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One Third of People Cannot See the Milky Way

Artificial light pollutes the night sky for more than 80% of the world’s population, and one third of humanity cannot see the Milky Way at night due to the luminescent glow of artificial light, according to a new world atlas that attempts to quantify the global impact of light pollution.

The research appears in the 10 June issue of the journal Science Advances.

The atlas displays population and land-based light pollution statistics for all countries, showing the magnitude of the problem for each and facilitating easy comparison of national and global levels of light pollution. Fabio Falchi at the Light Pollution Science and Technology Institute in Thiene, Italy, and an international team of colleagues, created the atlas.

The atlas will be an important tool for studying artificial light as an environmental pollutant with potential health and ecological consequences. It also sets a precise point against which to compare future increases or decreases in global light pollution.

Light pollution is no longer merely an annoyance for astronomers. The artificial brightening of the night sky is profoundly altering a fundamental human experience — the opportunity for each person to view and ponder the sky above in evening hours.

Fabio Falchi, who led the New World Atlas of the Artificial Sky Brightness project, with the map of light pollution in Europe.  | Photo by Riccardo Furgoni

Even small increases in night sky brightness degrade this experience, the authors say. Despite its global presence and potential environmental risk, light pollution has received relatively little attention. And unlike other pollutants, such as noise levels in the oceans, artificial light levels are poorly quantified. 

New research is likely to provide more information. Christopher Kyba, co-author of the study and researcher at the GFZ German Research Center for Geosciences in Potsdam, Germany, and his colleagues are working on an experiment to futher understand the impact of artificial light during nightime on ecosystems at at the LakeLab facility, slated to begin in late summer.

Over a decade ago, Falchi and colleagues created the first world atlas of artificial night sky brightness. In this new Science Advances study, they update their original work by creating another, more precise atlas that incorporates new tools and uses newly available imaging data from a high-resolution satellite, the Suomi NPP.

The atlas shows that 99% of the United States and Europe live under light polluted skies. The authors considered “polluted” to be the level of brightness at which artificial light substantially obscures astronomical observations.

“In terms of the statistics, I was really interested in seeing how Germany would come out, because I know that Germans are in general very conservative with light compared to many other countries,” said Kyba.

“It was very interesting to me to see that so many Germans can see the Milky Way from their home, despite the fact that Germany does not have the large areas of totally natural skies that you can find in other, more remote countries,” Kyba noted.

The atlas also reveals that in some places with high levels of light pollution, such as Singapore, people never experience conditions resembling true night because it is masked by artificial twilight; in such places, most of the population lives under skies so bright that their eyes cannot fully adapt to night vision.

A close-up image of Europe, Africa, the Middle East and India in New World Atlas of Artificial Sky Brightness, as seen in Google Earth. | Photo by manuscript authors. Prepared by Fabio Falchi. 

On the other hand, countries with populations least affected by light pollution are Chad, the Central African Republic, and Madagascar. More than three quarters of inhabitants in these places live under pristine, ink-black night sky conditions.

The authors note that the predictions made from the atlas are based on several assumptions such as atmospheric transparency, and that actual conditions may affect artificial sky brightness in ways that differ from the results presented in this study.

Ultimately, the authors say that lightning in cities should be improved, so that people living in densely populated areas can once again see the stars.

“The aim should be cities that have high quality, non-glaring, warm, welcoming light -- and brilliant stars above,” said Kyba. 

[Associated image credit: photo by Dan Duriscoe]