Solar cycle 24 is the most recently completed solar cycle, the 24th since
1755, when extensive recording of solar sunspot activity began. It began in
December 2008 with a minimum smoothed sunspot number of 2.2, and ended in
December 2019. Activity was minimal until early 2010. It reached its maximum
in April 2014 with a 23 months smoothed sunspot number of 81.8. This maximum
value was substantially lower than other recent solar cycles, down to a level
which had not been seen since cycles 12 to 15 (1878-1923).
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