The depths of a Canadian winter can test the hardiest souls. Depending on where you live, bitter cold, ceaseless winds, drifting snow and long hours of darkness can combine to drain your energy and fray your nerves. One compensation sure to lift spirits is the aurora borealis. Usually appearing as shimmering bands of otherworldly light rippling across the sky, the aurora arises from the excitement of molecules in Earth's upper atmosphere by charged particles emitted from the sun. Although at times appearing to nearly touch the ground, the aurora is actually generated about 100 kilometres (62 miles) above the earth. The corona surrounding the sun is an intensely hot region where electrons are stripped from atoms and combined with other charged particles to form a cosmic brew called plasma. Even the sun's immense gravity cannot hold the plasma in check, and it flows outward as a "solar wind." Most of this is diverted around the earth by the planet's magnetic field, but some of the solar wind's energy is transferred to particles in the upper atmosphere, creating an auroral glow at both poles: the aurora borealis or northern lights, and the aurora australis or southern lights. When eruptions occur on the sun's surface, solar flares may send millions of tonnes of electrically charged particles racing toward Earth. They trigger geomagnetic storms in our planet's magnetic field and, as a lovely byproduct, generate the bright arcs of auroras. The more intense the solar activity, the brighter and more active the aurora. In autumn 2003, three huge sunspots appeared. These indicators of intense solar magnetic activity produced auroras visible in places far south of where the northern lights are usually seen. In locations like Wichita, Kansas, and Atlanta, Georgia, sky watchers enjoyed a spectacular show. Green, red, purple, pink, blue, yellow - the colours we see in an aurora depend on the type and excitement level of atoms and molecules. Streetlights show a similar phenomenon as they emit either the orange glow of sodium or the blue of mercury vapour. Green, the most commonly observed auroral colour, is produced by oxygen atoms under conditions found about 100 kilometres (62 miles) above the earth's surface. The much rarer red also comes from oxygen atoms, at nearly twice the altitude. Some people report hearing swishing noises that change as the aurora shifts. Scientists have been unable to record any noises, but believe that the sound may be created inside the observer's head by tiny electrical signals leaking from nerves in the eyes into the area of the brain responsible for processing sounds. The sounds generated would be sensed only in a very quiet environment. Some explorers have indirectly confirmed this theory in reporting that the sound of the aurora disappeared when they covered their eyes. Northern cultures invented many stories to explain the aurora. In Danish legend, swans flew too far north and became trapped in the ice. The flapping of wings as the birds struggled to free themselves produced the flickering lights. Some Inuit tales describe a heavenly football game played by the ancestors, using a walrus head ball. In Siberia, the Ostyaks believed the aurora was a flame kept burning by the fish god to help those who fished at night. The Vikings saw the aurora as the bridge between earth and the gods' heavenly home of Asgard. No matter what the explanation, the aurora is magical. I've bundled up to sit on my deck at midnight in the middle of winter to watch it ebb and flow above me. It has kept me awake and fascinated during a 3 a.m. drive from Brandon, Manitoba to Winnipeg. Lying flat on my back in the middle of the Northwest Territories' barrenlands, I was engulfed in a downward explosion of red, white and green rays that left me speechless. Wave after wave of rippling ribbons writhed across the sky, undulating in an ancient rhythm unheard yet somehow capable of creating an echo. Such celestial fire brightens even the worst of winter. - REBECCA L. GRAMBO