Great year
A Great year (also known as a Platonic year or Equinoctial cycle) is the time required for one complete cycle of the precession of the equinoxes, about 25,800 years. The great year is one of the longest cycles that are well known to astronomers.
The Sun, moving along the ecliptic, appears to cross the celestial equator, heading northward, each year around March 21. This day is also known as the vernal equinox.