Gentle air pollution is uncontrolled

Concerns about global light pollution are growing. Astronomers are noticing its increasing impact on astronomical observations, just as predicted over the past few decades. Our artificial light, much of which is not essential, interferes with our science.

But there is more at stake than just scientific advances. Can humanity afford to ignore the night sky’s possibilities for wonder, awe and contemplation?

We’ve all seen satellite imagery of the Earth at night, showing glittering, interconnected cities aglow like holiday lights. These images show us how our global civilization has grown, how we have progressed and how advanced we have become. But in reality we also see light pollution. And we’re beginning to pay a price for that pollution.

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In January 2023, the organization Globe at Night published a paper based on 10 years of data on the night sky. The data didn’t come from satellites—an important point we’ll come back to later—but from citizen scientists around the world.

Globe at Night published a research article showing that the night sky is getting 10% brighter every year. Each year, more of the darkest stars in the sky are drowned out by skylight from streetlights, traffic lights, and other sources. For more and more people around the world, there are fewer and fewer stars in the sky, not to mention the great arc of the Milky Way.

Globe at Night collected over 50,000 individual naked-eye observations of the night sky and asked citizen scientists to find the darkest stars. The decline in the number of faint stars visible in these observations over the decade effort indicated a steadily brightening sky.

Map of GLOBE at Night attendance 2022. Click on the image for more information. Photo credit: GLOBE at Night / NOAO

If the “Globe at Night” article was a rallying cry, other researchers are responding. A pair of researchers have published their own short article that acts as a sort of addendum to the Globe at Night article. They are Fabio Falchi from the Department of Applied Physics at the Universidade de Santiago de Compostela in Spain and Salvador Bara, an independent researcher in Spain. Falchi is also affiliated with the Light Pollution Science and Technology Institute in Italy.

A startling analysis by Globe at Night — a citizen science program from NSF’s NOIRLab — concludes that stars are disappearing from human vision at an astounding rate. Additionally, the Milky Way is invisible in our cities, obscuring humanity’s connection to nature and the cosmos. Photo credits: NOIRLab/NSF/AURA, P. Marenfeld

Satellite data paints a less worrisome picture, but satellites have a different perspective. They can only measure the light that reaches them and only the wavelengths their instruments are tuned to. But the light that reaches them is not necessarily the light that drowns out the sky as seen by people on the surface of the earth. That’s why the Globe at Night initiative eschewed satellite data in favor of citizen scientists spread around the globe.

Projections based on satellite data suggested that light pollution would increase by 2% each year, but the Globe at Night initiative found the actual number to be 10%. That’s a big discrepancy and means that light pollution will double in less than eight years. This number should grab everyone’s attention, but why this discrepancy? Why can’t high-tech satellites do this?

“Some of this discrepancy could be explained by the inability of these satellites to see the blue light.
“This is emitted in large quantities by LED light that has been used outdoors for about a decade,” the two researchers write. “Furthermore, these satellites are not able to clearly see the light that is mainly emitted horizontally, such as that emitted by the increasing number of ultra-bright LED billboards and illuminated building facades.”

Falchi and Bara are pushing for the construction of next-generation satellites that can overcome this weakness. Multi-band sensitivity is required, as well as “…multi-angle surveillance capabilities,” according to the pair.

You are not the only ones. In 2020, a group of researchers addressed the topic in a paper titled “Remote Sensing of Night Lights: A Review and a Forward Look”. One of the authors was Christopher Kyba, who also co-authored the Globe at Night article.

