(meteorobs) Question about radiant drift

David Entwistle david at d-entwistle.fsnet.co.uk
Tue Jun 8 05:02:40 EDT 2004

In message <ca18ok+v2c5 at eGroups.com>, bgarcing <bgarcing at yahoo.com>
>What are the factors that affect these? And how to compute these 
>factors using elements unique to each stream? Thanks and clear skies.

Hello Bamm,

I don't have an answer for you, but I think I know what needs to
considered to arrive at an answer. My mathematics is a bit rusty, but
with a bit of help we should be able to work through it.

The position of the meteor shower radiant is dependant on the relative
velocity between the Earth and the shower meteoroids. This in turn is
determined by calculating the vector sum of the Earth's heliocentric
velocity (both speed and direction) and the meteoroids heliocentric
velocity (both speed and direction). there may be small correction
required for the Earth's attraction, but we'll ignore that.

McKinley [1] puts it as follows:


'The Earth's velocity is directed along the apex of the Earth's way. A
meteor moving with a heliocentric velocity Vh from a radiant located at
an angular distance c from the apex will have  a resultant geocentric
velocity Vg given by

Vg**2 = = Vh**2 + Ve**2 + 2 * Vh * Ve * cos(b)

and the radiant will appear to be shifted to an angular distance c from
the apex where 

sin c = (Vh * sin(b)) / Vg

<end quote>

That explains how to calculate the radiant position from the component
velocities, but we'll need to work backwards, from the radiant to find
the component velocities. Apply the factors causing the drift and then
put them through the above equations again. 

The radiant drift will be caused by changes in either the meteoroid's,
or the Earth's velocity. The meteoroids velocity may vary somewhat, but
I'd expect the variation in the Earth's velocity and particularly
variation in its direction, which will be dominant. It is the direction
of the Earth's way (apex) which will move along the ecliptic by
approximately 1 degree a day. 

[1] Meteor Science and Engineering - D W R McKinley
David Entwistle

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