c. 820-after 861

Due to some confusion over his name, a few historians suggest the lives of a father and son have been mingled. An astronomer-astrologist he also supervised the building of a canal (the Great Nilometer) at Cairo. Legend has it that he made the canal too high at one end preventing water flow. He wrote about sundials, astronomy, the astrolabe, and commentaries on Ptolemy, but most of his writings are now lost. His surviving astronomical work, Elements, was translated into Latin twice, and was very popular.