All over the country, dark places are disappearing from the map. Computer images based on NASA photos show a steady spread of lights across the land, and the projected view of 2025 imagines the entire country east of the Mississippi as one great rash of yellows and reds, the most intensely populated areas blisters of white. Even west of the great river, only scraps of black remain, each surrounded by a civilization gnawing at its ragged edges.
Seen from satellites at night, our planet’s continents burn as though on fire. Across the globe, the collected glow from streetlights, parking lots, gas stations, shopping centers, sports stadiums, office buildings, and individual houses clearly details borders between land and water, sometimes spreading even into the sea on squid fishing boats, their spotlights built to mimic noonday sun. It would be one thing if all this light were beneficial. But while some does good work—guiding our way, offering a sense of security, adding beauty to our nightscape—most is waste. The light we see in photos from space, from an airplane window, from our 14th-floor hotel room, is light allowed to shine into the sky, into our eyes, illuminating little of what it was meant to and costing us dearly. In ways we have long understood, in others we are just beginning to understand, night’s darkness has always been invaluable for our health and the health of the natural world, and every living thing suffers from its loss.
Not long ago, I decided to see for myself what was left of the night. I would travel from our brightest, most intensely lit cities into the desert west, to a place where I could experience real darkness.
We like to think that darkness “falls,” as though it were like snow, but as the earth turns its back to the sun, darkness actually rises from the east to wash and flood over land and sea. If you’ve ever stood at dusk and seen a gloaming on the eastern horizon, as though clouds were gathering, a thunderstorm brewing, that’s what you’re seeing—the earth’s shadow as we rotate into it. What we call “night” is the time when we are caught in that shadow, a shadow that extends into space like the cone to Earth’s ice cream, a hundred times taller than it is wide, its vertex 860,000 miles above the earth. Dawn comes as we rotate out of that shadow into the edges of direct sunlight.
Humanity evolved over millions of years to this rhythm of bright days and dark nights, and it’s only within the past century or so that we have disrupted this ancient pattern. The potential consequences—according to sleep researchers, epidemiologists, cancer researchers, and other scientists—are enormous. New research suggests that confusing our circadian rhythms and impeding our production of the darkness hormone, melatonin, has the power to dramatically harm our body’s ancient codes.
The World Health Organization now lists night-shift work as a probable carcinogen, and working at night has been linked to increased risk of diabetes, obesity, and cardiovascular disease. While those working third shift are affected far more than the rest of us, almost everyone living in the developed world is affected by nighttime light, including that coming from our electronic gadgets, and scientists are trying to determine how much light causes which problems.
Similarly, artificial light affects our ecosystems. Around 30 percent of all vertebrates and more than 60 percent of all invertebrates are nocturnal, and many of the rest are crepuscular (active at dawn and dusk). While most of us are inside and asleep, outside, the night world is wide awake with matings, migrations, pollinations, and feeding—all now suffering interference.