This is no camera trickery. It really is an upside down 'rainbow'.It was photographed in Cambridge by astronomer Dr Jaqueline Mitton who says she has never seen anything like it before.
Scientists call the optical phenomenon a circumzenithal arc.
Oddly, they don't need rain and cloud to form like conventional rainbows - they happen only when skies are blue and when ice crystals are present.
The arc appears when a low sun shines at a certain angle through a thin veil of cirrus clouds at between 20,000 and 25,000 feet.
It takes the shape of a quarter of a circle parallel to the horizon.
Dr Mitton said: "The conditions have to be just right: you need the right sort of ice crystals and the sky has to be clear. It's quite surprising for this to occur somewhere like Cambridge, usually it's in places that are colder."
The colours of a circumzenithal arc are reversed from those of a rainbow; the red range being closest to Earth.
In most cases, an arc will last at least half an hour. They are most common in colder climates, where ice crystals tend to collect in the sky with abundance.
It is also possible to see one from the inside of an aeroplane.
Scientists call the optical phenomenon a circumzenithal arc.
Oddly, they don't need rain and cloud to form like conventional rainbows - they happen only when skies are blue and when ice crystals are present.
The arc appears when a low sun shines at a certain angle through a thin veil of cirrus clouds at between 20,000 and 25,000 feet.
It takes the shape of a quarter of a circle parallel to the horizon.
Dr Mitton said: "The conditions have to be just right: you need the right sort of ice crystals and the sky has to be clear. It's quite surprising for this to occur somewhere like Cambridge, usually it's in places that are colder."
The colours of a circumzenithal arc are reversed from those of a rainbow; the red range being closest to Earth.
In most cases, an arc will last at least half an hour. They are most common in colder climates, where ice crystals tend to collect in the sky with abundance.
It is also possible to see one from the inside of an aeroplane.
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