"Chemtrails" Defoliant spray run, part of Operation Ranch Hand, during the Vietnam War by UC-123B Provider aircraft. A high-flying jet leaving a condensation trail (contrail) The chemtrail conspiracy theory hypothesis that some trails left by aircraft are chemical or biological agents deliberately sprayed at high altitudes for purposes undisclosed to the general public and directed by various government officials. This theory is not accepted by the scientific community, which states that they are just normal contrails, as there is no scientific evidence supporting the chemtrail theory. Because of the popularity of the conspiracy theory, official agencies have received thousands of complaints from people who have demanded an explanation. The existence of chemtrails has been repeatedly denied by scientists and government officials around the world, who say the trails are normal contrails Defoliant spray run, part of Operation Ranch Hand, during the Vietnam War by UC-123B Provider aircraft. A high-flying jet leaving a condensation trail (contrail) The chemtrail conspiracy theory posits that some trails left by aircraft are chemical or biological agents deliberately sprayed at high altitudes for purposes undisclosed to the general public and directed by various government officials.This theory is not accepted by the scientific community, which states that they are just normal contrails, as there is no scientific evidence supporting the chemtrail theory. Because of the popularity of the conspiracy theory, official agencies have received thousands of complaints from people who have demanded an explanation.The existence of chemtrails has been repeatedly denied by scientists and government officials around the world, who say the trails are normal contrails hypothesis "Vapor Trail" redirects here. For other uses, see Vapor Trail (disambiguation). For other uses, see Contrail (disambiguation). Aviaticus cloud Engine exhaust contrails Engine exhaust contrails Genus Cirrus (curl of hair), cirrocumulus, or cirrostratus Altitude Usually above 5,000 m (Usually above 16,500 ft) Classification Family A (High-level) Appearance long bands Precipitation cloud? No Sinuous vapor trail over south-east Poland. Contrails (/ˈkɒntreɪlz/; short for "condensation trails") or vapor trails are long thin artificial (man-made) clouds that sometimes form behind aircraft. Their formation is most often triggered by the water vapor in the exhaust of aircraft engines, but can also be triggered by the changes in air pressure in wingtip vortices or in the air over the entire wing surface. Like all clouds, contrails are made of water, in the form of a suspension of billions of liquid droplets or ice crystals. Depending on the temperature and humidity at the altitude the contrail forms, they may be visible for only a few seconds or minutes, or may persist for hours and spread to be several miles wide. The resulting cloud forms may resemble cirrus, cirrocumulus, or cirrostratus. Persistent spreading contrails are thought to have a significant effect on global climate.

• published: 13 Sep 2013
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