Stars Vanishing Before Our Eyes

Stars are vanishing from human sight at an astounding rate, according to a stunning analysis by Globe at Night, a citizen science project hosted by NSF's NOIRLab. According to the study, artificial lighting has degraded the night sky more quickly than satellite measurements suggest. The study, which was published in the journal Science, highlights the distinctive contributions that amateur researchers may make to important areas of study.

The unaided human eye should be able to distinguish several thousand stars on a clear, dark night, from the blazing arc of the Milky Way to dozens of complicated constellations. Sadly, increasing light pollution has robbed roughly 30% of people worldwide and about 80% of Americans of their nightly view of their home galaxy. According to a recent paper published in the journal Science, the issue is getting progressively worse.

Skyglow is a phenomenon that refers to the diffuse illumination of the night sky, which is a type of light pollution. New citizen-science-based research has put worrying light on this issue. The crowd-sourced observations for this study were gathered as part of Globe at Night, a project created by NRAO astronomer Connie Walker and run by NSF's NOIRLab. According to the research, skyglow is growing faster than satellite measurements of the Earth's surface brightness at night have shown.

"At this rate of change, a child born in a location where 250 stars were visible would be able to see only around 100 by the time they turned 18," said Christopher Kyba, a researcher at the German Research Centre for Geosciences and lead author of the paper detailing these results.
Not only does the practice of astronomy suffer from light pollution, but many other things as well. Since it interferes with the cyclical transition from sunlight to starlight that biological systems have developed alongside, it also has an effect on human health and animals. Additionally, the disappearance of visible stars represents a profound loss for human cultural history. Humans have enjoyed a spectacular view of the night sky for much of recorded history, and the impact of this natural wonder can be seen in the mythology it sparked and the constructions that were erected in harmony with the stars.

Despite being a widely acknowledged problem, there isn't much information available about how the brightness of the sky has changed over time, especially globally.

Since 2006, Globe at Night has gathered statistics on stellar visibility annually. Through the Globe at Night web application on a desktop or smartphone, anyone can contribute observations. A variety of star maps are displayed to participants once they enter the pertinent date, time, and location. The one that most closely matches what people can see in the sky without the aid of telescopes or other tools is then noted.

This calculates the "naked eye limiting magnitude," or the amount of brightness required for an object to be visible. Because fainter things become invisible as the sky gets brighter, this can be used to gauge how brilliant skyglow is.

More than 50,000 observations that were reported to Globe at Night between 2011 and 2022 were examined by the authors of the paper. To ensure consistency, they excluded observations that were impacted by factors like cloud cover and moonlight. Since these regions provided an adequate distribution of observations across the geographical area and throughout the decade under study, they concentrated on data from Europe and North America. According to satellite studies, artificial lighting is becoming more common in emerging nations, thus the sky is probably getting brighter more quickly there.

The authors discovered that the loss of visible stars recorded by Globe at Night indicated an increase in sky brightness of 9.6% each year during the last ten years after developing a new method to translate these data into estimates of the change in skyglow. This is substantially more than the roughly 2% global rise in surface brightness that satellites monitor every year.

"This shows that existing satellites aren't sufficient to study how Earth's night is changing," said Kyba. "We've developed a way to 'translate' Globe at Night observations of star visibility made at different locations from year to year into continent-wide trends of sky brightness change. That shows that Globe at Night isn't just an interesting outreach activity, it's an essential measurement of one of Earth's environmental variables."

Because there are currently no detectors observing the entire Earth that can detect wavelengths shorter than 500 nanometers, which corresponds to the color cyan, or greenish blue, existing satellites are not well suited to measuring skyglow as it looks to people. But because shorter wavelengths scatter more readily in the atmosphere, they make a disproportionately large contribution to skyglow. The peak emission wavelength of white LEDs, which are now utilized more frequently in high-efficiency outdoor lighting, ranges between 400 and 500 nanometers.