JA,
Obtaining a better "estimate" may help...but I'm trying to understand how to apply the result to assessing the noise (across the visible spectrum) from the night sky.
I cannot find a definitive reference for the formula currently used. It would be nice to be able to confirm it is correct.
http://astrosurf.com/buil/us/spectro8/spaude02_us.htm
See the N(sky) entries.......