Atlas shows night sky pollution

Homes and industry light up the night sky

Two thirds of the world's population never see a truly dark starry sky from where they live because light pollution from human activity obscures the view.

Large numbers of people in many countries have had their vision of the night sky severely degraded

Pierantonio Cinzano

In western Europe and the continental United States, the figure rises to 99%, say the scientists behind a new light pollution map of the world.

Awareness of the effects of light pollution has been growing in recent years but the US-Italian team say that their map is the first to properly quantify and link artificial illumination of the night sky with where people live.

Researchers from the Light Pollution Science and Technology Institute in Thienes, Italy, and the United States National Oceanic and Atmospheric Administration (Noaa) calculated the effect light coming from homes and industry would have on the visibility of the night sky using data from US Air Force satellites.

World Atlas

They are publishing their results as the World Atlas of Artificial Night Sky Brightness.

Oil and gas platforms light up the sky over the North Sea

The map clearly shows major population centres but also other features like the illumination from oil and gas platforms at sea.

"Large numbers of people in many countries have had their vision of the night sky severely degraded," said Pierantonio Cinzano, one of the Italian researchers.

"And our atlas refers to the situation in 1996-97. It is undoubtedly worse today," he said.

No Milky Way

The atlas shows that:

• More than 99% of the populations of the European Union and US, and two thirds of the world's population suffer some degree of light pollution
• More than two thirds of the US population, about half of the EU population and one fifth of the whole world's population live where they no longer have the possibility of seeing the Milky Way with the naked eye, and
• for 40% of the US population, one sixth of the EU's population and one tenth of the world's population, it is never dark enough at night for human eyes to become adapted to night vision.

Satellite data

The atlas is an improvement on previous maps because it shows more than just a satellite's eye view of the light coming from the Earth.

The raw satellite data has been processed to allow for the way that light is reflected back to Earth by the atmosphere.

"Many areas which were believed to be unpolluted because they appear completely dark in night-time satellite images, on the contrary show in the atlas non-negligible artificial brightness levels, due to the outward propagation of light pollution," the researchers write in the journal Monthly Notices of Royal Astronomical Society.

Romantic lighting

But the news is good for the inhabitants of Venice:

"We noticed that Venice is the only city in Italy with more than 250,000 inhabitants from which an average observer has the possibility to view the Milky Way from the city centre on a clear night in 1996-97.

"Even though Venice's historic centre is imbedded in the strong sky glow produced by the terra firma part of the city, its average artificial sky brightness is still lower than cities with 80,000 inhabitants in the nearby Veneto plane.

"This is due mainly to the unique low intensity romantic lighting of this city, which deserves to be preserved," they write.

Images: P Cinzano, F Falchi (University of Padua), C D Elvidge (NOAA National Geophysical Data Center, Boulder). Copyright Royal Astronomical Society. Reproduced from the Monthly Notices of the RAS by permission of Blackwell Science.