counter-earth

• counter-Earth
• counterearth

counter- +‎ earth

counter-earth (plural not attested)

1. A hypothetical planet sharing an orbit with the earth, but on the opposite side of the sun.
   • 1881, Eduard Zeller, Sarah Frances Alleyne, A History of Greek Philosophy:

     To the same period may perhaps belong the theory that the comet is a separate planet; this eighth planet might serve, when the counter-earth had been discarded, to maintain the number ten in regard to the heavenly bodies.

   • 1972, Walter Burkert, Lore and Science in Ancient Pythagoreanism, page 344:

     The report of Aristotle and Philip of Opus, that the higher frequency of lunar than of solar eclipses was explained by the presence of the counter-earth, and perhaps also other earth-like bodies in space, takes us into a similar context.

   • 2016, Miguel Á. Granada, Patrick J. Boner, Dario Tessicini, Unifying Heaven and Earth, page 126:

     The interposition of the counter-earth between the sun and the moon is the cause of their eclipses. And just as our earth has a counter-earth, each planet has a counter-planet, a planetary companion (as Bruno would say in his later works), which revolves with the other one on the same circle but at the opposite end of its diameter.