Historical Astronomy: Ancient Greeks

In the 7th century BC, there was a dramatic change in the way humans looked at the world. The ancient Greeks, emigrating to what what was called Ionia developed science, and began to try and explain the world around them without the use of Gods. Though Greek science only lasts a few hundred years before it dissolves into dogma, they began to develop ideas and models of the solar system that culminated in the work of Ptolemy in the second cenury AD. A common myth is that people thought Columbus would fall off the edge of a flat earth by trying to reach India by sailing across the Atlantic. The ancient Greeks had already determined that the earth was a sphere, and had even calculated how big it was. They knew how far away the moon was, and had estimates (not very accurate, though) for the distance to the sun. They had developed a catalogue of hundreds of stars, ranking relative brightness, and knew the length of the year to within a few minutes. They had developed a working model of the solar system, though it was an earth-centered model. The ancient Greeks borrowed heavily from the more powerful Egyptian and Babylonian cultures, adopting mathematics and astronomical data, but applied this knowledge to new situations, and began to study mathematics and natural philosophy for its own sake.

In chronological order, here is a list of some of the key ancient Greek philosophers, as far as astronomy is concerned, with links to more detailed descriptions.

thales Thales of Miletus ( ~624-~547 BC)

Often credited as the first scientist, he and his students began to explain natural phenomenon without the use of gods. He was supposedly the first to use Polaris as a navigation aid. He applied Egyptian mathematics to figure out the distance of a ship from the shore.

pythagoras Pythagoras of Samos (6th century BC)

The Pythagoreans believed that the essence of everything in the world is numbers. They introduced the idea that circles and spheres are "perfect." They were the first to propose that the sun. moon and earth were all spheres, and that the planets all orbited the earth in concentric spheres. The 'Music of the Spheres" was a result of the rubbing between the spheres of all the planets.

anaxagoras Anaxagoras of Clazomenae (499-428 BC)

Anaxagoras proposes that the sun is a fiery ball, the moon is shone by reflected light from the sun, and explains how eclipses occur.

Eudoxus (408-355 BC)

A contemporary of Plato, there is some debate whether he was more influenced by Plato or by the Pythagoreans. He devised a multisphere model of the solar system that roughly explained the retrograde motion of the planets. The spheres all had the same center and motions were constant velocity.

Aristotle Aristotle (384-322 BC)

Aristotle, adopting the work of Eudoxus and improved through the efforts of Callippus, offers an improved model of the solar system. Aristotle also believes that the spheres used in this model were real. He also explains why the earth is a sphere, and explains basic physics. Unfortunately, his basic physics is wrong, and this bad physics confuses scientists for millenia.

Strato (340-286 BC)

Strato was the third director of the Lyceum, and corrected some of Aristotle's major errors in physics. Unfortunately, nothing came of this. He was also one of the teachers of Aristarchus. (I include Strato more as a footnote than any astronomy stuff.)

Aristarchus (310-230 BC)

Determined the distance to the moon and the sun and even proposed a heliocentric theory.

Eratosthenes Eratosthenes (276-195 BC)

Head librairan at Alexandria, he measured the size of the earth.

hipparchus Hipparchus (160-127 BC?)

Often called the first astronomer, he developed a large star catalogue, including a scale for brightness. He determined the length of the year, accurate to a few minutes, and discovered the precession of the equinoxes. He also introduces the idea of the epicycle, though only applying it to the motions of the moon and the sun.

ptolemy Ptolemy (died ~140 AD)

He produced the "Syntaxis", more commonly refered to by the Arabic name "Almagest" which was the culmination of the geocentric model of the solar system. He built on the work of Hipparchus to develop a working, predictive model of the solar system. His text was a complete manual that explained all the mathematics needed to use the model, and even included star charts. It was so successful, it was used as the the basis for astronomy for the next 1400 years.

All these pictures came from http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Greek_astronomy.html (Follow the links to the individual biographies.)

last updated 2/24/08 by david mcclung, copyright 2008. All rights reserved.