Courtesy: Jack Justice; another circumzenithal arc sent into us on Nov. 20, from Pembroke, Ontario
Upside down rainbows, or 'circumzenithal arcs' as they're properly referred to, are a rare optical phenomenon similar in appearance to a rainbow. However, their make-up couldn't be any more different.
Unlike common rainbows which form when light reflects through raindrops, mist, or sea spray, a circumzenithal arc develops when ice crystals high up in the atmosphere bounce the rainbow's light rays back up into the sky.
The colours are in reverse order from a rainbow as well -- with violet on the top and red at the bottom.
The arc usually forms no more than one-quarter of a circle centred on the zenith (the arc is also referred to as "circumzenith arc" due to its unique positioning) and on the same side of the sun.
In most cases, the inverted rainbow will last at least half an hour -- giving you plenty of time to admire and photograph the beautiful arc.