NO doubt, in 1610, when Galileo Galilei began to examine the heavens through his telescope, he was careful, as we all must be, not to look through it directly at the sun. Whatever his methodology, he discovered dark circles on the surface of the solar disc. "Sun-spots", as they came to be called, became a familiar sight to generations of astronomers, and it was soon known that they varied greatly in number, size and lifespan over the years.
Twenty or 30 sunspots may be seen at any one time, each one anything from 1,000 to 20,000 miles across, and their life-cycle varies in length from a couple of hours to several months. As far as we know, they seem to be caused by the protrusion of a strong concentration of magnetic activity through the sun's surface; above the dark areas these magnetic forces act as a scaffolding to support the filaments of glowing gases which, when viewed at the appropriate angle, appear at the sun's edge as beautiful arched streamers of multicoloured bunting.
But in 1843 there came a very surprising development. An astute German astronomer called Heinrich Schwabe noticed that sunspots seemed to follow a pattern: their number increased to a maximum and then decreased again in a rhythmic cycle which was very close to 11 years in length. The "solar cycle" had been discovered.
Scientists now pored over the records of their predecessors and decided to put the whole thing into some kind of order. They defined a sunspot, cycle as beginning at the time when the number of sunspots was at a minimum, and lasting, through the maximum, until the next minimum about 11 years later. They called the cycle beginning in 1749 cycle zero, and numbered the rest consecutively. And their numbering system has stood the test of time: cycle 22 peaked in June 1989 and came to an end earlier this year. Sunspot numbers have now begun to increase again as we advance through the early stages of cycle 23.
Sunspot cycles vary in activity. Sometimes at the mid-cycle maximum the average number in a month may be as low as 60; at other times, for instance at the peak of cycle 19 in October 1957, there are a great many more in that case a monthly average of 254. The most recent maximum in 1989 peaked at a monthly mean of 196.
There has long been speculation that variations in solar activity affects our weather in some way, but although some tenuous links appear to have been established, only one or two brave souls have attempted to harness sunspots as predictive tools.