two photos of a sunspot
Sunspots are dark markings on the photosphere that can be easily seen. Typical sunspots measure a few tens of thousands of kilometers across. They are usually found in groups of several to a hundred spots, most of them small but often dominated by one or a couple large spots. They consist of two parts, a dark umbra and a lighter penumbra. Sunspots are areas where a concentrated magnetic field protrudes through the hot gases of the photosphere. The field inhibits convection from below, making sunspots about 2500 degrees K cooler than a typical patch of photosphere. That is why sunspots look dark in contrast to their brighter surroundings. Sunspots are manifestations of the 11 year solar cycle.