Light pollution has increased much more than previously thought. A worldwide analysis with observations by more than 50,000 people shows that this has a massive impact on the visibility of stars. Experts also warn of risks to the environment and ecosystem.
There used to be a lot more stars in the sky, didn’t they? This impression is not misleading. Light pollution in the night sky is increasing much more than previously expected and is causing star visibility to drop drastically. This is the result of an analysis published in the journal “Science”, for which scientists evaluated the observations of 51,351 people – mainly in Europe and North America – between 2011 and 2022. The researchers led by Christopher Kyba, an expert at the GFZ German Research Center for Geosciences in Potsdam and the Ruhr University Bochum, were surprised and concerned. “The speed at which stars are becoming invisible to people in urban environments is dramatic,” Kyba pointed out.
Light pollution refers to the artificial illumination of the night sky by light sources such as street lighting, illuminated facades, buildings, parks or illuminated digital advertising spaces. Stars are hardly or not at all recognizable in the brightened sky. The research team has now found that the sky brightness increases by 9.6 percent per year on average worldwide. Brightness increased by 6.5 percent per year in Europe and by 10.4 percent in North America.
If we stay with the global average of 9.6 percent more brightness in the sky every year, this means that a child who is born in a place where 250 stars are visible at birth will only be there on its 18th birthday Can see 100 stars, as Kyba told the German Press Agency. Will people no longer be able to enjoy twinkling stars in the foreseeable future, will the “Big Dipper” or “Libra” in the firmament become invisible to our naked eyes? Kyba said, “I hope the trend doesn’t continue like this, that there are more countermeasures. It’s up to us.”
The problem has been growing rapidly for a long time, he said. If the sky shines in an artificial twilight long after sunset, this has negative consequences for stargazing and astronomy – and not only that: there are also serious consequences for the environment, the research group warns. Many behaviors and physiological processes of living beings are determined by daily and seasonal rhythms – and are therefore influenced by light, explained the US co-author Constance Walker. “The skyglow affects both diurnal and nocturnal animals and also destroys an important part of our cultural heritage.”
Appropriate measurement methods are needed to gain more insight into the serious developments, Walker warned according to the announcement. Satellites are not precise and sensitive enough for this. Previously, based on satellite data, an annual increase in brightness of around 2 percent had been assumed, and there had even been indications of a minimal decrease.
About the methodology of the project: the 50,000 or so “civic scientists” looked at the night sky with the naked eye and entered 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 therefore represents 19,262 locations worldwide, including almost 3700 locations in Europe and almost 9500 in North America. In addition, a model for sky brightness based on satellite data from 2014 was used.
The association of star friends – members are amateur astronomers, public observatories and also planetariums – pointed out that even today in densely populated regions it is almost impossible to look at the starry sky with the naked eye. In conurbations such as the Ruhr area and in metropolitan areas, “unfortunately, you can only see disappointingly little,” said Andreas Hänel. The light bell from Berlin is so far-reaching 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 must also include the sky. The legislator has recognized light emissions as a problem and included them in the Federal Immission Control Act, reported Hänel. However, binding limits are needed. The environmental organization BUND also warned of negative effects on the ecosystem, on flora and fauna. In humans, a disturbed day-night rhythm as a result of increasing nocturnal lighting can suppress the production of the “sleep hormone” melatonin and cause sleep disorders. According to the WWF, the consequences are also serious for insect populations: around half of all insects are nocturnal and their natural behavior is disturbed.
Kyba emphasized: “Compared to other countries, Germany’s lighting is very conservative, that’s good.” The regions with a dark sky and a still good view of the stars included the Eifel, Rügen and the Mecklenburg Lake District. However, he believes that there is a need for even greater awareness, significantly more light savings and uniform regulations for public lighting. Hänel believes that if there is no real rethinking, “in the future there will only be a few places where you have to travel far to see the stars well”.
