We usually think of pollution as a harmful waste substance that threatens the air and water.【C1】______some people have become【C2】______about another kind of pollution. It can be everywhere, depending on the time of day.【C3】______it is not thought of as a【C4】______. It is light. The idea of light pollution has【C5】______with the increase of【C6】______in cities. In many areas, this light makes it【C7】______to observe stars and planets in the night sky. In 1922, the International Dark-Sky Association formed. This organization wants to reduce light pollution in the【C8】______sky. It also【C9】______the effective use of electric lighting. Light pollution is the【C10】______of wasted energy. Bright light that shines into the sky is not being used to provide light【C11】______it is needed on Earth.【C12】______designed【C13】______causes a great deal of light pollution. Lights that are brighter than【C14】______also cause light pollution. Most people in America are【C15】______to find out that they are not able to see our own galaxy, The Milky Way, with their own eyes.【C16】______about three-fourths of Americans cannot see the Milky Way because of【C17】______light. Objects in the night sky are【C18】______that provide everyone【C19】______wonder. But light pollution threatens to prevent those wonderful sights【C20】______being seen. 【C1】