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We searched the Net to find the answer to your question and, in the process, we discovered a simple definition, some great photos, an amazing trove of related information, and a little-known community of vigilant vapor-trail watchers. Our first step was to search Yahoo! using the phrase "vapor trail." That led us to a great little explanation from the University of Illinois that describes the birth of vapor trails, also known as "contrails": Contrails form through the injection of water vapor into the atmosphere by exhaust fumes from a jet engine. If there is sufficient
mixing between the cold upper tropospheric air and the hot exhaust gases to produce a state of saturation, ice crystals will develop. We were pleased to have found such a straightforward explanation, but, as always, we hungered for more. That meant trying another search. This time, we used the alternate term "contrails." The results were encouraging; the very first site pointed us to an amazing resource from Holger Pedersen, a researcher at the Copenhagen University Observatory. In 1999, Pedersen gave a speech on the increasing problem of jet contrails interfering with astronomical observations. The slide
show that accompanied his remarks is available online and offers dozens of interesting photographs and text descriptions of vapor trails. The real gem, however, has to be his collected notes, which contain hundreds of links and quotes relating to contrails and other atmospheric disturbances. Finally, returning to our search results, we came across many sites that raise the issue of chemicals and poisons being spread via these jet trails. Most of these sites use the term "chemtrails" to distinguish themselves. Check out the sites if you are a concerned citizen or just a fan of contrail photos. Speaking of which, we found a stunning
high-altitude photograph of contrails blanketing several states near your native Virginia.
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