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Re: (meteorobs) Moonlight and the IMO method



On Tue, 21 November 2000, Rainer Arlt wrote:
 
> I would tend to say that the low sporadic rates are mainly due
> to the fact, that the Leonid radiant is so close to the apex
> area from where a considerable number of sporadics come in the
> last morning hours -- just when observers were out for the
> Leonids. As we had to face a direction not favourable for radiant
> association -- because of the Moon -- it is very likely that a
> number of sporadics was simply counted as Leonids. I found my
> own notes of 17/18 with a single sporadic in about 1h effective 
> time!

I agree; the apex meteors probably polluted the Leonid numbers to some extent (1-2/hour?).

Speaking of which: I'm not experienced in interpreting unguided wide-field photos, but can anyone confirm that the "Leonid" on the Sky and Telescope web page "news" report is not a Leonid? Plotting points on a gnomonic map, it looks like the backward trace misses the radiant by a goodly distance to the north:

http://www.skypub.com/news/images2000/001118news01.jpg


> It may be interesting to compare this effect (of depleted sporadic 
> numbers during major-shower maxima) among the major showers
> QUA, PER, LEO and GEM with respect to their different distances
> from the apex. The GEMs should affect the sporadic rate least.

I think sporadic pollution may be more of a problem when shower rates are low. I remember getting sporadic rates of 31/hour during the 1997 Perseids (103 Perseids in same hour), 25/hour during the 1993 Geminids (73 Geminids in same hour), and 28/hour during the 1999 Leonids (73 Leonids). These were all during morning hours with excellent LM (~7). Perhaps sporadic rates get polluted with shower meteors during high rates. In looking at old reports, I think you'd have to investigate whether the observers separated out the minor showers. If Aquarid complex meteors are counted as sporadics during a Perseid observation, or Taurids counted as sporadics during the Leonids (which is probably just as well), the sporadic rates for those observers will be higher.

--
Wes Stone
Portland, OR

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