Return of the Northern Lights

Enlarge Image Image Gallery Curtains of color thrown across the sky. This September and October may see the northern lights moving south. DAVID PARKHURST

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0N THE NIGHTS OF MARCH 12 and 13, 1989,the phones of police and radio stations in southern parts of the country began ringing. People lucky enough to be outdoors marveled. A legend had become reality: The colored shapes of the aurora borealis glowed in skies as far south as the Caribbean and Central America. And there's a strong chance people across the U.S. may see the lights again. In fact, September and October of 1989 should offer some prime opportunities.

What to Look For

Northern lights are, indeed, usually a phenomenon of the Far North. Even in southern Canada they seldom cover the entire sky. A typical good auroral display in the northernmost U.S. begins with the formation of a slightly greenish horizontal arc of light low in the north. Next, several vertical rays may appear within, or extend up from, the arc and begin to restlessly search the northern sky. Up to this point, the aurora is already eerie and beautiful enough. But, if it goes to the next amazing stage, the observer will never forget the experience.

Multiple arcs appear. These may become entirely composed of fine rays and form auroral curtains that may ripple along seeming folds as if blown by some vast wind. Red, purple, green and various combinations of these colors may tinge parts of the curtains with patches of radiance, pulsing on and off all over the sky. This light can upstage a full moon, or on a moonless night be bright enough to read by. If a curtain extends to directly overhead, it may be seen as an awesome auroral corona, sometimes rotating, with its curving arms of light extending to all quarters of the sky. The aurora may flicker five to 10 times a second, or it may flame with waves of brightness rolling from the bottom to the top of a formation so that the sky appears to be on fire. After maybe an hour of ceaseless activity, peaceful cloudlike patches of northern lights may slowly fade as the heavens return to rest. There may, however, be a second or third firing of auroral splendors before dawn.

Your chances of seeing the greatest displays of the northern lights are tremendously increased, of course, if you find yourself above 40° north latitude. Last March's auroral storm in the southern U.S. consisted mostly of mighty patches of red aurora with only modest structure and movement. But you never can tell.

Scientists are still far from a full explanation of the aurora.In the 1980s, a new round of research investigated how atomic particles of the solar wind accelerate in the earth's magnetosphere, striking earth's upper atmospheric gases with enough energy to cause the aurora.

A great aurora often starts with a disturbance on the sun called a solar flare. These flares frequently take place in association with groups of sunspots, patches on the sun's surface that appear dark because they're slightly cooler than their surroundings. If the flare is pointed toward the earth, its particles may reach us in one or two days.

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