Dark-sky movement

The dark-sky movement is a campaign to reduce light pollution. The advantages of reducing light pollution include an increased number of stars visible at night, reducing the effects of electric lighting on the environment, and cutting down on energy usage. Earth Hour and National Dark-Sky Week are two examples of such efforts.

The movement started with professional and amateur astronomers alarmed that nocturnal skyglow from urban areas was blotting out the sight of stars. For example, the world-famous Palomar Observatory in California is threatened by sky-glow from the nearby city of Escondido and local businesses. For similar reasons, astronomers in Arizona helped push the governor there to veto a bill in 2012 which would have lifted a ban on illuminated billboards.

Nocturnal animals can be harmed by light pollution because they are biologically evolved to be dependent on an environment with a certain amount of hours of uninterrupted daytime and nighttime. The over-illumination of the night sky is affecting these organisms (especially birds). This biological study of darkness is called scotobiology. Light pollution has also been found to affect human circadian rhythms.

The dark-sky movement encourages the use of full-cutoff fixtures that cast little or no light upward in public areas and generally to encourage communities to adopt lighting regulations. A 2011 project is to establish "dark sky oasis" in suburban areas.

Skyglow is the illumination of the night sky or parts of it, resembling an orange "smog". It occurs from both natural and human-made sources. Artificial skyglow is caused by the over-illumination of the sky from large city centres, shopping centres, or stadiums. It consists of light that is either emitted directly upward or reflected from the ground that is then scattered by dust and gas molecules in the atmosphere, producing a luminous background or light dome. These artificial skyglows cause the sky to be 5–10 times brighter in urban areas than a naturally dark sky that is unaffected by artificial light. Natural skyglow can come from natural light sources, such as the Sun, the Moon, the stars, or auroras.

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