> > What I don't understand is why it's so common, it should be obvious; all
> > you have to do is look up when there's some clouds passing by.
>
> Umm, if you are talking about what I think you are(the visible "beams"
> of light caused by partial clouds and atmospheric scattering), that is a
> completely different illusion, caused by perspective. The beams appear
> to come from a point because they appear smaller and closer together the
> further away they are...the same effect that shows in railroad tracks,
> checkered planes, etc. If the light was parallel, you would still get
> that effect. I don't know how much a difference the divergence makes,
> but I doubt it would be obvious without side-by-side comparisons of
> images. It might be an interesting POV project though...

Yes, you're right, I wasn't thinking it through. Parallel rays would cause
the same effect.

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