Bringing Back the Stars: A Streetlight Test

Where Did the Stars Go?

1The astronomy club at Cedar Hollow Middle School meets once a month at the county observatory, 20 km outside town. On a clear, moonless night there, members can see the faint band of the Milky Way. From the school field in town, they can pick out only a few of the brightest stars. The difference comes from light pollution: artificial light that shines up into the sky, scatters off tiny particles in the air and makes the night sky glow.

2Light pollution is a human impact on the environment. Many animals that are active at night rely on darkness or on the light of the moon and stars. Bright lights near beaches can lead some newly hatched sea turtles away from the ocean, and brightly lit buildings can confuse some birds that migrate at night. Light that shines into the sky also wastes electricity, which costs money.

3To monitor the problem, the club used a star count. On clear nights with no moon, at 9 p.m., members looked at the same group of stars, the Great Square of Pegasus, and counted every star they could see inside the square. They counted at four sites at different distances from downtown and repeated the counts on three nights in October.

4Next, the club asked the town to test a design solution on Maple Street, which had 10 old streetlights. Each old lamp was an uncovered glass globe that sent light in all directions, including straight up. The town replaced them with LED lamps inside shields that aim the light downward. Before and after the change, the club counted stars from the end of Maple Street and used a light meter to measure how much light reached the sidewalk, in units called lux.

5The town listed what the new lamps should do: reduce the glow in the sky, use less energy and keep at least 10 lux on the sidewalk, its safety rule for people walking at night. The town also set limits. The lamps had to fit on the existing poles, and the whole project could cost no more than $6,000.