The Solar Cycle

Every 11 years (sometimes a little faster sometimes a little slower) the Sun changes appearance, from having lots of sunspots visible on its surface to having very few, and back again. The plot above shows the average number of sunspots seen on the Sun as time passes. Those times when the Sun has lots of sunspots are called times of solar maximum. At these times there are also many more flares and coronal mass ejections. The opposite portion of the solar cycle, when the Sun has few spots, only small flares, and fewer coronal mass ejections, is called solar minimum. Very soon after sunspots were first seen through telescopes, there was a much longer than normal period of time when very few sunspots could be found. Today we call this the Maunder minimum.

It is not just the number of sunspots which changes duing the solar cycle, but where on the Sun they are found. In the beginning of the cycle, sunspots appear at mid lattitudes. As the cycle progresses, they are found close and closer to the equator. If you plot the lattitude of the sunspots with time (above top) you get what solar physicists call the butterfly diagram. This change in position with time holds some important clues about the cause of sunspots, the solar dynamo.