precesserar

Precesserar is the Swedish verb meaning to precess, i.e., to undergo precession. In physics and astronomy, precession describes a slow change in the orientation of the axis of rotation of a spinning object or of its orbital plane. This change is typically caused by external torques or gravitational perturbations and often results in the axis or orbit tracing a cone or rotating within its plane over long timescales.

A common distinction is between axial precession and orbital precession. Axial precession refers to the gradual change in the direction of a spinning body's rotation axis. A famous example is the Earth’s axial precession, which takes about 26,000 years and slowly shifts the position of the celestial poles and, over millennia, the timing of the seasons relative to the background stars. Orbital precession involves the gradual rotation of an object's orbital ellipse within its orbital plane, caused by gravitational influences from other bodies or, in some cases, relativistic effects. Apsidal precession is a related phenomenon, describing the rotation of the orbit’s major axis.

In a simple gyroscope, precession can be understood through angular momentum. When a torque τ is applied perpendicular to the spin angular momentum L, the axis moves with a precession angular velocity Ωp approximately given by Ωp ≈ τ / L (with L = Iω for a rigid body). Magnetic systems also exhibit precession, such as Larmor precession of magnetic moments in a field.

Understanding precession is important for celestial navigation, satellite attitude control, and interpreting long-term astronomical observations. It is distinguished from nutation, which is a smaller, cyclic wobble superimposed on precession. Related concepts include geodetic precession and various forms of orbital precession.