"Col" wrote in message
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"Graham P Davis" wrote in message
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On Tue, 28 Jun 2011 09:39:54 +0100, Col wrote:

I've never seen anything like this before, at the end of a dissapating
contrail there was what can only be described as a black 'streak',
perfectly straight and very noticeable. The whole effect lasted a minute
at best.

A bit of Googling (unfortunately most of it's conspiracy theory
nonsense) suggests that this is the answer:
http://contrailscience.com/contrails...es-chemtrails/ I think the
"edge shadow (volumetric shadow)" is what I saw, the contrail was lined
up with the sun.

However contrails must be crossing the sun all the time and I've never
seen that effect before. I wonder if you only see it if the sun is at
exactly the right altitude and the observer is in exactly the right
position wrt the sun & contrail.

Has anybody else seen this effect, it was definately a what the hell is
*that* moment!

Here's one I prepared earlier. ;-)

http://farm7.static.flickr.com/6059/...797844f5_b.jpg

That's exactly what I saw. I don't know whether it went right to the
horizon as there is a building blocking the view.
Was that taken this morning?
--
Col

Bolton, Lancashire
160m asl

I have always taken that effect to be a shadow sact by the contrail in the
haze which otherwise makes the sky paler than it would otherwise be. Of
course the contrail has to be in the right location and direction, relative
to the sun (ie pointing nearly towards the sun so that the sun's rays are
significantly attenuated as they pass through the contrail) and the
observer, for the effect to be noticeable.

Roger