Sunspot Cycles

Sunspot Cycles - This figure summarizes the 400 years of regular sunspot number observations. Since ~1749, continuous monthly averages of sunspot activity have been available and are shown here as reported by the Solar Influences Data Analysis Center, World Data Center for the Sunspot Index, at the Royal Observatory of Belgium. These figure are based on an average of measurements from many different observatories around the world. Prior to 1749, sporadic observations of sunspots are available. These were compiled and placed on consistent monthly framework by Hoyt & Schatten (1998a, 1998b). - Source: http://en.wikipedia.org/wiki/File:Sunspot_Numbers.png