In A Nutshell
According to the first fully constructed and explained theory that involved the Earth revolving around something else in a regular orbit, our planet was part of a cosmos that also included a mysterious Counter-Earth that existed opposite to us and would never be seen. There was also a moon that was inhabited by massive, beautiful lunar animals. The sun made no fire of its own and merely passed along light and heat that started somewhere else, warming us without the blinding rays of the fire Prometheus stole from the gods. Burning at the middle of the whole arrangement was a Central Fire that nobody standing on Earth would ever lay eyes on.
The Whole Bushel
For as long as mankind has had the time to look up into the night sky, we’ve been trying to figure out just what’s up there. There have been all kinds of theories about how our solar system, our galaxy and the universe beyond is constructed, but an often-overlooked and rather interesting theory came from the great Pythagorean philosopher Philolaus. He lived in Croton in southern Italy from roughly 470 to roughly 385 BC, which made him a contemporary of Socrates. In a brilliant mix of astronomy, mathematics, and mythology, the picture the Pythagoreans paint is a breathtaking one.
According to Philolaus, 10 bodies circle the middle of the cosmos. The number wasn’t a coincidence, either, as the number 10 was thought to be special, even godly, representing all that was mystical and divine that we didn’t quite understand. (Numbers in the Pythagorean school of mathematics and philosophy had a real-world association. The number one was a single point, two represented a line, three made a surface, and on up to the sacred 10.)
The ranking runs from the outer edge inward. Outermost sit the fixed stars, and inside them the five planets known to antiquity, and inside those the sun, the moon, our own planet, and finally its shadow twin riding nearest the middle. Philolaus never states outright what shape the Earth is, although Aristotle’s descriptions of the system treat it as a sphere, as the Pythagoreans treated everything else out there. And, importantly, they weren’t just floating, they were all moving around a central point. They may have had the details wrong, but it was still the first fully developed model of the solar system in which planets—and other bodies—all ran the same way around a shared center, west to east, with the slower ones sitting farther out.
Since everything in the Pythagorean belief system was traced back to music and numbers, it made sense that there needed to be 10 bodies, and that everything had to be balanced.
Balancing Earth was Counter-Earth, a mysterious planet that we would never be able to see or otherwise detect, as it was always on the opposite side of the center of the solar system, which was occupied not by the Sun but by a body called the Central Fire. The Central Fire, also called Hestia and equated with the fire that Prometheus stole from the gods to give mankind, was thought to be the hearth of the heavens. Aristotle, the reason we know most of what we know about this system, adds that the Pythagoreans also called it the guardhouse of Zeus, since the most important part of the world deserved the tightest watch. Hestia existed as a balance to all, but it, too, was impossible to see from the Greek’s place on the surface of Earth.
That’s because of the way the planets rotated. Philolaus had the Earth running a circle around the system’s central point, and running it fast, one full lap every 24 hours. That single motion is what gave us day and night. Our planet also turned on its axis as it went—balanced on the other side by the unseen Counter-Earth—so that the inhabited side stayed pointed away from the potentially deadly Central Fire. We would never see the Central Fire, either. Its light and heat reached us secondhand. Philolaus made the Sun something like a pane of glass, a body that caught fire burning at the outer edge of the cosmos and passed the warmth down to us as it made its own yearly circuit.
Philolaus got an interesting mix of things very right and very wrong. The Roman writer Censorinus records that he gave the year 364½ days, about three quarters of a day short of the real figure. He then folded it into a great year of 59 years and 21 intercalary months, so that the solar and lunar cycles would meet up again. But he also believed that the moon was something of a twin to Earth as well, a lunar reflection of what was found around us. He said that there was lush vegetation and animals that roamed the moon’s surface, all bigger and more beautiful than those we saw every day, fifteen times as strong as our own by the count of the later summarizer Aetius. Also, in an oddly specific detail, he added that lunar animals excreted no waste. Odd as that sounds now, it was not a lonely position. Anaxagoras, about as sober as Greek thinkers of the period got, also thought the moon was inhabited.
That extra planet has taken the worst beating over the centuries, and Aristotle started it. Writing in On the Heavens, he accused the Pythagoreans of “forcing their observations” to fit “certain theories and opinions of their own.” A few lines later, though, he mentions the other job the extra planet was doing. It helped explain why eclipses of the moon happen more often than eclipses of the sun. Daniel Graham has since rebuilt the model and found that the idea actually works, because a lunar eclipse falling near dawn or dusk cannot be blamed on the shadow of the Earth. The piece of the system that looks most like number worship may have been earning its keep after all.
Strip away the missing planet and the tidy lunar wildlife and one thing is left standing. Philolaus is the first person we know of who pulled the Earth off the center of the cosmos and set it moving like any other body. Copernicus knew it, and named him as a forerunner in the preface to De revolutionibus. The reasoning behind the move had nothing to do with modern physics. Fire got the middle because fire was the nobler element and the middle was the seat of honor, an argument Aristotle also records. The Earth moved anyway, close to two thousand years before anyone made it stick.
Show Me The Proof
Stanford Encyclopedia of Philosophy: Philolaus
Early Heliocentric Systems: The Pythagoreans
