If you have ever watched an airplane fly across the sky, you will have noticed that sometimes a white track or trail is left behind.
While conspiracy theorists claim there is a sinister reason the trails occur, the real reason is much more straightforward.
Those tracks are called contrails and are trails of condensation that are formed at high altitude.
They form as the heat coming from the exhaust of the plane hits the cold atmosphere.
“The water vapor from the hot plane engine turns to ice mid-air which we see as white lines in the sky called contrails”, reports Tech Insider.
It’s the same phenomenon that occurs when you breathe out hot air on a cold day.
The contrails from a plane can also be used to help you predict the weather.
This is because long trails are formed when conditions are more humid, whereas shorter trails form in low humidity, Tech Insider says.
This means that a long trail could be a sign that stormy weather is coming, while a short trail could mean that the weather will remain fair.
Contrails, however, shouldn’t be confused with trails or messages made to look like clouds coming from a plane at an airshow.
These come from planes equipped with smoke machines to write messages or create patterns which are visible to the those watching from the ground.
The machines work when the pilot sprays oil onto the hot exhaust system which burns quickly to release a hot white smoke.