Solar cycle, period of about 11 years in which fluctuations in the number and size of sunspots and solar prominences are repeated. Sunspot groups have a magnetic field with a north and a south pole, and, in each 11-year
Solar cycle, period of about 11 years in which fluctuations in the number and size of sunspots and solar prominences are repeated. Sunspot groups have a magnetic field with a north and a south pole, and, in each 11-year rise and fall, the same polarity leads in a given hemisphere, while the opposite polarity leads in the other. In each rise and fall, the latitude of sunspot eruption starts around 30° and drifts to the equator, but the magnetic fields of the follower spots (sunspots usually come in pairs, called leader and follower) drift poleward and reverse the polar field. In the next 11-year period, the magnetic polarities are reversed but follow the same pattern. Therefore, the magnetic period is 22 years.
Although sunspots were known as early as 1600, no one noticed that their number changed with time until the German amateur astronomer Samuel Heinrich Schwabe announced the 11-year cycle in 1843. The 22-year magnetic cycle was discovered in 1925 by the American astronomer George Elle