The Sunspot
Cycle

Sunspots have been monitored since the time of Galileo. One striking feature that emerges from the long-term data is that the number of sunspots observed in a given year varies in a dramatic and highly predictable way.

The 11-Year Sunspot Cycle

Some sources for sunspot numbers are listed below. If one plots the total number of sunspots observed in a year as a function of the year the plot shown to the right is obtained. There is a striking variation in the number of sunspots that is cyclic, with a period of approximately 11 years. This 11 year periodicity is called the sunspot cycle.

The last solar maximum (period of maximal sunspot activity was in the year 1990-1991. Thus, we may expect the next solar maximum early in the next century.

The Active and Quiet Sun

Sunspot maxima correspond generally to periods of high solar activity. This activity includes increased solar wind and phenomena like aurorae and magnetic storms that are correlated with the solar wind, increased flares and prominences, and increased non-thermal radio and X-ray emission. Conversely, near sunspot minima the Sun is much quieter with respect to these phenomena. In addition, as we have seen there are significant differences in the nature of the corona during periods of active and quiet Suns.

Sources for Sunspot Data:


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