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Re: (meteorobs) Angular velocities
In a message dated 99-07-28 20:12:54 EDT, you write:
me<<
>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>>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? <<
In what way, essentially the same results can't be derived from using speed
scales and only by angular speed estimates? I know Malcolm and Bob prefer the
angular speed determination method, but that doesn't mean another scheme
won't work just as effectively and easier.
lew>>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... <<
Again in what way? I haven't heard any examples yet. He gave me one minor
disadvantage that doesn't stop Rainer from still being able to analyse and I
gave a more practical reason where a speed scale is better than
angle/duration estimates that would reduce possible plotting errors. I think
it would be more important to get good data first and worry about minor
computer program problems later. The disadvantage that malcolm presented is
essentially a software program problem....not any failures with what can or
cannot be determined with the speed scale method.
lew>>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?
>>
When plotting, a radiant distance is known for a given known shower because
you have the meteor's plot on a chart. When there isn't a known radiant and
looking for a possible new shower or something, you will first notice the
tell tale multiple intersections when you trace the plots back to draw your
attention....just like you would if you used angular speeds. Then to
determine if they are actually related, you have an assumed reference point
(possible new radiant) to relate the speed scale to from your intersecting
meteors....just like you would when using angular speeds estimations. Then
each meteor will have to be appropriate in their speed scale numbers for
their distance from the possible new radiant, magnitude, and path length. By
looking at the speed scale numbers that the various apparent related meteors
were assigned, some overall estimation of the shower's entry velocity can be
derived. It won't be very accurate...but neither will the estimation from
angular velocities. You can only be so accurate with the human eye...for more
accurate speeds, you will have to use something better....such as camera's
equipped with rotating shutters or other more advanced means.
GeoZay
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