(ORDO NEWS) — People around the world are seeing fewer and fewer stars in the night sky. The change in the visibility of stars is associated with an increase in the brightness of the sky by 7-10% per year.
A research team led by Christopher Kiba of the Ruhr University analyzed more than 50,000 naked-eye observations made around the world from 2011 to 2022 as part of the Globe at Night science project.
Over a large part of the earth’s surface, the sky continues to glow with artificial twilight after sunset. This “glow of the sky” is a form of light pollution that has a serious impact on the environment.
The change in skyglow over time has not previously been measured on a global scale. Although it could be measured using satellites, they do not have sufficient accuracy and sensitivity.
The Globe at Night project has been implemented since 2006. Participants look at the night sky and then report which of the eight available star maps best matches what they see.
Each chart shows a sky with different levels of light pollution. The researchers analyzed data from 51,351 participants worldwide, taken on cloudless nights between 2011 and 2022.
To calculate the rate of change in sky brightness from this data, the scientists used a global sky brightness model based on 2014 satellite data.
The researchers found that the change in the number of visible stars could be explained by an increase in the brightness of the night sky.
In Europe, the increase in brightness is 6.5% per year, and in North America it is 10.4%.
“If development continues at this rate, a child born in a place where 250 stars are visible will only be able to see 100 stars there on their 18th birthday,” says Kiba.
Interestingly, at the observer locations, the artificial brightness measured by the satellite decreased slightly (by 0.3% per year in Europe, by 0.8% in North America).
Christopher Kiba believes that the difference between human observations and satellite measurements is likely due to changes in illumination techniques.
“Satellites are most sensitive to light pointing upward towards the sky. But it’s the horizontally emitted light that makes up the bulk of the glow in the sky,” Kiba explains.
“So if advertising and facade lighting become more frequent, larger or brighter, they can have a big impact on sky glow without having much of an impact on satellite imagery.”
Another factor cited by the authors is the widespread shift from orange sodium lamps to white LEDs, which emit much more blue light.
However, the citizen science approach also has its limitations. The number of participants from different regions of the world determines the significance of spatial and temporal trends.
So far, people from North America and Europe have taken part in the experiment, and half of the Asian participants make observations in Japan.
“Most of the data comes from regions of the Earth where skyglow is currently most common. This is useful, but it means we can’t tell much about the change in skyglow in regions with few observations,” Kiba emphasizes.
The researchers draw two main conclusions: on the one hand, the results show that the current lighting policy has not yet resulted in any improvements, at least at the continental level, despite the growing awareness of light pollution.
“On the other hand, we were able to demonstrate that citizen science data represent an important addition to previous measurement methods,” says Kiba.
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