And it doesn’t take much: In one recent study of Western Snowy Plovers, Longcore and his colleagues found that even a small amount of artificial light-about the extra brightness of a half-moon in the sky-was enough to discourage the threatened shorebirds from roosting at a given site. Longcore, who has studied the ecological impacts of artificial lighting for more than 20 years, says sky brightness can affect avians and other animals in a number of ways, from drawing migrating birds off-course and into dangerous cityscapes to changing when and where they lay their eggs. Humans may miss seeing constellations, and there is strong evidence that light pollution negatively impacts sleep and overall health, but for other animals the impact can be even more dire. “The super interesting thing about this paper is that it shows how much the satellites are missing,” says Travis Longcore, a light pollution researcher at UCLA who was not involved in the study. As more lights around the world are replaced by blue-skewed LEDs, the gap widens between what satellites perceive and the reality of sky brightness. Satellites currently in orbit also do a poor job capturing blue-hued light. Because of the way light scatters through the atmosphere, Kyba says, lights that shine sideways contribute the most to overall sky brightness. That leaves out many sources of illumination like signs and house lights that cast their glow to the side. First, earth-orbiting satellites are best at capturing lights that either point straight up or straight down-and reflect back up-through the atmosphere. Satellites are likely to underestimate the true extent of artificial light at night for at least two reasons. The findings paint a much starker picture of light pollution than many earlier estimates, including Kyba’s own, which relied on satellite measurements. Put another way, a child born tonight under a sky with 250 visible stars would only be able to see about 100 by their 18th birthday. That means an overall doubling of sky brightness every seven years. Making use of a massive dataset of community scientist observations of visible stars, Kyba’s analysis suggests that between 20, night skies in North America and Europe brightened by almost 10 percent each year. “I really did not expect that the results were going to be as bad as we saw.” “I was very shocked,” says Christopher Kyba, a Canadian physicist at the German Research Center for Geosciences and first author of the paper. According to a study published in Science in January, light pollution is having an even bigger effect on night skies than previously measured. While on a very dark, clear night, most people could expect to see at least a couple thousand stars, artificial light is making it harder to see the stars from nearly everywhere on Earth, with potential consequences for birds, humans and many other species. If you’re one for wishing on a lucky star, you may have noticed your options are dwindling.
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