Aurora Borealis

- the northern lights

Franck Pettersen

The Northern lights are poetry, they are nature's light show, and they are quantum leaps in the oxygen atom. They are elementary particle physics, superstition, mythology and fairy tales. The northern lights have filled people with wonder and inspired artists; they have frightened people to think that the end is at hand. More exact explanations of the phenomenon could not be given until modern particle physics were developed, and knowledge about details in the earths magneto sphere has been based on measurements from satellites.
When the northern lights are seen over Tromsø, it happens in a set pattern, although this pattern varies considerably. The outbursts starts with a phosphorocent glow over the horizon in north west. The glow dies out and comes back, and then an arch is lit. It drifts up over in the sky. And new arches are lit and follow the first one. Small waves and curls move along the arches. (Picture 1).

Then within a few minutes a dramatic change is seen in the sky. A hailstorm of particles hit the upper atmosphere in what is called an aurora sub-storm. Rays of light shoot down from space, forming draperies which spread all over the sky. And they really remind us of draperies or curtains which are flickering in the wind. And you can see a violet and a red trimming at the lower and upper ends. Or the colors are mixed all together, woven into each other. The curtains are disappearing and forming all over again by new rays of light shooting down from space. Above our head we cans see rays going out in all directions forming what is called an aurora corona. After 10 to 20 minutes the storm is over and the activity decreases. The bands are spread out, disintegrating in a diffuse light all over the sky. We can not see individual pockets of light, but the total effect is bright enough to enable us to make out details of the countryside around us. If we look very carefully, we can see the remains of the northern lights display as faint, pulsating flames. Clouds of light which is turned on and off regularly every 5 - 10 seconds as though by an electric light-switch. The natures own gigantic light-show is over.

(Photo: Franck Pettersen)