A worldwide study reveals that city lights brighten the sky a little more each year. The stars are disappearing, much to the regret of astronomers and conservationists.
We’ll have to get used to starless nights. According to a German-American study published on January 19 in the journal Science, the brightness of the night sky has doubled in the space of 8 years. To reach this conclusion, the researchers compiled and analyzed the observations of 50,000 astronomers around the world. All have noted that it is becoming more and more difficult to observe the stars at night because of the light pollution that emanates from ever brighter cities. Because the phenomenon is progressive. Between 2011 and 2022, the sky cleared by 7 to 10% each year. To understand what this represents in concrete terms, scientists dare to predict: “a child born under a night sky with 250 stars visible would only see a hundred of them at the end of his schooling”.
The study also points to the fact that no region of the globe is spared. The greatest increase in luminosity is nevertheless observed in North America with an annual gain of 10.4%. Europe is less impacted with 6.5% more light per year. 7.7% on average for the rest of the world.
LED bulbs responsible for light pollution
To explain these worrying results, the researchers put forward the argument of city equipment, in particular public lighting. Municipalities have for several years been gradually converting to LED bulbs. Many have touted their merit: they are less greedy, less perishable and can produce more light than incandescent models for a given amount of energy. The problem is the blue light that they produce. This light has the particularity of having a shorter wavelength than traditional light, which allows it to disperse more easily in the atmosphere. Another disadvantage is that they are invisible to the eye of the satellites, which have therefore never noticed the general increase in luminosity on the planet. The data collected by the astronomers therefore contrast completely with the satellite estimates, which observed an annual increase in luminosity of only 2.2% between 2012 and 2016.
Satellites placed in low orbit are also implicated in the phenomenon of light pollution. Their shiny panels reflect the sun’s rays towards the earth and greatly complicate the work in an astronomical observatory. In addition, they emit radio waves similar to those of radio telescopes and disturb the data received.
Impacts on biodiversity
This study is accompanied by a long note of commentary written by Fabio Falchi and Salvador Bara, two physicists defending nature. They note: “Watching the images and videos from the International Space Station of the night hemisphere of the Earth, people are generally only struck by the beauty of the city lights, as if they were lights on a Christmas tree. They do not perceive that these are images of pollution”. The duo appeals to the responsibility of the public authorities, which according to them must consider light pollution in the same way as pollution of the air or natural spaces.
The effect of light also impacts ecosystems. Butterflies excited around a lamppost, birds singing in the middle of the night… All this disrupts the reproduction of these animals which find themselves faced with a drop in their population. It is estimated that nearly 40% of bats have disappeared in France due to light pollution. And this phenomenon affects the entire food chain: less batsmore mosquitoes.
In France, several actions have been implemented by associations such as “ night day and its slogan “turn off the lights, turn on the stars”. For its part, the government supports the creation of “black frames”, areas preserved from light to facilitate the life and movement of animals. In recent years, more and more cities, like Chambéry, Colmar or Nevers in 2022, have taken the decision to turn off their public lighting between midnight and 5 a.m., enough to save money and relieve the ‘environment. All in all, a brilliant idea.
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