Stand next to the Milky Way. Blocking out the night sky blocks us from nature, and that’s not good for humans. Photo credit: P. Horálek/ESO

In this article, the authors agree with Falchi and Bara that we need satellites that can sense the fast-spreading LED lights. They also indicate that we need a better understanding of the angular patterns of light emission. You don’t stop here. “Perhaps most importantly,” they write, “we believe that higher spatial resolution and multispectral sensors covering the blue to NIR range are needed to more effectively identify lighting technologies, map urban functions, and monitor energy use.” “

That’s great. Detailed, actionable data is part of any real effort. But we already know that light pollution is increasing. “People, the media and politicians are used to associating artificial light with thaumaturgic properties with road safety and personal safety that it apparently does not deserve,” emphasize the two researchers. “Year after year, more and more light is installed to illuminate the night.”

What can we do against it?

Something in the human psyche wants to remove the darkness. We want comfort, security, convenience and an overall sense of well-being and wealth. There’s nothing wrong with providing security when well-lit areas can fight crime. But is more and more light the answer? Is there a point where the yield drops? Not just for us, but for nature?

“Life on Earth evolved with sunlight during the day and with starlight at night and the moon, if any,” write Falchi and Bara. “If we introduce artificial light into ecosystems at levels a thousand times or more in excess of levels observed under natural conditions, animal behavior will change accordingly.” Increased nocturnal lighting could disrupt predator-prey relationships, alter mating behavior and even contribute to the extinction of some populations or species.

It’s not just stargazing and nature that pays the price of light pollution. Science is also affected as observatories near urban centers face the problem of light pollution. Take the 100-inch Hooker Telescope at Mt. Wilson Observatory near Los Angeles.

From its completion in 1917 to 1949 it was the largest aperture telescope in the world. But as light pollution increased, it became increasingly difficult to make useful astronomical observations. The light snuffed out faint constellations and it only got worse. Eventually, the Hooker telescope was shut down in 1985 in direct response to the growing problem with artificial light.

The Hooker telescope housing at Mt. Wilson Observatory. The telescope was shut down in 1985 due to light pollution. Image Credit: By Craig Baker – Own work, CC BY-SA 4.0,

That was no small thing. The telescope was in good condition and played an important role in determining extragalactic distances, studying the nature of spiral galaxies, and noting the expansion of the Universe, among other things. Other instruments at Mt. Wilson Observatory are still operational, but the Hooker Telescope’s potential has been stymied by excessive skyglow.

No thoughtful person would say they want species to be threatened with extinction and powerful telescopes to be shut down while they’re still functional. Also, no one who is thoughtful would want their view of the sky to be restricted. But one of the main problems in this matter is our prosperity. As lighting keeps getting cheaper – and LEDs are cheaper – we’re building more and more lights, illuminating roads and pathways that never needed them before. what can be done

For example, we probably won’t launch a mass campaign to remove streetlights, but people have been trying other things. “Attempts to control light pollution have been made in several places over the past few decades, from the local to the national level,” write Falchi and Bara. These attempts were unsuccessful, even when the lights were aimed to only shine below the horizon level. “It’s not that approach
sufficient, since each new light, even if shielded, increases pollution at night after its installation
reflected by the surfaces to be illuminated,” they explain.

Instead, we must limit lighting, just as we do with other forms of pollution. As an example, the authors refer to the Clean Air Act in the USA, which restricts the use of air pollutants such as carcinogenic solvents and toxic fuel additives.

It goes without saying that human activities have an impact on nature. But that doesn’t mean we can put on blinkers and just accept it. In a world grappling with the mounting catastrophe of the global climate crisis, light pollution doesn’t seem like a big deal. Can’t we just go to the internet and look at the sky in much more detail, even from different parts of the world? Sure, but computer monitors aren’t the same as sitting out under the sky, staring and letting the thoughts sink in. These activities form memories that we think about and that move us. Even the wildest, most hallucinogenic notions of technology from a techie like Zuckerberg can never replace that.

This is an astronomy news website. But astronomy, detached from the natural mind of mankind, is a poor undertaking. Without the simple observing of the stars and the ways in which they can stimulate our imagination and our sense of wonder and awe, most of us might not even be interested in the science of astronomy.

Embrace the dark.

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