Twenty-first-century people don't find their way in the dark by looking up at the stars. They use GPS. As kids used to learn in science class, though, GPS itself goes all the way back to the earliest measurements of stellar movements and positions: Thus, at least in principle, 21st-century navigation still depends on the stars.

Nowadays, however, science teachers are having more and more trouble getting this concept across. The problem isn't that the concept is so hard to grasp. The problem is that the stars are so hard to see.

Enter a citizen-science project called GLOBE at Night (www.globeatnight.org). It's designed for families, with special guides for children ages 3-12, but anyone can participate.

The purpose is to record the brightness of the night sky everywhere on the planet, or, conversely, the extent of light pollution. Maybe you've seen the NASA video “Planet Earth at Night.” Using photos from space satellites, it shows the vast splashes of electric light spreading across the developed world.

The GLOBE at Night project does something similar, but it looks up, not down. Each citizen-observer submits information from his/her community — let's say Milford. Inputs collected from observers world-wide yield a map showing the vast areas where artificial light from human settlements blocks clear views of the stars.

Observers identify themselves for the project by their local latitude and longitude. During certain specified winter/spring observation periods, they go outside between 8-10 p.m. and look in the sky to find one of the project's “specimen” constellations: Orion or Leo in the Northern Hemisphere, Leo or the Crux (Cross) in the Southern Hemisphere. They measure the constellation's brightness by comparing it with a set of sample images on the project's website, entering their selected match either via their smart phones during an observation (using a special app), or via their computers later. Observation periods last for 10 nights.

GLOBE at Night has two more observation periods scheduled for 2013: March 31-April 9, and April 29-May 8. Detailed instructions in many languages are available at the website. Why not sign up and see for yourself?

During the seven years the project has run, people in 115 countries have contributed over 83,000 observations. Their inputs have determined not only the locations of light pollution, but their magnitude. Also, the brightness data has been crossed with other datasets to analyze changes in nocturnal wildlife habits, human reproductive effects, weather variation, and more.

Most important are the educational benefits to observers.

1) Recognizing major constellations and learning about latitude/longitude.

2) Awareness that human activities can have a greater impact on Nature than at first seems plausible.

3) A sense of common cause: We share in creating environmental problems, yes, but through projects like Globe at Night we can also share in mapping and analyzing them. Thus, we may share in finding solutions.

4) The curiosity “rush” of science-with Nature, ever mysterious, beckoning just ahead toward one more question, one more answer.