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RE: (meteorobs) What I think I know (and don't know) ...


Considering observed encounters with the old trails 1903/11rev. (with very
small miss distance although relatively small fM=0.04, I recall) and
1868/8rev. (this 1868 encounter identification may not be generally known),
that produced maximum ZHR:s of the order of (only) 500, seem however to
indicate the existense and importance of non gravitational effects
scattering the meteoroids and affecting mainly the ZHR:s of old trail
encounters. Further support to this is given by the observed year 2000 ZHR
profiles (and 2000/8rev. maximum ZHR value).

It is mainly because of this that our prediction modell doesn't give quite
as high rates (as the modell of Robert and David) for the 2001/4 and 9rev.
(etc) encouters, giving about 5000 and 2600, and a (few) hundred for 10 and
11 rev.

A paper on the modeling of the nongravitational effects, and resulting
predictions for this year, was recently submitted to the WGN. According to
Marc Gyssens this "... may already appear in the August issue."

Esko Lyytinen

>
>And 1969 was even more extreme.  Since David and I made the point in early
>1999 that observational evidence coinfirms that dust trails have continuity
>at high density for some years after the comet's passage, there has still
>been much resistance to predictions of storm rates of the order of ZHR
15,000
>in 2001/2.  The fact is that rates this high haven't been seen this far
from
>the comet in the last 200 years *but such favourable geometrical encounters
>with dust trails* has never occured in the last 200 years.  Perhaps folks
>should reread the 1999 article to confirm we made this point clearly then.
>Readers of meteorobs should be aware that I've reitterated it many times
>since then.  And yes, were it not for Gary Kronk, we may not have known
about
>1969.  (later corrected:"Let's try 1869!  Stupid 33.3 year orbit ;-)") 
>This evidence really put the nail in the coffin as far as we were
>concerned.  Again, this is all discussed in the original article.  Marco
>analysed this data also I believe.

>Robert H. McNaught
>rmn@aaocbn.aaodot gov.au

>On Mon, 27 Aug 2001 Skywayinc@aol.com wrote:

>> In a message dated 8/25/01 1:43:20 PM Eastern Daylight Time, 
>> dfischer@astro.uni-bonndot de writes:
>> 
>> << The problem is that there has never been a
>>    situation like in 2001 (or 2002) when the Earth is coming
>>    rather close to certain dust trails, but several years after
>>    the parent comet Tempel-Tuttle came by.  >>
>> 
>>     Actually . . . the trail that is expected to give rise to the meteor 
>> storm over North America (from 1767) has apparently interacted with the
Earth 
>> before.  In 1869, a Leonid display which may have produced a ZHR of 1,000
to 
>> 2,000 was witnessed by a "Dr. C. Meldrum" from the Island of Mauritius in
the 
>> Indian Ocean (it was Gary Kronk who discovered this observation in the 
>> journal Nature).  In November 1869, 55P/Tempel-Tuttle was 3 years and 9 
>> months past perihelion, whereas in November 2001, the comet is 3 years
and 8 
>> months past perihelion.  Thus . . . it appears that Leonid storms are
still 
>> quite possible with the comet well past perihelion.  
>> 
>> -- joe rao  
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