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SCIENCE FILE: An exploration of issues and trends affecting science, medicine and the environment.

Q: How many stars can a person see at night with the naked eye?

A: Under ideal conditions, about 3,000 stars should be visible at night with the unaided eye, but many factors can reduce this number, including: a full moon (the sunlight reflected from the moon’s surface brightens the entire sky and obscures fainter stars); artificial lights of towns and cities (that’s why the telescopes on Mt. Wilson near Los Angeles are not as effective as they might be); smoke from fires; dust kicked up by wind, and high humidity. And, of course, clouds can block them out altogether.

Source: S. George Djorgovski, associate professor of astronomy at Caltech


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