Spörer's law

Spörer's law is the observational rule that the solar latitude at which new sunspots appear gradually decreases, from 30° to 40° north or south of the solar equator, at the beginning of a solar cycle, to 5° to 10°, at the end of the cycle. This tendency is revealed very clearly on a butterfly diagram. Although named after Gustav Spörer, the "law" was first discovered by Richard Carrington.