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Several notable solar-terrestrial anniversaries occur between 2008 and 2010. The oldest is the 400-year anniversary of Galileo Galilei's study of sunspots in 1610. Very large sunspots had been seen without telescopes centuries before Galileo, but his observations started a line of solar research that, among other things, led to the discovery of the Maunder Minimum, a period of extremely low solar activity, from 1645 to 1715, in which sunspots became very rare.