Upside-Down Rainbow
This is no fantasy or trick of the light, it is known as a circumsenithal arc. In the sky over Cambridge in the afternoon sunshine, it is often mistaken for a rainbow hanging upside down. The arc only appears when sunlight shines at a specific angle through a thin veil of wispy clouds at a height of around 20,000 to 25,000 feet. Meteorologists say the clouds must be convex to the sun with the ice particles lined up together in the right direction to refract the light.
Dr Jacqueline Mitton, an astronomer, was lucky to capture the optical phenomenon on camera near her home in Cambridge. “I’ve never seen anything like it. ‘It’s quite surprising for this to occur somewhere like Cambridge, usually it is in places that are colder.’We’re not sure how big an area it was visible over, but it was certainly very impressive.”
According to Dr Mitton, the colours in the rainbow were intensified by the position of the sun, which was at the optimum spot in the sky of 22 degrees. The “rainbow’” is much brighter and more concentrated than a rainfall rainbow. In a circumzenithal arc, the colours are in reverse order from a rainbow, with violet on the top and red at the bottom. Circumzenithal arcs are so named as they go around the zenith – the point in the sky directly above the observer- rather than the sun.
This arc also appears in China, Laiyang Town with three suns. Amazing…
