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> I saw some interesting phenomena from an aeroplane recently.
> One nice sub sun, and some glories.
>
> One glory interested me in particular. It was very very strong,
> to the extent that it wasn't just one ring of colours visible
> but 3 concentric cycles through the colours.
>
> Centred on the glory was a halo, large and faint but definitely there.
> I am very used to seeing 22 deg haloes, and this was bigger than
> that, wider too, but not as big as a right angle. So I estimate the
> radius of this halo to be 30-something degrees.
>
> Any ideas as to what that is called? (I didn't have a camera on me,
> unfortunately!)
>
> Sharon
You saw a glory, or anti-corona, and a fow-bow or cloud-bow.
Rainbows are formed by reflection and refraction inside water drops,
as you probably know. When the water drops get smaller, diffraction
effects start to have a significant influence on the appearance of
the rainbow: first so-called supernumerary bows form, inside the
regular rainbow. As the raindrops get smaller, the supernumerary
bows get brigher and wider, while the regular rainbow gets fainter.
If the drops get smaller still, the regular rainbow gets invisible,
and the colors of the supernumerary bows mix, and what we then get is
a white bow. This is the cloudbow. It is a few degrees smaller than
a regular (primary) rainbow and, as you've noticed, quite larger than
a regular halo.
Rainbows/cloudbows are formed by refraction/reflection/diffraction
in water drops, while haloes are formed by reflection/refraction
in ice crystals (diffraction doesn't seem to be signifcant there).
Paul Schlyter, Swedish Amateur Astronomer's Society (SAAF)
Grev Turegatan 40, S-114 38 Stockholm, SWEDEN
e-mail: pausch at saaf dot se
WWW: http://hem.passagen.se/pausch/index.html
http://home.tiscali.se/~pausch/
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