Sunspots come in pairs with opposite magnetic polarity. If we could bury a giant horseshoe magnet beneath the surface of the Sun, it would produce a magnetic field similar to that generated by a sunspot pair.
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Windows to the Universe original artwork by Randy Russell using an image from NASA's TRACE (Transition Region and Coronal Explorer) spacecraft.

Sunspots and Magnetic Fields

Sunspots are caused by very strong magnetic fields on the Sun. The best way to think about the very complicated process of sunspot formation is to think of magnetic "ropes" breaking through the visible surface (photosphere) of the Sun. Where the rope comes up from the solar surface is one sunspot and where the rope plunges into photosphere is another sunspot.

As you can see in the picture to the left, one sunspot has North magnetic polarity and one sunspot has South magnetic polarity.

Scientists believe the differential rotation of the Sun is the underlying cause of the magnetic ropes on the Sun. Since the gaseous sphere of the Sun rotates more quickly at its equator than at its poles, the Sun's overall magnetic field becomes distorted and twisted over time. The twisted field lines eventually come through the photosphere, showing their presence as sunspots.

When the tangled fields reach a "breaking point", like a rubber band that snaps when wound too tight, huge bursts of energy are released as the field lines reconnect. This can lead to solar flares and Coronal Mass Ejections (CMEs).

Last modified January 19, 2010 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA