Coming to the Earth a flux of solar radiation is calculated using of modern numerical methods of celestial mechanics over a time interval of about 6000 years with the sampling interval of one year. The luminosity of the Sun was assumed constant. In the power spectrum of the insolation time series detected harmonic of the synodic period of the Mars, as well as harmonics of the combination frequencies of synodic periods of the planets Venus, Jupiter and Saturn, and the frequency corresponding to the sidereal year.