The trails you see in the sky behind planes are called contrails, short for condensation trails.

They form when a plane’s hot engine exhaust—which contains water vapor—mixes with the cold air at high altitudes (typically above 26,000 feet or 8,000 meters). The water vapor condenses and freezes quickly into tiny ice crystals, creating those visible white streaks.

There are a few different types of contrails:

1. Short-lived contrails: Disappear quickly. This happens when the upper atmosphere is relatively dry.

2. Persistent contrails: Stay in the sky for a long time and can spread out to form cirrus-like clouds. This happens in moist, cold air.

3. Spreading contrails: These start as narrow lines and then widen into broader cloud-like formations, sometimes contributing to cloud cover.

Fun Fact:

Contrails can affect climate by trapping heat in the Earth’s atmosphere (a warming effect) or reflecting sunlight away (a cooling effect), depending on their thickness and coverage. Scientists study them as part of climate research.