"The rapid increase in light pollution is one of the most dramatic changes occurring in our natural environment," noted the Royal Astronomical Society, which published the study. The survey shows that truly dark, starry skies are unavailable to two-thirds of the world's population, including 99 percent of people in the continental United States and Western Europe. The report describes regions of the world where true night never occurs because it is blocked by lights from cities and towns. In night's darkest places, far from city lights, about 2,000 stars are typically visible. In major cities, that number shrinks to a few dozen at most.

Darkness for Health
Scientists have now discovered that darkness optimizes health. Only when it's really dark can the human body produce the hormone melatonin. Melatonin fights diseases, including breast and prostate cancer. "It turns off the cancer cells from growing," says Joan Roberts, a photobiologist.

But if there's even a little light around your bed at night, melatonin production switches off. "So there may be this natural way that Mother Nature has given us, that is, dark night to keep certain cancers under control," Roberts says. Nature needs darkness, too; the immune systems of animals grow weak when they're exposed to artificial light at night.

A Recoverable Resource
Unlike some natural resources that
are unrecoverable once lost‹species extinction or clear-cut old growth forests‹night sky darkness is potentially recoverable in many places. Lights that glare into the sky and wipe out the stars can be shielded and focused with reflectors to make them more efficient and to reduce light trespass. Or, lights can simply be turned off.

Pointing light where it doesn't need to go also wastes energy. For example,
by "going dark" nightly, some office buildings and school systems are saving as much as $1 million a year in energy costs. Police report that darkness is often safer, partly because neighbors soon learn to alert police if they see lights in a building.

Changing Practices
National Park Service policy dictates that parks must, to the extent possible, manage to preserve, protect, or enhance the night skies. This requires implementation of best management practices within their boundaries and working outside the park with local communities to promote night-lighting ordinances.

Here in the Golden Gate National Parks, we are implementing sound lighting practices by avoiding and eliminating unnecessary night lighting, and by using shielded light fixtures and low-intensity lights. Nationwide, the NPS will be partnering with local groups to develop measures to reduce light trespass from sources outside the parks. With your help, we can bring starry nights back to our parks.