A hastily made igloo offers shelter from a brutally cold wind-chill and a great view of auroral curtains on a winter's night north of Fairbanks.

			Excerpted from "Northern Lights: The Science, Myth, and Wonder of Aurora Borealis." Photographs by Calvin Hall and Daryl Pederson; essay by George Bryson. Published by Sasquatch Books (www.sasquatchbooks.com), 2001.

ONE HUNDRED years after the fabled Klondike gold rush of 1898, a great aurora began dancing over the Alaska Range. The date was Nov. 7, 1998. In Healy, Alaska, about 75 miles northeast of Mount McKinley, someone standing in the snow outside a log-cabin café pounded on the window and pointed to the sky. Science writer Ned Rozell of Fairbanks set down his cheeseburger and stepped outdoors to see what the stranger was intent on sharing — and then he saw it: a rare purple aurora flowing like a river overhead.

"Soon the entire restaurant staff and I were shivering outside," Rozell later wrote. "Even the sourdoughs who'd seen hundreds of displays started whooping. This was no ordinary aurora."

About 125 miles south of McKinley, residents of Anchorage saw the aurora, too. First it appeared as a giant curtain connecting the Chugach Mountains to the east with a distant horizon of active volcanoes to the west. Then the curtain began to ripple. Then it seemed to skip, tossing Technicolor rays at the watchers below.

A small cabin in the Talkeetna Mountains stands silent witness to a swirl of northern lights. The flag in a blur on the roof shows the strength of the wind; twilight at sunset creates the shades of vibrant blue.

Walking toward my barn in a mountain valley 15 miles to the southeast, I watched the colors shine even brighter beyond the lights of town. I saw them race across the darkness, eclipsing the stars. For a long while I forgot all about my chores and obligations and simply stared at the flashing sky.

Scientists tell us that the northern lights — the aurora borealis — are always present in the far north, even when we can't see them due to daylight or cloud cover. Usually they remain withdrawn inside the auroral zone, a vertical corridor that encircles the Northern Hemisphere along an oval track about a thousand miles from the magnetic North Pole. (Because the magnetic North Pole is about 800 miles south of the geographic North Pole, the northern lights are much more visible in Canada and Alaska than in Europe or Asia.)

When this auroral oval is relatively calm, its centerline transects the northern third of Alaska almost directly above the Arctic village of Fort Yukon. On dark, cloudless, winter nights in Fort Yukon, the chances of observing the northern lights are virtually 100 percent. In Anchorage, farther south, they dip to 40 percent, in Seattle to 5 percent. (A viewing probability of 1 percent means it's possible to glimpse an aurora three or four nights a year.)

	A blast of aurora light can provide enough illumination to read, although measurements conclude that even the brightest aurora is still less intense than full moonlight.

It's possible because every so often the solar wind (the ionized gas exhaled by the sun that powers the aurora) increases in speed and density. As it does, the solar particles excite the Earth's magnetic field in a way that causes the circumference of the auroral oval to expand and slip southward toward the equator. Aurora researchers liken the phenomenon to an expanding halo slipping down the "head" of the globe. Small increases in geomagnetic activity can easily propel the aurora as far south as Anchorage; larger increases can send it racing toward Vancouver, B.C. Which is just what occurred on that early November night as the world revolved a little closer toward a new millennium.

Alaskan photographer Daryl Pederson may have had the best vantage point of all: on a lonely roadside ledge halfway between Fairbanks and Anchorage, facing the highest mountain in North America. For once, everything was out. The mountain. The stars. The moon. And the most brilliant aurora Pederson had ever seen.

THROUGHOUT HUMAN history, the ancient hunters of the circumpolar regions probably stopped whatever they were doing and marveled when the northern lights appeared.

At a lower latitude, the medieval Christians of central Europe were invariably surprised by the northern lights, sometimes even terrorized (partly because they saw them so rarely). When they did appear there, historians say, the auroras were usually rich red (thoroughly disturbing the already active imaginations of the Middle Ages, or even the Renaissance).

