c (Bill Ferris) wrote in message ...
At best, I suspect such a conversion would get an observer in the ballpark,
perhaps to within 0.5 magnitude. Here's a table I'll throw out for
commentary. I'd be interested in hearing how well this reflects the real
life experiences of other observers:

NELM.(+/- 0.5)..===..Sky Brightness (mag./sq. arc sec.)
.......8.0............22.0
.......7.0............21.0
.......6.0............20.0
.......5.0............19.0
.......4.0............18.0

Bill, thank you for the post. I'll add an empirical test of the
relationship using Bartel's ODM program and your proposed table for
magnitude per square arcsecond (MPAS) to my observing list of
things-to-do for the summer season.

Regards - Kurt

P.S. references -

Bartel's version of Clark's ODM program:
http://www.efn.org/~mbartels/aa/visual.html
http://zebu.uoregon.edu/~mbartels/dnld/odm.zip

P.P.S. -

Your proposed table is the simplest to use. Perhaps a direct
relationship equation for MPAS to NELM can be teased out of equations
17 and 18 in Schaefer's 1990 paper (PASP 102:212 at 215), using
simplifying assumptions of observer visual acuity (F_s) = 1.0 and the
extinction coefficient to its mid-point of 0.25 in a range of 0.2 to
0.3? But the math is beyond me.