(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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