Night Skies Are Getting Brighter, Making Stars Harder to See

For people living in cities and suburbs, seeing a sky filled with stars is becoming increasingly difficult. New research suggests that artificial light is making the night sky brighter worldwide, causing more and more stars to disappear from view.

Scientists estimate that the brightness of the night sky is increasing by roughly 7 to 10 percent each year. At that rate, the sky can become twice as bright in less than a decade, dramatically reducing the number of stars visible to the naked eye.

Streetlights, buildings, parking lots and sports facilities all contribute to what scientists call skyglow — the glow that spreads through the atmosphere when artificial light is reflected and scattered.

Researchers examined more than 50,000 observations made by citizen scientists between 2011 and 2022. The data indicated that light pollution is increasing considerably faster than earlier estimates based on satellite measurements suggested.

One consequence is particularly easy to notice: fewer stars are visible from populated areas.

The problem goes beyond astronomy. Many animals depend on darkness to navigate, feed, reproduce and rest.

Migrating birds can become disoriented by artificial light, while insects and other nocturnal species can also be affected. Artificial lighting can alter natural behaviors and disrupt ecosystems that evolved around regular cycles of daylight and darkness.

Reducing light pollution does not necessarily mean turning off all outdoor lighting. Researchers and environmental groups point to measures such as using lower-intensity lights, directing light toward the ground and avoiding unnecessary illumination.

Warmer-colored lighting and better-designed fixtures can also reduce the amount of light escaping into the night sky.

Some communities are already changing the way they use outdoor lighting in an effort to preserve darker skies. Such measures could make it easier for people to see the stars while also reducing the impact of artificial light on wildlife.

For many people, however, the changing night sky is already noticeable. The view of a dark sky that previous generations took for granted is becoming increasingly rare in areas affected by growing light pollution.