A telescopic view of our sun through a strong solar filter. You can see several sunspots, the biggest were visible with the naked eyes ( through an appropriate filter of course!)and had roughly the diameter of our earth. They are areas where strong magnetic fields prevent the convection of hotter sub-surface material to the surface, which makes these spots considerably cooler ( up to 2000K) and less luminous than the surrounding areas.
There are also areas called "faculae" with higher temperatures and higher luminousity,looking brighter in the above picture