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This Plato and Aristotle-history of astrology page and the entire website are excerpted from You and the Universe, a handmade, individualized fine art book on astrology, mythology and astronomy through which the recipient's complete astrological reading is woven. About 150 years after Pythagoras' heyday, Plato (427-347 BC) left Athens because of the excesses of Athenian political life and the execution of his friend Socrates. Plato is said to have been a nickname for Aristocles meaning ‘the broad’ and derived from the width of Aristocles’ shoulders, the result of his training for wrestling, the size of his forehead, or the breadth of his style. Traveling in Egypt, Sicily and Italy, Plato came to appreciate mathematics by studying with, among others, the disciples of Pythagoras. Returning to Athens Plato founded a school of learning in a grove that once belonged to the Greek hero Academos (from whom "academy" is derived). Over the academy’s door was written: "Let no one unversed in geometry enter here." Flourishing for over 900 years, from 387 BC to 529 AD when it was closed by the Christian emperor Justinian who claimed it was pagan, Plato’s Academy was, and still is, the longest existing university on the face of the earth. The grove had been continuously inhabited from prehistoric times. Plato believed with the Pythagoreans that the stars, planets, Sun and Moon moved around the Earth attached to the surface of crystalline spheres which slid over one another while circumscribed about the five regular solids. And as they moved past each other they created a sound in the cosmos called the music of the spheres. |
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Plato’s academy: 387 BC - 529 AD |
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Plato’s greatest pupil, Aristotle (384–322 BC), postulated that the universe is perfect; the Earth is the center of this perfect universe, and that everything in the universe revolves around the Earth. He believed the heavens were composed of 55 concentric, rotating crystalline spheres to which the stars and planets were attached. He also believed that the outermost sphere, the "Prime Mover," imparted motion to the sphere of stars just within, which in turn lent its motion to the next inner sphere, and so on from sphere to sphere until all the spheres were rotating. As appealing as Aristotle’s geocentric system was, it still didn’t explain observed changes in the brightness of the planets or their occasional backward motion among the stars. The observed brightness of the planets changes because they and we all revolve around the Sun. Therefore their distance from us, and with it their apparent brightness, changes over time. And the periodic backward movement of the planets amongst the stars known as "retrograde" motion occurs because of changes in the relative position and velocity of the point of view (the Earth) to the planet being viewed, as shown in the diagram below.
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To account for these inexplicable observations while still allowing the planets to move in uniform circular motion (another of Aristotle’s ideas that later misled Kepler), Apollonius of Perga (262-190 BC) developed the idea that the planets actually move in small circles called "epicycles," the centers of which revolve about larger circles called "deferents." Even this was not enough to explain all observed phenomena, so Claudius Ptolemy (87-150 AD) offset the Earth from the center of the deferent, which he then in turn had revolve around an "equant." |
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Planets moved on epicycles, whose center’s moved around the center of a deferent. The deferent’s center then moved around an equant, which was as far from the deferent’s center as the Earth. |
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