“You hate to see all this blue light put in, which is supposed to have a 20-year life cycle. I’m thinking, ‘Oh, god,’” Duriscoe says.

Ironically, the spread of these lights will be harder to track in future atlas updates. The satellites that track light pollution don’t see this part of the light spectrum very well, so as LEDs proliferate, the robot’s-eye-view will actually seem better, while to our eyes it will look worse. Falchi and his colleagues estimated that if European cities continue adapting blue-light LEDs without blocking any of their glow, the sky will look two to three times brighter at night than it does now.

“This is not changing the lanterns. It’s simply changing the spectrum of light that we used,” Falchi says. “We are used to high-pressure sodium, which is yellow, and when we change to cool white LEDs, that is very bright to our eyes. The solution should be to use warm-light LEDs.”

Some cities are already worse than others, and this is not necessarily because of their populations. Munich and Milan each have roughly 1.5 million inhabitants, but Milan is much brighter than its German counterpart. The same is true of Rome and Berlin: The capital cities have about 3 million residents, but Rome shines far more brilliantly. Falchi, who is Italian, says he thinks his countrymen are just accustomed to brighter light levels.

Earth does have a few truly dark spots — which happen to include some of its poorest places — in Africa, southeast Asia, and South America. Just 1 percent of Mauritania does not have a pristine sky. A visitor can also see a virgin night in 99 percent of Greenland, and parts of New Zealand and the Australian Outback are pretty light-free.

But in the world’s most populous cities, like Singapore, New York, Tokyo, and others, a resident might never experience true darkness, let alone a pristine sky. Falchi and his colleagues estimate that in those places, the sky remains so bright at night that a person’s eyes don’t ever become truly dark-adapted. This is called scotopic vision, when the rods in the retina are the only cells processing light, and it is best experienced outside under starlight—sneaking down the hallway at night, guided by the glare of outdoor street lamps, doesn’t count.

Duriscoe hunted for a house in a community that has no such street lamps, and readily acknowledges that he is fortunate to have not only found one, but to be privileged enough to live there. You should not have to drive several hours into the nighttime wilderness merely to see the stars, he argues, and partly for political reasons.

“You are making it into an elite activity, where you have to be rich to enjoy it. You have to get a ticket to Mauritania or Namibia or the western United States to enjoy it. That’s really oppressive,” he says.

It’s easy to muse over what the loss of night means for civil rights or human culture. But much lowlier creatures than us are also sky watchers. Sea turtles are a famous example, and many species of birds are also thought to use moonlight to get their bearings. The humble dung beetle requires a view of the Milky Way to navigate and roll its precious balls of poop in the right direction. Other nocturnal creatures probably use the galactic plane in this way, too. But as the new atlas shows, the galaxy is disappearing from much of the Earth.

A rapidly growing community of scientists is studying what might happen as a result. The biological impacts of artificial light at night, from its effects on bats and insects to harms on human health, are just beginning to be appreciated. The atlas will serve as a crucial backdrop for these studies. Researchers will be able to quantify how bright a place is, and even study what happens if things change — if the lights get dimmer, and the natural nightscape returns.