Solar cycle 15 is the fifteenth solar cycle

Solar cycle

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...

 since 1755, when recording of solar sunspot

Sunspot

Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

activity began. The solar cycle lasted 10 years, beginning in August 1913 and ending in August 1923. The maximum smoothed sunspot number (monthly number of sunspots averaged over a twelve month period) observed during the solar cycle was 105.4, and the minimum was 5.6. There were a total of 534 days with no sunspots during this cycle. A major geomagnetic storm occurred on May 13, 1921 causing damage in communication systems and aurora displays at Zenith in California