A scientist once said that studying the stars from the earth is【C1】______ looking up at the sky from the bottom of a switching pool. Even on the clearest night the earth's dense atmosphere【C2】______ 30 percent of the light from any star. Air turbulence may cause stars to twinkle.【C3】______ a telescope the stars seem to jump around dizzily. Because the moon has no atmosphere, astronomers are looking forward to【C4】______ an observatory there. On the moon, there will be no clouds to【C5】______ the view. The sky will appear dark【C6】______ , so astronomers can work twenty-four hours a day. Because there is no air turbulence, the stars will appear【C7】______ through a telescope. 【C8】______ the moon is relatively near the earth, moon-based astronomers will see the stars in the familiar patterns known on【C9】______ . They will not need new star maps of the sky. Stars【C10】______ the moon will appear to move very slowly. Because the earth【C11】______ on its axis once every twenty-four hours earth based astronomers see the stars hurry 【C12】______ the sky each night. The moon rotates on its axis only once a month. To astronomers on the moon, the stars will appear to stand【C13】______ still. Moon-based astronomers will have much more time【C14】______ their telescopes and take time-exposure photographs. On the earth, mechanical radio noises【C15】______ the airwaves and interfere with the【C16】______ of radio signals from certain stars. A radio telescope【C17】______ on the far side of the moon will be permanently protected from such 【C18】______ . It won't be easy to put telescopes on the moon. However, astronomers are【C19】______ the job can be done. They are convinced that the moon is an【C20】______ place to set up an observatory. 【C1】