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Re: (meteorobs) Is It Possible to Detect the Composition of a Meteor By It's Spe
Tony Wrote:
>I read some years ago in Sky and Telescope that researchers were
>recording the spectra of meteors as they fell to earth. Is it
>possible to detect the composition of a meteor in this way?
>
>
> Tony Lea
To date, spectroscopy is the only way to study the composition of
meteors that burn up in the atmosphere. Information about the upper
atmosphere is also obtained. The spectrographs are very simple. You simply
ad an objective prism or transmission diffraction grating infront of a
conventional camera lens. No slit is required, as the meteor trail is
narrow and preforms this function. Transmission gratings are prefered over
prisms as the dispersion is linear or nearly so. To get the best spectrum
with a grating the meteors flight path must be parallel to the grating
grooves. If it is across the grooves no spectrum will be obtained. Adding
a dispersive element such as a prism or grating reduces the sensitivity or
speed of the camera system by about 2 or 3 magnitudes. Meteors must be
brighter than 0 to -1 magnitude to record the spectrum. The first spectrum
was secured by chance in 1897 during a routine stellar spectra patrol
program. If you want to try this, Learning Technologies Inc. sells an
inexpensive replica holographic grating that can be fitted to a normal
camera. Don't expect quick results however as only -3 magnitude or brighter
meteors will register a spectrum with such a system. Fainter magnitudes can
be reached using LLLTV and intensified video techniques but the spectra
arn't as good as photographic methods. This is the most efficient way to
obtain spectra of fainter meteors, however. The common lines found in
meteor spectra are, Na1, Mg1, Mg11, Fel, Fe11, Cal, Ca11, Si11, 01, Cr1, N2 etc.
I hope this answers your questions. Cheers: Ed
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Edward Majden epmajden@mars.ark.com
1491 Burgess Road Meteor Spectroscopy
Courtenay, B.C. AMS Affiliate
CANADA V9N-5R8 MIAC Associate
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