Strolling outside Arizona's Kitt Peak National Observatory during a work break, staff observer Paul Avellar at first thought the angry red glow in the night sky was caused by forest fires. Then, seeing a greenish fringe and vertical streamers stretching like ribbons above the horizon, he realized what was happening. He raced to a telephone and called his wife and friends, awakening them and insisting they share the view. "A chance like this doesn't come along very often," says Avellar. "To see the northern lights is very humbling and awe-inspiring. You realize the sun is just going about its business and making our nighttime sky glow without any trouble at all. It makes you wonder what would happen if the sun ever really got mad."
Some 93 million miles away, the sun was, at the very least, agitated. In early March, an area of sunspots large enough to contain 70 earth-size planets had come into view around the eastern rim* of the glowing orb. Created by intense magnetic fields and cooler than the surrounding gases, the sunspots were visible as dark blemishes on the fiery surface. Just as astronomers were turning their attention to the mottled region, a bright spot suddenly appeared in its midst. It spread like a prairie wildfire, glowing white hot on the sun's yellow face and quickly expanding to cover hundreds of thousands of square miles. The monster blotch was an unusually large solar flare, a stupendous explosion that belched radiation and billions of tons of matter far into space.
The great flare, and its coterie of sunspots, was an unmistakable signal. It heralded the imminent arrival of the solar maximum: the period every eleven years or so when the sun reaches its peak levels of activity and pointedly reminds earth dwellers of its awesome power. At maximum, the sun
bombards the planet with radiation and particles, causing unusually brilliant auroras, communications blackouts and power failures. But it also gives scientists a fresh opportunity to solve some of the mysteries surrounding the star that provides the earth with energy, drives the weather and sustains life itself.
During a maximum, marked by a jump in the number of sunspots and flares, giant loops of incandescent gases, called prominences, proliferate, shooting tens of thousands of miles above the solar surface, sometimes hanging suspended for months. The solar corona, the halo around the sun visible during total eclipses, becomes fuller and brighter; great blobs of the corona, containing billions of tons of hot gas, occasionally burst free, shooting into space at speeds as high as 2 million m.p.h. And the earth's upper atmosphere, pummeled by solar particles, is laced by electrical currents of as much as a million amperes. These in turn create powerful magnetic fields that raise havoc below.
Because the previous maximum occurred in late 1979, astronomers had targeted 1991 as the year when solar frenzy would again peak. But the sun is notably capricious. While the intervals between maximums average eleven years, some have been as short as seven, others as long as 17. Ever since the sun began revving up three years ago toward the next maximum, its activity has mounted with unprecedented speed.