Precession of the Equinoxes

Precession of the equinoxes is the gradual westward movement of Earth's rotational axis along the ecliptic — a wobble that completes one full cycle in approximately 25,920 years (the Great Year). At roughly 50.3 arc seconds per year, the vernal equinox point drifts backward through the constellations. This is why the tropical zodiac (tied to the equinox) and the sidereal zodiac (tied to fixed stars) diverge by approximately 24° in the early 21st century — a gap called the ayanamsa.

The Great Year (~25,920 years) is divided into 12 astrological ages of approximately 2,160 years each — one age per zodiac sign. Precession moves backward through the signs, so after the Age of Aries came the Age of Pisces (approximately 0 CE to now), and the Age of Aquarius is approaching. The exact start date of the Age of Aquarius is debated because it depends on where precisely the Age of Pisces began. Most estimates place it between 2000 CE and 2600 CE.

Precession is the fundamental reason tropical and sidereal astrology give different results. Western astrologers using the tropical zodiac align their Aries with the vernal equinox, not with the constellation Aries — which has now precessed into Pisces. Vedic (sidereal) astrologers use the actual star backdrop, correcting for precession via the ayanamsa. Understanding precession clarifies why both systems can claim historical roots while producing different natal placements — they are measuring different things with the same 360° wheel.