, politics, religion, ethics, poetry, and music. He wrote summaries of the works of Aristotle, the Roman physician Galen, Ptolemy, and Euclid. About 20 of Al Hazan's mathematical works are extant. One of these became known as "Al Hazan's problem." This is the mathematical problem of finding the point, on a surface of a given shape, that will reflect the light from a point opposite the surface to a second point opposite the surface.

At least 20 of Al Hazan's surviving works deal with astronomy and he authored an important commentary on the Almagest, the astronomical text written by Ptolemy in the second century. Al Hazan's most famous astronomical work, On the Configuration of the World, was translated into Spanish in the thirteenth century, and from Spanish into Latin. It also was translated into Hebrew and then into Latin and influenced the astronomers of the early Renaissance.