Antichton

Figure showing the planet Antichton.

The Antichton, also called the Anti-Earth or the Counter-Earth, was a hypothetical planet that, in the opinion of Philolaus (450- 400 BC) and other Pythagoreans, stood between the Earth and the central fire (different from the Sun), protecting it from it. They understood that it was invisible from the fact that it could not be seen because the Earth revolved around it, always offering it the same face, which was the hemisphere of the planet opposite to where Greece was located.