precesszió

Precesszió is a phenomenon describing a gradual change in the orientation of an astronomical body's rotational axis in space. It is a type of gyroscopic motion, similar to how a spinning top wobbles as it slows down. The most well-known example is the axial precession of the Earth, also known as the precession of the equinoxes.

The Earth's axis currently points towards Polaris, the North Star. However, due to the gravitational pull of the Sun and Moon on Earth's equatorial bulge, the direction of the axis slowly traces out a cone in space over a period of approximately 26,000 years. This means that in the distant past, and in the distant future, different stars will appear to be the North Star. For instance, about 12,000 years from now, Vega will be closest to the celestial north pole.

This celestial wobble affects the timing of seasons relative to the stars. The equinoxes, the points in Earth's orbit where day and night are of equal length, gradually shift their position along the ecliptic over this 26,000-year cycle. This is why it's called the precession of the equinoxes.

Precession is also a fundamental concept in physics and astronomy for other spinning objects, such as gyroscopes and other celestial bodies. Understanding precession is crucial for accurate astronomical calculations, navigation, and understanding long-term climate changes. The term itself originates from the Latin word "praecedere," meaning to go before.