I have been making sky brightness measurements using the SBIG STV.

The procedure I used for calibrating the STV can be found at:

http://home.twcny.rr.com/rkellog1/stv_br.htm

Last Saturday (5/19/01), I traveled to Cherry Springs, PA and measured the sky brightness there.

The value I got at 11:30 PM on 5/19/01, pointing toward the zenith, was:

21.2 V mag/square arc sec.

Conditions (at the time of measurement) were generally clear, 48 deg, heavy
dew.

For reference, at our local dark site (Darling Hill, Tully NY), on 4/19/01
at 10:25 PM, I got a value of:

20.6 V mag/square arc sec using the same method and instrument. During a
near full moon on 5/6/01 at 10:53 PM, I got a value of 17.7. The darkest
sites in the world vary from 21.3 to 22 depending on the solar cycle.

Even though I calibrated the STV, I am not sure of the absolute accuracy of
the readings. For relative readings, however, it should be quite good.
Thus, it is clear that it is much darker at Cherry Springs than at my local
site (Duh, why do you think I drive for 4 hours).

Note: This method of measurement does not speak to the ability to see stars,
just how dark the sky is. For example, at this site, had it been completely
overcast, one would not see any stars, but the reading would have been even
lower, as the sky light would have been blocked, and there is little light
pollution to reflect off of the clouds.

Rick Kellogg