Protecting Dark Skies

For most of human history, the night sky was filled with thousands of visible stars, a breathtaking sight that inspired art, religion, and the earliest science. Today, many people living in large cities can see only a handful of the very brightest ones. The reason is light pollution: the glow of streetlights, buildings, and advertising signs that scatters in the atmosphere and effectively hides the stars from view. As cities have grown ever larger, this artificial brightness has spread so far that a truly dark night sky has become surprisingly （ 1 ）.

The disappearance of the stars is far from the only concern. Excessive and badly designed lighting wastes vast amounts of energy and money, sending light uselessly upward into the empty sky. It also disturbs wildlife: birds that migrate at night, countless insects, and newly hatched sea turtles can all be confused and harmed by artificial light. Some researchers even worry that bright light at night may damage human health by disrupting our natural sleep. （ 2 ）, light pollution is now widely seen as a serious environmental problem, not merely an inconvenience for astronomers.

Unlike many environmental problems, this one has refreshingly straightforward solutions. Simply shielding lamps so that they shine downward, where the light is actually needed, rather than in every direction at once, keeps light out of the sky. Using lights only when and where they are necessary saves a great deal of energy as well. Some communities have even created "dark sky" reserves, where lighting is carefully controlled in order to protect the view of the stars. （ 3 ） such simple measures, the night sky can be returned to people and wildlife alike, often at very little cost.