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Re: (meteorobs) Normal lens
George Zay wrote:
>Last year I noticed an ad in the Starry Messenger where someone was trying to
>sell a 1 inch square grating..dot can't remember the cost now. but at the time I
>thought it was too small of a piece to use.
Be careful when buying a grating. You want a transmission grating, not a
reflection grating. The ruled area of the grating must be large enough to
accept the entire cone of light entering the lens. Remember, a meteor
spectrograph is slitless, the thin or narrow trail of the meteor performs
this function. I think I saw that ad in the Starry Messenger also. Wasn't
the grating a reflection type?
You wrote:
>
>Do you have any problems with getting too many interferring star spectra on
>the negative after about 20 or so minutes?
Star spectra do indeed record on the film. With a grating these spectra are
quite faint unless the star producing the spectra is very bright. Like Vega
for example. Stars less than magnitude two are quite faint and therfore
arn't a problem. The meteor spectrum may overlap but it can usually be
measured anyway. There is no way you can get around this other than
orienting the grating to produce a minimum star spectrum. This may not be
possible as one lines up his spectrograph to produce the best spectrum of
the meteor. The expected flight path is of course from the radiant of the
shower that you are working. You should get at least one good spectrum of
Vega or another bright AO star, as this spectrum is used for calibration
purposes. It's also a good way to check your spectrographs focus be
examining the Balmer series of hydrogen lines which a very prominent in
AO-star spectra.
Ed
>George Zay
>
-----------------------------------------------------------------
Edward Majden epmajden@mars.ark.com
1491 Burgess Road Meteor Spectroscopy
Courtenay, B.C. CCD's - P.E.P.
CANADA V9N-5R8 Amateur Astronomy