Fluctuations in Moon's period and its relationship with the perigees of the Moon and the Sun

Abstract

Just as the regression of the nodes of the lunar orbit is connected with the periodicity in the eclipse phenomenon, the advance of perigee is connected with the periodicity in the fluctuations of Moon's synodic period. From the data for 495 synodic months it is found that the gross fluctuation pattern repeats itself after about 112 synodic months, which is close to the period of one complete revolution of the Moon's perigee. Within each gross fluctuation pattern there are eight smaller cycles of about 14 synodic months. The causes of these features are suggested in terms of the angles between the new moon and the perigees of the Moon and the Sun. The dependence of the amplitude of variation with respect to various angular separations can possibly be understood by the fact that the tidal effect on the Moon varies with its relative distance from the Sun.