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Hasan Ibn al-Haytham, Father of Modern Optics

World Yen Doran 21-Jan-2020
Cropped version of the frontispiece of Johannes Hevelius, Selenographia, depicting Ibn al-Haytham (Alhazen). Credit: CC BY

Can you imagine a smartphone without a camera? Yet how many of you know the history of optics in the Islamic World? Without the input of Hasan Ibn al-Haytham, a Muslim scientist, we might never have had such a thing as a camera.

Ḥasan Ibn al-Haytham (Latinized as Alhazen, c. 965 – c. 1040) was among the greatest physicists, mathematicians, and astronomers of the Medieval period. A polymath, he was also a prolific philosopher and theologian.

Known as “the father of modern optics” he made an important contribution to our understanding of visual perception,  his most celebrated treatise being the Kitāb al-Manāẓir (“Book of Optics”), written during 1011–1021.

Born in Basra, he spent most of his productive period in Fatimid Cairo where he taught many noble families and published his work.

Al-Haytham was the first to show that vision is made possible by light reflecting from an object before passing inside the eye. He also discovered that vision takes place in the brain, rather than in the eyes.

Further, he can be credited with developing the scientific method, which maintains that hypotheses must be supported experiments and observable procedures, centuries before Renaissance scientists. He laid the groundwork for the modern science of physical optics.

In his study of motion, Al-Haytham discovered principle of inertia. He contributed to celestial physics and the science of statics as well as perfroming revolutionary research in optics and establishing it as a new science.

He studied the structure of the eye and correctly described the process of vision in the Kitab al-Manazir. As well, it contains the oldest existing diagram illustrating the eye and its connection to the central nervous system.

The book was copied at Basra in 1083, and altered and adapted by Al-Hazen’s Persian commentator, Kamal al-Din al-Farisi. The English translation of his description of the parts is still used today: retina, cornea, vitreous humour, and aqueous humour.

The book comprises seven volumes and has been ranked alongside Isaac Newton’s “Philosophiae Naturalis Principia Mathematica” as one of the most influential books ever written in physics, which drastically transformed the understanding of light and vision.

Because of his deep understanding of how the eye works and his ability to compare it to the camera obscura, he was able to study light itself, improving upon many earlier theories of light refraction and proposing his own theories about how colours were created.

He demonstrated that Ptolemy’s law that the angle of incidence is proportional to the angle of refraction is true for small angles only, and discarded the popular belief of the day that rays of light travelled from external objects into the eye and not the opposite way. He regarded eye as a passive receptor of light. His work on optics form is the first major advance after Euclid and Ptolemy, and in visual physiology after Gelen.

Another significant idea he contributed to was that light is a movement that admits variable speed, which is less in denser bodies. This was the beginning of colour theory.

Al-Haytham wrote as many as 200 books, although only 55 have survived. Some of his treatises on optics survived only through Latin translation. During the Middle Ages his books on cosmology were translated into Latin, Hebrew and other languages.

The impact crater Alhazen on the Moon is named in his honour, as was the asteroid 59239 Alhazen.In honour of Alhazen, the Aga Khan University (Pakistan) named its Ophthalmology endowed chair as “The Ibn-e-Haitham Associate Professor and Chief of Ophthalmology”.

Alhazen, by the name Ibn al-Haytham, is featured on the obverse of the Iraqi 10,000-dinar banknote issued in 2003, and on 10-dinar notes from 1982.The 2015 International Year of Light celebrated the 1000th anniversary of the works on optics by Ibn Al-Haytham.

In short, this Muslim scientist is responsible for some of the most amazing discoveries in history that have contributed to many subjects of science, including but not limited to physics, astronomy, and mathematics.

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