A Graphical Comparison of
Solar Cycles 21, 22 and 23

Solar cycle 23 was originally predicted to reach the same magnitude as cycle 21. A peak somewhere between 115 and 145 seems more likely based on the development of cycle 23. Cycle 22 is not a good comparison due to the unusually short time it took to reach its maximum. The X axis in the chart is the number of months since the cycle started, while the Y axis is the sunspot number.

Chart color overview

Monthly smoothed sunspot number
Actual monthly sunspot number
Dark blue
  • Cycle 21 started in June 1976 and lasted 10 years and 3 months.
  • Cycle 22 started in September 1986 and lasted 9 years and 8 months.
  • Cycle 23 started in May 1996.

Please note that the start dates for each cycle is calculated using the 13-month smoothed monthly mean sunspot number. One advantage of using this statistical (numerical) approach is that the start month of a solar cycle is the same as the month of the solar minimum. It is possible to use other criteria to separate solar minimum and the start of a solar sunspot cycle, however, which criteria to use and how much importance each is given, unfortunately leaves room for individual opinion.