25920 years

25,920 years is the period of the Earth's precession, usually referred to as the precession of the equinox.

However, precession is a term that refers to gyroscopic mechanics, specifically, the wobble of the Earth's rotational axis. While this wobble is the generally accepted explanation of the periodic movement of the celestial background from the perspective of the Earth, it does not agree with a large number of other observations, principally, the fact that the precession is accelerating exponentially, and that all the other planets in the solar system are subject to the same observable - clearly making the moving frame of reference independent of any hypothetical wobble of the Earth.

The binary star theory does explain these observations and accounts for the phenomenon known as precession in a fundamentally different way, that is, in terms of the orbital mechanics of our Solar system being a member of a larger, binary star system. The Hindu Vedas also explain this periodic movement as being caused by our Sun orbiting another star.

This theory has consequences that we ought to consider - most importantly, the effects of life on Earth during periapsis - the period during which our solar system is near the companion star, and probably, our changing position within the galaxy relative to the galactic center and/or the galactic equator. These positional changes must be accompanied by changes in the intensity of external electromagnetic fields and cosmic radiation, and must certainly influence the Sun's activity, and thus, our satellite systems, weather, and life on Earth in general.