The number of sunspots on the face of the Sun varies with an 11 year period called the sunspot cycle. Sunspots have strong magnetic fields, thousands of times stronger than Earth's. The magnetic fields help keep sunspots cool and also serve as a reservoir of energy for explosive events like solar flares. Sunspots were discovered by Galileo Galilei and Thomas Harriot around the end of 1610. Johannes Kepler may have been the first to see a sunspot in 1607, but he thought the dark spot was Mercury crossing the disk of the Sun.
Sunspots appear dark because they are cooler than the surface of the sun.
In fact they are very hot and bright. Today's white light picture of the Sun was captured at the Big Bear Solar Observatory in California. Click on the image for a larger picture. A series of solar flares and a coronal mass ejection could trigger auroral displays on Earth. Nevertheless, NASA scientists have developed methods to predict the time and date of the next solar maximum.