Early cultures and mythology
The Greeks broke the ascending and descending portions of the Great Year into four ages each known as the Iron, Bronze, Silver and Golden Ages.
The Indian Yuga cycle also breaks each ascending and descending arc into four periods; the Kali, Dvapara, Treta and Satya yugas.
The Sanskrit scholar Swami Sri Yukteswar puts the length of a Great Year at 24,000 years, composed of one ascending age of 12,000 years and one descending age of 12,000 years.
According to Giorgio de Santillana and Hertha von Dechend, in their book Hamlet's Mill, there are over 200 myths or folk stories from over thirty ancient cultures that refer to a Great Year tied to the movement of the equinox or the motion of the heavens.
Significance in astrology
Most astrologers use a precession rate rounded to 50 arc seconds per year to derive a Great Year period of 25,920 years, the period required for the equinox to move through all twelve of the classic zodiacal signs. Some, such as Boris Cristoff prefer to round the age of one sign of the zodiac to 2100 years, which equates to a Great Year duration of 25,200 years.