Sky Quality Monitoring in Tomintoul and Glenlivet

Within the Dark Sky Park we are monitoring and recording Sky Quality in three different ways: Photographs By taking standard full sky images with a fish eye lens at key places so that the levels of light pollution can be monitored over time. For example these images were taken at the junction of the A939 and B9008 just outside Tomintoul in late 2015 and again in October 2017. It shows the Milky Way and modest Aurora to the north. In 2015 the old street lights are visible in Tomintoul street lights with their associated light pollution. After the new “full cut off” lights were fitted in 2017 the reduction in light pollution was impressive. Sky Quality Meter A Unihedron sky quality meter is used to measure how dark the sky is at various sites throughout the Dark Sky Park. Measurements are made in mpsas (magnitudes per square arcsecond). Inner city skies may measure less than 18.0 mpsas. Rural skies typically measure 21.3 – 21.5 mpsas. Our sky quality is 21.7 – 21.8 mpsas away from the villages and distilleries. The darkest skies on earth are 22.0 mpsas. Bortle Classification Bortle classification is more subjective than the above methods, but is still a widely recognised means of evaluating light pollution. Various features of the night sky are assessed to arrive at the Bortle classification. These include the visibility of various celestial objects and phenomena as well as the level of cloud illumination and the presence of light pollution domes. Again these are carried out at key sites as with the methods above. The Bortle scale runs from 1 to 9. A rating of 1 is reserved for the darkest skies on the planet, whilst a rating of 9 would be typical of an inner city environment. Assessments within our villages and distilleries range from 4 to 5, whilst the more remote parts of our area score from 2 to 3.