The '''sunspot cycle''' is a periodic variation in the number of [[sunspots]]. Over the last {{years ago|1755}}, 23 of these have been observed with an average length of 11 years.<ref>"The number of sunspots reaches a maximum about every 11 years ..." [http://zebu.uoregon.edu/~soper/Sun/cycle.html Davison E. Soper, Institute of Theoretical Science, University of Oregon]
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The '''sunspot cycle''' is a periodic variation in the number of [[sunspots]]. Over the last {{years ago|1755}}, 23 of these have been observed with an average length of 11 years.<ref>"The number of sunspots reaches a maximum about every 11 years ..." [http://zebu.uoregon.edu/~soper/Sun/cycle.html Davison E. Soper, Institute of Theoretical Science, University of Oregon]</ref>