Solar minimum - Definition and explanation

Solar minimum represents the period of weak Sun's activity, and some scientists also refer to this as the Sun's quiet period. This period of weaker solar activity isn't always of the same length, and the latest occurred almost two years ago, in December 2008. The Sun's activity strengthens and weakens on a cycle that typically lasts 10.7 years. Since accurate records began more than 350 years ago, in 1755, there have been 24 such solar cycles.

However the 23rd cycle, which ended in December 2008, was somewhat strange compared to previous cycles. This cycle lasted both longer than average and had the smallest number of sunspots in the last 100 years. Sunspots represent areas of intense magnetic activity that are visible as dark spots on the star's surface. The 23rd cycle lasted 12.6 years, the longest in the last 200 years.

Scientist still cannot tell with certainty why this latest weak period was prolonged, and currently dominant theory explains that this is probably due to the changes in the Sun's "conveyor belt".

As scientists explain conveyor belt acts similar to the Earth's ocean currents. The Sun's conveyor transports burning plasma across its surface to the pole where the plasma sinks into the heart of the Sun before rising again at the equator. During the before mentioned 23rd cycle, the plasma traveled all the way to the poles, while in previous cycles plasma extended to about two thirds of the way.

Some scientists support different theories, for instance Dr David Hathaway, a solar physicist from Nasa's Marshall Space Flight Center in Alabama believes that it was the speed and not the extent of the conveyor that was of real importance for latest weak Sun's activity.