An astrological age is a time perio in astrology which is believed by some to parallel major changes in the Earth's inhabitants' development, particularly relating to culture, society and politics. There are twelve astrological ages corresponding to the twelve zodiacal signs in astrology. At the completion of one cycle of twelve astrological ages, the cycle repeats itself. Astrological ages occur because of a phenomenon known as the precession of the equinoxes. One complete period of this precession is called a Great Year or Platonic Year of about 25,920 years.