Sunspots are regions on the surface of the Sun that are cooler, and hence
appear darker, than their surroundings. The difference in temperature can
amount to 1500 degrees K.
Sunspots were discovered by Galileo when he first
used his telescope to look at the Sun.
The number, position and magnetic orientation of sunspot pairs varies throughout
the solar activity cycle.
There are a lot of nice web sites that talk about the solar cycle and sunspots.
Follow the links here: