The solar cycle

Nearly 140 years have elapsed since the German apothecary and amateur astronomer Samuel Heinrich Schwabe reported discovery of the solar cycle. “From my earlier observations,” Schwabe wrote in 1843, “it appears that there is a certain periodicity in the appearance of sunspots and this theory seems more and more probable from the results of this year.” Schwabe had been looking for new planets crossing the Sun's disk. The day-to-day records of sunspots he kept for 18 years as part of that search led him to realize that solar behavior is cyclic.