This generation can no longer see the stars: Light pollution is increasing by 10% per year | Science & Tech
Sirius, Vega, Arcturus, Canopus and perhaps two of the three constellations of Alpha Centauri: Scientists estimate that these will be the only stars that most people in Northern Hemisphere cities will be able to see by the end of this century. With the help of thousands of people looking up at the sky every night, researchers measured the brightness of the night produced by artificial lights: over the past decade, it has grown so much that it has darkened the sky.
The the problem of light pollution has continued to grow since astronomers had to leave the cities to observe the stars in the last century. But the magnitude has grown exponentially in this century. A paper published in 2016 estimated that 83% of the world’s population has polluted the night sky. The following year, another study led by Christopher Kyba, a researcher at the Geoscience Research Center in Potsdam, Germany, confirmed that nights on Earth were getting brighter and the glow produced by artificial lights was increasing by 2.2% per year. But things have turned out to be much worse.
In fact, along A study published in the journal Science, Earth’s artificial brightness at night has increased by 9.6% every year for at least ten years. It is almost five times the figures obtained so far. Kyba, the lead author of this new paper, says that “at this rate of change, a child born in an area with 250 visible stars will only be able to see 100 by the time he is 18.” Also, “maybe only the five brightest stars would still be visible” when that person turns 80, Kyba notes.
There’s a big difference between the 2.2 percent increase in the 2017 study and the 9.6 percent in this year’s paper. Neither figure is wrong, but they were obtained by very different methods. So far, almost all light pollution research on a global scale has been based on satellite data. There are some devices for measuring the artificial light coming from the Earth, such as NASA’s Finland National Polar-orbiting Partners (NPP) and the National Oceanic and Atmospheric Administration (NOAA) weather agency. You might think that these devices capture the night light from above well, but this is not the case.
Radiometers and satellite cameras do not effectively register horizontal light pollution, i.e. the light radiating from facades, shop windows and billboards, which also obscures our view of the sky. More importantly, Alejandro Sánchez de Miguel, a researcher at the School of Physics at Complutense University in Spain, explains that “these satellites have focused on the infrared and red and green parts of the spectrum. They are simply blind to blue. And it’s blue LEDs that cause nighttime light pollution, when LED technology replaces yellow or yellow sodium lamps.” Blue light is also “the light that spreads best in the sky and is most sensitive to the human eye at night,” adds Sánchez de Miguel, who was not involved in Kyba’s current study .
Another significant contribution from new research Science is that it included a human element after scientists observed a rapid increase in the brightness of the night. The calculations in this study are not based on what the satellites saw from above, but on what people saw from below. The results of Kyba’s work are based on more than 51,000 observations made by people around the world who installed the application The Globe at Night project, sponsored by the US National Science Foundation (NSF). The participants had to look at the sky and choose the star chart that best matched what they saw out of seven options. Over the course of 12 years, thousands of records were collected.
“Individual observations are not very precise, but the power of the method comes from the combination of thousands of observations, because the average of all those imprecise observations is actually very stable,” says Kyba. Another advantage of this approach is that it is based on human perception. “Imagine that I notice by instrumental observation that the red component of the brightness of the sky has decreased by 70%, but the blue component has increased by 30%. [the effects of the LED transition]. Has the situation improved or worsened? It’s hard to be sure with instruments. With the help of people’s observations, we immediately know what it means to people,” adds Kyba.
There is a weakness in the work, which is also due to the human factor: the majority of observations come from North America, Europe and East Asia (Japan and South Korea). In other words, the study’s conclusions only apply to these areas. For the rest of the planet, we still have to rely on what the satellites record.
Fabio Falchi, a researcher at Italy’s Istituto di Scienza e Tecnologia dell’Inquinamento Luminoso (Light Pollution Science and Technology Institute), says that “the human eye is no better; it just takes into account the precise passband of its sensitivity to convey the perceived brightness to the brain.” The emission band refers to the frequency range that can pass through a filter, in this case the human eye. “If we want to study the effect of light pollution on obscuring the visibility of stars, the eye is a good sensor, and satellites don’t have this passband,” he points out.
Falchi, who recently wrote a paper on the effect of nighttime brightness on the world’s telescopes, also published comment on Kyba’s work in Science, which he co-authored with Salvador Barán, his colleague at the Department of Applied Physics of the University of Santiago de Compostela (Spain). In it they note: “When looking at pictures and videos from the International Space Station from the night side of Earth, people are usually just amazed by the ‘beauty’ of the city lights, as if they were lights on a Christmas tree. They don’t realize that these are pictures of pollution.” They explain that “it’s like admiring the beauty of the rainbow colors produced by gasoline in water and not recognizing that it’s chemical pollution.”
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