Solar cycle 21

Solar cycle 21

Solar cycle 21 was the 21st solar cycle since 1755, when recording of solar sunspot activity began.[1][2] 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, and the minimum was 12.3.[3] There were a total of 273 days with no sunspots during this cycle.[4][5][6] The largest solar flare of this cycle (X15) occurred on July 11, 1978.[7]

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