<Li> Middle: sunspot close - up in the visible spectrum (left) and in UV, taken by the TRACE observatory . </Li> <Li> Bottom: A large group of sunspots stretching about 320,000 km (200,000 mi) across . </Li> <P> Sunspots are temporary phenomena on the Sun's photosphere that appear as spots darker than the surrounding areas . They are regions of reduced surface temperature caused by concentrations of magnetic field flux that inhibit convection . Sunspots usually appear in pairs of opposite magnetic polarity . Their number varies according to the approximately 11 - year solar cycle . </P> <P> Individual sunspots may last anywhere from a few days to a few months, but eventually decay . Sunspots expand and contract as they move across the surface of the Sun, with diameters ranging from 16 km (10 mi) to 160,000 km (100,000 mi). The larger variety are visible from Earth without the aid of a telescope . They may travel at relative speeds, or proper motions, of a few hundred meters per second when they first emerge . </P>

What are the dark spots on the sun called