A global study shows that city lights brighten the sky a little more every year. The stars are disappearing, much to the chagrin of astronomers and conservationists.
We’ll have to get used to starless nights. The brightness of the night sky has doubled in 8 years, according to a German-American study published Jan. 19 in the journal Science. To reach this conclusion, the researchers compiled and analyzed the observations of 50,000 astronomers around the world. Everyone has noticed that stargazing at night is becoming increasingly difficult due to light pollution emanating from cities that are getting brighter and brighter. Because the phenomenon is progressive. Between 2011 and 2022, the sky cleared by 7 to 10% each year. To understand what this means in concrete terms, scientists dare to predict: “A child born under a night sky with 250 visible stars would only see a hundred of them by the end of his school years”.
The study also points out that no region of the world is spared. However, the largest increase in luminosity can be observed in North America with an annual increase of 10.4%. Europe is less affected with 6.5% more light per year. 7.7% on average for the rest of the world.
LED lamps responsible for light pollution
To explain these worrying results, the researchers cite the argument of urban amenities, particularly public lighting. Municipalities have been gradually switching to LED lamps for several years. Many have touted their merits: 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 they produce. This light has the peculiarity of having a shorter wavelength than conventional light, which allows it to spread more easily in the atmosphere. Another disadvantage is that they are invisible to the eyes of the satellites, which have therefore never noticed the general increase in luminosity on the planet. The data collected by the astronomers is therefore in complete contrast to the satellite estimates, which observed an annual increase in luminosity of just 2.2% between 2012 and 2016.
Satellites in low orbit are also involved in the light pollution phenomenon. Their shiny discs reflect the sun’s rays to Earth, making work in an astronomical observatory much more difficult. They also emit radio waves similar to those from radio telescopes and interfere with the data received.
Impact on biodiversity
This study is accompanied by a long commentary written by Fabio Falchi and Salvador Bara, two physicists who defend nature. They state: “When viewing the images and videos from the International Space Station of Earth’s nighttime hemisphere, people are generally just struck by the beauty of the city lights, as if they were lights on a Christmas tree. They don’t realize that these are images of environmental pollution.” The duo appeal to the responsibility of public authorities, which they believe must treat light pollution in the same way as pollution of the air or natural spaces.
The effects of light also affect ecosystems. Butterflies excited around a lamppost, birds singing in the middle of the night… All this disrupts the reproduction of these animals, which are facing a decline in their population. It is estimated that almost 40% of bats in France have disappeared due to light pollution. And this phenomenon affects the entire food chain: fewer bats, more mosquitoes.
In France, several actions have been carried out by associations such as “Le jour de la nuit” and its slogan “Let’s turn off the lights, turn on the stars”. For its part, the government supports the creation of “black frames”, light-protected areas, to facilitate the life and movement of animals. In recent years, more and more cities, such as Chambéry, Colmar or Nevers in 2022, have made the decision to turn off their public lights between midnight and 5am, enough to save money and protect the environment. All in all a brilliant idea.
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