Re: [APML] Measuring Sky Background With an ST-4

[Aplanatic@aol.com]

Hello Jim, Chuck and Geoff.

Geoff found the link (thanks), see below.

Chuck writes:

>Yes I remember it but I don't remember the procedure. It's in the 
>archives somewhere but I know things can sometimes be hard to find. 
>Dave Rowe was the author but I remember him stating at some later date 
>that he didn't think it was as good of a method as he originally 
>thought. Where is Dave these days?

The method works fine, I think, and I still use it from time to time to 
evaluate the darkness of a site.  As long as the same camera is used to make the 
evaluation, relative results can be compared to each other with reasonable 
accuracy.

The problem occurs when different cameras are used, or absolute accuracy is 
desired.  Over the years I've had the opportunity to measure a few ST-4's 
side-by-side with my own and have found that they differ by as much as 0.75 
magnitude.  Unfortunately, this limits the usefulness of the test to "pretty rough," 
unless a calibration is performed with each individual camera.

I made such a calibration with my own ST-4 under several different sky 
conditions, at several different locations.  This allowed me to calibrate the ST-4 
to within about 0.25 magnitudes, which I consider to be quite good for such a 
simple method.  To make the calibration, the local sky background must be 
measured by stellar photometry, a science that is both interesting and involved in 
its own right.

Dave Rowe

> Jim writes:
>  > Could not find this in the archives so I thought I would see if some of 
> the
>  > long time members remember this.  A thread was done some time ago 
> regarding
>  > measuring sky background with an ST-4.  Does anyone remember this and 
does
>  > the information still exist somewhere?
>  
>   Hey Jim...
>  
>       Try this link: 
>           http://astro.umsystem.edu/apml/ARCHIVES/JAN01/msg01405.html
>  
>   Best...
>  
>  --
>   Geoff Powers
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