Let there be dark: to keep the cosmos in view, sky watchers must fight to keep the Earth from being enveloped in a fog of artificial light

Natural History, Oct, 2002 by Neil deGrasse Tyson

Astrophysics reigns as the most humbling of scientific disciplines. The astounding breadth and depth of the universe deflates our egos daily, and we are continually at the mercy of uncontrolled forces. A simple cloudy evening--one that would stop no other human activity--prevents us from making observations with a telescope that can cost $20,000 a night to run, regardless of the weather. We are passive observers of the cosmos, acquiring data when, where, and how nature reveals itself to us. To know the cosmos requires that we have windows onto the universe that remain unfogged, untinted, and unpolluted. But the spread of what we call civilization, and the associated ubiquity of modern technology, is generally at odds with this mission. Unless something is done about it, people will soon bathe the Earth in a background glow of light that will block all access to the frontiers of cosmic discovery.

The most obvious and prevalent form of astropollution comes from streetlamps. All too often, they can be seen from your airplane window during night flights, which means that these streetlamps illuminate not only the streets below but the rest of the universe. Unshielded streetlights, such as those without downward-facing shades, are most to blame. Municipalities with these poorly designed lamp housings find themselves buying higher-wattage bulbs because half the lamplight points upward. This wasted light, shot forth into the night sky, has rendered much of the world's real estate unsuitable for astronomical research. At a 1999 conference entitled "Preserving the Astronomical Sky," participants rightly moaned about the loss of dark skies around the globe. One paper reported that inefficient lighting costs the city of Vienna $720,000 annually, London $2.9 million, Washington, D.C., $4.2 million, and New York City $13.6 million. Note that London, with a population similar to that of New York City, is more efficient in its inefficiency by nearly a factor of five.

The astrophysicist's dilemma is not that light escapes into space but that the lower atmosphere supports a mixture of water vapor, dust, and pollutants that bounce some of the upward-flowing photons back down to Earth, leaving the sky aglow with the signature of a city's nightlife. As cities become brighter and brighter, dim objects in the cosmos become less and less visible, severing urban dwellers' access to the universe.

It's hard to exaggerate the magnitude of this effect. A penlight's

beam, aimed at a wall across a darkened dining room, is easy to spot. But gradually brighten the overhead light, and watch how the beam gets harder and harder to see. Under light-polluted skies, fuzzy objects such as comets, nebulae, and galaxies become difficult or impossible to detect. I have never in my life seen the Milky Way galaxy from within the limits of New York City, and I was born and raised here. If you observe the night sky from light-drenched Times Square, you might see a dozen or so stars, compared with the thousands that were visible from the same spot when Peter Stuyvesant was hobbling around town. No wonder ancient peoples shared a culture of sky lore, whereas modern peoples, who know nothing of the night sky, instead share a culture of evening TV.

The expansion of electrically lit cities during the twentieth century created a technology fog that forced astronomers to move their hilltop observatories from the outskirts of towns to remote places such as the Canary Islands, the Chilean Andes, and Hawaii's Mauna Kea. One notable exception is Kitt Peak National Observatory in Arizona. Instead of running away from the spreading and brightening city of Tucson, fifty miles away, the astronomers stayed and fought. The battle is easier-won than you might think; all you have to do is convince people that their choice of outdoor lighting is a waste of money. In the end, the city gets efficient streetlamps and the astronomers get a dark sky. Ordinance No. 8210 of the Tucson/Pima County Outdoor Lighting Code reads as though the mayor, the chief of police, and the prison warden were all astronomers at the time the code was passed. Section 1 identifies the intent of the ordinance:

   The purpose of this Code is to provide standards for outdoor lighting so
   that its use does not unreasonably interfere with astronomical
   observations. It is the intent of this Code to encourage, through the
   regulation of the types, kinds, construction, installation, and uses of
   outdoor electrically powered illuminating devices, lighting practices and
   systems to conserve energy without decreasing safety, utility, security,
   and productivity while enhancing nighttime enjoyment of property within the
   jurisdiction.

And after thirteen other sections that give strict rules and regulations governing citizens' choice of outdoor lighting, we get to the best part, section 15:

   It shall be a civil infraction for any person to violate any of the
   provisions of this Code. Each and every day during which the violation
   continues shall constitute a separate offense.