Light Pollution Clouds the Night Sky
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Credit: Photograph by Brad Goldpaint

Blinded by the Light

Researchers from the University of Padua, in Italy, working with the National Geophysical Data Center in Boulder, Colorado, have collaborated on the first World Atlas of artificial night-sky brightness, which measures global light pollution. The above images show light levels in the United States over the past five decades, along with a projection for 2025. Drawn from computer models based on upward light as measured by meteorological satellites, the images take into account other factors such as altitude and the way light is scattered by smog. Black space represents the darkest areas, traditionally clustered in sparsely populated western states, while the colored areas depict different levels of light pollution. Yellow represents twice the amount of natural night-sky brightness. In orange zones, the Milky Way is no longer visible. Red zones mean fewer than 100 stars can be seen. Finally, in the white and pink zones, most prevalent in the 2025 map, the North Star and the Big Dipper have disappeared.

The Worst Offender

Among American cities with significant light-pollution problems, like Los Angeles, New York, and Washington, D.C., Chicago stands out as perhaps the worst. In 2008, the city was named the single most light-polluted city in the country. Much of Chicago's problem stems from its profusion of billboards, improperly aimed streetlights, and outdated Victorian-style streetlamps. In a positive development, as part of a recent effort to prevent birds from striking brightly illuminated buildings at night and dying, 100 Chicago-area skyscraper owners agreed to dim their lights during the evening.