by Ned Potter, ABC News
A large flare from the sun was observed yesterday, and the resulting expulsion of charged particles is expected to sail past the Earth this afternoon. Images from the Solar and Heliospheric Observatory -- the SOHO space probe -- showed a bright flash near the Sun's equator. Several of SOHO's sensors were temporarily overwhelmed by the amount of radiation, officials say.
Such flares, known as coronal mass ejections, are actually fairly common, experts say. The Earth is well protected by both its atmosphere and its magnetic field.
Effects on Earth
The most visible effect: auroras -- the so-called Northern Lights, often seen over Alaska and Canada at night -- might be visible tonight over some northerly parts of the lower 48 states.
But in an increasingly electronic age, there are sometimes surprising effects.
In 1998 a communications satellite broke down because of the radiation striking it, cutting off pager signals, long-distance calls and some radio transmissions.
In 1989 there was a blackout in Quebec, and scientists decided afterwards that it was the result of a power surge directly related to a solar flare.
Long-haul airliners on routes over the Arctic are sometimes diverted south, since the Earth's magnetism offers less protection near the poles.
"It is a rare occurrence to have a strong event like this so late in the solar cycle," said Larry Combs, a forecaster at NOAA's Space Environment Center in Boulder, Colo. The frequency of solar flares fluctuates in an eleven-year pattern, and the last peak was in 2002.
The ten least protected human beings are those currently in orbit -- the crews of the Space Shuttle Discovery and the International Space Station.
This morning the astronauts were instructed to sleep in sections that are well-shielded from radiation. NASA said the shuttle mission schedule would not be changed because of the solar storm.
Two shuttle crew members, Robert Curbeam and Christer Fugelsang, are performing a spacewalk late today to update the space station's wiring. NASA says they are sticking to plan -- though if there's another flare, they may be told to return to the station's airlock.
But NOAA, which was on alert this morning, said the magnetic pulse was so far not of a type that was likely to cause major problems. On a scale used by scientists, this solar storm was a "G2," meaning it had moderate strength.
"So far, yes, there's been a magnetic disturbance," said Joe Kunches, chief of the Forecast and Analysis Branch at the Space Environment Center. "And yes, it's coming from the sun, but the reality is that it's been less than severe -- so far."