A NATURAL phenomenon usually seen at the North and South Poles has been spotted in the sky over Brighton.
A circumzenithal arc, shaped like an upside-down rainbow and giving the appearance of a smile in the sky, was seen above the city at around 4pm yesterday.
It is shown in these pictures, sent to The Argus by reader Sherrie Fox.
According to the Met Office, circumzenithal arcs are formed when sunlight refracts through horizontal ice crystals at an angle where the light enters the crystal through its flat top face and exits through a side prism face.
This is what causes the distinctive upside-down rainbow effect.
The arcs are commonly associated with cirrus clouds, where ice crystals readily form.
And although the arcs can occur throughout the year, they are usually obscured by clouds underneath and so cannot always be seen.
They differ from rainbows, which form when light penetrates raindrops and does not change direction as it exits the other side.
On its website, the Met Office says a combination of atmospheric conditions must be in place for a circumzenithal arc to be seen.
Pictures by: Chris Proctor
It says: "In order to be able to see a circumzenithal arc, a combination of atmospheric conditions must coincide.
"The height, depth and position of the ice clouds must be right as the cloud needs to be at a specific angle convex to the sun.
"The position of the observer is also important since its visibility can vary greatly over short distances."
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