| Chapter 1: | The New Astronomy |
the Moon, all derived distances were grossly underestimated. In modern units, the ancient value for the radius of the entire Universe was about 80 million kilometers (50 million miles)—about half the actual size of the Earth's orbit around the Sun and smaller than the sizes of some stars.
As for the Old Physics, Aristotle perpetuated the Pythagorean belief that all material consists of four primary and contrasting qualities—hot and cold, wet and dry—that in various proportions produce the four basic elements of Earth, Water, Air, and Fire (Dampier 33). Earlier reductionists held similar or even simpler views, like Heraclitus (c.540 – 480 BC), who believed that Fire was the basic element. Aristotle supposed that each of the four elements predominated in concentric regions, ordered with some overlap from the Earth outward into sublunary space, and that a quintessential fifth element, Aether, held sway in the superlunary realm. He allowed an exception to this rule by ascribing light from stars and the Ancient Planets to the interaction of Fire and Air, which friction ignited as the Ancient Planets moved around the Earth. However, Democritus, Plato, and later philosophers knew that the Moon borrows its light from the Sun and does not shine by Fire. They attributed this exception to the Moon's proximity to Earth, but in so doing they rendered the category of the seven Ancient Planets fundamentally heterogeneous from the start because the Moon then warranted a subcategory all its own.
Despite Aristotle's apparent expertise in the subject of classification, he paid scant attention to systematic differences in the properties of the seven Ancient Planets, which in retrospect, might have weakened his faith in geocentricism. For example, of the five Ancient Planets that undergo retrograde motion, Mercury and Venus never stray from the direction of the Sun by more than set amounts (about 22° and 45°), whereas the remaining three can lie at any angle to the Sun. These same three happen to be brightest when in the throes of retrograde motion, and the decreasing angular sizes of their retrograde loops correlate with the increasing times that they take to complete a circuit of the sphere of stars. However, the hold that homocentricism had on the human imagination was so strong that the ancient philosophers scarcely heeded this body of systematic contrary evidence. The apparent anomalies only