Monday, 23 June 2008

Rainbow cloud


Many thanks to the farmer who emailed me this link from National Geographic after having seen yesterday's post about the strange rainbow cloud. I think what I saw must have been a smaller-scale version of the same thing:

'. . . it is caused by light passing through wispy, high-altitude cirrus clouds. The sight occurs only when the sun is very high in the sky (more than 58° above the horizon). What's more, the hexagonal ice crystals that make up cirrus clouds must be shaped like thick plates with their faces parallel to the ground. When light enters through a vertical side face of such an ice crystal and leaves from the bottom face, it refracts, or bends, in the same way that light passes through a prism. If a cirrus's crystals are aligned just right, the whole cloud lights up in a spectrum of colors.'

The conditions here were absolutely right - the sun was at its zenith and this was a high-altitude cirrus cloud. I wish my photo had done it more justice - the full range of the spectrum doesn't show very well, but the yellows, greens and blue were definitely there.

If anyone knows any more about such phenomena, please do get in touch. Maybe it's quite common and I'm just very unobservant but I don't remember having seen a cloud like this before.

2 comments:

60 Going On 16 said...

I'm a bit late commenting on this, J, but was fascinated by that photo, as I am by clouds generally. Fellow cloud fans might be interested in the Cloud Appreciation Society's lovely website, which is at:
http://www.cloudappreciationsociety.org/

You should definitely send your photo for inclusion in their gallery!

Juliet said...

Hi D - actually I have already sent it to the Cloud Appreciation Society, and their photo gallery editor, a very nice man named Ian, emailed straight back and said it was 'a beauty' and 'well spotted' and that it would be up in their gallery 'very soon'! What excitement! I'll post a link when it's up, together with some more info about this phenomenon which he sent me.