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Re: (meteorobs) Linearids observed!





> On Wednesday night, Nov 10-11, I observed what almost
> certainly was a single Linearid meteor, at 7:45pm PT
> (03:45Z Nov. 11, or 16 hours before the time of closest
> passage). This observation was made from Chews
> Ridge, CA with a ZLM of 5.5-6.2. No further Linearid activity
> was observed up to 11:15pm PT.

It appears you observed for many hours, and with reasonably OK limiting
magnitude. I assume you saw quite many sporadic meteors overall. Now, if you
tell us how many, I am sure that someone out there (the International Meteor
Organization (IMO) perhaps) has a program that can plot the same number of
meteors randomly onto your field of view. Knowing the direction to the center of
your field of view would be helpful.

Running such simulations a couple of hundred times and then calculate the
fraction of these simulations where at least one random meteors fits good enough
with a Linearid trajectory to be mistaken for one within normal accuracy of
meteor plotting will indicate the probability that your Linearid was just a
sporadic meteor. The major weakness would of course be to know the accuracy of
trajectory plotting. I personally find it difficult to plot an accurate
trajectory for a meteor even if it lights up pretty close to the center of the
field of view and pretty close to bright stars. I think I have read somewhere
(in the IMO handbook perhaps) that double or multiple plot experiments show that
the error is often considerable. Hence, I do not attempt to plot meteors
anymore. Using statistical methods based on a large number of meteors will of
course to some extent cancel out the individual error for each meteor.

One more thing: Assume that say 20 fairly experienced meteor observers were
"brain washed" to believe that the Perseid radiant was in the middle of
Cassiopeia, and that these people were asked to plot meteors during the
perseids. My guess is that they would generally plot mostly Cassiopeids for a
long while provided the center of their field of view was sufficiently far away
from the real radiant (several meteors between the real radiant and the wrong
one would of course tell them that something was wrong). I'll bet they would be
inclined to twist the trajectory a bit to fit with the expected radiant. I doubt
they would even suspect that they did this for a long time. I am not saying that
this is the case for your Linearid, but you should be pretty sure about the
trajectory to rule out this possibility.

This being said, you may very well have seen a Linearid. I just make these
comments because people should be aware that given a lot of sporadic meteors,
some will always line up with a randomly chosen radiant, and that meteor
trajectory plotting is often quite inaccurate and not necessarily objective.

   Birger Andresen


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