You can help build the best global map of light pollution, the uniquely modern problem that has stolen starlight from most of the urbanized world.

From March 22 through April 6, the GLOBE at Night website will collect the public's measurements of the night sky. Anyone can participate by comparing their local view of specific constellations with magnitude charts on the site. The event is in its sixth year, and organizers hope to surpass the 17,800 observations they collected in 2010.

"With half of the world's population now living in cities, many urban dwellers have never experienced the wonderment of pristinely dark skies and maybe never will," says the GLOBE at Night. "This loss, caused by light pollution, is a concern on many fronts: safety, energy conservation, cost, health and effects on wildlife, as well as our ability to view the stars."

Light pollution is caused by stray artificial light from sources that are too bright, poorly aimed or both. Similar to how sunlight makes the sky glow blue, artificial light scatters in the atmosphere to create a dull glow that obscures stars and celestial objects. Airborne pollutants exacerbate the problem.

Aside from the loss of stars from view, light pollution has more quantifiably dangerous sides. One model of Los Angeles suggests it destroys about 7 percent of smog-eating chemicals that build up in the dark, leading to a 5 percent jump in wheeze-inducing ozone pollution during the day. Other studies show artificial light can thwart animal migrations and negatively impact human health.

Satellites can assess artificial brightness from space, but the view is very different from the ground. By crowdsourcing measurements, GLOBE at Night aims to both create the most accurate map of how light pollution hides the stars and raise awareness of the problem. They also hope to spark a push for local artificial light ordinances, such as those passed in Flagstaff, Arizona, and other municipalities.

People living north of the equator can access the organization's app to report night-sky conditions between March 22 and April 4. In the southern hemisphere, the window of opportunity is March 24 through April 6.

Images: 1) Historic and anticipated increases in artificial night sky brightness in the United States./NIH. 2) Worldwide measurements of light pollution submitted by 17,800 participants in 2010./GLOBE at Night.

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