If you’re finding it hard to see the stars in the sky where you live — you’re not alone.
Data collected by citizen scientists around the world over the past 12 years shows that the night sky is disappearing due to rapid increases in light pollution.
The data, reported in the journal Science, indicates the change in visibility reported is equivalent to an average increase in sky brightness of 9.6 percent per year.
“The rate at which people are reporting that they see fewer stars was shockingly fast,” said Christopher Kyba, who led the study.
Connie Walker, an astronomer and founding member of the Globe At Night program at NOIRLab in the US, said the finding indicated we were in danger of losing our night sky.
“If we lose the night sky, we lose part of our cultural heritage and we can’t get it back if we’re not good stewards,” Dr Walker said.
Light pollution also affects our environment and health.
“But the really good thing is that light pollution is one of the very easiest problems to redress,” she said.
“Every single person on Earth can do something about it.”
The power of people
Urban centres are surrounded by a halo produced by artificial light known as sky glow.
Satellites that whiz around our planet pick up specks of light coming from our growing towns and cities, but they can’t measure the total amount of light pollution.
“Satellite data is lacking in very, very many ways,” Dr Walker said.
For a start they cannot pick up light in the blue wavelength that comes from modern LED lights.
They also only pick up light coming directly upwards, not sideways from billboards or buildings in general.
But humans can.
The Globe At Night program asks citizen scientists to count the number of stars they can see in constellations such as Orion and the Southern Cross throughout the year.
Dr Kyba, from the Deutsches GeoForschungsZentrum Potsdam in Germany, worked with colleagues to analyse more than 51,000 observations taken on cloudless nights between 2011 and 2022.
Around 68 per cent of the observations were from North America and Europe, with a one-off campaign in Australia, and a smattering of observations from Asia, Africa and South America.
Light pollution is a local phenomenon, and varies from the global average depending upon your specific location.
At a continental level, North America experienced an average increase in light pollution of 10 per cent, while Europe experienced an average increase of 6.5 per cent.
While there’s not enough data for the other continents, Dr Kyba said the study provided a big picture snapshot that represented changes across the globe.
Fred Watson, Australia’s astronomer-at-large, said the result was striking.
“It’s surprising that that is so much more than what we see from the satellite images,” said Professor Watson, who is a dark-sky advocate but was not involved with this study.
Satellite images suggest light pollution is increasing on average by about 2 percent each year.
What’s happening in Australia?
The bulk of the Australian data in the study comes from a Guinness World Record attempt to record the night sky in 2020.
More than 11,000 people – 9,000 of them in Australia – recorded their observations of the Southern Cross in a single night.
“We broke the Globe at Night website,” said Marnie Ogg, founder of the Australasian Dark Sky Alliance.