re: Leonids, a question

From: Amara Graps (
Date: Tue Nov 20 2001 - 06:05:15 MST

Previously I said:

Amara Graps:
>Andrew Clough:
>This brings me to something I found a little
>>puzzling. Near the beginning of the shower, the meteors seemed to be
>>brighter than the ones that came later.

>I think it's simple geometry. The trajectories of the earlier meteors
>intersected the Earth face-on (say 70 km/sec) than the later ones
>(grazing). Picture in your mind how the Earth is rotatng as it
>intersects the trail(s).

BZZZT. I was wrong. Es tut mir leid. An explanation of 'geometry'
doesn't fly here because Earth's relative rotation of 500 METERS/sec
compared to the Leonids' 70 km/sec, is probably not even detectable.

A more likely explanation is particle size. The larger particles will
be brighter when they hit our atmosphere, and the three dust trails
for this shower (associated with the 1767, 1699, and 1866 perihelion
passages of comet Temple-Tuttle) are 'clumpy', with a steep size

I think that the explanation for why the particles were seen brighter
early, is that Earth was intersecting a denser part of the comet dust
trail(s) near the beginning of the shower, as seen from your
location. (Different locations on the Earth had a favorable viewing
geometry for a particular dust trail.)


P.S. One part of the definition of a meteor stream, like the Leonids,
is that they are all moving at the same velocity, and the Leonids is
no exception. Basically, all of the particles for this meteor stream
are moving at about 70 km/sec.


************************************************************************ Amara Graps, PhD | Max-Planck-Institut fuer Kernphysik Heidelberg Cosmic Dust Group | Saupfercheckweg 1 +49-6221-516-543 | 69117 Heidelberg, GERMANY * ************************************************************************ "Never fight an inanimate object." - P. J. O'Rourke

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