WORLDTECHNASA Earth Observatory Image Shows US Heartland Lights Before Dawn
An astronaut aboard the International Space Station photographed a wide-angle view of nighttime lights across the eastern United States at 4:54 a.m. Central Daylight Time, under nearly cloudless skies. The image, released by NASA Earth Observatory, shows how cities and highways stand out against the darkened landscape.
What the photograph captures
The frame was taken at 4:54 a.m. Central Daylight Time, which corresponds to 09:54 Universal Time. With almost no clouds in the sky, the astronaut had a broad view of illuminated cities of varying sizes spread across the dark terrain.
Mid-sized cities including Indianapolis in Indiana, Cincinnati in Ohio and Louisville in Kentucky stand out among the brightest points in the scene. The links between them along state and interstate highways also glow clearly.
Airglow along the horizon
Above the network of city lights and the lower atmosphere, a diffuse band of green and orange runs along the left horizon. NASA Earth Observatory identifies this as airglow, which is generated when sunlight hits atoms and molecules high in the atmosphere, prompting them to release photons.
On the right, the first light of the Sun traces an arc along the horizon. Sunrise was roughly an hour away on the East Coast and about two hours away in Chicago.
Why night imagery matters
Astronaut photographs and other remote sensing observations of nighttime lights are scientifically useful for following changes in the built environment. In the wide view, Chicago's lights look like a uniform pale yellow, yet a close-up photograph reveals a range of hues that reflect different kinds of lighting.
Researchers using NASA's Gateway to Astronaut Photography of Earth archive have built a method to tell apart lighting types within the pixels of night photographs. Measuring the brightness, colour and extent of urban lights in a systematic way can shed light on how cities expand and evolve.
Satellite data complement the photographs
Satellite sensors also monitor changes in lighting. NASA's Black Marble nighttime lights product suite draws on satellite observations to produce science-quality records of nighttime lights worldwide on daily, monthly and yearly scales.
In the eastern United States, scientists have used these data to follow power outages and their restoration after major storms, changes tied to new infrastructure, and the switch from older lamps to LEDs.