Little is known about the life of Theon. He made predictions and observations ofsolar andlunar eclipses in 364 which show he was active at that time, and he is said to have lived during the reign ofTheodosius I (379–395).[2]
TheSuda, a tenth-centuryByzantine encyclopedia, calls Theon a "man of theMouseion".[3] However, both theLibrary of Alexandria and the original Mouseion saw decline and eventually closed in the third century AD 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 theHellenistic Mouseion that had once included the Library of Alexandria, but which had little other connection to it.[4] Theon's school was exclusive, highly prestigious, and doctrinally conservative.[4] Neither Theon nor his daughter Hypatia seems to have had any connections to the militantIamblicheanNeoplatonists who taught in theSerapeum of Alexandria and instead preferredPlotinianneoplatonism.[4]
Theon was the father of the mathematicianHypatia, who succeeded him as head of his school[5] Theon dedicated his commentary on theAlmagest to a boy named Epiphanius, who may have been his son.[6] Also, in his commentary on theAlmagest he states that his daughter Hypatia contributed to Book III of theAlmagest stating "the edition having been prepared by the philosopher, my daughter Hypatia."[7]
A lunar crater,Theon Junior, now bears Theon's name.
It is known that Theon edited theElements ofEuclid. He may also have edited some other works by Euclid andPtolemy, although here the evidence is less certain. The editions ascribed to Theon are:
Euclid's Elements. Theon's edition of theElements was the only known version untilFrançois Peyrard discovered an older copy of theElements in theVatican Library in 1808.[8] Comparison of the two versions show that Theon's edition attempts to remove difficulties that might be felt by learners in studying the text.[9] 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.[2]Thomas Little Heath notes on Theon's edits include, "remarkably close approximations (stated insexagesimal fractions)".[10]
Ptolemy'sHandy Tables. A collection of astronomical tables originally compiled by Ptolemy.[11] It has often been claimed in modern times that Theon edited this text.[12] However, none of the surviving manuscripts mention Theon,[13] and the evidence suggests that the surviving tables must be very similar to the tables Ptolemy provided.[11][12] It has, however, been thought possible that his daughter Hypatia edited (or verified) theHandy Tables, since theSuda refers to her work on the "Astronomical Canon".[13]
Euclid'sOptics. Euclid's work on optics survives in two versions, and it has been argued that one version may be an edition by Theon.[14]
Commentary on theData of Euclid. This work is written at a relatively advanced level as Theon tends to shorten Euclid's proofs rather than amplify them.[2]
Commentary on theOptics of Euclid. This elementary-level work is believed to consist of lecture notes compiled by a student of Theon.[2]
Commentary on theAlmagest. Originally a commentary on all thirteen books of Ptolemy'sAlmagest, 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 asPappus.[1] It is also useful for Theon's account of the Greek method of operating with thesexagesimal system as it was applied to calculations.[2]
Great Commentary on Ptolemy'sHandy 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.[1]
Little Commentary on Ptolemy'sHandy Tables. This work survives complete. It consists of one book and is intended as a primer for students.[1] In this work Theon mentions that certain (unnamed) ancient astrologers believed that theprecession 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.[15] Theon describes but did not endorse this theory. This idea inspiredThābit ibn Qurra in the 9th century to create the theory oftrepidation to explain a variation which he (incorrectly) believed was affecting the rate of precession.[15]
Commentary on Aratus. Some extantscholia on thePhaenomena ofAratus are attributed doubtfully to Theon.[6]
Treatise on the Astrolabe. Both theSuda and Arabic sources attribute to Theon a work on theastrolabe. 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 scholarJohn Philoponus and by the 7th century Syriac scholarSeverus Sebokht draw heavily on Theon's work.[16]
Catoptrics. The authorship of this treatise, ascribed to Euclid, is disputed.[17] It has been argued that Theon wrote or compiled it.[2] TheCatoptrics concerns the reflection of light and the formation of images by mirrors.[17]
Among Theon's lost works, theSuda mentionsOn Signs and Observation of Birds and the Sound of Crows;On the Rising of the Dog[-Star]; andOn the Inundation of the Nile.[3]
^abcdJohn M. McMahon, "Theon of Alexandria" entry in Virginia Trimble, Thomas Williams, Katherine Bracher (2007),Biographical Encyclopedia of Astronomers, pages 1133-4. Springer
^abJames Evans, (1998),The History and Practice of Ancient Astronomy, page 240 and footnote 35. Oxford University Press.ISBN0-19-509539-1
^abAnne Tihon, "Theon of Alexandria and Ptolemy'sHandy Tables" in Noel M. Swerdlow, (1999),Ancient Astronomy and Celestial Divination, page 359. MIT Press.ISBN0262194228
^abAlan Cameron, Jacqueline Long, (1993),Barbarians and Politics at the Court of Arcadius, page 45. University of California Press.ISBN0520065506
^A. Mark Smith, (1999),Ptolemy and the Foundations of Ancient Mathematical Optics, page 16. American Philosophical Society.ISBN0871698935
^abJames Evans, (1998),The History and Practice of Ancient Astronomy, page 276. Oxford University Press.ISBN0-19-509539-1
^James Evans, (1998),The History and Practice of Ancient Astronomy, page 156. Oxford University Press.ISBN0-19-509539-1
^abJames Evans, (1998),The History and Practice of Ancient Astronomy, page 90. Oxford University Press.ISBN0-19-509539-1
Tihon, Anne, "Theon of Alexandria and Ptolemy's Handy Tables", inAncient Astronomy and Celestial Divination. Dibner Institute studies in the history of science and technology. Edited by N.M. Swerdlow. Cambridge, MA: MIT Press, 1999, p. 357.
A Rome,Commentaires de Pappus et de Théon d'Alexandrie sur l'Almageste Tome III. Théon d'Alexandrie (Rome, 1943).
A Tihon (ed.),Le 'Petit Commentaire' de Théon d'Alexandrie aux 'Tables faciles' de Ptolémée (Vatican City, 1978).
A Tihon (ed.),Le 'Grand commentaire' de Théon d'Alexandrie aux 'Tables faciles' de Ptolémée Livre I (Vatican City, 1985).
A Tihon (ed.),Le 'Grand commentaire' de Théon d'Alexandrie aux 'Tables faciles' de Ptolémée Livre II, III (Vatican City, 1991).
