Every year, the sky gets as much as 10 per cent brighter, according to a major new study. That means that vast numbers of stars that were once visible are now hidden from astronomers and the public.
A child born under 250 visible stars, for instance, would only be able to see 100 of them by the time of their 18th birthday, the scientists warn.
The light pollution that is blocking out those stars is growing far more rapidly than we have realised, even despite attempts to limit it. And it could have drastic results, not only for the visibility of the night sky but for the environment, with affects on the biological systems of animals and humans, and more.
Those are the findings of a major new study that analysed more than 50,000 observations from citizen scientists around the world, taken between 2011 and 2022. It aimed to fully understand the scale of the problem of “skyglow”, or the diffuse light of the night sky that is caused by human-made pollution.
Until now, the changes in the brightness of the sky have been little documented, because there is no easy way of gathering information from across the globe. To address that, scientists used information taken from an app that collects the view from places around the world and gathers it together.
That data can be used to gather data on the “naked eye limiting magnitude”, which measures the minimum brightness that an object in the sky must have if it can be seen. As the night sky brightens with pollution, those objects must be ever brighter if they are to be seen – otherwise they will disappear from the sky.
Those measurements suggest that the sky has increased in brightness by 9.6 per cent each year. Previous estimates gathered from satellites suggested that the brightness was increasing by only 2 per cent.
Satellites have been used to estimate the scale of the problem but suffer because there are none monitoring the whole Earth that are ale to account for the ways that humans see the sky. They are also less likely to see light that comes out horizontally, such as from windows, but those sources significantly contribute towards light pollution as seen by people on the ground.
An article on the findings, ‘Citizen scientists report global rapid reductions in the visibility of stars from 2011 to 2022’, is published in the journal Science.
In their conclusion, the researchers note the importance of citizen scientists in providing such data. But they also urge that the data is used by policymakers, noting that existing attempts to limit the problem of light pollution are not stopping the issue from getting worse.