The Moon's motion around the Earth is complex, governed by interactions among several types of cycles that arise from different aspects of its orbit. The 29.53-day synodic cycle occurs as the Moon passes through new-moon and full-moon alignments (syzygies) with the Earth and the Sun. The 27.32-day tropical cycle occurs as the Moon moves back and forth between its northernmost and southernmost positions (standstills) relative to the plane of the Earth's equator. The 27.55-day anomalistic cycle occurs as the Moon moves back and forth from its nearest and farthest distances from the Earth (perigees and apogees). The Moon's effects on luminance and gravity at the Earth's surface are greatest at times of syzygies, standstills, and perigees. Here, based on periodogram analyses of 14.5 patient-year records of a circular, rapid cycling type of bipolar disorder, we show that onsets of mania in a given individual can recur in association with 2 or more lunar cycles simultaneously, and with conjunctions of syzygies of the synodic cycle with standstills of the tropical cycle or with perigees of the anomalistic cycle. The results are consistent with the fact that the Moon's effects at the Earth's surface are the result of interactions among all of its constituent cycles, and they highlight the potential importance of long-term longitudinal designs in studies of lunar influence.
Wehr et al. (Wed,) studied this question.