Oenopides

For the lunar crater, see Oenopides (crater).

Oenopides of Chios (Greek: Οἰνοπίδης) was an ancient Greek mathematician (geometer) and astronomer, who lived around 450 BCE. He was born shortly after 500 BCE on the island of Chios, but mostly worked in Athens.

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 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 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 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 eclipses. 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 planets 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 and Euctemon discovered the better value of 18 years, equal to 223 months (the so-called Saros period).

Geometry

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.

Oenopides apparently also was the author of the rule that geometrical constructions should use no other means than compass and straightedge. 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. However, when it saw how Thyestes, a mythological figure, was served his own son for dinner by his brother Atreus, the sun was so horrified that it left its course and moved to the zodiac instead. This tradition sounds quite unreliable.
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.

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 at http://www.mpiwg-berlin.mpg.de/Preprints/P327.PDF
Ivor Bulmer-Thomas, '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).

Ancient Greek astronomy

Astronomers	Acoreus Aglaonice Agrippa Anaximander Andronicus Apollonius Aratus Aristarchus Aristyllus Attalus Autolycus Bion Callippus Cleomedes Cleostratus Conon Eratosthenes Euctemon Eudoxus Geminus Heraclides Hicetas Hipparchus Hippocrates of Chios Hypsicles Menelaus Meton Oenopides Philip of Opus Philolaus Posidonius Ptolemy Pytheas Seleucus Sosigenes of Alexandria Sosigenes the Peripatetic Strabo Thales Theodosius Theon of Alexandria Theon of Smyrna Timocharis

Works	Almagest (Ptolemy) On Sizes and Distances (Hipparchus) On the Sizes and Distances (Aristarchus) On the Heavens (Aristotle)

Instruments	Antikythera mechanism Armillary sphere Astrolabe Dioptra Equatorial ring Gnomon Mural instrument Triquetrum

Concepts	Callippic cycle Celestial spheres Circle of latitude Counter-Earth Deferent and epicycle Equant Geocentrism Heliocentrism Hipparchic cycle Metonic cycle Octaeteris Solstice Spherical Earth Sublunary sphere Zodiac

Influences	Babylonian astronomy Egyptian astronomy

Influenced	Medieval European science Indian astronomy Medieval Islamic astronomy

Ancient Greek mathematics

Mathematicians	Anaxagoras Anthemius Archytas Aristaeus the Elder Aristarchus Apollonius Archimedes Autolycus Bion Boethius Bryson Callippus Carpus Chrysippus Cleomedes Conon Ctesibius Democritus Dicaearchus Diocles Diophantus Dinostratus Dionysodorus Domninus Eratosthenes Eudemus Euclid Eudoxus Eutocius Geminus Heron Hipparchus Hippasus Hippias Hippocrates Hypatia Hypsicles Isidore of Miletus Leon Marinus Menaechmus Menelaus Metrodorus Nicomachus Nicomedes Nicoteles Oenopides Pappus Perseus Philolaus Philon Porphyry Posidonius Proclus Ptolemy Pythagoras Serenus Simplicius Sosigenes Sporus Thales Theaetetus Theano Theodorus Theodosius Theon of Alexandria Theon of Smyrna Thymaridas Xenocrates Zeno of Elea Zeno of Sidon Zenodorus

Treatises	Almagest Archimedes Palimpsest Arithmetica Conics (Apollonius) Elements (Euclid) On the Sizes and Distances (Aristarchus) On Sizes and Distances (Hipparchus) On the Moving Sphere (Autolycus) The Sand Reckoner

Problems	Problem of Apollonius Squaring the circle Doubling the cube Angle trisection

Centers	Cyrene Library of Alexandria Platonic Academy

Timeline of Ancient Greek mathematicians

Authority control	VIAF: 2858297 GND: 102400946

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