This week will be Sunspot Week in Weather Eye. We will mark the approaching maximum of sunspot Cycle 23, expected later this year, and examine the implications of that phenomenon nearly a hundred million miles away on this cool, sequestered vale of life we call the Earth.
As early as 1610 Galileo Galilei used his telescope to observe the setting sun, and noticed the dark spots which appear singly or in groups on its visible surface.
Later astronomers noticed that these spots increased and decreased in number over the years, and in 1843 a German astronomer, Heinrich Schawbe, found a pattern; he identified a more or less fixed cycle in the density of sunspots, with a period of about 11 years between one bout of maximum sunspot activity and the next.
During a minimum, the number of sunspots visible on the solar disc may be as low as 10. It is currently 106, and rising towards a maximum which has been predicted to occur around June or July this year. At the peak of Cycle 19 in October 1957, the most active recorded, there were well over 200 sunspots visible, and the last maximum in 1989 peaked at around 190.
If present predictions are correct the approaching maximum of Cycle 23 will have somewhere in the region of 140 sunspots in evidence on the solar disc.
But why all this fuss, you may wonder, about a few dark blobs so many million miles away? The problem is that unlike other astronomical phenomena, sunspots have a direct effect upon our planet. They are areas of intense magnetic activity, and solar flares send great bursts of energy towards the Earth; the more sunspots there are, the more intense these bursts of energy.
Solar radiation reaching the Earth consists in part of streams of tiny electrically-charged particles called the "solar wind"; they spiral outwards from the rotating sun like a mist of water droplets from a whirling hosepipe.
Surges in the solar wind at a sunspot maximum severely disrupt the Earth's magnetic field; among other things, they affect radio communications, facilitate more frequent and spectacular occurrences of aurora borealis, the northern lights, and have been known to disrupt the distribution of electrical power. Surges of solar energy also affect the density of our atmosphere, to the extent that spacecraft in low orbit may drift off course.
And there has long been speculation that sunspots may even affect our weather in some way, but so far any links in that respect are very tenuous indeed.