Artificial Night Sky Brightness

Where have all the dim stars gone? From many places on the Earth including
major cities, the night sky has been reduced from a fascinating display of
hundreds of stars to a diffuse glow through which only a handful of stars
are visible. The above map indicates the relative amount of light pollution
that occurs across the Earth. The cause of the pollution is artificial light
reflecting off molecules and aerosols in the atmosphere. Parts of the Eastern
United States and Western Europe colored red have an artificial night sky glow
over nine times that of the natural sky. In any area marked orange or red, the
central band of our Milky Way Galaxy is no longer visible. The International
Dark Sky Association suggests common types of fixtures that provide relatively
little amounts of light pollution.