Sun with sunspots over four days, from 2nd to 5th April 2006. Sunspots are dark regions on the surface of the Sun. They are seen moving from left to right due to the rotation 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. 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, and 2006 was close to the solar minimum, or quietest part of the cycle.