Sun Flips Out to Flip-Flop

The sun is a strange and turbulent place. The scorching hot ball of gas may look smooth from a safe distance, but dark spots, violent explosions, and massive eruptions constantly come and go on its surface.

Scientists have noticed that the sun gets especially stormy every 11 years or so—a period known as the solar cycle. At about the same time, our star’s magnetic poles suddenly flip: North becomes south. South becomes north.

This ultraviolet image shows part of a huge magnetic loop of hot gas (bottom) sticking out from the sun’s south pole.

NASA, European Space Agency

Researchers at NASA’s Goddard Space Flight Center in Greenbelt, Md., now think they’re getting closer to understanding what causes the sudden switch in direction. Huge clouds of electrically charged particles called coronal mass ejections (CMEs) might have something to do with it, they say. Spit out by the sun from time to time, such clouds can weigh billions of tons.

The researchers collected data from two, 11-year sun cycles. For both cycles, the researchers saw an increase in CMEs at the poles of the sun just before the magnetic switch happened. They think the clouds are blasted off the sun, carrying away old magnetic fields and preparing it for the switch.

Why does it happen every 11 years or so? That’s a question that no one has an answer for yet. Perhaps it’s just long enough for the sun to be ready for something different!—E. Sohn

Going Deeper:

Cowen, Ron. 2003. Solar flip-flops: Sun storms spawn magnetic reversal. Science News 164(Dec. 6):355-356. Available at http://www.sciencenews.org/20031206/fob2.asp .

You can learn more about the sun’s magnetic-field flips at www.gsfc.nasa.gov/news-release/releases/2003/03-97.htm (NASA Goddard Space Flight Center) and science.nasa.gov/headlines/y2001/ast15feb_1.htm (NASA).