Light Pollution Is Blotting Out the Starry Night Faster Than Ever

Since the industrial age began, light pollution has slowly transformed the night sky into a brighter scene that increasingly obscures our view of the stars, constellations, and other planets. Artificial lighting emanating from streetlamps, lit up buildings, dazzling advertisements, and a host of other sources can all cause an excess of luminescence that lingers into the night and produces what scientists call “skyglow.” Nearly a third of the world—including 80 percent of Americans—is unable to properly see the massive glowing arc of the Milky Way galaxy due to skyglow. None of this is new, but it’s happening at an astonishingly faster rate that we thought possible.

A new study run by an international team of researchers has found that light pollution is causing sky brightness to increase about 7 to 10 percent every year—faster than the 2 percent per year increase that satellite measurements have originally suggested. The average human who could see about 250 stars in the night sky today will probably only see about 100 stars in less than two decades.

The findings, published Jan. 19 in Science, were pulled together from an analysis of data from Globe at Night: a collection of 51,351 naked-eye observations made by citizen scientists scattered in 19,262 locations around the world, from 2011 to 2022. North America’s increase in skyglow seems to be the worst among the world’s continents, ticking up by roughly 10.4 percent every year.

The disappearance of the night sky’s starry view is more than a sentimental loss. Light pollution’s negative effects on wildlife has been well-documented. Newborn sea turtles, for example, rely on stars as a literal lodestar to tell them to head for the ocean after they hatch. Other animals need the veil of the night to hide from predators. Many, including humans, rely on a dark night to help them regulate their own sleep patterns that help modulate a host of different physiological behaviors.

Moreover, astronomers employing ground-based instruments have found it more and more difficult to do their research thanks to a brighter night sky.

Though the study included participation around the world, the majority of observations were made in North America and Europe—which means the progression of light pollution in other parts of the world is not as well known. The authors of the study note that sky brightening is likely occurring faster in developing parts of the world, thanks perhaps in great part to the modern day popularity of LED lights for outdoor lighting.

Ultimately, however, the study’s biggest impact may not really be in its impact at all, but its methodology. The inclusion of over 50,000 participants in a citizen science project is remarkable—and it points to the potential of amassing as much support for implementing solutions that could help reduce skyglow across the globe.

Those solutions, however, really all converge on the same approach: reducing artificial lighting. And it’s not yet clear whether there is enough appetite from the public to pass aggressive policies. In an accompanying essay in Science, Spanish astronomers Fabio Falchi and Salvador Bará wrote: “Most people associate artificial light with road safety and personal security, connections that are not well supported by evidence.” Eradicating light pollution might actually require a bigger rethinking of our relationship to light itself.