Goodbye, dark sky. The stars are rapidly disappearing from our night sky

A new study has found that the night sky may be brightening faster than once thought, and that has consequences for humans, ecosystems and more.

Study finds 7–10% annual increase in sky brightness over 12 years

The Milky Way stretches above a lake.
A new study says the night sky might be brightening faster than once thought, and that has consequences for humans, ecosystems and more. (Stefanie Harron)

Most Canadians are about as likely to see the Milky Way as they are to see a beaver riding on the back of a moose.

That's because almost three-quarters of Canadians live in brightly lit cities, leaving just a smattering of stars visible to the unaided eye. 

Now, a new study has found that the night sky may actually be brightening faster than once thought, and that has consequences for humans, ecosystems and more.

In a paper published in Science on Thursday, the authors used data collected from citizen scientists who took part in the outreach program Globe at Night, in which participants look at particular constellations and record how many stars they can see.

What they found was that, over the past 12 years, stars are becoming increasingly difficult to see, likely due to increasing light pollution. The change was a seven to 10 per cent annual increase in sky brightness, far more than what satellites have detected.

To put it in perspective, the authors noted that someone born in an area where 250 stars could be seen would see fewer than 100 in the same place 18 years later.

The Milky Way over a dark-sky site shows thick stars, but fewer and fewer stars are seen in the sky as it transitions into a city, where finally, no stars are seen.
This illustration shows the effects of light pollution on the night sky, from an excellent dark sky, left, to inner city sky. (NOIRLab/NSF/AURA, P. Marenfeld)

Satellite data previously put the growth in light emissions at 2.2 per cent per year from 2012-16 and 1.6 per cent during 1992-2017, which is in stark contrast to the new findings.

But there may be a reason for that.

Those satellites weren't purpose-built for the research, so they were limited in what they can see. As well, satellites could see light emitted straight up, but not from the sides.

Map of North America’s artificial sky brightness, in two-fold increasing steps, as a ratio to the natural sky brightness. Black represents little to no light pollution, while yellow, red and white represent the most light pollution where few stars are visible in the night sky. (Fabio Falchi, Christopher Kyba, et. al )

There may be other explanations including in the increased use of LEDs, which are brighter and contain more blue light.

"Blue light scatters more in the atmosphere, so you get more light scattering back down to Earth," said the study's lead author Christopher Kyba, a light pollution physicist at the GFZ German Research Centre for Geosciences in Bochum, Germany.

"[And] when our eyes are dark adapted, they're more sensitive to blue light. So replacing that long-wavelength light by blue light makes things look brighter and makes it harder to see the stars."

Kyba also theorizes that a trend toward more decorative lighting — on the sides of buildings and in people's homes, for example — that shine in directions other than upward, could be a factor. 

The research "confirms something that many of us have suspected for a while, which is that the rate at which light pollution is growing throughout the world is much faster than we previously appreciated," said John Barentine, the executive officer and principal consultant at Dark Sky Consulting, LLC and former head of the International Dark Sky Association, who was not involved in the study.

Brighter does not equal safer

There's the belief that the brighter an area is, the safer it is. But, that's not necessarily the case.

"You'll hear this term 'security lighting' — people put up exterior lighting, and they light their property, their yard or whatever. They leave that light on all night long out of a belief that it discourages criminal activity," said Barentine.

"But I think it would be better to call it insecurity lighting, because it's more about making people inside houses and buildings think that the outside world is a little more safe, because they've taken some kind of proactive step to make it."

He also noted that most crime happens during daylight hours.

Improper lighting can actually cause people to be less safe. 

"You put glare in people's eyes, it causes pupils to restrict; they lose depth the field, they lose the contrast of objects with the background, which is important for visual detection at night," Barentine said.

He acknowledges that the problem of light pollution may not be fully appreciated, and perhaps for good reason. 

"I think it's not still not on the radar of a lot of people, in part because we live in a complex world that faces very big and very present environmental challenges," Barentine said.

"And we at some level, are all suffering from issue fatigue, whether it's the pandemic, or climate change, or biodiversity loss. You know, we look at the world now, and in the near term future, and it looks pretty scary."

But it's more than a problem of cultural conservation, or how the night sky has influenced humanity from our earliest beginnings. There are potential consequences for human health, ecosystems and even climate change.

These birds all died due to striking buildings in Calgary's downtown core. (Helen Pike/CBC)

In October, on World Migratory Bird Day, the United Nations said light pollution contributes to the death of millions of migratory birds, as it upends their biological clocks. Birds may see artificial light at night as a longer day. Others may begin their migration earlier than other species, and may arrive at their summer destinations before food sources emerge.

Birds are also often killed by flying into brightly lit glass buildings.

"We should be thinking about the animals that we share the world with," Kyba said. 

Light pollution may also contribute to increased cancer risk in humans, and the wasted energy certainly doesn't help efforts to reduce CO2 emissions. 

"The bottom line with all of those things is, we are collectively as a species transforming the nighttime environment in a way that is unprecedented in the history of the Earth. We just do not know of anything that is so consequential and has happened so quickly," Barentine said. "You're only looking at a period of about 140 years or so since electric lighting was introduced and became widespread."

Kyba says the increased brightening can even be documented within just a couple of generations.

"My mother was born in Saskatchewan on a farm with no electricity," Kyba said. "And every night if she went outside, she would have seen, you know, the cosmos. And now, my children have rarely experienced that at all."


Nicole Mortillaro

Senior reporter, science

Based in Toronto, Nicole covers all things science for CBC News. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books. In 2021, she won the Kavli Science Journalism Award from the American Association for the Advancement of Science for a Quirks and Quarks audio special on the history and future of Black people in science. You can send her story ideas at