Alhazen the mathematician
Abu Ali al-Hasan Ibn al-Haytham
Abu Ali al-Hasan Ibn al-Haytham, named Alhazen, is a mathematician, physicist, and philosopher born in Basra, in ancient Iraq. He is the first physicist to understand why the moon and the sun appear larger when they are close to the horizon. He was also the first to understand that if we saw the Moon, it was because it was lit by the sun. Likewise, and unlike Ptolemy, he understands that our eyes do not send lights. If we see objects, it is because they are lit by light (from the sun) and that it is reflected towards our eyes.
Alhazen, a scientist yes, a madman no!
Legend has it that the Caliph asked him for help in building a huge dam on the Nile, a great river in Egypt. Deeming the work unfeasible and out of fear of the Caliph’s anger, Alhazen pretended to be mad. With this stratagem, he was allowed to stay at home, which he did until the death of the Caliph. During this time, he kept himself busy intelligently. Very gifted in applied mathematics, he wrote his book on optics. A book that allowed him to earn an income.
Lights on Alhazen's works
Our friend was not idle during his career and he discovered many properties of light. In his treatise, he explains that light travels in a straight line and that its speed varies according to the medium.
He explains the laws of light reflection and tries to understand the mechanism of colors. The most incredible thing is that he validates each of his hypotheses through scientific experiments. A modern method which seems normal today but which was far from being usual in the 11th century.