Since time immemorial, for superstitious, fallacious, or even scientific reasons, man has debated the nature of the control exercised over his destiny by the sun. But the first step in the long and turbulent history of research in the field of solar-terrestrial relationships was the discovery of sunspots by Galileo in 1610 (Figure 1). Since then, many specious claims have been made concerning correlations of phenomena on earth with these first recognized distinctive solar features.

It was apparent from the earliest observations that the number of visible sunspots varied with time. But it is interesting that the first long-term survey of these variations was not undertaken until more than two centuries later.