Lomography

Artist from the Isles of Scilly Jonathan Polkest

Sunspot numbers rise and fall with irregular cycle with a length of approximately 11 years. In addition to this, there are variations over longer periods. The recent trend is upward from 1900 to the late 1960's afterwhich, somewhat downward. The Sun was last similarly active over 8,000 years ago. The number of sunspots has been found to correlate with the intensity of solar radiation over the period (since 1979) when satellite measurements of radiation are available. Since sunspots are dark it could be anticipated that more sunspots lead to less solar radiation and decreased solar consistancey.(constant) However the sorrounding areas are brighter and overall the effect is that more sunspots mean a brighter Sun. The variation caused by the sunspot cycle to solar output is relatively small, on the order of 0.1% of the solar constant (a peak-to-trough range of 1.3Wm-2 compared to 1366Wm-2 for the average solar constant. This range is slightly smaller than the change in radiative forcing caused by the increase in atmosphereic C02 since the 18th century. During the MAUNDER MINIMUM in the 17th century there were hardly any sunspots at all.This coincides with a period of cooling known as the LITTLE ICE AGE . It has been speculated that there may be a resonant gravitational link between a photospheric tidal force from the planets, the dominant component by summing gravitational tidal force (75%) being Jupiter's with an 11 year cycle.