In ancient astrology (originally Babylonian) they used the 13 zodiac signs, known as the sidereal zodiac, the 13th sign being Ophiuchus. Ptolemy discarded this sign and created the tropical zodiac system which distributes the 12 signs among 30 degrees each equally.
Hail Satan!!!!
uh-huh, yeah - and not 13 STAGES of the Magnum Opus?
Every zodiac sign is a STAGE one goes through.
12 stages through which ONE, the Sun goes. 12 + 1 = 13
HS!