On the evening of September 26, 2019, the streets of Geneva in Switzerland went dark. This usually happens when there is a problem with the electricity, but this time the lights were turned off to allow people to go outside and look at the stars. This is often impossible in a city because of light population.
Light pollution is when light from streetlights or buildings makes the night less dark. There are many reasons why this is a problem. Animals sleep less because they think it is still daytime. Birds that fly to warmer countries in the autumn need to see the moon and stars to find their way, but light pollution makes this difficult. Insects and birds in cities often fly towards lights at night, knock into buildings and die.
Light pollution is also bad for us. It can stop us sleeping and give up headaches. Also, we don't see the same sky that people in the past did. This means we almost never see one of the greatest scenes in the world: the millions of stars. Hundreds of thousands of people have never seen it in their lives.
However, it is not difficult to do a few things to reduce (减轻) light pollution: we can all turn lights off when we don't need them and we can cover our windows. If there is less light pollution, we will once again be able to enjoy the beauty of the night sky.
