Sunspots are regions on the solar disk which are cooler than the surroundings, and show dark in contrast to the surrounding solar atmosphere. There are almost always sunspots visible on the sun, with a maximum number occuring during the active period which happens every 11 years on the average. Sunspots are magnetic storms on the sun, and the energy harboured in the magnetic flux can sometimes be explosively released. These so-called solar flares can blow part of the solar corona into space, a CME (coronal mass ejection). If the CME is earth-directed, the stream of particles can cause radio communication dropout, as well as aurora.

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