The aurora borealis, or northern lights as they are more commonly known, are one of the most spectacular astronomical phenomena. These dancing bands of light bring the night sky to life and this winter may provide one of the best shows in more than a decade.

Although the word aurora translates to mean "dawn", the lights always appear at night and are caused by gas particles high in the Earth's atmosphere. The particles originate on the sun and are emitted during solar flares within sunspots (large explosions caused when energy stored in twisted magnetic fields explodes) . These flares send out a stream of high energy particles, known as the solar wind, towards the Earth. Solar wind particles maintain an electrical charge and are deflected towards the Earth's magnetic poles. Besides being responsible for the aurora, they have also been known to disrupt high frequency radio communications.

As the solar wind enters the atmosphere, high energy particles collide with other gas particles, become excited and begin to glow. The colours of the aurora are caused by different gases present around the Earth. For instance, as the particles collide with oxygen atoms, they emit a greenish light. If the oxygen particle is excited even more, due to a very energetic collision, it glows bright red. Nitrogen atoms tend to also emit a greenish glow.

According to Bob Nelson of the Centennial Planetarium in Calgary, an intense study was undertaken in 1959-60 during which time all aurora were carefully observed. When appearing early in the evening, they followed a regular pattern of changes. Beginning as a large arch centred on the north-eastern sky, the aurora gradually climbs higher in the sky. As it moves it adds small rays until it resembles the familiar curtain-like aurora. During particularly good shows, it can progress to the point that the overhead sky just glows. Generally, they begin to disappear around 1:30 a.m.

The occurrence of aurora is very carefully linked to sunspot activity on the sun. These sunspots vary in number over an eleven year cycle. This year should see us near the maximum point in this cycle and so the shows can be dramatic. Since the NE horizon is often blocked by mountains, we generally see only the more spectacular shows--those that move high up into the night sky. By getting away from the townsite and moving to higher elevations, you may get the opportunity to see more aurora.