Light Pollution - Night Sky Brightness Measurement
Light pollution is an increasing problem, no only for astronomers,
see http://www.darksky.org/.
Astronomers prefer a really dark sky where you can see many stars like the milky way
and faint deep sky objects, e.g. galaxies and nebula.
Finding of good observing locations and conditions is facilitated by night sky brightness measurements.
In the German speaking forum
www.astronomicum.de Thomas Walt explains a method to measure the night sky brightness with a DSLR-camera.
Any star with known brightness could be used as reference.
This Excel-file contains the formula for quick calculation.