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Re: (meteorobs) Re: Average Orionid Magnitude
Well the clouds continue, so I'm heading onto a REAL theoretical limb now! :)
All these relative mean magnitudes seem near the high end of the range for
the "predicted" r-factor of 2.9 for the ORIs in the IMO Calendar, don't they?
(For newer folks, "r=2.9" means that on average, there will be 2.9 times as
many Orionids of magnitude 3 as there are of magnitude 2 - and also 2.9 times
as many mag 2 as mag 1, etc. This implies that Orionid meteors should have a
fairly faint mean magnitude, pretty close to the mean magnitude of sporadic
meteors which the observer sees that night.)
Now this also brings up a question, regarding geocentric velocity versus
meteor size: meteor magnitude is related to meteor kinetic energy, which
varies linearly with mass, but by the SQUARE of velocity. So would this
then imply that SPEEDY showers like the ORIs (v=66 km/s) actually have
an even BROADER mass distribution than their r of 2.9 implies? But then
again, magnitude is a logarithmic scale, so perhaps brightness will vary
linearly with speed but with the square root of mass? Hm... flux, energy,
magnitude, intensity... ?? :)
As for Orionids getting fainter after we pass the stream, Bob, I wonder if
orbital geometry actually implies this or the opposite?? I don't have a good
picture of Comet Halley's orbit in my head (never have), so forgive this
if it's a dumb question: but are we currently passing through the space-
ward side of the Orionids' "particle arc", or the sun-ward side?
(Again for the newer folks, the lighter/fainter particles in a meteoroid
stream spiral inward towards the sun faster over time than heavier ones.
The reasons for this are complex, but basically this means the faintest
part of the stream will usually be found to sun-ward, not space-ward.)
And now this brings up ANOTHER theoretical question: since light particles
in a stream generally shift into closer/lower-e orbits than heavy ones over
time, wouldn't this imply that exact geocentric velocity (and so apparent
brightness!) could actually decrease with particle size and mass??
Lordy, lordy - here's hoping for clear skies! ;>
Lew
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