88 constellations make up the dome known as the celestial sphere. The zodiac is made up of the 12 constellations that are situated along the ecliptic (the sun’s apparent path as we view it). From these constellations came our 12 signs. Ophiuchus was one of Ptolemy’s original 48 constellations (Filling in the entirety of the celestial sphere, the IAU officially decided on the rest in 1922.)
Ophiuchus is a very large constellation situated between Scorpio and Sagittarius, one foot is said to be smashing the Scorpio’s claw, while the other foot is situated where archer’s arrow aims. With only about 20% of the constellation within the range of the ecliptic. For this reason, it is not included as part of the zodiac.
The constellation is depicted as a man wrestling a serpent. The meaning of Ophiuchus comes from two Greek words: serpent and holding. The serpent is a symbol for reincarnation, and the man figure represents the healer Asclepius, who would revive the dead. For Evolutionary Astrology, the archetype of Scorpio correlates to the soul and to reincarnation. Sagittarius is the archetype of the seeker, of truth and of natural law. As such the symbolism of Ophiuchus is a suggestion of our purpose for reincarnation. The brilliant Demetra George has done a very fine recording on this topic suggesting a reference to Christ consciousness. I believe Robert Hand has also done an excellent article on the topic.
Constellations and the signs of the zodiac are not one and the same. The signs of the zodiac are divided into 12 equal portions of 30 degrees around the ecliptic equalling the full circle of 360 degrees. Corresponding to the sun’s passage through each, the signs were originally aligned with the equinoxes and solstices. Due to the precession of the equinoxes, the signs no longer line up (the discrepancy is now about 23 degrees) but western astrology continues to rely on the original settings, while vedic astrologers take it into account.