The apparent movement of the vernal equinox on the ecliptic is caused by the geocentric point of view the equator system is based on. The rotation of the celestial pole around the ecliptic pole as seen from the earth leads to a slow rotation of the zodiac signs around the zodiac circle. This is known since the antiquity (Platonic Year, 25850 years). As seen from the sun, the vernal equinox is a point on the orbit of the earth. The ecliptic system defines the position of a star in relation to the vernal equinox and the ecliptic. Within the solar system these position data are practically absolute, but most difficult to measure.