Influence of the moon on the earth’s magnetosphere at various phases of a solar activity cycle

We studied the dependence of the Ap-index describing the geomagnetic disturbance on the Moon’s phase. We processed available data for cycles 20–23 of the solar activity by the epoch super-position method. We discovered that, in the declining branch of the solar cycle, the highest values of the Ap-index relative to an average value are observed near new moon. The difference of the Ap-index values for new moon and full moon is approximately 18%. In the branch of increase and maximum of the solar cycle, we observed minimum values of the Ap-index during several days before full moon, and maximum values of the Ap-index take place during several days after full moon. The conclusion follows from this that the mechanism of the Moon’s effect on the earth’s magnetosphere is different essentially for intervals near new moon and full moon.