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Why are the northern lights green, and why are they sometimes red?

Colours come from gases in the air.

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Short answer

The colours of the northern lights come from gases in the upper atmosphere that give off light when particles from the Sun hit them. Green is the most common colour and comes from oxygen at heights up to about 240 km. Red comes from oxygen higher up, appears during very strong solar activity and is the rarest colour. Purple and blue light comes from nitrogen at lower heights, close to 100 km.

Weather and seasons

Why

  1. Each gas gives off its own colour when it is hit by solar particles.
  2. The height of the light decides which gas glows the most.
  3. Red only appears during extreme solar activity, so it is the rarest colour.

Details

Northern lights glow from about 90 to 500 km above the surface of the Earth.

Tip

Look low over the northern horizon from a dark place; in Denmark the lights often show only as a faint glowing cloud.

What may differ

How much colour you see depends on the strength of the solar storm and how dark the sky is.

Common misconception

Many believe red northern lights are a sign of danger or a special type of storm.

What actually happens

Red light is simply oxygen glowing above about 240 km during extreme solar activity.

People also ask

  • How high are the northern lights?
  • Can you see the northern lights in Denmark?
  • What causes the northern lights?

Sources

This answer is for reference only. Weather varies a lot from year to year, so check the DMI forecast before you travel.

Weather and seasons
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