Light pollution in urban centers creates a sky glow that can blot out the stars. The brighter the area in this map the harder it is to see stars and constellations in the night sky.
The Milky Way, the brilliant river of stars that has dominated the night sky and human imaginations since time immemorial, is just a faded memory for one third of humanity and 80 percent of Americans, according to a new global atlas of light pollution produced by Italian, Israeli, and American scientists.
“We’ve got whole generations of people in the United States who have never seen the Milky Way,” said Chris Elvidge, a scientist with NOAA’s National Centers for Environmental Information. “It’s a big part of our connection to the cosmos—and it’s been lost.”
The artificial sky brightness levels are those used in legend and indicate the following: up to 1% above the natural light (black); from 1 to 8% above the natural light (blue); from 8 to 50% above natural nighttime brightness (green); from 50% above natural to the level of light under which the Milky Way is no longer visible (yellow); from Milky Way loss to estimated cone stimulation (red); and very high nighttime light intensities, with no dark adaption for human eyes (white).
For the purpose of this atlas, we set the level of artificial brightness under which a sky can be considered “pristine” at 1% of the natural background.
The dark gray level (1 to 2%) sets the point where attention should be given to protect a site from a future increase in light pollution. Blue (8 to 16%) indicates the approximate level where the sky can be considered polluted on an astronomical point of view. The winter Milky Way (fainter than its summer counterpart) cannot be observed from sites coded in yellow, whereas the orange level sets the point of artificial brightness that masks the summer Milky Way as well. In areas that appear red, people never experience conditions resembling a true night because it is masked by an artificial twilight.