This was the sight that appeared in the skies over Headley Down just after half past five on the evening of Sunday, September 14 and photographed by a resident in Birch Road.

In fact, it was not the only upside-down rainbow that graced the skies in September.

Three days later, a similar 'Cheshire Cat' graced the skies in Cambridge in the afternoon sunshine, also captured on camera (see picture right).

But according to meteorologists, these upside down rainbows are not really rainbows at all.

They are known as circumzenithal arcs and are relatively rare in Britain.

The upside down arc only appears when sunlight shines at a specific angle through a thin veil of wispy cloud at a height of around 20,000 to 25,000 feet.

At this altitude the cirrus clouds are made of ice crystals, which are the size of grains of salt.

Experts say the clouds must be convex to the sun with the ice particles lined up together in the right direction to refract the light. This results in the sunlight bouncing off the ice crystals high into the atmosphere, sending the light rays back up and bending the sunlight like a glass prism into a spectrum of colour.

Mrs T Hollingdale, who captured the Headley Down 'Cheshire Cat'. said: "The weather is always a topic to look at and this really made me smile."

Renowned astronomer and writer Dr Jacqueline Mitton captured the optical phenomenon on camera in Cambridge, and commented: "We are not sure how big an area it was visible over, but it was certainly very impressive."

A Met Office spokesman said: "It is quite rare to see these arcs as vivid as they were. It depends on the position of the observer because their visibility can vary greatly; someone 10 miles away would probably not be able to see one at all."