Do you ever think about the white lines or smoky line an aircraft is leaving behind during its flight. Do you know what this is?? That white smoke is known as condensation trails in short “contrail”.
Contrails are the white lines that sometimes form behind high flying aircraft. They are actually a type of cloud. The cloud forms because jet exhaust contains quite a bit of water. If the humidity is high, then the contrails can persist for a long time, like clouds do.
(Contrails usually form above 8,000 meters/26,000 feet, depending on the temperature and other factors)
Their formation is most often triggered by the water vapour 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.
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..