Re: [APML] Astrophotography 2004 - Price Shock Horror

["Richard Crisp" <rdcrisp@earthlink.net>]

----- Original Message ----- 
From: "Stuart Heggie" <stuart.j.heggie@sympatico.ca>

> That is so cool. Just different from film. When Richard Crisp posts one of
his exotic line filter
> shots of an obscure galaxy I just marvel but I don't feel lessened by it
because I've got an old

No problem making the comment Stuart, but for the record, I use the emission
line filters on *nebulae* usually. Galaxies, except for the close ones with
lots of HII action, aren't very good targets for emission line imaging
except:

Turns out that if you are about 450MLY away that a Hydrogen Alpha line will
redshift to about the same wavelength as [SII] at rest: the 656.3nm Ha line
becomes about 674nm which means in theory you could look for Ha activity in
a 450MLY away galaxy (usually seen in spirals) using an [SII] filter. For
continuum subtraction, you could use a 10nm wide Ha filter with a 3nm wide
[SII] filter because nothing seems to shift into the slot occupied by Ha.

Nits, twits, and details. Sorry to bore you all....

rdc


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