Rare 'rainbow clouds' spotted in UK skies

Rare "rainbow clouds" have been spotted in skies above the UK.

A number of people across the country have been treated to views of the colourful nacreous clouds this week.

Lindsay Mackenna took some pictures of the natural phenomenon above Edinburgh on Tuesday night, describing the iridescent clouds as "gorgeous".

She told Sky News: "I'm 65 and I've only seen this once before, but never at sunset.

"I couldn't believe what I was seeing. It's amazing what nature can produce - just wonderous."

Read more:
UK weather: The latest Sky News forecast

The Sky News weather team explained that nacreous or polar stratospheric clouds are relatively rare due to the very specific conditions needed for them to appear.

They form high up in the stratosphere when temperatures are -78C (-108F), so you are more likely to see them in polar regions during the winter.

These shimmering "mother of pearl" clouds are some of our highest clouds, forming around 12 to 19 miles (19km to 31km) above the earth.

Nacreous clouds are best seen before sunrise and after sunset when the sun is just below the horizon.

The pastel-rainbow colours are due to iridescence, when tiny ice crystals or water droplets cause sunlight to be diffracted and spread out, creating colours similar to those seen on soap bubbles or oil.

Cloud iridescence itself is actually a fairly common phenomenon at lower levels in our atmosphere, and can often be seen on the edges of clouds near to the sun or moon, usually in altocumulus, cirrocumulus, lenticular and cirrus clouds.