The Natural Brightness of the Night Sky: Analyzing 44 of the Darkest Places in the World
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The Natural Brightness of the Night Sky: Analyzing 44 of the Darkest Places in the World:
A recent study analyses data collected at 44 of the darkest places in the world, including the Canary Island Observatories, to develop the first complete reference method to measure the natural brightness of the night sky using low-cost photometers.
Of the 44 photometers in the survey, the Roque de los Muchachos Observatory (Garafia, La Palma, Canary Islands) stands out at the darkest of all the skies analyzed.
The night sky is not completely dark; even in the remotest places there is a glow in the sky produced by natural components, both terrestrial and extraterrestrial, and by artificial lighting of human origin. Even though the main bright sources such as the Moon, the Milky Way, and the Zodiacal light are easily recognizable, there is a glow which dominates the sky brightness on the darkest nights, produced in the upper layers of the atmosphere, and whose strength depends on a set of complex factors such as the time of year, the geographical location, and the solar cycle.
[...] The glow produced by the scattering of artificial light at night (ALAN) by the components of the atmosphere (gas molecules, aerosols, clouds...) is known as artificial skyglow. Estimates suggest that more than 10% of the Earth's surface receives ALAN and that this figure increases to 23% if we include the atmospheric skyglow. Some 80% of the human population lives in places with light pollution, and around a third of them cannot see the Milky Way. There are few places left in the world where one can appreciate, observe, and measure the natural darkness.
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