Sunspots (NASA/ SDO /HM1)
Sunspots are relatively dark regions on the sun's photosphere, its visible surface.
Sunspots are caused by intense magnetic fields and often occur in pairs, one correspoding to the north magnetic pole, the other to the south.
In size, sunspots vary from about 16 km to about 160,000 km.
Individual sunspots persist for days or weeks.
A. Milovanov and L. Zeleny explain sunspots as a consequence of fractal clusters of magnetic field lines. The formation and lifetimes of sunspots simulated with this model agree well with observations.
Careful counts of sunspot numbers indicate an approximate 11 year cycle, though this may be superimposed on a much slower cycle.

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