Although only average for a star, the sun’s incredible physical
forces are sufficiently awesome to make even the worst manmade
snafus, such as the once-threatening Y2K phenomenon, look pretty
puny. The sun’s visible surface has a temperature of nearly
10,000 degrees Fahrenheit, and the temperature of its outer atmosphere,
or corona, reaches 1.8 million degrees. A second's worth of the
sun’s energy output would be enough to power the toasters,
television sets and refrigerators of Americans for roughly the
next 9 million years. Fortunately, solar storms transmit only
a minuscule fraction of the sun’s energy potential; but even
so, a relatively mild solar storm in January 1997 poured 1,400
gigawatts of power into our planet’s atmosphere over a two-day
period. That’s nearly double the power-generating capacity
of the United States.
The precise
cause of solar flares remains a mystery, but scientists link them
to sunspots, relatively cool areas that appear as dark marks on
the sun’s surface. A sunspot, which exists for anywhere from
several days to several weeks, is also a location where the lines
of the sun’s magnetic field have become twisted and temporarily
disrupted. Somehow, this “magnetic shear” results in
a solar flare — a temporary release of an enormous burst
of energy, equivalent to approximately 40 billion Hiroshima-size
atomic bombs. In 1997, the Solar and Heliospheric Observatory
(SOHO), a joint U.S.-European orbiting observatory, captured the
first close-up photographs of a solar flare and its effects —
dramatic images of a shock wave moving across the face of the
sun.
Flares are
sometimes (but not always) accompanied by "coronal mass ejections,"
huge bubbles of gas threaded with magnetic field lines. CMEs occur
about once a week during the sun’s quiet periods, but two
or three times a day during a solar maximum. CMEs can disrupt
the solar wind — the stream of magnetic gas that normally
flows from the sun toward Earth — and in the process, shake
our planet’s magnetic field in ways that wreak havoc.
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