A team of researchers investigating tens of thousands of citizen science observations of the night sky found that stars in the night sky are rapidly becoming harder to see due to human light pollution.
The team pored over 51,351 observations made around the world from 2011 to 2022 as part of the Globe at Night project run by NOIRLab. They found that stars are becoming harder to see, which the researchers suggest is due to the proliferation of human light pollution in the last decade.
According to the analysis, the night sky got 9.6% brighter each year from 2011 to 2022, meaning some dimmer stars would disappear altogether for many stargazers. “A location with 250 visible stars would see that number reduce to 100 visible stars over the same period,” the study explains. The research is published today in Science.
“The main finding is that the visibility of stars is decreasing at a remarkably fast rate — faster than we had anticipated based on satellite data and population growth, for example,” said Christopher Kyba, a researcher at Ruhr-Universität Bochum and Deutsches GeoForschungsZentrum Potsdam, in an email to Gizmodo. “It’s a sign that the efforts that exist to control light to date are not working, at least when considered on continental scales.”
Human light causes “skyglow,” a brightening of the night sky, which makes it difficult for Earth-based observers to see the more distant (and often faint) light from stars. The team noted that the advent of LED (light-emitting diode) lights may have contributed to the increase in light pollution.
“Since LEDs allow more light to be produced for the same amount of energy, one result of their development has been increased light use,” Kyba said. While the issue is primarily human’s overuse of LEDs, rather than the lights themselves, Kyba added that “the method they use to produce white ends up emitting a lot of blue light, and blue light is the most problematic for sky brightness.”
To better track what sort of light is contributing to skyglow, Kyba’s team has made an app for citizen scientists, amateur astronomers, and other interested parties to count and classify light sources. The Nightlights app is free and can be accessed here.
Fabio Falchi, a physicist specializing in light pollution at the the Universidade de Santiago de Compostela and a member of the Light Pollution Science and Technology Institute, and Salvador Bará, a researcher at the university, wrote a Perspectives article to accompany the analysis.
“Perhaps the most important message that the scientific community should glean from the Kyba et al. study is that light pollution is increasing, notwithstanding the countermeasures purportedly put in operation to limit it,” they wrote. “Awareness must greatly increase for artificial light at night to be perceived not as an always-positive thing, but as the pollutant it really is.”
Kyba suggested that using only the necessary amount of light to see where and when it’s needed would be a good step in reducing light pollution, as well as avoiding very cold white lights and those that produce ultraviolet light.
Besides harming our ability to observe the night sky, light pollution can have damaging effects for life on Earth. Creatures that rely on the ordinary patterns of light can suffer when artificial light is introduced to their environment.
Light sources in orbit — including satellite constellations like Elon Musk’s Starlink — have also proven a vexing problem for astronomers.
Exactly how light sources are managed in the future remains to be seen, but it’s clear that something needs to be done — both for our world and for seeing the light beyond it.
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