(meteorobs) Re: meteor stream motion

talcon wrote:
> When we saw few draconids here in Jordan, I wondered, did the earth crossed
> the dense part of the meteor stream or not?. and this question led me to
> another questions since I have read somewhere that the draconids are
> unpredictable., the question is what are the factors affecting the movement
> ( motion ) of the meteor stream.
> I hope that we can all participate in this question.
The Earth did indeed pass through the outer fringes of the dense portion
of the Giacobinid meteor stream. It must be remembered that we passed
through this area 50 days before the comet therefore the particle
intensity was not as great as it would have been had the comet arrived
first. Another factor is that the Earth is moving at a high rate of
speed and passes through this area in a very short time. It so happens
that the Earth encountered the greatest density just after dark for
those living in Eastern Asia. 
Particle density is also not uniform and this can cause variations in
observed rates from different longitudes. One would think that particle
density is greatest at the center of a meteor stream with diminishing
densities as you move outward. Due to planetary encounters (mainly with
Jupiter) the particles form clumps, filaments, and areas of sparse
populations. The Earth was positioned closest to the core of the orbit
at 21 UT Oct. 8 but the greatest activity occurred 8 hours earlier
meaning the greatest intensity was slightly outside the central area. My
interpretation of this is that we encountered a clump or filament just
outside the central area then at the time of closest approach the Earth
was in an area of sparse concentration therefore little activity was

This is a young stream and it is still evolving. If I were predicting
the next good Giacobinid shower I would once again look for the best
activity to occur some 8 hours before closest approach to the center of
the orbit.

The Leonids are a older stream and easier to predict except for the
particle density we may encounter. We shall see if this true one month
from now.

Well that is my thoughts on this subject and now that everyone is
thoroughly confused I will leave it to the other experts to explain it a
bit more clearly.

Best Wishes!

Bob Lunsford