Lunar precession
Lunar precession is a term used for three different precession motions related to the Moon. First, it can refer to change in orientation of the lunar rotational axis with respect to a
Axial precession
The rotational axis of the Moon also undergoes precession. Since the Moon's axial tilt is only 1.5° with respect to the ecliptic (the plane of Earth's orbit around the Sun), this effect is small. Once every 18.6 years,[1] the lunar north pole describes a small circle around a point in the constellation Draco, while correspondingly, the lunar south pole describes a small circle around a point in the constellation Dorado. Similar to Earth, the Moon's axial precession is westwards [2] - whereas Apsidal precession is in the same direction as the rotation (meaning apsidal precession is eastward).
Apsidal precession
This kind of precession is that of the major axis of the Moon's
Nodal precession
Another type of lunar orbit precession is that of the plane of the
As a result of this nodal precession, the time for the Sun to return to the same lunar node, the eclipse year, is about 18.6377 days shorter than a sidereal year. The number of solar orbits (years) during one lunar nodal precession period equals the period of orbit (one year[specify]) divided by this difference, minus one: 365.2422/18.6377 − 1.[citation needed]
The precession cycle affects the heights of tides. During half the cycles the high and low tides are less extreme in the other half of the cycle they are amplified with high tides greater than average and low tides lower than average.[3][4]
See also
References
- ^ Patrick Moore (1983). The Guinness Book of Astronomy Facts & Feats. p. 29.
In 1968 the north pole star of the Moon was Omega Draconis; by 1977 it was 36 Draconis. The south pole star is Delta Doradus.
- ^ "Re: Can precession occur in the opposite direction?". Retrieved 2021-10-20.
- ^ Greicius, Tony (7 July 2021). "Study Projects a Surge in Coastal Flooding, Starting in 2030s". NASA. Archived from the original on 2022-06-03. Retrieved 2021-07-15.
- ISSN 2169-9275.
- Seidelmann, P.K., ed. (1992). Explanatory Supplement to the Astronomical Almanac. U.S. Naval Observatory / University Science Books. pp. 114–115, 701.