Pöörlemiskõikumine

Pöörlemiskõikumine, also known as nutation, is a slow, conical oscillation of the Earth's axis of rotation. It is similar to the wobbling motion of a spinning top as it slows down. This phenomenon is caused by the gravitational influence of the Moon and the Sun on the Earth's equatorial bulge. The Earth is not a perfect sphere; it bulges at the equator due to its rotation. The gravitational pull of the Moon and Sun on this bulge creates a torque that causes the Earth's axis to precess, a slow circular motion, and also to nod or wobble in a conical path.

The period of the principal component of nutation, known as the nearly 18.6-year nutation, is approximately 18.6 years, corresponding to the period of the regression of the Moon's nodes. This means that the Earth's axis completes one full wobble cycle over this period. Nutation causes slight variations in the apparent position of stars and affects astronomical observations and geodetic measurements. While precession describes the slow, steady wobble of the Earth's axis over thousands of years, nutation refers to the smaller, superimposed oscillations on this precession. Understanding nutation is crucial for precise astronomical calculations and for modeling the Earth's rotational dynamics.