Significant rise in light pollution
Number of stars visible by eye has dropped by 10 per cent in a decade
7 Excellent dark-sky site 6 Dark-sky site 5 Rural sky 4 Suburban/ rural transition 3 Suburban sky The sky-ranking scale used in the study revealed that artificial lights are erasing stars at an alarming rate
The stars are disappearing from the night sky at a much higher rate than has been previously measured by satellites, according to a decade’s worth of measurements gathered by members of the public and analysed by scientists.
The Globe at Night programme run by NOIRLab has been gathering measurements from citizen scientists around the world since 2006. The project asks them to compare their view of the night sky to that shown on star charts, to give a rough estimate of the limiting magnitude at their location. This latest report found that in the period between 2011 and 2022, the average number of visible stars dropped by almost 10 per cent.
“At this rate of change, a child born in a location where 250 stars were visible would be able to see only about 100 by the time they turned 18,” says Christopher Kyba, one of the researchers at the GFZ German Research Centre for Geosciences that is leading this latest analysis.
2 Bright suburban site 1 City/ suburbia transition 0 City/ inner-city sky
This was significantly higher than the 2 per cent drop measured by satellites, partly because they are unable to measure the full extent of skyglow, the diffuse illumination of the night sky by light pollution, which is apparent from the ground. No current satellite can measure skyglow at wavelengths shorter than 500nm – yet this blue light contributes disproportionately to skyglow as it scatters more in the atmosphere. In addition, increasingly common outdoor white LED lights peak between 400 and 500nm.
“Since human eyes are more sensitive to these shorter wavelengths at nighttime, LED lights have a strong effect on our perception of sky brightness,” says Kyba. “Existing satellites aren’t sufficient to study how Earth’s night is changing. 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.” www.globeatnight.org