FORMER science teacher Vicki Cottrell couldn’t believe her eyes when she spotted an ‘upside-down rainbow’ in the sky over Didcot.

Ms Cottrell was in her garden at her home in Wessex Road on Monday when she saw the ‘smile in the sky’, otherwise known as a circumzenithal arc.

“It’s the first time I have ever seen anything like it,” said Ms Cottrell, who has lived in her three-bedroom semi-detached home since 1997.

“It was a warm night and I was lying on the grass in my garden with my cat Charlie and he seemed remarkably unfazed.

“I quickly took some pictures with my mobile phone because I thought what I was seeing would vanish quite quickly but it didn’t so I went inside to get a digital camera and took some more pictures with that.

“The rainbow lasted for about 20 minutes before slowly fading away.

“I wanted to tell my next-door neighbours what I had seen but when I looked around there was no-one about so they must have gone in for tea.

“From the brief research I have done it looks like sightings of these upside-down rainbows are quite rare, and are caused by refraction of sunlight through ice crystals in clouds, rather than raindrops.

“I was a science teacher at Didcot Girls’ School from 2004 until Christmas when I moved to a new job with a science publishing firm on Milton Park.

“This could well be something pupils at the school would be interested in taking a look at.”

Ms Cottrell spotted the arc about 7.20pm on Monday.

Former town mayor Peter Read, who lives in East Street, which runs parallel to Wessex Road, worked as a senior engineer in the space department at Rutherford Appleton Laboratory for 20 years.

He said: “I have seen halos around the sun before but not an upside-down rainbow and I missed this one.

“It was probably at quite high altitude, in the jet stream at about 30,000ft.”

Met Office spokeswoman Sarah Holland confirmed these pictures show a circumzenithal arc.

She said: “In order for conditions to be right for a circumzenithal arc to form, small, flat, six-sided ice crystals must be suspended high in the sky to create a field of tiny prisms.

“The sun’s rays enter the ice crystals and is refracted, projecting an arc in the sky which, if complete, would circle the zenith.

“Completely circular circumzenithal arcs are rare – most of them only take up a section of the sky.

“They are seen at times across the UK.”

How does it happen?

  • THE circumzenithal arc is similar in appearance to a rainbow – but no rain is involved.
  • The arc arises from refraction of sunlight through ice crystals contained in clouds. It forms no more than one quarter of a circle and its colours are clearer than those of the rainbow because there is less colour overlap.
  • Normal rainbows form when light refracts through raindrops, mist or sometimes sea spray.