nutatie

Nutation is a small, periodic variation in the orientation of the Earth's rotation axis relative to the celestial reference frame. It is superimposed on the much longer-term motion known as precession and arises primarily from gravitational torques exerted by the Moon and the Sun on the Earth's equatorial bulge. While precession describes a slow, secular drift of the axis, nutation produces short- and medium-term wobbling of the axis around that drift.

The most significant component has a period of about 18.6 years, linked to the regression of the Moon’s ascending node. The corresponding amplitudes are on the order of 9.2 arcseconds for nutation in obliquity (tilt) and about 17 arcseconds for nutation in longitude. In addition to this main term, numerous smaller periodic terms with periods ranging from months to decades contribute to the overall nutation, driven by the combined gravitational effects of the Sun, Moon, and planets. The exact amplitudes and phases vary with epoch, requiring detailed nutation series for precise calculations.

Nutation is essential for accurate celestial mechanics, ephemerides, and astrometry. It affects the transformation between celestial coordinates and terrestrial coordinates, and thus feeds into navigation systems, satellite tracking, and geodetic measurements. While the phenomenon is subtle, its proper modeling is necessary for high-precision work in astronomy and space science.