It is, of course, a trick of the light, but the photographer of this resplendent sight was not mistaken - it really is an upside down rainbow.

This rare spectacle - which curves up rather than down - was caught on camera at the weekend by an astronomer near her home in Cambridge.
The "smiling" band of brilliant colours is known as a circumzenithal arc. It occurs when sunlight bounces off ice crystals high in the atmosphere, sending the light rays back up towards the sky.

It differs from a normal rainbow where light penetrates raindrops and re-emerges on the other side heading towards earth, causing a drooping effect.

Upside down rainbows are rarely seen outside the polar regions and need a particular set of atmospheric conditions in order to occur.

Dr Jacqueline Mitton, a fellow of the Royal Astronomical Society who has written astronomy books for children, spotted the phenomenon near her home.