We humans need artificial light sources to find our way in the dark of night. But apparently, there is such a thing as too much light, which leads to light pollution, a “side effect” of the industrial civilization. This is when the use of artificial light is excessive, misdirected and/or obtrusive—a practice that is common in highly urbanized areas. Light pollution is something most people aren’t concerned with because it’s not as negatively perceived as other types of pollution. For example, air pollution has a very bad reputation because its symptoms are obvious (smog, haze, etc.) and affects us directly (difficulty in breathing). On the other hand, light pollution is much more subtle: It’s a waste of energy, disturbs and alters ecosystems, blocks our view of stars at night and is linked to circadian disruption in humans. This is why the Complutense University of Madrid, in partnership with various organizations, including NASA, is leading a crowdsourcing project called Cities at Night to raise awareness on light pollution. The campaign invites people all over the world to identify, locate and geo-reference images of different portions of the Earth taken by astronauts from the International Space Station in an effort to catalog the vast collection. By studying satellite images and those sent from the ISS, the goal of the researchers is to “measure the efficiency of lighting in many cities on the planet.”According to NASA, the project has three “citizen science” components: Dark Skies, Night Cities and Lost at Night. The first one “asks people to sort images into those of cities, stars and other objects. The simplest of the three projects, it requires no specific expertise.” Meanwhile, the second needs “citizen scientists [to] use their knowledge of local geography to identify points in night images and match them to positions on maps “ Finally, the third “requires the most skill, seeking to identify cities in images encompassing a circle 310 miles around.” Determining which areas are cause for concern is the first step in combating light pollution. The Web site, www.citiesatnight.org, says that it has “hundreds of thousands of images on file to discover” dating back to 2003. “Light pollution causes serious problems. Its effects can be measured from the inside of our bedroom to hundreds of kilometers away,” the site explains. “The light destroys the essence of the evening darkness. Humans have an ancestral fear of the dark, but too much light produces very negative effects on the ecosystem and our health.”