The Day the Lights Dimmed

According to the paper published by Falchi et al in June 2016 around 80% of the world’s population suffer from light pollution. The paper, ‘The new world atlas of artificial night sky brightness’, further noted that in Europe and the USA over 99% of people experience skyglow.

Skyglow is one part of light pollution, and refers to the brightening of the night sky over inhabited areas. The prominence of this feature was demonstrated last week in Puerto Rico when a large fire in the Aguirre Power Plant, in the area of Sanlinas, caused the lights to dim across the island.

The fire began when a power switch overheated causing an oil tank to explode. The resulting fire spread over a three acre area and effected power generation and cut off water supplies. Around one and half million people lost power equating to over 40% of the island’s population and 350,000 people were cut off from water.

This power loss gave a spectacular example of the skyglow effect, as it was possible to produce comparable night time pictures from satellites. Pictures twenty-four hours apart were taken by the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the Suomi NPP satellite. In a recent blog on the Rio Olympics, we described the instrument in detail.

Image of Puerto Rico, acquired on 21st September 2016 from the VIIRS instrument. Data courtesy of NASA/ NASA’s Earth Observatory

Image of Puerto Rico, acquired on 21st September 2016 from the VIIRS instrument. Data courtesy of NASA/ NASA’s Earth Observatory

On the right is the ‘before image’ acquired at 2.50am local time on the 21st September. On the North coast, just to the right of centre, the bright white concentration shows the light from the capital city, San Juan. This city is the centre for manufacturing, finance and tourism for the island, and the site of its key seaport. Light can also be seen around the edge of the island, which effectively maps the islands interstate highways. The power outage affected the whole island including the westerly cities of Mayagüez and Aguadilla, the southern coastal city of Ponce and Humacao on the east coast.

Image of Puerto Rico, acquired on 22nd September 2016 from the VIIRS instrument. Data courtesy of NASA/ NASA’s Earth Observatory

Image of Puerto Rico, acquired on 22nd September 2016 from the VIIRS instrument. Data courtesy of NASA/ NASA’s Earth Observatory

Compare this with the ‘after image’ to the right which was taken approximately twenty four hours later at 2.31am on the 22nd September. Power had already started coming back on by this point, but only 130,000 were connected in the first twelve hours, and so there is still a major outage. The concentration around San Juan is reduced significantly, as are the lights mapping the interstate highways. All the areas are still identifiable, but the reduction in skyglow is apparent and obvious.

Whilst the pictures of cities and islands at night can be amazing, light pollution does have negative impacts on both us and the natural world – particularly nocturnal wildlife.

These images demonstrate the impact of skyglow, and we should all look to try and reduce the amount of light pollution in own lives, cities and countries.