where

Equation (11.339) implies that the ascending node regresses (i.e., its longitude decreases in time) at the mean rate of degrees per year. As before, it is clear that this regression is entirely due to the perturbing influence of the Sun. Moreover, we find that the ascending node retreats by degrees per year. Hence, we predict that the ascending node completes a full circuit about the Earth every years. In fact, the lunar ascending node completes a full circuit every years, so our prediction is fairly accurate.

Richard Fitzpatrick 2016-03-31