"Bloody lances, heads separated from the trunk, armies in conflict were clearly distinguished in the sky," wrote 19th-century scholar Alfred Angot about perceptions of auroras in the 1500s. "At the sight of them people fainted . . . others went mad." Ancient Scandinavians saw the northern lights as the recently departed souls of strong, beautiful women hovering in the air. The Labrador Eskimos of eastern Canada believed the northern lights were the torches of friendly spirits trying to help anyone who had recently died to negotiate a narrow path over the chasm that separated the living world from the afterlife. Few people knew the aurora as well as the wide-ranging Inuit (the Eskimo people who populated the Arctic from Siberia to Alaska to Canada to Greenland). When they died, according to members of a tribe of Eastern Canadian Eskimos interviewed in the early 20th century, the most fortunate among them spent their next life in the sky, in the Land of Day, where dead Inuit occasionally clashed in a great auroral soccer game.

Because the moon was low and partly subdued by high clouds, it looked like a setting sun in this view of an aural curtain captured from the Pacer River Valley in August, 2000.

PARENTS ARE wrong today when they tell their children that an aurora is simply sunlight reflecting off the polar ice cap. It isn't. What is it, then? The answer has been a long time coming. Aristotle advanced one of the earliest theories some 24 centuries ago, insisting that the source of the aurora couldn't possibly be found in the heavens, since the sun and the stars never changed. In his Meteorologica, Aristotle attributed auroras to earthly vapors that rise into the upper atmosphere and periodically catch on fire.

The earthly vapors weren't completely off the mark; at least atmospheric gas was part of the equation. But as Candace Savage points out in her 1994 book "Aurora," Aristotle's insistence that the heavens never change managed to confuse natural philosophers for the next 19 centuries. Not until 1572, when Danish astronomer Tycho Brahe noticed the creation of a brand-new star in the constellation Cassiopeia, would academics again seek aurora explanations beyond the moon.

In the 1600s English physician William Gilbert demonstrated that the Earth is a gigantic magnet. In the 1700s astronomer Edmond Halley suggested that the northern lights might be influenced by that magnetism, helping explain why auroras are most often observed in the polar regions, where Earth's magnetic-field lines converge.

British explorer Capt. James Cook first gazed upon the southern lights in 1773 during his voyage south of the Antarctic Circle. Cook named them the "aurora australis," paraphrasing the recently adopted term for the northern lights, "aurora borealis." French scientist Pierre Gassendi had earlier coined the term aurora, Latin for "dawn," after Aurora, the ancient Roman goddess of dawn.

	An arc of light appears to circle back on itself in this unusual form photographed over the Alaskan village of Ambler, along the Kobuk River.

Around Cook's time, French scientist Jean Jacques d'Ortous de Mairan noticed a cause-and-effect relationship between solar activity and auroral activity. American statesman and amateur scientist Benjamin Franklin theorized that the northern lights were an electrical phenomenon.

In the latter half of the 19th century, British physicist Sir William Cooke showed that a gas isolated in a vacuum tube glows if electrons are transmitted through the tube, and that different gases glow different colors (just as they do in "neon" advertising signs). Moreover, when Cooke moved a magnet near the tube, he saw that the stream of light inside bent toward the magnet.

At the beginning of the 20th century, Norwegian physicist Kristian Birkeland finally made sense of it all: Rays of electrons explode off the sun in all directions as solar wind. As the electrons stream past Earth, our planet's magnetic field steers a portion of them toward the poles. Moving through the Earth's thin upper atmosphere, the electrons collide with molecules and atoms of atmospheric gas and cause them to glow, just as gas had glowed in Cooke's lab.

AURORA BOREALIS may well be the world's greatest optical illusion. In the Northern Hemisphere, an aurora usually first appears on the northern horizon as a diffuse band of hazy clouds with little color. Then the lights begin to coalesce into a gentle curtain-like arc, usually pale green, that stretches from the eastern to the western horizon. The apparent downward curve of the arc is deceptive; because the entire curtain may extend a thousand miles in length, it is simply curving around the globe — its entire lower edge staying 60 to 65 miles above sea level. The apparent height of the curtain is deceptive, too. It's actually much taller than it seems, soaring anywhere from 100 to 500 miles high.

