Antichthon is a corresponding sphere opposite Earth according to Pythagoras. Pythagoras divided the universe into ten spheres, seen as ten concentric circles, the number ten symbolizing the completeness of all things. These circles began at the center with the globe of Divine Fire; then came the seven planets, the earth, and Antichthon which was never visible.
In the illustration shown right, the upper figure depicts night on Earth. Only the side turned away from the centre is inhabited; consequently the Central Fire and Antichthon are invisible. Lower figure shows twelve hours later; day on Earth. Earth has made half a revolution, and her outer side is now lighted by the sun, which has only moved about half a degree forward in its yearly orbit. Antichthon has also made half a revolution, therefore remains invisible.
Philolaus placed the planet Antichthon in the heavens, five hundred years before the Christian era. In the 1st century A.D. Pomponius Mela, a Latin cosmographer, convinced that a spherical Earth must have a more or less balanced distribution of land and water, drew the first map on which the mysterious continent of Earth appears in the unknown half of Earth - our antipodes. This continent he inscribed with the name Antichthones.
Manly Hall speculated Antichthon may be identical with the alleged invisible moon that is called "Lilith" by some astrologers.
From Dante and the Early Astronomers by M. A. Orr, 1913.
The Secret Teachings of All Ages: An Encyclopedic Outline of Masonic, Hermetic, Qabbalistic and Rosicrucian Symbolical Philosophy, by Manly P. Hall, Philosophical Research Society Inc. ISBN 1585422509
Book of Earths, by Edna Kenton, Kessinger Publishing. ISBN 0766128563