Cause of the Aurora

Northern lights and aurora are two names for the same phenomenon. The aurora is caused by charged particles, electrons and protons, striking the earth's atmosphere. These particles stream downward along the earth's magnetic field, which at Fairbanks is nearly vertical.

The particles give energy to the oxygen and nitrogen molecules of the atmosphere. This energy is then given off in the form of light. Green is the main color in the average garden-variety aurora which occurs at an altitude near 100 km. When the incoming particles are especially energetic, they create red light on the lower edges of aurora; such auroras may be as low as 80 km.