What are contrails?
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Transcript
See that white line stretching across the blue sky behind the plane? Why does it appear?
A plane's engine sends out hot exhaust gas. It's full of tiny water vapor.
High in the sky, the air is very cold and thin. When the exhaust cools down, the water vapor turns into tiny ice crystals.
Your breath looking white on a cold winter day works the same way. Tiny ice crystals gather together and look like a white cloud.
A contrail is a cloud made when water vapor turns into tiny ice crystals.
For grown-ups: the science
A contrail is water vapor from a plane that cooled down and turned into a cloud of tiny ice crystals.
Contrails form when a jet engine's hot, water-vapor-rich exhaust mixes with the very cold, low-pressure air high in the sky and cools rapidly. The water vapor collects on tiny particles and freezes into ice crystals, which we see as a cloud. It's the same idea as seeing your breath turn white outside on a cold day, since both happen when water vapor in the air cools into tiny droplets or crystals. The difference is that breath is mostly made of fine water droplets, while contrails are mostly ice crystals. Whether a contrail stays thin and short or spreads out and lingers depends on the moisture, temperature, and wind up in the sky. Scientists are still studying how much contrails, especially the ones that spread and linger, affect global warming, and the exact amount isn't settled yet.