Sun with sunspots. Sunspots are dark regions on the surface of the Sun. They appear dark as they are cooler than the surrounding solar surface, although this is only an effect of contrast: they are still extremely bright in real terms. It is thought that they are cooler due to the presence of tangled magnetic fields in the convective layer of the Sun, which usually brings hot plasma to the surface. The magnetic fields inhibit the convection, thus making the area cooler. Sunspots vary in frequency on an 11 year cycle. This image was taken on 2nd April 2006, during the solar minimum, or quiet period of the cycle.