Normal rainbows are made when light penetrates raindrops and re-emerges out the other side in the same direction. But, the inverted types, known as circumzenithal arcs, are caused when sunlight bounces off ice crystals high in the atmosphere, sending the light rays back up. "The conditions have to be just right: you need the right sort of ice crystals and the sky has to be clear," said Mitton. "We're not sure how big an area it was visible over, but it was certainly very impressive," she added.
A spokesman for the Met Office confirmed the inverted rainbows are occasionally spotted in British skies.
"It is convex to the sun and is formed by refraction in suitably-oriented ice crystals and may show vivid rainbow colouring, as in this case," he said.