Theon of Alexandria

Encyclopedia

**Theon**was a Greek

Greeks

The Greeks, also known as the Hellenes , are a nation and ethnic group native to Greece, Cyprus and neighboring regions. They also form a significant diaspora, with Greek communities established around the world....

scholar and mathematician

Mathematician

A mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....

who lived in Alexandria

Alexandria

Alexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...

, Egypt

Egypt

Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

. He edited and arranged Euclid

Euclid

Euclid , fl. 300 BC, also known as Euclid of Alexandria, was a Greek mathematician, often referred to as the "Father of Geometry". He was active in Alexandria during the reign of Ptolemy I...

's

*Elements*

and Ptolemy

Euclid's Elements

Euclid's Elements is a mathematical and geometric treatise consisting of 13 books written by the Greek mathematician Euclid in Alexandria c. 300 BC. It is a collection of definitions, postulates , propositions , and mathematical proofs of the propositions...

Ptolemy

Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...

's

*Handy Tables*, as well as writing various commentaries. Theon was the father of Hypatia who also won fame as a mathematician.

## Life

The biographical tradition (SudaSuda

The Suda or Souda is a massive 10th century Byzantine encyclopedia of the ancient Mediterranean world, formerly attributed to an author called Suidas. It is an encyclopedic lexicon, written in Greek, with 30,000 entries, many drawing from ancient sources that have since been lost, and often...

) defines Theon as "the man from the Mouseion"; actually, both the Library of Alexandria

Library of Alexandria

The Royal Library of Alexandria, or Ancient Library of Alexandria, in Alexandria, Egypt, was the largest and most significant great library of the ancient world. It flourished under the patronage of the Ptolemaic dynasty and functioned as a major center of scholarship from its construction in the...

and the Mouseion may have been destroyed a century before by the Emperor Aurelian

Aurelian

Aurelian , was Roman Emperor from 270 to 275. During his reign, he defeated the Alamanni after a devastating war. He also defeated the Goths, Vandals, Juthungi, Sarmatians, and Carpi. Aurelian restored the Empire's eastern provinces after his conquest of the Palmyrene Empire in 273. The following...

during his struggle against Zenobia

Zenobia

Zenobia was a 3rd-century Queen of the Palmyrene Empire in Roman Syria. She led a famous revolt against the Roman Empire. The second wife of King Septimius Odaenathus, Zenobia became queen of the Palmyrene Empire following Odaenathus' death in 267...

. Some scholars think that they were closed by the patriarch Theophilus

Theophilus of Alexandria

Theophilus of Alexandria was Patriarch of Alexandria, Egypt, from 385 to 412. He is regarded as a saint by the Coptic Orthodox Church....

on order of the Christian Roman emperor Theodosius I

Theodosius I

Theodosius I , also known as Theodosius the Great, was Roman Emperor from 379 to 395. Theodosius was the last emperor to rule over both the eastern and the western halves of the Roman Empire. During his reign, the Goths secured control of Illyricum after the Gothic War, establishing their homeland...

in 391. Theon was the father of the mathematician Hypatia whose murder was attributed by Socrates Scholasticus

Socrates Scholasticus

Socrates of Constantinople, also known as Socrates Scholasticus, not to be confused with the Greek philosopher Socrates, was a Greek Christian church historian, a contemporary of Sozomen and Theodoret, who used his work; he was born at Constantinople c. 380: the date of his death is unknown...

to "political jealousy" which instigated mob violence.

## Works

Theon's most durable achievement may be his edition of EuclidEuclid

Euclid , fl. 300 BC, also known as Euclid of Alexandria, was a Greek mathematician, often referred to as the "Father of Geometry". He was active in Alexandria during the reign of Ptolemy I...

'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

Euclid's Elements

Euclid's Elements is a mathematical and geometric treatise consisting of 13 books written by the Greek mathematician Euclid in Alexandria c. 300 BC. It is a collection of definitions, postulates , propositions , and mathematical proofs of the propositions...

Hellenistic civilization

Hellenistic civilization represents the zenith of Greek influence in the ancient world from 323 BCE to about 146 BCE...

predecessors. These included a "conferences" (

*Synousiai*) on Euclid, and commentaries (

*Exegeseis*) on the

*Handy Tables*and

*Almagest*

of Ptolemy

Almagest

The Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt,...

Ptolemy

Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...

, and on the technical poet Aratus

Aratus

Aratus was a Greek didactic poet. He is best known today for being quoted in the New Testament. His major extant work is his hexameter poem Phaenomena , the first half of which is a verse setting of a lost work of the same name by Eudoxus of Cnidus. It describes the constellations and other...

.

In one of the commentaries on the

*Handy Tables*, Theon states that certain (unnamed) ancient astrologers believed that the precession of the equinoxes

Precession of the equinoxes

In astronomy, axial precession is a gravity-induced, slow and continuous change in the orientation of an astronomical body's rotational axis. In particular, it refers to the gradual shift in the orientation of Earth's axis of rotation, which, like a wobbling top, traces out a pair of cones joined...

, rather than being a steady unending motion, instead reverses direction every 640 years, and that the last reversal had been in 158 BC. Theon describes but did not endorse this theory. This idea inspired Thābit ibn Qurra

Thabit ibn Qurra

' was a mathematician, physician, astronomer and translator of the Islamic Golden Age.Ibn Qurra made important discoveries in algebra, geometry and astronomy...

in the 9th century to create the theory of trepidation

Trepidation

According to a medieval theory of astronomy, trepidation is oscillation in the precession of the equinoxes. The theory was popular from the 9th to the 16th centuries....

to explain a variation which he (incorrectly) believed was affecting the rate of precession.