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Re: Radiants, was Re: (meteorobs) A blank meteor reporting form


Jim>>Hello George,
if you will recall, you just went through this same conversation with Sirko
Molau, concerning the discrepancy between the photographic radiant size
(generally less than 1-2 deg), and the visual plotting/shower association
size (of about 5-10 deg, depending upon distance from the radiant).<<

Yes, and it was apparent that Sirko was misunderstanding what the issue was in
that discussion. Looking at your paragraph above, it is apparent that you are
misunderstanding what I'm getting at also. The key difference is the part
"about 5-10 degrees, depending upon the distance from the radiant". This I
agree about..."depending upon the distance from the radiant". What I don't
agree about was the assigning of 5 degrees for one shower such as the Leonids,
10 degrees for the Orionids, 4 degrees for the eta aquarids, 8 degrees for the
alpha capricornids, 6 degrees for the kappa cygnids and other variants without
depending upon any distance from a radiant while the actual radiants for all
are under 2 degrees. What is there that makes all the different size of
assuming radiants necessary? This is what IMO use to list a few years ago on
their Shower Calendars. Apparently the shower calendar makers didn't get the
word and continued to print the same radiant sizes. These apparently aren't
assuming radiants they had listed. They appear to be errors that are getting
perpetuated and now confused with the enlarging of radiant sizes as the meteor
appears further from the radiant. IMO does not list these radiant sizes in
their handbooks nor provide a place on their recording forms to show these
radiant sizes anymore. 

Jim>>  if the meteor traces back to an
area roughly 5 or so degrees in diameter about the known radiant point, and
IF the meteor also meets the correct angular speed and path length
criteria, then  it is probably a good bet that this meteor was a shower
meteor.<<

This is correct...but this is not what is being debated. The remnants of
what's listed in the IMO shower calendar lists these values of 5, 10, 8, 6, 4
degrees etc, not on the premise of being assumed values, but as factual and
actual diameters...which are all incorrect. They are listed right next to
factual information about a shower such as the radiant location, radiant
drift, population index, velocity etc. If the radiant diameters are assumed
values, why are they listed with other factual information?

Jim>>What the form should be asking for is the approximate radiant diameter
used
by the observer to differentiate shower members from sporadic meteors. <<

This would be fine and dandy if all the meteors would show up at the same
distance from the radiant. But as we know, this is not the case. I guess an
observer could do this, but why would they want to when it's already
understood that meteors coming within a reasonably large diameter around a
radiant is acceptable? 

Jim>>For a beginning observer this might be as large as 20 degrees (two fist
widths
at arms length for myself).  <<

Even for an experienced observer, it might be 23 degrees if the meteor
appeared about 70 degrees from the radiant as shown in table 8-3.

Jim>> Thus, my own suggestion is that observers
fil in their own personal criteria used in the field while observing that
particular shower, with the IMO calendar values used as a guideline for
plotters and more experienced observers.<<

If the IMO calendar degrees are assumed values then it would seem that they
were drawn out of a hat indiscriminately and assigned to various showers?
It's already assumed that any meteors coming within a certain distance
centered around a radiant is acceptable, dependent upon the meteors distance
from the radiant. Is a beginner or experienced observer really gonna know the
difference if a radiant is listed with an assumed value of 4 degrees and not 5
degrees as in the case of the eta aquarids?
George Zay