A less and less starry sky
Light pollution has made the stars less and less visible over the past 14 years.
The night sky is less and less nocturnal: urban lighting would have made it 7 to 10% brighter each year between 2011 and 2022, according to observations collected from more than 51,000 amateur astronomers around the world. world.
These “ citizen scientists ” are among those who have been involved for 14 years in an international project, Globe at Night, which aims to raise awareness of the impacts of light pollution. They submit their observations of the stars that, in their region, are visible to the naked eye. Four researchers from Germany and the United States had the idea of diving into this database to check whether it would be possible to discern a trend. Their analysis was published on January 19 in the journal Science.
The authors propose as a comparison that a person who could see 250 stars in the 2000s could only see 100 in the same place today.
At present, the only data available on light pollution are those collected for this purpose by certain satellites. The estimates of these satellites are more “optimistic” than those of this study: there is talk of an increase in brightness of 2.2% per year between 2012 and 2016. The researchers partly explain this difference by the inability of the satellites to detect blue light from LEDs (light emitting diodes), which began to be used outdoors in the last decade.
It should be noted that this estimate of an increase in gloss of 7 to 10% per year is an international average, but which mainly covers Europe and North America, where the majority of the 51,000 enthusiasts come from. astronomy. In addition, some countries have introduced rules in the last 15 years to reduce night lighting; a few have even created regions called “dark sky preserves”, characterized by a severe limitation of light pollution. However, these efforts are themselves mainly in Europe and North America, which has not however prevented observers from reporting a deterioration of the situation.
Light pollution is not not just a problem for stargazers, it's also an environmental problem, remind two Spanish physicists in a comment accompanying the article. An increase in artificial light at night induces behavioral changes in an ecosystem – predators can take advantage of it and prey can become downright endangered species – and reduces the production of melatonin, a hormone which, the two authors recall, controls biological clocks. , ours like those of animals. They see it as an argument for making limits on light pollution the equivalent of limits on air pollution imposed by laws from the 1970s.