Sunspots

These are dark regions which appear on the surface of the Sun. They are darker because they are cooler than the regions surrounding them. (They are not actually dark at all but only appear so when compared with the rest of the Sun's surface. 5000K instead of 5700K))

 They are huge, as large as planets. They consist of a darker region, the umbra, surrounded by a less dark region, the penumbra.

They usually appear in pairs and usually last from 50 to 100 days.

When one observes the surface of the Sun over several days one sees that sunspots move as shown above, clear evidence that the Sun is rotating. Galileo was one of the first people to notice this. We also notice that the Sun rotates faster near its equator (period = 25 days) than it does near its poles (period = 36 days).

The Sunspot Cycle
The number of sunspots present seems to vary over an 11 year cycle from almost zero up to over 100.

Sunspots appear at high latitudes, 35 to 40 degrees, then as the cycle progresses they appear closer to the equator. At solar max they are around 15 degrees. As the cycle fades they move even closer to the equator to about 7 degrees.

         pic NASA

Scientists now think that this cycle is due to twisting of the Sun's magnetic field. Because the Sun rotates faster near its equator its magnetic field lines become twisted and distorted. Pairs of sunspots are the Norths and Souths of these disturbances. Charged particles from the Sun travel in huge loops due to these twists in the Sun's field.

(Where the magnetic field exits and enters the Sun there is less convection so it is cooler.)

Imagine twisting rubber bands more and more, eventually they will snap with a huge release of energy in the form of solar flares. This is what happens at "solar max" when the number of sunspots is  maximum. This is usually accompanied by a big increase in the amount of solar wind which arrives at Earth.

After this release of energy the Sun settles down and the cycle starts again.