(meteorobs) Imagining ourselves following a vehicle along a dusty road...

[Nikola Biliškov]

At 11:28 20.02.06, you wrote:
>Hello all, I am a new member of the mailing list, and I have a question
>which has built up in my mind and which I wondered if I might empty into
>your gracious inboxes, with permission.
>
>Its about radiants. Now as I understand it, meteor showers are the
>product of the intersection of our spherical earth with a somewhat
>cylindrical region of comet/asteroid debris. This being the case, how is
>it that meteors appear to radiate from a single point in the sky? I
>would have imagined that they would appear from along a path in the sky
>that is traced out by the length of the debris trail. The only time I
>would expect meteors to come from a single point at any one time would
>be if the path of the comet/asteroid was very similar to that taken by
>the earths orbit, then it would appear like we were following a jet's
>vapour trail through the sky, or a vehicle along a dusty track, which in
>each case would produce a 'radiant' or source of material which was a
>single point.

It's very simple.. just an effect of perspective. You can find it well 
explained in every book about meteor astronomy.
Shortly, it's just like a long railroad: railroad is parallel, but it seems 
to you that it radiates from one point far on the horizon.
Similarly, orbits of the meteors of the same shower will be parallel to 
each other, but they seem to radiate from one point in the sky, just 
because their orbits are parallel.
Nikola