When an airplane flies in the sky, why does a white line form behind it?
Introduction
Have you ever carefully observed an airplane flying in the clear blue sky? Often, we feel that a long line like white smoke is forming behind the airplane, which slowly fades away or sometimes remains in the sky for hours.
This sight looks beautiful as well as mysterious.
Common people consider it to be smoke, but in reality, it is not smoke. This white line is called “Contrail” in scientific language, whose full name is Condensation Trail.
Now the question arises as to why it is formed. Let us understand it in detail.
1. Airplane engine and the gases emitted
Aviation fuel (kerosene-type fuel) is burnt in the engine of the airplane.
Burning of this fuel releases two main things:
1. Water Vapor
2. Carbon dioxide and other gases
This gas coming out of the engine is very hot.
2. Atmospheric conditions at high altitude
Airplanes usually fly at an altitude of 8–12 kilometers.
The temperature at this altitude is very low, often –40°C to –55°C.
The air here is very thin and cold.
3. Condensation and formation of ice particles
As soon as the hot steam coming out of the engine hits the cold air, it immediately cools down and condenses.
This steam turns into tiny water droplets or simply ice crystals.
When millions of such ice particles are formed together, we see a white stripe-like line.
4. Why does it look white?
When the sun’s rays hit these tiny ice crystals, they scatter the light in every direction.
This scattering of light appears white to our eyes.
This is why contrail always looks white, whether the plane is black or blue.
5. How long does a contrail last?
It depends on how much humidity is in the air at that altitude.
1. Low-humidity air:
The ice quickly melts and disappears.
The contrail lasts only for a few minutes.
2. High-humidity air:
The ice crystals remain and spread out to look like clouds.
This contrail can last in the sky for hours.
6. Is it smoke?
No
People often think it is smoke, but this is wrong.
Smoke contains carbon particles and is black, while a contrail is made up entirely of white ice/steam.
That is, it is the effect of nature’s “cloud-forming machine”.
7. Everyday examples
Have you ever exhaled your breath into cold air in winter?
At that time, the steam coming out of your breath immediately turns into white mist.
In the same way, the engine of an airplane also releases hot steam, which cools down on reaching up and forms a white line.
That is, the contrail of an airplane is a “bigger version” of our winter breath.
8. Types of contrail
Scientists have divided contrails into several types:
1. Short-lived contrail:
Forms quickly and disappears in a few minutes.
2. Persistent contrail:
Persists for a long time and spreads to form a layer in the sky.
3. Spreading contrail:
Gradually widens and turns into thin clouds.
9. Effect on the environment
Contrails may look beautiful, but it has little effect on the environment.
It can block the heat radiation coming to the Earth and emanating from the Earth by forming a cloud-like layer.
It is said that it may affect global warming.
Scientists are continuously doing research on this.
10. Myth and truth
Many people think that these are chemicals released from ships (Chemtrails).
But science says that these are only water vapor and ice particles.
No poisonous gas or chemical is involved in it.
11. Effect on farmers and meteorology
Meteorologists use contrails to understand the condition of humidity in the upper air.
If the contrail disappears quickly, it means that there is less moisture in the air.
If the contrail remains for a long time, it means that there is more moisture in the air, and perhaps the weather may change in the coming days.
12. Simple understanding for children
If you want to explain it to a child, you can say this:
“Just as you exhale from your mouth in winter and a white mist is formed, similarly, when an airplane goes up, it releases hot steam in the cold air, and that steam turns into ice and forms a long white line.”
Conclusion
When an airplane flies in the sky, the hot steam and gases coming out of its engine collide with the cold air above and form small ice crystals.
These icy particles shine in the sunlight and appear to us as a white line (contrail).
Sometimes it disappears in a few minutes, and sometimes it remains in the sky for hours. This is not any smoke or poisonous substance, but only water vapor and ice particles.
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