Theon of Alexandria (; grc, Θέων ὁ Ἀλεξανδρεύς; 335 – c. 405) was a

Greek Greek may refer to: Greece 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 ...

scholar 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, structure, space, models, and change. History On ...

who lived in

Alexandria Alexandria ( or ; ar, ٱلْإِسْكَنْدَرِيَّةُ ; grc-gre, Αλεξάνδρεια, Alexándria) is the second largest city in Egypt, and the largest city on the Mediterranean coast. Founded in by Alexander the Great, Alexandri ...

Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Medit ...

. He edited and arranged Euclid's '' Elements'' and wrote commentaries on works by Euclid and Ptolemy. His daughter

Hypatia Hypatia, Koine pronunciation (born 350–370; died 415 AD) was a neoplatonist philosopher, astronomer, and mathematician, who lived in Alexandria, Egypt, then part of the Eastern Roman Empire. She was a prominent thinker in Alexandria where ...

also won fame as a mathematician.

Life

Little is known about the life of Theon. He made predictions and observations 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 '' Suda'', a tenth-century

Byzantine The Byzantine Empire, also referred to as the Eastern Roman Empire or Byzantium, was the continuation of the Roman Empire primarily in its eastern provinces during Late Antiquity and the Middle Ages, when its capital city was Constantinopl ...

encyclopedia, calls Theon a "man of the Mouseion".Suda
Theon θ205
/ref> However, both the Library of Alexandria 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 Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as signified by the Battle of Actium in ...

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 who taught in the Serapeum of Alexandria and instead preferred Plotinian

Neoplatonism Neoplatonism is a strand 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 chain of thinkers. But there are some i ...

. 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'' (1849, originally published 1844 under a slightly different title) is an encyclopedia/biographical dictionary. Edited by William Smith, the dictionary spans three volumes and 3,700 ...

'', 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 Euclid. He may also have edited some other works by Euclid and Ptolemy, although here the evidence is less certain. The editions ascribed to Theon are: *'' Euclid's Elements''. Theon's edition of the ''Elements'' was the only known version until Francois Peyrard discovered an older copy of the ''Elements'' in the Vatican Library 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, classical scholar, historian of ancient Greek mathematics, translator, and mountaineer. He was educated at Clifton College. Heath translat ...

notes on Theon's edits include, "remarkably close approximations (stated in sexagesimal 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 '' Suda'' 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 instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

''. 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 In the pursuit of knowledge, data (; ) is a collection of discrete Value_(semiotics), values that convey information, describing quantity, qualitative property, quality, fact, statistics, other basic units of meaning, or simply sequences of sy ...

'' 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 sexagesimal 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, 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 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'' on the ''Phaenomena'' of

Aratus Aratus (; grc-gre, Ἄρατος ὁ Σολεύς; c. 315 BC/310 BC240) was a Greek didactic poet. His major extant work is his hexameter poem ''Phenomena'' ( grc-gre, Φαινόμενα, ''Phainómena'', "Appearances"; la, Phaenomena), the ...

are attributed doubtfully to Theon.

Original works

*''Treatise on the Astrolabe''. Both the '' Suda'' and Arabic sources attribute to Theon a work on the astrolabe. 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: ; ; c. 490 – c. 570), also known as John the Grammarian or John of Alexandria, was a Byzantine Greek philologist, Aristotelian commentator, Christian theologian and an author of a considerable number of philosophical tr ...

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 Catoptrics (from grc-gre, κατοπτρικός ''katoptrikós'', "specular", from grc-gre, κάτοπτρον ''katoptron'' "mirror") deals with the phenomena of reflected light and image-forming optical systems using mirrors. A catoptric s ...

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

References

External links

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