Have you ever watched an airplane fly across a clear blue sky? Sometimes it’s easy to trace an airplane’s path, because it leaves behind a white streak across the sky. After a while, though, the plane’s track fades and disappears into thin air.

Those white streaks planes leave behind are actually artificial clouds. They’re called contrails, which is a shortened version of the phrase “condensation trail.”

Airplane engines produce exhaust, just like car engines do. As hot exhaust gases escape from a plane, the water vapor in the fumes hits the air. At heights of 26,000 feet or more, the air is extremely cold (sometimes more than -40° F!).

The cold air causes the water vapor to condense. This means the water vapor gases turn into tiny water droplets or even freeze into tiny ice crystals before eventually evaporating. This condensed water vapor and mixture of ice crystals make up the cloud-like trails you see in the sky.

If you’ve ever seen an air show, you may have seen airplanes creating messages in the sky with what look like clouds. Are these contrails? Not exactly…

Skywriters use small airplanes equipped with special smoke machines to fly in special patterns to create written messages visible from the ground. The smoke machines usually consist of pressurized containers full of oil. At a pilot’s command, the machines spray oil onto the plane’s hot exhaust system, where it burns quickly and creates clouds of dense white smoke.

Pilots have to learn how to fly special patterns and work the smoke machine carefully to be able to create their unique messages in the sky. From advertisements to marriage proposals, the messages can be practical, personal or just plain silly.

Skywriting goes way back. There are reports of successful skywriters before World War I, possibly as early as 1915. Today, skywriters take advantage of satellite navigation to program messages before flight, thereby increasing accuracy.

17 Join the Discussion

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    • Hi there, Tera, thanks for joining us at Wonderopolis today! We sure are glad that you commented on our flying Wonder, too! Those artificial clouds in the sky are actually exhaust gases from the airplane. You might have seen exhaust gases from the tailpipe of a car– the same is true for airplanes! We hope you have a great day, Tera! Please come back and visit us soon! :)

  1. Tera’s right… They are spraying! If there are trails that stay long in the air, I don’t know what that is… But, if it disappears, than it’s normal cloud. Other “stories” are fake.

    • Hi EH! Thanks for WONDERing with us! Planes leave the lines behind them as the exhaust leaves the engine and combines with the air vapors! Thanks for WONDERing with us! :)

    • Hi Rich! Thanks for WONDERing with us! It could be used for communication purposes! Some airplanes even write words in the sky with their tracks! Have you ever seen that before? Thanks for WONDERing with us! :)

  2. If that is true, why don’t I have to drive back through my exhaust a few hours later if I am returning from where I just drove, or see auto exhaust fumes that linger all day long next to roadways? Planes leaves these contrails in the skies all day sometimes and change the sky to a nasty white haze. It just doesn’t add up to harmless water vapor. More like geoengineering. No matter how you look at it, there is too much of this going on in our atmosphere, and that cannot be great for the environment, or the air we breathe, because what goes up, must also fall down.

    • Excellent argument, Laney! Keep in mind the reason contrails linger in the sky so long has a lot to do with the temperature at that height. Thanks for WONDERing with us, today! :-)

  3. Here’s the thing, I am over 70 years old and I love a blue, blue sky or large beautiful clouds and have always gazed at the sky everytime I am outside (almost always). These so called chemtrails are something new and I do not think it’s normal procedure for a jet to fly back and forth (or several planes) until the sky is covered with these trails Whatever it is, you can bet it’s not normal.

    • Thanks for sharing your thoughts, Jan! We think it’s WONDERful that you spend so much time outside! We think you’re right, that it’s not normal procedure to fly back and forth and completely cover the sky with contrails — usually planes are just passing through, getting from point A to point B! :)

  4. But some time we seen two same that type of airplane in the sky but one airplane leave track for few minute and another airplane leave for more time…….?

    • That’s true, Mohit Dagar. Why do you think that is? We are glad you shared your thoughts on this WONDER. Have a WONDERful day!

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Have you ever wondered…

  • Why do airplanes leave tracks in the sky?
  • What are contrails?
  • How do pilots use planes to write in the sky?

Wonder Gallery

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Try It Out

Ready to make your own contrails? OK! Grab the keys to your family’s airplane and head on up into the sky! What do you mean your family doesn’t have an airplane? Well, now that we think about it…even if they did have an airplane, they probably wouldn’t let you fly it just yet! Don’t worry, though, you can still have fun checking out one or more of the following fun activities with a friend or family member:

  • Do you ever make homemade cards for your friends and family members on their birthdays? There’s nothing quite like a heartfelt message written by hand in a card you made yourself. Of course, paper limits you a bit in terms of the impact your message can have. But what if you had the whole sky as your canvas? What would you skywrite to a friend or family member if you had the chance to write any message in the sky for them to see? Think about it and then tell that person what you would write if you could write in the sky. You never know when you just might make someone’s day!
  • Is it cloudy outside today? We hope so! Why? Because this activity requires some clouds. Head outside with some friends or family members and lay out a blanket so you can comfortably gaze at the clouds as they cross the sky. What shapes do you see? Pick out a certain area of the sky and see what you can see. Do your friends or family members see the same things you do? Compare your observations. How are they similar? How are they different? Have fun cloudgazing and using your imagination to give the random clouds some meaning!
  • If you’re up for a challenge, try this fun experiment at home with just a few simple supplies. Grab a clear plastic 2-liter bottle, matches (you’ll need an adult to help with this experiment) and some warm water. Just follow the directions to create your very own Cloud in a Bottle!

Still Wondering

Visit Illuminations’ Long Distance Airplanes lesson to make paper airplanes and explore attributes related to increasing flight distances.


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