Lights out : city lights are erasing the stars, wasting energy, and hurting wildlife. Find out what's being done to darken the night.

A century ago, stargazers could look up and see a black sky speckled with 2,500 or so twinkling stars. They could easily make out the broad cluster of stars called the Milky Way galaxy, home to our solar system. Today, only 1 in 10 Americans can see this vision of the universe. And on a typical evening, most city dwellers glimpse just a few dozen stars. An eerie, orange sky blots out the rest.

The switch from dark nights to glowing skies began during the early 1900s, when Thomas Alva Edison invented a long-lasting light bulb that was bright enough to replace dim gas and kerosene lamps. Power lines began to snake their way across the U.S., electrifying the nation. At the same time, the country's population skyrocketed from 76 million in 1900 to over 300 million today. The result: More people living in sprawling cities and suburbs are slowly turning night into day.

Thirty years ago, astronomers were the first to express alarm about the artificial light that was obstructing the stars and planets that they study. Now, ecologists, or scientists that study animals and their environment, are also worried about the effects of this so-called light pollution.

NIGHT LIGHTS

Light pollution is caused by excess light beamed up into the sky by office buildings, street lamps, headlights, billboards, houses, and other sources.

The artificial light reflects off low clouds, or moisture and dust in the air, creating "sky glow," says Travis Longcore, an ecologist with the Urban Wildlands Group, a conservation organization in Los Angeles, California. Roughly one third of all lighting in the U.S. illuminates the sky rather than its intended target. Not only is this light wasted, but it is also damaging to the environment. According to the U.S. Department of Energy, coal-burning power plants generate 51 percent of the country's electricity. These power plants pollute the air with sulfur dioxide (a component of harmful acid rain), carbon dioxide (a heat-trapping greenhouse gas that is causing Earth's average temperature to rise), and nitrogen oxides (gases that create smog).

Wasted lighting also costs the U.S. approximately $10 billion per year in energy expenses, according to the International Dark-Sky Association (IDA), an environmental group in Tucson, Arizona.

FATAL FLIGHTS

Biologists have shown that our lit-up world also takes a toll on wildlife. Light pollution disrupts the way some animals behave. "Over millions of years, animals have come to depend on seasonal, monthly, and daily patterns of light and dark," says Longcore. "Only recently have humans lit up the night on a global scale."

Artificial lighting takes the largest toll on birds. Approximately 450 species, including most songbirds and many shorebirds, take to the wing at night for their twice-yearly migrations across North America. Like a captain at sea, they use the constellations and the moon for navigation. "When birds fly through brightly lit areas, they become disoriented," says Michael Mesure, executive director of the Fatal Light Awareness Program (FLAP), a Toronto-based environmental organization. As a result, the birds often crash into brilliantly lit buildings or broadcast towers, and die.

Sometimes whole flocks perish. According to Mesure, 50,000 birds died at Robins Air Force Base in Georgia over two nights in 1954 when they were drawn to upward-pointing spotlights. Disoriented by the bright lights, the birds flew straight into the ground. And in 1981, over 10,00O birds slammed into floodlit smokestacks at Canada's Hydrox Generating Plant near Kingston, Ontario.

ANIMALS AT RISK

Artificial lights take their toll on other nocturnal animals too. Sea turtles, which come ashore at night to lay their eggs, are very sensitive to light. Few females will venture onto lit-up beaches, like those along Florida's coastline, to nest. And newly hatched turtles need a dark night sky to orient themselves toward the sea, but artificial lights from beachfront properties lure them away. Biologists have found hatchlings wandering aimlessly on beaches, city streets, and in hotel parking lots. Once daylight arrives, the lost turtles are vulnerable to daytime predators and risk getting hit by cars as people travel to work and school.

Another study found that artificial lighting causes problems for salamanders. These nocturnal amphibians rely on the darkness of night to protect themselves from hungry predators. When exposed to artificial lighting, they remain hidden underneath leaves, waiting for later, darker hours before emerging for a meal. That might not sound like such a big deal, but "the later they come out, the less food they may be able to eat," says Sharon Wise, an ecologist at Utica College in New York, who was involved in the study.

Wise's colleague, Bryant Buchanan, had a similarly alarming finding: He discovered that artificial lights at night make nocturnal frogs stop calling to one another. If the males aren't calling, the females can't find mates to breed with, and the animals disappear.

TAKING BACK NIGHTTIME

A movement is afoot to return visible stars to the sky and to protect night creatures. Hundreds of communities around the U.S. and five states have passed lighting ordinances. "Light pollution is not the inevitable result of having well-lit streets and cities," says David Crawford, executive director of IDA. It's a relatively easy problem to fix, he says.

Miami and other cities are replacing inefficient streetlights with ones that shine directly downward. Some new state and county laws also require companies and citizens to shield fixtures so they don't "leak" light into the sky. And many towns and businesses are beginning to turn off unnecessary lights in parking lots and office buildings overnight. "At the flick of a switch, this problem could disappear," says Mesure.

