We see less and less stars in the sky

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We see less and less stars in the sky

Observations made between 2011 and 2022 by volunteers around the world through the citizen science platform globe at night reveal a worrying trend: stars in the night sky are becoming harder to see due to rapidly increasing light pollution. The results are published in the journal Science.

The change in visibility of these objects detected by ‘citizen scientists’ is equivalent to an annual increase of 9.6% in sky brightness, a faster rate than satellites indicate and despite policies that try to mitigate the impact of artificial light on our environment.

The increased brightness of the night sky reveals that in a matter of 18 years you go from 250 stars to only about 100

To put it in perspective, and although the data was collected over twelve years, the authors point out that, at this rate, a child born in an area where 250 stars were seen is likely to see about 100 in the same location 18 years later. “The idea behind this comparison is to put the increase in sky brightness in more easily understandable terms,” explains lead author Christopher Kyba, from the Ruhr University of Bochum (Germany), to SINC.

Kyba points out that participants submitted their naked eye observations – 51,351 were evaluated in total – through the Globe at Night program of the US National Science Foundation (NSF) laboratory NOIRLab “and everyone is invited to continue collaborating, as the project is still is running: plus version in EnglishIt is possible to contribute using a Spanish version of the application and there is also another in catalan”.

Everyone is invited to collaborate on the project through ‘Globe at Night’, which has versions in Spanish and Catalan

Christopher Kyba (Ruhr University Bochum)

During the survey, volunteers were asked to compare night sky star maps of various levels of light pollution with what they could see with their own eyes via the online platform.

Sky twice as bright in eight years

According to the results, the brightness of the night sky increased due to artificial light between 7 and 10% per year, which is equivalent to doubling in less than eight years. This increase is much higher than the estimates of the evolution of artificial light emissions (about 2% per year) recorded by satellites.

The increase in brightness detected in the sky is much greater than that indicated by satellites, which often do not see the LED lights that have dominated lighting for the last decade.

From space, these spacecraft can measure global sky brightness with limited resolution and sensitivity and are often blind to the wavelengths of light produced by the modern LED lights that have dominated lighting for the last decade.

In many inhabited places on Earth, the night sky is never completely dark. Instead, it glows with an artificial twilight caused by anthropogenic light scattering in the atmosphere. This type of light pollution, called skyglow, is responsible for the visible glow of the night sky and our ability to see the stars.

A serious problem with solutions

The results of this and other studies confirm the growing problem of light pollution: “It is an extraordinarily serious problem for amateur astronomers, because most people live in highly polluted areas and the situation is rapidly getting worse. Celestial bodies that are faint or difficult to see today are likely to disappear completely from view soon,” warns Kyba.

“Our results cannot be generalized to professional astronomers, because their observatories are located much further away from where our participants participated,” he adds, “but recently a report was published. article in MNRASwhere it is stated that light pollution is a serious threat to professional astronomers”.

To reduce light pollution, it is advisable to light only the necessary area, for the necessary time, use the necessary amount of light and avoid using ultraviolet and blue light

The researcher underlines that the solution to light pollution has been known for many years: “Illuminate only the necessary area, only the necessary time, using the necessary amount of light and avoid using lights with ultraviolet radiation and try to minimize blue light emissions .

Much more light does not improve visibility

“Our collective failure stems from the fact that many or most people who install lights do not follow these good design principles. People often have the idea that more light improves visibility, but in reality this is not true: visibility depends on the same design principles that minimize light pollution”, concludes Kyba, who has analyzed many drawings of lighting.

Example of poorly and well lit stairs in Potsdam (Germany). / Christopher Kyba

Reference:

Christopher CM Kyba et al. “Citizen scientists report rapid global reductions in star visibility from 2011 to 2022”. Science, 2023

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