Noctilucent Clouds Observed from Paris, France

August 20, 2020

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3aAugust  2020 Viewer's Choice

Photographer: Bertrand Kulik
Summary Authors: Bertrand Kulik; Jim Foster

The photos above showing noctilucent clouds were captured at 11:10 p.m. on July 5 (2020), from my home in Paris, France. These night-shining clouds are composed of water ice that forms as water vapor condenses around tiny particles in the upper atmosphere. They can only be observed if the upper atmosphere (mesosphere) is sufficiently cold and if the Sun is at the proper angle to illuminate them -- between 6 and 16 degrees below the horizon. Because the mesosphere is counter-intuitively coldest (120 degrees C or about 150 kelvin). in late spring, noctilucent clouds are most frequently reported at this time of year and also in early summer. The photo at bottom is a close-up that shows some wavy characteristics of these particular clouds.

Photo Details: Top - Camera Canon EOS 5D Mark III; Software Adobe Photoshop 21.2 (Windows); Exposure Time 1.600s; Aperture ƒ/5.0; ISO 400; Focal Length 100.0mm. Bottom - same except: Exposure Time 5.000s; Aperture ƒ/5.6; Focal Length 400.0mm.