For the next few years, you don’t have to travel to the land of polar bears to see the northern lights. But you do have to have good timing.
Years ago, at the end of a canoe trip along the Canada-Minnesota border, I stepped out of my tent and into one of nature’s most spectacular night scenes. Surrounding me in a dome that reached from one end of the sky to the other were shimmering bands of brilliant green light. The bands pulsed and sparkled as if cosmically painted.
“It’s the aurora borealis, the northern lights,” said my husband, who had walked up behind me.
As if on cue, the lights intensified, then swirled wildly in a dance across the sky. I don’t know how long we stood there before they dissipated. Maybe 20 minutes. Had I known that auroras often make an encore, I would have stood there all night. I didn’t, though, and despite numerous trips to the northern reaches of the Lower 48 states since then, I have yet to see the fabulous northern lights again.
But this year or next, I may get my wish — and not just in that region but from almost any state south of the Canadian border.
Every 11 years or so, the solar activity that drives the aurora borealis peaks, often resulting in spectacular displays that spill beyond their usual range near the polar region. In unusual cases they reach as far south as Alabama. For aurora hopefuls like myself, this means that instead of heading for the land of polar bears, I can hunt for aurora south of the permafrost.
EVIL SPIRITS AND EARTHLY VAPORS
Aurorae encircle Earth’s geomagnetic poles like crowns: The aurora borealis is at the Arctic, and its southern cousin, the aurora australis, is at the Antarctic.
The source of their ethereal glow has fueled folklore for centuries — and some scientific theories have been nearly as colorful. Eskimos from the Yukon, for instance, described them as dancing souls, and the Mandan Indians believed them to be the fires of northern warriors cooking their enemies in large pots.
Among scientists, notions of earthly vapors and heavenly fires dominated debates for 22 centuries. The understanding of magnetism and electricity began to spice up their theories in the 1700s, with most of the puzzle pieces finally falling into place in the early 1900s. But it wasn’t until the advent of rocketry in the late 1950s when scientists could launch observation equipment 40 to 400 miles above Earth’s surface (where the aurorae form) that they found the source — and even then, it took until the 1970s to confirm it.
Today, scientists agree that the sun fuels the aurorae. A stream of highly charged particles called plasma continually boils up from the sun’s surface, forming a solar wind that bombards Earth’s outer magnetic field. Most plasma are deflected, like a river around a boulder, but some are pulled back around and accelerate as they are drawn toward Earth’s magnetic poles. As the charged particles near Earth, they collide with atoms in the upper atmosphere, causing them to emit bursts of light. If the bursts are bright enough, they can be seen from below as the aurora.
Periodically, other forces come into play and intensify the solar winds. Holes may open in the sun’s corona and blast plasma into space like water through a fire hose. During the 11-year solar maximum, the sun may also emit solar flares, which accelerate the solar wind as well as massive bubbles of plasma called coronal mass ejections. When these slam into Earth three or four days later, they trigger large geomagnetic storms that expand aurorae southward, wrapping the globe as if in a blaze. In fact, during the Middle Ages, a rare crimson aurora over Europe caused such a panic in Paris that thousands of penitents besieged its great church, certain that the Armageddon was at hand.
Several times in the past year, the index scientists use to gauge auroral activity — the Kp (the planetary magnetic) index — has spiked to seven on a scale of nine, according to Roger W. Smith of Alaska’s Geophysical Institute. At Kp=5, the aurora extends from Canada into the upper Midwest; at Kp=7, it reaches Chicago; at Kp=9, St. Louis and Washington, D.C.
Regarding the next few years, Smith says, “I would not be surprised if it reached nine on some occasions.” He’s optimistic because he knows that the best stuff usually happens on the downward side of the solar cycle, which starts about now.