Photos from ISS help measure light pollution on Earth

Scientists are tapping into photographs taken by astronauts aboard the International Space Station (ISS) to reliably measure the amount of light pollution worldwide.
Light pollution is excessive or obtrusive artificial (usually outdoor) light. Too much light pollution washes out starlight in the night sky, interferes with astronomical research, and disrupts ecosystems.
The new study by scientists from the Universidad Complutense de Madrid, Spain, and the Cegep de Sherbrooke in Canada, not only includes the well-known signatures of cities and streets, but also the effects of faint indirectly scattered light, which up to now had not been measured quantitatively, researchers said.

The new results confirm that this diffuse glow, which is seen from space, is scattered light from streetlights and buildings.
This is the component responsible for the brightening of the night skies in and around cities, which drastically limits the visibility of faint stars and the Milky Way.
The team also concluded that European countries and cities with a higher public debt also have higher energy consumption for street lighting per inhabitant, and that the total cost of the energy consumption for street lights is 6,300 million euros/year in the European Union.

In the study, researchers together with members of the public, worked on a project called Cities at Night.

The aim is to produce a global colour map of the Earth at night from pictures taken by astronauts on the ISS using a standard digital camera.
Starting in July 2014, this huge project required the cataloguing of over 130 000 images - the ISS's entire high-resolution archive - and geo-referencing them to place them on a map.
The images were also calibrated using the stars in the background sky over the ISS, as well as ground-based measurements of the night sky brightness.
The images were also calibrated using the stars in the background sky over the ISS, as well as ground-based measurements of the night sky brightness.

Previously, light pollution measurements had to be done in situ and would contribute only a single measurement to the light pollution map.
This new method, connecting space-based measurements of light pollution with ground-based night sky brightness measurements, makes it possible, for the first time, to map light pollution reliably over extended areas.
Previously, light pollution measurements had to be done in situ and would contribute only a single measurement to the light pollution map.
This new method, connecting space-based measurements of light pollution with ground-based night sky brightness measurements, makes it possible, for the first time, to map light pollution reliably over extended areas.

The findings were presented at the 2015 IAU General Assembly in Honolulu, Hawaii.