On a moonless night this month, you can look up at Orion, count the visible stars in the constellation — if there are any — and make a report online for a worldwide survey of light pollution, hosted by the National Optical Astronomy Observatory.
Stargazers of all ages are invited to participate, tonight through March 16, sending their measurements to the GLOBE at Night Web site. Orion will be in the southern sky at 8 p.m. around the world, looking much like an hourglass at arm's length, a couple of fists above the horizon.
Participants in the survey can record their latitude and longitude, then match the brightness of Orion with online charts of stellar magnitude, reporting the brightness or faintness of the stars.
This year is GLOBE at Night's fifth annual citizen-science campaign. Last year, 15,300 observations were sent in from 70 countries, mostly from children in the U.S., Europe and Chile. Twenty percent of the data came from a school district in South Bend, Ind., where students presented their findings to city officials.
"You know how sometimes it's not until you do something that you understand how important it can be?" asked Connie Walker, an astronomer who directs the campaign. "We want to put people in a position where they understand light pollution. They might become more socially conscious about wasted energy and what they can do about it."
GLOBE at Night chose early March for the survey, Walker said, because children everywhere are in school this time of year. Young or old, the survey participants can take one measurement, she said, or send in multiple observations from points at least 0.6 mile apart, on the same night or different nights, between 8 and 10 p.m.
"If you want to make the best use of your time, you can measure the sky above your town as if on a grid map or along the spokes of a wheel," Walker said.
Light pollution is a man-made phenomenon. It is the artificial light from cars, streetlights, parking lots, billboards, stadiums, office buildings and homes that leaks sideways or upward into the night sky, dimming the stars. Light pollution wastes energy and money, disrupts sleep, confuses wildlife and makes it hard for astronomers to study the skies.
"Many urban dwellers have never experienced the wonderment of pristinely dark skies and maybe never will," Walker said.
Walker and her observatory are members of the International Dark Sky Association, a Tucson, Ariz.-based nonprofit group that advocates for federal, state and local regulations to reduce light pollution. Streetlights, for example, can be shielded so that the light points directly downward. Interior lighting in office buildings can be turned off at night or placed on sensors. Outdoor lights at homes can be outfitted with low-wattage bulbs.
According to the observatory, only one out of three Americans can see the Milky Way galaxy arching across the dark night sky. Sky glow from cities dims the stars all over the world. The glow is visible on the horizon in rural areas as far as 200 miles away.
Hundreds of stars are visible in Orion in a magnitude 7 night sky, as might be the case in a national park. At that magnitude, 14,000 stars can be seen across the night sky. By comparison, only two stars are visible in Orion in a magnitude 1 sky, as in New York City. Only 10 stars can be seen across an entire magnitude 1 night sky.