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Despite these early observations, it was only after the invention of the telescope, in 1609, that any real study of sunspots was possible. In 1610 (though he was not the first) the astronomer and mathematician Galileo Galilei made one of the first serious studies of sunspots. However, the quality of telescopic optics was still very primitive and it was some years before any conclusive theories were established. Daily observations were started at the Zurich Observatory in 1749 and, with the addition of other observatories, continuous observations began in 1849.
Although we have known of the existence of sunspots for many centuries, our understanding of them has been far less certain. Since they moved across the surface of the Sun, some thought they might be small planets in orbit; sceptics felt they were simply imperfections within the telescope optics themselves.
The theory behind sunspots
The number of sunspots follows a cyclical period of about 11 years, something that was first noted by Heinrich Schwabe in 1843. This year (2000) is a peak of the cycle, a period known as the Solar Maximum. This period of high activity will drop steeply over the next few years and begin building again in around five years time. There are two ways of plotting this cycle. One is to simply count the number of spots and by plotting the numbers against a time scale a periodicity can be determined. Another is by means of the so called 'Butterfly Diagram’. At the beginning of a new sunspot cycle sunspots appear mainly close to the Sun's north and south poles. As the sunspot cycle progresses, more sunspots appear closer to the Sun's equator.
Sunspots are usually seen in groups of two. One set will have positive or north magnetic field while the other set will have negative or south magnetic field. All but the smallest spots show a dark central portion called the umbra with a lighter outer area called the penumbra. Perhaps the biggest 'unknown’ in our understanding of sunspots is the fact that their magnetic field flips between cycles. After Solar Maximum there is a short period of overlap where some spots of the old cycle have a polarity that is opposite to that of the new ones.
Although the 11 year cycle has been consistent in modern times, there was a period, approximately between 1645 and 1715, when there were virtually no spots at all. This period is known as the 'Maunder Minimum’, after the British astronomer who discovered it from the records in 1890. This might itself be a part of a cyclical period though it is impossible to be sure since we have been recording them for a relatively short period of time.
Scientists have not found any measurable connection between the number of sunspots on the Sun or any other measure of the solar cycle and the day-to-day variation in the weather on Earth. However, some scientists make do make a link between climate-change on Earth and state of the solar cycle.
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