(meteorobs) The value of visual meteor observations. -Siddartha
Ed Majden
epmajden at shaw.ca
Mon Jul 30 02:08:07 EDT 2007
Wayne:
Back in the late 1960's and early 1970's Dr. Gale A. Harvey NASA/LRC
used some large aperture 15-cm f/1.3 slitless spectrographs to record
meteor spectra. These cameras used ASA ~8000 films which would fog
after a short 2 second exposure. They developed a photo-electric
meteor detection shutter system that would only take an exposure when a
meteor entered the field. This was an effort to obtain spectra of
meteors in the +1 to -3 magnitude range. Today, image intensifiers are
used to obtain even fainter meteor spectra. These systems each have
their own problems. Image intensifiers have poor blue end sensitivity
and are small in aperture so high dispersion meteor spectra is not
practical as you will only capture a portion of the spectrum. As an
experiment I'm going to try and use a Canon D20 DSLR which has had its
IR-blocking filter removed to obtain spectra. This is also a small
format, so only part of a spectrum will be recorded. Ideally one
should use large format film 4X5 or 8X10 to capture a complete high
dispersion spectrum of rather bright meteors. Too bad they don't make
inexpensive CCD detectors of this size to eliminate film use
altogether. With Kodak getting out of the film business it is becoming
difficult to obtain good films for spectroscopy. I normally use Kodak
Tri-X pan films for this.
Incidentally I don't do the spectral analysis myself but have
professionals do this for me. This requires expensive equipment and
also expertise in spectral analysis. One has to use judgment in some
cases to identify some features as they often overlap which makes
things difficult.
I'm pretty sure radio detection will not work for this purpose or
professional spectroscopist would have investigated such methods.
Photoelectric systems such as the type used by Gale A. Harvey do
however work. I tried to find one of these cameras on the surplus
market but have not had any success finding one.
Ed Majden
Courtenay, B.C. CANADA
On 29-Jul-07, at 9:58 PM, stange34 at sbcglobal.net wrote:
> The real value is determining your own direction of "special interest"
> while in support of those before you.
>
> One of the more interesting aspects of meteor observations is Ed
> Majdens spectral analysis.
>
> If you can determine by radio detection amplitudes or other RF
> characterization, what meteors will produce good spectral spreads on
> film....you could trigger a camera with that signal possibly. This
> could save costly unproductive film exposures of general meteor
> spectral photos. That is one such specialized use or research
> direction possible, and it could also lead you into a new areas of
> research later.
>
> Application of Radio or Visual Astronomy is only limited by curiosity
> & weight of pocketbook.
>
> YCSentinel
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