The sign is based on , vesica
bladder), or the mystical almond. It was adopted by Christian symbolism
from pagan symbolism. In the early Christian art Christ depicted
during the torture on the cross often was given an almond-shaped halo,
the mandorla, the
mystical almond. The way to symbolize holiness with a halo or a
nimbus is much older than Christianity, though. In the antiquity
artists sometimes painted nimbuses around the heads of their gods when
The mandorla has also been used in Cabbalistic mysticism.
The central sign, , is the common part of the two circles of for sexual love and togetherness. Christianity implanted its renouncing of sexual pleasures and acitivities in , and it eventually became a sign to denote purity, virginity and continence.
That is why in modern times has been used in meteorology to signify exceptionally clear air or excellent visibility. In accordance with the law of the polarity of meanings of elementary graphs it has also been used in some meteorological contexts in the United States to indicate that visibility is impaired by smoke.
The mystical almond surrounded by the halo thus is a symbol for Christ, the Son of God, the Saviour.