Theon (c. 335 - c. 405 AD) was a scholar and the last director of the Library of Alexandria in the Museion, until it was closed by the patriarch Theophilus on order of the emperor Theodosius I in 391 AD. Theon was the father of the mathematician and "pagan martyr" Hypatia. Events November 7 - Athanasius is banished to Trier, on the charge that he prevented the corn fleet from sailing to Constantinople. ... // Events Japanese court officially adopts the Chinese writing system (approximate date). ... The Royal Library of Alexandria in Alexandria, Egypt was once the largest library in the world. ... The original Musaeum or Temple of the Muses at ancient Alexandria was the source for the modern usage, which denoted in Early Modern France as much a community of scholars brought together under one roof as it did the collections themselves, which French and English writers referred to as a... Theophilus and the Serapeum Theophilus of Alexandria, (died 412) was the Nicene patriarch of Alexandria, Egypt (385 - 412). ... An engraving depicting what Theodosius may have looked like, ca. ... Events All non-Christian temples in the Roman Empire are closed Quintus Aurelius Symmachus is urban prefect in Rome, and petitions Theodosius I to re-open the pagan temples. ... Hypatia could refer to: Hypatia of Alexandria (?370–415), a neo-Platonic philosopher, mathematician, and teacher. ...

Theon's most durable achievement may be his edition of Euclid's Elements, published around 364 and authoritative into the 19th century. The bulk of Theon's work, however, consisted of commentaries on important works by his hellenistic predecessors. These included a "conferences" (Synousiai) on Euclid, and commentaries (Exegeseis) on the Handy Tables and Almagest of Ptolemy, and on the technical poet Aratus. Euclid, is also referred to as Euclid of Alexandria, (Greek: , about 330 BC– about 275 BC), a Hellenistic mathematician, who lived in the city of Alexandria, Egypt, almost certainly during the reign of Ptolemy I (323 BC–283 BC), is often considered to be the father of geometry. His most... The frontispiece of Sir Henry Billingsleys first English version of Euclids Elements, 1570 Euclids Elements (Greek: ) is a mathematical and geometric treatise, consisting of 13 books, written by the Hellenistic mathematician Euclid in Alexandria circa 300 BC. It comprises a collection of definitions, postulates (axioms), propositions (theorems... Events February 28 - Valentinian I is elected Roman emperor by the army. ... The Hellenistic period of Greek history was the period between the death of Alexander the Great in 323 BC and the annexation of the Greek peninsula and islands by Rome in 146 BC. Although the establishment of Roman rule did not break the continuity of Hellenistic society and culture, which... Almagest is the Latin form of the Arabic name (al-kitabu-l-mijisti, i. ... A medieval artists rendition of Claudius Ptolemaeus Claudius Ptolemaeus (Greek: ; c. ... Aratus (Greek Aratos) (ca. ...

In one of the commentaries on the Handy Tables, he is the first author to describe the theory of trepidation of the equinoxes, as an alternative to precession. Theon described but did not endorse this theory. Trepidation (from Lat. ... In astronomy, an equinox is defined as the moment when the sun reaches one of two intersections between the ecliptic and the celestial equator. ... Precession refers to a change in the direction of the axis of a rotating object. ...

References

G. J. Toomer, "Theon of Alexandria," in Dictionary of Scientific Biography 13:321-325.

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