Aurora Explained: What Causes the Northern Lights

What causes an aurora?

The Sun constantly sheds charged particles into space — the solar wind. Most of that stream is deflected around Earth by our planet's magnetic field, but some particles are funnelled down along the field lines toward the poles. There they collide with oxygen and nitrogen in the upper atmosphere, exciting those atoms to a higher energy state. As the atoms settle back down, they release the extra energy as light. Billions of these tiny collisions, all at once, are what we see as an aurora.

Why the poles?

Earth's magnetic field runs from pole to pole, and it channels incoming particles down two funnels — one at each end. That's why auroras form ovals centred on the magnetic poles rather than appearing evenly across the sky. In the north it's the aurora borealis, the Northern Lights; in the south, the aurora australis. A strong solar storm can push that oval further from the poles, which is when an aurora becomes visible from latitudes that rarely see one.

Why the colours differ

Colour comes down to which gas is struck and how high up the collision happens. Oxygen glows green at lower altitudes — the most common aurora colour — and a rarer red at the very top of the atmosphere, over 150 miles up. Nitrogen produces the blues and purples along the lower edge of a display, which mix with oxygen's green to give the pink and violet fringes seen in the strongest storms.

When and where to see one

You need three things: darkness, a clear sky, and geomagnetic activity high enough to bring the oval within reach. That means the depths of winter at high latitudes — Norway, Iceland, northern Canada, Alaska — well away from city light. Activity runs in an eleven-year solar cycle, and displays get stronger and reach further south near its peak.

Aurora as wall art

An aurora is one of the hardest things in nature to photograph honestly — the eye and a long exposure see it differently, and neither quite captures being underneath one. Our Aurora print renders it as art rather than a snapshot: colour drawn the way the display actually reads to a naked eye stood beneath it, printed gallery-grade on archival stock or canvas. You'll find it alongside the wider night sky in astronomy prints, or browse space gifts if it's for someone else.