Arab physicist and pioneer of optics
Alhazen, also known as al-Basri, meaning that he came from the city of Basri in present day Iraq but he is also know as al-Misri indicating that he originated from Egypt. Little is know of his personal life but he did write an autobiography in 1027 which survives to this day, but deals mainly with his science. Early in his life he studied the conflicting religious views of the time and came to the realization that none of them represented the truth.
One of Alhazen major works was Optics, dealing with lenses, mirrors, the eye, colour and even camera obscura (pinhole camera). Up to this time, the ancient Greeks like Euclid and Ptolemy believed that light was emitted by the eye but Alhazen stated that light reflected off objects and the light rays entered the eye.
At the time, the Nile had a devastating annual flood and Alhazen had the idea to regulate the flow of water down the Nile. Egypt at that time was ruled by al-Hakim the Fatimid caliph, he requested Alhazen to come to Egypt and carry out the changes to the Nile. Alhazen made a survey of the Nile and realized that it was not possible to regulate the floods. Fearing for his life from the hand of al-Hakim he decided to pretend to be mad and was confined to his house until the death of al-Hakim in 1021.
Caliph – Al-Hakim
Al-Hakim was highly eccentric, for example he ordered the sacking of al-Fustat, he ordered the killing of all dogs since their barking annoyed him, and he banned certain vegetables and shellfish. Apart from this he was a patron of the sciences employing top quality scientists such as the astronomer Ibn Yunus.
Sometimes the moon appears bigger in the sky when it is closer to the horizon. Alhazen realized that objects like trees on the horizon fool our brains into thinking that the moon is getting bigger. When the moon is high in the sky we don’t have a reference on the ground to compare it with therefore it looks smaller.