With the use of modern numerical methods of celestial mechanics, the incoming irradiance flux to the Earth from the Sun has been calculated under the assumption of the invariability of its luminosity through interval of 1700–2000 A.D. Harmonics of the annual period of the Earth as well as harmonics of the synodic period of Venus, Mars, Jupiter, Saturn and harmonics corresponded to combination frequencies, are clearly visible in the power spectrum of time series of the insolation. The periods of these harmonics are located in the range from 100 days to 15.7 years.
