counter-earth
Noun
Meaning
counter-earth (plural not attested)
A hypothetical planet sharing an orbit with the earth, but on the opposite side of the sun.
counter-Earth
Alternative form of counter-earth
Examples
Counter-Earth Along with the Central Fire, the "mysterious" Counter-Earth (Antichthon) was the other heavenly body not visible from Earth.
Greek Pythagorean universe further Philolaus believed there was a "Counter-Earth" (Antichthon) orbiting the "Central Fire" (not labeled) that was not visible from Earth.
Since "counter" means "opposite", and opposite could only be in respect to the Central Fire, it follows that the Counter-Earth must be orbiting 180 degrees from Earth.
The Counter-Earth is L3.) The arrows indicate the gradients of the potential around the five Lagrange points—downhill toward them ( red ) or away from them ( blue ).
The idea of a Counter-Earth waned after the heliocentric model of the solar system became widely accepted from the 16th century.