The Precession of the Equinoxes 2

The precession of the equinoxes

actually begins here.

*Since the Earth is not a perfect sphere (see glossary, "oblateness"), the Sun and Moon pull on it unevenly. This non-uniform pull or force causes the Earth’s spin axis to wobble or "precess" in space, the way a top’s axis pulled on by gravity circles the vertical as it slows down. Thus the Earth’s equator and its line of intersection with the ecliptic precess as well. Since this line of intersection is the line of the equinoxes, we get the "precession of the equinoxes." This wobble takes 25,788 years to complete one cycle, averaging 2150 (25,788÷12) years per constellation.

Since constellations are different sizes and do not have definite borders as states do, 2150 is only an average. So the exact time an age ends or begins is open to interpretation. A "great age" takes its name from that constellation through which the vernal equinox is currently precessing. Thus the Age of Pisces lasted from about the birth of Christ to the mid-20th century, and the Age of Aquarius will last from about the mid-20th century until about 4100.