The richness of how humans sprinkle their lights across the nightscape is striking when viewed from orbit. These lights present a spectacular display, like tendrils outlined with the glimmer of a Broadway marquee. They also display a recognizable form of pollution by light. Colored patterns caught in a triangle between technology, geography, and culture radiate into space something about who we are.
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If the lights are mercury vapor, cities appear blue-green. Sodium vapor yields yellow-orange. Some cities are mostly dark, yet adorned with bright main arteries. In others, whole urban areas resemble the "yellow zone" on a standard atlas. Some cities have major streets in north-south, east-west grids; in others, streets radiate outward like a spider web. The countryside in some areas displays a fractal pattern that resembles a snapshot from Mandelbrot space.
Political boundaries emerge as well, but distinct from those seen by day, and most surprisingly from the vantage point of orbit.
In the ocean, as if forming a constellation of stars, fishing boats with intense xenon lights create unfamiliar members of the Zodiac.
Like the spectacular sunsets caused by air pollution, cities at night (a form of light pollution) may be among the most beautiful unintentional consequences of any human act. Las Vegas, as if a beacon for humanity, appears as truly the brightest spot on Earth.
Cities around the world each project something different into the night. Could their designers and builders have anticipated this? It’s doubtful.
The unaided eye sees incredible detail when gazing upon cities during a 40-minute pass around the dark side of the planet. Efforts to record this beauty on film are only a natural extension of human desire. But capturing clear images of cities at night has eluded the best efforts of astronauts for years. Detail becomes a fleeting phenomenon due to orbital motion, which scoots by at an amazing speed of 4.4 miles per second. The very act of getting a daytime picture is hard enough. During an exposure of 1/1000th of a second, 23 feet of Earth move past, and the resulting image gets blurred. Appreciating the effects of this motion is something that every rookie learns after arriving on orbit. When using the monstrous 800mm telephoto lens, it takes a month or more of practice until new crewmembers can achieve its ground resolution of 10 feet.
Clear images of cities at night require such slow shutter speeds that, if taken on Earth, they’d require a tripod. To compensate, you float over the window and slowly pan the camera while looking through the viewfinder. This manually cancels out orbital motion, while, to the best of your ability, you hold the camera still in all other axes. Then you depress the shutter button and make the exposure. The slightest jitter results in a blurry image.
Such photos tend to disappoint because of how poorly they compare to the real spectacle. It was no different for me and my crewmates, commander Ken Bowersox and flight engineer Nikolai Budarin, of Expedition 6, aboard the International Space Station from November 2002 to May 2003. Our best efforts at obtaining images of cities at night fell far below what we saw through the window. After numerous failures to capture this beauty, you tend to revert to taking it in with your eyes, simply enjoying the temporary satisfaction of being there.