They're easier to spot once you know what you're looking for :o)

Caught it on the way back from more general scrabbling around in the dark...




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Ok - here's what you need:-

1. A full or nearly-full moon, fairly low in the sky.
2. A showery weather situation - lots of breaks in the cloud.

and here's what to look for:-

With the moon behind you and a shower ahead, a moonbow appears as a faint grey-or white arc in the sky: you don't see the colour with the naked eye. It seems to take a good few seconds of looking at what looks like it might be a 'bow before it becomes properly apparent. That's why it helps to know the conditions are right in the first place.

I was lucky with this one as the moon and shower were nicely lined up with the wind-direction, so the movement of the clouds appears to be coming out of the 'bow.
I did get a bit wet when it all caught up with me though!