Have you seen long streaks of smoke up in the sky on a clear day?

Question

Some days on a very clear day outside, you see white smoke coming out of a jet. I've always wondered how they do that, why do they even do that?

Answer 1

It is called a contrail.
What are contrails?
Contrails are clouds of ice particles formed around the small particles (aerosols) which are in aircraft exhaust. When these persist after the passage of the plane they are of great interest to researchers. Under the right conditions, clouds initiated by passing aircraft can spread with time to cover the whole sky. See an article by CERES researcher Dr. Pat Minnis.

Where do contrails form?
Contrails are human-induced clouds that only form at very high altitudes (usually above 8 km - about 26,000 ft) where the air is extremely cold (less than -40°C). Because of this contrails form not when an airplane is taking off or landing, but while it is at cruise altitude. Thus, people who live under major air traffic routes, not those who live near major airports, are those who will see the most contrails. (However, some major airports are also under major air traffic routes, which can lead to confusion.) You can use an Appleman chart to predict contrail formation for your area. Of course, a contrail cannot form if no airplane passes through.

Contrail Formation
If the air is very dry, a contrail will not form behind the plane. If the air is somewhat moist, a contrail will form immediately behind the aircraft and make a bright white line that lasts for a short while (a short-lived contrail). Persistent contrails form immediately behind the airplane in very moist air. These long-lived contrails will usually grow wider and fuzzier as time passes. You may wish to review the GLOBE Contrail Formation Guide (available in several languages).

Contrail Evolution
Sometimes contrails will actually take on the characteristics of a natural cirrus cloud and no longer look like contrails after only a half hour or so. Persistent contrails can exist long after the airplane that made them has left the area. They can last for a few minutes or longer than a day. However, because they form at high altitudes where the winds are usually very strong, they will often move away from the area where they were born. When we look up into the sky, we may see old persistent contrails that formed somewhere else but moved overhead because of the wind. An example of several very persistent contrails is shown in the S'COOL cloud chart. Persistent contrails are those most likely to affect climate.

Answer 2

Just to add to the other posts.

It is exactly the same as the white puff that come out of your mouth on a cold day. The moist warm air that you exhale forms a small cloud when the air is suddenly cooled, causing the moisture in the air to condense.

Answer 3

Those are called vapour trails! Actually the vapour is coming out of the jet engine exhausts, because at the alitude of an average jet (30000 ft) the outside tempis approx -50 degrees celcius!

Answer 4

It's call a con trail. Formed by the moisture from burnt fuel condensing to form a trail of white cloud behind the plane. If you get binoculars and look it doesn't form as it comes out of the engine. It forms some distance behind the aircraft.

Answer 5

they are chemtrails
google it

I had airplanes pass all the time near my house and they didn't leave those contrails....and then all the sudden they started showing up.
These chemtrails are linked to all kinds of skin diseases and they weaken the immune system. We are being systematically poisoned

again Google CHEMTRAILS.....it will be explained alot better

Answer 6

There is no such thing as chemtrails. If they wanted to chem you then they wouldn't be so high. See the other answers to see why sometimes you see them and other times you don't.

Answer 7

it a ufo!!!