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Re: (meteorobs) Fw: continuum emission in meteor spectra
>I am surprised at Jiri's surprise. Would we not expect to see at least some
>thermal continuum in the visible radiation from a hot meteor, even though it
>is surrounded by excited gaseous atoms and ions? Maybe I don't fully
>understand what a video spectrum is.
Paul, I think to understand Jiri's surprise, it might be useful to get some
perspective on meteors and meteoroids. In particular, keep in mind both the
distances between observer and particle, and the particle sizes involved: a
fireball of magnitude -3 might result from a particle as small as a few cm.,
again depending on velocity and some other factors. That tiny particle will
generally be observed from a distance of at least 50 km, but more likely on
the order of 100-300 km, and perhaps as much as 1000 km from the observer.
The amount of thermal radiation required to register at that distance, with
that small an emitter is (I would guess) pretty staggering, especially if we
consider the significant ablation and fragmenting that the particle probably
undergoes in flight. Speaking of which, folks, is it possible the continuum
component in meteor spectra could be partly the result of thermal emission
from the surrounding column of atmosphere?
BTW, from Ed's excellent site and other info on the Web, it seems a video
spectrum is nothing more than a spectrum captured on video rather than film,
so allowing for the use of an image intensifier between the grating and (I
ASSUME) the video camera. Is that right, Ed?
Lew
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