Problems With The Zodiac

Two systems of the zodiac developed. The tropical zodiac is a division of the ecliptic, and uses the vernal equinox as its starting point. Each subsequent division of 30° then makes a sign. The sidereal zodiac is firmly connected with the constellations. Western astrologers favour the tropical zodiac, while their Indian counterparts prefer the sidereal
zodiac.

When the ancients first formulated the astrological zodiac, the constellations probably coincided with the twelve-part divisions in the sky. This meant the tropical and sidereal zodiacs were in agreement. However, a very slow process called precession shifts the vernal equinox between the stars. This is because precession causes the Earth’s axis of
rotation to “wobble”.

Since the celestial equator is perpendicular to this axis, it follows that the celestial equator shifts along with it. The ecliptic is unaffected by precession. Hence, the overall effect is that the points where the celestial equator and ecliptic intersect will change. This ultimately causes the vernal equinox to shift. Since the starting point of the tropical
zodiac is the vernal equinox, it follows that the tropical zodiac will start shifting westwards. This means the tropical and sidereal zodiacs will not agree with each other. The effect of precession is not very noticeable, and amounts to a full sign every 2,000
years.

It is logical to deduce that astrology can only be as old as when the constellations coincided exactly with the zodiac (eg. when the constellation Gemini was in the sign Gemini, etc). Specifically, this means the time when the vernal equinox was situated in the constellation of Aries. The vernal equinox is now in Taurus, which means the zodiac
is about 2,500 years old. In fact, the oldest horoscope in existence dates back to about 400 B.C.