These depressing photos show what we don’t see in the night sky

If you were to look at the night sky, it could range from a dusty glow to a grainy black expanse with thousands of twinkling stars, depending on where you are.

On a clear night, it is estimated that 2,000 stars are visible to the naked eye, but the glare of light pollution from the lights of the city and small towns prevents us from seeing the cosmos in all its glory.

In order to describe the amount of light pollution at a given location, astronomers use the Portel scale, which ranks visibility from levels I to IX. It was first described by John Portel in a 2001 issue of Sky and telescopeAstronomy Journal.

Each level ranks the night sky based on their cosmic views. You can find the Bortle Scale for your night sky using the interactive map tool at lightpollutionmap.info.

These photos show how many stars you can see in a truly dark sky, outside of cities, suburbs, and other human light sources:

The ninth level ranks the inner city sky, and is the worst for stars. (Tony Flanders)

What can be seen: The Moon, the nearest planets and a handful of the brightest stars

Where to find it in the United States: New York City, Las Vegas, Los Angeles

A sky with very bright light pollution, which is mostly found over major cities, lights up orange. While it may not be as harmful as other types of pollution, light pollution can affect human health.

Multiple studies have indicated that exposure to light at night can disrupt the body’s biological clock, which has been linked to health complications, including obesity, depression, and sleep disturbances.

The eighth level classifies the city sky, where you might only be able to see the faint constellations. Follow Favorite

What can be seen: Towers may be slightly visible

Where to find it in the United States: Boston, Massachusetts; Austin, Texas; Indianapolis, Indiana

At level eight, the sky can be so bright from light pollution that you can read it. To the naked eye, most stars and even constellations would be invisible.

Level 7 ranks the transition from urban to suburban, and it’s the third-worst transition in the stars. Follow Favorite

What can be seen: The M44 star cluster and the Andromeda galaxy are very blurred, and the Milky Way is almost or completely invisible.

Where to find it in the United States: Seattle, Washington; Savannah, Georgia; Salt Lake City, Utah

Light pollution in these regions causes the entire sky to appear a light gray, and the Milky Way is effectively invisible.

A 2016 study estimated that even on the clearest night, a third of humanity cannot see the Milky Way.

The sixth level categorizes bright suburban skies where only a few stars are visible. (Tony Flanders)

What can be seen: The Andromeda Galaxy appears faint

Where to find it in the United States: Albuquerque, New Mexico; Lincoln, Nebraska; Bloomington, Indiana

At the sixth level, the clouds appear rather bright and the sky lights up a greyish-white. Light pollution under these conditions is very bright.

Level 5 ranks suburban skies where you may be able to see the Milky Way faintly. Follow Favorite

What can be seen: The Milky Way can appear faint

Where to find it in the United States: Burlington, Vermont; Santa Fe, New Mexico; Grand Junction, Colorado

Most of us spend our lives at this Bortle Scale or higher, according to telescope shop OPT Telescopes.

At level five, light pollution will be visible in most, if not all, directions. The clouds are brighter than the sky itself, and the Milky Way is dimmer.

The fourth level categorizes the transition from the suburbs to the rural areas, where you can see the Milky Way. Follow Favorite

What can be seen: Milky Way Galaxy, Triangle Galaxy

Where to find it in the United States: Twin Falls, Idaho; Flagstaff, Arizona; Wind River Indian Reservation, Wyoming

Light pollution is visible in many directions. Under these skies, the background of the sky begins to appear gray instead of black.

The third level ranks the country sky where you can see the dusty Milky Way. Follow Favorite

What can be seen: Milky Way and dense groups of stars such as M4, M5, M15 and M22

Where to find it in the United States: Yosemite National Park, California; Everglades National Park, Florida; Great Smoky Mountains National Park, Tennessee

You can see the Milky Way, but the fine details are gone. Some clouds light up towards the light sources, but the upper clouds remain dark.

The second level ranks typical dark sky locations, which are the second best viewing locations for the cosmos. Follow Favorite

What can be seen: Milky Way, Magellanic Clouds

Where to find it in the United States: Cherry Springs State Park, Pennsylvania; Adirondack Park, New York; Joshua Tree National Park, California

The Milky Way is highly visible to the naked eye. Skyglow, a haze of light from light sources scattered on the ground, may be faintly visible along the horizon.

The first level ranks premium dark sky sites, which are best for stargazing. Follow Favorite

What can be seen: Milky Way Galaxy, Andromeda Galaxy, Orion Nebula

Where to find it in the United States: Big Bend National Park, Texas; Grand Canyon National Park, Arizona; Denali National Park, Alaska

The first-level sky provides an unobstructed view of the universe, comparable to that seen by Galileo. The night sky is filled with stars, making it difficult to analyze the faint constellations. The Milky Way is so bright that it is capable of casting shadows.

This article was originally published by Business Insider.

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