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Light pollution is erasing the night sky. Can we bring it back?

Light pollution obscures the night sky in Tenerife, Spain.
Light pollution obscures the night sky in Tenerife, Spain.

The night sky is slowly vanishing.

Cities in the United States and Europe now emit so much artificial light after dusk that it's becoming harder and harder for most of us to see the stars — even if we hike out to remote rural areas. And that's not always a good thing: There's evidence that too much "light pollution" may be messing up our sleep and the wildlife around us.

How bad is it? "Scientists estimate that in about 10 years, America will have only three dark patches of land where people will be able to clearly see the Milky Way," wrote Megan Finnerty in a fascinating recent feature for the Arizona Republic. (The predicted dark spots include southeastern Oregon, western Utah, and northern Arizona.)

City-dwellers have long realized that the glare from streetlights, buildings, and cars turns the night sky into an opaque haze — making it impossible to see the constellations as, say, the ancient Greeks saw them. Now nighttime lighting is becoming so pervasive that it's even encroaching on rural areas.

Yet there's an optimistic side to this story, too. As researchers pile up more evidence of the dangers of excessive light pollution — from energy waste to sleep disruption — more and more places are finding ways to cut back. Los Angeles has been replacing its old streetlights with LEDs, leading to a dramatic reduction in glare. France just passed a national law cracking down on light pollution. Many US parks are taking new measures to preserve what remaining dark skies we have.

"We're definitely seeing a growing interest in night sky protection," says Scott Kardel, the Public Affairs Director for the International Dark-Sky Association, a non-profit that works to reduce light pollution. While it's implausible to think that cities would ever voluntarily go dark at night, there are plenty of easier ways to reduce the harm from light pollution — and protect what dark spots we have remaining.

The night sky is vanishing in many parts of the world

Dark skies are becoming much rarer in the continental United States. Here's a "light pollution atlas" created back in 2002 by researcher Pierantonio Cinzano that shows the amount of artificial light over and above natural background levels:

US light pollution growth

The first three maps give a sense for the dramatic shift over the past half-century. (Those projections for 2025, by contrast, assume a constant 6 percent annual growth rate in artificial lighting, and won't necessarily pan out exactly.)

In the orange areas (that is, in the cities where most Americans now live), the Milky Way is no longer visible to the naked eye at night. And in the red areas, where the local artificial light is 9 to 27 times the natural brightness level, then relatively few stars are visible in the sky. If light pollution keeps growing, many areas will be unable to see even the Big Dipper at night.

Meanwhile, the remaining patches of darkness are steadily shriveling. Finnerty's story in the Arizona Republic focuses on three areas that are likely to be particularly precious to astronomers and nocturnal wildlife researchers — southeastern Oregon/western Idaho; northeastern Nevada and western Utah; and northern Arizona/southeastern Utah. Yet even the latter two dark areas on the Colorado Plateau are now being threatened by the bright lights of Phoenix and Las Vegas, which can travel for hundreds of miles.

By the way, here's a light-pollution map for the entire world — though this is circa 1997, and artificial lighting has grown since then. Note that dark skies are extremely rare in western Europe and Japan:

world atlas light pollution

(Cinzano et al 2001)

From Cinzano's paper: "Assuming average eye functionality, about one-fifth of the World population, more than two-thirds of the United States population and more than one half of the European Union population have already lost naked eye visibility of the Milky Way."

Does it really matter if we can't see the stars?

milky way in california

The Milky Way rises above the rocky South Tufa outcrops of Mono Lake, California. (Joe Parks/Flickr)

At first blush, it's hard to imagine why light pollution is a big deal. Sure, it's nice to be able to see the stars at night. But artificial lighting is also incredibly valuable — we can now do all sorts of things in the dark that were once hard to do. We don't have to squint to read by candlelight or hold up a lantern to walk down streets at night.

Or, put another way: No one looks at that satellite image of North Korea enshrouded in darkness at night and thinks they're better off than brightly-lit South Korea next door.

Still, it's possible that modern-day lighting has gone a bit overboard. In recent years, scientists have found that excessive artificial lighting at night can actually have a surprising number of adverse consequences. Here are four big ones:

1) Light pollution can disrupt our sleep. Some research suggests that exposure to certain wavelengths of light at night can suppress our bodies' ability to produce melatonin — and disrupt our slumber. This is why it's harder to fall asleep right after staring at your computer screen all evening (blue light is particularly disruptive). But excessive lighting in cities may also play a role here.

