Storm on the Sun

It was as if a poltergeist had suddenly gone on a global rampage. At higher latitudes, large glowing streaks and patches of light appeared in the nighttime sky. Short-wave radio communications were disrupted, compass needles danced dizzily back and forth, and utilities braced for stray surges of current that could knock out their power lines. Even the navigational ability of pigeons was believed to be temporarily impaired. These strange doings were not the work of an earthly ghost, but had their source in very real events occurring some 93 million miles away. With no forewarning, the sun underwent a series of violent eruptions that caused some of the worst magnetic storms on earth in recent years.

The storms were triggered by the streams of particles--mostly protons --spewed from the sun's turbulent surface during the eruptions. As these particles reach the vicinity of the earth, they ionize the gases of the upper atmosphere, causing such spectacular displays as the Northern Lights, blacking out radio transmissions and creating a host of other electromagnetic disturbances. The bombardment is not hazardous to terrestrial life, because most of the particles are absorbed by the atmosphere or deflected by the earth's magnetic field. But they could cause illness and perhaps death to space travelers shielded only by the thin walls of their spacecraft.

The solar outbreak came at an unusual time--only about three years after sunspot activity (usually associated with such eruptions) had reached its maximum in what is generally an eleven-year solar cycle. Said Solar Forecaster Robert Doeker at the National Oceanic and Atmospheric Administration's observatory in Boulder, Colo.: "It's like getting snow in Atlanta in July."

Recorded observations of sunspots were made by Chinese astronomers as long as 2,000 years ago, but it is only recently that scientists have begun to understand how they are formed and how they relate to other events on the sun's surface, or photosphere. The spots are apparently products of intense magnetic fields generated by currents of as high as a trillion amperes, and usually occur in pairs consisting of one positively charged and one negatively charged spot. As a result of this opposing polarity, lines of magnetic force link the spots, keeping gases trapped within them. Because hotter plasma from the sun's interior cannot move into the sunspots, they remain relatively cooler (and darker) than the rest of the photosphere.

Solar astronomers do not know why the formation of sunspots is cyclical, but the related eruptions usually seem to take place near the spots when there are many of them on the surface and the magnetic patterns have become more complex. Most likely, the eruptions are the result of the tremendous release of energy that occurs when there is a lightning-like discharge from nearby regions of opposing polarity. During these upheavals, huge areas of the sun become extremely bright, and hails of particles and intense electromagnetic radiation, including powerful X rays, shoot into space.

To learn more about these flare-ups--and also how to predict them--scientists have established some 45 solar observatories around the world.

Using batteries of instruments that include solar telescopes equipped with cameras, spectroscopes and magnetographs, they maintain constant vigilance of the sun, looking for the smallest sign of unusual solar activity. But the accurate forecasting of flare-ups is still what Solar Physicist Robert Noyes of the Harvard and Smithsonian observatories calls "very much a black art," a description that is fully supported by last week's dramatic--and unexpected--events on the sun.

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