Kyba and his team applied a model to the NoirLab data, finding that each year the brightness of the sky increased by about 6.5 percent in Europe, 10.4 percent in North America and 7.7 per cent. percent in the rest of the world, with a global average of 9.6 percent. Globe at Night volunteers have also reported that fainter stars are becoming less visible and in some cases even disappearing from the sky. While Kyba was conducting the search for him, a few people contacted him to report that they could no longer distinguish the Pleiades or the famous strip of stars of the Milky Way.
Change is still possible
“At first I was a bit stunned”says Connie Walker, a scientist at NoirLab, director of Globe at Night and co-author of the study. The research results far exceed the 2 percent increase previously estimated by weather satellites, which are completely blind to blue light and have missed an important part of the trend, Walker said. In the last ten years, many cities have switched from yellow high-pressure sodium streetlights to LED models, more energy efficient but also bluer (the eyes of people, and those of some wild animals, are particularly sensitive to blue light at night). The satellites, then, also escape the lights that point sideways, such as those of billboards. In general, brightness builds up from sources like lights installed on the sides of homes or businesses, as well as those on roads, stairs and signs.
While air pollution could partially explain the trend in some areas, there’s no way it’s increasing to such an extent, Kyba says. Also, while an individual volunteer’s ratings may vary or have some inaccuracies, they are negated by averaging the reports submitted by hundreds of thousands of volunteers. Light pollution, concludes the scientist, is the mainly responsible for the disappearance of the stars.
So what can be done to counter the problem? Light pollution comes from many sources, and lighting decisions are made by many different people. Unlike climate change, however, it is not difficult to reverse the trend and the benefits would be felt immediately. For example, using only the minimum amount of light needed, installing timed lights would not be complicated or expensive. It’s just about convince the many thousands of people involved in the decisions on lighting to make better choices.
The Tucson model
Walker and other astronomers fear an entire generation could no longer have access to the starry sky: “As an astronomer, the idea of losing the inspiration that draws people into our field is terrifying. There are millions of people in big cities who are lucky to see Venus and Saturn. They only have the moon”says Teznie Pugh, superintendent of the McDonald Observatory at the University of Texas do Austin and co-chair of the American astronomical society’s committee on light pollution, radio interference and space debris.
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