A dark sky survey in Wales

2013 September 30

Martin Griffiths

One of the most common complaints amongst astronomers is that of light pollution. It is impossible to ignore the glare from villages, towns and cities that pervades the night sky. This affects visibility of the Milky Way and reduces the numbers of stars seen. It also intrudes on photographic images.

Scattered between the brighter areas are regions of darkness that have astronomical potential which should be exploited. The Brecon Beacons National Park has one of the darkest night skies in southern Britain and has good links to north and south Wales and the Midlands of England. To support use of this dark sky resource, in 2012 March the Brecon Beacons National Park Authority (BBNPA) applied for Dark Sky Reserve status through the International Dark Sky Association (IDA). This reserve, the first in Wales, would meet the criteria of the IDA in ‘possessing an exceptional or distinguished quality of starry nights and nocturnal environment that is specifically protected for its scientific, natural, educational, cultural, heritage and/or public enjoyment mission of a large peripheral area’.

International Dark Sky Reserves are formed through a partnership of multiple landowners and administrators that have recognised the value of the starry night through regulation, formal agreement and long term planning. In the case of the national park, this covers local authorities, landowners and the park authority itself. To assist the BBNPA to gain IDA status, a sky survey was undertaken to ascertain the average darkness of the park by gauging the faintest naked eye limiting magnitude (NELM) of stars. These readings reflect the core and peripheral areas and pinpoint the darkest accessible sites. The results of this survey are reported in this paper.