For the study, which was recently published in the Monthly Notices of the Royal Astronomical Society, scientists assessed light pollution levels over nearly 50 observatories around the world, ranging from the world’s largest professional observatories to smaller amateur observatories.
The international team of scientists, including scientists from Chile, Italy and Spain, said the skies above two-thirds of all large observatories are affected by light pollution, calling for urgent action to reduce the amount of pollution caused by artificial light.
“The results show that most of the major astronomical observatories are already at high risk from artificial light, and some of them have very polluted skies,” the scientists wrote in the paper.
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The term light pollution refers to the pollution resulting from abnormal artificial lighting at night, such as the external and internal lighting of buildings, shops and street lights.
Here, scientists applied a model of how light travels through the Earth’s atmosphere to night views captured by satellites.
Indications of light pollution were assessed across the entire night sky. This included the brightness of the sky, in what is known as the “zenith sky brightness: a point to which the line extending from the center of the Earth ends on the straightness of a person’s stature and meets it at the end of the diagonal extending towards the feet.” As well as brightness at heights of 10 and 30 degrees above the horizon.
The team also measured the overall average brightness across the sky, as well as ground illumination due to artificial light from the night sky.
One of the main metrics used was to compare these artificial values with the natural sky brightness caused by the faint emission of light from Earth’s atmosphere, light from stars, and the Milky Way.
Only seven out of 28 major astronomical observatories – sites that host telescopes of 3 meters or more in diameter – have “azimuthal brightness” tinged with light pollution below the expected threshold of 1% of normal sky brightness.
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The scientists said the remaining 21 major sites — three-quarters of all major observatories — are all above this level.
Even worse, only one of the 28 major sites the scientists examined had light pollution below the 1% threshold at 30 degrees above the horizon.
Even while the International Astronomical Union set the maximum allowable artificial brightness threshold for major observatories at 10% in the 1970s, the study shows that light pollution in the atmospheres of two-thirds of Earth’s observatories has now exceeded that upper limit.
“To maintain our ability to conduct high-quality astronomical research, it is imperative that the artificial light at night that affects observatories be dimmed as quickly as possible,” the scientists wrote.
The study’s lead author, Fabio Falchi of the University of Santiago de Compostela in Spain, said the least polluted of these sites is a hostel in Namibia that hosts many telescopes rented to amateur astronomers.
He added: “I was there recently and I can confirm that it is the least light-polluted site I have ever seen. We must try to reduce light pollution levels at other sites in order to protect the future of terrestrial astronomy.”
Source: The Independent
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