pumeco: exactly. That's what I always thought. Yet I saw it. I swear this is not an Apr 1 joke! I really did see it! But it was the SAME light shining through the SAME atmosphere (albeit through a hole in the cloud). Had it been just in the area under the cloud, I'd be happy. But it wasn't. The effect showed up in the clear sky beyond the cloud (ie, closer and more overhead). Just in case it has any relevance, I was looking near due west at the time.. My thoughts are tending towards the light being partly attenuated by going through an (almost, but not quite) clear part of the cloud and thus affecting the visual result. But I still can't work out how a a "diluted" light (the shaft) could possibly affect the undiluted light of the clear sky... Damn! I WISH I'd had my camera with me so I could show you all the effect! Ahh, well, Cheers, Diolma