(meteorobs) Meteoroid Streams and the Moon

[Gural, Peter S.]

All;
 
Regarding the question put forth by Chris et.al. - does the Moon occasionally
shield places on Earth from a stream? I actually published a paper recently on this prospect for the Meteoroids 2007 conference entitled "Lunar Gravitational Focusing of Meteoroid Streams and Sporadic Sources" in "Advances in Meteoroid and Meteor Science" pp183-189. For stream velocities of 34km/sec or less there is a focus point (and associated flux enhancement) at the Earth-Moon distance if the Moon is close to the radiant position. Higher than 34 km/sec and the flux enhancmeent point moves beyond the Earth-Moon range, and an eclipse occurs so to speak. The Geminids are 35 km/sec so are on the hairy edge. The region of focus is very, very narrow - just a few thousand km wide so the alignment must be nearly perfect for any flux enhancement to occur. The journal article concerned itself with GEO belt encounters but extrapolating to the Earth radius, the Moon's alignment with the radiant position would need to be within one degree to see any effect. This would appear as Geminid meteors moving along non-Geminid radiant directions and a reduction in flux from normal rates. I would have to work out the diameter of the eclipse region. Just how close is the radiant to the Moon in this year's encounter ? If more than a degree then the focusing/eclipse effect will be mostly non-existant.

Cheers... Pete Gural