Theon of Alexandria

Theon of Alexandria (Ancient Greek: Θέων ὁ Ἀλεξανδρεύς; c. 335-c. 405) was a Greek mathematician and astronomer, known especially for his edition of Euclid's Elements.

Semblance

Theon settled in the Egyptian city of Alexandria, where he wrote a vast commentary on Ptolemy's Almagest and on a Catoptrica, which was based on works by Archimedes and Heron. He is also credited with the recasting of the Elements and of Euclid's Optics.

The Last Philosopher of the Second Library of Alexandria

Theon, father of Hypatia, was the last director or curator of the so-called second Library of Alexandria (a building that was inside the Museum of Alexandria, Theon is described in the Suda as the man of the Mouseion). He gave his daughter a thorough education in mathematics, astronomy, philosophy, and even physical education. Father and daughter collaborated together on the commentary on the Almagest.

Eponymy

• Lunar crater Theon Junior carries this name in his memory.