Night sky photometry and spectroscopy performed at the Vienna University Observatory

- We performed night sky brightness photometry and spectroscopy in and around Vienna.
- The level of light pollution in the city ranges from 15 to 19.25 mag arcsec−2.
- In Vienna, the curfew at 11 p.m. and 12 p.m. was detected.
- Fluorescent lamps are responsible for the strongest lines of Vienna's night sky.
- Circalunar rhythm of night sky brightness is extinguished due to light pollution.

We present night sky brightness measurements performed at the Vienna University Observatory and at the Leopold-Figl-Observatorium für Astrophysik, which is located about 35 km to the southwest of Vienna. The measurements have been performed with Sky Quality Meters made by Unihedron. They cover a time span of roughly one year and have been carried out every night, yielding a luminance value every 7 s and thus delivering a large amount of data. In this paper, the level of skyglow in Vienna, which ranges from 15 to 19.25 magSQM arcsec−2 is presented for the very first time in a systematic way. We discuss the influence of different environmental conditions on the night sky brightness and implications for human vision. We show that the circalunar rhythm of night sky brightness is almost extinguished at our observatory due to light pollution.Additionally, we present spectra of the night sky in Vienna, taken with a 0.8 m telescope. The goal of these spectroscopic measurements was to identify the main types of light sources and the spectral lines which cause the skyglow in Vienna. It turned out that fluorescent lamps are responsible for the strongest lines of the night sky above Vienna (e.g. lines at 546 nm and at 611 nm).