TABLE 1. Visitor Proposals for Time on the Three Largest Telescopes at KPNO February 1, 1979 to July 31, 1979 At present, the primary man-made source of sky brightness is outdoor light from cities and towns. Astronomers have attempted to combat this light pollution in a number of ways—the most obvious, building telescopes in remote locations well away from city lights. For example, the detailed site surveys that precede construction of a major observatory always include assessments of the sky brightness. In some cases, urban areas have grown up adjacent to observatories. At some of these observatories, observations are limited to the kinds of of objects observed during "bright" observing time at darker sites as is the case at Mt. Wilson Observatory where the light pollution from Los Angeles and nearby cities makes the sky very bright. At other observatories, observatory staffs have attempted to convince local public officials that it is possible to control light pollution and minimize the effects of outdoor lighting on astronomy. Tucson, Arizona and Richland, Washington, among others, have very strong light abatement ordinances specifically tailored to preserve dark skies.
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