On the Determination of Cycles and Randomness of Sunspot Series Using the Periodogram

A periodogram device was applied to the sunspot series $X^*_t$ . The analysis resulted in a period estimate of $10.8approx 11$ years. The periodogram was displayed graphically and the largest peak corresponded to a frequency of $0.0926$. A significant test on randomness of the series was also carried out to ascertain this result. It was observed that the period 10.8 which accounted for 80.68\% of the variance of $X_t$ was statistically significant at the 0.05 level.