A rainbow.
Strange?
It is when only one colour – yellow.
.
Two very odd cloud effects.
1) Flying back to Bristol I think, from Glasgow in the middle of the day we were above a complete sea of cloud right across the country. It was split by a single, nearly straight rift of clear air that would have been well under a mile wide, stretching away Eastwards into the distance.
Whilst I have seen other cloud patterns that suggest very long (miles) wavelength pressure-waves, eddies, shears and such-like in the air, this feature defied any basic physics.
.
2) Late one night, in a clear and moonless sky some distance from any towns, seeing what appeared to be a vapour-trail form. Then three more developed, creating something like the letter 'Pi' in the sky (couldn't resist that), with a diagonal across it.
Vapour-trails? Well, central Dorset is not far from Hurn Airport, and only 70-80 miles from each of Exeter, Bristol and Southampton Airports; but these things developed along their full length not from the leading "end". and there were no signs of aircraft lights. Also they did not disperse in the way exhaust trails usually do, and the entire pattern slowly drifted away, gradually fading as it went.