As the aurora becomes more active, it develops fine vertical folds and the color grows stronger. Then the rays begin to ripple sideways, like a curtain brushed by wind. We might see parallel rows of curtains, as though we were looking up a ruffle of petticoats.

A rising full moon, left, illuminates Alaska's Mount McKinley during a major solar storm on Nov. 7, 1998.

While the overall length of any auroral curtain can span from the Pacific Ocean to North Dakota, its width — just a mile — is thin by comparison. Still, as it passes overhead to the south of a viewer, the curtain appears to break apart, and observers may briefly see a "corona," which looks like a sunburst. Actually, it's just another optical illusion; the rays are all approximately vertical.

The colors of the aurora are determined primarily by the kinds of atoms or molecules the electrons strike. The most common color, greenish-white, appears when electrons bombard atoms of oxygen at relatively low elevations. Electrons colliding with nitrogen molecules at the highest elevations when twilight shines on the upper atmosphere may produce dramatic blue and violet auroras. The strongest electron storms of all can turn the entire sky blood red when atomic oxygen is bombarded throughout the ionosphere.

The best time of day to view auroras is between 9 in the evening and 3 in the morning. The best time of year is between September and April. Since geomagnetic storms usually last longer than a day, one good night is often followed by another.

	Moonless nights in the fall provide good opportunity to create reflection images of the northern lights, such as this one on the Knik River in Alaska, above. The cottonwood trees still have their leaves in this September scene.

Finally, there are aurora-rich years and aurora-lean years. They trend up or down depending on exactly where we are in the 11-year-long sunspot cycle. In this cycle, sunspot frequency should remain high through 2004.

THE NORTHERN LIGHTS of March 13 and 14, 1989, blew in as a 10-million-miles-per-hour solar hurricane that painted a blood-red aurora over most of the Lower 48. The magnetic storm knocked out all the power in the province of Quebec. Nothing quite so dramatic was anticipated for the evening of April 6, 2000. Still, power companies all across the northern-tier states were taking precautions. A big solar wind had already entered the upper atmosphere. Over Seattle, with any luck, the weather would be clear and the lights would be prime.

Up in Anchorage, however, there was no such luck. A low-pressure system had arrived by early evening, and an aurora watcher had to look hard to find a hole in the clouds. Daryl Pederson thought he'd found one about 30 miles north of town. He'd set up his tripod and pointed his camera at 4,326-foot Mount Susitna. A shimmering green curtain might arch over her snow-covered bed, he thought. Pederson turned his attention north and waited.

A great green auroral ring hovers over the Knik River just as ice starts to form on an October evening.

But the lights never came from the north that night. They were already far advanced to the south, and a cloud bank to the south was right in Pederson's line of sight. He could see an aurora shimmering just beyond it. He needed to get higher fast.

Stowing his gear, Pederson jumped into his van and began driving up the Old Glenn Highway. By the time he reached Pioneer Peak, the lights had begun to explode. He set up his tripod on the side of the road to take pictures as best he could, but his position was still compromised by clouds.

Having started the night farther north than Pederson, Calvin Hall had time to drive to Willow, about 80 miles north of Anchorage. He set up his camera and began to wait.

Around 11 o'clock, his perseverance finally paid off. The display began as a brilliant red glow in the southeast. "Then you could see some yellows trying to come in," Hall recalls. "Then about three minutes later, it shifted from magentas to more yellow. Then to more and more yellow. Then orange!"

Before the night was through, Calvin Hall would witness — and photograph — the richest, reddest aurora he'd ever seen. An aurora capable of striking fear in the hearts of medieval Europeans.

Calvin W. Hall is a professional photographer based in Anchorage, Alaska. His published work has appeared in a number of magazines, including National Geographic, and has been used by Rand McNally.

Daryl Pederson is a photographer from Girdwood, Alaska. His pictures can be found world-wide in magazines, calendars and cards and on Web sites.

George Bryson writes for the Anchorage Daily News and teaches at the University of Alaska, Fairbanks.