This is a photo of a large sunspot group. The photo was taken on 19 June 2001 from Belcamp, Maryland. I used my Canon AE-1 Program camera, my Celestron 8" telescope, and a full aperture Thousand Oaks Optical solar filter. You can see some graininess to the photo. Some of that is due to the resolution of the film, and some is due to actual granulation on the sun. The sun's surface is not perfectly smooth- there are regions of superheated gas moving up and down, and these different areas show up as grainy patches. You can also see an effect called limb darkening around the edge of the solar disk. It looks darker because the surface of the sun has basically the same brightness everywhere, but the portions nearer the edge of the visible disk, or the limb, are seen through a very steep angle. This creates a nice three dimensional effect, reminding us that the sun is a sphere, not a disk, in space.
Sunspots are disturbances on the surface of the sun. They look black because they are somewhat cooler than the surrounding areas. Sunspots often harbor intense magnetic fields and can unleash powerful solar flares.