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Re: (meteorobs) Leonid max
I guess everyone will be getting a bit fed up with my messages, but I must
point out again that the orbital plane of the comet has no direct physical
relevance to the time of the meteor shower maximum. It is the time of the
orbital plane crossing of the ejected DUST, taking account of the full
planetary perturbations from ejection to Earth passage. This is not
speculation but has been fully verified for past showers of the Leonids
and Draconids (regarding the Draconids, Reznikov's prediction of 1998 Oct
08.550 UT was published about a decade ago). The evidence is overwhelming
that the time of a dust trail passage can be predicted with around 5
minutes uncertainty. The big question is, are all the dust trails
predicted? In 1999 there is only one young dust trail predicted.
Again, so as not to produce follow up questions, I must state that I'm
only aware of Peter Brown having modelled the background activity and you
would have to look at his work to see when the background is predicted to
peak. From Brown historical reanalysis of Leonid rates in Icarus this
year, there are years with ZHR approaching 500 when no dust trail
accproches occur. It is thus possible that rates could be of this order
in 1999 away from the predicted dust trail encounter.
As an aside, there has been a discussion on the Minor Planet Mailing List
in the last 24 hours regarding predicting asteroid positions over a short
period after discovery using simple linear extrapolation or using an
assumed (Vaisala) orbit. Dave Tholen summed the situation up nicely by
stating that one involves maths and the other maths and rigorous physical
theory. The parallel with some approaches to Leonid maximum prediction
seems clear.
Cheers, Rob
Robert H. McNaught
rmn@aaocbn.aaodot gov.au
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