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| Even at night, "sun pillars" may be visible -- from nearby streetlights,
| if there are ice crystals in the lower air.
Sun pillars and other halos around artifical light sources are really
interesting since they can produce clear 3D-efects around you. I just got
word
from Oulu that there was a nice halo display around lights of football
field.
There was at least pillar, subsun, 22degree halo, tangent arcs,
circumzenithal
arc, 46degree halo and parhelic circle.
| > 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".
Multible scattering is very interesting topic indeed. Circular halos
(halos
which are produced by random oriented ice crystals) doesn't give any
change to
see secondary halos as Paul correctly explained it.
The main issue with multiple scattering halos are halosforms which are
produced
by oriented ice crystals. Parhelia of parhelia which is called as a 46
degree
parhelia and Kern arc (circumzenithal arc of parhelic circle or other way
around) are haloforms which has been usually claimed to be multible
scattering
halos. In theoretically speaking they can be produced by this mechanism
but
they can be explained also by other theories. Kern arc has never
photographed
as far as I know. 46 degree parhelia has been photographed at least in
Saskatoon display in 1970 but those photographed 46 degree parhelia
doesn't
look like a multible scattering 46 degree parhelia should look. There is
at
least four theories for 46 degree parhelia (2 good and 2 bad ones).
Regards,
Jarmo Moilanen
Finnish Halo Observing Network
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