Starless Night

Light pollution extinguishes the stars

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The ability to see a clear sky in daylight has been part of the American environmental ethic since at least 1977, when the Clean Air Act Amendments established visibility in U.S. parks and wilderness areas as an environmental goal of national priority. But the night sky has had no such protection. The post-World War II growth of the U.S. population and mushrooming development in the countryside have brought with them an unchecked surge of light pollution. The sky above a typical suburban neighborhood is now about five to ten times as bright as the natural night sky; over city centers, it may be as much as 25 to 50 times as bright as its natural level.

Astronomers, naturally, were among the first to be alarmed. Our brightening skies are gradually forcing on every astronomer a kind of professional blindness. The Mount Wilson observatory in southern California, a major facility with a 100-inch reflecting telescope, has been rendered virtually useless for deep-space work by the growth of Los Angeles. Even the large observatories on Hawaii's Mauna Kea, almost 14,000 feet above sea level and one of the world's most pristine astronomical sites, are beginning to feel the effects of light pollution. Amateur astronomy, once a backyard hobby, is becoming an expensive and peripatetic pursuit; its devotees are spending more and more of their time and money traveling to conferences in Nebraska, Australia, and other places that are still dark enough for them to see from. If the trend continues, one can imagine astronomy students of the future who have never seen the universe through a telescope with their own eyes.

But with the slow creep of light pollution has come a far wider, and perhaps more profound, loss to the human spirit. The night sky has inspired rapture and wonder at least since the beginning of recorded human history. Golden stars in a midnight-blue sky adorn the ceilings of ancient Egyptian temples; stars figure in the Anasazi petroglyphs. From Stonehenge to the Hubble telescope, humans have gone to great lengths to make sense of the sky, and from those efforts have come some of our greatest scientific revolutions.

Yet the night sky has now been lost to millions of people. Under ideal conditions, the sky is crowded with visible stars, about 2,500 in all, that loom large and close and extend to the horizon in all directions; if there is no haze, the Milky Way, too, will stretch all the way to the horizon. That sight is granted now to fewer than 10 percent of all Americans. Even in a thinly populated suburb or a small village, at roughly double the natural level of sky brightness, much is lost: the contrast and delicate details in the Milky Way, the vast number of stars, and the sense that the stars are large and nearby. In a moderately illuminated suburb, the night sky has only 200 to 300 visible stars. In large cities, people are lucky if they can see more than a few dozen.

Children who live in cities are astonished when they get to summer camp for the first time and find out what the stars really look like. Some grow up without ever having the chance. In my own introductory astronomy classes, the number of students who have already seen the Milky Way before enrolling has dropped, in just 20 years, from half to a handful.



Light pollution also interferes with ecological functions that are keyed to celestial patterns. Bright lights on tall buildings or reflecting off low clouds can confuse migratory birds. The British Trust for Ornithology estimates that at any given hour on any given night, 10,000 English robins are serenading a false dawn. The circadian rhythms of some plants can change under 24 hours of bright light, as when deciduous trees near streetlights retain their leaves too late in the year.

There is also the waste of energy involved in lighting the night sky. The International Dark-Sky Association, organized in 1988 to find and publicize solutions to the problem of light pollution, estimates that the light shining above the horizontal plane--some one-third of the total nighttime illumination--costs more than $1 billion annually in the United States alone. Most of that electricity is still being generated by coal-fired power plants, the source of massive environmental destruction in the form of acid rain, smog, mining damage, and greenhouse gas emissions.