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Re: (meteorobs) streetlights in the cold....
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.meteorosdot de
And Finnish observer and antarctic denizen Jarmo Moilanen has a great site:
http://wwwdot 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@jovian.com>
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