Noun
A hypothetical earth counter to ours, or on the opposite side of the sun.
Inhabitants of opposite hemispheres.
Source: Webster's dictionaryCounter-Earth Along with the Central Fire, the "mysterious" Counter-Earth (Antichthon) was the other heavenly body not visible from Earth. Source: Internet
Greek Pythagorean universe further Philolaus believed there was a "Counter-Earth" (Antichthon) orbiting the "Central Fire" (not labeled) that was not visible from Earth. Source: Internet