One of the pleasures of a Canadian winter is the night. Stars spangle the heavens, and between their radiant points, the universe flows outward into endless black. We look up and feel ourselves falling into cosmic emptiness-blank space without matter or movement. But then, if luck is with us, the sky begins to ripple with soft, shimmering curtains of light that fill this seemingly empty cosmos with energy and life. Aurora borealis, or the northern lights. So faint they are seldom seen in summer, these luminous wraiths are a gift of winter's darkness.

The northern lights stand at the boundary between visible and invisible worlds, giving us a glimpse into a little-known universe. In times past, people thought that the lights must be spirits: fairies, magic beasts or bright souls. Even today, while scientists have a good idea of the physical forces involved, they still view the spectacle of the aurora with old-fashioned awe.

Physicist Dave Knudsen, an assistant professor in the department of physics and astronomy at the University of Calgary, is a case in point. Raised in Iowa (where the aurora rarely appears), he was in his twenties before he first saw the northern lights in action. Yet, despite the novelty of the experience, Knudsen was never in any doubt about what he was looking at. "I've always been driven by a desire to understand electricity and magnetism," he explains, "and this was so obviously a display of electromagnetism. I knew there must be basic laws governing it, but it was so inexplicably complex. My mind was just racing with excitement!"

To Knudsen, the northern lights are more than a source of delight. To him they are a manifestation of turbulent forces that bluster and roil throughout the dark universe. "If you go even 100 kilometres above Earth, to the base of the auroral curtains," he says, "you already find yourself in a different world. The behaviour of the physical system is dramatically different there than what we find here on the ground. It's not hard to imagine that things get even more interesting and complex as you move farther out."

With this thought in mind, Knudsen recently initiated a multimillion-dollar international research project known as GEODESIC or, to give its full moniker: Geo-electrodynamics and Electro-Optical Detection of Electron and Suprathermal Ion Currents. The effort literally got off the ground in February 2000, when Knudsen and his team launched a sounding rocket (built by Winnipeg's Bristol Aerospace) from the Poker Flat rocket range, near Fairbanks, Alaska. The main purpose of the six-year study is to investigate the otherworldly behaviour of charged particles in and around the auroral curtains.

Space is occupied not by the solids, liquids and gases that we earthlings know so well. Instead, it is filled with a fourth state of matter known as plasma-a kind of improbably thin, electrically active vapour. Although natural plasmas are rare on Earth (found only in exotic phenomena such as ball lightning), they are exceedingly common in space. In fact, about 99 percent of the matter in the universe is thought to exist in the plasma state. Unlike air, which is electrically inert, plasmas consist of charged molecules and atoms that not only respond to familiar physical forces (such as pressure and gravity) but are also highly sensitive to electromagnetic fields. Pushed and pulled by all these conflicting forces, plasma is even more chaotic and dynamic than air, many times more changeable than weather.

Yet all the cosmicSturm and Drang1 of the plasma might pass us by unnoticed-if it weren't for the aurora. Like whitecaps on a storm-tossed sea, the northern lights are the visible crests of invisible plasma waves that batter Earth. (Much of this bombardment originates in the sun, which spews out streams of plasma as the so-called solar wind.) Drawn toward the polar regions of Earth along magnetic lines of force, plasma cascades ever downward until-about 1,000 kilometres overhead-it begins to run into atmospheric gases. As high-speed electrons in the plasma collide with oxygen and nitrogen in the air, the gases receive an energetic jolt, which they emit as faint bursts of colour (greenish white for oxygen, pink for nitrogen). When millions of energized molecules go off at the same time, the night sky begins to dance with all the tumultuous vigour of the plasma currents. Down on Earth, we look up and emit gasps of delight.

If we want to understand the cosmic forces that whirl through space, we cannot do better than to study auroral displays. "The northern lights provide us with a natural laboratory for studying plasma structures," says Knudsen. We can be pretty sure that whatever is simmering in the northern lights is boiling over somewhere else in the universe." For example, there are fine structures within the aurora-tubes less than 50 metres across-that appear to serve as a kind of charged-particle gun, or accelerator. Through some unknown mechanism, these tubes transfer energy from plasma to atmospheric ions and send them zooming off into outer space. If Knudsen and his GEODESIC colleagues can figure out how these accelerators work, they will have made a small contribution to understanding the northern lights and a larger one to solving an outstanding problem in plasma physics.

As the GEODESIC rocket blasted off from Poker Flat and through a display of northern lights, its payload of sensitive instruments took a rapid-fire series of measurements, at the rate of about 10 million bits per second. Translated into graphical images, these data trace the moment-by-moment behaviour of charged particles in a series of accelerators. The entire mission, from takeoff to crash landing in the frozen Beaufort Sea, took 17 minutes flat. But decoding and figuring out what the data mean will keep Knudsen and his colleagues busy until about 2003.

Meanwhile, Knudsen is preparing an instrument for another rocket that will be launched from Norway's Svalbard Archipelago in December 2001. Again, his plan is to make measurements inside accelerators. But his larger mission-the purpose that drives his research-is to understand the fundamental forces raging through the universe. They are out there every second, whether we can see them or not, dancing over our heads in the infinite darkness.

1. If you had lived in times long past, how do you think you would have explained the northern lights? What must it have been like to see them then?

2. Making Connections Use Internet resources to find another literature selection - for example, a poem, story, folk tale, myth, or non-fiction item - that is about the northern lights. Discuss this work briefly, comparing any descriptions of the northern lights and the role they play with this essay "Night Spirits"(Text Above).

3. Creative Writing Wri te a descriptive paragraph about a physical experience that impacted you on a visceral level. Employ descriptive language to appeal to the senses. (Doesn't have to be personal. could be a random example)