HANDS-ON SCIENCE (No Lab Required)

PREDICT

The purpose of outdoor lighting is to make it easier for people to see at night. But many light fixtures are open on the top and sides, sending light in every direction. Covering the top of a light source can focus light where it's needed most and help reduce light pollution. Which material do you think will make a more effective shield for a light--glass, paper, cardboard, or tin foil?

MATERIALS

lined notebook paper * pen * small flashlight * glass plate * paper plate * paper bag *

DIRECTIONS

1 Lay a blank sheet of lined notebook paper on top of your desk.

2 Write your name on a line in the center of the sheet of paper.

3 Turn on the flashlight and stand it upright on the paper with its light shining toward the ceiling. Position the base of the flashlight to about 4 centimeters (1.5 inches) below your name.

4 When everyone's flashlight is set up, your teacher will close all window blinds and turn off the classroom lights.

5 Look at the piece of paper. Note whether or not you can easily read your name. Imagine that the piece of paper is a street and the flashlight is a streetlight. Consider whether this type of lighting would be very helpful to people walking on the street. Where does most of the light actually end up?

6 Now hold the glass plate about 4 centimeters (1.5 inches) above the flashlight. Note how well you can read your name and how much light shines up at the ceiling.

7 Repeat Step 6 using the paper plate, paper bag, and tin foil in place of the glass plate.

CONCLUSIONS

1. Which shield made your name the most visible?

2. Which material blocked the most amount of light from reaching the ceiling?

3. Based on your observations, how does shielding a light help decrease light pollution? How does it make objects on the ground more visible?

ANSWERS

1. The paper plate made your name the most visible.

2. The tin foil blocked the most amount of light from reaching the ceiling.

3. Shielding a light helps decrease light pollution by blocking light that would shine up into the night sky. Shielding a light focuses light on the ground, making objects on the ground more visible.

PRE-READING PROMPTS

Jump-start your lesson with these pre-reading questions:

* According to the U.S. Department of Energy, almost 25 percent of the energy used in American homes is used for lighting and appliances. Approximately how much of the energy used for lighting is considered Wasted energy? Why?

* There are seven species of sea turtles in the world, six of which are considered endangered or threatened species. How does artificial lighting affect these species' survival?

CRITICAL THINKING:

* As a class, come up with a list of l0 benefits and a list of 10 risks of using artificial lighting. Then, have students brainstorm to come up with solutions on how they could continue to use artificial lighting and reduce light pollution at the same time.

CROSS-CURRICULAR CONNECTIDNS:

SOCIAL STUDIES: Create a map of your hometown that features some of the town's major landmarks or structures. As a class, pinpoint which areas may be more significant contributors to light pollution than others. Then, hold a discussion on why those areas may be producing more light pollution than others, and why the usage of artificial lights in those areas can or cannot be reduced. For help on how to identify sources of light pollution, visit: www.astrosociety.org/education/publications/tnl/44/lightpoll2.html

RESOURCES

* For an article on light pollution and to see a diagram comparing different types of light bulbs, read "Turn Down the Lights," by Eric Scigliano, Discover, July 2003. You can find the article online at:

www.discover.comlissues/jul-03/features/featlights/

* This Web site from the Florida Fish and Wildlife Conservation Commission has answers to frequently asked questions about how artificial lighting affects sea turtle hatchlings: http://research.myfwc.com/features/view_article.asp?id=2156

* Visit the Web site of the Urban Wildlands Group to find out more about the ecological effects of artificial lighting. Go to: www.urbanwildlands.org

* This Science NetLinks Web site has a lesson plan on light pollution: www.sciencenetlinks.com/lessons.cfm?doclD=242

* To learn more about Thomas Alva Edison and his inventions, visit this Rutgers University Web site: http://edison.rutgers.edu/

CHECK FOR UNDERSTANDING

DIRECTIONS: Answer the following in complete sentences.

1. What causes light pollution?

2. Why does the sky glow from light pollution?

3. How do coal-burning power plants damage the environment?

4. How does light pollution affect nocturnal salamanders?

5. What are some communities doing to help fight light pollution?

ANSWERS

1. Light pollution is caused by excess light beamed up into the sky by street lamps, headlights, billboards, office buildings, houses, and other sources.

2. As artificial light beams up into the sky, it reflects off low clouds, or moisture and dust in the air, creating "sky glow."

8. Coal-burning power plants generate 51 percent of the country's electricity. These power plants pollute the air with sulfur dioxide (a component of acid rain), carbon dioxide (a heat-trapping greenhouse gas), and nitrogen oxides (gases that create smog).

4. Nocturnal salamanders rely on the darkness of night to protect them from predators. When exposed to artificial lighting, they remain hidden underneath leaves and wait for later, darker hours before emerging for a meal. The later they come out, the less food they may be able to eat.

5. Some communities are replacing inefficient streetlights with ones that shine directly downward. Some new state and county laws also require companies and citizens to shield fixtures so they don't "leak" light into the sky. And many towns and businesses are beginning to turn off unnecessary lights in parking lots and office buildings overnight.