The bright lights in many cities block all the stars in a hazy glow, as seen in this still from the new documentary "The City Dark."
Light pollution is so common that hardly any stars are visible in many cities around the world.
Astronomers have been forced to go farther and farther afield to find dark enough skies.
Migrating birds can become disoriented by brightly lit buildings at night, causing many of them to crash into walls.
Some of the best night skies are found in extremely remote locations, far from any city lights.
The documentary "The City Dark" explores what happens to people and animals when the stars are no longer visible at night.
The filmmakers behind "The City Dark" travel to some of the few spots left on the globe with pristine views of the sparkling night sky.
Frustrated skywatchers in big cities may find it hard to spot even a single star from some brightly-lit locales.
Some people, such as residents of the dark-sky community Arizona Sky Village, are choosing to live as far from city lights as possible.
There is some evidence that exposure to bright lights at night may lead to increased cancer rates.
New York City is one of the most light-polluted spots on an increasingly over-lit Earth.
Light pollution from seaside buildings can confuse newborn sea turtles who have only a short time to make it to the ocean after hatching on the beach.