From Van Gogh’s paintings to Lamartine’s poems and films Star Wars, the stars have always illuminated our collective imagination. But light pollution interferes with their observation. A study published Thursday, January 19, 2023 in the journal Science estimates that the number of stars observable with the naked eye could be halved in less than twenty years in some places.
Light pollution is progressing, the number of visible stars is falling
The team of four researchers behind this article relied on observations made by just over 51,000 “citizen researchers” in North America and Europe between 2011 and 2022. These contributions have enabled scientists to establish the following observation: “a place where 250 stars are visible would see that number reduced to 100 visible stars” in the space of eighteen years.
The reason ? The increase in light pollution, caused by human lighting. According to the study, the brightness of the sky increases by 7 to 10% per year. “The more artificial light we have emitted into the atmosphere, the more we make the sky greyish and the more we reduce the contrast with faintly bright objects, which are then difficult to distinguish from the background of the sky”explains Samuel Challéat, researcher at the CNRS and coordinator of the Night Environment Observatory.
The increase in light pollution is greater than estimated by previous studies. The reason: the latter were based on satellite observations. However, they are not sensitive to the wavelengths of the LEDs and to the lights emitted horizontally. Hence the conclusion of the study: “The use of naked-eye observation by citizen researchers provides additional information to satellite data. »
Observatories flee inhabited areas
According to these new results, the number of stars observable with the naked eye could be halved in less than twenty years in some places. What harms scientific research? “It’s bound to be a problem.explains Florence Durret, astronomer emeritus at the Institute of Astrophysics in Paris. As professionals, we must go to sites where there is as little pollution as possible. » The observation had to move to more distant places, such as the Andes or Namibia.
The Paris Observatory was surrounded by fields when it was built in 1667: “Today, it no longer allows you to see much, except perhaps Jupiter”, said Florence Durret. In France, only a few observatories, such as that of the Pic du Midi de Bigorre (Hautes-Pyrénées), are still used by researchers. Astronomical research also benefits from technological innovations, such as the James-Webb telescope, which observes the stars directly from space.
Researchers also point to another form of light pollution: that of satellites, whose trails alter scientific photographs. In particular, the satellites of Starlink, the telecommunications company of Elon Musk, are targeted. They will be 12,000 in orbit by 2025.
For amateurs, “it’s becoming more and more an impossible mission”
Amateur astronomers are the first to suffer from the proliferation of light pollution. Some telescope filters can limit its effects. But they are ineffective when the brightness of the sky is too high. “We are forced to move away from the big cities, and even from the villagesregrets Corine Yahia, president of the association Astronomie Gironde 33. Last night, I even had trouble seeing the tail of the Big Dipper because it was drowned in the lights of Bordeaux. »
“Amateur astronomers are used to saying that their first observing instrument is their car, not their telescope”, jokes Samuel Challéat. They have to travel long distances to find sufficiently dark skies. “A few years ago, we could still go to the Saclay plateau to have reasonable observation conditions, but today it is no longer possible.», observes Didier Schneider, member of the astronomy club of Boulogne-Billancourt (in the Paris suburbs). «You have to go to the Perche (a hundred kilometers from Paris)or even further afield, in the Baronnies (in the Southeast) ; It’s becoming more and more mission impossible.” he completes.
Beyond astronomy enthusiasts, light pollution impacts anyone who sometimes likes to lift their head to admire starry summer skies. “Before, when people went out at night, they were kind of confronted with the cosmossays Christopher Kyba, physicist at the GFZ Center in Potsdam, Germany and one of the authors of the study of Science, quoted by AFP. And now it’s like it’s become an unusual event. »
Some children grew up in the city without ever having seen completely starry skies: “There is an extinction of the experience of nature which participates in a generational environmental amnesia”, notes Samuel Challéat. With increasingly bright nights, we will have fewer and fewer stars in our eyes.