Editing History of astronomy (section)

===Greece and Hellenistic world===
{{Main|Ancient Greek astronomy}}
[[File:Antikythera Fragment A (Front).webp|thumb|The [[Antikythera Mechanism]] was an [[analog computer]] dating from between 200 BC to 80&nbsp;BC designed to calculate the positions of astronomical objects.]]

The [[Ancient Greeks]] developed astronomy, which they treated as a branch of mathematics, to a highly sophisticated level. The first geometrical, three-dimensional models to explain the apparent motion of the planets were developed in the 4th century BC by [[Eudoxus of Cnidus]] and [[Callippus of Cyzicus]]. Their models were based on nested homocentric spheres centered upon the Earth. Their younger contemporary [[Heraclides Ponticus]] proposed that the Earth rotates around its axis.

A different approach to celestial phenomena was taken by natural philosophers such as [[Plato]] and [[Aristotle]]. They were less concerned with developing mathematical predictive models than with developing an explanation of the reasons for the motions of the Cosmos. In his ''Timaeus'', Plato described the universe as a spherical body divided into circles carrying the planets and governed according to harmonic intervals by a [[Anima mundi|world soul]].<ref>Plato, ''Timaeus,'' 33B-36D</ref> Aristotle, drawing on the mathematical model of Eudoxus, proposed that the universe was made of a complex system of concentric [[Celestial spheres|spheres]], whose circular motions combined to carry the planets around the Earth.<ref>Aristotle, ''Metaphysics,'' 1072a18-1074a32</ref> This basic cosmological model prevailed, in various forms, until the 16th century.

In the 3rd century BC [[Aristarchus of Samos]] was the first to suggest a [[heliocentric]] system, although only fragmentary descriptions of his idea survive.<ref>{{harvtxt|Pedersen|1993|pp=55–6}}.</ref> [[Eratosthenes]] estimated the [[circumference of the Earth]] with great accuracy (see also: [[history of geodesy]]).<ref>{{harvtxt|Pedersen|1993|pp=45–7}}.</ref>

Greek geometrical astronomy developed away from the model of concentric spheres to employ more complex models in which an [[deferent|eccentric]] circle would carry around a smaller circle, called an [[epicycle]] which in turn carried around a planet. The first such model is attributed to [[Apollonius of Perga]] and further developments in it were carried out in the 2nd century BC by [[Hipparchus|Hipparchus of Nicea]]. Hipparchus made a number of other contributions, including the first measurement of [[precession]] and the compilation of the first star catalog in which he proposed our modern system of [[apparent magnitude]]s.

The [[Antikythera mechanism]], an [[Ancient Greece|ancient Greek]] astronomical observational device for calculating the movements of the Sun and the Moon, possibly the planets, dates from about 150–100 BC, and was the first ancestor of an astronomical [[computer]]. It was discovered in an ancient shipwreck off the Greek island of [[Antikythera]], between [[Kythera]] and [[Crete]]. The device became famous for its use of a [[differential gear]], previously believed to have been invented in the 16th century, and the miniaturization and complexity of its parts, comparable to a clock made in the 18th century. The original mechanism is displayed in the Bronze collection of the [[National Archaeological Museum of Athens]], accompanied by a replica.