Protecting and restoring the sky quality at astronomical observatories

This paper addresses the need of preserving the quality of the night sky, ensuring that the artificial sky brightness is kept below the maximum admissible limits, now and in the foreseeable future. Because skyglow is a cumulative immission problem, effective observatory protection requires enforceable emission budgets rather than relying solely on source by source control. The present approach is based on setting clear red-lines for the maximum admissible anthropogenic radiance at astronomical observatories, and enforcing the corresponding limit on the total artificial light emissions in their surrounding territories. Keywords: Light pollution; Site protection; Restoration; Astronomical observatories; Radiometry; Photometry