Fewer and fewer stars visible in the night sky

That’s according to an analysis published in the journal “Science”, for which scientists evaluated the observations of some 51,300 people – mainly in Europe and North America – from 2011 to 2022.

The researchers, led by Christopher Kyba, an expert at the GFZ German Research Center for Geosciences in Potsdam and the Ruhr University in Bochum, were surprised and concerned: “The rate at which stars become invisible to humans in urban environments is dramatic,” Kyba stressed. .

Artificial brightening of the night sky
Light pollution refers to the artificial illumination of the night sky by light sources such as street lights, illuminated facades, buildings, parks or illuminated digital advertising spaces. The result: Stars are not or hardly recognizable in the cleared sky. The researchers have now discovered that global sky clarity is increasing by an average of 9.6 percent per year. Brightness increased by 6.5 percent per year in Europe and 10.4 percent in North America.

If we stick to the global average of 9.6 percent more brightness in the sky per year, this means that a child born in a place where 250 stars are visible at birth will not be able to see 100 stars there until his 18th birthday. as Kyba said.

Negative consequences in many areas
The problem has been increasing rapidly for some time, the expert continued. If the sky shines in an artificial twilight long after sunset, it has negative consequences for stargazing and astronomy – and not only that: the scientists warn that there are also serious consequences for the environment. Many behaviors and physiological processes of living beings are determined by diurnal and seasonal rhythms – and are therefore influenced by light, explains American co-author Constance Walker. “The skyglow affects both diurnal and nocturnal animals and also destroys an important part of our cultural heritage.”

Comparison with cards
About the project’s methodology: The 50,000 or so “citizen scientists” observed the night sky with the naked eye and filled out an online form to indicate which of the eight star charts best matched what they had seen. Each map showed the sky with different levels of light pollution. The information thus represents 19,262 locations worldwide, including nearly 3,700 locations in Europe and nearly 9,500 in North America. In addition, a sky brightness model based on satellite data from 2014 was used.

“Disappointingly few” stars in metropolitan areas
The Association of Star Friends — members include amateur astronomers, public observatories, and planetariums as well — pointed out that even today in densely populated areas, it’s almost impossible to see the starry sky with the naked eye. In agglomerations such as Germany’s Ruhr and in metropolitan areas, “unfortunately, you see disappointingly little,” said astronomer Andreas Hänel, spokesman for the Astronomical Society’s Light Pollution Commission. Berlin’s light clock extends so far that it can be seen up to 80 kilometers away. There are more and more local projects and measures to reduce artificial light, but they are not enough.

The association demanded that environmental protection should also include the air and required binding limit values. In Germany, the environmental organization BUND also warned of negative effects on the ecosystem, on flora and fauna. In humans, a disturbed day-night rhythm due to increasing nighttime lighting can suppress the production of the “sleep hormone” melatonin and cause sleep disturbances. Hänel believes that if there is no real rethinking, “there will only be a few places in the future where you have to travel far to see the stars properly”.