A project dubbed Cities at Night uses photos that were taken by astronauts who work at the International Space Station (ISS) to measure the amount of light pollution across the globe.

The aim of the project is to come up with a global color map of the Earth at night based on the photos that were taken from the ISS using standard digital camera.

The project, which started last summer and required the mapping of over 130,000 high resolution photos using geocentric details, does not only take into account the amount of light produced by cities around the world. It also looks at the effects of smaller sources of scattered light, which to date has not yet been quantitatively measured.

The ISS is the only location where it is possible to estimate the amount of the different types of lighting technologies that are tapped by cities worldwide and to measure the effects of light pollution on human health and the environment.

 "Satellite images help us measure and compare large illuminated areas. With the colors of the images taken by astronauts on the International Space Station, we can measure the efficiency of lighting in many cities on the planet," the project's website reads.

The images were calibrated with the aid of the stars in the background sky over the orbiting laboratory and ground-based measurements of the brightness of the night sky.

The method used in the project, which connects measurements of light pollution from space with ground-based measurement of the night sky brightness, has for the first time allowed for the reliable mapping of light pollution over extended areas.

The project already helped confirm that the diffused glow around cities that are visible from space comes from street lighting and this is separate from lights that come from building and vehicles.

Scientist though, could not determine the diffuse lighting's exact origin based on low-resolution satellite images alone.

Alejandro Sanchez de Miguel, from the Universidad Complutense de Madrid in Spain, and colleagues found that the countries and cities in Europe with higher public debt also happen to have higher energy consumption for street lighting for each inhabitant.

The study also estimated that the total cost of energy consumption for streetlight in the European Union is 6,300 million euros per year.

The scientists involved in the project said that the next step would be to gather funding that would keep the project running so that the color map of the nightside of our planet can be extended. 

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