Re: [APML] Sky fog

[Aplanatic@aol.com]

Rick,

> I have seen some papers that claim for really dark sites (the big
>  observatories, Hawaii, etc), values ranging from 21.3 to 21.9 V mag/square
>  arc-sec, with the variation due to the 11 year solar cycle.

I don't think we should assume that the ST-4 or STV can measure the precise 
value of sky background without individual calibration.  It's encouraging 
that I'm measuring values that are close to what I expect.  At the moment I'm 
using it more as a relative measure of sky background than as an absolute 
measurement, but I would like to calibrate it in the future.
  
>  What I haven't seen is published figures for brightness of the various
>  nebulas or galaxies that one might be trying to shoot.
>  
>  Michael Covingtons's "Astrophotography for the Amateur" has some values in
>  Appendix A.  He has bright nebula as 16.5, faint nebula as 21, and the 
outer
>  regions of galaxies as 21.  But I am looking for other sources to verify
>  those numbers.

I used the POSS plates to find the brightness of several dim nebulae.  As I 
recall (and I don't have my notes handy) the region around the "nose" of the 
Witch-head Nebula has a brightness of 21 magnitudes/arcsec^2 in blue and 21.5 
in red light.  In red light the background brightness on Palomar was 21.1.  I 
did the photometry by finding and plotting a stellar cal sequence; not too 
difficult, just time consuming and subject to some error due to the nonlinear 
behavior of film.  I suspect that many amateur CCD images of nebula could be 
used to find the surface brightness, as long as the raw, unprocessed image 
was used.  The same technique of making a stellar cal sequence would suffice, 
and the results should be quite accurate.  You certainly could do this with 
your STV.

Dave Rowe

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