Light pollution preventing clear view of space for most major astronomical observatories, study finds

Sky above nearly two-thirds of all large observatories affected by light pollution, scientists say

Artificial light pollution on Earth prevents a clear view of space for most of the world’s large astronomical observatories, a new study warns.

The research, published in the journal Monthly Notices of the Royal Astronomical Society, assessed the light pollution levels above nearly 50 observatories across the globe, including the world’s largest professional observatories, as well as smaller observatories for amateurs.

An international team of scientists, including those from Chile, Italy and Spain, said the sky above two-thirds of all large observatories is affected by light pollution, calling for urgent action to decrease the amount of contamination coming from artificial light.

“The results show that most astronomical major observatories are already significantly endangered by artificial light and some of them are very heavily polluted,” scientists wrote in the study.

The researchers applied a model of light propagation in the Earth’s atmosphere to night-time satellite data.

Light pollution indicators across the entire night sky were assessed. This included directly overhead sky brightness – also known as zenith sky brightness – as well as brightness at altitudes of 10 and 30 degrees above the horizon.

The overall average brightness across the sky as well as illuminance of the ground due to artificial light coming from the night sky was also measured.

One key measure used was the comparison of values with the natural sky brightness caused by the faint emission of light by the Earth’s atmosphere and the light from stars and the Milky Way galaxy.

Only seven of the 28 major astronomical observatories – sites that host a telescope with a diameter of 3m or more – have a zenith sky brightness with light pollution below the expected threshold of 1 per cent of natural sky brightness.

Researchers said the remaining 21 other major sites – three-quarters of all the major observatories – are all above this level.

For ground-based telescopes, the lowest pointing direction is about 30 degrees above the horizon and only one of the 28 major observatories had light pollution in this direction below the 1 per cent threshold.

Even as the International Astronomical Union set a more relaxed threshold of 10 per cent in the 1970s, the study showed light pollution at two-thirds of the ground-based observatories has now crossed this higher limit.

“To maintain our ability to carry out top-grade astronomical research, it is necessary that the artificial light at night affecting observatories is reduced as soon as possible,” researchers wrote.

The least contaminated of all these sites is a lodge in Namibia that hosts several telescopes rented to amateur astronomers, said study lead author Fabio Falchi from the Universidade de Santiago de Compostela in Spain.

“I was recently there and I can confirm that it is the least light-polluted site I’ve ever seen,” he said in a statement.

“We must try to decrease the light pollution levels at other sites in order to protect the future of ground-based astronomy,” Dr Falchi added.