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- Forwarded message from "L-Soft list server at Finnish University and
Date: Thu, 13 Jan 2000 13:27:53 +0100 (MET)
From: Paul Schlyter <pausch_at_saaf.se>
Subject: Re: Rainbow
> On Thu, 13 Jan 2000, Veikko Makela wrote:
>
>> In case of winter and diamond dust in the air may be so close enough
>> the reflecting surface the reflected halo effect is possible. You
>
> Interesting conversation! I saw once how sunlight reflected from
ordinary
> windows caused "sun pillars" in a weak diamond dust halo display. I
don't
> think such a sight is a very uncommon one.
Even at night, "sun pillars" may be visible -- from nearby streetlights,
if there are ice crystals in the lower air.
> Halos caused by other halos, i.e. secondary halos, i.e. multiple
> scattering halos, are another, very interesting topic. I believe there
is
> no very good evidence of their existence.
They certainly exist, but I don't think they're observable: they'll
just causea general brightening of a large part of the sky. Think of
it like this: the Sun is essentially a point source, which casues a halo.
Any point on that halo can of course cause a halo of its own - a
"secondary halo". The whole "primary halo" thus causes a whole
"family" of "secondary haloes", which cover the entire sky from the Sun
out to twoce the radius of the "primary halo".
- End forwarded message -----
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