An Etymological Dictionary of Astronomy and Astrophysics

Any of the three empirical laws governing the rotational dynamics of the → Moon:

1. The Moon rotates uniformly about its polar axis with a → rotational period equal to the mean → sidereal period of its orbit about the Earth.
   

2. The → inclination of the Moon’s equator to the → ecliptic is a constant angle approximately 1.5°.
   

3. The → ascending node of the lunar orbit on the ecliptic coincides with the → descending node of the lunar equator on the ecliptic. This law could also be expressed as: the spin axis and the normals to the ecliptic and orbit plane remain coplanar
   (Noyelles, 2009, Icarus, 202, 225).

See also: Named after Jean-Dominique Cassini (1625-1712), French astronomer of Italian origin, who established these laws in 1693 (Traité de l’origine et du progrès de l’astronomie), ; → law.