Measurement of light pollution at the Iranian National Observatory

The problem of light pollution became important mainly since 1960, by growth of urban development and using more artificial lights and lamps at the nighttimes. Optical telescopes share the same range of wavelengths as are used to provide illumination of roadways, buildings and automobiles. The light glow that emanates from man made pollution will scatter off the atmosphere and affects the images taken by the observatory instruments. A method of estimating the night sky brightness produced by a city of known population and distance is useful in site testing of the new observatories, as well as in studying the likely future deterioration of existing sites. Now with planning the Iranian National Observatory that will house a 2-metre telescope and on the way of the site selection project, studying the light pollution is propounded in Iran. Thus, we need a site with the least light pollution, beside other parameters, i.e. seeing, meteorological, geophysical and local parameters. The seeing parameter is being measured in our four preliminary selected sites at Qom, Kashan, Kerman and Birjand since two years ago using an out of focus Differential Image Motion Monitor. These sites are selected among 33 candidate sites by studying the meteorological data obtained from the local synoptic stations and the Meteosat. We measured and used the Walker's law to estimate the Sky brightness for three of these sites