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Re: (meteorobs) Fewer fireballs from LEO 2001 (China) than LEO 1998 (USA)?

Hi, Lew,

I observed for the whole night (Teff=6.40) in the city of Beijing on
November 16/17, 1998. Fortunately, I escaped from the serious light
pollution, and my limiting magnitude reached +5.3. There were quantities
of fireballs, indeed.

About one year later, I heard of the new model of dust trails. It
successfully predicted the Leonid activity in 1999, and was able to
explain that in 1998 well. In that model, we knew that we came across a
dust trail which had been out from the parent comet (55P) since 1366.
More revolutions caused more fireballs, since the small particles could
get more time to be blown away from the main dust trail by the press of
solar radiation, leaving only big particles. So, when we happen to travel
through the old dusts, we may see more fireballs.

The population index is a value to measure the mass distribution in a
meteor shower. In a particular shower, all meteors have the same
geocentric velocity, so the mass distribution is just the magnitude
distribution. This distribution usually appears as an exponent function.
If we transform it by logarithm, it will turn linear. And the "slanting
rate" of the line is the population index's "normal logarithm". Every
meteor shower, or even every dust trails of a same shower, has its own
value of the population index. Mathematically, you see, if the number of
the shower meteors hunted is certain, small population index always
corresponds to more fireballs, namely, it corresponds to old dust trails.

So, before you start to observe, you can generally know how many
fireballs you will see during your "Teff"s by the limiting magnitude, the
approximate population index, the approximate ZHR, and the effective time
(Teff). But I'm not sure if the population index can be well estimated by
the number of revolutions.

Of course, the real number of fireballs can be known only by real
observation. ;-)

I didn't calculate (estimate) how many fireballs we would see at Xinglong
on November 18/19 of this year. (I was sleeping during the daytime, and
didn't wake up until 22:30 LT.) But I had the same feeling with you, that
the number of fireballs is not more than that in 1998. The dust trails
(meteors) on the peak night which we saw at Xinglong, is much younger
than that in 1998, so the population index is larger. I think this is
just the most important reason why we saw fewer fireballs.


All best wishes and Clear skies!
Huan Meng  <meteorobs_menhu@hotmail.com>


----- Original Message -----
From: Lew Gramer <dedalus@alum.mitdot edu>
To: Meteor Observing Mailing List <meteorobs@atmob.org>
Sent: Friday, December 07, 2001 12:54 PM
Subject: (meteorobs) Fewer fireballs from LEO 2001 (China) than LEO 1998
(USA)?


>
> An interesting note: I'm (finally) preparing my full IMO
> report from the Leonid storm night in China, and noticed
> that I had 74 fireballs total during 6.77 hours of Teff.
> (For newcomers, 'Teff' is the actual time you spend with
> eyes on the sky, exluding any breaks OR recording time.)
>
> That is approximately 11 fireballs per hour on average.
>
> This was wonderful! However, during the "fireball shower"
> of the Leonids on 16/17 Nov 1998, I logged *36* fireballs
> in just *ONE* hour of Teff... So it would seem (based on
> an admittedly different sample size of course), that '98
> was indeed a stronger year for fireballs than 2001??
>
> This is based on a sole observer's visual data: So does
> this comparison between these two years pan out the same
> way in other people's video, photographic or visual data?
>
> I'm particularly interested in hearing from anyone who
> had clear skies and observed the whole time the Leonid
> radiant was up, during BOTH of these amazing nights...
>
> Just curious,
> Lew Gramer
>
>





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