It’s called a circumzenithal arc. Unlike a normal rainbow, which is caused by total internal refraction within a (or, rather, millions of) water droplets, circumzenithal arcs are caused by light scattering in ice crystals in the upper atmosphere. They are generally only visible on very clear days as any cloud in the lower atmosphere will prevent them from being seen.
-- Best regards, Barry Wainwright > On 17 Aug 2016, at 15:24, Jackie Jones <jac...@waitrose.com> wrote: > > Dear Sundial folk, > > I know this is not really sundial related, but I am sure someone will be able > to explain this odd rainbow. The picture was taken yesterday just before 6pm > British Summer Time on a hot sunny day. Looking west to the low sun, there > was a rainbow above it with the ends of it curving upwards. Below it there > was a very faint second one in the same curve. How does this happen on a dry > day; normally the sun is in the opposite direction to the rainbow? > > With best wishes in anticipation of an explanation, > Jackie > > Jackie Jones > 50° 50’ 09” N 0° 07’ 40” W > > <Rainbow above sun.jpg>--------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > <https://lists.uni-koeln.de/mailman/listinfo/sundial>
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