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Re: (meteorobs) Re: NM South Delta Aquarid ZHR



GeoZay wrote in reply to Bob Lunsford:
> All this mental exercise with each meteor just for shower association? It's 
> not needed really. Shower association could be done a lot more efficiently 
> with less hassle using a numeric scale.  It's a waste of time to try to 
> figure any accurate velocities for a meteor since they won't be anywhere  
> near as accurate as a camera or other electronic means. For what purpose 
> other than shower association is visual meteor speed estimates used for?  I 
> can't think of any. However good you get at estimating angular velocity, it 
> won't be accurate enough to replace the results gained by high tech 
> equipment.  All you need to be is accurate enough to provide for adequate 
> shower association. You don't need to measure anything or estimate any 
> durations or do any kind of math in your head....just record the speed 
> impression you get from Slow to Very Fast and have some rough sense of the 
> meteor's distance from radiant and know what it means.

If you are plotting meteors to investigate minor showers, then a
reasonable estimate of the speed is important.  Given a precise speed
and position it would define the radiant.  The speed specifies the
distance of the meteor from the radiant, and the position and
orientation define the great circle containing the radiant.  The
intersection is the apparent radiant.

In visual observing the speed does have considerable uncertainty
whether measured in degrees/s or on a scale.  Thus we have a
probability distribution in the vicinity of the radiant (unless the
plot and speed are grossly inaccurate) of the radiant's position.
Likewise there is the plotting uncertainty which broadens this spread,
and gives rise to a lateral probaility distribution.  Without the
speed you just have a fuzzy great circle.

When you combine lots of observations and sum up the various
probabilities at different locations on the celestial sphere, e.g.
with RADIANT, the radiants will become obvious.  If you don't include
the velocity you may well still see a prominent radiant, but the
signal to noise is greatly reduced and weaker showers are lost.

One disadvantage to a scale over degrees/s is that the normalisation to
degrees/s needs to be determined for radiant analyses.  Also perhaps the
quantisation is slightly less in the RADIANT plots (more of a problem
with telescopic observation where the field of view is much smaller).

Malcolm


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