Sunspot populations quickly rise and more slowly fall on an irregular cycle about every 11 years. Significant variations of the 11-year period are known over longer spans of time. For example, from 1900 to the 1960s the solar maxima (the period of greatest activity in the solar cycle of the sun) trend of sunspot count has been upward; from the 1960s to the present, it has diminished somewhat. The Sun is presently at a markedly heightened level of sunspot activity and was last similarly active over 8,000 years ago.


The number of sunspots correlates with the intensity of solar radiation over the period (since 1979) when satellite measurements of absolute radiative flux were available. Since sunspots are darker than the surrounding photosphere it might be expected that more sunspots would lead to less solar radiation and a decreased solar constant. However, the surrounding margins of sunspots are hotter than the average, and so are brighter; overall, more sunspots increase the sun's solar constant or brightness. During the Maunder Minimum in the 17th Century there were hardly any sunspots at all. The Maunder Minimum is the name given to the period roughly from 1645 to 1715, when sunspots became exceedingly rare, as noted by solar observers of the time. It is named after the solar astronomer Edward W. Maunder (1851-1928) who discovered the dearth of sunspots during that period by studying records from those years. During one 30-year period within the Maunder Minimum, for example, astronomers observed only about 50 sunspots, as opposed to a more typical 40,000-50,000 spots. This coincides with a period of cooling known as the Little Ice Age.


2) During the "Maunder Minimum", there were: