For much of Earth’s history, stars have been easily visible in the darkness of the night sky. But today, artificial lighting has changed the landscape. What can lawmakers do about nighttime “light pollution”? In 19 US states, they have enacted laws to literally turn down (or turn off) the lights.
In the 1970s, astronomers started complaining about light pollution when they realized they could no longer clearly see certain stars and celestial bodies.
Under normal nighttime conditions, stargazers should be able to see over 2,000 stars. But people in a typical American suburb can usually see only a few hundred stars, and in a large city, residents would be lucky to see a few dozen stars.
The US National Park Service estimates that as much as 60% of light from most light sources is wasted.
About half of that wasted light bounces off molecules and aerosols in the atmosphere, returning to Earth to form what is called urban sky glow.
Some 10% of the sky glow impacts our vision through glare.
John E. Bortle created the Bortle Scale in 2001 to help classify night skies from Class I (pristine and natural) to Class 9 (large, compact cities).
Nineteen US states, the District of Columbia and Puerto Rico have enacted “dark skies” laws to reduce light pollution on public buildings and roads.