Light that is made by humans is called artificial light. Often it comes from electricity. This lights up our homes, buildings, and streets. But sometimes, it causes problems, too.

Light pollution is when there is too much artificial light at night. It affects people and animals. It also makes it harder for us to see stars at night.

Urban Areas Full of Light Pollution

Light pollution is a worldwide problem. Scientists created a map of the Earth in 2016. It shows where lights are on at night. Major parts of North America, Europe, the Middle East and Asia have lights on at night. Only hard to reach places are dark. These include Siberia in Russia, the Sahara Desert in Africa and the Amazon in South America.

Light pollution causes sky glow. This is when the night sky becomes brighter. It happens mostly over cities. Cars, street lamps, and buildings cause it.

More than 80 percent of people live under sky glow. That's over six billion people. In these places, people can only see a few stars at night. Astronomers have a hard time seeing stars and planets.

Health Problems

Light pollution can cause health problems. It confuses the clocks inside our bodies. It is called the circadian rhythm. It affects what happens in the body.

One example of this is the hormone melatonin. Hormones are chemicals the body makes that help organs work.

Melatonin helps us sleep. Our bodies create it when it is dark. They do not create it when it is light. When we see a lot of nighttime light, melatonin does not work right. It causes problems sleeping.

Animals And Light Pollution

Light pollution also affects animals. Sea turtles use the moon's light to guide their migration. They usually travel long distances. Light pollution makes them confused and lose their way.

Light pollution also affects insects and birds. Lights draw insects in. They die when they hit light sources. Light pollution makes birds wake up and sing earlier. It also affects animals in the ocean.

Trying To Help

Several groups work to reduce light pollution. The International Dark Sky Association is one of them. It educates people about light pollution.

Everyone can help reduce light pollution at home. Only use outside lights when it is needed. Close curtains at night. This keeps the light inside.