Cities At Night Seen From Space!

Don Pettit built and installed a "barn-door tracker" to enable him to take nighttime photographs from the International Space Station. Astronauts use the tracker to keep a camera steady during long exposures while the station moves above the Earth's surface.

A barn-door tracker is a camera mount commonly used by astronomers and photographers on the ground to capture images of stars and planets in the night sky. The camera is mounted on a hinged platform that can be moved very slowly and precisely (by turning a knob). On the ground, the device allows photographers to compensate for the rotation of the Earth relative to the stars. In space, it allows astronauts to compensate for the movement of the Space Station relative to the Earth below. The careful coordination keeps the targeted city in the same position in the camera's field of view during the long exposure, even though both the station and Earth's surface are moving.

Pettit's tracker and nighttime photography techniques produced hundreds of images of cities from around the world that had estimated resolutions (level of detail) of about 60 meters. Since then, a few other crew members have been able to successfully master night photography techniques. In late 2007 through early 2008, Expedition 16 Flight Engineer Dan Tani acquired a number of striking images of cities at night, including some exciting images taken with the longer, 400 mm lens, producing images with an estimated ground resolution of less than 10 meters.

Border cities like Ciudad Juaréz, Mexico, and El Paso, Texas, illustrate different city patterns side-by-side, suggesting cultural influences on the development and growth of cities and infrastructure. Ciudad Juaréz, supports at least 1,300,000 people.

On the U.S. side of the Rio Grande, El Paso is marked by the brightly-lit Interstate Highway I-10 that cuts across the city. Although the area of El Paso, with an estimated population of slightly more than 600,000 is roughly on the order of the area of built-up Ciudad Juaréz, the density of settlement evidenced by the distribution of lights, is much less.

The rapid growth in Jiddah and Mecca in Saudi Arabia can be mapped from the lighting patterns, and the road connecting them stands out as a bright string in the surrounding dark desert.

Cities from different regions of the Earth are also identified by differences in their nighttime lights. Japanese cities glow a cooler blue-green than other regions of the world. Newer developments along the shore of Tokyo Bay are characterized by orange sodium vapor lamps, while the majority of the urban area has light green mercury vapor lamps.

Chicago, Illinois, is home to roughly three million people, but the wider metropolitan area includes nearly 10 million. By day (top), the cement-colored urban center of the city blends almost imperceptibly into the gray-green colors of suburbs and then farmland. By night (lower), the region's ten million people cannot be missed.

A beautiful high resolution photograph from NASA of the Earth's city lights. The brightest areas of the Earth are the most urbanized but not necessarily the most populated. This can be seen when comparing China and India with western Europe. You can find the high resolution 2400 x 1200 jpeg from NASA here.