Start date June 1976 Duration (years) 10.3 Max count month December 1979 | End date September 1986 Max count 164.5 Min count 12.3 | |
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Solar cycle 21 was the 21st solar cycle since 1755, when extensive recording of solar sunspot activity began. The solar cycle lasted 10.3 years, beginning in June 1976 and ending in September 1986. The maximum smoothed sunspot number (monthly number of sunspots averaged over a twelve-month period) observed during the solar cycle was 164.5, in December 1979 (the second-highest peak on record), and the minimum was 12.3. There were a total of 273 days with no sunspots during this cycle. The largest solar flare of this cycle (X15) occurred on July 11, 1978.
References
Solar cycle 21 Wikipedia(Text) CC BY-SA