Unusual photograph was taken by Dr. Jacqueline Mitton (Jaqueline Mitton). Scientists call the inverted rainbow effect zenith arc (circumzenithal ark). It is curious that it does not need either of rain or clouds necessary for the appearance of an ordinary rainbow – an arc equal in length to a quarter circle, appears on a clear blue sky in the presence of ice crystals.
Inverted rainbow appears only when the sun is at an angle through a thin curtain of cirrus clouds at an altitude of 6000-7500 meters. "We need very precise terms: a certain kind of ice crystals and clear skies. Surprising that this has happened in a place like Cambridge. Usually happens in colder areas," – said Dr. Mitton.
Scientists say most of the inverted rainbow in the sky is no longer than half an hour. Traditionally, it is a natural phenomenon can watch people in countries with cold climates, where the sky is going to a huge amount of ice crystals. In addition, a rainbow can be seen from an airplane window.