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Re: (meteorobs) Re: Leonid max
David,
I get frustrated at having to answer many individual questions in this
regard simply because David Asher and I have had no outlet for the
detailed explanation and verification of our work in the large circulation
astronomy magazines. Thus it is not your fault that you are not aware
of the extent that the dust trail theory has been validated in its
predictions of the time of Leonid storms (although I have given lengthy
explanations several times on meteorobs and still get asked exactly the
same questions). The issue of predicting past events raises a number of
issues in the philosophy and sociology of science that I'll cover only
briefly (and by the way Marco, if Popper was to be believed then our
theory is the only one that is not yet falsified) but I'll try not to be
too verbose. Note that in the following I'm presenting extreme positions
that could be true and thus could influence the way people think.
Science is done by people in a cultural context and whilst the cynical
attitude I present is not likely to be held by most meteorobs readers, it
is likely to be held by much of the community. These remarks are, I hope,
a totally honest expression of my beliefs without being emotionally
influenced (but then who am I kidding).
1) Predicting the time of maximum uses ONLY the comet orbit. No
information on meteor activity is involved in the predictions, thus the
timing of when the events occur, past or future, has no bearing on the
*validity* of the theory.
2)But it does have a bearing on the sociological aspect of how others
should accept it. Sure, we could be lying or somehow mistaken about not
having used this knowledge in developing the theory. After all, how many
people have gone out and checked the results? But if we are lying, then so
too are Kondrat'eva, Reznikov, and Murav'eva and Lyytinen as all three
groups come up with the same timings and all three groups have predicted
some trails others missed that had been later confirmed by other
groups. We could also be lying or somehow mistaken about all three groups
being independent. After all, the first study by Kondrat'eva et al has
been around for 15 years and Reznikov's development of the theory, for
even longer.
3) Prior to Peter Brown's detailed reanalysis of the historical Leonid
activity, in which he calculates the time and rate of maximum for all
years with available data, I had to rely on a range of sources for
this information. This left it open to question on how the data was
selected. Peter's study made it easy to just go with his
comprehensive results. I hope there is no way this could be considered to
introduce any bias.
4) Gary Kronk knows that David Asher and I were unaware of the time or
strength of the 1869 outburst (unless it were to be assumed that I was
lying or somehow mistaken about having no knowledge of his reference to
this activity), so the agreement to 5 minutes for 1869 is additional
confirmation *for us*, but again others just have to take us on trust.
5) Reznikov has used his version of what David Asher and I later called
the dust trail theory to make predictions for both the Leonids (with
Kondrat'eva and Murav'eva) and the Draconids. I don't have his paper at
hand, but his prediction for the 1998 Draconid display was made at least a
decade ago and predicted 1998 Oct 08.550 UT (note the third decimal).
Thus for the Draconids in particular, but also the theory in general, a
prediction of a yet to happen event *has* been made and been shown to be
correct WITHIN OBSERVATIONAL ERROR.
If you read what I've written in the past, I doubt if I have ever
written an article, or sent a message to meteorobs that doesn't go to
pains to point out that these predictions are for young dust trails only
and that older dust trails and the background activity have *not* been
predicted by this model and that the activity of these could be
substantial. From Peter Brown's historical reanalysis, the ZHR in years
outwith young dust trail encounters can reach up to 500. This
would still be a very impressive shower. But the simple fact is that the
dust trail theory predicts *every* storm or short duration outburst
(like 1869 and 1969) to an uncertainty of close to 5 minutes. I should
not have to apologise for this :-)
Dealing quickly with some critical comments I've received. Joe Rao
correctly points out that our predictions for 2001 and 2002 are further
in time from the comet's passage than has been observed before. In the
period we covered, the last 200 years, we are in full agreement. There
was no young dust trail encounter that far from the comet during this
period. Dust trail encounters are fickle but fully predictable.
Another comment on a web page was that we used an unrealistic dust
ejection model. As I understand it, we used the same model as others but
even if the comment was true, is this suggesting that all the valid
predictions of the time of maximum and the close fit of the storm
intensities to our density model are just chance? The fact is that
particles can only take a single route from point A at time A (comet at or
near perihelion) to point B at time B (Earth in some specific November)
unless you assume some ridiculous ejection velocities or very old trails
(when an extra orbit can take place). The dynamics here is rigorous and
the introduction of solar radiation pressure on the particles appears not
to affect the timing of maximum in David's modeling. If the dust
ejection model were seriously wrong, then it would affect only the
distribution of dust within the trail. The geometry of the trail has been
more than adequately verified as far as we are concerned.
However I would love to receive critical comments on our work. There are
clearly aspects of the dust trail profile and density, and fitting of the
ZHR to our density model that are in need of further study. To a large
extent any further progress is limited by the lack of data. This year
shall produce only one more data point.
All of this aside, I'm very excited about this years Leonids regardless of
what happens. I've been awaiting 1999 since I was kid but that was based
solely on 1966+33!
Cheers, Rob
Robert H. McNaught
rmn@aaocbn.aaodot gov.au
On Thu, 21 Oct 1999, FIPT LBTS1b(con)3, D Cross wrote:
> As last year, many are asking the best time and place to watch for
> Leonids.
>
> As a (very) casual observer, the lesson I drew from last year is that
> the best place is anywhere outside (but as dark as possible helps) and
> the best time is whenever the radiant is above the horizon, or not too
> far below, and the sky is at least partly clear, for as many nights
> around the expected peak as you can manage.
>
> This is on the basis that the predictions are *only* predictions, so the
> more time you spend watching the sky the more chance you have of getting
> lucky - wherever you are. We seem to have detailed analyses of why last
> year's Leonids went off the way they did, and I have no reason to doubt
> their accuracy, but they *are* after the event. I don't believe that a
> *consensus* of last year's predictions (as reflected in postings to
> meteorobs) would have led observers to expect what actually happened.
> (Individual predictors may have got it right - I don't recall.) Of
> course, the data from last year has improved our understanding, so
> predictions should in principle be better this year, but they surely
> can't approach certainty.
>
> I don't want to offend the experts, and please put me right (gently, if
> possible) if I'm missing something here, but should we really be
> encouraging people to think of this as an event that happens at a
> definitely predictable time in a predictable part of the world? It gives
> me no pleasure at all to be the only one among my friends and relatives
> who saw last year's outburst because I was the only one who got up the
> night before the media said it would happen.
>
> Keep watching the skies!
>
> David Cross
>
>
>
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