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One-fifth of the world's population cannot see the Milky Way at night because of so-called sky glow. This NASA composite image of Earth at night shows particularly impacted areas like Europe, Japan, and North America
Source: Image by Craig Mayhew and Robert Simmon/NASA GSFC

Light pollution generally refers to human-designed, artificial lighting that illuminates areas other than those the light was designed to illuminate. A classic example of light pollution would be a streetlight that is constructed to illuminate a sidewalk or street to allow walkers and motorists to travel with greater ease and safety at night. Depending on the design and construction of the light fixture, the light can either be directed directly to the ground beneath it or, alternatively, can release light in every direction. ...

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