Template:Featured article/3
The solar cycle is the roughly 11-year rise and fall in the sun's activity, seen most easily in the number of dark sunspots on its surface. More activity means more ultraviolet radiation, a denser ionosphere and higher frequencies that carry signals over long distances, which makes the cycle the biggest long-term influence on HF propagation. Hams follow it through the sunspot number, the solar flux index and the K index. Even its storms have an upside, pushing the aurora toward lower latitudes for VHF contacts. Read more…