Residents across County Durham have been left delighted after seeing a rare cloud phenomenon over the skies of the region over the last few evenings. 

If you were looking up at the sky and saw 'rainbow clouds' - it's not just your imagination, it is a rarity for people in the UK to see it at all. 

The phenomenon, known as nacreous clouds, is considered rare because the clouds are usually found only in extremely cold air – around minus 78C- and form at 70,000ft above ground level.

The colourful hues come from ice crystals refracting the sun's rays to give the rainbow effect and residents across the region grabbed their cameras and phones to capture the breath-taking sight.

Nacreous clouds form in very cold conditions over polar regions and within the stratosphere, around 12-19 miles (19-31km) high, far above our normal clouds.

Get the latest news, sports, and entertainment delivered straight to your device for just £4 for 4 months, click here.

Most read

According to the Met Office: "Occasionally cold polar air, locked in place by strong winds high up in the atmosphere - called the polar vortex - weakens and allows this colder air to sink south to our latitude.

"Formed in the air that is around -80C, tiny ice crystals reflect sunlight, giving the cloud pearly colours - the reason why it is also called mother-of-pearl.

"Nacreous clouds are mostly seen a couple of hours either side of sunset or sunrise and, being so high, they are still lit by sunlight which makes them appear even brighter in our evening sky."

And now we know what the clouds are, here are the best images of the 'rainbow clouds':

Steve Curtis (Darlington):

The Northern Echo: The Northern Echo:

Ian Maggiore (Seaburn)

The Northern Echo: The Northern Echo:

Anne-Marie Maddison (Durham City)

The Northern Echo:

Jane Parker (Bearpark)

The Northern Echo: