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Session 13 - Surveys, SETI and Pollution.
Display session, Monday, June 08
We discuss a simple extension of our night sky brightness program to include a layer of polluted air ('smog'). Two possibilities are discussed, a layer with density decreasing exponentially with height above the ground, and a layer of constant density and finite thickness. The ground level density is determined by the visibility. We check our models against observations in Cincinnati and Los Angeles. Either model can be used if the observatory in question is well above the smog layer. Application is made to study the history of the development of light pollution at the Mount Wilson Observatory. The night sky brightness due to Los Angeles was calculated for the years from 1920 to 1990, using census data for the population growth and neglecting changes in lighting technology, but with and without a smog layer, the density of which we assumed to increase from zero in 1920 to appropriate values for the years from 1950 to the present. The large increase in sky brightness is mainly due to the growth of the population in the Los Angeles basin. An average smog layer reduces the visual brightness by 6 per cent and so smog has reduced the light pollution somewhat.
Program listing for Monday