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What exactly is the white we see coming off an airplane in the sky. Sometimes in the summer you can lookup and see many streaks in the sky. They are much longer and last longer in the summer than winter. Please tell me what causes this and why they last longer in the summer.

The white streaks you see coming off airplanes are called contrails. That is short for condensation trail. Contrails are actually clouds made by the airplanes.

An airplane's exhaust has some water vapor in it, just like the air. Sometimes when the exhaust mixes with the air, it has so much water vapor that the air can't hold it all. The water vapor then turns into clouds. That's why you sometimes see contrails following jet airplanes.

The air has more water vapor in it during the summer. That means that it's more humid than during the winter. Contrails will last longer during the summer because the clouds won't evaporate very fast in the humid air.


Submitted by Stephanie (Ohio, USA)
January 16, 1998



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