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Re: (meteorobs) Two questions about Leonids 2000

> Earth is going threw old meteoroids stream that have escaped from the 
> comet surface several decades or centuries ago. In that case, why 
> doesn't our planet cross them during two perihelion passages of its 
> parent comet? Why did meteor storms occur just in 1833, 1866...?

Sorry, I missed this first question.  Leonid dust trails, in our analysis,
are very narrow, measured in tens of Earth diameters.  Each time the
parent comet goes thru perihelion, a new dust trail is formed.  The comet
thus has numerous dust trails "attached" to it, but due to the different
ages and perturbation histories, these trails separate from each other
the further one goes from the comet.  The densest part (in terms of
experienced ZHR) also lies at different distances from the comet with
older trails having the densest region further back (due to solar
radiation pressure) from the comet but these regions have also become
attenuated in the older trails due to increased stretching of the trail.

All orbits around the Sun are affected by the gravity of other planets.
This means that the body does not follow the exact same ellipse every
time it comes around.  The gas giants have a major effect on the Leonids
and on some returns, the comet and its attached dust trails have been
shifted sufficiently that the Earth doesn't encounter any dust trails.
Even if the Earth goes through the "high density" region of dust trails
shortly behind the comet, it is still never certain that the Earth will
actually intersect close enough to the core of any specific dust trail to
produce high rates.  Several years behind the comet, the individual dust
trails are widely separated, so more often than not, the Earth can
pass between dust trails with no high activity.  The most fortunate
geometry in 2001 and 2002 has the Earth have almost direct hits with
dust trails, a situation that has not occured in the last 200 years.
It is for this reason that high rates can be expected in these years.

Cheers, Rob

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