Over the Horizon

By James Marusek

It is December 2010 and time once again to reassess the sun’s transition into Solar Cycle 24. What lies ahead just over the horizon?

What are Solar Cycles?

The sun goes through a periodic change around every eleven years where the polarity of the sun’s magnetic field changes poles. Essentially the sun’s magnetic north pole becomes the south pole and vice versa. This is a normal process. As these poles realign and the magnetic field is the weakest, there is an absence of sunspots and this period is referred to as a solar minimum. A solar cycle or SC for short is measured from one solar minimum to the next. But even though the cycle repeats, the intensity of the solar cycle varies significantly. Scientists have been monitoring sunspots since the 1700’s. There observations have shown when the sun gets deafly quiet such as during the Maunder and Spörer Minimums; the world experiences great cold periods. These periods were so cold they were referred to as the Little Ice Ages.

What is different about Solar Cycle 24 and why is it relevant?


Since the sun has finally entered solar cycle 24 (SC24) with the resurgence of sunspots, most people have turned away from tracking the strength of the rebound. Had they looked, they would have found that the surge into this next solar cycle so far has been rather weak.

The Average Magnetic Planetary Index (Ap index) is a proxy measurement for the intensity of solar magnetic activity as it alters the geomagnetic field on Earth. It has been referred to as the common yardstick for solar magnetic activity. Ap index measurements began in January 1932. The quieter the sun is magnetically, the smaller the Ap index.

This solar minimum is rather unusual. If we define a period of quiet sun as those months that produced an Ap index of 6 or less and compare the total number of quiet months within each solar minimum, then the results would be: .....Follow this link for the rest of the article.  RK

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