UNLIKE most other astronomical phenomena, the little dark blobs on the surface of the solar disc that we call "sun spots" are known to have an effect upon our planet. Sunspots are areas of intense magnetic activity, and solar flares in their vicinity send great bursts of energy towards the Earth. The more sunspots there are, the more intense these bursts of energy.
Among other things, for example, solar flares at their most active cause erratic variations in the Earth's magnetic field, affect radio communications and interfere with power lines, and lend a spectacular appearance to the aurora borealis, the northern lights. They also affect the density of our atmosphere to the extent that spacecraft in low orbit may drift from their intended paths.
In the closing years of the last century an astronomer called Edward Maunder made a rather startling discovery about sunspots. Browsing through the meticulous records left by astronomers since the invention of the telescope, he noticed that while the 11 year cycle of increasing and decreasing numbers of sunspots was clearly evident over the centuries, there was a long period between 1645 and 1715 when no spots appeared to have been seen at all. Maunder published his findings in 1894 and again in 1922 to a scientific world that bubbled over with indifference: it was assumed that he had got it wrong, or that the original solar watchers had been lax.
But in the early 1970s, another astronomer, Jack Eddy, blew the dust from Maunder's old reports, and confirmed that what has come to be called the Maunder Minimum really did exist. Going even further, he related the historical waxing and waning of sunspot activity to variations in the amount of the radioactive element carbon 14 to be found in contemporary timber in this way, using even older wood, he was able to extend the record of sunspot activity backwards to periods long before the era of the telescope.
The carbon 14 measurements confirmed the Maunder Minimum most convincingly. And Eddy also identified another two anomalies: the so called Sporer Minimum from 1400 to 1510, and the Medieval Maximum, a period of unusually high sunspot activity from AD 1100 until 1250. Meteorologists were quick to note that the two minima coincided nicely with the worst excesses of the "Little Ice Age", and that the Medieval Maximum occurred at a time when we know the climate of the northern hemisphere to have been unusually benign. The finding added fuel to a controversy that is still going on the possible relationship between sunspots and the global climate.