Friday, March 23, 2007

The Magnetic Sun

This week, the recently launched "Hinode" satellite returned some stunning new photos and video of our Sun. Focusing near the edge of our star, the space telescope documents the turbulent boiling of the solar surface in exquisite detail. But look a little closer and you will notice that as the hot material flows away from the surface, it does not simply stream off in any direction. It follows the invisible lines of a pervasive and dynamic magnetic field.

Galileo was the first to point a telescope at the Sun, revealing the dark spots that litter the surface. We now know that these "sunspots" are areas where the magnetic field is stronger, inhibiting the boiling motion and keeping the surface cooler -- and thus darker -- than its surroundings. Each spot is enormous, typically the size of our entire planet. But sunspots are only the beginning of the story of our magnetic Sun.

If you watched the Sun closely over many years, and you counted the total number of sunspots regularly, you might notice an interesting pattern. Every 11 years, the Sun seems to show a few sunspots, then many more, and then fewer again. What's more, when there are only a few spots they seem to show up in two bands, about halfway between the Sun's equator and poles. Over the course of this 11 year "solar cycle" they increase in number, migrate toward equator, and gradually fade away.

As the decades go by, you would notice that some of the cycles are stronger than others -- generating far more sunspots during the peak. Best of all, you would undoubtedly notice the huge explosions on the Sun's surface that eject hot gas out into space, sometimes directly at the Earth. When there are many sunspots, these explosions are more frequent and more dangerous. They are powerful enough to threaten astronauts and orbiting satellites, disrupt our communications systems, and occasionally bring down electricity grids.

With this new eye in the sky, astronomers will study the underlying order in these patterns -- eventually helping us predict the explosions and protect ourselves from the boiling magnetic Sun.

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