Light pollution is rapidly reducing the number of stars visible to the naked eye, study finds

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The poet Henry Wadsworth Longfellow wrote, “There is no light on earth or in heaven / But the stars have cold light.”

But for countless writers and artists, that inspiration may be fading, as research reveals that light pollution is rapidly reducing the number of stars visible to the naked eye. The study, published in the journal Science, suggests that places that currently have 250 visible stars will have only 100 visible stars in 18 years.

“If these trends continue, eventually it will be very difficult to see anything in the sky, not even the brightest constellations. Orion’s belt will start to disappear at some point,” said Dr. Christopher Kyba, of the German Geosciences Research Center and lead author of the study.

Related: Milky Way is no longer visible to one-third of humanity, according to light pollution atlas

The team writes that the glow produced by artificial lighting grew exponentially in the 20th century with population growth, new technologies, and the expansion of towns and cities.

However, the impact of the transition to light-emitting diodes (LEDs) in recent years is unclear. Satellites that can measure sky glare have limited resolution and cannot detect some wavelengths of light emitted by LEDs.

To dig deeper, the team analyzed 51,351 citizen scientist observations of stars visible to the naked eye between 2011 and 2022 as part of a project called the Globe at Night. Participants were asked to use a website to view a series of star maps for their location – each showing the increasing number of stars that exist in that part of the sky – and choose the map that best matches what they can see. The researchers then built a model that correlated the number of visible stars with the brightness of the night sky.

While citizen science observations are rarely made multiple times in exactly the same place, the researchers were able to group together those with similar brightness of the night sky in a given year and record the change over time.

Milky Way in the night sky

In 2016, scientists discovered that the Milky Way is no longer visible to a third of humanity. Photo: Amr Dalsh/Reuters

The results reveal that, on average, where participants observed, sky brightness increased 9.6% per year, slightly lower in Europe at 6.5% and slightly higher at 10.4% in North America.

Related: Treat artificial light like any other type of pollution, scientists say

The study has limitations, including that the observations were largely made in Europe and the USA and in residential areas. Kyba noted that the night sky in developing countries may be glowing faster than the global average suggested by the new study, as they are electrified for the first time. But the more people involved in the citizen science project, the easier it will be for the team to focus on different regions or even individual cities.

The study isn’t the first to reveal the effect of light pollution on our ability to see the night sky. In 2016, scientists discovered that the Milky Way is no longer visible to a third of humanity.

Kyba said the results shed light on the money and energy wasted in night lighting, which also has environmental impacts.

Planetarium astronomer Dr. Greenwich Royal Observatory, who was not involved in the study. Greg Brown said light pollution is already limiting the ability of astronomers to observe the night sky. “This work demonstrates the stark reality of the problem and highlights how vulnerable unobstructed views of the cosmos really are in modern society,” he said.

Royal astronomer Martin Rees said protecting the night sky isn’t just an issue for astronomers. “The night sky is part of our natural environment – ​​a truly unique piece as it has been shared by people all over the world throughout human history,” he said.

Dr Constance Walker, another author of the study at the National Optical-Infrared Astronomy Research Laboratory in the US, agrees. “There is an irreplaceable fascination with the natural night sky that a sky without light pollution provides. It inspires you and connects you with all the wonders of the cosmos.”

“If that inspiration is diminished by the pale, light-polluted sky, then we lose a part of ourselves and what we could strive to be. It is part of our cultural heritage,” he said.

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