UKC

In reply to Jimmy O:

Snow on the rest of the ridge, meaning the its shadow is literally not as dark as that of the Aiguille?

In reply to Jimmy O:

I think it's the 3D shadow of the peak on which you are standing. To either side of you, the ridge is lower, and so light passes below your level and is backscattered from dust particles, resulting in haze. In the central cone-shaped region, there is no light to be backscattered, as it is being blocked by the peak.

If you could look upwards from your position against a black background, the effect would not be visible, as the atmosphere would be evenly illuminated.

Hope that makes sense,

Cheers,

Nick

In reply to Nick Lambert:

Thanks for that. That makes a lot of sense. We have just come up with the same solution here at work!

James.

In reply to Jimmy O:

Yeah, I think Nick is correct when he says that the difference between the dark and light areas of the shadow is because the Tsa is very pointy and extends above the height of the rest of the ridge. Therefore you see the scattered light from dust to the sides but not directly ahead.

In reply to Jimmy O:

p.s. the perfect triangle is actually because it's a parallel sided tunnel of shadow that you are viewing along it's length, so you get a perspective effect:

http://www.atoptics.co.uk/atoptics/mtshad.htm