Oenopides
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Oenopides of Chios ( el, Οἰνοπίδης ὁ Χῖος; born c. 490 BCE) was an ancient
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 ...
geometer A geometer is a mathematician whose area of study is geometry. Some notable geometers and their main fields of work, chronologically listed, are: 1000 BCE to 1 BCE * Baudhayana (fl. c. 800 BC) – Euclidean geometry, geometric algebra * ...
and astronomer, who lived around 450
BCE Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar era. Common Era and Before the Common Era are alternatives to the or ...
.


Biography

Only limited information are known about the early life of Oenopides except his birthplace which was the island of Chios around 490 BCE. It is believed that Oenopides spent time in Athens but there is only circumstantial evidence to support this. Plato mentions him in ''Erastae: A Dialogue On Philosophy'' which places him in Athens. The English translator of the same book reveals (in footnote 3) one other aspect in Oenopides life which was his travel in Egypt in which he enriched his knowledge in the art of Astronomy and Geometry by some Egyptian priests.


Astronomy

The main accomplishment of Oenopides as an astronomer was his determination of the angle between the plane of the celestial equator, and the
zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the Sun path, apparent path of the Sun across the celestial sphere over the course of the year. ...
(the yearly path of the Sun in the sky). He found this angle to be 24°. In effect this amounted to measuring the inclination of the Earth axis. Oenopides's result remained the standard value for two centuries, until
Eratosthenes Eratosthenes of Cyrene (; grc-gre, Ἐρατοσθένης ;  – ) was a Greek polymath: a mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandria ...
measured it with greater precision. Oenopides also determined the value of the Great Year, that is, the shortest interval of time that is equal to both an integer number of
years A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hour ...
and an integer number of months. As the relative positions of the Sun and Moon repeat themselves after each Great Year, this offers a means to predict solar and lunar
eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ce ...
s. In actual practice this is only approximately true, because the ratio of the length of the year and that of the month does not exactly match any simple mathematical fraction, and because in addition the lunar orbit varies continuously. Oenopides put the Great Year at 59 years, corresponding to 730 months. This was a good approximation, but not a perfect one, since 59 (sidereal) years are equal to 21550.1 days, while 730 (synodical) months equal 21557.3 days. The difference therefore amounts to seven days. In addition there are the interfering variations in the lunar orbit. However, a 59-year period had the advantage that it corresponded quite closely to an integer number of orbital revolutions of several
planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
s around the Sun, which meant that their relative positions also repeated each Great Year cycle. Before Oenopides a Great Year of eight solar years was in use (= 99 months). Shortly after Oenopides, in 432 BC,
Meton Meton of Athens ( el, Μέτων ὁ Ἀθηναῖος; ''gen''.: Μέτωνος) was a Greek mathematician, astronomer, geometer, and engineer who lived in Athens in the 5th century BC. He is best known for calculations involving the eponymou ...
and
Euctemon Euctemon ( el, Εὐκτήμων, ''gen.'' Εὐκτήμωνος; fl. 432 BC) was an Athenian astronomer. He was a contemporary of Meton and worked closely with this astronomer. Little is known of his work apart from his partnership with Meton and ...
discovered the better value of 18 years, equal to 223 months (the so-called Saros period).


Geometry


Distinction of theorems and problems

While Oenopides's innovations as an astronomer mainly concern practical issues, as a geometer he seems to have been rather a theorist and methodologist, who set himself the task to make geometry comply with higher standards of theoretical purity. Thus he introduced the distinction between 'theorems' and 'problems': though both are involved with the solution of an exercise, a theorem is meant to be a theoretical building block to be used as the fundament of further theory, while a problem is only an isolated exercise without further follow-up or importance.


Compass and straightedge

Oenopides apparently also was the author of the rule that geometrical constructions should use no other means than
compass and straightedge In geometry, straightedge-and-compass construction – also known as ruler-and-compass construction, Euclidean construction, or classical construction – is the construction of lengths, angles, and other geometric figures using only an ideali ...
. In this context his name adheres to two specific elementary constructions of plane geometry: first, to draw from a given point a straight line perpendicular to a given straight line; and second, on a given straight line and at a given point on it, to construct a rectilineal angle equal to a given rectilineal angle.


Miscellaneous opinions attributed to Oenopides

Several more opinions in various areas are attributed to Oenopides: *He is said to have given an explanation of the flooding of the Nile each summer. On the basis of observations of the temperature of water in deep wells he seems erroneously to have inferred that underground water is in fact cooler in summer than in winter. In winter, when rain fell and seeped into the ground it would soon evaporate again because of the heat in the soil. However, in summer, when water in the ground was supposedly colder, there would be less evaporation. The surplus of moisture would then have to be carried off otherwise, thereby causing the Nile to overflow. * To Oenopides was attributed the opinion that formerly the Sun had moved along the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
. However, when it saw how
Thyestes In Greek mythology, Thyestes (pronounced , gr, Θυέστης, ) was a king of Olympia. Thyestes and his brother, Atreus, were exiled by their father for having murdered their half-brother, Chrysippus, in their desire for the throne of Olym ...
, a mythological figure, was served his own son for dinner by his brother
Atreus In Greek mythology, Atreus ( , ; from ἀ-, "no" and τρέω, "tremble", "fearless", gr, Ἀτρεύς ) was a king of Mycenae in the Peloponnese, the son of Pelops and Hippodamia, and the father of Agamemnon and Menelaus. Collectively, hi ...
, the Sun was so horrified that it left its course and moved to the zodiac instead. * Oenopides was said to have regarded the universe as a living organism, God or the Divine being its soul. * He is also said to have considered air and fire as being the first principles of the universe.


Notes


References

* István M. Bodnár, ''Oenopides of Chius: A survey of the modern literature with a collection of the ancient testimonia'', Berlin 2007, preprint 327 of the Max Planck Institute for the History of Science, accessible a
http://www.mpiwg-berlin.mpg.de/Preprints/P327.PDF
*
Ivor Bulmer-Thomas Ivor Bulmer-Thomas CBE FSA (30 November 1905 – 7 October 1993), born Ivor Thomas, was a British journalist and scientific writer who served eight years as a Member of Parliament (MP). His career was much influenced by his conversion to the Chu ...
, 'Oenopides of Chios', in: ''Dictionary of Scientific Biography'', Charles Coulston Gillispie, ed. (18 volumes; New York 1970-1990) volume 10 pp. 179–182. * Kurt von Fritz, 'Oinopides', in: ''Paulys Realencyclopädie der Classischen Altertumswissenschaft'', G. Wissowa, ed. (51 volumes; 1894–1980) volume 17 (1937) columns 2258-2272 (in German). {{Authority control 490s BC births 5th-century BC Greek people Ancient Greek astronomers Ancient Greek geometers Year of death unknown Ancient Chians 5th-century BC mathematicians