2) It really messes with wildlife. In the last decade, scientists have begun to realize that artificial lighting at night can muck up animals and ecosystems in all sorts of unexpected ways. Sea turtles get confused by the lighting from coastal cities and lose their ability to navigate in the ocean. Migrating birds often get bewildered by tall buildings that are lit up and smash right into them. Some scientists even suspect that artificial lighting at night makes it harder for fireflies to find each other and mate.

These ecological impacts can affect humans, too. There's some evidence that artificial lighting can, for example, make it harder for zooplankton to eat away at harmful algae in lakes, which lowers water quality.

3) It's a big waste of energy. Yes, lighting at night is useful. But do we need so much of it? Many street lamps are built so that they shine light in every direction (including up at the sky) rather than focusing on the ground. And many streetlights shine even in the wee hours when no one actually needs them. By some estimates, 40 percent of a city's electric bill goes toward street lighting — and about half of that is simply wasted. That would imply the US wastes about $3.5 billion on excessive lighting each year.

4) It can diminish our sense of the universe. Okay, this one's admittedly a bit more abstract. But some astronomers really do think it's a tragedy that we're cut off from the stars. "Increasingly, urban youth only see constellations on computer screens or in planetariums," one scientist reportedly lamented at a 2012 AAAS conference on the subject. "The lack of the night sky may therefore affect their sense of the scale of the universe and their place in it."

More cities are trying to cut back on artificial lighting

LA before and after LEDs

The 6th Street Bridge in Los Angeles before (left) and after (right) the LED conversion (Bureau of Street Lighting)

And as light pollution becomes a bigger issue, some towns are starting to cut back on excessive lighting.

The best known example to date is in Los Angeles, which is replacing its old bulbous streetlamps that scattered light in every direction with newer, more efficient LEDs that only send light downward. As Ucilia Wang recently illustrated in Forbes, the reduction in glare has been dramatic, and the skies overhead are now noticeably darker. (That said, cities interested in reducing light pollution need to be careful about color selection. Many LEDs largely emit blue light, which brightens the night sky more than any other color.)

There are other lighting technologies cities could adopt, too. "We now have the ability to dim lights in ways that we couldn't before," says Kardel. "And we can even equip streetlights with sensors so that they only turn on when traffic or people are nearby."

Kardel notes that more and more cities are taking a closer look at these technologies — although it's usually done to save money, and not necessarily to bring back the night sky.

Obviously a city like Los Angeles is always going to be too big and bright for people to be able to see all of the stars or the Milky Way. For that, people will still have to travel out to rural areas. But there's also increasing interest in protecting these "dark sky" regions for astronomers, nocturnal wildlife researchers, and the growing number of tourists who want to see what the night sky actually looks like.

A number of parks and communities — both in the United States and elsewhere — have applied to be "international dark-sky places." For communities that apply — like Sedona, Arizona — this typically means following stringent lighting codes at night (like shielding lights under a canopy, dimming them when possible, and even turning them off after a certain hour.)

The National Park Service, too, is now working with communities around the Colorado Plateau to try to preserve the nighttime sky in this region — which is both a popular tourist destination and an important area to astronomers.

As Finnerty reports in the Arizona Republic, however, this isn't always easy to do. In theory, northern Arizona has plenty of reason to protect its dark skies, since its astronomy and tourism programs bring in millions of dollars and hundreds of thousands of tourists each year.

But the responses from different cities has been mixed. On the one hand, Tucson implemented lighting codes 30 years ago and hasn't gotten any brighter at night since, despite growing rapidly. On the other hand, light from Phoenix remains a problem, since it can travel 200 miles in every direction. And the city has been slow to update its lighting codes — or enforcing the ones on the books.

Kardel, for his part, notes that most of the biggest dark-sky preservation efforts are still taking place within the Colorado Plateau —campaigners haven't yet focused on how to deal with light from surrounding metropolises like Phoenix and Las Vegas. "This place is already world-recognized for its dark skies, and many places are taking an increased interest in ways to preserve that resource."

More: These before-and-after photos by Todd Carlson of Sky News offer a vivid look at the effects of light pollution. When a massive blackout hit Ontario, Canada in 2003, the Milky Way was suddenly visible in the night sky. When the power returned, the stars vanished.

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