If you have ever seen the Milky Way galaxy, you know what a beautiful sight it is: a truly massive group of shining stars stretching across the night sky.

But a new study finds that one-third of the world's population no longer can see the Milky Way at night.

The findings were reported in the journal Science Advances.

The new report says that in the United States, it is even harder to see the Milky Way. For 80 percent of Americans, it is impossible or very difficult to see the galaxy at night.

The problem is light pollution. The sky is brightened at night by street lights and other artificial, or man-made, lighting. This is especially true in big cities.

Light pollution not only blocks our viewing of the stars and planets; it can also affect natural events or activities here on Earth.

What is the Milky Way?

The Milky Way is a spiral structure. Earth is actually part of the galaxy, so we cannot take a picture of the entire formation.

From where we are, the Milky Way has looked like a massive star formation stretching across the night sky.

NASA, the American space agency, says the Milky Way is about 100,000 light years across, from one end to the other. Our galaxy has hundreds of billions of stars.

Position of Sun in the Milky Way Galaxy

And where does the Milky Way, our galaxy home, fit into the universe? It is just one of hundreds of billions of galaxies in the known universe, according to NASA.

Since the beginning of time, humans have gathered to look at stars in the night sky. The Milky Way at first might look like a group of storm clouds. But actually, it is many stars in cloud-like groups. They shine so brightly they give off white light – the same color as milk.

The ancient Greeks had a story that said the white band of stars was milk left in the sky by a goddess.

Light Pollution Study

The study in the journal Science Advances is the work of an international team of scientists. The team created a series of maps that show where the world's light pollution is strongest and weakest. Their maps were based on from satellite data and sky brightness measurements.

"I hope that this atlas will finally open the eyes of people to light pollution," said the study's lead author Fabio Falchi. He works for the Light Pollution Science and Technology Institute in Italy.

The Institute says its goal is to limit light pollution and the negative effects on the night environment. The new guide is a follow up to the first World Atlas describing light pollution in 2001.

The new study found that Singapore, Italy and South Korea have the most widespread light pollution.

There are only small areas in Western Europe with low levels of light pollution. Those places are mostly in Scotland, Sweden and Norway. The western United States has huge amounts of wide open space. But the study found that nearly half of the U.S. experiences light pollution.

The researchers found that two other countries, Canada and Australia, have the most ‘dark sky' – or night-time light levels low enough to see the stars.

Dan Duriscoe of the U.S. National Park Service was the study's co-author. He says that U.S. national parks are just about the last havens of darkness. He pointed out that places such as Yellowstone and the desert southwest have the darkest night skies.

"We're lucky to have a lot of public land that provides a buffer from large cities," said Duriscoe.

Researchers have looked into the increase of artificial light over the years. They say not only does it affect our view of the Milky Way, but it has been shown to have a big impact on human health and on wildlife, too.

Scientists have found that artificial light can confuse insects, birds and sea turtles. It can also put them in situations that can kill them.

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Words in This Story

galaxy – n. a big collection of stars

viewing – n. the ability to see

spiral – n. a circular curving line that goes around a central point, and gets closer and farther away from it

entire – adj. complete or full

fit – v. how something goes into a space

band – n. a thick line

negative – adj. harmful or bad

haven – n. a place where you are protected from trouble or danger

buffer – n. something that give protection by separating things

confuse – v. to make something difficult to understand