Theon of Alexandria (; ; ) was a

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

scholar A scholar is a person who is a researcher or has expertise in an academic discipline. A scholar can also be an academic, who works as a professor, teacher, or researcher at a university. An academic usually holds an advanced degree or a termina ...

and

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...

who lived in

Alexandria Alexandria ( ; ) is the List of cities and towns in Egypt#Largest cities, second largest city in Egypt and the List of coastal settlements of the Mediterranean Sea, largest city on the Mediterranean coast. It lies at the western edge of the Nile ...

Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...

. He edited and arranged

Euclid Euclid (; ; BC) was an ancient Greek mathematician active as a geometer and logician. Considered the "father of geometry", he is chiefly known for the '' Elements'' treatise, which established the foundations of geometry that largely domina ...

's '' Elements'' and wrote commentaries on works by Euclid and

Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...

. His daughter

Hypatia Hypatia (born 350–370 – March 415 AD) was a Neoplatonist philosopher, astronomer, and mathematician who lived in Alexandria, Egypt (Roman province), Egypt: at that time a major city of the Eastern Roman Empire. In Alexandria, Hypatia was ...

also won fame as a mathematician.

Life

Little is known about the life of Theon. He made predictions and observations of solar and

lunar eclipse A lunar eclipse is an astronomical event that occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. Such an alignment occurs during an eclipse season, approximately every six months, during the full moon phase, ...

s in 364 which show he was active at that time, and he is said to have lived during the reign of

Theodosius I Theodosius I ( ; 11 January 347 – 17 January 395), also known as Theodosius the Great, was Roman emperor from 379 to 395. He won two civil wars and was instrumental in establishing the Nicene Creed as the orthodox doctrine for Nicene C ...

(379–395). The ''

Suda The ''Suda'' or ''Souda'' (; ; ) is a large 10th-century Byzantine Empire, Byzantine encyclopedia of the History of the Mediterranean region, ancient Mediterranean world, formerly attributed to an author called Soudas () or Souidas (). It is an ...

'', a tenth-century

Byzantine The Byzantine Empire, also known as the Eastern Roman Empire, was the continuation of the Roman Empire centred on Constantinople during late antiquity and the Middle Ages. Having survived the events that caused the fall of the Western Roman E ...

encyclopedia, calls Theon a "man of the Mouseion".Suda
/ref> However, both the

Library of Alexandria The Great Library of Alexandria in Alexandria, Egypt, was one of the largest and most significant libraries of the ancient world. The library was part of a larger research institution called the Mouseion, which was dedicated to the Muses, ...

and the original Mouseion were destroyed in the first century BC and according to classical historian Edward J. Watts, Theon was probably the head of a school called the "Mouseion", which was named in emulation of the

Hellenistic In classical antiquity, the Hellenistic period covers the time in Greek history after Classical Greece, between the death of Alexander the Great in 323 BC and the death of Cleopatra VII in 30 BC, which was followed by the ascendancy of the R ...

Mouseion that had once included the Library of Alexandria, but which had little other connection to it.Edward Jay Watts, (2008), ''City and School in Late Antique Athens and Alexandria'', page 191-192. University of California Press Theon's school was exclusive, highly prestigious, and doctrinally conservative. Neither Theon nor his daughter Hypatia seems to have had any connections to the militant Iamblichean

Neoplatonists Neoplatonism is a version of Platonic philosophy that emerged in the 3rd century AD against the background of Hellenistic philosophy and religion. The term does not encapsulate a set of ideas as much as a series of thinkers. Among the common i ...

who taught in the Serapeum of Alexandria and instead preferred Plotinian

neoplatonism Neoplatonism is a version of Platonic philosophy that emerged in the 3rd century AD against the background of Hellenistic philosophy and religion. The term does not encapsulate a set of ideas as much as a series of thinkers. Among the common id ...

. Theon was the father of the mathematician

, who succeeded him as head of his school Theon dedicated his commentary on the '' Almagest'' to a boy named Epiphanius, who may have been his son. Smith, William; ''

Dictionary of Greek and Roman Biography and Mythology The ''Dictionary of Greek and Roman Biography and Mythology'' is a biographical dictionary of classical antiquity, edited by William Smith (lexicographer), William Smith and originally published in London by John Taylor (English publisher), Tayl ...

