A stunning analysis from Globe at Night – a citizen science program run by NSF’s NOIRLab – has concluded that stars are disappearing from human view at an astonishing rate. The study found that, to human eyes, artificial lighting dimmed the night sky more quickly than satellite measurements indicated. The study, published in the journal Science, showcases the unique contributions citizen scientists can make to core areas of research.
From the glowing arc of the Milky Way to dozens of complex constellations, the naked human eye should be able to perceive many thousands of stars on a clear, dark night. Unfortunately, increasing light pollution has robbed about 30% of people around the world and about 80% of people in the United States the night view of their home galaxy. A new paper published in the journal Science concludes that the problem is getting worse rapidly.
New citizen science-based research sheds a troubling light on the problem of “skyglow” – the diffuse illumination of the night sky that is a form of light pollution. The data for this study came from group observations collected from around the world as part of the Globe at Night program, a program run by NSF’s NOIRLab and developed by NRAO astronomer Connie Walker. The research reveals that the celestial glow is increasing faster than what is seen in satellite measurements of the brightness of the Earth’s surface at night.
said Christopher Kyba, a researcher at the German Research Center for Geosciences and lead author of the paper detailing these findings.
Light pollution is a familiar problem with many harmful effects, not only on the practice of astronomy. It also has an impact on human health and wildlife, as it disrupts the cyclic transition from sunlight to starlight with which biological systems have evolved. Moreover, the loss of visible stars is a grave loss of human cultural heritage. Until relatively recently, humans throughout history enjoyed a magnificent view of the starry night sky, and the influence of this nocturnal spectacle was evident in ancient cultures, from the myths that inspired it to the structures built in alignment with the celestial bodies.
Although a well-recognised problem, changes in sky brightness over time have not been well documented, particularly on a global scale.
Globe at Night has been collecting data on stellar visibility every year since 2006. * Anyone can submit feedback through the Globe at Night web app on their desktop or smartphone. After entering the relevant date, time, and location, participants are shown a number of star maps. Then they record the best he can see in the sky without any telescopes or other instruments.
This gives an estimate of what’s called the naked eye’s specific magnitude, which is a measure of how bright an object should be for it to be seen. This can be used to estimate the brightness of a heavenly glow, because as the sky brightens, fainter objects disappear from view.
The paper’s authors analyzed more than 50,000 observations submitted to Globe at Night between 2011 and 2022, ensuring consistency by removing entries that were affected by factors including cloud cover and moonlight. They focused on data from Europe and North America, as these regions had a sufficient distribution of observations across the land area as well throughout the decade studied. The paper notes that the sky is likely to brighten more quickly in developing countries, as satellite observations indicate that the prevalence of artificial lighting is increasing at a higher rate.
After devising a new method to convert these observations into estimates of variability in celestial glow, the authors found that the loss of visible stars reported by Globe at Night indicates an increase in sky brightness of 9.6% per year over the past decade. This is much greater than the global increase in surface brightness measured by satellite of about 2% per year.
“This shows that the current satellites are not sufficient to study how Earth’s night changes,” Kiba said. “We have developed a way to ‘translate’ Globe at Night observations of stellar vision made at different locations from year to year into continent-wide trends in sky brightness change. This shows that Globe at Night is not just an interesting outreach activity, it is a basic measurement of an environmental variable.” to the earth.”
Current satellites aren’t as well-suited for measuring celestial glow as it appears to humans, because there are no current instruments that observe the entire Earth that can detect wavelengths shorter than 500 nanometers, which corresponds to a cyan or teal color. However, shorter wavelengths contribute disproportionately to sky glow, because they scatter more effectively through the atmosphere. White LEDs, which are now commonly used in high-efficiency outdoor lighting, have an emission peak between 400 and 500 nanometers.
“Because human eyes are more sensitive to these shorter wavelengths at night, LED lights have a strong effect on our perception of sky brightness,” Kiba said. “This may be one reason for the discrepancy between satellite measurements and sky conditions reported by Globe at Night participants.”
Beyond wavelength differences, space instruments don’t measure light emitted horizontally well, like signs or illuminated windows, but these sources contribute significantly to the glow of the sky as seen from Earth. Therefore, observations gathered from crowd sources will always be invaluable for investigating direct human effects of sky brightness.
“The increase in celestial glow over the past decade underscores the importance of redoubling our efforts and developing new strategies to protect dark skies,” Walker said. “The Globe at Night dataset is indispensable in our ongoing assessment of changes in celestial glow, and we encourage everyone who can participate to help protect the starry night sky.”
* From 2006 to 2010, globe at night The data was collected based on a paper rather than an online form, so it was inconsistent and was not included in this analysis.