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Wayne noted:
>No, it is not random...the flat crystals align themselves biased toward
>being parallel with the horizon. Why? I can't tell you that at the
>moment...more research required, but that is the facts of life.
According to an excellent article I read in a recent Sky & Telescope about
possible halos and arcs which might be observed in the atmosphere of Mars
(it
was December's S&T I *think*), flattened ice crystals align themselves
parallel
to the ground (NOT the observer's horizon!) simply because of air
resistance.
Drop a sheet of paper from a sufficient height, and it will orient itself
the
same way and gently drift to the ground - or even stay suspended, if it's
high
enough up and winds are at work. Note that this is highly sensitive on the
SPEED
at which an object is falling: meteoroids have the tendency to do exactly
the
OPPOSITE, i.e., aerodynamically stablize themselves along their NARROWEST
axis.
(This is why it is so highly unlikely that meteoroids continue to "spin"
after
they have entered our atmosphere! Basically, the only spin which will
survive a
30000-150000 mph entry into the atmosphere is one which is an aerodynamic
artifact of the shape itself - and meanwhile, the object is busy ablating
and
probably obliterating any such corkscrew shape to begin with!)
BTW, folks, please be aware that there is a WHOLE EMAIL MAILING LIST which
is
specifically devoted to these types of phenomena!!! It's called the
"meteoptic"
mailing list (for "meteorological optical phenomena"), and you can find
out much
more about it at the following Web site. Note the great links here!
http://www.funet.fi/astro/eng/obs/meteoptic/
Note that US deep-sky heavyweight Tom Polakis is among the contributors,
as is
the IMO's own Sirko Molau and Juergen Rendtl! As Sirko mentioned, the AKM
in
Germany also has a great Web site on both halos AND meteors:
http://www.meteoros.de
And Finnish observer and antarctic denizen Jarmo Moilanen has a great
site:
http://www.netppl.fi/~jarmom/haloguid/index.htm
Also note that, apparently due to a Y2K bug(!), the meteoptic LISTSERV is
NOT
accepting new subscribers now! Still, peruse the site and its links.
Now, none of this is to say this thread shouldn't be pursued on OUR list
as
well! After all, cloud-related phenomena are the only naked-eye sky fun
some of
us get to have with any regularity! But draw your own conclusions... ;>>
Clear skies - or hazy if you prefer!
Lew Gramer <owner-meteorobs_at_jovian.com>
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