Northern Ireland

What are the Northern Lights and what causes them?

The phenomenon is set to return to the skies tonight across Britain and Ireland

Aurora borealis, also known as the northern lights, fill the sky over The Bathing House in Howick, Northumberland in August
The Northern Lights light up the night sky with various colours. (Owen Humphreys/PA)
By Mark Robinson

The Northern Lights are set to the return to the skies over Britain and Ireland tonight, although cloud coverage could hinder their visibility in some places.

The phenomenon can sometimes be seen in the night skies across these isles, but it is most common in the northern parts of Scotland.

Earlier this year, the aurora borealis were visible further south than normal – reaching as far south as Cork and Cornwall.

More: How to see the Northern Lights in Northern Ireland: times and best locations for aurora borealis

But what are the Northern Lights and what causes them?

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The Northern Lights over the Giant’s Causeway in Northern Ireland
The Northern Lights over the Giant’s Causeway in Northern Ireland (John O'Neill/PA)

What are the Northern Lights?

The Northern Lights, or aurora borealis, appear as large areas of colour in the sky, ranging from pale greens to shades of red, pink and even purple.

They typically appear in the night sky in a northerly direction and extend between 50 and 400 miles above the Earth’s surface.

What causes the Northern Lights?

The phenomenon is caused by the reaction between charged particles released from the sun in the ‘solar wind’ and our atmosphere.

‘Solar winds’ comprise of charged particles ejected from the sun into space – when the charge on these particles is opposite to the Earth’s magnetic field, they are pulled to the poles and the particles react with the upper atmosphere there.

When more particles are released from the sun from normal – a Coronal Mass Ejection (CME) – the area of the atmosphere interacting with these particles increases, making the Northern Lights visible at lower latitudes.

This is why they are expected to be visible in the skies above the UK and Ireland tonight.

Why are the aurora different colours?

The colours of the Northern Lights depend on which gas molecules in the atmosphere are hit by charged particles.

Different molecules release different amounts of energy and as such release different wavelengths of light, resulting in different colours.

Oxygen particles give off green light, for example, when they are hit around 60 miles above Earth.