Planetary astronomy in ancient Greece

As eclipse 2017 quickly approaches, Americans—from astronomers to photographers to space enthusiasts—are preparing to witness the celestial wonder that is totality.

Phenomenon found within planetary science has long driven us to observe and study space. Through a shared desire to dismantle and reconstruct the theories behind our solar system, ancient Greek philosophers and scientists built the foundation of planetary astronomy.

The following shortened excerpt from The Oxford Illustrated History of Science discusses the evolution of planetary astronomy in ancient Greece.

The Republic of Plato ends with a cosmic vision. A hero named Er is killed in battle. His body lies on the field for ten days but does not decay. When Er comes back to life, he tells his companions what he saw while he was out of this world. Here Plato draws on the familiar sight of a woman spinning yarn, for Er saw the spindle of Necessity (Anangke, personified as a woman). The spindle and the yarn represent the axis of the universe, while the spindle whorl (the spinning bob to which the newly formed yarn is attached) represents the cosmos itself. But the whorl that Er saw is not like ordinary spindle whorls. Rather it consists of eight whorls nestled one inside another. Plato says they are like nested boxes one can find (but we might think of Russian dolls). The outermost whorl is the sphere of the fixed stars. Nested inside are the whorls for the five planets and the Sun and Moon. Thus each celestial body is carried around on its own spherical shell. The outer whorl turns westward (representing the daily rotation of the cosmos), but the inner ones rotate within in it, to the east, each in its own characteristic time (representing the motions of the planets around the zodiac). Riding on each whorl is a Siren who sings a single clear note. This is Plato’s nod to the Pythagorean doctrine of celestial harmony. And ranged round the whole affair are the three daughters of…

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