Photo Courtesy of the nice folks at NASA's Solar and Heliospheric Observatory.Solar
& Heliospheric Observatory (SOHO). SOHO is a project of international
cooperation between ESA and NASA.
The sun goes through many different periodic cycles of activity. One of the most well documented cycles, which has shown to have many different effects here on Earth is the eleven-year solar cycle. In the image above shows several images around three years apart that show very well some types of solar activity. This eleven year cycle has many different characteristics from changes in the number of sunspots, the number of coronal mass ejections, Solar flare activity, are just a few. This activity does have effects that reach us here on the Earth. Several of these effects are disscussed in various parts of this website.
For everything you ever wanted to know about the solar cycle NASA has a very good website that explains most of the different behaviors in the sun. Just visit them at www.sunspotcycle.com.