The Milky Way disappears in artificial light originated by the city light of Berlin. Light pollution dims the view at the stars and affects ecosystems. Credit: A. Jechow / IGB
At night, can you see the Milky Way? If so, you are part of a dwindling percentage of the human species.
An international research team has assembled a second atlas of worldwide artificial sky brightness due to light pollution (Sci. Adv., doi:10.1126/sciadv.1600377). The group, led by an Italian scientist with collaborators in three other countries, used high-resolution, low-light images from a satellite launched in 2011, supplemented with ground-based background-sky measurements.
Among the 2016 findings: More than 80 percent of the world's population lives under light-polluted skies, up from two-thirds of humanity when the first light-pollution atlas was compiled in 2001. (The definition of “light-polluted” is an artificial sky brightness greater than 14 microcandelas per square meter at the zenith point.) Nearly 60 percent of Europeans and almost 80 percent of North Americans cannot distinguish the Milky Way from the background sky.
Fifteen years ago, the original atlas was based on data from a U.S. Defense Department satellite. This time around, the team analyzed images taken with the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite, jointly operated by the U.S. National Oceanic and Atmospheric Administration (NOAA) and NASA. Each pixel covers a spatial resolution of 742 m.
The VIIRS sensor that the group used picks up light from 500 nm to 900 nm, which only partially overlaps with human vision. The atlas team calibrated the space-based observations with “citizen scientist” data from handheld meters at more than 20,000 sites around the world.
As Earth's cities convert high-pressure sodium exterior lighting to “white” LED fixtures with a 4000-K color temperature, the researchers predict, the background brightness of the night sky could more than double—and this effect won't be detectable by the VIIRS sensor, which cannot see at blue wavelengths. Lead author Fabio Falchi, of Italy's Light Pollution Science and Technology Institute, said in a statement, "Unless careful consideration is given to LED color and lighting levels, this transition could unfortunately lead to a 2-3 fold increase in skyglow on clear nights."
Besides Falchi, scientists from NOAA, the U.S. National Park Service, the University of Colorado (USA), two German institutions and the University of Haifa (Israel) participated in the new atlas project.