Sunspot Detail

Shown here is a detail of a sunspot from the Sun. They emerge when magnetic field pops up at the solar surface from below in the form of many thin, bent strands, called magnetic flux loops tubes. These are less than about 150 km across and clump together at the surface, forming greater concentrations of magnetic field. When theses concentrations are a few hundred kilometers across, they show up as pores. When the pores grow to be about 2400 km across, they develop a penumbra and change into sunspots. On our Sun they generally grow for a few days, and then start to slowly decay again. The biggest of sunspots may live for up to a few weeks.
Approximate Diameter: 
 Pores:  100-1000 km 
Penumbra:  2500-50000 km 
Umbra:   1500-35000 km