and methods \[sec:methods\]
=============================================

Measurement sites
-----------------

First measurements began in November 2011 at the IfA. Since April 2nd, 2012 the measuring device (label “IFA”) is mounted at its ultimate place and points exactly to the zenith. About the same time (March 21st, 2012) we started measuring the NSB at our remote mountaintop site too. Currently we use three devices in total, two of which are located at LFOA (label “FOA” and “FOA2”). The geographical positions of our sites are given below.

   Location (altitude)         Longitude                 Latitude
  --------------------- ------------------------ ------------------------
       IfA (240m)        16$^{\circ}$ 20’ 03’ E   48$^{\circ}$ 13’ 54” N
       LFOA (880m)       15$^{\circ}$ 55’ 24” E   48$^{\circ}$ 05’ 03” N

  : Geographical coordinates of our measurement sites. The distances of the sites IfA and LFOA from the city center are 3.5km and 35km, respectively.

\[t:sites\]

Photometric measurements
------------------------

### Units used for our photometric measurements

The devices that we use for our NSB measurements yield data in a unit which is very widespread in astronomy, namely magnitudes per square arcsecond (mag/ arcsec$^2$). This unit corresponds to a luminance, but is a logarithmic measure derived from stellar photometry, where larger values correspond to fainter objects. In the same way, larger NSB values 