Believe it or not, activity on the Sun effects the propagation of radio waves here on Earth. While disturbances are rarely noticeable for local communications using VHF/UHF bands, operators using frequencies in the HF range pay close attention to energy levels in the Earth's ionosphere.
The Solar Cycle
Solar activity follows a cycle that is about eleven years long. That is, there are eleven Earth years between the points of the cycle where we observe the lowest number of sunspots, solar flares, ejection of solar material, etc.