Star visibility erodes rapidly as night sky gets brighter: study

Star visibility erodes rapidly as night sky gets brighter: study

The rapid growth of light pollution (sky glare) makes it more difficult to see the stars in the night sky with the naked eye.

The rapid growth of light pollution (sky glare) makes it more difficult to see the stars in the night sky with the naked eye.

Light pollution is growing rapidly, and in some places the number of stars visible to the naked eye in the night sky is more than halving in less than 20 years, according to a study published Thursday.

The researchers, whose findings were published in the journal ScienceHe said the increase in light pollution — skyglow — they found was much greater than that measured by satellite observations of Earth at night.

To study the change in global sky brightness due to artificial light, the researchers used stellar observations from 2011 to 2022 submitted by more than 51,000 “citizen scientists” from around the world.

Participants in the “Globe at Night” project run by the US National Optical and Infrared Astronomy Research Laboratory were given star maps and asked to compare them to the night sky at their location.

The reported change in the number of visible stars was equivalent to an annual increase in sky brightness of 9.6 percent per year, averaged over the locations of the participants, the researchers said.

Over an 18-year period, given that change in star brightness, a location with 250 visible stars would see that number reduced to 100.

Credit: NOIRLab

Most naked-eye star observations came from Europe and the United States, said Christopher Kyba, one of the study authors, but there was also good participation from Uruguay, South Africa and Japan.

“The global trend in sky brightness that we measured probably underestimates the trend in countries with the fastest increases in economic development, because the rate of change in light output is highest there,” the researchers said.

The study coincided with the replacement of many outdoor lights with light-emitting diodes (LEDs), but the researchers said the impact on sky brightness of the transition to LEDs is unclear.

“Some researchers have predicted that it will be beneficial; others, that it could be detrimental due to spectral changes or a rebound effect, in which the high luminous efficacy of LEDs causes more or brighter lights to be installed or to last longer operating hours”, they said.

According to the study, the global market share of LEDs for new general lighting grew from less than one percent in 2011 to 47 percent in 2019.

“The visibility of stars is rapidly deteriorating, despite (or perhaps because of) the introduction of LEDs in outdoor lighting applications,” the researchers said.

“Existing lighting policies are not preventing increases in sky brightness, at least on a continental and global scale.”

‘Confronted with the cosmos’

Kyba, a physicist at the German Research Center for Geosciences, told AFP that while the team was able to assess the erosion of star visibility due to sky brightness, not much research has been done on its ecological impact.

“There is tons of research on light shining directly on animals and plants,” he said. “But it’s really hard to do experiments on the impact of sky brightness.

“You’re not going to do something like turn off New York City and see what happens in the East River.”

Science aside, light pollution has changed the character of the night sky.

“Throughout all of human history, when people took to the streets at night, they were facing the cosmos, at least on clear moonless nights,” Kyba said.

“You would walk outside and there are the stars, there is the Milky Way. It is there and it lights you up,” he said.

“And now that’s like a really unusual experience,” he said. “It sure makes a difference to us as people who don’t have this experience that used to be a very universal experience.”

The Globe at Night campaign hosts an interactive data map at and is seeking volunteers to collect more observations in 2023.

More information:
Christopher CM Kyba, citizen scientists report rapid global reductions in the visibility of stars from 2011 to 2022, Science (2023). DOI: 10.1126/science.abq7781.

Fabio Falchi et al, Light pollution is skyrocketing, Science (2023). DOI: 10.1126/science.adf4952 ,

More information about “Globe at Night” can be found here.

© 2023 AFP

Citation: Visibility of stars erodes rapidly as night sky gets brighter: study (January 22, 2023) accessed January 22, 2023 at star-visibility-eroding-rapidly-night.html

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