What Causes the Northern Lights?

The northern lights — the aurora borealis — are one of nature’s great light shows. They happen when charged particles from the Sun collide with gases high in Earth’s atmosphere, guided to the poles by our planet’s magnetic field.

Step by step

1. The Sun sends out particles. The Sun constantly streams charged particles (the solar wind), and occasionally erupts with bursts called coronal mass ejections.
2. Earth’s magnetic field catches them. Our planet’s magnetic field deflects most of this wind, but funnels some particles down toward the magnetic poles.
3. Particles hit the atmosphere. Around 100–300 km up, these particles slam into oxygen and nitrogen atoms.
4. The gases glow. The collisions excite the atoms; as they relax, they release light — just like a neon sign.

Why the colours differ

The colour depends on which gas is struck and at what altitude:

• Green — oxygen at ~100–150 km (the most common aurora colour).
• Red — oxygen at very high altitude (above ~200 km).
• Blue and purple — nitrogen at lower altitudes.

Why near the poles?

Because Earth’s magnetic field lines funnel the particles toward the magnetic poles, auroras form in rings around them — the auroral ovals. That is why Norway, Iceland, Alaska and northern Canada are prime viewing spots. The southern version is the aurora australis.

When are they strongest?

Auroras intensify when the Sun is active. The Sun follows an 11-year activity cycle, and during its peak, geomagnetic storms can push auroras to lower latitudes than usual. Space-weather agencies forecast this activity days in advance.

Related: how do magnets work? — the same magnetism that shields Earth shapes the aurora.

FAQ