c. 1260-c. 1320

Islamic mathematician and optical thinker who made important contributions to number theory and the optics of the rainbow. A pupil of the astronomer and mathematician Qutb al-Din al-Shirazi (1236-1311), he is best known for his nearly correct explanation of the optical mechanism of the rainbow, which followed from his exhaustive critical study of ibn al-Haytham's (965-1039) great Optics and writing his own Revision of Optics. He correctly noted the fundamental idea that the appearance of a rainbow was due to two refractions of light on a cloud droplet but he was not sure of the number of reflections and was incorrect in his explanation for the colors of the rainbow. Al-Farisi also made important contributions to number theory, introducing ideas concerning factorization and combinatorial methods.