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Re: (meteorobs) Non-Asherian models bite the dust ?!

In a message dated 11/17/00 1:37:12 PM Eastern Standard Time, 
dfischer@astro.uni-bonndot de writes:

<< And so, before even the main peak of the Leonids of 2000 has arrived, can 
we
 not say that all the alternative models are now basically gone for good? >>

    Well, Dan . . . I would have to say that at least one of the "alternative 
(non-Asherian) models" did quite well with the Y2K Leonids.  That of the team 
of Esko Lyytinen (Finland) and Tom Van Flandern (USA) suggested a ZHR of 215 
at 07:50 UT on November 17, based on interaction with outer portions of 
debris shed at the 1932 perihelion of 55P/Tempel-Tuttle.  According to the 
IMO's Marc Gyssens, a possible peak at 8:10 UT (+/- 10 min.) on November 17 
is cited, producing a ZHR of 150 (+/- 20).  

    As for the second night of Leonid activity, Lyytinen and Van Flandern 
suggested a ZHR of 700 at 3:40 UT on November 18, based on interaction with 
debris shed in 1733.  A disclaimer was attached to this particular 
prediction, however, indicating that it would be strongly effected by what 
the above authors called the "A2 effect" 
(" . . . this shower could reach storm levels, or could no-show.  Observers 
are cautioned to temper their expectations accordingly").  

    Actually, the peak apparently came near 3:45 UT with a ZHR of ~300.  A 
third Leonid peak was projected to occur at 7:50 UT on November 18, based on 
interaction with debris shed in 1866, again with a ZHR of 700.  

    Interestingly, Lyytinen and Van Flandern commented that while the 
projected ZHR with this third peak matched their projection for the second 
peak, it comes 
". . . with considerably less uncertainty."  The end result of this third 
outburst of Leonid activity points toward a peak near 7:10 UT with a ZHR of 
~420.  Of course, as Gyssens has already pointed out, the wide scatter of all 
observations, plus the bright waning Moon were significant/disturbing factors 
which were not easy to account for.  

    Nonetheless, I certainly would not automatically dismiss all the 
"non-Asherian models" and would, in fact, judge the Lyytinen and Van Flandern 
predictions for 2000 as being the best overall . . . at least in terms of 
forecasting the probable intensities of each projected peak of activity.

    However . . . we (the meteor observing community) owe ALL the forecasters 
who suggested significant Leonid activity for the morning of November 18 a 
debt of gratitude.  Just a couple of years ago, it was generally accepted 
that the greatest Leonid activity in the year 2000 would likely only come 
around the time of the Earth's closest passage to the descending node of 
55P/Tempel-Tuttle (8:00 UT on November 17).  The predictions of the teams of 
Asher and McNaught and Lyytinen and Van Flandern for possible noteworthy 
activity some 20 to 24 hours AFTER the nodal crossing allowed observers 
across Europe and western Asia, as well as North America to be on high alert. 

    There were far fewer observations and reports made on the Leonids for the 
night of November 18-19, as most observers had likely determined that the 
heaviest activity had passed.  Yet, without the rigorous computations of the 
above calculators, it might just as well had been assumed by most that the 
night of November 17-18 would also not offer anything out of the ordinary.  
Indeed, without these computations, many would have concentrated solely on 
November 16-17 and likely would have completely missed out on the heavy 
activity of November 17-18! 

-- joe rao
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