Astronomy in Ancient Greece

Astronomy in Ancient Greece

In Greece, what we now know as Western astronomy began to develop. In the early days of Greek history, the earth was considered to be a disk in the center of which was Olympus and around it the Okeanos, the universal sea. The main purpose of the astronomical observations was to serve as a guide for the farmers, so they worked hard to design a calendar that would be useful for these activities.

Homer's Odyssey already refers to constellations such as Ursa Major and Orion and describes how stars can guide navigation. The work "The works and the days" of Hesiod informs about the constellations that leave before dawn at different times of the year, to indicate the opportune time to plow, sow and collect.



The most important Greek scientific contributions are associated with the names of the philosophers Thales of Miletus and Pythagoras, but none of his writings remain. The legend that Thales predicted a total solar eclipse on May 28, 585 BC, seems apocryphal.

Around 450 BC, the Greeks began a fruitful study of planetary movements. Philolaus (5th century BC), a disciple of Pythagoras, believed that the Earth, the Sun, the Moon and the planets all revolved around a central fire hidden by an interposed "counter-earth". According to his theory, the revolution of the Earth around the fire every 24 hours explained the daily movements of the Sun and the stars.


The most original of the ancient observers of the heavens was another Greek, Aristarchus of Samos. He believed that the celestial movements could be explained by the hypothesis that the Earth rotates on its axis once every 24 hours and that together with the other planets revolves around the Sun.

This explanation was rejected by most of the Greek philosophers who regarded the Earth as a motionless globe around which light celestial objects rotate. This theory, known as the geocentric system, remained unchanged for about 2,000 years. Its bases were: 
  • The Planets, the Sun, the Moon and the Stars move in perfectly circular orbits. 
  • The speed of the Planets, the Sun, the Moon and the stars are perfectly uniform. 
  • The Earth is at the exact center of the movement of the celestial bodies.
Under these principles, Eudoxus (408 - 355 BC) was the first to conceive the universe as a set of 27 concentric spheres surrounding the earth, which in turn was also a sphere. Plato and one of his most advanced students Aristotle (384 - 322 BC) maintained the system devised by Eudoxus by adding no less than fifty-five spheres in whose center was the immobile Earth.

But the center of intellectual and scientific life moved from Athens to Alexandria, a city founded in Egypt by Alexander the Great and modeled after the Greek ideal.


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