These 'upside-down rainbows' or 'smiles in the sky' were spotted in southern England on Saturday.
A smile in the sky in Coopers Green, East Sussex
Although they look like rainbows they are actually an optical illusion known as a circumzenithal arc or Bravais' arc.
A circumzenithal arc in Chilham, Kent
Circumzenithal arcs form when sunlight is refracted through ice crystals rather than raindrops.
Gaps in the cloud make for an unusual circumzenithal arc in Brent Cross, London
The meteorological phenomenon usually forms high up in the sky among cirrus and cirrostratus clouds.
Tim photographed this vibrant smile above Brighton
Unlike normal rainbows, the colours are in reverse order with violet on the top and red at the bottom.
A circumzenithal arc was also visible at Langston Harbour, Hampshire
They form fairly frequently but are usually obscured by layers of clouds beneath.
Another interesting effect in Burghfield, West Berkshire
