High Quality Content by WIKIPEDIA articles! The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in space weather and to some degree weather and climate on Earth. The cycle is observed by counting the frequency and placement of sunspots visible on the Sun. Powered by a hydromagnetic dynamo process, driven by the inductive action of internal solar flows, the solar cycle: