SCIENCE THURSDAY -- June 7, 2012 at 4:10 PM EDT
Where Have All the Stars Gone?
The thrill of gazing into a night sky packed with stars, constellations and a stretch of our Milky Way galaxy is primal and timeless -- and it's become increasingly rare. Skyglow from city lights can travel up to 200 miles, which means even in the far outskirts of a city, light pollution can spoil the stars. In fact, it's not uncommon for children to be only exposed to stars through a planetarium, said Debra Elmegreen, professor of astronomy at Vassar College.
For astronomers like Elmegreen, who is also president of the American Astronomical Society, light pollution is a heartwrenching reality.
"I don't see how you can really appreciate or connect to something bigger than ourselves here on Earth if you can't look at the sky and know that it's there," she said. "I think that we would have evolved differently if our only perspective was the Earth."
Recently, Hari Sreenivasan spoke with Elmegreen about the effects of light pollution across different cities, the influence of handheld astronomy apps on smartphones and the darkest places on Earth -- remote regions in South Africa, Australia and Chile top the list, she says. (See the video at the top of this post.)
Also, take a look at this map from the NOAA's National Geophysical Data Center, which maps light pollution worldwide. Zoom in to see how your region fares.
But it's not necessarily a lost cause, said Scott Kardel of the International Dark Sky Association. Many towns and parks are working to reclaim their view of the stars with plans that involve reducing the amount of light used at night, directing the lights downward and relying increasingly on low-sodium and lower temperature lights. Places like Flagstaff, Arizona boast the ability to see the Milky Way from downtown. Hungary and the United Kingdom have declared dark sky preserve areas.
Electric light at night does more than dampen the stars. Light pollution may also contribute to chronic sleep deprivation and cause unwanted physiological changes, said Steve Lockley, who studies sleep and artificial light at Harvard Medical School.
Electric light, whether it's from a streetlight, computer, television or smart phone, signals to our body that it's daytime, raising our heart rate and our body temperature, he says. Even with our eyes closed, light sends signals to our brain to stay alert. Sleep with the light on, and your brain and body simply don't rest as well. And a lack of deep sleep contributes to a host of other health problems, including increased rates of obesity, diabetes, and depression, Lockley said.
"The eyes don't care where the light is coming from," Lockley said. "Light is light."
Many studies have shown that exposure to artificial light at night inhibits the production of melatonin, the hormone that signals to the brain that it's nighttime and slows down tumor growth in animal studies. This may increase the risk of certain cancers among night workers or people who self-identify as "night people." Richard Stevens, a cancer epidemiologist at the University of Connecticut, has studied this since the 1980s. This exposure to light at night creates a disruption in our circadian rhythm, throwing off our timing and production of hormones and other processes.
"It's not that light is bad," Stevens said. "It's a matter of timing. We're getting out of sync."
This applies to wildlife too, said Travis Longcore, science director at the Urban Wildlands Group. Like humans, animals and plants evolved to rely on a regular light cycle to set their own circadian rhythms. These light cycles time growth and migration to mating. But light at night can disrupt these patterns. Sea turtles, which wander toward the brightest horizon after hatching, have been known to get confused by a lit window or a parking lot, and struck by cars or eaten by predators. Songbirds too, which are drawn to light from radio towers or skyscrapers, are victims, Longcore said. An estimated 6.8 million birds in the United States and Canada die by crashing into communication towers, according to a study authored by Longcore and published in the journal PLOS 1.
"At some point we [humans] say, 'It's dark.' But there's a whole order of magnitude of light that those species are reacting to," he said.