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ScienceShot: The Mystery of the Absent Sunspots

The sun is usually a predictable beast, at least as far as its sunspot cycle goes. Every 11 years or so, the sun's magnetic activity peaks and then troughs, resulting in relatively high and then low numbers of dark spots and flares on the solar surface. But in the cycle that has just finished, the trough went on for much longer than normal, with more than twice as many days without sunspots compared with previous cycles. To figure out what caused this, researchers used a computer simulation of the churning hot plasma inside the sun. As each cycle progresses, the movement of this plasma (black loop) shifts the solar magnetic fields (gold strands)—from which sunspots erupt—from the sun's midlatitudes to its equator. An extended minimum occurs whenever the plasma moves quickly at the beginning of a cycle—preventing a large buildup of magnetic fields—but then slows down toward the end, delaying the onset of the next cycle, the team reports online today in Nature. This knowledge won't help in predicting individual solar storms, the researchers say, but it should give scientists a better idea of how stormy the sun will be in the years to come. And that should help to limit the worst effects of storms, be it damage to satellites in orbit or harm to people flying close to the poles.

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