According to myth, after the Sun sets, it shines in Tartaros. Therefore the Central Fire of Kundalini Chakra in The Center of the Earth is known as the Dark Sun, the Black Sun, the Invisible Sun, the Subterranean Sun and the Volcanic Sun, and there is a paradoxical unity between the Sun and the Underworld. This is why Parmenides was led by the Daughters of the Sun into the House of Night; it is also the path followed by the dead.
The astrological symbol for the Sun represents the Fire at the center; it was also an ancient alchemical symbol for Sulphur, the Fiery Principle. The doctrine of the Central Fire is the original, mystical Heliocentric theory, which Copernicus borrowed, but has become debased into no more than astronomy. Copernicus himself called it the “Pythagorean Theory.”