1. Trailblazer

    Trailblazer Moderator Staff Member

    A section of this video (starting at 4:27) is doing the rounds on Facebook.



    eg

    upload_2014-11-18_11-39-9.

    What we are seeing here appears to be a contrail that is almost perfectly aligned with the low sun (which is apparently close to the horizon, hidden behind the building). The aircraft is heading towards the camera, and then makes a left-hand turn.

    The angle of the sun is such that the bottom of the near-vertical section of contrail, facing us, is in shadow and appears black against the brightly lit surroundings.

    Once the aircraft turns, it is no longer aligned with the sun and the contrail appears sunlit, while casting a shadow onto the clouds. The shadow is most defined where it lines up with a long portion of the trail, and becomes very diffuse after the turn takes the trail out of alignment.

    Do you agree with this analysis?

    shadow.
     
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  2. Mick West

    Mick West Administrator Staff Member

    Yes. It's an interesting combination of a contrail that is self-shadowing, and creating an edge shadow that extends beyond the contrail itself. Here's a slider comparison of how it evolves over time (90 seconds between the two shots).
    [​IMG] [​IMG]


    Here's another example:
    http://contrailscience.com/contrails-dark-lines-chemtrails/
    [​IMG]

    A big clue that these dark contrails are just normal contrails in shadow is that they only ever happen in certain lighting conditions. Also, if he had kept filming for a few more minutes, he would have seen that all the trails would be the same color when the sun dipped enough below the horizon.
     
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