How to Measure Darkness

Abstract

Now that we've gotten an idea of what the Earth looks like at night, it's time to assess the actual relationship between stray light directed upwards (measured by satellites) and the perceived quality of the sky as seen by us Earthlings. As we have come to understand in the search for shooting stars, what really worsens the quality of the sky are the halos caused by the scattering of stray light by molecules and aerosols in the air. We are talking about humidity and dust, naturally present in the atmosphere, and, in general, about everything that is capable of diffusing light, creating the halos of diffuse brightness that amplify and extend the effect of city lighting for tens or hundreds of kilometres.