14 DAY TRIAL // A collaboration of physicists and ecologists in Germany has recently determined that cloud covers are largely responsible for the brightness of the night sky above the world's major cities. The atmospheric features also contribute to increasing light pollution, the team explains.
What's interesting to note here is that clouds generally tend to block light trying to reach the ground. In natural environments, they filter starlight, and contribute to creating complete darkness.
But it seems that this effect is entirely reversed above major metropolises, say experts at the Free University of Berlin (FU) and the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB).
Datasets used in this study were collected over a period of five months, in the spring and summer of 2010. Scientists took clear and cloudy sky brightness measurements with the help of a set of scientific tools called the “Sky Quality Meters.”
Two of the measuring stations the collaboration used were located 10 and 32 kilometers from the center of Berlin, respectively. This helped the experts distinguish between the effects that clouds had on urban and natural environments.
“We found that overcast skies were almost three times brighter than clear at our rural location, and ten times as bright within the city itself,” explains Dr. Christopher Kyba, who holds an appointment as a physicist at the FU Institute for Space Sciences.
He is also the lead author of the new study, which is published in the March 2 issue of the open-access, peer-reviewed scientific journal PLoS ONE. The magazine is edited by the Public Library of Science.
“The astronomers who founded the study of light pollution were concerned with how sky glow obscured the stars on perfectly clear nights,” Kyba goes on to say.
“Researchers studying the potential influences of sky glow on human or ecosystem health often cite the results from satellite measurements taken on clear nights,” the expert explains further.
He says that the overall level of light amplification that clouds were found to be responsible for is considerable, and that it should be taken into account when trying to assess the biological impacts this type of pollution has on humans and the environment.
“Recognition of the negative environmental influences of light pollution has come only recently,” adds ecologist Dr. Franz Hölker, who was also an author of the PLoS ONE paper.
“"Now that we have developed a software technique to quantify the amplification factor of clouds, the next step is to expand our detection network,” he explains.
“The Sky Quality Meter is an inexpensive and easy to operate device, so we hope to recruit other researchers and citizen-scientists from around the world to build a global database of nighttime sky brightness measurements,” Hölker concludes.