# Contrails - not a conspiracy question

**URL:** <https://boards.straightdope.com/t/contrails-not-a-conspiracy-question/587512>\
**Category:** Factual Questions\
**Created:** [July 1, 2011, 3:14pm UTC](https://boards.straightdope.com/t/contrails-not-a-conspiracy-question/587512 "2011-07-01T15:14:16Z")\
**Posts on this page:** 1\
**Page:** 2

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [July 25, 2011, 12:14pm UTC](https://boards.straightdope.com/t/contrails-not-a-conspiracy-question/587512/21 "2011-07-25T12:14:10Z")

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> [@brewha](#):
>
> Ha! Contrails can be caused by low pressure as a result of lift OR Jet exhuast. Have a look at the recent shuttle landing. There’s no engines running at all - still we have contrails:
> 
> [Shuttle Landing](http://news.yahoo.com/photos/image-provided-nasa-space-shuttle-atlantis-touches-down-photo-112009198.html)

**LSLGuy** is right: contrails are, by definition, the visible trails due _only_ to the condensation of engine exhaust. Although wingtip vortices may be rendered visible by condensation and/or dust, they are not called contrails.

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