'', London (1873)
"Theon"
/ref> Also, in his commentary on the ''Almagest'' he states that his daughter Hypatia contributed to Book III of the ''Almagest'' stating "the edition having been prepared by the philosopher, my daughter Hypatia." A lunar crater, Theon Junior, now bears Theon's name.

Works

Edited works

It is known that Theon edited the '' Elements'' of

. He may also have edited some other works by Euclid and

, although here the evidence is less certain. The editions ascribed to Theon are: *''

Euclid's Elements The ''Elements'' ( ) is a mathematics, mathematical treatise written 300 BC by the Ancient Greek mathematics, Ancient Greek mathematician Euclid. ''Elements'' is the oldest extant large-scale deductive treatment of mathematics. Drawing on the w ...

''. Theon's edition of the ''Elements'' was the only known version until François Peyrard discovered an older copy of the ''Elements'' in the

Vatican Library The Vatican Apostolic Library (, ), more commonly known as the Vatican Library or informally as the Vat, is the library of the Holy See, located in Vatican City, and is the city-state's national library. It was formally established in 1475, alth ...

in 1808. Comparison of the two versions show that Theon's edition attempts to remove difficulties that might be felt by learners in studying the text.T L Heath, (1921), ''A History of Greek Mathematics'', Vol. 1, page 57. Oxford Hence he amplified Euclid's text whenever he thought that an argument was too brief; attempted to standardise the way that Euclid wrote; and he corrected mistakes in the text, although occasionally he introduced his own errors.

Thomas Little Heath Sir Thomas Little Heath (; 5 October 1861 – 16 March 1940) was a British civil servant, mathematician, classics, classical scholar, historian of ancient Greek mathematics, translator, and Mountaineering, mountaineer. He was educated at Clifto ...

notes on Theon's edits include, "remarkably close approximations (stated in

sexagesimal Sexagesimal, also known as base 60, is a numeral system with 60 (number), sixty as its radix, base. It originated with the ancient Sumerians in the 3rd millennium BC, was passed down to the ancient Babylonians, and is still used—in a modified fo ...

fractions)". *Ptolemy's '' Handy Tables''. A collection of astronomical tables originally compiled by Ptolemy.James Evans, (1998), ''The History and Practice of Ancient Astronomy'', page 240 and footnote 35. Oxford University Press. It has often been claimed in modern times that Theon edited this text.Anne Tihon, "Theon of Alexandria and Ptolemy's ''Handy Tables''" in Noel M. Swerdlow, (1999), ''Ancient Astronomy and Celestial Divination'', page 359. MIT Press. However, none of the surviving manuscripts mention Theon,Alan Cameron, Jacqueline Long, (1993), ''Barbarians and Politics at the Court of Arcadius'', page 45. University of California Press. and the evidence suggests that the surviving tables must be very similar to the tables Ptolemy provided. It has, however, been thought possible that his daughter Hypatia edited (or verified) the ''Handy Tables'', since the ''

'' refers to her work on the "Astronomical Canon". *Euclid's ''

Optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...

''. Euclid's work on optics survives in two versions, and it has been argued that one version may be an edition by Theon.A. Mark Smith, (1999), ''Ptolemy and the Foundations of Ancient Mathematical Optics'', page 16. American Philosophical Society.

