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Re: (meteorobs) Rob McNaught
Mr. Lunsford:
Here! Here! And Ditto! That was such a wonderful "Thank you" you wrote to
the 'experts'. I only wish I could have said it myself. I'm sure all of us
feel exactly as you do. I just want to through out my "Thank you" to you
for such fine wording.
Sincerely,
Starr Hernandez
-----Original Message-----
From: Robert Lunsford <lunro.imo.usa@prodigy.com>
To: meteorobs@jovian.com <meteorobs@jovian.com>
Date: Wednesday, June 23, 1999 12:21 PM
Subject: (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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