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Seeing Stars
If you look up at a clear night sky when you are far away from cities, you will probably see over 2000 stars. If you look at the night sky when you are in the middle of a large city, you might see only 10 stars. Why?
Stars shine constantly. We see them only at night because they are brighter than the night sky. The daytime sky is very bright, so no stars are visible. Why can you not see a lot of stars from a large city at night? All the city lights make the night sky brighter. We see only the stars that shine brighter than the night sky.
Light Pollution
Many cities create much more light at night than people really need. Bright, flashing billboards and store signs create light when most people are at home sleeping. Some office buildings keep the lights on all night. Light that we do not really need is called light pollution. Without light pollution, people could see many more stars from cities.
How important is it to see lots of stars at night? For astronomers, it is very important. They use telescopes in observatories to study stars. Some observatories were built many years ago, in places far away from bright lights. Over time, cities have been created close to some of these observatories. As the cities grow, they create more light pollution. Then astronomers at the observatories can see fewer stars.
Reducing Light Pollution Is Not Just About Seeing Stars
People who want to reduce light pollution point out that turning off unnecessary lights at night means people save money on electricity. Generating electricity can create air pollution, so using less electricity for light is good for the environment. One astronomer gives another reason for reducing light pollution. “I believe every child should have a chance to see the night sky filled with thousands of stars,” she said. “It helps them understand that we are part of a huge universe that is amazing and, in many ways, still a fascinating mystery.”
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