Night Sky Brightness and it's Measurement

The knowledge about the night sky brightness and the methods of measuring night sky brightnes are introduced in this paper. A convenient luminometer developed by authors is also introduced. The main specifications of the luminometer are as follow: accuracy: ±5.4%(corresponding to±0.06mag); resolution: 10^-6cd/m²(corresponding to 27.4mag/□"); weight: 3.5kg.