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Re: (meteorobs) Those pesky path lengths (was Re: OBSERVATION Aug 6/7 GRALE)
Hello Lew and others,
Path lengths are always a concern and while the '2 times length to radiant'
is a good rule of thumb there are exceptions, and indeed one has to develop
some feeling for that and keep a clear judgement of factors involved.
Wat Lew actually means I think is that at larger distance from the radiant
even true stream meteors can be of rather short lenght if they are faint
(is this a coorect interpretation Lew?).
Now that is valid, I think, for the reason that meteors start faint, then
brighten somewhat and then fade out again. With faint meteors, you can have
the situation that only the brightest part of the trajectory crosses the
visibility treshold, i.e. you are only seeing PART of the trajectory. I
always try to keep this in mind with fainter meteors.
In addition, meteors (also brighter: maybe especially brighter since faint
meteors at large distance become invisible) that appear at a very large
distance from the radiant are actually seen 'on the tail', similar to 'head
on' close to the radiant and in that way shorten too. So a Perseid low in
Ophiuchus in the lower sky opposite the radiant direction might seem rather
short because you happen to look it 'tail on'.
Basically, I think that those commenters that said that in classification
it is a judgement of several factors are right. And indeed, you have to
develop some feeling for that. Always try to visualize the atmospheric
trail situation in 3d when in doubt.
-Marco (former DMS visual section coordinator)
Leonids-'98? A once (twice?) in your lifetime appearance! You can't afford
to miss it!
Casper ter Kuile, Akker 145, NL-3732 XD, De Bilt, The Netherlands
Phone: +31-30-2203170; Fax: +31-30-2202695; GSM: +31-6-54723974
E-mail1: pegasoft@cc.ruudot nl; E-mail2: casper.ter.kuile@rivmdot nl
WWW: http://www.pidot net/~terkuile/meteors/dms.htm
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