Clouds at Night Comparison

September 07, 2011

Cloud_comparison (2)

Photographer: Ray Stinson; Christopher Kyba; Christopher's Web site
Summary Author: Christopher Kyba; Jim Foster

These two images contrast the impact that clouds have on the nighttime sky under pristine and light polluted conditions. The photo at left, taken by Ray Stinson in Glacier National Park, Montana, shows that when no light pollution is present, clouds appear inky-black and act to darken the sky further. In and nearby cities, however, the situation is reversed, as is shown in the photo at right, taken by Christopher Kyba in Berlin, Germany. In this case, the summer night sky is 10 times brighter on overcast nights than on clear nights.

Artificial brightening of the sky has consequences on flora and fauna alike. For instance, jet-black overcast nights above oceans and seas allow zooplankton to rise close to the surface and feast on phytoplankton without risk of being seen and eaten by fish. Though, in urban areas located on coasts, zooplankton stay further beneath the surface to remain unseen. Brightening of the sky by clouds is expected to take the zooplankton even deeper. In humans, there’s some suspicion that skyglow is related to increased incidence of prostate and breast cancers, possibly as a result of disruption of circadian rhythms. This hypothesis may be tested in future studies by comparing the rates of these cancers in equally bright cities that experience different rates of clear and cloudy skies. Glacier National Park photo was taken on July 29, 2011 and Berlin, Germany photo was taken on August 16, 2010.

Photo details: Glacier National Park - Canon EOS REBEL T1i camera; 35 mm focal length; 25 second exposure time; ISO equivalent of 6400. Berlin - Canon EOS 400D camera; 22 mm focal length; 13 second exposure time; ISO equivalent 800.