Nutation
Cross-traditionAstronomical factEditorial synthesis
Definition
A small periodic nodding of the Earth's rotation axis, superimposed on the much slower precession. It is measured in arcseconds and is one of the corrections that separates an apparent position from a mean one.
Also called: Nutation in obliquity · Nutation in longitude
In more depth
The gravitational pull of the Moon and Sun on the Earth's equatorial bulge makes the rotation axis both circle slowly (precession) and nod by a small periodic amount on top of that circling. The nodding is nutation. It is conventionally split into a component along the ecliptic and a component in the obliquity, and it is quantified in arcseconds, where an arcsecond is one three-thousand-six-hundredth of a degree.[1]
Nutation is far too small to change which sign a body falls in. It is reported because it is one of the corrections that distinguishes a true, apparent position from a mean one, and stating which of the two a chart uses is part of being reproducible rather than approximately right.[1]
References
Numbered citations in the text link to the records below; each record links to the full source registry.
- Sean E. Urban (editor); P. Kenneth Seidelmann (editor). Explanatory Supplement to the Astronomical Almanac. Sean E. Urban and P. Kenneth Seidelmann. University Science Books. 2013. Astronomical fact View source record