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例一： Light Night，Dark Stars 1. Thousands of people around the globe step outside to gaze at their night sky.On a clear night， with no clouds, moonlight，or artificial lights to block the view，people can see more than 14,000 stars in the sky，says Dennis Ward，an astronomer with the University Corporation for Atmospheric Researchin Boulder，Colo.But when people are surrounded by city lights.he says，theyre lucky to see 150 stars. 2. If youve ever driven toward a big city at night and seen its glow from a great distance, youve witnessed light pollution.It occurs when light from streetlights，office buildings，signs，and other sources streams into space and illuminates the night sky.This haze of light makes many stars invisible to people on Earth.Even at night，big cities like New York glow from light pollution, making stargazing difficult。 3. Dust and particles of pollution from factories and industries worsen the effects ot light pollution.If one city has a lot more light pollution than another，Ward says，that city will suffer the effects of light pollution on a much greater scale. 4. Hazy skies also make it far more difficult for astronomers to do their jobs. 5. Cities are getting larger.Suburbs are growing in once dark，rural areas.Light from all this new development is increasingly obscuring tile faint light given off by distant stars.And if scientists cant locate these objects，they cant learn more about them. | 
