Theon of Alexandria

Theon of Alexandria (/ˌθiːənˌ -ɒn/; Ancient Greek: Θέων ὁ Ἀλεξανδρεύς; c. AD 335 – c. 405) was a Greekscholar and mathematician who lived in Alexandria, Egypt. He edited and arranged Euclid's Elements and wrote commentaries on works by Euclid and Ptolemy. His daughter Hypatia also won fame as a mathematician.

Little is known about the life of Theon. He made predictions and observances of solar and lunar eclipses in 364 which show he was active at that time, and he is said to have lived during the reign of Theodosius I (379–395). The biographical tradition of the tenth century Byzantine Suda defines Theon as "the man from the Mouseion"; however, both the Library of Alexandria and the original Mouseion were probably destroyed by the fourth century, although there may have been a new Mouseion established on a different site. Theon was the father of the mathematician Hypatia who was killed by a Christian mob in 415 during a period of religious and sectarian conflict. Theon dedicated his commentary on the Almagest to a boy named Epiphanius, who may have been his son.

A lunar crater, Theon Junior, now bears Theon's name.

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