A database of 130,000 photographs taken by astronauts aboard the International Space Station (ISS) is being used to measure the Earth’s light pollution, and now its findings show that street lights are behind a mysterious glow over cities.
The major light pollution survey was undertaken by members of the Cities at Night citizens science project, which managed to obtain the entire ISS high-resolution image catalogue.
Since its foundation, the aim of the project has been to produce a global colour map of the Earth at night using a standard digital camera and, over a year later, has geo-referenced it to place cities on a map.
Until now, light pollution measurement was only conducted on the ground in a particular city, which was not only time consuming but not terribly efficient.
Now, however, this new method allows for connecting space-based measurements of light pollution with ground-based night sky brightness measurements, which for the first time allowed them to map light pollution reliably over extended areas.
An image of Milan taken earlier this year by ESA astronaut Samantha Cristoforetti.
With this new data, the Cities at Night project team has been able to confirm the origins of a mysterious glow seen over cities at night detected by the US Defense Meteorological Satellite Program.
With its new high-resolution photography and sky-brightness surveys, it has been able to observe the direct relationship between the diffuse light observed and light pollution from artificial lights, particularly street lights.
A heat map of Madrid at night. The white colour indicates the brightest light. Image via A. Sánchez de Miguel, J. Zamorano/NASA/ESA
Interestingly, the new findings have been able to show that there is a direct correlation in Europe between a city’s public debt and it having a higher energy consumption of street lighting per inhabitant.
It has also been able to calculate that the European Union (EU) spends €6.3bn each year on energy for street lights, calculated from the energy output in these photos.
The Cities at Night’s team now has plans to create an interactive Google Maps-style map to allow someone see what levels of light pollution there are in their city, which they hope to achieve with the backing of a €50,000 Kickstarter campaign.
In the meantime, it has created a basic map showing the results of some of its findings, including a snapshot of Dublin at night.
Light pollution over Dublin image via Shutterstock
