Thursday 29th August 2013, 6.30pm (day 735)
I’ve only ever seen this a couple of times before — a rainbow, or at least a spectrum, high in the air, nowhere near the ground and with no rain in sight. I guess it must be caused by light refracting through ice crystals in the upper atmosphere. Bad weather on the way perhaps. Let’s hope not: I intend to spend next weekend walking in Norway.
POSTSCRIPT: Have discovered this is something called a ‘circumzenithal arc’. They are not rare as such, but apparently only appear when the sun is at exactly the right angle to ice crystals in high-level clouds, and thus can be seen only in very restricted locations on the ground. So if you do see one, feel privileged – it may well only be visible in a space a few metres around you.