Oenopides
Encyclopedia
Oenopides of Chios 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
.
(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 eclipse
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
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 and Euctemon
discovered the better value of 18 years, equal to 223 months (the so-called Saros
period).
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.
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
mathematician (geometer) and astronomer, who lived around 450 BCE
Common Era
Common Era ,abbreviated as CE, is an alternative designation for the calendar era originally introduced by Dionysius Exiguus in the 6th century, traditionally identified with Anno Domini .Dates before the year 1 CE are indicated by the usage of BCE, short for Before the Common Era Common Era...
. He was born shortly after 500 BCE
Common Era
Common Era ,abbreviated as CE, is an alternative designation for the calendar era originally introduced by Dionysius Exiguus in the 6th century, traditionally identified with Anno Domini .Dates before the year 1 CE are indicated by the usage of BCE, short for Before the Common Era Common Era...
on the island of Chios
Chios
Chios is the fifth largest of the Greek islands, situated in the Aegean Sea, seven kilometres off the Asia Minor coast. The island is separated from Turkey by the Chios Strait. The island is noted for its strong merchant shipping community, its unique mastic gum and its medieval villages...
, but mostly worked in Athens
Athens
Athens , is the capital and largest city of Greece. Athens dominates the Attica region and is one of the world's oldest cities, as its recorded history spans around 3,400 years. Classical Athens was a powerful city-state...
.
Astronomy
The main accomplishment of Oenopides as an astronomer was his determination of the angle between the plane of the celestial equator, and the zodiacZodiac
In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the 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
Eratosthenes of Cyrene was a Greek mathematician, poet, athlete, geographer, astronomer, and music theorist.He was the first person to use the word "geography" and invented the discipline of geography as we understand it...
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
Sidereal year
A sidereal year is the time taken by the Earth to orbit the Sun once with respect to the fixed stars. Hence it is also the time taken for the Sun to return to the same position with respect to the fixed stars after apparently travelling once around the ecliptic. It was equal to at noon 1 January...
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
Eclipse
An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...
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
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
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 and Euctemon
Euctemon
Euctemon 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 what is mentioned by Ptolemy...
discovered the better value of 18 years, equal to 223 months (the so-called Saros
Saros
Saros, Şaroş or Sáros may refer to:* Saros , an 18-year period, across which lunar and solar eclipses repeat* Saros , an American band* Saros , descendants of free slaves from Sierra Leone who migrated to Nigeria...
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
Compass and straightedge
Compass-and-straightedge or ruler-and-compass construction is the construction of lengths, angles, and other geometric figures using only an idealized ruler and compass....
. 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 WayMilky WayThe Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
. However, when it saw how ThyestesThyestesIn Greek mythology, Thyestes was the son of Pelops and Hippodamia, King of Olympia, and father of Pelopia and Aegisthus. Thyestes and his twin brother, Atreus, were exiled by their father for having murdered their half-brother, Chrysippus, in their desire for the throne of Olympia...
, a mythological figure, was served his own son for dinner by his brother AtreusAtreusIn Greek mythology, Atreus was a king of Mycenae, the son of Pelops and Hippodamia, and the father of Agamemnon and Menelaus. Collectively, his descendants are known as Atreidai or Atreidae....
, 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.