what is the white line that some airplanes leave above cities from time to time? not all planes do that.?

Answer 1

It's called a contrail. It's formed by the condensation of atmospheric and exhaust moisture. Its appearance depends to some extent on the composition and (hot) temperature of the exhaust, but mostly depends on the air temperature, pressure, and humidity of the air at that altitude. Think of it as being the way you can see your exhaled breath on a cold day.

Answer 2

Contrails ... Condensation Trails. They're formed when the hot jet exhaust hits the cold, moisture laden air. The high heat immediately makes the moisture condense into a cloud like water vapor, just like the exhaust from a car tailpipe on a cold day.

Answer 3

they are called contrails. it is merely condensation behind engines. when a jet flies through a cold pocket of air the hot air from the engine turns the tiny ice crystals that form in moist frigid air, into human made cirrus clouds. they are nothing more than clouds that we make and the reason that they disappear is that the air eventually cools back down behind the plane and refreezes the moisture.

Answer 4

I think a better explanation is that fuel burns into carbondioxide and water. That's the water. It just doesn't cool down enough to condense at lower altitudes.

Answer 5

they are called contrails.
after a plane reaches 30,000 feet they will come. some planes dont have them because they don't go that high. most of those planes above 30,000 will be going international.

Answer 6

Contrails,It is cold at 45000 ft.Also jet engs. run at about 630 celius or 1150 fh. so heat hits cold contraill

Answer 7

The are called contrails

Here is a site that tells you all about how the are created etc...

http://privatejetcharter.spaces.live.com/

Answer 8

They are messages from the other side.
Don't stare at them too long.