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Re: (meteorobs) Angular velocities

GeoZay(?) remarked:
> >There is nothing that can be determined with angular speed estimates that 
> >can't be estimated just about as accurately [when] one uses speed scales. 

Lew replied:
> This is sure one poster's opinion here. However, the above seems to imply
> this is also the opinion of Malcolm, Bob and others: that doesn't seem to
> be the case, I think? Malcolm's comments suggest to me that a rigorous
> angle/duration estimate is FAR more useful for minor shower analysis than
> a simple 1-5 estimate... After all, any "conversion scheme" from 1-5 into
> angular speed would have to assume a radiant distance is known: naturally,
> if a minor shower's radiant is what one is seeking, it doesn't make sense
> to assume radiant distances for the observed meteors a priori, does it?

I think Lew is overstating and misunderstanding my point.

From a comparison doubly observed meteors we can estimate the errors
for the angular-speed method.  The AKM guys did this, the results
being published in WGN, and the figures incorporated into RADIANT.
Looking at these there seemed to be about six distinct (1-sigma)
ranges, implying a scale is viable too.  The important features are:
the scale is consistent and it is calibrated.  The calibration will
vary from observer to observer, so it's up to each to quantify their
scale into physical units and include in their data submission.

The degree/s method does tend to reduce artifacts for small samples in
the RADIANT plots compared with a scale because of the smearing out
effect.  As to whether there is more information there, that's a
matter of debate.  You could define ranges for each step of your speed
scale, and use a random number between those limits in your
submission, and possibly achieve the same effect.

We really need observers who have used both methods to comment on the
comparative ease of use and accuracy.  As George indicates, some people
like the scale and others feel comfortable with a number.  BTW I use
letters A--F (oh what a giveaway!) to discrimate from 1--6 degrees/s.
It's not that I don't like the degree/s method, it's because the
telescopic meteors whiz by so fast.  I was able to calibrate my
speed scale into degrees/s reasonably well, but less accurately
than a visual observer would be able to do.  In doing telescopic
analyses combining various observers, calibration is a big problem.
Not all are regular observers, and not all record the speed.

Repeating Lew for convenience:
> angular speed would have to assume a radiant distance is known: naturally,
> if a minor shower's radiant is what one is seeking, it doesn't make sense
> to assume radiant distances for the observed meteors a priori, does it?

Where does the radiant distance come in?  The speed scale is
independent of radiant distance and shower, or should be.  To me it's
a kind of lookup table.  Speed 1 equals say 1-3 deg/s, 2=4-8, etc.
[I'd be interested to learn how George generates his scale, and what
it is.]

I imagine that some plotters will be able to quote degrees/s just
based on years of experience.  In just the same way we do a
seat-of-the-pants job making a shower assignment during counting. The
mind is trained to take all the factors into account, and it becomes
second nature.  Of course, at first it can be daunting as there is so
much to remember.  It appears that the degree/s method is more
difficult to learn than the scale for some.

I thought that observers who quote degrees/s, replay the meteor, and
estimate how far the meteor would travel in one second.  This is
in contrast to estimating the path length and duration.  My impression
was that with a little practice it became automatic.

Malcolm

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