The troubling reason stars are seen less often

Less than a century ago, from anywhere you could look up and see a spectacular starry night sky. Now millions of children around the world will never experience the Milky Way where they live.

The increasing and widespread use of artificial light at night not only damages our view of the universe, but it also negatively affects our environment, our safety, our energy consumption and our health, says the International Dark Sky Organization, a non-profit NGO that seeks to increase the awareness of the negative effects of light pollution.

Is that the observations made by citizens around the world over the past 12 years have confirmed a worrying trend: it is increasingly difficult to see the stars because there is more and more artificial light at nightmuch more than we thought.

According to data from a macro-study on light pollution published this Thursday in Sciencebetween 2011 and 2022, the brightness of the sky increased by 9.6% on an annual averagethat is, it is twice as high as when the study began and much higher than measured by satellites.

To put that into perspective, the study explains that light pollution is such that a child is born in an area where 250 stars have been seen probably would see fewer than 100 stars in the same place 18 years later, says the EFE agency.

For years, in many inhabited places on Earth, the night sky has not darkened completely because, instead, an artificial twilight caused by the anthropogenic diffusion of light in the atmosphere prevents it.

This type of light pollution, called “sky glow”not only does it prevent us from seeing the stars, but it also has a worrying environmental impact.

However, it is difficult to calculate exactly how and how much artificial light is grown, especially since the satellites do not detect the blue emissions of the LED lights which in recent years have established themselves in all types of lighting, especially in public lighting.

Furthermore, satellites are sensitive to light directed towards the sky, but they also do not detect horizontally emitted light, as advertising and lighting on facadeswhich are the ones that contribute the most to the “skyglow”.

According to the NGO’s website darksky.orgthe inappropriate or excessive use of artificial light, known as light pollution, can have serious environmental consequences for humans, wildlife and our climate.

The components of light pollution include:

° Glow: excessive brightness causing visual discomfort

° sky glow : brightness of the night sky over population centers

° light transgression: light that falls where it is not expected or needed

° I disturb : Bright, confusing, and excessive groupings of light sources.

Light pollution is a side effect of industrial civilization. Its sources include exterior and interior lighting for buildings, advertisements, commercial properties, offices, factories, street lights and illuminated sports facilities.

The fact is that much of the outdoor lighting used at night is inefficient, too bright, poorly focused, poorly shielded and in many cases completely useless. This light, and the electricity used to create it, is wasted by pouring it into the sky, instead of focusing it on the actual objects and areas that people want to illuminate.

To find out to what extent light pollution is hindering the view of the stars, Christopher Kyba, from the German Research Center for Geosciences (GFZ) and Ruhr-Universität Bochum, together with scientists from the NOIRlab research center for optical astronomy ( EE USA) analyzed 51,351 observations made by citizens between 2011 and 2022.

In a great example of Citizen Science, Kyba and his team have asked volunteers from all over the world to participate in the project. “Globe at Night” in which they had to compare star maps of the night sky with what light pollution allowed them to actually see.

“Together, the contributions of all these people functioned as a global sensor network,” emphasizes Christopher Kyba.

The initiative obtained data from 19,262 locations worldwide, including 3,699 locations in Europe and 9,488 locations in North America.

According to the results, the brightness of the night sky caused by artificial light it grew between 7 and 10% a year (which is equivalent to twice as much light in about a decade).

However, according to measurements made by satellites, the emission of artificial light has only been growing by 2% per year.

“Skyglow affects both diurnal and nocturnal animals and also destroys a significant portion of our cultural heritage,” while having “adverse effects for stargazing and astronomy,” warns Constance Walker, study co-author and Globe project lead at Night at NOIRlab.

In a related perspective, Fabio Falchi, of the Institute of Light Pollution Science and Technology (ISTIL) and Salvador Bará, Professor of Optics at the Spanish University of Santiago de Compostela, believe that “the most important message that the scientific community should extract from the studio is that light pollution is on the risedespite the measures that would have been put in place to limit it”.

“Awareness still has to increase a lot so that artificial night light is not perceived as something positive, but rather as the pollutant it really is,” both experts conclude, EFE says.