Colourful rainbow cloud forms in the sky in Missouri

Video: https://www.dropbox.com/s/moqg7k64r24ekt6/VRP32417.mp4?dl=0

This is the spectacular moment a colourful rainbow cloud formed in the sky in Missouri.

Footage shows the stunning weather phenomenon, also known as cloud iridescence, among the clouds on May 11 shortly before sunset at around 6pm.

Onlooker Chris Christman said: ‘It was an amazing experience to see it across the clouds in front of my window.’

A rainbow cloud forms because of something called cloud iridescence. This is also known as ‘irisation’. Both terms come from the word ‘Iris’, which is the Greek personification of the rainbow. This only happens when clouds are thin. They are usually altocumulus, cirrocumulus, lenticular and cirrus clouds.

Small water droplets or crystals are suspended in the clouds. For the iridescence to happen, the water droplets or crystals should be around the same size. The angle is important, too. Water droplets should be about 10 degrees from the Sun. So rainbow clouds form when the sun is relatively low, late in the afternoon.

The iridescent clouds form because of diffraction. The sun shines through the cloud and the light is scattered and reflected through the clear water droplets like a prism.

Sometimes the effect is spectacular. All of the colours of the rainbow can be seen hovering over the edge of the cloud. Sometimes the rainbow clouds can resemble giant spaceships floating in the sky.