Raising Awareness on Nocturnal Light Pollution around Astronomical Cultural Heritage Sites

Abstract

A side effect of our modern civilization is the ever increasing level of illumination in and around inhabited areas. Architectural and natural monuments that in numerous cases were built and used in connection with celestial events have already lost or are in danger of losing their original appearance that would allow experiencing them in the original context and intention of the builders or users. To provide authentic views and intact night time environment, site managers responsible for the protection of astronomical cultural heritage should be concerned not only about the building or instrument, but also about its environment and presentation to the public. If site managers decide to apply nocturnal artificial illumination to a monument, this completely changes the original appearance both on the natural lighting situation and the respective authentic lighting culture. Note that many sites often will have been used in moonlight, with the many festival calendars connected to the changing appearance and light of our satellite. The astronomy and world heritage thematic study (Ruggles and Cotte, 2010) and the extended case studies on astronomy and world heritage, in particular the “Windows to the Universe” (Marín et al., 2010), point to the core/buffer zone light management as detailed in the “Starlight Reserve Document”. They essentially call for minimum light, oriented on the Moon in the core zones and downward directed, demand-based illumination in the buffer. National or provincial legislation should control light intrusion from a far zone that may be hundreds of kilometers wide. The remoteness of light-protected areas is somewhat contradicting the often populated cultural “bright”-spots. The tool for such areas is the Starlight Oasis. While light levels in such a place are typically significantly above natural, the most important features of light at night – such as its lunar illumination cycle - and the culturally most important features of the night sky – such as the constellations of the respective culture, e.g. the ones of the Zodiac - are still intact. That leads to a typical zenithal visual limiting magnitude of 6 for moonless clear skies that also provides impressive views of the Milky Way. An example is the Großmugl Starlight Oasis (Wuchterl 2010) about 35 km north of Vienna’s centre. Protected by three mountain ridges, the visual limiting magnitude is a robust 6.3 and even the zodiacal light is still a visible phenomenon. To visualize sites with and without nocturnal illumination at least in a qualitative way, a new feature has recently been added to the popular open-source desktop planetarium Stellarium by one of the authors. In addition to the previously existing global light pollution settings which simulate the artificially brightened sky with its reduced star visibility, the respective landscape panorama can now be enhanced by a site-dependent nocturnal light layer that can illustrate e.g. the direct glare of foreground street lights, illuminated windows, floodlit buildings and also the direction-dependent sky glow along the horizon near larger cities. This new feature may help site managers and proponents of light pollution measures to better visualize their concerns.