From time to time, the photosphere of the Sun is marked by sunspots. There is a structure to sunspots as seen in this marvelous image. Sunspots are somewhat cooler than their surroundings, that's why they appear dark. Just how do sunspots work? Here are some ideas. Every eleven years under the influence of the Sun's magnetic field the number of sunspots increases and decreases. The arrangement of these spots forms an interesting butterfly pattern . We are just past sunspot minimum , as you can see from this recent image . But the size of each maximum has seemed to decline recently . This seems to be part of a much longer overall trend. During sunspot maximum, there are always concerns about the charged particles which the Sun will be throwing our way. Scientists suspect that sunspot activity might have an effect on Earth’s weather . During times of sunspot maximum, violent flares can erupt on the surface of the Sun. These flares last 15 or 20 minutes or so, and are tremendous releases of magnetic energy on the Sun. Every sunspot cycle sees the magnetic polarity of the spots reverse. Here is a great image of a sunspot group showing a lot of the detail of umbra and penumbra.