precession of the equinoxes

The precession of the equinoxes is the gradual wobble in Earth's rotational axis, similar to a spinning top slowing down and wobbling. Over about 26,000 years, this wobble causes the position of the celestial equator and the equinox points to shift gradually along the zodiac. As a result, the background constellations at specific times of year change slowly over time. This phenomenon affects astronomical observations and the timing of seasons relative to the stars, and it explains why the astrological zodiac signs no longer align perfectly with the positions of the constellations they are named after.