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(meteorobs) Rob McNaught

Rob and All,

I want to publicly thank you for taking the time to post such wonderful
and informative messages. While reading your reply to NASA News Articles
I was saying to myself how lucky we all are to be able to read such
informative material and to have such knowledgeable scientists such as
yourself share their knowledge with the wide variety of people
subscribed to this list. I would imagine that Rob has a very busy
schedule and for him to take time to write such long and detailed
messages is a blessing for all of us.

Rob, many thanks to you and to the other professionals who take the time
from their busy lives to share their knowledge with us. It certainly
makes the off topic threads and fish stories a bit easier to take!

Sincerely,

Robert Lunsford



Rob McNaught wrote:
> 

> I enjoyed the piece on the upcoming Leonids.  It fueled by enthusiasm
> which has hardly dimmed since the amazing show last year.  There are a
> couple of points that I felt might be worthy of note.
> 
> 1) 5 minute uncertainty
> The predictions by David Asher and I have been checked
> by comparison with all reasonably well observed outburst maximum times and
> ZHRs (1866, 1867, 1869, 1966 and 1969).  In every case, using ONLY the
> comet orbit, the standard model of dust ejection and the rigorous
> application of gravitational perturbations, we predict a time which fits
> all the above outbursts with residuals of around 5 minutes or better. It
> is thus reasonable to expect this sort of accuracy in our future
> predictions, as we didn't use any historic Leonid data in creating
> the predictions.  All the ZHRs derived by Peter Brown for these
> outbursts in his re-analysis of historic Leonid showers, fit our dust
> trail density model very closely.
> 
> 2) Confirmation of Soviet research.
> The times we calculate confirm work done by Kondrat'eva and Reznikov in
> 1985, that has been basically ignored.  Their more recent work in 1997
> with Murav'eva is again confirmed by our work.  Reading the Transactions
> of the IAU, Commission 22 reports in 1985, 1988 and 1991, there are more
> references to Leonid work by these astronomers from Kazan than from all
> other groups put together.  Some of these studies are in English and can
> easily be obtained through the library services:
>   E.D. Kondrat'eva and E.A. Reznikov, "Comet Tempel-Tuttle and the Leonid
>       Meteor Swarm",  Solar System Research, Vol 19 pp96-100, (1985)
>   E.D. Kondrat'eva, I.N. Murav'eva and E.A. Reznikov, "On the Forthcoming
>       Return of the Leonid Meteoric Swarm", Solar System Research, Vol 31,
>       pp 546-549, (1997)
> 
> David Asher and I were ourselves unaware of the research done at Kazan
> when we started looking at the rigorous, continuous, evolution of dust
> from  ejection from the comet to passage close to the Earth.  It seemed to
> us that the IRAS dust trails demonstrated that the main component of
> recent comet activity would be a dust trail, and calculation of each young
> dust trail's position in any given year would indicate the location of the
> densest regions within the Leonid shower.  Each time the comet returns, a
> new dust trail is created, but differential perturbations soon separate
> these out from each other the further one goes from the comet.
> 
> Most of the visual meteors are caused by meteoroids of a size that tends
> to lag the comet by about 6 months per orbit due to the effect of solar
> radiation pressure, so passage through the appropriate part of a dust
> trail after the comet has passed perihelion will give the highest rates.
> Dust trails become depleted with time, but the overall structure
> stretches, rather than dissipates in three dimensions.  However, the
> portions of the dust trails that are in the same resonance with Jupiter as
> the comet, do not become depleted with time.
> 
> The ability to predict the time of a Leonid maximum to within several
> minutes accuracy has a very specific consequence for the satellite threat.
> At the predicted time of maximum, should a suitable orbital geometry
> exist, the satellite can be located within the Leonid shadow of the
> Earth, or at the side of the orbit furthest from the center of the dust
> trail (or a combination of the two).  This would minimise any threat to
> that satellite.
> 
> Details of this work, which includes times and rates of maxima for
> approaches to dust trails over the next several years and at the next
> return of 55P/Tempel-Tuttle, and details of the threat to satellites,
> appears in:
> 
> R.H. McNaught and D.J. Asher "Leonid Dust Trails and Meteor Storms", WGN,
>     the Journal of the IMO, Vol 27, pp85-102, (1999).
> 
> and the basis of the work, in more technical form, in
> 
> D.J. Asher "The Leonid meteor storms of 1833 and 1966", MNRAS, 1999 in
>     press.
> 
> We have a number of other articles, in press, submitted and in
> preparation.
> 
> Surprising as it may seem, we are not saying that the work by other
> researchers who look at the dynamics of ejected dust have made errors in
> their studies.  The problem is one of temporal resolution.  We looked ONLY
> at the dust that was emitted at each perihelion and crossed its node at
> the time the Earth was close to the node.  Dust that has a different
> orbital period will arrive at its node before or after this time and
> could have no bearing on Leonid meteors in the Earth's atmosphere.  If we
> had looked at the orbits that crossed the node over a spread of time, the
> narrow dust trails would have become computationally diluted.  It would be
> like trying to assess the distribution of quartz in an area, without
> knowing the specific location each specimen was collected from.  You know
> from the collected specimens that quartz must be common in the general
> area, but not that there are several narrow veins crossing it.
> 
> Cheers, Rob
> 
> Robert H. McNaught
> rmn@aaocbn.aaodot gov.au
> 
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