a strong aurora borealis near Tromso, Northern Norway. Auroras are the result of collisions between gaseous particles (in the Earth?s atmosphere) with charged particles (released from the sun?s atmosphere). Variations in colour are due to the type of gas particles that are colliding. The most common aurora colour which is green, is produced by oxygen molecules located about 60 miles above the earth. The rarer red auroras are produced by high-altitude oxygen, at heights of up to 200 miles. Nitrogen produces blue or purple aurora.