Double Contrail Shadows

June 02, 2017

Double_Contrail_Shadows_HimmLL Sparg L3 III++ 069 - det1 - heko2 (1)

Photographer: Hans Juergen Heyen
Summary Authors: Hans Juergen Heyen; Jim Foster

This photo shows a conspicuous contrail with not one shadow but two, above Meerbusch, Germany, in the lower Rhine region. Since the upper troposphere this day was relatively clear and also somewhat moist, I noticed a number of contrails crossing the sky. Many of these contrails were casting shadows on thin cirrus clouds. On the photo above, because there are two shadow projections, this means that that were are at least two cloud layers; the fainter shadow is being cast upon a layer a little further away than the layer responsible for projecting the first shadow.

Note that a required condition for the shadow of a contrail to be observed is that the contrail itself must point toward the Sun. But how contrail shadows are positioned relative to the contrail frequently seems at odds with how we think they should look -- they often appear to be cast on clouds above the contrail. The primary reason for this is perspective. We're viewing them as we look toward the source of illumination, the Sun, instead of away from it, which is the way we're used to seeing shadows. Photo taken on March 25, 2017.

Photo Details: Camera Maker: Panasonic; Camera Model: DMC-FZ300; Focal Length: 68.1mm (35mm equivalent: 379mm); Aperture: ƒ/7.1; Exposure Time: 0.0006 s (1/1600); ISO equiv: 100; Software: Microsoft Windows Photo Gallery 6.0.6001.18000.