What Causes the Northern Lights?

The process begins on the sun, which constantly emits a stream of charged particles called the solar wind. During solar flares and coronal mass ejections, the sun releases especially large bursts of these particles into space at speeds of up to 1,000 km per second.

When these charged particles reach Earth (typically after 2–3 days of travel), most are deflected by Earth's magnetic field. However, some particles are funneled along magnetic field lines toward the poles, where they enter the upper atmosphere at altitudes of 100–300 km.

As these energetic particles collide with oxygen and nitrogen molecules in the atmosphere, they transfer energy to those molecules. The excited molecules then release this energy as photons (light). Oxygen produces green and red light, while nitrogen produces blue and purple hues. The specific colors depend on the altitude and type of gas involved.

The aurora occurs in an oval-shaped ring around the magnetic poles, which is why they're most commonly seen at high latitudes (60–75° north or south). During strong solar storms, however, the auroral oval expands, and the Northern Lights can be visible much farther south — even as far as the Mediterranean in rare cases.