|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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