'Upside down rainbow' caused by freak weather

By Jessica Salter Last Updated: 11:01am BST 16/09/2008 Freak atmospheric conditions rarely seen outside the polar regions have been credited with causing the formation of an "upside down rainbow". 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 "smiley faces in the sky" need extremely specific conditions not usually found above Britain. This picture was reportedly captured on camera by astronomer Dr Jacqueline Mitton near her home in Cambridge last Sunday. She said: "I've never seen anything like it before - and I'm 60. "The conditions have to be just right: you need the right sort of ice crystals and the sky has to be clear. advertisement "We're not sure how big an area it was visible over, but it was certainly very impressive." A spokesman for the Met Office confirmed the inverted rainbows are occasionally spotted in British skies. He said: "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."