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(2009-03-10 15:57:46)






分类: 世界网文摘译




1 Light Night, Dark Stars



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 Research (UCAR) in Boulder, Colo 1 . But when people are surrounded by city lights, he says, they're lucky to see 150 stars.



If you've ever driven toward a big city at night and seen its glow from a great distance, you've 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 stargazing2 difficult.


Dust and particles of pollution from factories and industries worsen the effects of 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. "


Hazy skies also make it far more difficult for astronomers to do their jobs.


Cities are getting larger. Suburbs are growing in once dark, rural areas. Light from all this new development is increasingly obscuring the faint light given off by distant stars. And if scientists can't locate these objects, they can't learn more about them.


Light pollution doesn't only affect star visibility. It can harm wildlife too. It's clear that artificial light can attract animals, making them go off course3. There's increasing evidence, for example, that migrating birds use sunsets and sunrises to help find their way, says Sydney Gauthreaux Jr., a scientist at Clemson University in South Carolina. "When light occurs at night," he says, "it has a very disruptive influence. " Sometimes birds fly into lighted towers, high-rises, and cables from radio and television towers. Experts estimate that millions of birds die this way every year.



2 Hair Detectives


Scientists have found a way to use hair to figure out where a person is from and where that person has been. The finding could help solve crimes, among other useful applications.



Water is central to the new technique. Our bodies break water down into its parts: hydrogen and oxygen. Atoms of these two elements end up in our tissues and hair.



But not all water is the same. Hydrogen and oxygen atoms can vary in how much they weigh. Different forms of a single element are called isotopes. And depending on where you live, tap Water1 contains unique proportions of the heavier and lighter isotopes of hydrogen and oxygen.



Might hair record these watery quirks2? That's what James R. Ehleringer, an environmental scientist at the University of Utah in Salt Lake City3, wondered.



To find out, he and his colleagues collected hair from barbers and hair stylists in 65 cities in 18 states across the United States. The researchers assumed that the hair they collected came from people who lived in the area.



Even though people drink a lot of bottled water these days, the scientists found that hair overwhelmingly reflected the concentrations4of hydrogen and oxygen isotopes in local tap water. That's probably because people usually cook their food in the local water. What's more, most of the other liquids people drink including milk and soft drinks contain large amounts of water that also come from sources within their region.



Scientists already knew how the composition of water varies throughout the country. Ehleringer and colleagues combined that information with their results to predict the composition of hair in people from different regions. One hair sample used in Ehleringer's study came from a man who had recently moved from Beijing, China, to Salt Lake City. As his hair grew, it reflected his change in location.



The new technique can't point to exactly where a person is from, because similar types of water appear in different regions that span a broad area. But authorities can now use the information to analyze hair samples from criminals or crime victims and narrow their search for clues.



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