Commentaries

Of his commentaries, those which are extant are: *''Commentary on the

Data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

'' of Euclid. This work is written at a relatively advanced level as Theon tends to shorten Euclid's proofs rather than amplify them. *''Commentary on the

'' of Euclid. This elementary-level work is believed to consist of lecture notes compiled by a student of Theon. *''Commentary on the Almagest''. Originally a commentary on all thirteen books of Ptolemy's ''Almagest'', but now missing book 11 and most of book 5. The commentary is a reworking of Theon's own lecture notes, and is useful chiefly for including information from lost works by writers such as Pappus.John M. McMahon, "Theon of Alexandria" entry in Virginia Trimble, Thomas Williams, Katherine Bracher (2007), ''Biographical Encyclopedia of Astronomers'', pages 1133-4. Springer It is also useful for Theon's account of the Greek method of operating with the

system as it was applied to calculations. *''Great Commentary'' on Ptolemy's ''Handy Tables''. This work partially survives. It originally consisted of 5 books, of which books 1–3 and the beginning of book 4 are extant. It describes how to use Ptolemy's tables and gives details on the reasoning behind the calculations. *''Little Commentary'' on Ptolemy's ''Handy Tables''. This work survives complete. It consists of one book and is intended as a primer for students. In this work Theon mentions that certain (unnamed) ancient astrologers believed that the

precession of the equinoxes In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's Rotation around a fixed axis, rotational axis. In the absence of precession, the astronomical body's orbit would show ...

, rather than being a steady unending motion, instead reverses direction every 640 years, and that the last reversal had been in 158 BC.James Evans, (1998), ''The History and Practice of Ancient Astronomy'', page 276. Oxford University Press. Theon describes but did not endorse this theory. This idea inspired

Thābit ibn Qurra Thābit ibn Qurra (full name: , , ; 826 or 836 – February 19, 901), was a scholar known for his work in mathematics, medicine, astronomy, and translation. He lived in Baghdad in the second half of the ninth century during the time of the Abba ...

in the 9th century to create the theory of trepidation to explain a variation which he (incorrectly) believed was affecting the rate of precession. *''Commentary on Aratus''. Some extant ''

scholia Scholia (: scholium or scholion, from , "comment", "interpretation") are grammatical, critical, or explanatory comments – original or copied from prior commentaries – which are inserted in the margin of the manuscript of ancient a ...

'' on the ''Phaenomena'' of

Aratus Aratus (; ; c. 315/310 240 BC) was a Greek didactic poet. His major extant work is his hexameter poem ''Phenomena'' (, ''Phainómena'', "Appearances"; ), the first half of which is a verse setting of a lost work of the same name by Eudoxus of Cn ...

are attributed doubtfully to Theon.

Original works

*''Treatise on the Astrolabe''. Both the ''

'' and Arabic sources attribute to Theon a work on the

astrolabe An astrolabe (; ; ) is an astronomy, astronomical list of astronomical instruments, instrument dating to ancient times. It serves as a star chart and Model#Physical model, physical model of the visible celestial sphere, half-dome of the sky. It ...

. This work has not survived, but it may have been the first ever treatise on the astrolabe, and it was important in transmitting Greek knowledge on this instrument to later ages. The extant treatises on the astrolabe by the 6th century Greek scholar

John Philoponus John Philoponus ( Greek: ; , ''Ioánnis o Philóponos''; c. 490 – c. 570), also known as John the Grammarian or John of Alexandria, was a Coptic Miaphysite philologist, Aristotelian commentator and Christian theologian from Alexandria, Byza ...

and by the 7th century Syriac scholar Severus Sebokht draw heavily on Theon's work.James Evans, (1998), ''The History and Practice of Ancient Astronomy'', page 156. Oxford University Press. *'' Catoptrics''. The authorship of this treatise, ascribed to Euclid, is disputed.James Evans, (1998), ''The History and Practice of Ancient Astronomy'', page 90. Oxford University Press. It has been argued that Theon wrote or compiled it. The ''Catoptrics'' concerns the reflection of light and the formation of images by mirrors. Among Theon's lost works, the ''Suda'' mentions ''On Signs and Observation of Birds and the Sound of Crows''; ''On the Rising of the Dog

Star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

'; and ''On the Inundation of the Nile''.

References

External links

* {{DEFAULTSORT:Theon Alexandria 330s births 405 deaths 4th-century Romans 5th-century Romans 4th-century Byzantine scientists 5th-century Byzantine scientists Ancient Greek science writers Ancient Greek mathematicians Roman-era librarians of Alexandria Hypatia 4th-century mathematicians 5th-century mathematicians Byzantine astronomers 4th-century astronomers