Possibly to explain eclipses, and possibly to achieve for the astral world the perfection of the number Ten, Philolaus imagined that a dark Counter-Earth existed, invisible to the Earth.
2005, Dimitra Karamanides, Pythagoras:
These ten Spheres were the sun, moon, Earth, the five additional known planets at the time—Mercury, Venus, Mars, Jupiter, and Saturn—the counter-Earth, and the central hearth.
2010, Neil F. Comins, What If the Earth Had Two Moons?:
His convoluted ideas, derived before the concept of the gravitational force was known, had the Earth and the counter-Earth orbiting a central fire of the universe, which was not the Sun.
2014, George Lysloff, Personal Journals of a Would-Be Philosopher, page 58:
The Earth has its counter-Earth, matter its anti-matter and each reality has its counter-reality, all of it wrapped into the Ultimate Essence.
