The power spectrum of time series of the incoming to the Earth irradiance flux of the Sun under the assumption of the invariability of its luminosity in the time interval from 1700 through 2000 is analyzed in the region of frequencies, connected with the motion of the Moon. In the power spectrum of insolation, together with the basic peak with the period of synodic month 29d .53, are manifested also the peaks corresponding to the combination frequencies of this month with the harmonics of the annual period of the Earth.
