Light Pollution Atlas Shows Why 80 Percent of North Americans Can’t See the Milky Way

Back in 1994, the Northridge Earthquake caused major blackouts in the Los Angeles area. During the hours of darkness, something strange happened. People began to call 911 to report a strange ethereal light in the sky.

What they were actually seeing was the Milky Way. Light pollution was so bad in the City of Angels that many people had never seen our galaxy.

And that raises an interesting question. Just how bad has light pollution become in the years since then, and how is it set to change?

Today we get an answer thanks to the work of Fabio Falchi at the Light Pollution Science and Technology Institute in Thiene, Italy, and a few pals, who have measured light pollution levels across the globe in unprecedented detail.

These guys report that the luminous fog that began to fill the atmosphere during the Industrial Revolution has never been thicker, and that most people in Europe and America cannot see the night sky clearly.

Their method makes use of a polar orbiting satellite called the Suomi National Polar-Orbiting Partnership satellite, a weather satellite operated by the National Oceanic and Atmospheric Administration. It orbits the globe from pole to pole once every 24 hours and so peers down on every part of the planet as it rotates beneath.

In this way it can build up a composite image over time to allow for cloud cover and changes in artificial lighting on the surface. The new data was gathered over six months in 2014. Falchi and co then crunched this data to produce a new generation of maps of light pollution.

The results make for impressive viewing. Falchi and co have created an atlas of light pollution for the entire planet that reveals how bad the problem has become. “We found that about 83% of the world’s population and more than 99% of the U.S. and European populations live under light-polluted skies,” they say.

One measure of the severity of the problem is whether people can see the Milky Way. By this reckoning, the problem is severe. “Due to light pollution, the Milky Way is not visible to more than one-third of humanity, including 60% of Europeans and nearly 80% of North Americans,” say Falchi and co.

Not everywhere is drowning in light, though. The team say the countries with the populations least affected by light pollution are Chad, Central African Republic, and Madagascar, with more than three-quarters of inhabitants living under pristine sky conditions.

Others are not so lucky. The worst affected country is Singapore, where the entire population lives under skies so bright that their eyes cannot fully dark-adapt to night vision. Here the night never gets darker than early twilight.

And the problem is set to get worse as many countries switch from high pressure sodium lighting to white light LEDs, which are much more energy-efficient. The problem with these LEDs is that they generate light across a much broader part of the spectrum visible to the human eye. Falchi and co say they are 2.5 times more light-polluting.

Another problem is brewing because the sensors on the Suomi satellite are unable to pick up light in the blue part of the spectrum, and so will not register it in future measurements of light pollution.

Nevertheless, there is hope. Various places have begun to enact light-pollution legislation to prevent further damage to the night sky—for example, Lombardia and most other Italian regions, Slovenia, two regions in Chile, and part of the Canary Islands. 

Such legislation is hugely important for astronomers but it has other consequences, too. Not least is the cultural importance of seeing the night sky and understanding Earth’s place within it.

Falchi and co imagine two future scenarios. “Perhaps the current generation will be the final generation to experience such a light-polluted world, as light pollution is successfully controlled,” they say. “Alternatively, perhaps the world will continue to brighten, with nearly the entire population never experiencing a view of the stars, as in Isaac Asimov’s Nightfall novel and short story.”

The prospect of people so scared by the pristine night sky that they call the police is a sad one that is already a reality. Let’s hope the former scenario comes to fruition. If nothing else it will significantly increase the beauty of the night sky for all.

Ref: arxiv.org/abs/1609.01041: The New World Atlas of Artificial Night Sky Brightness