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Re: (meteorobs) Leonid radiant rise
> Looking back over emails from last November I noted this reference (below)
> to the time of Leonid radiant rise at 111km elevation.
Thanks, Rob, for clarifying the radiant elevation problem.
> It seemed the case last year that Earth grazers were at a great
> height. Their angular velocity was quite low compared to Leonids
> with the radiant higher in the sky. I assume someone can quantify this
> from observational data.
Visual observers tend to give a wrong impression here. If this
result is from video, I'd be surprised. A shower meteor appearing
overhead from a radiant at 0deg elevation has maximum angular
speed. (Because angular speed depends on sin(hR) and sin(distance
from radiant).)
The mistake is that a very loooong meteor must be a very sloooow meteor.
If one sees an Earth-grazer of 120 deg length lasting an impressive
4 seconds -- imagine a 4-sec meteor, which is really lengthy --, it
has an angular speed of 120/4 = 30 deg/sec though and is thus one
of the fastest meteors in the sky.
Leonids could appear slower if higher in the atmosphere. This can
certainly be quantified from video data. I suppose speeds may vary
by ~30% due to varying heights. But this change does not cover the
low speeds sometimes reported by visual observers.
Best wishes,
Rainer
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