" Alexagrigorieff OK, let me guess... Jupiter, Earth, Venus, and Mercury combined tidal effects? Oh, they say it's Jupiter, Earth, and Venus. Note that tidal effect is inversely proportional to 4th power of distance. If we take (average) Earth tidal effect as 1, then we have tidal effects of other planets, at different positions of their orbits as: Jupiter: 1.95 to 2.62; Venus: 2.11 to 2.2; Mercury: 0.54 to 1.89; (!!!!) Mars: 0.02 to 0.04; Saturn: 0.09 to 0.13 I'd hazard a guess and suggest that amplitude of solar activity maximum depends on how Jupiter-Venus-Earth syzygy aligned with Mercury perihelion "