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| 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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