General Astronomy/The Solar Cycle

The solar cycle is the repeating rise and fall of "solar activity" (which see). This consists of a roughly 11-year cycle in which the numbers of sunspots rises to a maximum and then falls back to some minimum level. Actually the exact time period has varied, from about 7 to about 13 or 14 years, and the maximum number of sunspots varies as well. Some cycles are more "active" than others.

Shortly after each maximum, the magnetic polarity of the sunspots reverses and it maintains that polarity until the next maximum, roughly 11 years later. Thus the solar cycle is not just 11 years, but 22 years since after 22 years the magnetic polarity returns to approximately its original configuration.

The cycle is sometimes unpredictable. During the Maunder Minimum, solar activity was drastically reduced for about fifty years. In 2008, the then current sunspot minimum was noted as the "quietest" in 50 years. As of late 2009, solar activity began a slow increase.

While the sunspot cycle is certainly related to other activity on and in the Sun, many attempts have been made to relate it to various cycles on the Earth ranging from the quality of wines to fashion trends and the stock market. No such relation has been proven, and in fact no strong relation between the sunspot cycle and earthly weather patterns has yet been conclusively shown.

The period of Maunder Minimum, from about the middle of the 17th through the early part of the 18th centuries, was attended by abnormally cool and damp weather worldwide. Attempts have been made to correlate this climatic aberration to the absence of sunspots, but if the relation is real, no causal mechanism has been identified.

In addition, one tentative relation to temperature variation in an upper layer of Earth's atmosphere appears likely, but no other direct and predictable relation has yet been shown.