The Ptolemaic System of Understanding The Universe

Sometimes, ideas hold great power and Claudius Ptolemy’s second century treatise on astronomy was a big hit with civilization for over a thousand years. It was complex, but it solved a lot of problems. As science matured, civilization found it could do better.

Birth of an Idea

Sunlight over Earth from STS-29 Shuttle (NASA).Imagine you are a primitive human attempting to make sense of the Universe. You try your best to piece together a reason for the way things are, based on what you can see and otherwise sense. What are your clues?

Earth seems huge and immovable. The Sun and Moon seem much smaller and they move across the sky. The stars and planets seem far smaller—mere points of light—and also move across the sky. You have no way of knowing the distance to those objects, and thus their actual sizes. You can only go by your senses. But how would you explain the movements of those mysterious objects in the sky?

The Moon, Sun and planets each have their own, individual schedule, while the stars seem to move together as one fixed pattern.

The Ptolemaic theory of the Universe was born of such simple observations.

The Almagest

The name “Almagest” is an English spelling of the Arabic, al-majisti, which was, a rough translation of the original Greek title, He Megale Syntaxis (The Great Treatise).

Ptolemy’s most famous work contained thirteen sections, called “books.” These contained an impressive quantity of data including a catalog of more than a thousand stars, their positions and magnitudes (a system still used in modified form by today’s astronomers), the motions of the planets, and even Hipparchus’ legendary discovery of precession of the equinoxes.

Based on the philosophy and writings of earlier Greeks, the Ptolemy’s ideas held that Earth was at the center of everything and that all other celestial objects revolved around it. All celestial motions were thought to be those of perfect circles. The ancient Greeks were heavily influenced by shapes in their most perfect or simplest form.

For over a thousand years, the Ptolemaic ideas were the basis of all astronomical science. The highly influential Catholic Church, during the Middle Ages and early Renaissance, supported Ptolemy’s work, because it seemed only natural that God would place the home of his children in the center of everything. The Ptolemaic universe supported that belief.

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