SOHO image of the current Sun showing large sunspots, and
indication of solar rotation.
Pictures of Sun: try following URLs: www.sunspotcycle.com and science.msfc.nasa.gov.
Sunspots are cooler regions on the surface of the Sun; by about 1000-1500 K.
They are also regions of strong magnetic field. Magnetism is crucial to the nature of
the phenomena we see on the solar surface.
A good picture of a sunspot is given in Figure 17.17 of your textbook. Its structure
is even remininscent of iron filings in a magnetic field. Large sunspots are larger in
size than the whole planet Earth.
Figure 17.17 of your book also shows another interesting and important feature.
Granulation, which corresponds to convection cells, or boiling of the
solar surface. This convection means that the interior of the Sun is even hotter than
its surface.