Light pollution is a global problem, according to the results of a study conducted by researchers from the National Oceanic and Atmospheric Administration's National Geophysical Data Center in Boulder, Colo., and the University of Padua in Italy. Using global population density data and images from defense satellites of the upward flux of artificial light, the team estimates that one in five people cannot see the Milky Way at night.

Two-thirds of all people are affected by light pollution, the study found. One-fourth live in areas where the light from artificial sources exceeds the luminance of the full moon.