When we look at the sun (carefully), it appears to be a uniform, unchanging star. But scientists and engineers have a much different perspective. To them, the sun is a dynamic, chaotic, and poorly understood caldron of thermonuclear forces, one that can spit out fierce bursts of radiation at any time.

And when Earth lies in the path of that blast, the flare can play havoc with power grids, disrupt radio communications, and disturb or disable satellites. Fifty years into the Space Age, Earth has avoided the worst the sun can deliver – so far.

But with the sun entering a period of increased activity, more frequent solar flares could be headed our way. This has many astronomers and companies asking if satellites and power grids are ready.

Solar flares are a product of the sun’s complex chemistry, says Haimin Wang, director of the Space Weather Research Lab at the New Jersey Institute of Technology in Newark. The internal processes of the sun create whirlpools of magnetic force, which slightly lower the surface temperature of the sun, causing what we see as sunspots.

Every 11 years, the sun flips its magnetic north and south. This swap churns up an increased number of sunspots, with the next volatile peak due in 2012. Magnetic energy can build up on the solar surface and then suddenly be released in a massive burst.

This flare, a wave of particles moving at near the speed of light, arrives at Earth shortly after the light itself, which takes about eight minutes to cross the 93 million miles. In other words, sky-watchers won’t know there has been a solar flare until shortly before the radiation arrives.

The burst is largely cushioned by Earth’s atmosphere, according to Madhulika Guhathakurta, program director for the National Aeronautics and Space Administration’s STEREO mission, which studies solar forces from a pair of spacecraft orbiting the sun.

Because of atmospheric padding, the burst poses little risk to people on the ground. However, airplanes at cruising altitude and spacecraft are much more vulnerable. The flash also can zap electronics on satellites, which lie entirely outside the safety of Earth’s atmosphere.

While this initial burst can be dangerous, there’s a much slower wave of energy – a coronal mass ejection (CME) – that really can mess with electronics.

Not every flare produces a CME, and they often occur when no flare is present. When they do spew out, CMEs send strong waves of electromagnetic force our way. The most visible signs of this are the colorful northern and southern lights. But it also has more serious consequences.

For one, it can cause electrical transformers to trip or fail, which can lead to widespread power outages. A particularly powerful CME storm hit Earth in 1921, before electricity played as big a role in daily life. If a burst of similar magnitude hit today, it would interrupt power for as many as 130 million people, according to a recent report by the National Academy of Sciences. In 1989, a geomagnetic storm knocked out power to 6 million people in Quebec.

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