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Are you a stargazer? Whether you’re a beginning astronomer or just like to enjoy the twinkling stars, you’ve probably noticed that you can see more of them when you’re away from towns and cities.

Imagine living 300 years or so ago. Homes and businesses were lighted by candles or gas flames. When you didn’t need the light, you extinguished, or put out, the flame.

Today we let lights burn all night – streetlights, porch lights, office lights – even when we don’t need the illumination. Scientists call this light pollution.

This week, the Mini Page learns more about light pollution and how it affects humans and animals.

Not all lights are pollution

Modern humans need artificial light. It allows us to work indoors and throughout the day and night. Imagine hospital workers trying to take care of sick people without artificial light. How well do you think people could drive cars without streetlights and headlights showing the road?

What is light pollution?

The International Dark-Sky Association works to reduce light pollution. It defines light pollution as any negative effect of artificial light, including light that creates sky glow, glare, light trespass, light clutter, bad visibility at night and energy waste.

• Sky glow is the brightening of the night sky over cities.

• Light trespass is light falling where it’s not needed or wanted.

• Glare is too much brightness.

• Light clutter is bright and confusing groupings of lights.

Natural light

As the Earth turns, people and animals experience hours of light from the sun and hours of darkness, when our part of the planet is turned away from the sun. As humans were evolving, these changes in light affected when people slept, when they worked and how they felt. These are called circadian rhythms. (Circadian means a 24-hour period.)

Human-made lights highlight more developed or populated areas of the Earth’s surface, including large cities in the United States. Can you identify cities across the U.S. by looking at this nighttime photo from satellites flying through space? Discuss with your family or class why so many cities are clustered along the coasts and major rivers.