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Sun flips magnetic field

The sun's magnetic poles flip like clockwork about every 11 years  

(CNN) -- The poles of the sun's powerful magnetic field have reversed, signaling a time of peak solar activity that could spell trouble for planet Earth, astronomers said this week.

The sun's magnetic north and south poles were in their respective northern and southern hemisphere several months ago. Yet since then they have migrated to the opposite sides of the star.

The bipolar flip did not take astronomers by surprise. It takes place like clockwork on the sun, once about every 11 years.

"This always happens around the time of solar maximum," NASA physicist David Hathaway said in a statement. "The magnetic poles exchange takes place at the peak of the sunspot cycle. In fact, it's a good indication that Solar Max is really here."

During Solar Max or solar maximum, the sun tends to exhibit more sunspots and eruptions, and jettison more solar flares, which send powerful streams of charged particles into the solar system.

Solar blasts heading toward Earth can stoke up beautiful auroras in the nighttime sky, and wreak havoc on communications satellites and electrical power grids.

Astronomers consider the current solar maximum more powerful than average, but less intense than the last two in 1989 and 1979.

Earth's magnetic fields also change places but with much less predictability and frequency. The reversals take place between intervals lasting from 5,000 to 5 million years. The last one happened 740,000 years ago, scientists estimate. Some suggest the planet is overdue for another one.

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The Solar and Heliospheric Observatory

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4:30pm ET, 4/16

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