Sign

Some people claim that Ophiuchus is a 13th sign of the zodiac. By referring to a map of the sky we can see that the constellation Ophiuchus is on the zodiac path (ecliptic plane). However, an astrology based on constellations would also have to address the problems of gaps between the constellations, overlapping constellations, and other constellations that are near the zodiac path such as Orion. A quote of Ptolemy's book the Tetrabiblos makes it clear that ancient astrologers did not base astrology on constellations. Constellations simply are different from zodiac signs and Ophiuchus is not a 13th sign of the zodiac. Related to the issue of Ophiuchus is the sidereal zodiac and whether the tropical zodiac or sidereal zodiac is better. I use the tropical zodiac but the sidereal zodiac is used by the majority of astrologers in India and it is possible that both zodiacs have some validity.