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Re: (meteorobs) P/2000 G1 & Vgeo



----- Original Message -----
From: "Lew Gramer" <dedalus@latrade.com>
To: "Meteor Observing Mailing List" <meteorobs@jovian.com>
Sent: Monday, June 05, 2000 2:13 PM
Subject: Re: (meteorobs) P/2000 G1 & Vgeo


> I know I'm talking based purely on hearsay, but the conventional
> wisdom I've always understood is that meteor luminosity, and therefore
> magnitude, is much more significantly dependent on Vg (recall a recent
> thread where THAT was discussed), than on any property inherent in the
> meteoroid body itself. (Keep in mind where all the energy input for the
> meteor phenomenon is coming from: KE = 1/2 m v^2.)
>
> This is because (so I've always understood), the bulk of visible light
> from the "meteor" phenomenon is actually a result of atmospheric ioniz-
> ation caused by the direct conversion of Kinetic Energy into radiation.
> (I'm not sure how much of the radiation itself is in visible light, nor
> if it's truly negligible or just a lesser partner in meteor brightness.)
>
> Thus if two meteoroids strike the atmosphere, one at 11 km/s while the
> other is going 72 km/s (the minimum and maximum for solar-system bodies),
> the brightness difference between the two should be very predictable, ir-
> regardless whether one's iron and the other cometary dust-bunny, one flat
> and the other conical, one 20 cm across and the other 5 cm across, etc.
>
> That being said, I also recall something which might seem to contradict
> this conventional wisdom somewhat: namely, that "terminal bursts" often
> seen at the end of a fireball track are the result of the fragmentation
> of the meteoroid - suddenly creating much more SURFACE AREA, and there-
> fore markedly increasing the efficiency of KE-radiation conversion. So
> it must be the case that meteoroid shape (and also composite shape and
> binding) plays more of a role than the simple 1/2mv^2 picture indicates.
>
> However, that said, it's hard to see how the thermal conductivity of the
> meteoroid body would much affect the all-important rate of conversion of
> kinetic E to radiation: Am I (and my conventional wisdom) way off here?

> Lew Gramer

It seems to me that meteor luminosity has two sources: the incandescent
surface of the meteor itself and the ionized air surrounding it. All
incandescent sources emit a continuous spectrum, all ionized gas sources
emit a line spectrum (specific wavelengths that depend on the type of atoms,
in this case nitrogen and oxygen).

As an incandescent source gets hotter, its luminosity increases dramatically
and its peak wavelength shifts toward the blue. As the ionized gas gets
hotter, more atoms emit (greater luminosity) but the emitted light doesn't
change wavelength.

POJ


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