Everything about Sunspot Cycle totally explained
Sunspot numbers rise and fall with an irregular
cycle with a length of approximately 11 years. In addition to this, there are variations over longer periods. These cycles are called the
Sunspot cycle. The recent trend is upward from 1900 to the 1960s, then 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 might be expected that more sunspots lead to less solar radiation. However, the surrounding areas are brighter and the overall effect is that more sunspots means a brighter sun. The variation is very small (of the order of 0.1%).
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.
Wainwright has 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.
Sunspot activity has a major effect on long distance
radio communications particularly on the
shortwave bands although medium wave and low
VHF frequencies are also affected. High levels of sunspot activity lead to improved signal propagation on higher frequency bands. Although they also increase the levels of
solar noise and ionospheric disturbances. These effects are caused by impact of the increased level of solar radiation on the
ionosphere.
Since the mid 18th century sunspot cycles have been numbered. As of early 2008 we're seeing the end of "cycle 23" and the beginning of "cycle 24"
(External Link
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