Dark Skies Initiatives Aim to Boost Stargazing

John Roach
for National Geographic News
May 16, 2006
As light pollution worsens across the United States, astronomers are urging citizens to protect their night skies.

"Light has little utility when it shines up into the sky and does nobody good whatsoever," said William Brown, an astronomy professor at Colorado State University in Pueblo (Colorado map).

Brown and his students use telescopes to search the sky for asteroids that could potentially crash into Earth.

"It's a very difficult process, and it just makes it far more difficult if there's excess light in the sky," he said. "These asteroids are incredibly dim—they only reflect a tiny, tiny bit of light from the sun."

So last year Brown helped enact a dark-sky ordinance in Pueblo County, which requires all outdoor light fixtures to shine downward only.

The ordinance prohibits light streaming up into the night sky, where it interferes with astronomers attempting to get a clear view.

"There are a lot of fixtures that do that," he said. "[Shining lights upward is] a terrible waste of energy and a terrible waste of a dark sky."

Seeing Stars

According to the Tucson, Arizona-based International Dark Sky Association, an estimated 1,000 cities and towns in the U.S. have enacted some form of dark-sky ordinance.

But as the population grows and cities get bigger, the problem of light pollution is getting worse, not better, Brown says.

"In quite a few places that were excellent [for stargazing] it's getting more and more difficult," he said. (Related feature: Explore an interactive star chart.)

David Crawford is the executive director of the International Dark Sky Association. He says dark skies are good for human health and safety as well as for people's pocketbooks.

In recent years scientific studies have shown a link between light pollution and breast and colon cancers, perhaps because of the body's failure to produce certain light-related hormones.

Studies have also found that some people's immune systems are weakened by disrupted circadian rhythms, which are tied to natural light and dark cycles, Crawford says.

When it comes to safety at night, people often assume a brightly lighted area will help them steer clear of shady characters. Not so, Crawford says.

The bright lights increase the contrast between light and dark, giving criminals darker shadows for lurking. And overlighting can cause a blinding glare.

"Suppose you go to a grossly overlit gas station at night and get back on the road. You can't see for a while. You can't see what you're driving into," he said.

Excess lights are also a waste of energy and money, Crawford says. "I haven't noticed energy becoming cheaper lately."

Good Lights

"What we need is good light at night, not overlighting," Crawford added.

Good lights are those that shine toward the ground only, Brown, of Colorado State, says. When light hits the ground, its intensity decreases substantially and very little leaks back into the sky, he says.

In Tucson, where astronomy is big business, legislators enacted an ordinance that permits lights at night to shine only in a part of the spectrum that is easily filtered out by equipment on telescopes.

"That makes the extra ambient light almost insignificant to astronomers," Brown said.

But such lights are expensive and their use is controversial, Brown says. For example, one side effect is poor color rendition at night, making it difficult for police to distinguish between oil and blood on the street.

Nevertheless, Brown encourages cities, no matter their size, to at least adopt ordinances that prevent light leakage above the horizontal rim of the fixture.

"There's a whole heritage of the wonders of the night sky and all there is above to be seen and appreciated," he said. "That's what the average person has to lose if we lose the dark skies."

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