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Re: (meteorobs) Angular Speed Equations



me>> I forgot to add....a good angular speed measurement can be used to 
roughly 
> estimate the shower radiant position for one meteor, when combined with the 
> path length, IF you have good alignment as well. Without good alignment and 
> any intersects, it's anybodies guess.  How do you know if a visual 
observers 
> alignment isn't off for any one meteor? You don't. This is the reason for 
> visual observing purposes, a  known radiant location is enlargened. I 
> personally prefer multiple intersects to direct me into estimating a new 
> radiant position. I still haven't seen any practical use for angular speed 
> estimates other than shower association. Just like the speed scale I use.  
<<

malcolm>>Without the angular-speed estimate you can plot the intersections of
most pairs of meteors.  Yes this will work for strong radiants, but
for weak minor showers the additional noise of false radiants can
drown out the real ones. <<

Yes, any kind of errors from path length, alignment, distance from radiant 
will magnify any inaccuracies. The intersections of pairs of meteors for a 
minor shower will be less accurate than for a major shower. Do you declare a 
new radiant with just one or two meteors by working with angular speeds? 
Probably not....at least I wouldn't. Otherwise you can probably expect 
several "discoveries" from each observer with each night they plot. More than 
likely there will be a higher number of meteors involved. At least there 
should be to draw attention that something new may be present.  This number 
of meteors would have enough intersections to come up with a close enough 
approximation for a radiant location. Close enough that any additional use of 
angular speed estimations probably wouldn't help. The more meteors that 
intersect and to work with, the more refined a radiant location will be. 

 malcolm>>Apart from the path-length constraint the
radiant can be anywhere along half of the great circle of its
prolongated path (for simplicity I'm ignoring the observation errors
in the position). Using an estimate of angular speed, be it from a
scale converted to deg/s or deg/s directly, gives a much reduced arc
where the radiant can be.  Thus the number of false radiants is
reduced and the real ones become more evident.   <<

In theory this is true for non fireball meteors. You are basically saying 
that, "The apparent path length of a shower meteor amounts at most to half 
the distance from the radiant to the start point". If the data was 
photographic, this would be easy to note. However in practice, meteors 
plotted will often not be this accurate. Rainer a few years back has told me 
that most meteor lengths are over plotted and that twice this distance would 
still be acceptable for shower association. This would introduce inaccuracies 
to any radiant determined from estimated angular velocities. The fewer 
meteors involved, the greater uncertainty for a true radiant location. The 
same as if one went just by meteor intersects. So a greater number of meteors 
in the sample would help radiant determinations both by intersects and 
angular velocity estimates. Personally, I would rather narrow down a radiant 
location by the intersects than by angular velocity. I would then just have 
the inaccuracies of intersects due to misalignments to deal with and not the 
added path length inaccuracies to compound the problem. I haven't heard of 
anyone determining radiant locations with angular velocities alone? From all 
the reports I've seen, it appears that intersects is what is being used. 
Angular velocities is just used to weed out unrelated meteors. 
GeoZay

malcolm>>George, you didn't say what your speed scale calibration is.  Please
can you elaborate.<<

I don't have a speed scale calibration that would relate to angular 
velocities as you've earlier indicated. I have an entirely different scheme 
where it's sole purpose is for shower association....apparently very similar 
to the one Norman McLeod indicated a few days ago. I will try to post it in 
another message.
GeoZay

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