(meteorobs) Correction re: Mars meteor

Bruce McCurdy bmccurdy at telusplanet.net
Tue Jun 7 12:58:33 EDT 2005


    You learn something new every day. Yesterday I wrote:

>    The wording of the quoted section "If you could trace the meteor back 
> and **below the horizon** " is surely in error and should be disregarded. 
> Reporter probably doesn't understand the concept of the radiant.

    I guess it's me who doesn't understand the concept of radiant. Thanks to 
Brian Skiff who responded to me privately rather than risking embarrassing 
me in this forum, but my view is that the facts are much more important than 
my misinterpretation of them. Brian wrote:
*****
>         In fact the 'Nature' paper indeed says the radiant was below the
horizon by about 10 degrees.  And, no, the odds of it being merely a
sporadic was _not_ evaluated in the paper.  So this is a fairly speculative
result, mainly resting on the intersection the great-circle path with the
radiant, and the event occurring within a few days of the predicted
Martian Cepheids meteor shower (or node intersection).  Also it was moving
fairly slowly, consistent with association with the shower. ... The paper 
says the radiant can be as low as -20 deg and still get grazing meteors. 
The meteor was something like 115 deg from the radiant---I've seen that on 
Perseids when the radiant was up!
*****
    A true Mars grazer! I would guess that the enhanced curvature of the Red 
Planet might make these below-the-horizon angles a little more extreme, but 
obviously I did not think through the fact that since meteors occur in the 
atmosphere, a surface-bound observer is effectively *inside* the sphere and 
thus has a skewed view of the effective horizon.

    Returning to terrestrial meteors, anybody on the list have a good 
account of an identified shower meteor occurring when the radiant was below 
your local horizon? How far below?

    Bruce

 




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