MEASURING THE NIGHT SKY BRIGHTNESS WITH THE LIGHTMETER

We present a newly developed, low-cost photometer for long-term monitoring of the night sky brightness and light pollution on Earth. The so-called Lightmeter is an as far as possible stand-alone operational, fully weatherproof, and maintenance-free device. It provides a high data sampling rate of up to 1 Hz as well as a superb sensitivity covering the whole brightness range down to the darkest night time conditions. The excellent performance of the Lightmeter allows a continuously monitoring of the night sky brightness and opens a wide range of applications at an observatory site like determining overall sky conditions in real time, cloud detection and estimation of their velocity, measuring relative changes in extinction as well as the detection of long term trends in brightness caused by an increase of artificial illumination. We will present first results of measurements taken at Cerro Armazones, one of the best observing sites in the world and the selected site of the planned European Extremely Large Telescope (E-ELT).