Light Pollution

Learn about the effects of excess light coming from cities at night.

In most situations, light helps us see. But when it comes to looking at the night sky, light is actually a kind of pollution.

It hampers our view of some of life’s most spectacular sights: stars, planets, and even galaxies. “When I was a little boy, I loved the night sky,” recalls Robert Gent of the International Dark-Sky Association, an organization working to reduce light pollution.

“I remember looking up and the sky was filled with stars, and I asked, ‘How many are there? How far away are they? Can we visit them?’ I became an astronomer because I was amazed by their beauty,” he says. “Now in most big cities kids can’t see the stars like I did.”

Normally, about 2,500 individual stars are visible to the human eye without using any special equipment. But because of light pollution, you actually see just 200 to 300 from today’s suburbs, and fewer than a dozen from a typical city.

Only one in three Americans can see our own galaxy, the dazzling Milky Way, with the naked eye. Those people live far away from the lights of big cities, office buildings, and shopping malls.

Fortunately, there is a solution that is inexpensive and has benefits right away, says Gent. “If we shine lights down at the ground instead of up into the sky, and use lower brightness levels, we can save enormous amounts of energy and preserve the beauty of the night skies.”

Many cities and towns have passed laws limiting lights at night, making sure enough shine for safety without creating a lot of light pollution.

Light pollution affects more than our view of the heavens. Research shows that lots of nighttime light can harm wildlife.

Migrating birds sometimes fly over cities and become confused by the brightness, flying in circles until they drop from exhaustion. Sea turtles need dark beaches for nesting and won’t approach bright lights. Too much light at night may even affect human health; scientists are still learning more.

For all these reasons, researchers are working on ways to use lights only when and where they are truly needed. “Everyone deserves to look up at the infinite sky and wonder about the unbounded universe,” says Gent.

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Katherine Johnson
Space Explorer