June 10, 2016
Michelle Z. Donahue
The Milky Way illuminates the sky over Dinosaur National Monument, which spreads across Colorado and Utah. Photograph by Dan Duriscoe
The Milky Way galaxy, that torrent of stars that slashes across a deeply darkened night sky, has been a deep well of inspiration from humanity’s earliest days. The ancient Egyptians saw it as a pool of cow’s milk, while in Hindu mythology the arcing galactic arm was likened to a dolphin swimming through the sky. Countless scientists, philosophers, and artists, including Galileo, Aristotle, and Vincent Van Gogh, have drawn upon the galaxy as their muse. (Read “How Much Does the Milky Way Weigh?”)
But a new atlas of the night sky across the entire globe shows that more than 80 percent of the planet’s land areas—and 99 percent of the population of the United States and Europe—live under skies so blotted with man-made light that the Milky Way has become virtually invisible.
Fabio Falchi, a researcher at the Light Pollution Science and Technology Institute (ISTIL) in Thiene, Italy, announced Friday the release of a new survey that quantifies nighttime sky quality for every region in the world. Produced using over 35,000 ground-based observations and six months of data from 2014 collected with the Suomi National Polar-orbiting Partnership (NPP) satellite, the atlas is an update to a 2001 work and shows the planet’s darkest and brightest locations in stark contrast.
NASA/Goddard Suomi NPP satellite
Woe to Singapore, a place of eternal twilight, with the entire population living under skies so bright their eyes cannot fully adjust to night vision, let alone see the Milky Way. Kuwait, Qatar, and the United Arab Emirates have it nearly as bad.
On the other hand, more than 75 percent of the population of Chad, the Central African Republic, and Madagascar live under near-pristine skies, or places where background light represents less than one percent of the sky’s overall brightness. And according to Falchi’s analysis, residents of the Azores have the distinction of living the farthest from land with unspoiled skies: They’d have to travel nearly 1,100 miles, to the western Sahara, to experience an ancestrally darkened landscape (unless they travel out into the ocean).
Light pollution clouds the view over Joshua Tree National Park, California. Photograph by Dan Duriscoe
“In the first atlas we had a hint of what was happening, but these numbers are shocking,” Falchi says. “We have lost the connection with our roots, of literature, of philosophy, of science, of religion—all are connected with the contemplation of the night sky. A new generation can no longer appreciate this beauty.” (“See a Stunning New View of the Milky Way.”)
Study co-author Dan Duriscoe, a physical scientist with the National Park Service’s Natural Sounds and Night Skies Division, has worked in the Park Service for 36 years and has collected light measurements in national parks since 1994. On the East Coast, apart from a few scattered points in West Virginia, Pennsylvania, and New England, it’s extremely difficult to get to a place with an unfettered view of stars.
“People could get that experience closer to home decades ago, but now they’re forced out into Utah or Death Valley or Yellowstone, somewhere far from their backyards,” Duriscoe says. “There’s an increased public awareness of how this is a rare experience and becoming one that will cost them some money to go see.”
High-Tech Eyes on the Sky
Sweeping over the Earth’s poles 14 times a day, the Suomi satellite generates a complete global set of high-resolution day and night images every 24 hours. Falchi, along with ISTIL colleague Pierantonio Cinzano, worked with data from partners including the National Park Service (NPS) and the National Oceanographic and Atmospheric Administration (NOAA) to produce the atlas. The 2001 atlas looked at only light escaping from Earth into space, while the new data reveal where light is reflected from the sky down to the Earth’s surface. (Read “Graveyard of Stars May Lie at Milky Way’s Center.”)
Falchi plans to release a print version of the atlas, and an interactive digital atlas, similar to one from 2006 produced using the 2001 data, is also in the works.
A map illustrates light pollution in North and South America. Illustration by Fabio Falchi, Google Earth
Chris Elvidge, a co-author of the study and a scientist with NOAA’s National Centers for Environmental Information, says he expects that the satellite data and analysis will be useful not only for astronomers, who have a vested interest in a dark night sky, but also for biologists studying light impacts on nocturnal organisms, medical researchers interested in the human health effects, and city planners.
One drawback of the satellite’s imaging instruments is limited detection of the blue and violet parts of the visible spectrum—the very zone where white LEDs would show up on satellite scans. Though highly efficient, white LEDs can be excessively bright, and as municipalities begin to install them in streetlights and for other outdoor purposes, the impact of LEDs may actually worsen overall light pollution in the long run.
“Several cities have jumped on the LED bandwagon without getting their citizens’ approval,” says Connie Walker, an astronomer with the National Optical Astronomy Observatory in Tucson, Arizona, and a board member of the International Dark-Sky Association. Jurisdictions interested in effectively reducing light pollution can turn to the two atlases to research before-and-after maps, and compare what’s worked and what hasn’t, she says.
“This atlas affords a consistent way of comparing light pollution in different areas of the world over the last 15 years,” she says.
This map shows light pollution in the Eastern Hemisphere. Illustration by Fabio Falchi, Google Earth
Falchi’s work, done completely in his off hours as a labor of love, helps put the extent of the problem into perspective, Duriscoe says.
“To tackle this on a global scale, nobody else before has attempted it,” he says. “When you can stand back and look at the whole Earth and the impact of our modern lifestyle on the ability of all cultures to enjoy the natural nocturnal environment, it shows how we just take it for granted.”
Protecting Natural Cycles
At one time, communities with large telescopes, like the Palomar Observatory outside of San Diego, California, prided themselves on their efforts to protect the night sky, though that attitude seems to have waned over the last several decades, Duriscoe notes. Now, however, with more research emerging about the negative impacts on humans of overexposure to light, there has been an uptick of interest in combating the 24-hour lifestyle.
Falchi has been personally involved in his own community in changing approaches to outdoor lighting. As the current president of the nonprofit CieloBuio dark skies advocacy organization, he spearheaded a petition effort in the late 1990s to enact lighting reform laws in Lombardia, the region where he lives and works. With controls on the types of new fixtures being installed and limits on light intensity in given areas, despite a twofold increase in the number of new lights, light-pollution levels in the region have remained constant from 2000 to today.
Though much of Italy is now governed by similar laws, it’s still only a start, Falchi says.
“This is not a sufficient measure for controlling light pollution, but simply a stop in the increase,” he adds. “For almost all other pollutants—chemical, particulate, carbon monoxide, or anything else, graphs show that almost all of them have decreased over the last 20 years. We need to decrease pollution from light as well.”
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