The idea of light pollution has developed with the increase of lights in cities. In many areas, this light makes it difficult or impossible to observe stars and planets in the night sky. There are a number of reasons why light pollution is important. One has become clear at the Mount Wilson Observatory near Los Angeles, California. Today, light from Los Angeles makes the night sky above Mount Wilson very bright. It is no longer an important reasearch center because of light pollution. Light pollution threatens to reduce the scientific value of research telescoples in other important observatories. They include Lick Observatory near San Jose, California and Yerkes Observatory near Chicago, Illionis. Light pollution is the result of wasted energy. Bright light that shines into the sky is not being used to provide light where it is needed on Earth. Poorly designed lighting causes a great deal of light pollution. Lights that are brighter than necessary also cause light pollution. Most people in America are surprised to find out that they are able to see our own galaxy(星系)，the Milky Way, with their own eyes. But about threefourths of Americans cannot see the Miky Way because of manmade light. Objects in the night sky are resources that provide everyone with wonder. But light pollution threatens to prevent those wonderful sights from being seen. 小题1:Light pollution usually occurs________.
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