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(meteorobs) Re: Orionids
Lew Gramer wrote:
>
> 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.)
>
Perhaps some observers were overestimating the magnitudes of their
Orionids
or overestimating their limiting magnitude?
> 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?
>
While passing through the Orionids we encounter the space ward side
first
so one would think that the Orionids would get progressively fainter as
the shower progresses.
> (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??
>
This is a possibility as the geocentric velocities for particles within
any shower are not a perfect match.
Bob Lunsford
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