Undoubtedly, you have all wondered what is this white line of clouds that planes leave in the sky when in flight. Why does it happen? Is it something dangerous? What exactly do planes do? These are some of the questions.

If you have not noticed until today, the next time you hear a plane flying overhead, look up at the sky and you will probably notice a white trail of smoke in its passage.

Let's take a look at this phenomenon.

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The main factors of creating traces of condensation are temperature, humidity and flight altitude. Depending on the value of these factors is also the time of possible observation, which ranges from a few seconds to a few minutes.

Photo: unsplash.com/omeganova

Most clouds you see are the result of moist warm air rising. As it gets higher, the air cools down to the temperature of the surrounding air. When it reaches the dew point, a visible cloud forms. 

So the condensation trails behind aircraft are simply clouds. When airplanes fly at high altitudes, jet engines emit extremely hot air and water vapor,  along with other combustion exhaust particles like carbon dioxide. More specifically, most aircraft fly at altitudes above 30,000 feet from the sea level, i.e. at altitudes where temperatures range between -45 and -61 degrees Celsius.  

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Low temperatures and low pressures at these altitudes result in water forming visible ice crystals. Like the upper-level cirrus clouds, the ice crystals will blow and scatter with the wind conditions. The results are white clouds known as contrails, which is short for condensation trails.