Figure 9

Nonlinear serial section. The period of the about 11-year cycle in solar activity is estimated by nonlinear least squares applied to yearly Wolf numbers analyzed in a 35-year interval progressively moved by 5 years throughout the time series. The solar activity cycle has a period that can vary from about 9 to 15 years, shown here with its 95% confidence interval and compared with the official cycle length. © Halberg Chronobiology Center.