When we were small, we used to look up to the sky and often see a white trail left by a jet aircraft. Rocket! Rocket! We used to yell, jump up with joy, clap our hands and strain our eyes as the ‘rocket’ disappeared into the horizon.
Soon, the white streak would change into a broken, twisted cloud path. And we were told that it was the fairies’ trail.
What causes this white streak?
The white streak is actually a cloud, though the aircraft is a normal jet liner and not a rocket. This white streak is called a ‘contrail’ or a condensation trail. The engine of a jet aircraft releases after- burners or fumes just like our cars and motorcycles.
These fumes contain a lot of water vapour. At very high altitudes, where the temperature is as low as -38 degree celsius (water freezes at zero degrees), the water vapour freezes into tiny ice crystals almost instantly before evaporating.
A contrail can spread out and form a horizontal sheet of cloud, as winds which blow at high altitudes blow it apart. It disappears eventually when the water vapour evaporates.
Contrail or chemtrail?
The fumes emanating from an aircraft contain several harmful chemicals which pollute the air at high altitudes. So, environmentalists have coined a new term for it – chemtrail or chemical trail. So much for the fairies’ trail.