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Re: Lyrid Meteor Shower Reminder

In a message dated 98-04-17 17:49:17 EDT, you write:

terrafirma>>My problem is with the major premise, that
 shower meteors move in parallel orbits.  Are you saying that  shower
 meteors always move in concentric or parallel eliptical orbits?<<

As long as they are members of a meteor stream, they move in somewhat parallel
orbits. The paths of the stream can become quite wide. Some showers such as
the Taurids are very wide...encountering other planets such as Venus and
Mercury as well as the earth. Once they leave, they are no longer part of that
stream and become a sporadic. 

 terrafirma>> It
 would seem that the dynamics of parallel orbiting would only come into
 play the closer to the observer's planet they are?  Surely they do not
 travel parallel to each other until they are locked into an orbit around
 a body. <<

yes they do travel pretty much parallel. Meteors from a meteor shower are
traveling too fast to get locked into an orbit around a planet. Here on earth,
as a meteor approaches it, it feels the earths gravitational tug at the last
moment. This causes the radiant to appear to have moved just a little towards
the Zenith. This is called the Zenithal Attraction. Actually all meteors
whether they are shower members or not experiences a little Zenithal
Attraction. The faster a meteor is, the less this zenithal attraction will be.
For the very fast meteors, very little change in position will be noted. But
the very slow meteors can have the radiant appear to have shifted towards the
zenith by several degrees. 

  terrafirma>>  I'm just trying to get a picture
 of how meteor showers start.  I'm pretty sure they don't start out
 parallel, so it must be the gravitional pull of a body they approach.<<

As a shower member, they start out loosely parallel. The gravitational pull
that makes it appear non parallel to the remainder of the stream in orbit
happens the last few seconds in a meteors life before encountering the earth. 

 terrafirma>>But then the word orbit seems misleading.  If meteors are
orbiting how
 do they ever 'move on' so to speak and not become a minor, OK,
 miniscule,  satellite?  <<

A meteor doesn't orbit the earth...it encounters it. It's velocity is much too
fast for the earth to capture it. 

terrafirma>>And wouldn't this mean that for a meteor to land
 on Earth each meteorite is the result of a bump out of orbit?  What?<<

It's the result of a lot of lucky circumstances. Such as the meteorite has to
be made up of stronger material than what youj will find in a meteor shower.
The velocity should be sufficiently slow so it won't burn up or explode.
usually this means the encounter is best to occur in the late afternoon or
early evenings.
 George Zay
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