Al-Hazen discussed the density of the atmosphere, and correctly explained the refraction of light in the atmosphere. From his studies of refraction he determined that the atmosphere has a definite height, which he calculated to be about 50 km, and also that twilight is caused by refraction of solar radiation from beneath the horizon. For his pioneering work in these areas, he became known as the Father of Optics.

Stamps issued by Malawi (2008), Pakistan (1969) and Qatar (1971) in honour of Ibn al-Haytham

At the end of the tenth century, a brilliant scientist left his home town of Basra in Iraq to pursue an ambitious project in Egypt. He had noticed how, seasonally, the river Nile flooded large parts of the delta. But in winter water levels fell so low that cultivation was almost impossible. What, he thought, if the surplus flood water could be stored and used when most needed? He devised a scheme – to regulate the Nile, so that the people could derive benefit at its ebb and flow.

His plan required building a three-way embankment dam near Aswan. He sent the proposal to the Fatimid Caliph, Imam al-Hakim in Cairo. The Caliph was so impressed that he issued a royal commission for him to come to Cairo and build the dam.

The young scientist was Ibn al-Haitham, known to the West as Al Hazen. He spent the next two decades in his laboratory in Cairo where he developed and refined the technique of experimental method; worked on spherical and parabolic mirrors, spherical aberration, the magnifying power of lenses and atmospheric refraction.

He noted how rays of light originate in the object seen and not in the eye – as commonly believed by the Greeks – and correctly explained the apparent increase in size of the sun and the moon when near the horizon. He formulated the laws of reflection and refraction and proclaimed experiment and empirical investigation the foundation of all scientific work.

“He (Ibn al-Haitham) was the greatest Muslim physicist and student of optics of all times. Whether it be in England or faraway Persia, all drank from the same fountain. He exerted a great influence on European thought from Bacon to Kepler,” wrote George Sarton in his History of Science (1927).

He wrote over 200 books on astronomy, mathematics, physics and philosophy. His greatest achievement, Kitab al-Manazir, translated into Latin in the late thirteenth century as the Book of Optics, was the first comprehensive treatment of the subject. In this work, Ibn al-Haytham refuted the theory of Euclid and Ptolemy that the eye sends out visual rays to the object of vision, arguing that the form of the perceived object passes into the eye through a transparent body (lens). The correctness of this theory was established several centuries later among European scientists. Al Hazen had a great influence on Roger Bacon and Kepler as well as other western scientists.

Ibn al-Haitham was inspired by the spirit of the Qur’an. Al-Haitham, wrote not only scientific but also religious treatises. He made two Qur’anic verses, one stating “believers should urge one another to truth” (Chapter 103: verse 1) the other that “truth claims should be tested” (Chapter 33: verse 8), the basis of his scientific work.

He wrote:

“Truth is sought for its own sake. (But) finding the truth is difficult, and the road to it is rough.”

Science, he suggested, should be based on severe criticism, and the claims of scientists themselves should be put to critical tests.

The anotomy of the eye by Kamal al-Din al-Farasi based on Ibn al-Haitham's idea

He also noted:

“God has not preserved the scientist from error and has not safeguarded science from shortcomings and faults… A person, who studies scientific books with a view of knowing the truth, ought to turn himself into a hostile critic of everything that he studies . . . He should criticize it from every point of view and in all its aspects. And while thus engaged in criticism he should also be suspicious of himself and not allow himself to be easy-going and indulgent with regard to (the object of his criticism). If he takes this course, the truth will be revealed to him and the flaws . . in the writings of his predecessors will stand out clearly.”