Aurora borealis: Stunning pictures of northern lights over the UK - what causes them?

The northern lights were visible across the UK on Sunday and could appear again on Monday evening.

The Met Office said there is a chance to see the natural phenomenon in parts of the UK for the second night in a row.

It tweeted a series of pictures of the aurora borealis taken from various areas of the country on Sunday.

In a rare occurrence, the northern lights were visible as far south as Cornwall and Kent.

A Met Office spokesperson said the rare sightings of the aurora borealis further south in the UK on Sunday night were due to the “strength” of a geomagnetic storm and the “strip of cloudless skies” in southern regions.

Watch: Northern lights seen across the UK

The best chance of seeing the aurora is on dark and clear nights with little light pollution.

The Met Office tweeted on Monday: "Did you see the northern lights last night?

"Share any photos you took using #LoveUKWeather to be in with a chance of featuring later.

"There's another chance to see the aurora tonight."

Read more: Stunning Northern Lights appear in rare display over southern England

The most colourful displays on Sunday evening were seen in Scotland and northern England, where the aurora was comprised of greens and reds.

The phenomenon was also visible in Northern Ireland, Norfolk and south Wales.

On Sunday, the Met Office tweeted: “A coronal hole high speed stream arrived this evening combined with a rather fast coronal mass ejection leading to aurora sightings across the UK.”

What are the northern lights?

The aurora, or polar lights, can be seen near the poles of both the northern and southern hemisphere.

In the north, the display is known as the aurora borealis, while in the south it is called the aurora australis.

What causes the northern lights?

Interestingly, the aurora are sparked by activity on the sun.

According to the Royal Observatory in Greenwich, the lights are caused by solar storms on the surface of the sun giving out clouds of electrically charged particles which can travel millions of miles and collide with the Earth.

Most particles are deflected away but some are captured in the Earth’s magnetic field and accelerate down towards the north and south poles, colliding with atoms and molecules in the Earth’s atmosphere.

The lights are the product of this collision between atoms and molecules from the Earth’s atmosphere and particles from the sun.

Royal Observatory astronomer Tom Kerss said: “These particles then slam into atoms and molecules in the Earth’s atmosphere and essentially heat them up.

"We call this physical process ‘excitation’, but it’s very much like heating a gas and making it glow.”

The aurora's wavy patterns and "curtains" of light are made by the lines of force in the Earth's magnetic field, the Royal Observatory said.

How far are the northern lights away?

The lowest part of an aurora is usually about 80 miles above the surface of the Earth, but the top part may extend several thousands miles above the Earth, according to the Royal Observatory.

Why do the aurora have different colours?

The colours are caused by the two main gases in the Earth's atmosphere, nitrogen and oxygen.

Different gases give off different colours when they are heated.

The green in an aurora is characteristic of oxygen, while nitrogen is behind the purple, blue and pink.

Kerss said: “We sometimes see a wonderful scarlet red colour, and this is caused by very high altitude oxygen interacting with solar particles.

“This only occurs when the aurora is particularly energetic.”