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Re: (meteorobs) Leonid "aerolites" of 1833, drawn in 1864



In answer to the below question:

>>3) With all the debris falling during the 1833 Leonid storm perhaps some 
>>particles hit each other and ricocheted off in odd directions.  Did anyone 
>>see that happen during last years Leonids in Jordan or Spain?
>


Here is a quick fermi (back of the napkin) calculation on the flux density
of a "storm" level meteor stream, just to give you an idea of the
inter-particle distances involved.  

Place an observer flat on his back, looking up at the layer of atmosphere
in which meteors occur, at an average altitude of 95 km (59 miles).  Let's
give this observer an average field of view radius of 50 degrees.

The radius of the circle of the disk of atmosphere observed would be:
95 km * tan(50 deg) = 113 km

The area of this disk would be:  40,270 km^2

Now add in a Leonid meteor storm of say 100,000 visual meteors per hour,
coming from a radiant directly overhead (no radiant altitude correction).
The speed of the Leonids is 70.7 km/sec.

Over the course of the hour, the observer would "see" the visual meteors
travelling in a column which is:
(70.7 km / sec)*(3600 sec / 1 hr) = 254,500 km  long.

Thus, the volume of space which the 100,000 particles would exist in has a
volume of:
40,270 km^2  *  254,500 km  = 1.025E10 km^3

The average volume occupied by a single particle would be:
1.025E10 km^3 / 100,000 = 102,500 km^3

This would be a cube having sides 46.80 km in length, for a very crude
average distance between particles of around 47 km (29 miles).  

(note that this is not meant to be accurate, only within an order of
magnitude of the correct value)

Considering that most of the particles would probably measure only up to a
few centimeters in diameter,  The chances of colliding with each other or
with a satellite in orbit is quite small indeed (remember that we are
discussing visible meteors only -- the non-visible small stuff is more
numerous, and therefore more closely spaced).

**BUT** the most important thing to remember in discussing a meteor stream
is that the particles are travelling in PARELLEL  paths -- like cars all
travelling in the same direction on the freeway.  As long as everyone is
going the same speed and have no relative lateral motion between them (no
one is changing lanes), then they aren't going to collide with each other
at all -- even if they are relatively close to each other.  

Thus, the chances of witnessing an in-flight collision between two entering
meteoroids from the same stream are virtually insignificant.  

While collisions between meteoroid stream particles do occur, this is a
long-term effect, and is often neglected in meteoroid stream modelling (as
far as I know - Rob?).  There are several other factors which play a larger
role in the stream evolution.

Best regards,

     Jim



------------------------------------------------------------------------
James Richardson
Department of Physics (undergraduate student)
Florida State University (FSU)
315 Keen Building
Tallahassee, FL  32306-4350

home email:  richardson@digitalexp.com   
home phone:  (850) 219-9159
school email:  jrich@csit.fsudot edu
school phone:  (850) 644-5559

Operations Manager 
American Meteor Society (AMS)
http://www.amsmeteors.org
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